ayres

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Author name code: ayres
ADS astronomy entries on 2022-09-14
author:"Ayres, Thomas R." OR author:"Ayres, Tom"

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Title: The Beat Goes On
Authors: Ayres, Thomas
2022cxo..prop.6408A Altcode:
Chandra has been following magnetic heartbeats of late-type stars
via high-contrast coronal X-rays. Goal is to provide fundamental
observational constraints for contemporary and future studies of the
underlying magnetic dynamo, whose internal workings remain elusive. The
Sun's high-energy modulations play an important space weather role in
our heliosphere, as do stellar counterparts for their exoplanets. A
3-year continuation (joint with HST) is proposed for current cycles
targets Xi Boo (G8V+K4) and 70 Oph (K0V+K5V). Key questions: (1)
origin of diverging branches in rotational period vs. cycle duration,
where Sun sits isolated in the middle, possibly in a transitional
state; (2) extent of high-energy variability bias, which can affect
interpretations of large surveys.

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Title: HST STIS Observations of ζ Aurigae A's Irradiated Atmosphere
Authors: Harper, Graham M.; Bennett, Philip D.; Brown, Alexander;
Ayres, Thomas R.; Ohnaka, Keiichi; Griffin, Elizabeth
2022AJ....164...16H Altcode:
The details of the processes responsible for heating the chromospheres
of evolved cool stars remain uncertain. While most spectroscopic
diagnostics measure spatially-integrated emission, here we examine
diagnostics sensitive to localized atmospheric regions that are
specific to cool evolved stars in binary systems with hot main-sequence
companions: emission from Si I and C I resulting from the ultraviolet
irradiation of the evolved star's atmosphere. HST Space Telescope
Imaging Spectrograph (STIS) high-spectral-resolution near-ultraviolet
observations of ζ Aurigae A+B (K4 Ib + B5 V) were obtained at
three orbital phases, including total eclipse, to search for Si I
and the corresponding C I line emission. Si I 2987.645 Å emission
was detected at phases ϕ = .101 and .448 (from periastron) in-line
with predictions from a previous study of optical Si I 3905 Å and
Si I 4102 Å emission lines. No other Si I line emission is apparent,
and the analogous C I lines at 2478.561 Å and 2582.901 Å also are not
detected. High-spectral-resolution HST STIS and Goddard High Resolution
Spectrograph spectra confirm the results of a previous study that showed
that the intrinsic chromospheric fluxes on the visible hemisphere of ζ
Aur A, observed during total eclipse, are representative of the single
K supergiant λ Vel (K4 Ib). Furthermore, the HST spectra show that
the chromospheric turbulent velocities are very close to those in this
spectral-type proxy. These combined results highlight the importance
of detailed spatially-resolved chromospheric models of ζ Aur systems,
based on sequences of atmospheric eclipse spectra, to help constrain
the poorly understood mechanisms that heat the atmospheres and drive
stellar winds in cool evolved stars.

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Title: The Origin of Weakened Magnetic Braking in Old Solar Analogs
Authors: Metcalfe, Travis S.; Finley, Adam J.; Kochukhov, Oleg; See,
Victor; Ayres, Thomas R.; Stassun, Keivan G.; van Saders, Jennifer L.;
Clark, Catherine A.; Godoy-Rivera, Diego; Ilyin, Ilya V.; Pinsonneault,
Marc H.; Strassmeier, Klaus G.; Petit, Pascal
2022ApJ...933L..17M Altcode: 2022arXiv220608540M
The rotation rates of main-sequence stars slow over time as they
gradually lose angular momentum to their magnetized stellar winds. The
rate of angular momentum loss depends on the strength and morphology
of the magnetic field, the mass-loss rate, and the stellar rotation
period, mass, and radius. Previous observations suggested a shift in
magnetic morphology between two F-type stars with similar rotation
rates but very different ages (88 Leo and ρ CrB). In this Letter, we
identify a comparable transition in an evolutionary sequence of solar
analogs with ages between 2-7 Gyr. We present new spectropolarimetry of
18 Sco and 16 Cyg A and B from the Large Binocular Telescope, and we
reanalyze previously published Zeeman Doppler images of HD 76151 and
18 Sco, providing additional constraints on the nature and timing of
this transition. We combine archival X-ray observations with updated
distances from Gaia to estimate mass-loss rates, and we adopt precise
stellar properties from asteroseismology and other sources. We then
calculate the wind braking torque for each star in the evolutionary
sequence, demonstrating that the rate of angular momentum loss drops
by more than an order of magnitude between the ages of HD 76151 and
18 Sco (2.6-3.7 Gyr) and continues to decrease modestly to the age
of 16 Cyg A and B (7 Gyr). We suggest that this magnetic transition
may represent a disruption of the global dynamo arising from weaker
differential rotation, and we outline plans to probe this phenomenon
in additional stars spanning a wide range of spectral types.

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Title: The Wind Temperature and Mass-loss Rate of Arcturus (K1.5 III)
Authors: Harper, Graham M.; Ayres, Thomas R.; O'Gorman, Eamon
2022ApJ...932...57H Altcode:
In this paper we aim to constrain the wind temperature, outflow and
turbulent velocities, ionization state, and mass-loss rate of the single
red giant Arcturus (α Boo K1.5 III) using high spectral resolution
Hubble Space Telescope Space Telescope Imaging Spectrograph profiles of
Si III 1206.5 Å , O I 1304 Å and 1306 Å, C II 1334 Å and 1335 Å,
and Mg II h 2802 Å. The use of the E140-H setting for α Boo allows the
Si III 1206.5 Å line to be cleanly extracted from the echelle format
for the first time. The ratios of the wind optical depths of lines from
different species constrain the temperature at the base of the wind
to T wind ~ 15,400 K. The mass-loss rate derived is 2.5 ×
10-11 $\,{{M}_{\odot }\,{\rm{yr}}}^{-1}$ for Epoch 2018-2019,
smaller than previous semiempirical estimates. These results can be
reconciled with multiwavelength Very Large Array radio continuum fluxes
for Epoch 2011-2012 by increasing the temperature to T wind
~ 18,000 K, or increasing the mass-loss rate to 4.0 × 10-11
$\,{{M}_{\odot }\,{\rm{yr}}}^{-1}$ . Interpreting the wind acceleration
and turbulence in terms of a steady WKB Alfvén wave-driven wind reveals
that the wave energy damping length increases with increasing radius,
opposite to the trend expected for ion-neutral damping of monochromatic
waves, confirming a previous result by Kuin and Ahmad derived for
ζ Aur binaries. This implies that a spectrum of waves is required
in this framework with wave periods in the range of hours to days,
consistent with the photospheric granulation timescale. Constraints on
a radial magnetic field (B) at 1.2 R * are an upper limit
of B ≤ 2 G from the implied wave heating, and B ≥ 0.3 G to avoid
excessive wave amplitudes.

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Title: Intrinsic Lyman alpha Profiles of High-Velocity G, K, and
M Dwarfs
Authors: Youngblood, Allison; Pineda, J. Sebastian; Ayres, Thomas;
France, Kevin; Linsky, Jeffrey; Wood, Brian; Redfield, Seth; Schlieder,
Joshua
2022AAS...24011801Y Altcode:
Observations of H I Lyman alpha, the brightest UV emission line of
late-type stars, are critical for understanding stellar chromospheres
and transition regions, modeling photochemistry in exoplanet
atmospheres, and measuring the abundances of neutral hydrogen and
deuterium in the interstellar medium. Yet, Lyman alpha observations are
notoriously challenging due to severe attenuation from interstellar gas,
hindering our understanding of this important emission line's basic
morphology. We present high-resolution far- and near-UV spectroscopy
of five G, K, and M dwarfs with radial velocities large enough to
Doppler shift the stellar Lyman alpha emission line away from much of
the interstellar attenuation, allowing the line core to be directly
observed. We detect self-reversal in the Lyman alpha emission line core
for all targets, and we show that the self-reversal depth decreases with
increasing surface gravity. Mg II self-reversed emission line profiles
provide some useful information to constrain the Lyman alpha line core,
but the differences are significant enough that Mg II cannot be used
directly as an intrinsic Lyman alpha template during reconstructions. We
show that reconstructions that neglect self-reversal could overestimate
intrinsic Lyman alpha fluxes by 60-100% for G and K dwarfs and 40-170%
for M dwarfs.

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Title: Wilson-Bappu 2022
Authors: Ayres, T.
2022fysr.confE..26A Altcode:
The Wilson-Bappu Effect (WBE) has long fascinated astronomers (well,
at least a few of us) and the general public (see Season 3, Episode
21 of the "Big Bang Theory" [viewer discretion advised]). O.C. Wilson
and M.K.V. Bappu made the original discovery in the mid-1950's: a
striking systematic correlation between the absolute visual magnitudes
of late-type stars and the widths of their 395 nm Ca II H \&amp; K
chromospheric emission cores as measured on photographic plates. The
Ca II width-luminosity relation tracks seamlessly from intrinsically
faint red dwarfs to the most luminous yellow supergiants. Initially
attributed to chromospheric kinematics, the WBE is now seen as a
consequence of an intricate interplay between outer-atmosphere heating,
hydrogen ionization and surface gravity. This is a progress report
on a new effort to analyze the existing vast collection of HST NUV
spectra of the analogous 280 nm Mg II h \&amp; k resonance lines,
to re-script the Wilson-Bappu story for the modern era.

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Title: X-Ray Chronicles of Alpha Centauri: The Swooning of α Cen B
Authors: Ayres, Tom
2022RNAAS...6...24A Altcode:
The central AB binary of Alpha Centauri has been visited regularly
by Chandra X-ray Observatory since late 2005. Up to mid-2020, the B
component, an early K dwarf, had traced out a relatively smooth 8 yr
coronal (T ~ 2 MK) activity cycle. Recently, however, B's X-ray count
rate suddenly dipped, from cycle maximum levels to near minimum in
just 16 months. Previous cycle decays were 3-4 yr. The significance
of the swoon remains to be seen.

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Title: Intrinsic Lyα Profiles of High-velocity G, K, and M Dwarfs
Authors: Youngblood, Allison; Pineda, J. Sebastian; Ayres, Thomas;
France, Kevin; Linsky, Jeffrey L.; Wood, Brian E.; Redfield, Seth;
Schlieder, Joshua E.
2022ApJ...926..129Y Altcode: 2022arXiv220101315Y
Observations of H I Lyman α, the brightest UV emission line of
late-type stars, are critical for understanding stellar chromospheres
and transition regions, modeling photochemistry in exoplanet
atmospheres, and measuring the abundances of neutral hydrogen and
deuterium in the interstellar medium. Yet Lyα observations are
notoriously challenging owing to severe attenuation from interstellar
gas, hindering our understanding of this important emission line's basic
morphology. We present high-resolution far- and near-UV spectroscopy
of five G, K, and M dwarfs with radial velocities large enough
to Doppler-shift the stellar Lyα emission line away from much of
the interstellar attenuation, allowing the line core to be directly
observed. We detect self-reversal in the Lyα emission-line core for
all targets, and we show that the self-reversal depth decreases with
increasing surface gravity. Mg II self-reversed emission-line profiles
provide some useful information to constrain the Lyα line core,
but the differences are significant enough that Mg II cannot be used
directly as an intrinsic Lyα template during reconstructions. We show
that reconstructions that neglect self-reversal could overestimate
intrinsic Lyα fluxes by as much as 60%-100% for G and K dwarfs and
40%-170% for M dwarfs. The five stars of our sample have low magnetic
activity and subsolar metallicity; a larger sample size is needed to
determine how sensitive these results are to these factors.

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Title: On the Same Wavelength as the Space Telescope Imaging
Spectrograph
Authors: Ayres, Thomas R.
2022AJ....163...78A Altcode:
The Hubble Space Telescope Imaging Spectrograph (STIS) is a powerful
tool for high spectral resolution ultraviolet (UV; 1150-3200 Å) studies
of bright cosmic sources. However, achieving the superb wavelength
precision inherent in its UV echelle channels is hampered by subtle
camera distortions that are not fully compensated for by the CALSTIS
pipeline. The systematics arise from the low-order (n = 2) bivariate
polynomial dispersion model employed in the echellegram processing. The
formulation does remarkably well given its simplicity (only seven terms
in the current implementation), but cannot account for apparent higher
frequency undulations in the STIS spectral images. Previous correction
schemes have built elaborate distortion maps, with up to thirty-six
terms, operating on the individual echelle orders in the pipeline
"x1d" file, prior to merging the orders. There is, however, a more
straightforward, although partial, solution: a polynomial formula in
the wavelength domain applied to the order-merged spectrum; just n =
3 for most of the STIS settings, although up to n = 5 for a few of
the more recalcitrant ones.

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Title: In the Trenches of the Solar-stellar
Connection. V. High-resolution Ultraviolet and X-Ray Observations
of Sun-like Stars: The Curious Case of Procyon
Authors: Ayres, Thomas R.
2021ApJ...923..192A Altcode:
A joint X-ray (0.2-2 keV) and ultraviolet (1150-3000 Å) time-domain
study has been carried out on three nearby bright late-type stars,
bracketing the Sun in properties. Alpha Cen A (HD 128620: G2 V) is
a near twin to the Sun, although slightly more massive and luminous,
slightly metal-rich, but older. Alpha Cen B (HD 128621: K1 V) is cooler
than the Sun, somewhat less massive and lower in luminosity. Procyon
(HD 61421: F5 IV-V) is hotter, more massive and more luminous than
the Sun, half the age, but more evolved. Stellar observations
were from Chandra X-ray Observatory and Hubble Space Telescope
(HST). The Sun provided a benchmark through high-energy spectral
scans from solar irradiance satellites and novel high-dispersion
full-disk profiles of key UV species-Mg II, C II, and Si IV-from the
Interface Region Imaging Spectrograph. Procyon's flux history was
strikingly constant at all wavelengths, in contrast to the other three
cycling-dynamo stars. Procyon also displays a strong subcoronal (T ~
1 × 105 K) emission excess, relative to chromospheric Mg
II (T ≲ 104 K), although its X-rays (T ~ 2 MK) appear
to be more normal. At the same time, the odd sub-Gaussian shapes,
and redshifts, of the subgiant's "hot lines" (such as Si IV and C IV)
are remarkably similar to the solar counterparts (and α Cen AB). This
suggests a Sun-like origin, namely a supergranulation network supplied
by magnetic flux from a noncycling "local dynamo."

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Title: HD 41004: A Photometric Sheep in Wolf's Clothing?
Authors: Ayres, Tom; Buzasi, Derek
2021RNAAS...5..243A Altcode:
HD 41004 is an unusual multiple star/planet system. Recent TESS
photometry revealed a striking 31 hr period, far too short for the
slowly rotating K dwarf primary. Instead, the modulation likely is
from the diminutive dM secondary, spun-up to synchronous rotation by
its close-in brown dwarf companion, and suffering intense magnetic
activity as a result. If so, the red dwarf is perhaps destined to
someday return the favor by cannibalizing its substellar partner.

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Title: Alpha Centauri and Environs
Authors: Ayres, Thomas
2021cxo..prop.6169A Altcode:
Chandra has been tracking coronal activity cycles of late-type
stars via high-contrast soft X-rays, jointly with HST to capture UV
tracers. Objective is to provide fundamental observational constraints
for contemporary and future studies of the underlying magnetic dynamo,
whose inner workings remain elusive. The Sun's high-energy modulations
play an important "Space Weather" role in our heliosphere, as do stellar
counterparts for their exoplanets. 3-year time-domain campaign (joint
with HST) is proposed for iconic Alpha Centauri, already followed by
HRC-I since 2006. The Alpha Cen field also is rich in serendipitous
sources, including flaring red dwarfs and several possibly cycling
F-K stars.

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Title: Alpha Centauri and Environs
Authors: Ayres, Thomas R.
2021hst..prop16834A Altcode:
(Note: this is the HST part of a joint Chandra/HST project: the
original Chandra proposal abstract follows.) Chandra has been
tracking coronal activity cycles of late-type stars via high-contrast
soft X-rays, jointly with HST to capture UV tracers. Objective is to
provide fundamental observational constraints for contemporary and
future studies of the underlying magnetic Dynamo, whose inner workings
remain elusive. The Sun's high-energy modulations play an important
"Space Weather" role in our heliosphere, as do stellar counterparts
for their exoplanets. 3-year time-domain campaign (jointly with HST)
is proposed for iconic Alpha Centauri, already followed by HRC-I
since 2006. The Alpha Cen field also is rich in serendipitous sources,
including flaring red dwarfs and several possibly cycling F-K stars.

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Title: In the Trenches of the Solar-stellar Connection. IV. Solar
Full-disk Scans of C II, Si IV, and Mg II by the Interface Region
Imaging Spectrograph
Authors: Ayres, Thomas; De Pontieu, Bart; Testa, Paola
2021ApJ...916...36A Altcode:
About once a month, the Interface Region Imaging Spectrograph conducts
day-long raster scans of the full Sun in three ultraviolet spectral
channels. These full-disk mosaics are valuable in the solar context,
but provide a unique connection to the distant, unresolved stars. Here,
10 deep-exposure scans (4-8 s per slit step), collected during the
peak and decline of sunspot Cycle 24, were analyzed. Spatial spectra
(2″ pixels) of resonance lines of C II (T ~ 104 K), Si IV
(8 × 104 K), and Mg II (8 × 103 K) were fitted
with a pseudo-Gaussian model to track the emission strengths, widths,
and shifts in the various surface features that comprise the quiet
Sun and active regions. The full-disk mosaic spectra compare well to
tracings of solar-twin α Centauri A (HD 128620; G2 V). The contrast
between disk-average spectra from cycles MIN and MAX is relatively
modest (~50% in Si IV), but, remarkably, the brightest solar pixels
in active regions, at 2″ resolution, exceed the global-average
intensities of the most active Sun-like stars, suggesting a deeper
solar-stellar connection. Si IV shows a conspicuous bright ring at the
limb, whereas optically thicker C II and Mg II are suppressed (more
so for the latter). The Si IV emission favors the bright knots of the
large-scale supergranulation network, while the cooler Mg II emission
is more ubiquitous and C II intermediate. The non-Gaussian profile
of full-disk C IV, similar in formation temperature to Si IV, was
previously interpreted as a combination of narrow and broad dynamical
components, but the prevalence of the characteristic line shape in the
finest resolution spatial pixels of Si IV here provides support for
alternative formation scenarios, for example, invoking κ-distributions.

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Title: Cycles and the Seven Dwarfs
Authors: Ayres, Thomas R.
2021hst..prop16787A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of late-type
stars are relevant for understanding the Sun's analogous high-energy
modulations, in turn crucial to Earth-impacting "Space Weather"
(SW). Similarly, stellar SW counterparts can have equivalent, or
more severe, adverse effects on their exoplanets. The solar decadal
oscillations are symptomatic of a deep-seated magnetic pump -- the
Dynamo -- whose internal workings remain elusive. Key question: is
Sun's 11-year cycle normal, or instead a transition state? A 3-year
addition to earlier long-term joint Chandra/HST programs (previously
involving Alpha Cen [G2V+K1V] and Procyon [F5IV]), will be carried
out for two new targets, the nearby binaries Xi Bootis (G8V+K4) and
70 Ophiuchi (K0V+K5V). The HST part of the program will measure
FUV subcoronal (T~100,000 K) emission lines, like Si IV 140 nm, C
IV 155 nm, and density-sensitive O IV 140 nm, as well as important
chromospheric (T~10,000 K) features, like O I 130 nm, C II 133 nm, and
C I 165 nm, in both pairs of stars, with one COS visit per system each
year. Analyses of these emissions, including dynamical information
encoded in Doppler shifts and distortions of the line shapes, can
provide insight concerning the thermal/pressure structure of the
anomalously hot outer layers of these stars; and how these structural
properties change with the ebb and flow of a magnetic activity cycle.

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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.

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Title: In the Trenches of the Solar-Stellar Connection. III. The
HST/COS Ecliptic-poles Stellar Survey (EclipSS)
Authors: Ayres, Thomas R.
2021ApJ...910...71A Altcode:
The Ecliptic-poles Stellar Survey (EclipSS) collected far-ultraviolet
(FUV: 1160-1420 Å) spectra of 49 nearby (d ≲ 100 pc) F3-K3
main-sequence stars, located at high ecliptic latitudes (north
and south), using the Cosmic Origins Spectrograph of the Hubble
Space Telescope. The ecliptic poles receive higher exposures from
scanning missions like the Transiting Exoplanet Survey Satellite
(high-precision optical photometry) and Extended Roentgen Survey with
an Imaging Telescope Array (X-ray monitoring), which can deliver
crucial contextual information, not otherwise easily secured. The
objective was to support theoretical studies of stellar hot outer
atmospheres—chromospheres (∼104 K) and coronae (≳1
MK)—which, among other things, can adversely impact exoplanets
via host-star "space weather." Flux-flux diagrams (e.g., C II 1335 Å
versus O I 1306 Å) were constructed for the EclipSS stars, solar Cycle
23/24 irradiances, and long-term FUV records of α Cen A (G2 V) and B
(K1 V). The EclipSS cohort displays similar minimum ("basal") fluxes
to the Sun and solar twin α Cen A, in chromospheric O I 1306 Å. In
hotter C II 1335 Å, a downward slump of the basal fluxes—noted in
previous, less controlled surveys—can now be explained as an effect
of subsolar abundances. The consistent basal minima in chromospheric
and higher temperature species at solar metallicity favor the idea
that stellar analogs of the solar supergranulation network provide a
baseline of high-energy emissions. The magnetic network is replenished
by a "local dynamo" independently of the stellar spin. It can operate
even when the starspot-spawning internal dynamo has ceased cycling,
as during the Sun's 17th century Maunder Minimum.

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Title: A Multiwavelength Look at the GJ 9827 System: No Evidence of
Extended Atmospheres in GJ 9827b and d from HST and CARMENES Data
Authors: Carleo, Ilaria; Youngblood, Allison; Redfield, Seth;
Casasayas Barris, Nuria; Ayres, Thomas R.; Vannier, Hunter; Fossati,
Luca; Palle, Enric; Livingston, John H.; Lanza, Antonino F.; Niraula,
Prajwal; Alvarado-Gómez, Julián D.; Chen, Guo; Gandolfi, Davide;
Guenther, Eike W.; Linsky, Jeffrey L.; Nagel, Evangelos; Narita,
Norio; Nortmann, Lisa; Shkolnik, Evgenya L.; Stangret, Monika
2021AJ....161..136C Altcode: 2021arXiv210106277C
GJ 9827 is a bright star hosting a planetary system with three
transiting planets. As a multiplanet system with planets that sprawl
within the boundaries of the radius gap between terrestrial and gaseous
planets, GJ 9827 is an optimal target to study the evolution of the
atmospheres of close-in planets with a common evolutionary history
and their dependence from stellar irradiation. Here we report on the
Hubble Space Telescope (HST) and CARMENES transit observations of GJ
9827 planets b and d. We performed a stellar and ISM characterization
from the ultraviolet HST spectra, obtaining fluxes for Lyα and Mg
II of F(Lyα) = (5.42 ${}_{-0.75}^{+0.96}$ ) × 10-13
erg cm-2 s-1 and F(MgII) = (5.64 ± 0.24)
× 10-14 erg cm-2 s-1. We also
investigated a possible absorption signature in Lyα in the atmosphere
of GJ 9827b during a transit event from HST spectra, as well as Hα
and He I signature for the atmosphere of GJ 9827b and d from CARMENES
spectra. We found no evidence of an extended atmosphere in either
of the planets. This result is also supported by our analytical
estimations of mass loss based on the measured radiation fields for
all three planets of this system, which led to a mass-loss rate of
0.4, 0.3, and 0.1 planetary masses per Gyr for GJ 9827b, c, and d,
respectively. These values indicate that the planets could have lost
their volatiles quickly in their evolution and probably do not retain
an atmosphere at the current stage.

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Title: In the Trenches of the Solar-Stellar Connection. II. Extreme
Ultraviolet Flux-Flux Correlations across Solar Cycle 24
Authors: Ayres, Thomas R.
2021ApJ...908..205A Altcode:
Solar extreme-ultraviolet (EUV: 100-1100 Å) radiation rises in the
104 K upper chromosphere and hotter layers extending into
the million-degree corona. Much of the EUV normally is not visible in
other stars owing to interstellar H I absorption. The present study
derived power-law scaling relations for EUV species based on irradiance
spectra from the Extreme Ultraviolet Variability Experiment on board the
Solar Dynamics Observatory, over the rise and fall of recent sunspot
Cycle 24. These relations not only can test solar models, but also
allow "invisible" stellar EUV emissions to be reconstructed from more
accessible ultraviolet (UV: 1100-3000 Å) proxies, with implications
for heating, ionization, and erosion of exoplanet atmospheres by
Sun-like hosts. Hot EUV coronal tracers like Si XII 520 Å (8 MK)
show strongly curved power laws relative to chromospheric H I 1025 Å
Lyβ, as was seen in Paper I for 0.2-2 keV soft X-rays versus Mg II
2800 Å. The brightest EUV feature, He II 303 Å, exhibits a nearly
1:1 correlation with Lyβ (and H I 1215 Lyα, but slightly steeper
than 1:1 relative to Mg II). The second brightest, C III 977 Å,
has a shallower power-law slope of ∼0.5. Correlations for low first
ionization potential species, such as Mg, Si, and Fe, might be affected
by cycle-dependent chemical fractionation. Parameterized flux-flux
relations are presented for most of the strong EUV (and selected UV)
features, together with fluxes of individual lines and broad EUV
wavelength bands at the highs and lows of Cycle 24.

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Title: Measuring the fine-structure constant on a white dwarf surface;
a detailed analysis of Fe V absorption in G191-B2B
Authors: Hu, J.; Webb, J. K.; Ayres, T. R.; Bainbridge, M. B.; Barrow,
J. D.; Barstow, M. A.; Berengut, J. C.; Carswell, R. F.; Dumont, V.;
Dzuba, V.; Flambaum, V. V.; Lee, C. C.; Reindl, N.; Preval, S. P.;
Tchang-Brillet, W. -Ü. L.
2021MNRAS.500.1466H Altcode: 2020MNRAS.tmp.3074H; 2020MNRAS.500.1466H; 2020arXiv200710905H
The gravitational potential ϕ = GM/Rc2 at the surface of the
white dwarf G191-B2B is 10 000 times stronger than that at the Earth's
surface. Numerous photospheric absorption features are detected, making
this a suitable environment to test theories in which the fundamental
constants depend on gravity. We have measured the fine-structure
constant, α, at the white dwarf surface, used a newly calibrated
Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph
spectrum of G191-B2B, two new independent sets of laboratory Fe V
wavelengths, and new atomic calculations of the sensitivity parameters
that quantify Fe V wavelength dependency on α. The two results
obtained are: Δα/α0 = (6.36 ± 0.35stat ±
1.84sys) × 10-5 and Δα/α0 = (4.21
± 0.48stat ± 2.25sys) × 10-5. The
measurements hint that the fine-structure constant increases slightly
in the presence of strong gravitational fields. A comprehensive search
for systematic errors is summarized, including possible effects
from line misidentifications, line blending, stratification of the
white dwarf atmosphere, the quadratic Zeeman effect and electric
field effects, photospheric velocity flows, long-range wavelength
distortions in the HST spectrum, and variations in the relative Fe
isotopic abundances. None fully account for the observed deviation
but the systematic uncertainties are heavily dominated by laboratory
wavelength measurement precision.

---------------------------------------------------------
Title: CYRA: the cryogenic infrared spectrograph for the Goode Solar
Telescope in Big Bear
Authors: Yang, Xu; Cao, Wenda; Gorceix, Nicolas; Plymate, Claude;
Shumoko, Sergey; Bai, XianYong; Penn, Matt; Ayres, Thomas; Coulter,
Roy; Goode, Philip R.
2020SPIE11447E..AGY Altcode: 2020arXiv200811320Y
CYRA (CrYogenic solar spectrogRAph) is a facility instrument of the
1.6-meter Goode Solar Telescope (GST) at the Big Bear Solar Observatory
(BBSO). CYRA focuses on the study of the near-infrared solar spectrum
between 1 and 5 microns, an under-explored region which is not only
fertile ground for photospheric magnetic diagnostics but also allows a
unique window into the chromosphere lying atop the photosphere. CYRA is
the first-ever fully cryogenic spectrograph in any solar observatory
with its two predecessors, on the McMath-Pierce and Mees Telescopes,
being based on warm optics except for the detectors and order
sorting filters. CYRA is used to probe magnetic fields in various
solar features and the quiet photosphere. CYRA measurements will
allow new and better 3D extrapolations of the solar magnetic field
and will provide more accurate boundary conditions for solar activity
models. The superior spectral resolution of 150,000 and better allows
enhanced observations of the chromosphere in the carbon monoxide (CO)
spectral bands and will yield a better understanding of energy transport
in the solar atmosphere. CYRA is divided into two optical sub-systems:
The Fore-Optics Module and the Spectrograph. The Spectrograph is
the heart of the instrument and contains the IR detector, grating,
slits, filters, and imaging optics all in a cryogenically cooled
Dewar (cryostat). The sensor is a 2048 by 2048 pixel HAWAII 2 array
produced by Teledyne Scientific and Imaging, LLC. The cryostat interior
and the readout electronics are maintained at 90 Kelvin by helium
refrigerant-based cryo-coolers, while the IR array is cooled to 30
Kelvin. The Fore-Optics Module de-rotates and stabilizes the solar
image, provides scanning capabilities and transfers the GST image
to the Spectrograph. CYRA has been installed and is undergoing its
commissioning phase. This paper reports on the design, implementation,
and operation of CYRA in detail. The preliminary scientific results
have been highlighted as well.

---------------------------------------------------------
Title: In the Trenches of the Solar-Stellar Connection. I. Ultraviolet
and X-Ray Flux-Flux Correlations across the Activity Cycles of the
Sun and Alpha Centauri AB
Authors: Ayres, Thomas R.
2020ApJS..250...16A Altcode:
This study focuses on high-energy proxies of stellar magnetic activity
over long-term starspot cycles of three low-activity Sun-like stars: α
Centauri A (HD 128620: G2 V), α Cen B (HD 128621: K1 V), and the Sun
itself. Data sets include: daily solar ultraviolet irradiance spectra
and X-ray fluxes from the Solar Radiation and Climate Experiment,
during recent sunspot Cycles 23 and 24; Interface Region Imaging
Spectrograph long-slit stigmatic imaging of solar Mg II h (2803 Å)
and k (2796 Å) in quiet and active regions; and Hubble Space Telescope
Imaging Spectrograph ultraviolet, and Chandra X-ray, campaigns on α
Cen AB. Established stellar "flux-flux" relations, for example X-rays
(T ∼ 1 MK) versus Mg II (T ∼ 8000 K), showed increasing power-law
slopes with increasing formation temperature, but these give way on
the Sun to bent power laws, and surprising inversions in the activity
hierarchy: Si III is more "active" (steeper power laws) than N V,
despite the latter's four times higher formation temperature. The Sun's
flux-flux behavior, nevertheless, remarkably parallels its low-activity
solar twin α Cen A. In contrast, the cooler, somewhat more active, K
dwarf companion displays correlations more in line with the previous
stellar paradigm. The new flux-flux relations offer a way to vet
numerical spectral simulations and proxy-based irradiance models,
and extrapolate solar global activity indices into regimes below or
above the grasp of contemporary records, or to exoplanet hosts at the
low end of the Sun-like activity ladder.

---------------------------------------------------------
Title: The Bad Attitude Project
Authors: Ayres, Thomas
2020cxo..prop.5812A Altcode:
Spacecraft heating causes parts of Chandra's sky -- especially the
Ecliptic poles (EP) -- to be undesirable for scheduling. Normally, the
EP are a celestial sweet spot: always 90 degrees from Sun (good for
satellites and ground-based) and high-exposure for scanning missions
like TESS and eROSITA. HST's recent Ecliptic poles Stellar Survey
(EclipSS) identified 10 FUV-extreme stars among 49 late-type dwarfs of
the sample. Objective is to obtain short exposures of these objects
with HRC-I (best soft response), to link coronal X-rays to existing
FUV material. Jointly, HST/COS will cover key parts of the spectrum
(C IV and Mg II) reluctantly sacrificed in original survey. While
the EP target attitudes are bad, the exploration science is great,
and well worth the extra scheduling effort.

---------------------------------------------------------
Title: The (Chandra) Bad Attitude Project
Authors: Ayres, Thomas R.
2020hst..prop16376A Altcode:
Spacecraft heating causes parts of Chandra X-ray Observatory's
sky -- especially the Ecliptic poles (EP) -- to be undesirable for
scheduling. Normally, the EPs are celestial sweet spots. Always 90
degrees from the Sun, they are good for observations by satellites
and from the ground, and receive high exposurse by scanning missions
like TESS and eROSITA. HST's recent "Ecliptic poles Stellar Survey"
(EclipSS) identified 10 FUV-extreme stars among 49 late-type dwarfs
of the original target sample. Objective is to obtain short exposures
of these objects with Chandra's HRC-I camera (best soft response
of the available sensors), to link coronal X-rays to the existing
FUV material. Jointly, HST/COS will cover key parts of the spectrum
(especially C IV 155 nm) reluctantly sacrificed in the original fast
survey (single orbit per target). While the EP target attitudes are
"bad" (for Chandra heating), the exploration science is great, and
well worth the extra scheduling effort.

---------------------------------------------------------
Title: Stellar X-ray Cycles: the Shape of Things to Come
Authors: Ayres, Thomas R.
2020hst..prop16254A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of late-type
stars are relevant for understanding the Sun's analogous high-energy
modulations, in turn crucial to Earth-impacting "Space Weather"
(SW). Similarly, stellar SW counterparts can have eqivalent, or
more severe, adverse effects on their exoplanets. The solar decadal
oscillations are symptomatic of a deep-seated magnetic pump -- the
Dynamo -- whose internal workings remain elusive. Key question: is
Sun's 11-year cycle normal, or instead a transition state? A 3-year
continuation of previous long-term Chandra/HST programs will be carried
out for Alpha Cen AB (G2V+K1V) and Procyon (F5IV), nearby bright stars
that bracket the Sun in their fundamental stellar properties. HST
part of the program will measure FUV subcoronal (T~100,000 K) emission
lines, like Si IV 140 nm and C IV 155 nm, as well as the important
NUV chromospheric (T~10,000 K) emission doublet of Mg II at 280 nm,
in all three stars, with one visit of STIS echelle spectroscopy per
system each year. Non-standard wavecals provide better wavelength
calibrations, so that subtle Doppler shifts of the high-excitation
emissions can be assessed. Dynamical information also is encoded in
distortions of the line shapes, captured using combinations of FUV
medium- and high-resolution echelle settings.

---------------------------------------------------------
Title: Cycles and the Seven Dwarfs
Authors: Ayres, Thomas R.
2020hst..prop16253A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of late-type
stars are relevant for understanding the Sun's analogous high-energy
modulations, in turn crucial to Earth-impacting "Space Weather"
(SW). Similarly, stellar SW counterparts can have equivalent, or
more severe, adverse effects on their exoplanets. The solar decadal
oscillations are symptomatic of a deep-seated magnetic pump -- the
Dynamo -- whose internal workings remain elusive. Key question: is
Sun's 11-year cycle normal, or instead a transition state? A 3-year
addition to earlier long-term joint Chandra/HST programs (previously
involving Alpha Cen [G2V+K1V] and Procyon [F5IV]), will be carried
out for two new targets, the nearby binaries Xi Bootis (G8V+K4) and
70 Ophiuchi (K0V+K5V). The HST part of the program will measure
FUV subcoronal (T~100,000 K) emission lines, like Si IV 140 nm, C
IV 155 nm, and density-sensitive O IV 140 nm, as well as important
chromospheric (T~10,000 K) features, like O I 130 nm, C II 133 nm, and
C I 165 nm, in both pairs of stars, with one COS visit per system each
year. Analyses of these emissions, including dynamical information
encoded in Doppler shifts and distortions of the line shapes, can
provide insight concerning the thermal/pressure structure of the
anomalously hot outer layers of these stars; and how these structural
properties change with the ebb and flow of a magnetic activity cycle.

---------------------------------------------------------
Title: A Sensitive Test for Far Ultraviolet CO absorption in the
Outflow of our Nearest Supernova Progenitor - Antares
Authors: Harper, Graham M.; Ayres, Thomas R.; Guinan, Edward F.;
Ohnaka, Keiichi
2020hst..prop16256H Altcode:
The massive red supergiant Antares (alpha Sco A: M1 Iab) is an excellent
star to test theoretical models of mass loss because its distance,
age, stellar parameters, mass-loss rate, and interstellar reddening are
well established. The early-M supergiants pose a particular challenge
for models of mass loss driven by radiation pressure on molecules
and/or dust: The circumstellar molecular abundances and dust-to-gas
mass ratios are lower than for later-M spectral-types, but they
still manage to drive massive winds. We request deep FUV and NUV
observations to perform an extremely sensitive test for the most robust
circumstellar molecule, CO, by observing its Fourth-Positive electronic
bands against the FUV continuum of the M supergiant Antares. These
observations will enable us measure any CO present in the outflow,
and to place upper-limits on the effective radiation acceleration it
can provide. The proposed observations will also provide an invaluable
dataset for Antares, the oft neglected southern twin of Betelgeuse,
and our nearest Type II supernova progenitor.

---------------------------------------------------------
Title: What can ISM and non-photospheric highly ionised lines in
white dwarf spectra reveal about the β CMa tunnel?
Authors: Finch, Nicolle L.; Preval, S. P.; Barstow, M. A.; Casewell,
S. L.; Ayres, T.; Welsh, B.; Bainbridge, M.; Reindl, N.
2020IAUS..357..220F Altcode:
White dwarfs are useful objects with which to study the local
interstellar medium (ISM). High ionisation state absorption
features that cannot be attributed to the photosphere or the ISM
have been observed along the line-of-sight to a number of white dwarf
stars. Suggested origins of these lines include ionisation from past
supernovae, stellar winds, circumstellar disks, photoionisation from
nearby hot stars or also from the white dwarf itself. In this study we
consider the origin of these non-photospheric highly ionised lines in
two stars towards a rarefied region of the galaxy known as the extended
β CMa Tunnel. We present preliminary results from our analysis of
the first of these two stars.

---------------------------------------------------------
Title: VizieR Online Data Catalog: ASTRAL: reference spectra for
evolved M stars (Carpenter+, 2018)
Authors: Carpenter, K. G.; Nielsen, K. E.; Kober, G. V.; Ayres, T. R.;
Wahlgren, G. M.; Rau, G.
2019yCat..18690157C Altcode:
This paper focuses on the evolved cool stars γCru and αOri and
compares their spectral characteristics to the well-studied K1.5III
star αBoo (Hinkle+ 2005uaas.book.....H). The observational strategy
for α Ori and γ Cru, as for the other objects in the ASTRAL Cool
Star Program, was crafted to find the optimal combination of spectral
resolution and signal-to-noise over the complete FUV and NUV spectra
(1150-3159Å). All of the HST Space Telescope Imaging Spectrograph
(STIS) spectra for the two objects are splined in a top-level data set
covering the entire wavelength region. An overview of the data used in
this paper is presented in Table 1, and a more detailed description
of the data, including the observing strategy, data reduction,
coaddition, and splicing, can be found on the Advances Spectral
Library (ASTRAL) website (http://casa.colorado.edu/~ayres/ASTRAL/)
and at the Mikulski Archive for Space Telescopes (MAST)
(http://archive.stsci.edu/prepds/astral/). (4 data files).

---------------------------------------------------------
Title: Cycles and the Seven Dwarfs
Authors: Ayres, Thomas
2019cxo..prop.5712A Altcode:
Chandra has been following magnetic heartbeats of late-type stars
via high-contrast coronal X-rays. Goal is to provide fundamental
observational constraints for contemporary and future studies of
underlying magnetic Dynamo, whose internal workings remain elusive. The
Sun's high-energy modulations play important "Space Weather" role in our
heliosphere, as do stellar counterparts for their exoplanets. 3-year
time series (joint with HST) is proposed for promising new candidates
Xi Boo (G8V+K4) and 70 Oph (K0V+K5V), adding four more dwarfs to the
three in current "Cycles." Key question involves origin of diverging
branches in rotational period vs. cycle duration, where Sun's iconic
11-yr example sits in the middle, possibly in a transitional state.

---------------------------------------------------------
Title: Cycles and the Seven Dwarfs
Authors: Ayres, Thomas R.
2019hst..prop16003A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of late-type
stars are relevant for understanding the Sun's analogous high-energy
modulations, in turn crucial to Earth-impacting "Space Weather"
(SW). Similarly, stellar SW counterparts can have equivalent, or
more severe, adverse effects on their exoplanets. The solar decadal
oscillations are symptomatic of a deep-seated magnetic pump - the
Dynamo - whose internal workings remain elusive. Key question: is
Sun's 11-year cycle normal, or instead a transition state? A 3-year
addition to earlier long-term joint Chandra/HST programs (previously
involving Alpha Cen [G2V+K1V] and Procyon [F5IV]), will be carried
out for two new targets, the nearby binaries Xi Bootis (G8V+K4) and
70 Ophiuchi (K0V+K5V). The HST part of the program will measure
FUV subcoronal (T 100,000 K) emission lines, like Si IV 140 nm, C
IV 155 nm, and density-sensitive O IV 140 nm, as well as important
chromospheric (T 10,000 K) features, like O I 130 nm, C II 133 nm, and
C I 165 nm, in both pairs of stars, with one COS visit per system each
year. Analyses of these emissions, including dynamical information
encoded in Doppler shifts and distortions of the line shapes, can
provide insight concerning the thermal/pressure structure of the
anomalously hot outer layers of these stars; and how these structural
properties change with the ebb and flow of a magnetic activity cycle.

---------------------------------------------------------
Title: A far-UV survey of three hot, metal-polluted white dwarf stars:
WD0455-282, WD0621-376, and WD2211-495
Authors: Preval, Simon P.; Barstow, Martin A.; Bainbridge, Matthew;
Reindl, Nicole; Ayres, Thomas; Holberg, Jay B.; Barrow, John D.; Lee,
Chung-Chi; Webb, John K.; Hu, Jiting
2019MNRAS.487.3470P Altcode: 2019MNRAS.tmp.1440P; 2019arXiv190512350P
Using newly obtained high-resolution data (R ∼ 1 × 105)
from the Hubble Space Telescope, and archival UV data from the Far
Ultraviolet Spectroscopic Explorer, we have conducted a detailed UV
survey of the three hot, metal-polluted white dwarfs WD0455-282,
WD0621-376, and WD2211-495. Using bespoke model atmospheres, we
measured Teff, log g, and photospheric abundances for these
stars. In conjunction with data from Gaia, we measured masses, radii,
and gravitational redshift velocities for our sample of objects. We
compared the measured photospheric abundances with those predicted
by radiative levitation theory, and found that the observed Si
abundances in all three white dwarfs, and the observed Fe abundances
in WD0621-376 and WD2211-495, were larger than those predicted by an
order of magnitude. These findings imply not only an external origin
for the metals, but also ongoing accretion, as the metals not supported
by radiative levitation would sink on extremely short time-scales. We
measured the radial velocities of several absorption features along
the line of sight to the three objects in our sample, allowing us
to determine the velocities of the photospheric and interstellar
components along the line of sight for each star. Interestingly, we
made detections of circumstellar absorption along the line of sight
to WD0455-282 with three velocity components. To our knowledge, this
is the first such detection of multicomponent circumstellar absorption
along the line of sight to a white dwarf.

---------------------------------------------------------
Title: Make STIS Great Again!
Authors: Ayres, Thomas R.; Proffitt, Charles R.; Welty, Daniel E.
2019hst..prop15948A Altcode:
STIS is the premier high-resolution UV spectrograph in space, carrying
out state-of-the-art investigations of a dizzying array of cosmic
phenomena. While the instrument performance is superb, the CALSTIS
pipeline wavelength scales can be improved in two significant ways:
(1) collect new wavecal lamp exposures for echelle settings currently
lacking adequate calibration coverage in the modern (post-SM4) era; and
(2) build easy-to-apply corrections to compensate for small wavelength
distortions introduced by the low-order polynomial dispersion model
currently incorporated in the pipeline. In fact, success of the second
improvement depends on availability of "missing" calibrations delivered
by the first part. A modest expenditure of calibration time can enhance
the extensive legacy of STIS, now and into the future.

---------------------------------------------------------
Title: Constraining the magnetic field on white dwarf surfaces;
Zeeman effects and fine structure constant variation
Authors: Hu, J.; Webb, J. K.; Ayres, T. R.; Bainbridge, M. B.; Barrow,
J. D.; Barstow, M. A.; Berengut, J. C.; Carswell, R. F.; Dzuba, V. A.;
Flambaum, V. V.; Holberg, J. B.; Lee, C. C.; Preval, S. P.; Reindl,
N.; Tchang-Brillet, W. -Ü. L.
2019MNRAS.485.5050H Altcode: 2019MNRAS.tmp..796H; 2018arXiv181211480H
White dwarf (WD) atmospheres are subjected to gravitational potentials
around 105 times larger than occur on Earth. They provide
a unique environment in which to search for any possible variation
in fundamental physics in the presence of strong gravitational
fields. However, a sufficiently strong magnetic field will alter
absorption line profiles and introduce additional uncertainties in
measurements of the fine structure constant. Estimating the magnetic
field strength is thus essential in this context. Here, we model the
absorption profiles of a large number of atomic transitions in the WD
photosphere, including first-order Zeeman effects in the line profiles,
varying the magnetic field as a free parameter. We apply the method
to a high signal-to-noise, high-resolution, far-ultraviolet Hubble
Space Telescope/Space Telescope Imaging Spectrograph spectrum of the
WD G191-B2B. The method yields a sensitive upper limit on its magnetic
field of B &lt; 2300 G at the 3σ level. Using this upper limit, we find
that the potential impact of quadratic Zeeman shifts on measurements
of the fine structure constant in G191-B2B is 4 orders of magnitude
below laboratory wavelength uncertainties.

---------------------------------------------------------
Title: Stellar X-ray Cycles: the Shape of Things to Come
Authors: Ayres, Thomas R.
2019hst..prop15963A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of late-type
stars are relevant for understanding the Sun's analogous high-energy
modulations, in turn crucial to Earth-impacting "Space Weather"
(SW). Similarly, stellar SW counterparts can have eqivalent, or
more severe, adverse effects on their exoplanets. The solar decadal
oscillations are symptomatic of a deep-seated magnetic pump - the
Dynamo - whose internal workings remain elusive. Key question: is
Sun's 11-year cycle normal, or instead a transition state? A 3-year
continuation of previous long-term Chandra/HST programs will be carried
out for Alpha Cen AB (G2V+K1V) and Procyon (F5IV), nearby bright stars
that bracket the Sun in their fundamental stellar properties. HST
part of the program will measure FUV subcoronal (T 100,000 K) emission
lines, like Si IV 140 nm and C IV 155 nm, as well as the important
NUV chromospheric (T 10,000 K) emission doublet of Mg II at 280 nm,
in all three stars, with one visit of STIS echelle spectroscopy per
system each year. Non-standard wavecals provide better wavelength
calibrations, so that subtle Doppler shifts of the high-excitation
emissions can be assessed. Dynamical information also is encoded in
distortions of the line shapes, captured using combinations of FUV
medium- and high-resolution echelle settings.

---------------------------------------------------------
Title: Cool, evolved stars: results, challenges, and promises for
the next decade
Authors: Rau, Gioia; Montez, Rodolfo, Jr.; Carpenter, Kenneth;
Wittkowski, Markus; Bladh, Sara; Karovska, Margarita; Airapetian,
Vladimir; Ayres, Tom; Boyer, Martha; Chiavassa, Andrea; Clayton,
Geoffrey; Danchi, William; De Marco, Orsola; Dupree, Andrea K.;
Kaminski, Tomasz; Kastner, Joel H.; Kerschbaum, Franz; Linsky,
Jeffrey; Lopez, Bruno; Monnier, John; Montargès, Miguel; Nielsen,
Krister; Ohnaka, Keiichi; Ramstedt, Sofia; Roettenbacher, Rachael;
ten Brummelaar, Theo; Paladini, Claudia; Sarangi, Arkaprabha; van
Belle, Gerard; Ventura, Paolo
2019BAAS...51c.241R Altcode: 2019arXiv190304585R; 2019astro2020T.241R
This White Paper identifies compelling scientific opportunities in
the field of Cool, Evolved Stars, describing the observational and
theoretical challenges to our understanding, and the key advancements
made. We portray the pathway towards understanding, and identify,
through recommendations, which advancements are necessary in 2020-2030
&amp; beyond.

---------------------------------------------------------
Title: STROBE-X: X-ray Timing and Spectroscopy on Dynamical Timescales
from Microseconds to Years
Authors: Ray, Paul S.; Arzoumanian, Zaven; Ballantyne, David;
Bozzo, Enrico; Brandt, Soren; Brenneman, Laura; Chakrabarty, Deepto;
Christophersen, Marc; DeRosa, Alessandra; Feroci, Marco; Gendreau,
Keith; Goldstein, Adam; Hartmann, Dieter; Hernanz, Margarita;
Jenke, Peter; Kara, Erin; Maccarone, Tom; McDonald, Michael;
Nowak, Michael; Phlips, Bernard; Remillard, Ron; Stevens, Abigail;
Tomsick, John; Watts, Anna; Wilson-Hodge, Colleen; Wood, Kent; Zane,
Silvia; Ajello, Marco; Alston, Will; Altamirano, Diego; Antoniou,
Vallia; Arur, Kavitha; Ashton, Dominic; Auchettl, Katie; Ayres, Tom;
Bachetti, Matteo; Balokovic, Mislav; Baring, Matthew; Baykal, Altan;
Begelman, Mitch; Bhat, Narayana; Bogdanov, Slavko; Briggs, Michael;
Bulbul, Esra; Bult, Petrus; Burns, Eric; Cackett, Ed; Campana,
Riccardo; Caspi, Amir; Cavecchi, Yuri; Chenevez, Jerome; Cherry,
Mike; Corbet, Robin; Corcoran, Michael; Corsi, Alessandra; Degenaar,
Nathalie; Drake, Jeremy; Eikenberry, Steve; Enoto, Teruaki; Fragile,
Chris; Fuerst, Felix; Gandhi, Poshak; Garcia, Javier; Goldstein,
Adam; Gonzalez, Anthony; Grefenstette, Brian; Grinberg, Victoria;
Grossan, Bruce; Guillot, Sebastien; Guver, Tolga; Haggard, Daryl;
Heinke, Craig; Heinz, Sebastian; Hemphill, Paul; Homan, Jeroen;
Hui, Michelle; Huppenkothen, Daniela; Ingram, Adam; Irwin, Jimmy;
Jaisawal, Gaurava; Jaodand, Amruta; Kalemci, Emrah; Kaplan, David;
Keek, Laurens; Kennea, Jamie; Kerr, Matthew; van der Klis, Michiel;
Kocevski, Daniel; Koss, Mike; Kowalski, Adam; Lai, Dong; Lamb, Fred;
Laycock, Silas; Lazio, Joseph; Lazzati, Davide; Longcope, Dana;
Loewenstein, Michael; Maitra, Dipankair; Majid, Walid; Maksym,
W. Peter; Malacaria, Christian; Margutti, Raffaella; Martindale,
Adrian; McHardy, Ian; Meyer, Manuel; Middleton, Matt; Miller, Jon;
Miller, Cole; Motta, Sara; Neilsen, Joey; Nelson, Tommy; Noble,
Scott; O'Brien, Paul; Osborne, Julian; Osten, Rachel; Ozel, Feryal;
Palliyaguru, Nipuni; Pasham, Dheeraj; Patruno, Alessandro; Pelassa,
Vero; Petropoulou, Maria; Pilia, Maura; Pohl, Martin; Pooley, David;
Prescod-Weinstein, Chanda; Psaltis, Dimitrios; Raaijmakers, Geert;
Reynolds, Chris; Riley, Thomas E.; Salvesen, Greg; Santangelo, Andrea;
Scaringi, Simone; Schanne, Stephane; Schnittman, Jeremy; Smith, David;
Smith, Krista Lynne; Snios, Bradford; Steiner, Andrew; Steiner, Jack;
Stella, Luigi; Strohmayer, Tod; Sun, Ming; Tauris, Thomas; Taylor,
Corbin; Tohuvavohu, Aaron; Vacchi, Andrea; Vasilopoulos, Georgios;
Veledina, Alexandra; Walsh, Jonelle; Weinberg, Nevin; Wilkins, Dan;
Willingale, Richard; Wilms, Joern; Winter, Lisa; Wolff, Michael; in
't Zand, Jean; Zezas, Andreas; Zhang, Bing; Zoghbi, Abdu
2019arXiv190303035R Altcode:
We present the Spectroscopic Time-Resolving Observatory for Broadband
Energy X-rays (STROBE-X), a probe-class mission concept selected for
study by NASA. It combines huge collecting area, high throughput, broad
energy coverage, and excellent spectral and temporal resolution in a
single facility. STROBE-X offers an enormous increase in sensitivity
for X-ray spectral timing, extending these techniques to extragalactic
targets for the first time. It is also an agile mission capable of
rapid response to transient events, making it an essential X-ray
partner facility in the era of time-domain, multi-wavelength, and
multi-messenger astronomy. Optimized for study of the most extreme
conditions found in the Universe, its key science objectives include:
(1) Robustly measuring mass and spin and mapping inner accretion
flows across the black hole mass spectrum, from compact stars to
intermediate-mass objects to active galactic nuclei. (2) Mapping out
the full mass-radius relation of neutron stars using an ensemble of
nearly two dozen rotation-powered pulsars and accreting neutron stars,
and hence measuring the equation of state for ultradense matter
over a much wider range of densities than explored by NICER. (3)
Identifying and studying X-ray counterparts (in the post-Swift era)
for multiwavelength and multi-messenger transients in the dynamic sky
through cross-correlation with gravitational wave interferometers,
neutrino observatories, and high-cadence time-domain surveys in other
electromagnetic bands. (4) Continuously surveying the dynamic X-ray
sky with a large duty cycle and high time resolution to characterize
the behavior of X-ray sources over an unprecedentedly vast range of
time scales. STROBE-X's formidable capabilities will also enable a
broad portfolio of additional science.

---------------------------------------------------------
Title: Chandra’s Stars
Authors: Ayres, Thomas
2019HEAD...1710502A Altcode:
Stars are the powerhouses and chemical factories of galaxies; hosts of
exoplanets that in some cases might harbor life. It is not surprising,
then, that stars are principal objects of interest to astronomers. What
is surprising: normal stars are frequent targets of kilo-volt X-ray
observatories, given that stellar surfaces have temperatures no
more than 0.01 keV (extreme O-type stars, at that). Nevertheless,
hydrodynamic and magnetic phenomena on stars conspire to create
conditions hundreds of times hotter than the tepid photospheres,
to drive copious X-ray emissions in many cases. Examples include:
radiative instability shocks in the warm, fast winds of early-type
supergiants; accretion splash-down spots on protostars; magnetic
coronae of Main-sequence cool stars; and high-energy flares from a
wide variety of objects. Chandra has played a key role in stellar
X-ray studies over the past two decades because, among many examples,
the high spatial resolution can associate X-ray sources with optical and
IR counterparts in crowded star-forming regions; the low-resolution CCD
spectra can characterize faint point sources, such as planet-hosts and
young embedded protostars; and the transmission gratings can diagnose
plasma conditions in shocked stellar winds, T-Tauri accretion columns,
and hyperactive stellar coronae. In addition to a general overview
of Chandra’s impact on stellar astronomy, the presentation will
mention long-term coronal activity cycles of the two sunlike stars of
the nearby Alpha Centauri triple system, with relevance to planetary
habitability; and the temporal behavior of serendipitous sources in
the Chandra HRC-I field around Alpha Cen, as a guide to what might be
anticipated in large-area X-ray surveys of the future.

---------------------------------------------------------
Title: The extreme O-type spectroscopic binary HD 93129A. A
quantitative, multiwavelength analysis
Authors: Gruner, D.; Hainich, R.; Sander, A. A. C.; Shenar, T.; Todt,
H.; Oskinova, L. M.; Ramachandran, V.; Ayres, T.; Hamann, W. -R.
2019A&A...621A..63G Altcode: 2018arXiv181107820G
Context. HD 93129A was classified as the earliest O-type star
in the Galaxy (O2 If*) and is considered as the prototype of its
spectral class. However, interferometry shows that this object is
a binary system, while recent observations even suggest a triple
configuration. None of the previous spectral analyses of this object
accounted for its multiplicity. With new high-resolution UV and optical
spectra, we have the possibility to reanalyze this key object, taking
its binary nature into account for the first time. Aims: We
aim to derive the fundamental parameters and the evolutionary status
of HD 93129A, identifying the contributions of both components to
the composite spectrum Methods: We analyzed UV and optical
observations acquired with the Hubble Space Telescope and ESO's Very
Large Telescope. A multiwavelength analysis of the system was performed
using the latest version of the Potsdam Wolf-Rayet model atmosphere
code. Results: Despite the similar spectral types of the two
components, we are able to find signatures from each of the components
in the combined spectrum, which allows us to estimate the parameters of
both stars. We derive log(L/L⊙) = 6.15, Teff
= 52 kK, and log Ṁ = -4.7 [M⊙ yr-1] for
the primary Aa, and log(L/L⊙) = 5.58, Teff
= 45 kK, and log Ṁ = -5.8 [M⊙yr-1] for the
secondary Ab. Conclusions: Even when accounting for the binary
nature, the primary of HD 93129A is found to be one of the hottest
and most luminous O stars in our Galaxy. Based on the theoretical
decomposition of the spectra, we assign spectral types O2 If* and O3
III(f*) to components Aa and Ab, respectively. While we achieve a good
fit for a wide spectral range, specific spectral features are not fully
reproduced. The data are not sufficient to identify contributions
from a hypothetical third component in the system. Based on
observations made with the NASA/ESA Hubble Space Telescope, obtained
(from the Data Archive) at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555. These observations
are associated with program GO-13346.Based on observations collected
at the European Organisation for Astronomical Research in the Southern
Hemisphere under ESO programme 095.D-0234(A).

---------------------------------------------------------
Title: Chapter 2 - Stellar and Solar Chromospheres and Attendant
Phenomena
Authors: Ayres, Thomas R.
2019sgsp.book...27A Altcode:
This chapter describes several aspects of stars that inform us about the
Sun, especially characteristics that might have changed significantly
on our star's journey to its present evolutionary state. The focus
is on stellar "chromospheres," an important byproduct of magnetic
"activity," because this is a key area in solar physics today and one
in which the stars can be most informative. The main topic is why
chromospheres exist: the warm, extensive outer atmospheres of cool
stars, a consequence of nonradiative heating mainly devolving from
magnetic effects. Ancillary topics consider two different aspects of
the underlying magnetic activity: the rotation-age-activity connection,
primary signature of magnetic evolution over time; and activity cycles,
outward manifestations of an enigmatic, poorly understood, and perhaps
equally poorly synchronized magnetic clock deep in the stellar interior.

---------------------------------------------------------
Title: HST/COS Ecliptic-poles Stellar Survey (EclipSS)
Authors: Ayres, Thomas R.
2019AAS...23336303A Altcode:
Ecliptic-poles Stellar Survey (EclipSS) currently is collecting
far-ultraviolet spectra (115-143 nm), using HST's ultra-sensitive Cosmic
Origins Spectrograph (COS), of a sample of 49 F2-K2 dwarf stars in the
North and South ecliptic polar regions, to further advance studies of
magnetic activity among cool Main sequence stars similar to the Sun. The
ecliptic poles are favored places for current and up-coming astronomical
survey satellites, including TESS (exoplanets and asteroseismology) and
eROSITA (coronal X-rays). These instruments scan along lines of ecliptic
longitude, and thus accumulate their deepest exposures close to the
ecliptic poles. EclipSS targets were selected to be bright enough for
eROSITA, not too bright for TESS, and just right for COS. The combined
photometric (starspots), asteroseismic, FUV, and X-ray measurements will
provide synergistic information concerning rotation periods, radii,
masses, metallicities, ages, activity levels, and coronal properties
to inform community-wide efforts to explore stellar activity and its
underlying magnetic engine, the Dynamo. As of September 2018, about
half of the EclipSS sample has been successfully observed by COS.

---------------------------------------------------------
Title: Serendipitous X-Ray Sources in the Chandra HRC Field around
Alpha Centauri
Authors: Ayres, Thomas R.
2018AJ....156..274A Altcode: 2018arXiv181011674A
For more than a decade, Alpha Centauri AB (G2 V+K1 V) has been
observed by Chandra, in a long-term program to follow coronal (T ∼
106 K) activity cycles of the two sunlike stars. Over
2008.4-2017.8, 19 HRC-I exposures were taken, each about 10 ks in
duration, and spaced about six months apart. Beyond monitoring the AB
X-ray luminosities, the HRC-I sequence represents a unique decadal
record of the dozen, or so, serendipitous X-ray sources in the α
Cen field, which is at low Galactic latitude and thus dominated by
nearby stars. For the present study, the 10 brightest candidates
were considered. Only a handful of these were persistent; most were
variable, some highly so, flaring in a few epochs, weak or absent
in the others. All 10 X-ray sources have Gaia objects within about
2″ mostly late-type dwarfs, but a few giants. However, two of the
proposed optical counterparts have statistically significant offsets,
and possible conflicts between the X-ray and optical properties. Another
of the candidates brightened by a factor of 100 in X-rays during
a single exposure, briefly attaining super-flare status. The Gaia
counterpart is anomalously blue for its absolute G-magnitude and likely
is a WD+dM pair. To the extent that the low Galactic latitude field
is representative, the Chandra time-domain view emphasizes that the
high-energy stellar sky is biased toward transient sources, so any
snapshot survey surely will miss many of the most interesting objects.

---------------------------------------------------------
Title: The Advanced Spectral Library (ASTRAL): Reference Spectra
for Evolved M Stars
Authors: Carpenter, Kenneth G.; Nielsen, Krister E.; Kober, Gladys V.;
Ayres, Thomas R.; Wahlgren, Glenn M.; Rau, Gioia
2018ApJ...869..157C Altcode: 2018arXiv181111865C
The HST Treasury Program Advanced Spectral Library Project: Cool Stars
was designed to collect representative, high-quality UV spectra of eight
evolved F-M type cool stars. The Space Telescope Imaging Spectrograph
(STIS) echelle spectra of these objects enable investigations of a broad
range of topics, including stellar and interstellar astrophysics. This
paper provides a guide to the spectra of the two evolved M stars, the
M2 Iab supergiant α Ori and the M3.4 giant γ Cru, with comparisons to
the prototypical K1.5 giant α Boo. It includes identifications of the
significant atomic and molecular emission and absorption features and
discusses the character of the photospheric and chromospheric continua
and line spectra. The fluorescent processes responsible for a large
portion of the emission-line spectrum, the characteristics of the
stellar winds, and the available diagnostics for hot and cool plasmas
are also summarized. This analysis will facilitate the future study of
the spectra, outer atmospheres, and winds, not only of these objects
but of numerous other cool, low-gravity stars, for years to come. Based on observations with the NASA/ESA Hubble Space Telescope
obtained at the Space Telescope Science Institute, which is operated
by the Association of Universities for Research in Astronomy, Inc.,
under NASA contract NAS5-26555.

---------------------------------------------------------
Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
2018A&A...619L...6N Altcode: 2018arXiv181005223N
We present an overview of high-resolution quiet Sun observations,
from disk center to the limb, obtained with the Atacama Large
millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
regions were observed at a resolution of up to 2.5″ by 4.5″. We
produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full-disk
solar images. The images show well the chromospheric network, which,
based on the unique segregation method we used, is brighter than the
average over the fields of view of the observed regions by ∼305
K while the intranetwork is less bright by ∼280 K, with a slight
decrease of the network/intranetwork contrast toward the limb. At 3
mm the network is very similar to the 1600 Å images, with somewhat
larger size. We detect, for the first time, spicular structures,
rising up to 15″ above the limb with a width down to the image
resolution and brightness temperature of ∼1800 K above the local
background. No trace of spicules, either in emission or absorption,
is found on the disk. Our results highlight the potential of ALMA for
the study of the quiet chromosphere.

---------------------------------------------------------
Title: Stellar X-ray Cycles: the Shape of Things to Come
Authors: Ayres, Thomas R.
2018hst..prop15618A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of late-type
stars are followed with highest sensitivity in coronal X-rays. Sun's
high-energy modulations are crucial to Earth-impacting Space Weather, as
stellar counterparts are for their exoplanets. The decadal oscillations
are symptomatic of a deep-seated magnetic pump - the Dynamo - whose
internal workings remain elusive. Key question: is solar 11-year cycle
normal, or instead a transition state? 3-year continuation of previous
CXO/HST program is proposed for Alpha Cen AB (G2V+K1V) and Procyon
(F5IV). Alpha Cen cycles bracket solar behavior, although true period
of sunlike A is uncertain. So far, Procyon is a flat-liner. Shape of
rise and fall of cycle is a key diagnostic, most clearly traced at
high energies.\n\nHST part of the program will measure FUV subcoronal
(T 100,000 K) emission lines, like Si IV 140 nm and C IV 155 nm, as
well as the important NUV chromospheric (T 10,000 K) emission doublet
of Mg II at 280 nm, in all three stars, with one visit of STIS echelle
spectroscopy per system each year. Non-standard wavecals are used to
provide better wavelength calibrations, so that subtle Doppler shifts of
the high-excitation transitions can be assessed. Dynamical information
also is incoded in distortions of the emission lineshapes, which are
captured using a combination of FUV medium- and high-resolution echelle
settings. This program builds on previous long-term Chandra/HST time
series on both systems.

---------------------------------------------------------
Title: Beyond the Coronal Graveyard
Authors: Ayres, Thomas R.
2018AJ....156..163A Altcode: 2018arXiv180806092A
New Chandra High Resolution Camera pointings on the “non-coronal”
red giant Arcturus (HD 124897; α Boo: K1.5 III) corroborate a
tentative soft X-ray detection in a shorter exploratory exposure
16 years earlier. The apparent source followed the (large) proper
motion of the nearby bright star over the intervening years, and there
were null detections at the previous location in the current epoch,
as well as at the future location in the earlier epoch, reducing
the possibility of chance coincidences with unrelated high-energy
objects. The apparent X-ray brightness at Earth, averaged over the 98
ks of total exposure and accounting for absorption in the red giant’s
wind, is ∼2 × 10-15 erg cm-2 s-1
(0.2-2 keV). Systematic errors in the energy conversion factor,
devolving from the unknown spectrum, amount to only about 10%, smaller
than the ∼30% statistical uncertainties in the count rates. The
X-ray luminosity is only 3 × 1025 erg s-1,
confirming Arcturus as one of Chandra’s darkest bright stars.

---------------------------------------------------------
Title: Stellar X-ray Cycles: the Shape of Things to Come
Authors: Ayres, Thomas
2018cxo..prop.5446A Altcode:
Somewhat erratic, unpredictable long-term starspot cycles of
late-type stars are followed with highest sensitivity in coronal
X-rays. Sun's high-energy modulations are crucial to Earth-impacting
"Space Weather," as stellar counterparts are for their exoplanets. The
decadal oscillations are symptomatic of a deep-seated magnetic pump --
the Dynamo -- whose internal workings remain elusive. Key question:
is solar 11-year cycle normal, or instead a transition state? 3-year
continuation of previous CXO/HST program is proposed for Alpha Cen AB
(G2V+K1V) and Procyon (F5IV). Alpha Cen cycles bracket solar behavior,
although true period of sunlike A is uncertain. So far, Procyon is
a flat-liner. Shape of rise and fall of cycle is a key diagnostic,
most clearly traced at high energies.

---------------------------------------------------------
Title: An Accurate Mass of the 31 Cygni Red Supergiant
Authors: Bennett, Philip, D.; Brown, Alexander; Ayres, Thomas R.
2018csss.confE..46B Altcode:
Red supergiants are massive, evolved stars that are among the brightest
stars in the near infrared. But the uncertain physics of mass loss
limits the ability of evolutionary models to accurately represent
these stars in detail. Lacking a fundamental, predictive theory of mass
loss, this process is normally incorporated into stellar models using
simple parametric formulas such as Reimer’s Law. In this situation,
it is important to constrain theoretical models evolved using such mass
loss parametrizations by observation. A key stellar parameter
is mass. In combination with a star’s position in the H-R diagram, a
well-determined mass provides a strong constraint on stellar evolution
models. Unfortunately, there are very few red supergiants with masses
known to even 5% accuracy. In response, the objective of Hubble Space
Telescope GO program 14070 (PI: Bennett) was to determine the mass
of the red supergiant K star in the long-period eclipsing binary 31
Cygni (K4 Ib + B3 V) accurate to 1%. To obtain this accuracy requires
the incorporation of new optical radial velocity observations of the
supergiant; that work is in progress. But the observational program
of GO-14070 is now complete, and these new HST/STIS observations
of the 31 Cyg binary in the ultraviolet have provided an immediate
determination of the secondary orbit radial velocity amplitude,
K2, accurate to 1%. This result suffices to determine the masses of
both 31 Cyg stars to an accuracy of about 2%, and provides a useful
constraint on the evolution of the intermediate-mass red supergiant
in this well-separated binary system.

---------------------------------------------------------
Title: Chandra X-ray Time-Domain Study of Alpha Centauri AB, Procyon,
and their Environs
Authors: Ayres, Thomas R.
2018AAS...23231714A Altcode:
For more than a decade, Chandra X-ray Observatory has been monitoring
the central AB binary (G2V+K1V) of the α Centauri triple system with
semi-annual pointings, using the High-Resolution Camera. This study has
been extended in recent years to the mid-F subgiant, Procyon. The main
objective is to follow the coronal (T~1MK) activity variations of the
three stars, analogous to the Sun's 11-year sunspot cycle. Tentative
periods of 20 yr and 8 yr have been deduced for α Cen A and B,
respectively; but so far Procyon has shown only a slow, very modest
decline in count rate, which could well reflect a slight instrumental
degradation rather than intrinsic behavior. The negligible high-energy
variability of Procyon sits in stark contrast to the dramatic factor of
several to ten changes in the X-ray luminosities of α Cen AB and the
Sun over their respective cycles. Further, although sunlike α Cen A
has been observed by successive generations of X-ray observatories for
nearly four decades, albeit sporadically, there are key gaps in the
coverage that affect the determination of the cycle period. In fact,
the most recent pointings suggest a downturn in A's count rate that
might be signaling a shorter, more solar-like cycle following a delayed
minimum in the 2005--2010 time frame (perhaps an exaggerated version
of the extended solar minimum between recent Cycles 23 and 24). Beyond
the coronal cycles of the three stars, the sequence of periodic X-ray
images represents a unique time-domain history concerning steady as well
as variable sources in the two 30'x30' fields. The most conspicuous of
the variable objects -- in the α Cen field -- will be described here.

---------------------------------------------------------
Title: The Carbon Isotope Ratio of the Sun and Implications for the
Solar Nebula
Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R.
2018LPI....49.2907L Altcode:
The solar C isotope ratio is -45 permil PDB. The 13C enrichment of the
terrestrial planets may be due to CO self-shielding in the nebula or
parent cloud.

---------------------------------------------------------
Title: Cracking the Conundrum of F-supergiant Coronae
Authors: Ayres, Thomas R.
2018ApJ...854...95A Altcode: 2018arXiv180202552A
Chandra X-ray and HST far-ultraviolet (FUV) observations of three
early-F supergiants have shed new light on a previous puzzle involving
a prominent member of the class: α Persei (HD 20902: F5 Ib). The warm
supergiant is a moderately strong, hard coronal (T∼ {10}7
K) X-ray source, but has 10 times weaker “subcoronal” Si IV 1393
Å (T∼ 8× {10}4 K) emissions than early-G supergiants
of similar high-energy properties. The α Per X-ray excess was
speculatively ascribed to a close-in hyperactive G-dwarf companion,
which could have escaped previous notice, lost in the glare of the
bright star. However, a subsequent dedicated multi-wavelength imaging
campaign failed to find any evidence for a resolved secondary. The
origin of the α Per high-energy dichotomy then devolved to (1) an
unresolved companion or (2) intrinsic coronal behavior. Exploring
the second possibility, the present program has found that early-F
supergiants do appear to belong to a distinct coronal class,
characterized by elevated X-ray/FUV ratios, although sharing some
similarities with Cepheid variables in their transitory X-ray
“high states.” Remarkably, the early-F supergiants now are seen
to align with the low-activity end of the X-ray/FUV sequence defined
by late-type dwarfs, suggesting that the disjoint behavior relative
to the G supergiants might be attributed to thinner outer atmospheres
on the F types, as in dwarfs, but in this case perhaps caused by a
weakened “ionization valve” effect due to overly warm photospheres.

---------------------------------------------------------
Title: Alpha Centauri Beyond the Crossroads
Authors: Ayres, T. R.
2018RNAAS...2...17A Altcode: 2018RNAAS...2a..17A
No abstract at ADS

---------------------------------------------------------
Title: Procyon: New Candidate for the Dynamo Clinical Trial
Authors: Ayres, Thomas
2017hst..prop15327A Altcode:
This is the third year of a joint Chandra/HST program to follow
the evolution of the high-energy (X-ray and UV) activity cycles of
the nearby mid-F subgiant Procyon. This bright star has high-energy
attributes that are similar to the Sun, yet it is a hotter star, at the
edge of the region in the H-R diagram where surface convection occurs
(the power source for stellar magnetic activity). The HST part is to
record STIS UV spectra of the bright star on a semiannual basis at
high echelle resolution and high S/N, especially to capture the FUV
Fe XII 124,134 nm coronal forbidden lines, which can tie together
the non-simultaneous Chandra X-ray and HST pointings; as well as to
record other key high-energy species like Si IV, C IV, and N V. The
latter display Doppler-shifted, bimodal distorted emission profiles
that signify high-powered dynamics in the interface regions of the
stellar atmosphere between the super-hot corona (&gt;1 MK) and the
cold photosphere (&lt;6000 K). The associated flows are a hot topic in
contemporary solar physics, and one focus of a new space-based solar
imaging spectrometer called IRIS. The solar and stellar FUV views are
strongly complementary. The HST part of the program has two general
objectives: (1) follow changes in the FUV spectra associated with any
slowly evolving X-ray activity cycle of Procyon; and (2) combine the
multiple epochs of echelle spectra to provide the highest possible
S/N for identifying weak, but diagnostically important, emission lines
(absorption, in some cases), and for decomposing the high-temperature
line profiles (e.g., Si IV, C IV) into multiple dynamical components
(which are though to be symptomatic of coronal heating and cooling
processes).

---------------------------------------------------------
Title: Ecliptic-poles Stellar Survey (EclipSS)
Authors: Ayres, Thomas
2017hst..prop15300A Altcode:
BACKGROUND: Now and in coming years, a number of orbiting
observatories will be scanning the skies for astrometry (Gaia),
transiting exoplanets (TESS), and high-energy sources (eROSITA). A
key characteristic of these surveys is their high degree of exposure
in the ecliptic polar regions, north and south; a natural consequence
of their preferred scanning orientation. Further, JWST, although not a
scanning instrument, also holds the ecliptic poles in special regard
because they are accessible at all times (continuous viewing zones),
a key advantage for exo-planet studies.THIS PROPOSAL: Record FUV
spectra, with COS G130M, of a well-defined sample of sunlike dwarfs
(F2V-K2V) at the ecliptic poles to take advantage of the enhanced,
wholistic information concerning rotation periods, sizes, masses,
metallicities, ages, activity levels, and coronal properties that will
be available for bright e-polar stars over the next few years. There
is a sweet spot at about 8th magnitude where sunlike stars are not
too bright for TESS, bright enough for eROSITA, and just right for
COS. The G130M channel captures a wide range of ionization states,
especially of Si, N, O, and C; the hydrogen Lyman-alpha emission;
and also coronal forbidden transitions of Fe XII (124 nm) and Fe XXI
(135 nm); altogether reflecting gas temperatures from 10,000 K to 10 MK
in the magnetically disturbed stellar outer atmospheres. The combined
photometric (starspots), asteroseismic, FUV, and X-ray measurements
will inform community-wide efforts to explore stellar activity and its
underlying magnetic machine, the Dynamo. This is a unique opportunity,
and one - like a solar eclipse - too good to pass up.

---------------------------------------------------------
Title: The Initial C Isotope Ratio for the Solar System
Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R.
2017LPICo1967.4186L Altcode:
Using spectroscopic observations of CO in the solar photosphere,
we have determined the 13C/12C ratio for the Sun, and therefore for
the bulk initial solar system. The Sun is light in 13C by 50 permil
compared to bulk Earth and marine carbonates.

---------------------------------------------------------
Title: The Carbon Isotope Composition of the Sun: Implications for
Solar System Formation
Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R.
2017LPICo1987.6370L Altcode:
Following a new analysis of CO spectral lines in the solar
photosphere, we have obtained a C isotope ratio of d13C = -48 ± 7‰
VPDB. Enrichment of terrestrial planets in 13C may have occurred due
to CO self-shielding in the parent cloud.

---------------------------------------------------------
Title: VizieR Online Data Catalog: New FeI level energies from
stellar spectra. II. (Peterson+, 2017)
Authors: Peterson, R. C.; Kurucz, R. L.; Ayres, T. R.
2017yCat..22290023P Altcode:
All of the new space-based UV spectra were obtained at a two-pixel
resolution of 110000 with the E230H echelle grating of the Space
Telescope Imaging Spectrograph (STIS) on HST, under program GO-14161
(R. Peterson, PI). See section 2 for further explanations. (2
data files).

---------------------------------------------------------
Title: An abundance analysis from the STIS-HST UV spectrum of the
non-magnetic Bp star HR 6000
Authors: Castelli, F.; Cowley, C. R.; Ayres, T. R.; Catanzaro, G.;
Leone, F.
2017A&A...601A.119C Altcode: 2017arXiv170109172C
Context. The sharp-line spectrum of the non-magnetic, main-sequence Bp
star HR 6000 has peculiarities that distinguish it from those of the
HgMn stars with which it is sometimes associated. The position of the
star close to the center of the Lupus 3 molecular cloud, whose estimated
age is on the order of 9.1 ± 2.1 Myr, has lead to the hypothesis
that the anomalous peculiarities of HR 6000 can be explained by the
young age of the star. Aims: Observational material from the
Hubble Space Telescope (HST) provides the opportunity to extend the
abundance analysis previously performed for the optical region and
clarify the properties of this remarkable peculiar star. Our aim was
to obtain the atmospheric abundances for all the elements observed in
a broad region from 1250 to 10 000 Å. Methods: An LTE synthetic
spectrum was compared with a high-resolution spectrum observed with the
Space Telescope Imaging Spectrograph (STIS) equipment in the 1250-3040
Å interval. Abundances were changed until the synthetic spectrum fit
the observed spectrum. The assumed model is an LTE, plane-parallel,
line-blanketed ATLAS12 model already used for the abundance analysis of
a high-resolution optical spectrum observed at ESO with the Ultraviolet
and Visual Echelle Spectrograph (UVES). The stellar parameters are
Teff = 13450 K, log g = 4.3, and zero microturbulent
velocity. Results: Abundances for 28 elements and 7 upper
limits were derived from the ultraviolet spectrum. Adding results
from previous work, we have now quantitative results for 37 elements,
some of which show striking contrasts with those of a broad sample of
HgMn stars. The analysis has pointed out numerous abundance anomalies,
such as ionization anomalies and line-to-line variation in the derived
abundances, in particular for silicon. The inferred discrepancies could
be explained by non-LTE effects and with the occurrence of diffusion
and vertical abundance stratification. In the framework of the last
hypothesis, we obtained, by means of trial and error, empirical step
functions of abundance versus optical depth log (τ5000)
for carbon, nitrogen, silicon, manganese, and gold, while we failed
to find such a function for phosphorous. The poor results for carbon,
and mostly for phosphorus, suggest the possible importance in this
star of NLTE effects to be investigated in future works.

---------------------------------------------------------
Title: New Fe I Level Energies and Line Identifications from
Stellar Spectra. II. Initial Results from New Ultraviolet Spectra
of Metal-poor Stars
Authors: Peterson, Ruth C.; Kurucz, Robert L.; Ayres, Thomas R.
2017ApJS..229...23P Altcode:
The Fe I spectrum is critical to many areas of astrophysics, yet many of
the high-lying levels remain uncharacterized. To remedy this deficiency,
Peterson &amp; Kurucz identified Fe I lines in archival ultraviolet
and optical spectra of metal-poor stars, whose warm temperatures favor
moderate Fe I excitation. Sixty-five new levels were recovered, with
1500 detectable lines, including several bound levels in the ionization
continuum of Fe I. Here, we extend the previous work by identifying
59 additional levels, with 1400 detectable lines, by incorporating new
high-resolution UV spectra of warm metal-poor stars recently obtained
by the Hubble Space Telescope Imaging Spectrograph. We provide gf
values for these transitions, both computed as well as adjusted to
fit the stellar spectra. We also expand our spectral calculations to
the infrared, confirming three levels by matching high-quality spectra
of the Sun and two cool stars in the H-band. The predicted gf values
suggest that an additional 3700 Fe I lines should be detectable
in existing solar infrared spectra. Extending the empirical line
identification work to the infrared would help confirm additional Fe I
levels, as would new high-resolution UV spectra of metal-poor turnoff
stars below 1900 Å.

---------------------------------------------------------
Title: The Hubble Spectroscopic Legacy Archive
Authors: Peeples, M.; Tumlinson, J.; Fox, A.; Aloisi, A.; Fleming,
S.; Jedrzejewski, R.; Oliveira, C.; Ayres, T.; Danforth, C.; Keeney,
B.; Jenkins, E.
2017cos..rept....4P Altcode:
With no future space ultraviolet instruments currently planned,
the data from the UV spectrographs aboard the Hubble Space Telescope
have a legacy value beyond their initial science goals. The goal of
the Hubble Spectroscopic Legacy Archive(HSLA) is to provide to the
community new science-grade combined spectra for all publicly available
data obtained by the Cosmic Origins Spectrograph (COS)and the Space
Telescope Imaging Spectrograph (STIS). These data are packaged into
"smart archives" according to target type and scientific themes to
facilitate the construction of archival samples for common science
uses. A new "quick look" capability makes the data easy for users
to quickly access, assess the quality of,and download for archival
science. The first generation of these products for the far-ultraviolet
(FUV) modes of COS was made available online via the Mikulski Archive
for Space Telescopes (MAST) in early 2016 and updated in early 2017;
future releases will include COS/NUV and STIS/UV data.

---------------------------------------------------------
Title: Fundamental Physics from Observations of White Dwarf Stars
Authors: Bainbridge, M. B.; Barstow, M. A.; Reindl, N.; Barrow,
J. D.; Webb, J. K.; Hu, J.; Preval, S. P.; Holberg, J. B.; Nave, G.;
Tchang-Brillet, L.; Ayres, T. R.
2017ASPC..509..375B Altcode:
Variation in fundamental constants provide an important test of theories
of grand unification. Potentially, white dwarf spectra allow us to
directly observe variation in fundamental constants at locations of
high gravitational potential. We study hot, metal polluted white dwarf
stars, combining far-UV spectroscopic observations, atomic physics,
atmospheric modelling and fundamental physics, in the search for
variation in the fine structure constant. This registers as small but measurable shifts in the observed wavelengths of highly ionized
Fe and Ni lines when compared to laboratory wavelengths. Measurements
of these shifts were performed by Berengut et al (2013) using
high-resolution STIS spectra of G191-B2B, demonstrating the validity
of the method. We have extended this work by; (a) using new
(high precision) laboratory wavelengths, (b) refining the analysis
methodology (incorporating robust techniques from previous studies
towards quasars), and (c) enlarging the sample of white dwarf
spectra. A successful detection would be the first direct measurement
of a gravitational field effect on a bare constant of nature. We
describe our approach and present preliminary results.

---------------------------------------------------------
Title: Probing the Gravitational Dependence of the Fine-Structure
Constant from Observations of White Dwarf Stars
Authors: Bainbridge, Matthew; Barstow, Martin; Reindl, Nicole;
Tchang-Brillet, W. -Ü.; Ayres, Thomas; Webb, John; Barrow, John; Hu,
Jiting; Holberg, Jay; Preval, Simon; Ubachs, Wim; Dzuba, Vladimir;
Flambaum, Victor; Dumont, Vincent; Berengut, Julian
2017Univ....3...32B Altcode: 2017arXiv170201757B
Hot white dwarf stars are the ideal probe for a relationship
between the fine-structure constant and strong gravitational
fields, providing us with an opportunity for a direct observational
test. We study a sample of hot white dwarf stars, combining far-UV
spectroscopic observations, atomic physics, atmospheric modelling
and fundamental physics, in the search for variation in the fine
structure constant. This variation manifests as shifts in the observed
wavelengths of absorption lines, such as quadruply ionized iron (FeV)
and quadruply ionized nickel (NiV), when compared to laboratory
wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801)
demonstrated the validity of such an analysis using high-resolution
Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS)
spectra of G191-B2B. We have made three important improvements by:
(a) using three new independent sets of laboratory wavelengths, (b)
analysing a sample of objects, and (c) improving the methodology by
incorporating robust techniques from previous studies towards quasars
(the Many Multiplet method). A successful detection would be the first
direct measurement of a gravitational field effect on a bare constant of
nature. Here we describe our approach and present preliminary results
from nine objects using both FeV and NiV.

---------------------------------------------------------
Title: A Closer Look at the Alpha Persei Coronal Conundrum
Authors: Ayres, Thomas R.
2017ApJ...837...14A Altcode: 2017arXiv170201310A
A ROSAT survey of the Alpha Per open cluster in 1993 detected
its brightest star, the mid-F supergiant α Persei: the X-ray
luminosity and spectral hardness were similar to coronally active
late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins
Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV)
coronal-proxy Si IV unexpectedly weak. This, and a suspicious offset
of the ROSAT source, suggested that a late-type companion might be
responsible for the X-rays. Recently, a multifaceted program tested
that premise. Ground-based optical coronography and near-UV imaging
with Hubble Space Telescope (HST) Wide-Field Camera 3 searched for any
close-in faint candidate coronal objects, but without success. Then,
a Chandra pointing found the X-ray source single and coincident with
the bright star. Significantly, the Si IV emissions of α Per, in a
deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as
part of the joint program, are aligned well with chromospheric atomic
oxygen (which must be intrinsic to the luminous star), within the
context of cooler late-F and early-G supergiants, including Cepheid
variables. This pointed to the X-rays as the fundamental anomaly. The
overluminous X-rays still support the case for a hyperactive dwarf
secondary, albeit now spatially unresolved. However, an alternative
is that α Per represents a novel class of coronal source. Resolving
the first possibility now has become more difficult, because the easy
solution—a well-separated companion—has been eliminated. Testing
the other possibility will require a broader high-energy census of
the early-F supergiants.

---------------------------------------------------------
Title: The Carbon Isotope Composition of the Sun
Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R.
2017LPI....48.2309L Altcode:
Analysis of CO spectral data for the solar photosphere shows that
the Sun has d13C = -48 permil VPDB. The inner solar system is highly
enriched in 13C.

---------------------------------------------------------
Title: Beyond the Coronal Graveyard
Authors: Ayres, Thomas
2017cxo..prop.5283A Altcode:
Iconic Arcturus is member of a populous class of low-mass red giants
whose warm winds are a life-blood of Galactic ecology. How their mass
outflows are powered has remained elusive. A solar-like coronal wind
seemed unlikely, because the red giants have a very low incidence
of high-energy detections. In fact, Arcturus, itself, is one of
the weakest X-ray sources known among the bright cool stars. An
intriguing possibility is that red giants do have significant
magnetic activity and coronae, but mostly hidden beneath their
puffy chromospheres. Unfortunately, the X-ray spectra that could
test the "buried corona" conjecture are beyond reach of contemporary
facilities. However, a new, robust X-ray detection of Arcturus would
inform the next generation of high-energy observatories, whether such
advanced measurements in fact would be feasible.

---------------------------------------------------------
Title: Alpha Centauri: Mind the Gap!
Authors: Ayres, Thomas
2017cxo..prop.5281A Altcode:
Cycle 19 proposal to continue long-term monitoring of coronal X-ray
activity cycles of sunlike Alpha Centauri A (G2V) and B (K1V) was not
approved. New Cycle 20 request will address panel's concerns. Even
if Cycle 20 proposal is approved, still will be unpleasant gap in the
semi-annual coverage, ongoing since 2005. Long-term HRC X-ray series on
AlpCen is unique, fundamentally important: key contribution of Chandra
to understanding cycling "Dynamos" of late-type stars, high scientific
priority in solar-stellar physics. Although stellar cycles are known
from CaII monitoring, X-rays contribute uniquely owing to 50X larger
contrast at high-energies. A 5 ks pointing in mid-2018 would fill the
gap. In fact, most recent AlpCen-A L_X (Ayres: 2018, RNAAS) shows a
possible, unusual, rapid downturn, in the declining phase of its cycle
(previous decline 2001-05 missed by lack of observations). Only Chandra
can resolve AB at present.

---------------------------------------------------------
Title: HST/STIS Observations of the Local Interstellar Medium toward
Very Nearby Stars: A Detailed Analysis of the a Centuari Sight Line
Authors: Dann, Julian; Redfield, Seth; Ayres, Thomas R.
2017AAS...22934004D Altcode:
The Local Interstellar Medium (LISM), a region extending about
100 parsecs and in which the Sun is currently immersed, can only
be studied using UV/optical absorption features against bright
background stars. Perhaps in the future in-situ measurements will be
possible (e.g., the Voyager spacecraft or Breakthrough Starshot-style
missions). Using high-resolution observations with the Space Telescope
Imaging Spectrograph (STIS) on-board the Hubble Space Telescope (HST),
we have analyzed several very nearby sight lines to measure physical
properties of the LISM. The data used in this study is a part of the
Advanced Spectral Library (ASTRAL) Project, an HST Large Treasury
Project, in which we have analyzed the spectra of fourteen nearby
stars. LISM absorption features in these stellar spectra reveal key
information about the abundances, temperature, and turbulence in the
intervening gas. We have fit ion transitions in the near-UV for MgII,
FeII, CII, DI, SiII, and OII. These absorption features provide direct
measurements of the radial velocity, Doppler broadening parameter,
and the column density along the line of sight. The presence of
multiple local minima in the deep and narrow ISM profile is evidence
of multiple clouds moving at different radial velocities.Included
in our data set is the a Centauri sight line. We provide a detailed
analysis of these new observations and a comparison with previous HST
observations that were observed more than 20 years ago. A discussion
of the physical properties along this line of sight is provided
within the context of a Breakthrough Starshot mission. These high
resolution and high signal-to-noise spectra will be important for
making accurate estimations of the interstellar environment to help
inform such an interstellar mission.We would like to acknowledge NASA
HST Grant GO-12278 and GO-13346 awarded by the Space Telescope Science
Institute, which is operated by the Association of Universities for
Research in Astronomy, Inc., for NASA, under contract NAS 5-26555,
and a student fellowship from the Connecticut Space Grant Consortium
for their support of this research.

---------------------------------------------------------
Title: Alpha Centauri at a Crossroads
Authors: Ayres, Tom
2017ChNew..24....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Multi-Observatory View of the Alpha Persei Coronal Conundrum
Authors: Ayres, Thomas R.
2017AAS...22923902A Altcode:
A ROSAT pointed survey of the Alpha Per open cluster in the 1990's
detected its brightest star, mid-F supergiant α Persei, with an X-ray
luminosity and spectral hardness similar to coronally active late-type
dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph
SNAPshot observation of α Per found far-ultraviolet (FUV) coronal-proxy
emissions (specifically Si IV 1393 Å) unexpectedly weak. Together
with a slight, but suspicious, offset of the ROSAT source, these
anomalies raised the possibility that an unrecognized late-type
companion might be responsible for the coronal X-rays. Recently, a
multi-observatory program was carried out to test that premise; on the
one hand to directly detect the putative companion, but on the other
to better characterize the FUV spectrum of α Per in case it also was
captured in X-rays. Initially, ground-based optical coronography from
the Apache Point 3.5m, and later near-UV imaging with HST Wide Field
Camera 3, searched for any close-in faint objects that plausibly could
be significant X-ray emitters, but without success. Then, a Chandra
pointing showed that the X-ray source is single and coincident with the
bright star. In tandem, HST COS collected a much deeper FUV spectrum of
α Per than the earlier brief SNAP. In hindsight, F supergiant Canopus
(α Car: F0 Ib) also has a high X-ray luminosity and the same type of
low Si IV/X-ray index as α Per. Significantly, the FUV Si IV emissions
of both α Per and Canopus align well with the chromospheric atomic
oxygen emissions (which must be intrinsic to the luminous stars),
within the context of cooler late-F and early-G supergiants, including
Cepheid variables. This pointed to the X-rays as the fundamental
anomaly. Ironically, the over-luminous X-rays still support the case for
a hyperactive dwarf secondary, albeit now spatially unresolved. However,
an equally viable alternative is that both F supergiants are members
of a novel class of X-ray emitters. Resolving the first possibility
now has become more difficult, because the easy solution -- a well
separated hyperactive companion -- has been eliminated; while testing
the second will require a broader high-energy census of the early-F
supergiant class.

---------------------------------------------------------
Title: The Fe Group Abundances in the B3 IV Standard ι Herculis
Determined from ASTRAL II Observations
Authors: Peters, Geraldine J.; Proffitt, Charles R.; Adelman, Saul J.;
Ayres, Thomas R.
2017AAS...22915105P Altcode:
Iota Herculis is an ultrasharp-lined B3 IV star that historically
has been considered as an abundance standard for the early B
stars. This star was one of the targets in the HST Treasury Program
Advanced Spectral Library II: Hot Stars (ASTRAL II) that produced
uninterrupted spectra of high to medium resolution in the region
1150-3100 Å. The abundances for the Fe group elements (Ti, V, Cr,
Mn, Fe, Co, &amp; Ni) in ι Her were determined mostly from STIS
E140H and E230H (resolving power of 114,000) observations. Measurable
lines from the Fe group, except for a very few multiplets of Fe II,
III are not found in optical spectra. Whereas the light elements
are delivered to the ISM by core-collapse supernovae (CCSNe), the Fe
group elements are believed to come mostly from low/intermediate mass
binaries containing white dwarfs that undergo SNe Ia explosions. A
single SNe Ia can deliver 0.5 solar masses of pure Fe (and maybe Mn)
to the ISM compared with about 0.07 solar masses from a CCSNe. The
HST/STIS data were supplemented with optical spectra obtained at the
Dominion Astrophysical Observatory (resolving power about 60,000). The
abundance analysis was carried through with the NLTE code TLUSTY/SYNSPEC
(Hubeny &amp; Lanz, ApJ, 439,875,1995). The model parameters adopted
for the ι Her are Teff = 17750 ± 250 K, log g = 3.75 ±
0.05 dex, Vturb = 0 km s-1, and v sin i = 5 km
s-1. Solar abundances appear to prevail for the lighter
elements but the abundances of Fe group elements are 0.3 - 0.7 dex
below solar values determined by Grevesse et al. (2010, Ap&amp;SpSci,
328, 179). It appears that ι Her was formed in a region our Galaxy
mostly enriched by CCSNe.The authors appreciate support from STScI
grants HST-GO-09848 and HST-GO-13346. SJA was a guest observer at DAO.

---------------------------------------------------------
Title: CO isotopologue ratios in the solar photosphere
Authors: Lyons, James R.; Gharib-Nezhad, Ehsan; Ayres, Thomas R.
2016IAUFM..29A.307L Altcode:
We re-evaluate the CO dipole moment function in order to obtain more
accurate isotope ratios for the solar photosphere using previous
infrared observations. We used a new set of dipole moments from HITEMP
which were accurately determined by both semi-empirical and ab initio
methods. Preliminary values of isotope ratios using the new dipole
moments are in better agreement with the inferred photosphere values
from Genesis, showing that the solar photosphere is isotopically
similar to primitive inclusions in meteorites.

---------------------------------------------------------
Title: Cracking the Conundrum of F Supergiant Coronae
Authors: Ayres, Thomas
2016cxo..prop.4856A Altcode:
Mid-F supergiant Alpha Persei, of the eponymous young cluster, is a
strong X-ray source given its minimal FUV emission, with a narrow-line
FUV spectrum unlike other yellow supergiants. A slight positional
offset in a ROSAT image suggested that a hyperactive companion might be
responsible for the X-ray anomaly. However, a recent Chandra pointing
found that the source in fact is coincident with Alpha Per. Further,
the related supergiant Canopus also exhibits the same X-ray and FUV
peculiarities, with a surprising connection to Cepheids in their FUV
low states. New X-ray and FUV observations of additional F supergiants
could help decide whether the coronal anomalies are due to unseen
companions, or instead are a normal attribute of this exotic class,
at the extreme edge of convection.

---------------------------------------------------------
Title: Cracking the Conundrum of F Supergiant Coronae
Authors: Ayres, Thomas R.
2016hst..prop14848A Altcode:
This is the HST part of a joint Chandra/HST program. BACKGROUND:
Mid-F supergiant Alpha Persei, of the eponymous young cluster, is a
strong X-ray source, given its minimal FUV emission, with a narrow-line
FUV spectrum unlike other yellow supergiants. A slight positional offset
in a 1990's ROSAT image suggested that a hyperactive companion might be
responsible for the X-ray anomaly. However, a recent Chandra pointing
found that the source seen by ROSAT in fact is coincident with Alpha
Per. Further, the related supergiant Canopus also exhibits the same
X-ray and FUV peculiarities, with a surprising possible connection
to Cepheid variables in their FUV low states. THIS PROPOSAL:
New X-ray and FUV observations of additional F supergiants could help
decide whether the coronal anomalies of Alpha Per and Canopus are
due to unseen (unresolved) hyperactive dwarf companions, or instead
are a normal attribute of this exotic class, at the extreme edge of
convection. This is a key missing piece in the unfolding narrative of
hot (1-10 MK) stellar coronae.

---------------------------------------------------------
Title: Alpha Centauri at a Crossroads
Authors: Ayres, Thomas R.
2016hst..prop14341A Altcode:
Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized
solar-like dwarf stars, which also have the best studied multi-MK
coronal X-ray activity cycles, extending back to the 1970's. Objective
is to continue tracking the evolving multi-decadal high-energy
narrative of Alpha Cen with semiannual X-ray pointings in Chandra
Cycles 16-18, as the system reaches a coronal crossroads: solar twin
A rising toward starspot cycle maximum, K-type companion B sinking
into a minimum. HST/STIS UV spectra will support and leverage the
X-ray measurements by probing chromospheric and subcoronal dynamics,
with connection to the corona through the FUV Fe XII 1242 forbidden
line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen
orbit also reaches a crossroads in 2016 (only 4" separation), and only
HST/STIS can measure the bright Alpha Cen stars with sufficient UV
spectral resultion and wavelength coherence. What's more, the recent
validation of the STIS NDA,B,C long slits for echelle use now make
feasible NUV E230H measurements (e.g., of key chromospheric tracers
Mg II 2800 and Mg I 2852) which heretofore were not practical in a
long-term program of this nature.

---------------------------------------------------------
Title: A Study of the Elements Copper through Uranium in Sirius A:
Contributions from STIS and Ground-Based Spectra
Authors: Cowley, C. R.; Ayres, T. R.; Castelli, F.; Gulliver, A. F.;
Monier, R.; Wahlgren, G. M.
2016ApJ...826..158C Altcode: 2016arXiv160508399C
We determine abundances or upper limits for all of the 55 stable
elements from copper to uranium for the A1 Vm star Sirius. The
purpose of the study is to assemble the most complete picture
of elemental abundances with the hope of revealing the chemical
history of the brightest star in the sky, apart from the Sun. We
also explore the relationship of this hot metallic-line (Am) star to
its cooler congeners, as well as the hotter, weakly- or non-magnetic
Mercury-manganese (HgMn) stars. Our primary observational material
consists of Hubble Space Telescope (HST) spectra taken with the Space
Telescope Imaging Spectrograph in the ASTRAL project. We have also
used archival material from the COPERNICUS satellite, and from the
HST Goddard High-Resolution Spectrograph, as well as ground-based
spectra from Furenlid, Westin, Kurucz, Wahlgren, and their coworkers,
ESO spectra from the UVESPOP project, and NARVAL spectra retrieved
from PolarBase. Our analysis has been primarily by spectral synthesis,
and in this work we have had the great advantage of extensive atomic
data unavailable to earlier workers. We find most abundances as well as
upper limits range from 10 to 100 times above solar values. We see no
indication of the huge abundance excesses of 1000 or more that occur
among many chemically peculiar stars of the upper main sequence. The
picture of Sirius as a hot Am star is reinforced.

---------------------------------------------------------
Title: The Carbon Isotope Composition of the Solar Photosphere
Authors: Lyons, J. R.; Gharib Nezhad, E.; Ayres, T. R.
2016LPICo1921.6544L Altcode:
We have reanalyzed infrared CO absorption line data of the solar
photosphere. We obtain d18O = -51 ± 11‰l VSMOW, consistent with the
inferred Genesis value. For carbon we find d13C = -48 ± 7‰l VPDB,
lighter than previously reported.

---------------------------------------------------------
Title: The Cold Heart Of The Solar Chromosphere
Authors: Ayres, Thomas
2016csss.confE..92A Altcode:
A power-point presentation describing potential impact of ALMA on
probing cold gas in the solar chromosphere.

---------------------------------------------------------
Title: The Dynamo Clinical Trial
Authors: Ayres, Thomas
2016csss.confE..93A Altcode:
Poster concerning the coronal activity cycles of Alpha Centauri A and B,
the nearest sun-like stars, as observed by several generations of X-ray
observatories including ROSAT, XMM-Newton, and most recently Chandra.

---------------------------------------------------------
Title: Assessing the dependency of the fine structure constant on
gravity using hot DA white dwarfs
Authors: Barstow, Martin; Ayres, Thomas R.; Bainbridge, Matthew;
Barrow, John; Berengut, Julian Carlo; Burleigh, Matthew; Casewell,
Sarah; Dapra, Mario; Dougan, Darren; Dumont, Vincent; Dzuba, Vladimir;
Flambaum, Victor; HU, Jiting; Holberg, Jay B.; Joyce, Simon; Nave,
Gillian; Preval, Simon Paul; Reindl, Nicole; Salumbides, Edcel;
Ubachs, Wim; Webb, John K.
2016hst..prop14791B Altcode:
Variation of fundamental constants is a common theme of many theories
of quantum gravity and Grand Unification. Using spectra obtained
with the Hubble Space Telescope, it has been shown by Berengut et
al. (2013), and Bagdonaite et al. (2014), that it is possible to
place strong constraints on gravitational variations of the fine
structure constant (alpha), and the proton to electron mass ratio (mu)
in white dwarf stars. As part of the UV initiative, we propose
to observe four hot DA white dwarf stars using STIS with the E140H
grating, totalling 12 orbits. These four stars have been chosen so
as to have a wide range of masses, allowing a full exploration of the
compactness parameter space (M/R). We will measure several absorption
features of Fe V and Ni V, and extract any potential variation in alpha
in a manner similar to Berengut et al. (2013). This proposal
will be a significant advance in the effort to detect gravitational
variations in alpha. A confirmed detection of alpha variation would
have extensive consequences for fundamental physics, cosmology, and
would also signal the breakdown of Einstein's Equivalence principle,
and hence, general relativity. Furthermore, a null detection would also
allow strong limits to be placed on any potential alpha variation in
a strong gravitational field.

---------------------------------------------------------
Title: Procyon: New Candidate for the Dynamo Clinical Trial
Authors: Ayres, Thomas R.
2016hst..prop14789A Altcode:
This is the second year of a joint Chandra/HST program to follow
the evolution of the high-energy (X-ray and UV) activity cycles of
the nearby mid-F subgiant Procyon. This bright star has high-energy
attributes that are similar to the Sun, yet it is a hotter star, at the
edge of the region in the H-R diagram where surface convection occurs
(the power source for stellar magnetic activity). The HST part is to
record STIS UV spectra of the bright star on a semi-annual basis at
high echelle resolution and high S/N, especially to capture the FUV
Fe XII 124,134 nm coronal forbidden lines, which can tie together
the non-simultaneous Chandra X-ray and HST pointings; as well as to
record other key high-energy species like Si IV, C IV, and N V. The
latter display Doppler-shifted, bimodal distorted emission profiles
that signify high-powered dynamics in the interface regions of the
stellar atmosphere between the super-hot corona (&gt;1 MK) and the
cold photosphere (&lt;6000 K). The associated flows are a hot topic in
contemporary solar physics, and one focus of a new space-based solar
imaging spectrometer called IRIS. The solar and stellar FUV views are
strongly complementary. The HST part of the program has two general
objectives: (1) follow changes in the FUV spectra associated with any
slowly evolving X-ray activity cycle of Procyon; and (2) combine the
multiple epochs of echelle spectra to provide the highest possible
S/N for identifying weak, but diagnostically important, emission lines
(absorption, in some cases), and for decomposing the high-temperature
line profiles (e.g., Si IV, C IV) into multiple dynamical components
(which are though to be symptomatic of coronal heating and cooling
processes).

---------------------------------------------------------
Title: Alpha Centauri at a Crossroads
Authors: Ayres, Thomas R.
2016hst..prop14788A Altcode:
Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized
solar-like dwarf stars, which also have the best studied multi-MK
coronal X-ray activity cycles, extending back to the 1970's. Objective
is to continue tracking the evolving multi-decadal high-energy
narrative of Alpha Cen with semiannual X-ray pointings in Chandra
Cycles 16-18, as the system reaches a coronal crossroads: solar twin
A rising toward starspot cycle maximum, K-type companion B sinking
into a minimum. HST/STIS UV spectra will support and leverage the
X-ray measurements by probing chromospheric and subcoronal dynamics,
with connection to the corona through the FUV Fe XII 1242 forbidden
line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen
orbit also reaches a crossroads in 2016 (only 4" separation), and only
HST/STIS can measure the bright Alpha Cen stars with sufficient UV
spectral resolution and wavelength coherence. What's more, the recent
validation of the STIS NDA,B,C long slits for echelle use now make
feasible NUV E230H measurements (e.g., of key chromospheric tracers
Mg II 2800 and Mg I 2852) which heretofore were not practical in a
long-term program of this nature.

---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.

---------------------------------------------------------
Title: The Dynamo Clinical Trial
Authors: Ayres, Thomas R.
2016HEAD...1511703A Altcode:
The Dynamo Clinical Trial evaluates long-term stellar magnetic health
through periodic X-ray examinations (by the Chandra Observatory). So
far, there are only three subjects enrolled in the DTC: Alpha Centauri
A (a solar-like G dwarf), Alpha Cen B (an early K dwarf, more active
than the Sun), and Alpha Canis Majoris A (Procyon, a mid-F subgiant
similar in activity to the Sun). Of these, Procyon is a new candidate,
so it is too early to judge how it will fare. Of the other two, Alpha
Cen B has responded well, with a steady magnetic heartbeat of about 8
years duration. The sickest of the bunch, Alpha Cen A, was in magnetic
cardiac arrest during 2005-2010, but has begun responding to treatment
in recent years, and seems to be successfully cycling again, perhaps
achieving a new peak of magnetic health in the 2016 time frame. If
this is the case, it has been 20 years since A's last healthful peak,
significantly longer than the middle-aged Sun's 11-year magnetic
heartbeat, but perhaps in line with Alpha Cen A's more senescent state
(in terms of "relative evolutionary age," apparently an important
driver of activity). (By the way, don't miss the exciting movie of
the Alpha Cen stars' 20-year X-ray dance.)

---------------------------------------------------------
Title: Division G Commission 36: Theory of Stellar Atmospheres
Authors: Puls, Joachim; Hubeny, Ivan; Asplund, Martin; Allard, France;
Allende Prieto, Carlos; Ayres, Thomas R.; Carlsson, Mats; Gustafsson,
Bengt; Kudritzki, Rolf-Peter; Ryabchikova, Tatiana A.
2016IAUTA..29..453P Altcode:
Different from previous triennial reports, this report covers the
activities of IAU Commission 36 `Theory of Stellar Atmospheres'
over the past six years†, and will be the last report from the
`old' Commission 36. After the General Assembly in Honolulu (August
2015), a new Commission `Stellar and Planetary Atmospheres' (C.G5,
under Division G, `Stars and Stellar Physics') has come into life,
and will continue our work devoted to the outer envelopes of stars,
as well as extend it to the atmospheres of planets (see Sect. 4).

---------------------------------------------------------
Title: The Oxygen Isotope Composition of the Solar Photosphere
Determined from CO Observations
Authors: Lyons, J. R.; Gharib Nezhad, E.; Ayres, T. R.
2016LPI....47.2509L Altcode:
A new analysis of observations of CO in the solar photosphere yields
delta18O = -50±11‰, consistent with the Genesis inferred value from
solar wind.

---------------------------------------------------------
Title: The Rapid Acquisition Imaging Spectrograph Experiment (RAISE)
Sounding Rocket Investigation
Authors: Laurent, Glenn T.; Hassler, Donald M.; Deforest, Craig;
Slater, David D.; Thomas, Roger J.; Ayres, Thomas; Davis, Michael; de
Pontieu, Bart; Diller, Jed; Graham, Roy; Michaelis, Harald; Schuele,
Udo; Warren, Harry
2016JAI.....540006L Altcode:
We present a summary of the solar observing Rapid Acquisition
Imaging Spectrograph Experiment (RAISE) sounding rocket program
including an overview of the design and calibration of the instrument,
flight performance, and preliminary chromospheric results from the
successful November 2014 launch of the RAISE instrument. The RAISE
sounding rocket payload is the fastest scanning-slit solar ultraviolet
imaging spectrograph flown to date. RAISE is designed to observe the
dynamics and heating of the solar chromosphere and corona on time
scales as short as 100-200ms, with arcsecond spatial resolution and
a velocity sensitivity of 1-2km/s. Two full spectral passbands over
the same one-dimensional spatial field are recorded simultaneously
with no scanning of the detectors or grating. The two different
spectral bands (first-order 1205-1251Å and 1524-1569Å) are imaged
onto two intensified Active Pixel Sensor (APS) detectors whose focal
planes are individually adjusted for optimized performance. RAISE
reads out the full field of both detectors at 5-10Hz, recording up
to 1800 complete spectra (per detector) in a single 6-min rocket
flight. This opens up a new domain of high time resolution spectral
imaging and spectroscopy. RAISE is designed to observe small-scale
multithermal dynamics in Active Region (AR) and quiet Sun loops,
identify the strength, spectrum and location of high frequency waves
in the solar atmosphere, and determine the nature of energy release
in the chromospheric network.

---------------------------------------------------------
Title: FK Comae Berenices, King of Spin: The COCOA-PUFS Project
Authors: Ayres, Thomas R.; Kashyap, V.; Saar, S.; Huenemoerder,
D.; Korhonen, H.; Drake, J. J.; Testa, P.; Cohen, O.; Garraffo, C.;
Granzer, T.; Strassmeier, K.
2016ApJS..223....5A Altcode: 2016arXiv160103305A
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Comae Berenices (FK Com:
HD117555; G4 III). This single star is thought to be a recent
binary merger, and is exceptionally active by measure of its
intense ultraviolet (UV) and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with the Hubble Space Telescope
in the UV (1200-3000 Å), using mainly its high-performance Cosmic
Origins Spectrograph, but also high precision Space Telescope Imaging
Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5-10 keV),
utilizing its High-Energy Transmission Grating Spectrometer; together
with supporting photometry and spectropolarimetry in the visible
from the ground. This is an introductory report on the project. FK Com
displayed variability on a wide range of timescales over all wavelengths
during the week-long main campaign, including a large X-ray flare;
“super-rotational broadening” of the far-ultraviolet “hot
lines” (e.g., Si IV 1393 Å 8 × 104 K) together with
chromospheric Mg II 2800 Å and C II 1335 Å (1-3 × 104
K); large Doppler swings suggestive of bright regions alternately on
advancing and retreating limbs of the star; and substantial redshifts
of the epoch-average emission profiles. These behaviors paint a picture
of a highly extended, dynamic, hot (∼10 MK) coronal magnetosphere
around the star, threaded by cooler structures perhaps analogous to
solar prominences and replenished continually by surface activity
and flares. Suppression of angular momentum loss by the confining
magnetosphere could temporarily postpone the inevitable stellar
spindown, thereby lengthening this highly volatile stage of coronal
evolution. COordinated Campaign of Observations and Analysis,
Photosphere to Upper Atmosphere, of a Fast-rotating Star.

---------------------------------------------------------
Title: The High-Energy Environs of the Anomalous Coronal Source
Alpha Persei
Authors: Ayres, Thomas R.
2016hst..prop14349A Altcode:
This is a joint Chandra/HST program to investigate the F-type supergiant
Alpha Persei, brightest star in the young (50 Myr) open cluster that
bears its name. The central question is whether the bright ROSAT X-ray
source identified as Alpha Per truly is associated with the supergiant
(which would make it quite an anomalous object in its class), or
instead is due to a low-mass coronally active cluster member in the
immediate vicinity of Alpha Per, but which has escaped detection owing
to the glare of the very bright star nearby. In fact, the ROSAT LX
is similar to that of active G dwarfs in the young cluster, and the
X-ray source appears to be shifted slightly from the optical position
of the bright star. Furthermore, a brief COS SNAPshot FUV spectrum of
Alpha Per appeared to lack significant high-energy features (e.g., Si
IV 140 nm) expected from a powerful X-ray source, although the bright
FUV photospheric continuum of the warm supergiant was a major source
of interference. The observational objectives of the HST part of the
program are: (1) image the field with WFC3 to pin down positions of
any faint, low-mass stars in the immediate vicinity of the supergiant
(chromospherically active dwarfs have a large contrast advantage,
for example, at Mg II 280 nm); and (2) take a deeper COS FUV spectrum
than was possible in the Cycle 17 SNAPshot program, including the
important Lyman Alpha region, which was forbidden in the SNAP program
owing to safety issues. We now know that the Lyman Alpha observation
would be safe, and access to the G130M side-B spectrum would capture
key "hot lines" like N V 124 nm, where the FUV continuum is weaker,
to help characterize the activity levels of the iconic supergiant.

---------------------------------------------------------
Title: Ultraviolet emission lines of Si II in cool star and solar
spectra
Authors: Laha, Sibasish; Keenan, Francis P.; Ferland, Gary J.;
Ramsbottom, Catherine A.; Aggarwal, Kanti M.; Ayres, Thomas R.;
Chatzikos, Marios; van Hoof, Peter A. M.; Williams, Robin J. R.
2016MNRAS.455.3405L Altcode: 2015arXiv151008755L
Recent atomic physics calculations for Si II are employed within the
CLOUDY modelling code to analyse Hubble Space Telescope (HST) STIS
ultraviolet spectra of three cool stars, β Geminorum, α Centauri A
and B, as well as previously published HST/GHRS observations of α
Tau, plus solar quiet Sun data from the High Resolution Telescope
and Spectrograph. Discrepancies found previously between theory and
observation for line intensity ratios involving the 3s23p
2PJ-3s3p2 4P_{J^' }}
intercombination multiplet of Si II at ∼ 2335 Å are significantly
reduced, as are those for ratios containing the 3s23p
2PJ-3s3p2 2D_{J^' }}
transitions at ∼1816 Å. This is primarily due to the effect of
the new Si II transition probabilities. However, these atomic data
are not only very different from previous calculations, but also show
large disagreements with measurements, specifically those of Calamai
et al. for the intercombination lines. New measurements of transition
probabilities for Si II are hence urgently required to confirm (or
otherwise) the accuracy of the recently calculated values. If the new
calculations are confirmed, then a long-standing discrepancy between
theory and observation will have finally been resolved. However,
if the older measurements are found to be correct, then the agreement
between theory and observation is simply a coincidence and the existing
discrepancies remain.

---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W Altcode:
This document was created by the Solar Simulations for the Atacama
Large Millimeter Observatory Network (SSALMON) in preparation of
the first regular observations of the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA), which are anticipated to start
in ALMA Cycle 4 in October 2016. The science cases presented here
demonstrate that a large number of scientifically highly interesting
observations could be made already with the still limited solar
observing modes foreseen for Cycle 4 and that ALMA has the potential
to make important contributions to answering long-standing scientific
questions in solar physics. With the proposal deadline for ALMA Cycle
4 in April 2016 and the Commissioning and Science Verification campaign
in December 2015 in sight, several of the SSALMON Expert Teams composed
strategic documents in which they outlined potential solar observations
that could be feasible given the anticipated technical capabilities
in Cycle 4. These documents have been combined and supplemented
with an analysis, resulting in recommendations for solar observing
with ALMA in Cycle 4. In addition, the detailed science cases also
demonstrate the scientific priorities of the solar physics community
and which capabilities are wanted for the next observing cycles. The
work on this White Paper effort was coordinated in close cooperation
with the two international solar ALMA development studies led by
T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
further updated until the beginning of Cycle 4 in October 2016. In
particular, we plan to adjust the technical capabilities of the solar
observing modes once finally decided and to further demonstrate the
feasibility and scientific potential of the included science cases by
means of numerical simulations of the solar atmosphere and corresponding
simulated ALMA observations.

---------------------------------------------------------
Title: The Hubble Spectroscopic Legacy Archive
Authors: Peeples, Molly S.; Tumlinson, Jason; Fox, Andrew; Aloisi,
Alessandra; Ayres, Thomas R.; Danforth, Charles; Fleming, Scott
W.; Jenkins, Edward B.; Jedrzejewski, Robert I.; Keeney, Brian A.;
Oliveira, Cristina M.
2016AAS...22744401P Altcode:
With no future space ultraviolet instruments currently planned,
the data from the UV spectrographs aboard the Hubble Space Telescope
have a legacy value beyond their initial science goals. The Hubble
Spectroscopic Legacy Archive will provide to the community new
science-grade combined spectra for all publicly available data obtained
by the Cosmic Origins Spectrograph (COS) and the Space Telescope
Imaging Spectrograph (STIS). These data will be packaged into "smart
archives" according to target type and scientific themes to facilitate
the construction of archival samples for common science uses. A new
"quick look" capability will make the data easy for users to quickly
access, assess the quality of, and download for archival science
starting in Cycle 24, with the first generation of these products for
the FUV modes of COS available online via MAST in early 2016.

---------------------------------------------------------
Title: The Ultraviolet Spectroscopic Legacy of HST
Authors: Ayres, Thomas R.
2016AAS...22722206A Altcode:
Hubble Space Telescope has been a spectacularly successful platform for
spectroscopy in the diagnostic-rich far-ultraviolet (FUV: 120-170 nm)
and near-ultraviolet (NUV: 170-310 nm) regions. HST has hosted four
generations of UV instruments, beginning with Faint Object Spectrograph
(FOS) and Goddard High-Resolution Spectrograph (GHRS) in the original
1990 payload, followed by Space Telescope Imaging Spectrograph (STIS)
in 1997, and more recently Cosmic Origins Spectrograph (COS) as part of
Servicing Mission 4 in 2009. The latter two instruments have contributed
by far the lion's share of HST's spectroscopic archive: STIS, because
of its longevity (thirteen years in operation so far, although with
a hiatus between 2004-2009); and COS because of its high sensitivity,
which allows efficient observations, and thus many more targets in a
typical GO program. STIS benefits from a compact echelle design, and
the sharp stable imaging of HST, to provide high-resolution (3-7 km
s-1) spectra of bright objects, including stars, nebulae,
quasars, novae, and so forth. COS achieves astounding sensitivity in
the FUV by a sophisticated design that compensates for the spherical
abberation of HST's primary mirror, disperses the target's light, and
focuses the spectral image all with just a single optical element. While
the spectral resolution of COS (about 18 km s-1) is not
as high as that of STIS, it is adequate for diverse investigations,
including faint broad-lined AGN at the edge of the Universe, hot
stars in nearby galaxies, and magnetically active planet-hosting red
dwarfs in the solar neighborhood. Thanks in part to the "UV Initiative"
in recent HST proposal cycles, there have been several large efforts
involving both STIS and COS, to assemble important spectral collections,
including full UV atlases of representative hot and cool stars at high
resolution with STIS; long time series of archetype AGN ("reverberation
mapping") with COS; and hundreds of sightlines to distant quasars to
probe the Cosmic Web, also with COS. Altogether, these diverse spectral
observations constitute one of the key legacies of HST, and hopefully
one that will continue to be built upon in the coming years.

---------------------------------------------------------
Title: Scientific problems addressed by the Spektr-UV space project
(world space Observatory—Ultraviolet)
Authors: Boyarchuk, A. A.; Shustov, B. M.; Savanov, I. S.; Sachkov,
M. E.; Bisikalo, D. V.; Mashonkina, L. I.; Wiebe, D. Z.; Shematovich,
V. I.; Shchekinov, Yu. A.; Ryabchikova, T. A.; Chugai, N. N.; Ivanov,
P. B.; Voshchinnikov, N. V.; Gomez de Castro, A. I.; Lamzin, S. A.;
Piskunov, N.; Ayres, T.; Strassmeier, K. G.; Jeffrey, S.; Zwintz,
S. K.; Shulyak, D.; Gérard, J. -C.; Hubert, B.; Fossati, L.; Lammer,
H.; Werner, K.; Zhilkin, A. G.; Kaigorodov, P. V.; Sichevskii, S. G.;
Ustamuich, S.; Kanev, E. N.; Kil'pio, E. Yu.
2016ARep...60....1B Altcode:
The article presents a review of scientific problems and methods of
ultraviolet astronomy, focusing on perspective scientific problems
(directions) whose solution requires UV space observatories. These
include reionization and the history of star formation in the Universe,
searches for dark baryonic matter, physical and chemical processes
in the interstellar medium and protoplanetary disks, the physics of
accretion and outflows in astrophysical objects, from Active Galactic
Nuclei to close binary stars, stellar activity (for both low-mass and
high-mass stars), and processes occurring in the atmospheres of both
planets in the solar system and exoplanets. Technological progress
in UV astronomy achieved in recent years is also considered. The
well advanced, international, Russian-led Spektr-UV (World Space
Observatory—Ultraviolet) project is described in more detail. This
project is directed at creating a major space observatory operational
in the ultraviolet (115-310 nm). This observatory will provide an
effective, and possibly the only, powerful means of observing in this
spectral range over the next ten years, and will be an powerful tool
for resolving many topical scientific problems.

---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
2015AdSpR..56.2679W Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.

---------------------------------------------------------
Title: The Intersection of Atomic Physics and Astrophysics:
Identifying UV Fe I Lines from Metal-Poor Turnoff Stars
Authors: Peterson, Ruth C.; Ayres, Thomas R.; Kurucz, Robert L.
2015hst..prop14161P Altcode:
Observational surveys are expanding, recording ever-fainter sources
from the ultraviolet to the infrared. Needed to characterize them are
observational ultraviolet templates at high spectral resolution and low
metallicity for the oldest populations, and the laboratory astrophysics
data essential to model objects such as stars and nebulae at all ages,
metallicities, and redshifts. We address this by proposing to
complete the high-resolution UV spectral coverage of four key metal-poor
turnoff stars. These are ideal as metal-poor templates of old stars and
as the "laboratory source" for the identification of the thousands of
lines of neutral iron that appear in stellar spectra, but are absent
from or not identified in laboratory spectra. By matching existing
stellar spectra to calculations of energy levels, line wavelengths,
and gf-values, Peterson &amp; Kurucz (2015) identified 66 Fe I levels
with energies up to 8.4eV, yielding 2000 new lines from 1600 Angstroms
to 5.4 microns, and empirical gf-values for 640 of these. The proposed
work should yield ~500 new levels and ~10,000 new Fe I lines. The
new energy levels and line parameters also will be posted on the Kurucz
website. The new spectra, and supporting theoretical calculations,
will be integrated into the publicly available HST Advanced Spectral
Library (ASTRAL) Treasury Project. This will leverage the utility of
these archival spectral templates and atlases in such diverse areas as
nucleosynthesis at early epochs, infrared analysis of dust-obscured
giants, reconstructing the populations of nearby globular clusters
and dwarf galaxies from their integrated light, and deriving age and
metallicity for old, distant galaxies.

---------------------------------------------------------
Title: Procyon: New Candidate for the Dynamo Clinical Trial
Authors: Ayres, Thomas R.
2015hst..prop14350A Altcode:
This is the first year of a joint Chandra/HST program to follow
the evolution of the high-energy (X-ray and UV) activity cycles of
the nearby mid-F subgiant Procyon. This bright star has high-energy
attributes that are similar to the Sun, yet it is a hotter star, at the
edge of the region in the H-R diagram where surface convection occurs
(the power source for stellar magnetic activity). The HST part is to
record STIS UV spectra of the bright star on a semi-annual basis at
high echelle resolution and high S/N, especially to capture the FUV
Fe XII 124,134 nm coronal forbidden lines, which can tie together
the non-simultaneous Chandra X-ray and HST pointings; as well as to
record other key high-energy species like Si IV, C IV, and N V. The
latter display Doppler-shifted, bimodal distorted emission profiles
that signify high-powered dynamics in the interface regions of the
stellar atmosphere between the super-hot corona (&gt;1 MK) and the
cold photosphere (&lt;6000 K). The associated flows are a hot topic in
contemporary solar physics, and one focus of a new space-based solar
imaging spectrometer called IRIS. The solar and stellar FUV views are
strongly complementary. The HST part of the program has two general
objectives: (1) follow changes in the FUV spectra associated with any
slowly evolving X-ray activity cycle of Procyon; and (2) combine the
multiple epochs of echelle spectra to provide the highest possible
S/N for identifying weak, but diagnostically important, emission lines
(absorption, in some cases), and for decomposing the high-temperature
line profiles (e.g., Si IV, C IV) into multiple dynamical components
(which are though to be symptomatic of coronal heating and cooling
processes).

---------------------------------------------------------
Title: CxO (x=16,17,18) isotopologue ratios in the solar
photosphere
Authors: Lyons, James; Gharib-Nezhad, Ehsan; Ayres, Thomas
2015DPS....4750709L Altcode:
Determination of the oxygen isotope ratios in the solar photosphere
is essential to constraining the formation environment of the solar
system. The solar CO fundamental and first-overtone bands were
previously measured by the shuttle-borne ATMOS Fourier transform
spectrometer (FTS), and with the National Solar Observatory
FTS on the McMath-Pierce telescope at Kitt Peak. Analyzing
the rovibrational bands from these photospheric spectra, a 3D
convection model was employed to calculate ratios with improved
uncertainties (16O/17O=2738±118 and
16O/18O =511±10 Ayres et al. 2013), which
fall between the terrestrial values and those inferred from solar
wind measurements by the Genesis spacecraft. However, differences
in published CO dipole moment functions yielded a range of isotopic
ratios spanning ~ 3 % in δ18O. Here we re-evaluate the
CO dipole moment function in order to obtain more accurate isotope
ratios for the photosphere. We used a new set of dipole moments from
HITEMP which were accurately determined by both semi-empirical and
ab initio methods. Preliminary values of isotope ratios using the new
dipole moments are in better agreement with the inferred photosphere
values from Genesis, showing that the solar photosphere is isotopically
similar to primitive inclusions in meteorites, but different from the
terrestrial planets by ~ 6 %. New spectral observations are needed to
reduce uncertainties in photospheric C17O abundances.

---------------------------------------------------------
Title: The High-Energy Environs of the Anomalous Coronal Source
Alpha Persei
Authors: Ayres, Thomas
2015hst..prop14349A Altcode:
This is a joint Chandra/HST program to investigate the F-type supergiant
Alpha Persei, brightest star in the young (50 Myr) open cluster that
bears its name. The central question is whether the bright ROSAT X-ray
source identified as Alpha Per truly is associated with the supergiant
(which would make it quite an anomalous object in its class), or
instead is due to a low-mass coronally active cluster member in the
immediate vicinity of Alpha Per, but which has escaped detection owing
to the glare of the very bright star nearby. In fact, the ROSAT LX
is similar to that of active G dwarfs in the young cluster, and the
X-ray source appears to be shifted slightly from the optical position
of the bright star. Furthermore, a brief COS SNAPshot FUV spectrum of
Alpha Per appeared to lack significant high-energy features (e.g., Si
IV 140 nm) expected from a powerful X-ray source, although the bright
FUV photospheric continuum of the warm supergiant was a major source
of interference. The observational objectives of the HST part of the
program are: (1) image the field with WFC3 to pin down positions of
any faint, low-mass stars in the immediate vicinity of the supergiant
(chromospherically active dwarfs have a large contrast advantage, for
example, at Mg II 280 nm); and (2) take a deeper COS FUV spectrum than
was possible in the Cycle 17 SNAPshot program, including the important
Lyman Alpha region, which was forbidden in the SNAP program owing to
safety issues. We now know that the Lyman Alpha observation would be
safe, and access to the G130M side-B spectrum would capture key hot
lines like N V 124 nm, where the FUV continuum is weaker, to help
characterize the activity levels of the iconic supergiant.

---------------------------------------------------------
Title: Alpha Centauri at a Crossroads
Authors: Ayres, Thomas
2015hst..prop14341A Altcode:
Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized
solar-like dwarf stars, which also have the best studied multi-MK
coronal X-ray activity cycles, extending back to the 1970's. Objective
is to continue tracking the evolving multi-decadal high-energy
narrative of Alpha Cen with semiannual X-ray pointings in Chandra
Cycles 16-18, as the system reaches a coronal crossroads: solar twin
A rising toward starspot cycle maximum, K-type companion B sinking
into a minimum. HST/STIS UV spectra will support and leverage the
X-ray measurements by probing chromospheric and subcoronal dynamics,
with connection to the corona through the FUV Fe XII 1242 forbidden
line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen
orbit also reaches a crossroads in 2016 (only 4 separation), and only
HST/STIS can measure the bright Alpha Cen stars with sufficient UV
spectral resultion and wavelength coherence. What's more, the recent
validation of the STIS NDA,B,C long slits for echelle use now make
feasible NUV E230H measurements (e.g., of key chromospheric tracers
Mg II 2800 and Mg I 2852) which heretofore were not practical in a
long-term program of this nature.

---------------------------------------------------------
Title: Procyon: A New Candidate for the Dynamo Clinical Trial
Authors: Ayres, Thomas
2015cxo..prop.4728A Altcode:
Procyon (Alp CMi; F5IV-V) is a bright, nearby subgiant; similar in
X-ray emission to the Sun, but very different in mass, luminosity,
and evolutionary status. Historical Mt Wilson CaII monitoring was
inconclusive whether Procyon has a solar-like 11-yr magnetic cycle,
or instead is a "flat-activity" star, as might be guessed from its
late-MS-age. However, CaII is a poor magnetic proxy for F-types owing
to low spectral contrast. X-rays are better. In fact, Procyon - with
some X-ray/UV attention over the past two decades - is an excellent
candidate for the ongoing "Dynamo Clinical Trial" sponsored by Chandra,
XMM, and HST; ultimately to provide a "calibration" of novel theoretical
models that seek to couple the inside Dynamo with the outside corona.

---------------------------------------------------------
Title: The High-Energy Environs of the Anomalous Coronal Source
Alpha Persei
Authors: Ayres, Thomas
2015cxo..prop.4590A Altcode:
Alpha Persei (F5Ib) is brightest member of the eponymous young (50 Myr)
cluster, and strong ROSAT source. Paradoxically, HST/COS found only
weak FUV emissions, far out of line with the X-rays. Young clusters are
teeming with active low-mass stars, so the "Alpha Per" source might
be an unrelated object. Alternately, the anomaly might be genuine,
signaling a novel pathway for coronal activity. Objectives: (1) image
with HRC-I to obtain definitive detections of Alpha Per and any close-by
sources; (2) extend earlier COS SNAPshot to capture crucial diagnostic
spectra at shorter wavelengths; (3) image with WFC3 to characterize
any active stars in Alp Per's neighborhood. F supergiants lie at the
edge of convection; keystones for testing theories of coronal activity.

---------------------------------------------------------
Title: The Hubble Space Telescope Advanced Spectral Library Project
Authors: Ayres, Thomas
2015IAUGA..2244967A Altcode:
Advanced Spectral Library (ASTRAL) is a Hubble Large Treasury Project,
whose aim is to collect high-quality ultraviolet (1150-3100 Å)
spectra of bright stars, utilizing the echelle modes of powerful Space
Telescope Imaging Spectrograph; with resolution and signal-to-noise
rivaling the best that can be achieved at ground-based observatories
in the visible. During HST Cycle 18 (2010-2011), ASTRAL was allocated
146 orbits to record eight representative late-type ("cool") stars,
including well-known cosmic denizens like Procyon and Betelgeuse. In
Cycle 21 (2013-2014), ASTRAL was awarded an additional 230 orbits
to extend the project to the hot side of the H-R diagram: 21 targets
covering the O-A spectral types, including household favorites Vega
and Sirius. The second part of the program was completed in January
2015. I describe the scientific motivations for observing hot and cool
stars in the UV; the unique instrumental characteristics of STIS that
enabled a broad survey like ASTRAL; progress in the program to date;
and prospects for the future.

---------------------------------------------------------
Title: The abundance pattern of heavy elements in Sirius: Impact of
modern observations (STIS) and improved Atomic data
Authors: Ramsay Cowley, Charles; Ayres, Thomas; Wahlgren, Glenn;
Carpenter, Kenneth
2015IAUGA..2236931R Altcode:
The abundance pattern of heavy elements in Sirius: Impact of modern
observations (STIS) and improved atomic data. We determine abundances
or upper limits for the 55 stable elements from copper to uranium for
the A1 Vm star Sirius. The primary observational material consists of
Hubble Space Telescope (HST) spectra taken with the Space Telescope
Imaging Spectrograph (STIS) from the ASTRAL project (Ayres 2010,
ApJS, 187, 149). We have also used archival material from COPERNICUS
(retrieved from the MAST) and from HST/GHRS, as well as the ground-based
Furenlid, Westin, and Kurucz Sirius Atlas (FWK). The GHRS observations
were described by Wahlgren, et al. (1993, Bull. AAS, 25, 1321). We
also used the monumental study of Sirius by Klaus Kohl (1964,
Zs. f. Ap. 60, 115, 1964, see also 1964, Das Spektrum des Sirius,
3100 - 8863A, Kiel thesis). Abundance determinations are based on
the photospheric model of Landstreet (2011, A&amp;A, 528, 132). The
atomic data base is significantly improved since the pioneering work
by Sadakane (1988, PASP, 100, 811; 1991, 103, 355). The basic source
was VALD3 (http://vald.inasan.ru/~vald3/php/vald.php), supplemented
for all species by the essential NIST bibliographic data base
(http://physics.nist.gov/cgi-bin/ASBib1/TransProbBib.cgi). We determine
abundances and upper limits by synthesizing short wavelength regions
around strong lines. Virtually all of the abundance/upper limit results
show excesses over the solar composition of between 1 and 2 dex. This
result is in general agreement with overall results for metallic line
stars, though we have no information on possible severe depletions
for most elements. We conclude that the mechanisms causing abundance
anomalies in Sirius have not acted to produce the extreme excesses of 4
or more dex (Pt, Hg), or deficiencies (Zn) seen in many HgMn stars.CRC
thanks Stefano Bagnulo for the UVESPOP Sirius spectrum. Robert Kurucz
was most helpful with older Sirius UV and visual spectra.

---------------------------------------------------------
Title: CO isotopologue ratios in the solar photosphere
Authors: Lyons, James; Gharib-Nezhad, Ehsan; Ayres, Thomas
2015IAUGA..2257564L Altcode:
Determination of the oxygen isotope ratios in the solar photosphere
is essential to constraining the formation environment of the solar
system. The solar CO fundamental and first-overtone bands were
previously measured by the shuttle-borne ATMOS Fourier transform
spectrometer (FTS), and with the National Solar Observatory
FTS on the McMath-Pierce telescope at Kitt Peak. Analyzing
the rovibrational bands from these photospheric spectra, a 3D
convection model was employed to calculate ratios with improved
uncertainties (16O/17O=2738±118 and
16O/18O =511±10 Ayres et al. 2013), which
fall between the terrestrial values and those inferred from solar
wind measurements by the Genesis spacecraft. However, differences
in published CO dipole moment functions yielded a range of isotopic
ratios spanning ~ 3 % in δ18O. Here we re-evaluate the
CO dipole moment function in order to obtain more accurate isotope
ratios for the photosphere. We used a new set of dipole moments from
HITEMP which were accurately determined by both semi-empirical and
ab initio methods. Preliminary values of isotope ratios using the new
dipole moments are in better agreement with the inferred photosphere
values from Genesis, showing that the solar photosphere is isotopically
similar to primitive inclusions in meteorites, but different from the
terrestrial planets by ~ 6 %. New spectral observations are needed to
reduce uncertainties in photospheric C17O abundances.

---------------------------------------------------------
Title: A Giant Far-Ultraviolet Flare on Young Solar Analog EK Draconis
Authors: Ayres, Thomas
2015IAUGA..2244956A Altcode:
A particularly impressive far-ultraviolet flare (corresponding to
a GOES X25,000-class event: 50 is largest ever recorded on the Sun)
was captured serendipitously by Hubble's Cosmic Origins Spectrograph,
during a campaign on young (~50 Myr) solar analog EK Draconis. The
large outburst was like a classical solar 2-ribbon flare: it lasted
several hours and all the atmospheric temperature regimes -- from C
II (30,000 K) through C IV (100,000 K), and up to Fe XXI (10 MK) --
were affected simultaneously. Scaling laws suggest that the EK Dra
event was in the upper echelons of the historical sample of stellar
high-energy outbursts, but the first to be captured in the FUV with the
unprecedented sensitivity, spectral resolution, and high time cadence
of an instrument like COS. Remarkably, time-resolved line profiles of
hot species like Si IV and C IV displayed strong, highly redshifted
components during the event; contrary to the blueshifts one might
naively anticipate from an isotropic stellar explosion. Instead, the
conspicuous redshifts probably are signatures of a post-flare cooling
process, analogous to "coronal rain" or "super-arcade downflows"
associated with large solar events. Flares of this magnitude probably
are common on young hyperactive sunlike stars, occurring perhaps twice a
day on EK Dra itself. The transient doses of FUV radiation probably are
not a significant impediment to planetary habitability, compared with
the "quiescent" FUV output of the star (if you can call an object with
1000 times the X-ray luminosity of the Sun "quiet"), but the associated
very hard X-ray and γ-ray fluences could have a much larger impact
on the ionization of a primitive planetary atmosphere, boosting its
exposure to gas-stripping by stellar winds or coronal mass ejections.

---------------------------------------------------------
Title: Fluorescence Processes in the Outer Atmospheres of the Evolved
M-Stars Alpha Ori (M2 Iab) and Gamma Cru (M3.4 III)
Authors: Carpenter, Kenneth; Kober, Gladys; Nielsen, Krister; Ayres,
Thomas; Wahlgren, Glenn
2015IAUGA..2242446C Altcode:
The prototypical M-giant and M-supergiant stars, Gamma Cru (M3.4
III)) and Alpha Ori (M2Iab), have been observed as part of the
"Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI =
T. Ayres). "ASTRAL-Cool Stars" is an HST Cycle 18 Treasury Program
designed to collect, using the Space Telescope Imaging Spectrograph
(STIS), a definitive set of representative, high-resolution (R~46,000
in the FUV up to ~1700 Å, R~30,000 for 1700-2150 Å, and R~114,000
&gt;2150 Å) and high signal/noise (S/N&gt;100) UV spectra of eight F-M
evolved cool stars. These extremely high-quality UV echelle spectra
are available from the HST archive and through the University of
Colorado (http://casa.colorado.edu/~ayres/ASTRAL/). In this paper,
we use the very rich emission-line spectra of the two evolved M stars
in the sample, Gamma Cru (GaCrux) and Alpha Ori (Betelgeuse), to study
the fluorescence processes operating in their outer atmospheres. We
summarize the pumping transitions and fluorescent line products known
on the basis of previous work and newly identified in our on-going
analysis of these extraordinary new “Treasury” spectra. Detailed
descriptions of selected processes are given to illustrate their
operation. The wide variety of fluorescence processes in operation in
these outer atmospheres, both molecular and atomic, suggest that there
is a mixture of warm and cool plasmas present and that H I Ly-alpha in
particular is locally very strong, even though, in the case of Alpha
Ori, no flux is seen at earth due to strong circumstellar absorption
at that wavelength. Many new fluorescence line products and several
new processes have been identified in these spectra, which are more
complete and of higher S/N than previously available for these stars.

---------------------------------------------------------
Title: The Flare-ona of EK Draconis
Authors: Ayres, Thomas R.
2015AJ....150....7A Altcode: 2015arXiv150502320A
EK Draconis (HD 129333: G1.5 V) is a well-known young (50 Myr) solar
analog. In 2012, Hubble Space Telescope returned to EK Dra to follow up
a far-ultraviolet (FUV) SNAPshot visit by Cosmic Origins Spectrograph
(COS) two years earlier. The brief SNAP pointing had found surprisingly
redshifted, impulsively variable subcoronal “hot-line” emission of
Si iv 1400 Å (T ∼ 8 × 104 K). Serendipitously, the 2012
follow-on program witnessed one of the largest FUV flares ever recorded
on a sunlike star, which again displayed strong redshifts (downflows) of
30-40 km s-1, even after compensating for small systematics
in the COS velocity scales, uncovered through a cross-calibration by
Space Telescope Imaging Spectrograph (STIS). The (now reduced, but
still substantial) ∼10 km s-1 hot-line redshifts outside
the flaring interval did not vary with rotational phase, so cannot be
caused by “Doppler imaging” (bright surface patches near a receding
limb). Density diagnostic O iv] 1400 Å multiplet line ratios of EK
Dra suggest ne ∼ 1011 cm-3, an order
of magnitude larger than in low-activity solar twin α Centauri A, but
typical of densities inferred in large stellar soft X-ray events. The
self-similar FUV hot-line profiles between the flare decay and the
subsequent more quiet periods, and the unchanging but high densities,
reinforce a long-standing idea that the coronae of hyperactive dwarfs
are flaring all the time, in a scale-free way; a flare-ona if you
will. In this picture, the subsonic hot-line downflows probably are a
byproduct of the post-flare cooling process, something like “coronal
rain” on the Sun. All in all, the new STIS/COS program documents a
complex, energetic, dynamic outer atmosphere of the young sunlike star.

---------------------------------------------------------
Title: Characterizing the Habitable Zones of Exoplanetary Systems
with a Large Ultraviolet/Visible/Near-IR Space Observatory
Authors: France, Kevin; Shkolnik, Evgenya; Linsky, Jeffrey; Roberge,
Aki; Ayres, Thomas; Barman, Travis; Brown, Alexander; Davenport,
James; Desert, Jean-Michel; Domagal-Goldman, Shawn; Fleming, Brian;
Fontenla, Juan; Fossati, Luca; Froning, Cynthia; Hallinan, Gregg;
Hawley, Suzanne; Hu, Renyu; Kaltenegger, Lisa; Kasting, James;
Kowlaski, Adam; Loyd, Parke; Mauas, Pablo; Miguel, Yamila; Osten,
Rachel; Redfield, Seth; Rugheimer, Sarah; Schneider, Christian; Segura,
Antigona; Stocke, John; Tian, Feng; Tumlinson, Jason; Vieytes, Mariela;
Walkowicz, Lucianne; Wood, Brian; Youngblood, Allison
2015arXiv150501840F Altcode:
Understanding the surface and atmospheric conditions of Earth-size,
rocky planets in the habitable zones (HZs) of low-mass stars is
currently one of the greatest astronomical endeavors. Knowledge of
the planetary effective surface temperature alone is insufficient
to accurately interpret biosignature gases when they are observed
in the coming decades. The UV stellar spectrum drives and regulates
the upper atmospheric heating and chemistry on Earth-like planets,
is critical to the definition and interpretation of biosignature
gases, and may even produce false-positives in our search for biologic
activity. This white paper briefly describes the scientific motivation
for panchromatic observations of exoplanetary systems as a whole (star
and planet), argues that a future NASA UV/Vis/near-IR space observatory
is well-suited to carry out this work, and describes technology
development goals that can be achieved in the next decade to support
the development of a UV/Vis/near-IR flagship mission in the 2020s.

---------------------------------------------------------
Title: RAISE (Rapid Acquisition Imaging Spectrograph Experiment):
Results and Instrument Status
Authors: Laurent, Glenn T.; Hassler, Donald; DeForest, Craig; Ayres,
Tom; Davis, Michael; DePontieu, Bart; Diller, Jed; Graham, Roy;
Schule, Udo; Warren, Harry
2015TESS....140203L Altcode:
We present initial results from the successful November 2014 launch of
the RAISE (Rapid Acquisition Imaging Spectrograph Experiment) sounding
rocket program, including intensity maps, high-speed spectroheliograms
and dopplergrams, as well as an update on instrument status. The
RAISE sounding rocket payload is the fastest high-speed scanning-slit
imaging spectrograph flown to date and is designed to observe the
dynamics and heating of the solar chromosphere and corona on time
scales as short as 100-200ms, with arcsecond spatial resolution and a
velocity sensitivity of 1-2 km/s. The instrument is based on a class of
UV/EUV imaging spectrometers that use only two reflections to provide
quasi-stigmatic performance simultaneously over multiple wavelengths
and spatial fields. The design uses an off-axis parabolic telescope
mirror to form a real image of the sun on the spectrometer entrance
aperture. A slit then selects a portion of the solar image, passing its
light onto a near-normal incidence toroidal grating, which re-images
the spectrally dispersed radiation onto two array detectors. Two
full spectral passbands over the same one-dimensional spatial field
are recorded simultaneously with no scanning of the detectors or
grating. The two different spectral bands (1st-order 1205-1243Å and
1526-1564Å) are imaged onto two intensified Active Pixel Sensor (APS)
detectors whose focal planes are individually adjusted for optimized
performance. RAISE reads out the full field of both detectors at 5-10
Hz, allowing us to record over 1,500 complete spectral observations in
a single 5-minute rocket flight, opening up a new domain of high time
resolution spectral imaging and spectroscopy. RAISE is designed to
study small-scale multithermal dynamics in active region (AR) loops,
explore the strength, spectrum and location of high frequency waves
in the solar atmosphere, and investigate the nature of transient
brightenings in the chromospheric network.

---------------------------------------------------------
Title: CxO (x=16,17,18) Isotopologue Ratios in the Solar Photosphere
Authors: GharibNezhad, E.; Lyons, J. R.; Ayres, T. R.
2015LPI....46.1592G Altcode: 2015LPICo1832.1592G
Using revised f-values of CO isotopologues, preliminary isotope ratios
for the solar photosphere were determined, and are found to be similar
to Genesis values.

---------------------------------------------------------
Title: Characterising exoplanets and their environment with UV
transmission spectroscopy
Authors: Fossati, L.; Bourrier, V.; Ehrenreich, D.; Haswell, C. A.;
Kislyakova, K. G.; Lammer, H.; Lecavelier des Etangs, A.; Alibert,
Y.; Ayres, T. R.; Ballester, G. E.; Barnes, J.; Bisikalo, D. V.;
Collier, A.; Cameron; Czesla, S.; Desert, J. -M.; France, K.; Guedel,
M.; Guenther, E.; Helling, Ch.; Heng, K.; Homstrom, M.; Kaltenegger,
L.; Koskinen, T.; Lanza, A. F.; Linsky, J. L.; Mordasini, C.; Pagano,
I.; Pollacco, D.; Rauer, H.; Reiners, A.; Salz, M.; Schneider, P. C.;
Shematovich, V. I.; Staab, D.; Vidotto, A. A.; Wheatley, P. J.; Wood,
B. E.; Yelle, R. V.
2015arXiv150301278F Altcode:
Exoplanet science is now in its full expansion, particularly after
the CoRoT and Kepler space missions that led us to the discovery of
thousands of extra-solar planets. The last decade has taught us that
UV observations play a major role in advancing our understanding of
planets and of their host stars, but the necessary UV observations can
be carried out only by HST, and this is going to be the case for many
years to come. It is therefore crucial to build a treasury data archive
of UV exoplanet observations formed by a dozen "golden systems" for
which observations will be available from the UV to the infrared. Only
in this way we will be able to fully exploit JWST observations for
exoplanet science, one of the key JWST science case.

---------------------------------------------------------
Title: Serendipitous Discovery of a Dwarf Nova in the Kepler Field
Near the G Dwarf KIC 5438845
Authors: Brown, Alexander; Neff, James E.; Ayres, Thomas R.; Kowalski,
Adam; Hawley, Suzanne; Berdyugina, Svetlana; Harper, Graham M.;
Korhonen, Heidi; Piskunov, Nikolai; Saar, Steven; Walkowicz, Lucianne;
Wells, Mark A.
2015AJ....149...67B Altcode:
The Kepler satellite provides a unique window into stellar temporal
variability by observing a wide variety of stars with multi-year,
near-continuous, high precision, optical photometric time series. While
most Kepler targets are faint stars with poorly known physical
properties, many unexpected discoveries should result from a long
photometric survey of such a large area of sky. During our Kepler
Guest Observer programs that monitored late-type stars for starspot and
flaring variability, we discovered a previously unknown dwarf nova that
lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This
dwarf nova underwent nine outbursts over a 4 year time span. The two
largest outbursts lasted ∼17-18 days and show strong modulations with
a 110.8 minute period and a declining amplitude during the outburst
decay phase. These properties are characteristic of an SU UMa-type
cataclysmic variable. By analogy with other dwarf nova light curves,
we associate the 110.8 minute (1.847 hr) period with the superhump
period, close to but slightly longer than the orbital period of the
binary. No precursor outbursts are seen before the super-outbursts
and the overall super-outburst morphology corresponds to Osaki &amp;
Meyer “Case B” outbursts, which are initiated when the outer edge
of the disk reaches the tidal truncation radius. “Case B” outbursts
are rare within the Kepler light curves of dwarf novae. The dwarf nova
is undergoing relatively slow mass transfer, as evidenced by the long
intervals between outbursts, but the mass transfer rate appears to
be steady, because the smaller “normal” outbursts show a strong
correlation between the integrated outburst energy and the elapsed time
since the previous outburst. At super-outburst maximum the system was
at V ∼ 18, but in quiescence it is fainter than V ∼ 22, which will
make any detailed quiescent follow-up of this system difficult.

---------------------------------------------------------
Title: The Far-Ultraviolet Ups and Downs of Alpha Centauri
Authors: Ayres, Thomas R.
2015AJ....149...58A Altcode:
Four years (2010-2014) of semiannual pointings by the Hubble Space
Telescope Imaging Spectrograph (STIS) on nearby Alpha Centauri have
yielded a detailed time history of far-ultraviolet (FUV: 1150-1700
Å) emissions of the solarlike primary (A: G2 V) and the cooler but
more active secondary (B: K1 V). This period saw A climbing out of
a prolonged coronal X-ray minimum, as documented contemporaneously
by Chandra, while B was rising to, then falling from, a peak of its
long-term (∼8 year) starspot cycle. The FUV fluxes of the primary
were steady over most of the STIS period, although the [Fe xii] λ1242
coronal forbidden line (T∼ 1.5 MK) partly mirrored the slowly rising
X-ray fluxes. The FUV emissions of the secondary more closely tracked
the rise and fall of its coronal luminosities, especially the “hot
lines” Si iv, C iv, and N v (T∼ 0.8-2 × 105 K), and
coronal [Fe xii] itself. The hot lines of both stars were systematically
redshifted, relative to narrow chromospheric emissions, by several km
s-1, showing little change in amplitude over the four-year
period, especially for α Cen B, despite the significant evolution of
its coronal activity. Further, the hot lines of both stars, individually
and epoch-averaged, displayed non-Gaussian shapes, which most trivially
could be decomposed into two components, one narrow (FWHM ∼25-45 km
s-1), the other broad (60-80 km s-1). A bimodal
Gaussian strategy had been applied previously to the α Cen stars, but
this was the first opportunity to evaluate any time dependence. In fact,
not much variation of the component properties was seen, even over the
major cycle changes of B. Curiously, the line fluxes were about equally
divided between the narrow and broad components for both stars. The
fact that there is minimal activity dependence of the narrow/broad flux
partition, as well as densities derived from O iv] line ratios, either
during the cycle evolution of B or between A and B, suggests that there
is a dominant “quantum” of FUV surface activity that is relatively
unchanged during the cycle, aside from the fractional area covered.

---------------------------------------------------------
Title: Predicting the Extreme-UV and Lyman-α Fluxes Received by
Exoplanets from their Host Stars
Authors: Linsky, Jeffrey L.; France, Kevin; Ayres, Thomas R.
2015csss...18..831L Altcode:
Extreme-UV (EUV) radiation from the chromospheres, transition
regions, and coronae of host stars (spectral types F, G, K, and
M) ionize and heat the outer atmospheres of exoplanets leading
to mass loss that is observed during transits and can change the
exoplanet's atmosphere. Lyman-α emission from host stars controls
the photochemistry in the upper layers of planetary atmospheres by
photodissociating important molecules including H_2O, CO_2, CH_4,
thereby increasing the oxygen and ozone mixing ratios important for
habitability. Both the EUV and strong Lyman-α radiation are largely
absorbed by the interstellar medium and must be reconstructed or
estimated to understand the radiation environment of exoplanets. In two
recent papers, tet{Linsky2013} and tet{Linsky2014}, we have presented
robust methods for predicting the intrinsic Lyman-α and EUV fluxes from
main sequence cool stars. Solar models and satellite observations (HST,
FUSE, and EUVE) provide tests for the feasibility of these methods.

---------------------------------------------------------
Title: The HST Treasury “Advanced Spectral Library” (ASTRAL)
Programs
Authors: Carpenter, Kenneth G.; Ayres, Thomas R.
2015csss...18.1041C Altcode: 2014arXiv1411.1419C
The “Advanced Spectral Library (ASTRAL)” Project (PI = T. Ayres)
consists of two Treasury Programs: the Cycle 18 “Cool Stars”
(GO-12278) Program and the Cycle 21 “Hot Stars” (GO-13346)
Program. The primary goal of these programs is to collect, for the use
of the astronomical community over the coming decades, a definitive
set of representative, high-resolution (R∼30,000-100,000), high
signal/noise (S/N&gt;100) spectra, with full UV coverage (∼1150 -
3100 Å) of prototypical stars across the HR diagram, utilizing the
high-performance Space Telescope Imaging Spectrograph (STIS). The
Cycle 18 program obtained spectra of 8 F-M evolved late-type
stars, while the Cycle 21 program is in the process of observing
21 early-type stars, which span a broad range of spectral types
between early-O and early-A. All of these data will be available
from the HST archive and, in post-processed and merged form, at
http://casa.colorado.edu/ãyres/ASTRAL/. These data will enable
investigations of a broad range of problems - stellar, interstellar,
and beyond - for many years into the future. We describe here the
details of the observing programs, including the program targets and the
observing strategies utilized to optimize the quality of the spectra,
and present some illustrative examples of the on-going scientific
analyses, including a study of the outer atmospheres and winds of
the two evolved M stars in the sample and a first look at a “high
definition” UV spectrum of a magnetic chemically peculiar “Ap” star.

---------------------------------------------------------
Title: Mining the HST "Advanced Spectral Library (ASTRAL)": Winds
of the Evolved M Stars Alpha Ori (M2 Iab) and Gamma Cru (M3.4 III)
Authors: Carpenter, Kenneth G.; Nielsen, Krister E.; Kober, Gladys V.;
Ayres, Thomas R.
2015AAS...22534408C Altcode:
The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI
= T. Ayres) is an HST Cycle 18 Treasury Program that collected a
definitive set of representative, high-resolution (R=30,000-100,000)
and high signal/noise (S/N&gt;100) UV spectra of eight F-M evolved
cool stars. These extremely high-quality STIS UV echelle spectra are
available from the HST archive and through the ASTRAL website at the
University of Colorado at http://casa.colorado.edu/~ayres/ASTRAL/ and
will enable investigations of a broad range of problems -- stellar,
interstellar, and beyond -- for many years. In this paper, we examine
the wealth of wind diagnostics contained in the very rich spectra
of the two evolved M stars in the sample, the M3.4 III giant Gamma
Crucis (GaCrux) and the M2 Iab supergiant Alpha Orionis (Betelgeuse)
and characterize the winds at the time of these STIS observations in
2011 and compare the results with those obtained from more limited data
taken at earlier epochs with HST/GHRS and IUE. In particular we study
the variation of the numerous Fe II profiles with intrinsic strength
in the two stars. The shifting wavelengths of the wind absorptions
relative to the emission peaks and the changes in relative strengths
of the emission peaks reflect the acceleration of the wind from the
base of the chromosphere. Although the characteristics of the Gamma
Cru wind are relatively stable with time, the Alpha Ori wind outflow
appears significantly smaller than seen by Carpenter et al. (1997,
ApJ, 479, 970) in GHRS observations taken in 1992 (and in earlier IUE
observations). There might in fact be evidence in these STIS spectra
that the outflow has turned into an inflow, as reported at epochs
prior to IUE by Boesgaard and Magnan (1975 ApJ 198, 369) and Boesgaard
(1979 ApJ 232, 485) based on a limited number of lines in the extreme
blue end of ground-based spectra.

---------------------------------------------------------
Title: Flares and Antiflares on Young Solar Analog EK Draconis
Authors: Ayres, Thomas R.
2015AAS...22513823A Altcode:
EK Draconis (HD129333: G1.5 V) is a well-known young (50 Myr) solar
analog. In 2012, Hubble Space Telescope returned to EK Dra to follow
up a far-UV SNAPshot visit by HST's Cosmic Origins Spectrograph
two years earlier. The brief SNAP pointing had found surprisingly
redshifted subcoronal Si IV (T~ 8x104 K), which also
displayed impulsive variability, curiously uncorrelated with species
at lower temperatures (C II: 2x104K) or higher (Fe XXI:
1x107K). Serendipitously, the follow-on program witnessed
one of the largest FUV flares ever recorded on a sun-like star,
which nevertheless displayed even stronger redshifts (downflows)
than had been seen earlier, contrary to the violent blueshifts
expected from such explosive events. At the same time, a velocity
cross-calibration by Space Telescope Imaging Spectrograph (STIS)
uncovered systematic deviations in the wavelength scales of COS,
that were partly, but not entirely, responsible for the previously
reported SNAP redshifts. However, the (now smaller, but still about 10
km s-1) Si IV redshifts did not vary with rotational phase,
so are not likely caused by "Doppler imaging' effects. Instead, the
downflows might be signatures of catastrophic coronal cooling events
(`"antiflares'). All in all, the new COS/STIS program documents a
complex, energetic, dynamic outer atmosphere of the young solar analog.

---------------------------------------------------------
Title: X-ray Emission from Young Stars in the TW Hya Association
Authors: Brown, Alexander; Herczeg, Gregory J.; Ayres, Thomas R.;
France, Kevin; Brown, Joanna M.
2015csss...18..203B Altcode: 2014arXiv1408.4062B
The 9 Myr old TW Hya Association (TWA) is the nearest group (typical
distances of ∼50 pc) of pre-main-sequence (PMS) stars with ages less
than 10 Myr and contains stars with both actively accreting disks and
debris disks. We have studied the coronal X-ray emission from a group of
low mass TWA common proper motion binaries using the Chandra and Swift
satellites. Our aim is to understand better their coronal properties
and how high energy photons affect the conditions around young stars
and their role in photo-exciting atoms, molecules and dust grains in
circumstellar disks and lower density circumstellar gas. Once planet
formation is underway, this emission influences protoplanetary evolution
and the atmospheric conditions of the newly-formed planets. The X-ray
properties for 7 individual stars (TWA 13A, TWA 13B, TWA 9A, TWA 9B,
TWA 8A, TWA 8B, and TWA 7) and 2 combined binary systems (TWA 3AB and
TWA 2AB) have been measured. All the stars with sufficient signal
require two-component fits to their CCD-resolution X-ray spectra,
typically with a dominant hot (~2 kev (25 MK)) component and a
cooler component at ~0.4 keV (4 MK). The brighter sources all show
significant X-ray variability (at a level of 50-100% of quiescence)
over the course of 5-15 ksec observations due to flares. We present
the X-ray properties for each of the stars and find that the coronal
emission is in the super-saturated rotational domain.

---------------------------------------------------------
Title: The Ups and Downs of Alpha Centauri
Authors: Ayres, Thomas
2014fysc.confP...6A Altcode:
Nearby Alpha Centauri is destined for a pivotal chapter in human
history, as first stop of future starfarers from Earth: 3x closer
than the next nearest star; three very different objects to visit --
Alpha Cen A (G2V), B (K1V), and C (M6V); and B hosts an Earth-mass
companion, albeit in a hot, lifeless orbit. For its part, Chandra
has been keeping intent watch on the high-energy starspot cycles of
AB, with semi-annual pointings over the past decade. Only HRC-I can
separate AB as they plunge toward a close approach of 4" in 2016;
and LETGS has countered that an abrupt 50x drop in XMM count rate of
sun-like A in early 2005, ominously reported as the "darkening of the
solar twin," simply is a soft sensitivity issue, not an unprecedented,
inexplicable case of corona interrupta.

---------------------------------------------------------
Title: Searching for a gas cloud surrounding the WASP-18 planetary
system
Authors: Fossati, L.; Ayres, T. R.; Haswell, C. A.; Jenkins, J. S.;
Bisikalo, D.; Bohlender, D.; Flöer, L.; Kochukhov, O.
2014Ap&SS.354...21F Altcode:
Near-UV (NUV) Hubble Space Telescope (HST) observations of the extreme
hot-Jupiter WASP-12b revealed the presence of diffuse exospheric
gas extending beyond the planet's Roche lobe. Furthermore the NUV
observations showed a complete lack of the normally bright core
emission of the Mg ii h&amp;k resonance lines, in agreement with
the measured anomalously low stellar activity index (log R'
HK ). Comparisons with other distant and inactive stars, and
the analysis of radio and optical measurements of the intervening
interstellar medium (ISM), led us to the conclusion that the system
is surrounded by a circumstellar gas cloud, likely formed of material
lost by the planet. Similar anomalous log R' HK index
deficiencies might therefore signal the presence of translucent
circumstellar gas around other stars hosting evaporating planets;
we identified five such systems and WASP-18 is one of them. Both
radio and optical observations of the region surrounding WASP-18
point towards a negligible ISM absorption along the WASP-18 line of
sight. Excluding the unlikely possibility of an intrinsic anomalously
low stellar activity, we conclude that the system is probably surrounded
by a circumstellar gas cloud, presumably formed of material lost by
the planet. Nevertheless only a far-UV spectrum of the star would
provide a definite answer. Theoretical modelling suggests WASP-18b
undergoes negligible mass loss, in contrast to the probable presence
of a circumstellar gas cloud formed of material lost by the planet. The
solution might be the presence either of an extra energy source driving
mass loss (e.g., the reconnection of the stellar and planetary magnetic
fields inside the planet atmosphere) or of an evaporating third body
(e.g., moon).

---------------------------------------------------------
Title: An HST COS "SNAPshot" Spectrum of the K Supergiant λ Vel
(K4Ib-II)
Authors: Carpenter, Kenneth G.; Ayres, Thomas R.; Harper, Graham M.;
Kober, Gladys; Nielsen, Krister E.; Wahlgren, Glenn M.
2014ApJ...794...41C Altcode:
We present a far-ultraviolet spectrum of the K4 Ib-II supergiant λ Vel
obtained with the Hubble Space Telescope's Cosmic Origins Spectrograph
(COS) as a part of the SNAPshot program "SNAPing coronal iron" (GO
11687). The observation covers a wavelength region (1326-1467 Å)
not previously recorded for λ Vel at a spectral resolving power
of R ~ 20,000 and displays strong emission and absorption features,
superposed on a bright chromospheric continuum. Fluorescent excitation
is responsible for much of the observed emission, mainly powered by
strong H I Lyα and the O I (UV 2) triplet emission near λ1304. The
molecular CO and H2 fluorescences are weaker than in the
early-K giant α Boo while the Fe II and Cr II lines, also pumped
by H I Lyα, are stronger in λ Vel. This pattern of relative line
strengths between the two stars is explained by the lower iron-group
element abundance in α Boo, which weakens that star's Fe II and
Cr II emission without reducing the molecular fluorescences. The
λ Vel spectrum shows fluorescent Fe II, Cr II, and H2
emission similar to that observed in the M supergiant α Ori, but
more numerous well-defined narrow emissions from CO. The additional CO
emissions are visible in the spectrum of λ Vel since that star does
not have the cool, opaque circumstellar shells that surround α Ori
and produce broad circumstellar CO (A-X) band absorptions that hide
those emissions in the cooler star. The presence of Si IV emission in
λ Vel indicates a ~8 × 104 K plasma that is mixed into
the cooler chromosphere. Evidence of the stellar wind is seen in the
C II λλ1334,1335 lines and in the blueshifted Fe II and Ni II wind
absorption lines. Line modeling using Sobolev with Exact Integration for
the C II lines indicates a larger terminal velocity (~45 versus ~30 km
s-1) and turbulence (~27 versus &lt;21 km s-1)
with a more quickly accelerating wind (β = 0.35 versus 0.7) at the
time of this COS observation in 2010 than derived from Goddard High
Resolution Spectrograph data obtained in 1994. The Fe II and Ni II
absorptions are blueshifted by 7.6 km s-1 relative to the
chromospheric emission, suggesting formation in lower levels of the
accelerating wind and their widths indicate a higher turbulence in
the λ Vel wind compared to α Ori. Based on observations with
the NASA/ESA Hubble Space Telescope obtained at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

---------------------------------------------------------
Title: The Far-Ultraviolet Ups and Downs of Alpha Centauri
Authors: Ayres, Thomas R.
2014arXiv1411.0038A Altcode:
Four years (2010-2014) of semiannual pointings by Hubble Space
Telescope Imaging Spectrograph (STIS) on nearby Alpha Centauri have
yielded a detailed time history of far-ultraviolet emissions of the
solar-like primary (A: G2V) and the cooler, but more active, secondary
(B: K1V). This period saw A climbing out of a prolonged coronal X-ray
minimum, as documented by Chandra, while B was rising to, then falling
from, a peak of its long-term (8 yr) starspot cycle. The FUV fluxes
of the primary were steady over most of the STIS period, although the
[Fe XII] 124 nm coronal forbidden line (T= 1.5 MK) partly mirrored
the slowly rising X-ray fluxes. The FUV emissions of the secondary
more closely tracked the rise and fall of its coronal luminosities,
especially the "hot lines" like Si IV, C IV, and N V (T= 80,000-200,000
K), and coronal [Fe XII] itself. The hot lines of both stars were
systematically redshifted, relative to narrow chromospheric emissions,
by several km/s, showing little change in amplitude over the 4-year
period; especially for Alpha Cen B, despite the significant evolution
of its coronal activity. Further, the hot line profiles of both stars,
individually and epoch-averaged, could be decomposed into two nearly
equal components, one narrow (FWHM~ 25-45 km/s), the other broad
(60-80 km/s). Not much variation of the component properties was seen
over the 4-year period, even over the major cycle changes of B. This
suggests that there is a dominant "quantum" of FUV surface activity
that is relatively unchanged during the cycle, aside from the fractional
area covered.

---------------------------------------------------------
Title: Molecular absorption in transition region spectral lines
Authors: Schmit, D. J.; Innes, D.; Ayres, T.; Peter, H.; Curdt, W.;
Jaeggli, S.
2014A&A...569L...7S Altcode: 2014arXiv1409.1702S
 Aims: We present observations from the Interface Region Imaging
Spectrograph (IRIS) of absorption features from a multitude of cool
atomic and molecular lines within the profiles of Si IV transition
region lines. Many of these spectral lines have not previously
been detected in solar spectra. Methods: We examined spectra
taken from deep exposures of plage on 12 October 2013. We observed
unique absorption spectra over a magnetic element which is bright in
transition region line emission and the ultraviolet continuum. We
compared the absorption spectra with emission spectra that is
likely related to fluorescence. Results: The absorption
features require a population of sub-5000 K plasma to exist above
the transition region. This peculiar stratification is an extreme
deviation from the canonical structure of the chromosphere-corona
boundary. The cool material is not associated with a filament or
discernible coronal rain. This suggests that molecules may form in
the upper solar atmosphere on small spatial scales and introduces a
new complexity into our understanding of solar thermal structure. It
lends credence to previous numerical studies that found evidence
for elevated pockets of cool gas in the chromosphere. Movies
associated to Figs. 1 and 2 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424432/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Alpha Centauri at a Crossroads
Authors: Ayres, Thomas
2014cxo..prop.4335A Altcode:
Nearby Alpha Centauri (G2V+K1V) contains the two best characterized
solar-like dwarf stars, which also have the best studied X-ray activity
cycles, extending back to the 1970's. Objective is to continue tracking
the evolving multi-decadal high-energy narrative of Alpha Cen with
semiannual HRC-I pointings in Cycles 16-18, as the system reaches a
coronal crossroads: solar twin A rising toward cycle maximum, K-type
companion B sinking into a minimum. HST/STIS UV spectra will support and
leverage the X-ray measurements by probing subcoronal dynamics, with
connection to the corona through the FUV Fe XII forbidden line. Only
Chandra can resolve the AB X-ray sources as the Alpha Cen orbit also
reaches a crossroads in 2016.

---------------------------------------------------------
Title: The Stellar-IRIS Connection: Four Years of FUV Measurements
of Alpha Centauri by HST/STIS
Authors: Ayres, Thomas R.
2014AAS...22432312A Altcode:
Since 2010 January, shortly after the miraculous repair of Hubble's
Space Telescope Imaging Spectrograph (STIS) by SM4, the two sun-like
stars of Alpha Centauri ("A" [G2V] and "B" [K1V]) have been recorded
on a semi-annual basis utilizing STIS's far-ultraviolet (115-170 nm)
medium resolution mode (about 8 km/s FWHM resolving power), jointly
with an X-ray imaging study of AB by the Chandra Observatory. Both
efforts are intended to assess the long-term behavior of high-energy
(multimillion K) coronal, and subcoronal, processes on the two
relatively low-activity solar-age dwarfs. In fact, the near-solar-twin
Alpha Cen A has been mired in a coronal lull since 2005, originally
recognized by XMM-Newton, and only recently has begun to climb out of
the extended X-ray minimum. Meanwhile, the lower mass, lower luminosity,
but coronally more active secondary has displayed a clear 8-year X-ray
cycle, extending from the mid-1990's ROSAT era. The current study
focuses on properties of the "transition zone" lines ( 100,000 K)
of the Alpha Centauri stars, namely the bulk redshifts exhibited by
the Si IV, C IV, and N V doublets; the multi-component nature of the
hot-line profiles; behavior of the Fe XII 124 nm coronal forbidden line;
and variability of the FUV fluxes relative to the higher-energy X-ray
time series. These stellar measurements, with their high precision
in wavelength and flux, complement the detailed high-spatial and
high-temporal resolution spectral mapping of the solar corona and
lower atmosphere being carried out by NASA's Interface Region Imaging
Spectrograph (IRIS). [This work supported by GO grants 12758, 13060,
and 13465 from Space Telescope Science Institute.]

---------------------------------------------------------
Title: The Structure of the Local Interstellar Medium. VI. New Mg II,
Fe II, and Mn II Observations toward Stars within 100 pc
Authors: Malamut, Craig; Redfield, Seth; Linsky, Jeffrey L.; Wood,
Brian E.; Ayres, Thomas R.
2014ApJ...787...75M Altcode: 2014arXiv1403.8096M
We analyze high-resolution spectra obtained with the Space Telescope
Imaging Spectrograph onboard the Hubble Space Telescope toward 34 nearby
stars (&lt;=100 pc) to record Mg II, Fe II, and Mn II absorption due
to the local interstellar medium (LISM). Observations span the entire
sky, probing previously unobserved regions of the LISM. The heavy
ions studied in this survey produce narrow absorption features that
facilitate the identification of multiple interstellar components. We
detected one to six individual absorption components along any given
sight line, and the number of absorbers roughly correlates with the
pathlength. This high-resolution near-ultraviolet (NUV) spectroscopic
survey was specifically designed for sight lines with existing far-UV
(FUV) observations. The FUV spectra include many intrinsically broad
absorption lines (i.e., of low atomic mass ions) and are often observed
at medium resolution. The LISM NUV narrow-line absorption component
structure presented here can be used to more accurately interpret the
archival FUV observations. As an example of this synergy, we present a
new analysis of the temperature and turbulence along the line of sight
toward epsilon Ind. The new observations of LISM velocity structure
are also critical in the interpretation of astrospheric absorption
derived from fitting the saturated H I Lyα profile. As an example, we
reanalyze the spectrum of λ And and find that this star likely does
have an astrosphere. Two stars in the sample that have circumstellar
disks (49 Cet and HD141569) show evidence for absorption due to disk
gas. Finally, the substantially increased number of sight lines is
used to test and refine the three-dimensional kinematic model of the
LISM and search for previously unidentified clouds within the Local
Bubble. We find that every prediction made by the Redfield &amp; Linsky
kinematic model of the LISM is confirmed by an observed component in
the new lines of sight.

---------------------------------------------------------
Title: Reconstructing the Stellar UV and EUV Emission that Controls
the Chemistry of Exoplanet Atmospheres
Authors: Linsky, Jeffrey L.; France, Kevin; Ayres, Tom
2014IAUS..293..309L Altcode:
Lyman-α and extreme-ultraviolet radiation from exoplanet host stars are
critically important for evaluating the phototchemistry of planetary
atmospheres, but these emissions are largely or completely absorbed
by hydrogen in the interstellar medium. We describe a new technique
for estimating the intrinsic Lyman-α and EUV fluxes of F, G, K,
and M stars using correlations with observable emission lines.

---------------------------------------------------------
Title: Superflares on Sun-Like Stars: Bane of Habitability?
Authors: Ayres, T.
2014hwat.confE...1A Altcode:
A key aspect of planetary habitability is the existence of rare,
but catastrophic events. One Earthly example is the attribution of
several geological mass extinctions to asteroid collisions. Indeed,
the Late Heavy Bombardment, during which the 600 Myr old Earth was
pummeled persistently by impactors over a period of perhaps a hundred
Myr, likely significantly delayed the permanent foothold of life on our
planet. Another, less well known, example is the proposed existence of
"superflares" on Sun-like stars. Although the quantity of energy in a
superflare is negligible compared with the time-integrated X-ray dose
from the quiescent multi-MK corona, the quality of the radiation (i.e.,
composition dominated by gamma rays) released from the transient,
but extreme, outburst is what could be of concern to the survival
of primitive lifeforms struggling for existence on a semi-habitable
world. However, existing reports of superflares mainly involve
interpretations of historical materials, such as long-term astronomical
plate collections; there are very few concrete examples of such events
observed by modern techniques at the most relevant wavelengths, namely
ultraviolet or X-rays. The lack of good examples is mostly because
these rare events are, well, rare. However, a recent HST Cosmic Origins
Spectrograph program to record the ultraviolet spectrum of young
( 50 Myr) solar analog EK Draconis, fortuitously captured a giant,
hour-long FUV transient, in hot lines like the C IV 155 nm doublet
(T 100,000 K), and very toasty Fe XXI 124 nm coronal forbidden line
( 10 MK). If translated into the equivalent GOES 0.1-0.8 nm X-ray
fluence, the event would correspond to an X25000-class flare (most
extreme observed on the Sun might reach as high as a mere X50). The EK
Dra giant flare, as viewed with the excellent wavelength resolution,
broad coverage, and high sensitivity of COS, provides the opportunity
to deduce properties of such events to help inform possible impacts
on planetary habitability, especially in the context of the early
development of life on Earth-like planets orbiting young Sun-like stars.

---------------------------------------------------------
Title: The Ups and Downs of α Centauri
Authors: Ayres, Thomas R.
2014AJ....147...59A Altcode: 2014arXiv1401.0847A
The following is a progress report on the long-term coronal (T ~ 1
MK) activity of α Centauri A (HD 128620: G2 V) and B (HD 128621: K1
V). Since 2005, Chandra X-Ray Observatory has carried out semiannual
pointings on AB, mainly with the High Resolution Camera, but also on
two occasions with the Low-Energy Transmission Grating Spectrometer,
fully resolving the close pair in all cases. During 2008-2013,
Chandra captured the rise, peak, and initial decline of B's coronal
luminosity. Together with previous high states documented by ROSAT and
XMM-Newton, the long-term X-ray record suggests a period of 8.1 ± 0.2
yr, compared to 11 yr for the Sun, with a minimum-to-peak contrast
of 4.5, about half the typical solar cycle amplitude. Meanwhile,
the A component has been mired in a Maunder-Minimum-like low state
since 2005, initially recognized by XMM-Newton. But now, A finally
appears to be climbing out of the extended lull. If interpreted
simply as an overlong cycle, the period would be 19.2 ± 0.7 yr,
with a minimum-to-peak contrast of 3.4. The short X-ray cycle of B,
and possibly long cycle of A, are not unusual compared with the diverse
(albeit much lower amplitude) chromospheric variations recorded, for
example, by the HK Project. Further, the deep low state of A also is not
unusual, but instead is similar to the L X/L bol
of the Sun during recent minima of the sunspot cycle.

---------------------------------------------------------
Title: Mining the HST "Advanced Spectral Library (ASTRAL) - Hot
Stars": The High Definition UV Spectrum of the Ap Star HR 465
Authors: Carpenter, Kenneth G.; Ayres, T. R.; Nielsen, K. E.; Kober,
G. V.; Wahlgren, G. M.; Adelman, S. J.; Cowley, C. R.
2014AAS...22315105C Altcode:
The "Advanced Spectral Library (ASTRAL) Project: Hot Stars" is a Hubble
Space Telescope (HST) Cycle 21 Treasury Program (GO-13346: Ayres
PI). It is designed to collect a definitive set of representative,
high-resolution ( 30,000-100,000), high signal/noise (S/N&gt;100),
and full UV coverage 1200 - 3000 A) spectra of 21 early-type stars,
utilizing the high-performance Space Telescope Imaging Spectrograph
(STIS). The targets span the range of spectral types between early-O
and early-A, including both main sequence and evolved stars, fast
and slow rotators, as well as chemically peculiar (CP) and magnetic
objects. These extremely high-quality STIS UV echelle spectra will be
available from the HST archive and, in post-processed and merged form,
at http://casa.colorado.edu ayres/ASTRAL/. The UV "atlases" produced by
this program will enable investigations of a broad range of problems --
stellar, interstellar, and beyond -- for many years to come. We offer a
first look at one of the earliest datasets to come out of this observing
program, a "high definition" UV spectrum of the Ap star HR 465, which
was chosen as a prototypical example of an A-type magnetic CP star. HR
465 has a global magnetic field of ~2200 Gauss. Earlier analyses of IUE
spectra show strong iron-peak element lines, along with heavy elements
such as Ga and Pt, while being deficient in the abundance of some ions
of low atomic number, such as carbon. We demonstrate the high quality
of the ASTRAL data and present the identification of spectral lines
for a number of elements. By comparison of the observed spectra with
calculated spectra, we also provide estimates of element abundances,
emphasizing heavy elements, and place these measurements in the context
of earlier results for this and other Ap stars.

---------------------------------------------------------
Title: The "Horns" of FK Comae and the Complex Structure of its
Outer Atmosphere
Authors: Saar, Steven H.; Ayres, T. R.; Kashyap, V.
2014AAS...22315116S Altcode:
As part of a large multiwavelength campaign (COCOA-PUFS*) to explore
magnetic activity in the unusual, single, rapidly rotating giant FK
Comae, we have taken a time series of moderate resolution FUV spectra
of the star with the COS spectrograph on HST. We find that the star
has unusual, time-variable emission profiles in the chromosphere and
transition region which show horn-like features. We use simple spatially
inhomogeneous models to explain the variable line shapes. Modeling
the lower chromospheric Cl I 1351 Å line, we find evidence for a very
extended, spatial inhomogeneous outer atmosphere, likely composed of
many huge "sling-shot" prominences of cooler material with embedded in
a rotationally distended corona. We compare these results with hotter
hotter transition region lines (Si IV) and optical spectra of the
chromospheric He I D3 line. We also employ the model Cl I profiles,
and data-derived empirical models, to fit the complex spectral region
around the coronal Fe XXI 1354.1 Å line. We place limits on the flux
of this line, and show these limits are consistent with expectations
from the observed X-ray spectrum. *Campaign for Observation of the
Corona and Outer Atmosphere of the Fast-rotating Star, FK Comae This
work was supported by HST grant GO-12376.01-A.

---------------------------------------------------------
Title: The Advanced Spectral Library (ASTRAL) Project
Authors: Ayres, Thomas R.; The ASTRAL I & Science Teams, II
2014AAS...22325437A Altcode:
The Advanced Spectral Library (ASTRAL) is an HST Treasury Program
whose aim is to secure definitive ultraviolet (115-310 nm) spectra
of representative bright stars utilizing the venerable -- yet still
state-of-the-art -- Space Telescope Imaging Spectrograph (STIS). The
initial Cycle 18 installment of the program (146 orbits in 2010-2011)
focused on late-type (“cool’’) stars, acquiring high-S/N, high
spectral resolution measurements of eight pivotal targets, including
iconic objects like Betelgeuse and Procyon. The latest episode, in
current Cycle 21 (230 orbits in 2013-2014), is designed to record
very high-S/N (&gt;100) STIS echellegrams, at the highest resolution
feasible ( 30,000-100,000), of 21 representative bright early-type
(“hot’’) stars, including equally iconic objects like Vega,
Sirius, Regulus, and Zeta Puppis. The targets span a broad range of
spectral types between early-O and early-A, encompassing main sequence
and evolved stars, fast and slow rotators, as well as chemically
peculiar and magnetic objects. These high-quality STIS UV spectra
will be publicly available immediately after observation from the
HST archive; and, in post-processed and merged form, at the project
website: http://casa.colorado.edu ayres/ASTRAL/. The UV "atlases"
produced by the ASTRAL Program will enable investigations of a broad
range of astrophysical problems -- stellar, interstellar, and beyond --
for many years to come. Supported by Guest Observer grants from STScI.

---------------------------------------------------------
Title: HST/STIS Advanced Spectral Library (ASTRAL)
Authors: Ayres, T. R.
2014ASInC..13....1A Altcode:
ASTRAL is a Hubble Space Telescope Large Treasury Program whose aim
is to collect full-coverage ultraviolet (1150-3100 Å) echelle spectra
of representative stars of spectral types O-M, with resolution and S/N
comparable to the best now obtained routinely in optical observations
from the ground. First part of the program - Cool Stars - was completed
in 2011. Second part - Hot Stars - is in progress (2013-2014). Resulting
high-level processed UV "atlases" are available from the ASTRAL site:
http://casa.colorado.edu/ ayres/ASTRAL/

---------------------------------------------------------
Title: HST/STIS Advanced Spectral Library (ASTRAL)
Authors: Ayres, T. R.
2014ASInC..11....1A Altcode:
ASTRAL is a Hubble Space Telescope Large Treasury Program whose
aim is to collect full-coverage ultraviolet (1150--3100 &amp;Aring)
echelle spectra of representative stars of spectral types O--M, with
resolution and S/N comparable to the best now obtained routinely in
optical observations from the ground. First part of the program --
Cool Stars -- was completed in 2011. Second part -- Hot Stars -- is
in progress (2013--2014). Resulting high-level processed UV "atlases"
are available from the ASTRAL site: http://casa.colorado.edu/
ayres/ASTRAL/

---------------------------------------------------------
Title: Advanced Spectral Library II: Hot Stars
Authors: Ayres, Thomas
2013hst..prop13346A Altcode:
Stars are the bright matter of the Universe. Without them, it would
be a dull and dreary place indeed: no light, no heavy elements, no
planets, no life. It also is safe to say that stellar spectroscopy is a
cornerstone of astrophysics, providing much of what we know concerning
temperatures and masses of stars, their compositions, planets, and the
dynamics and evolution of the galaxies they inhabit. This is especially
true for the satellite ultraviolet, owing to the rich collection of
atomic and ionic transitions found there. Unfortunately, the archive
of Space Telescope Imaging Spectrograph rarely achieves the high S/N
of the best ground-based spectra, and relatively few objects have the
full wavelength coverage for which the powerful, highly multiplexed,
second generation Hubble instrument was designed. Our aim is to collect
STIS UV echelle spectra - comparable in S/N and resolution to the
best ground-based material - for a diverse sample of representative
stars, to build an Advanced Spectral Library; a foundation for
astrophysical exploration: stellar, interstellar, and beyond. Our
first effort, in Cycle 18, involved cool stars. Now we turn attention
to the hot side of the H-R diagram.Our Treasury program will provide
detailed stellar "atlases," based on advanced processing of the STIS
echellegrams. Members of our broad collaboration will analyze these
data for specific purposes, such as dynamics of O-star mass-loss;
detection of rare species in sharp-lined B stars; and properties and
kinematics of local interstellar clouds; but public release {based on
the "ASTRAL-I" model} will enable many other investigations by a much
wider community, for decades to come.

---------------------------------------------------------
Title: Alpha Cen: Climbing out of a Coronal Recession? {year 3
continuation}
Authors: Ayres, Thomas
2013hst..prop13465A Altcode:
Nearby Alpha Centauri contains the two best characterized G and K
dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved
angular diameters, and well understood co-evolutionary state. Alpha
Cen A &amp; B also have the best studied stellar X-ray activity
cycles, extending back to the 1970's. Present proposal is to continue
tracking the evolving multi-decadal high-energy narrative of Alpha Cen
with semiannual HRC-I pointings in Cycles 13-15, as solar twin A is
expected to be rising to cycle maximum following an extended coronal
recession. STIS E140M spectra will support and leverage the broad-band
X-ray measurements by probing subcoronal dynamics and providing a
low-T boundary condition for DEM modeling, with connection to the
X-rays through the FUV Fe XII coronal forbidden line.

---------------------------------------------------------
Title: The Ups and Downs of Alpha Centauri
Authors: Ayres, Thomas R.
2013SPD....44..152A Altcode:
The nearby Alpha Centauri triple system has two solar-type stars
in a relatively close orbit (20 au separation), and a dim red dwarf
companion -- Proxima -- about 10,000 au away, on the Sun-ward side
of the group. The heaviest star -- Alpha Cen A -- is a close twin of
the Sun. Its slightly less massive companion -- Alpha Cen B -- is a
K-type dwarf, and is the closest star thought to host an exoplanet
(Earth-sized, but in a much tighter orbit). The close pair has been
scrutinized for more than a decade in X-rays by XMM and Chandra,
on a semiannual basis since 2003 and 2005, respectively. However,
in recent years only Chandra has been able to cleanly separate the
pair, which are approaching closest separation on the sky (only a
few arcseconds) in their 80-year orbit. For the past 3 years, the HST
STIS spectrograph has joined the crowd, also capturing FUV snapshots
of the pair every six months. The Alpha Cen stars provide an important
complement to long-term studies of the Sun at high energies. The K-star
has displayed a clear 8-year cycle in recent years, while the G-star
remains mired in a Maunder-like minimum.

---------------------------------------------------------
Title: Red Giant Atmospheres, through the Lens of UV Spectroscopy
Authors: Ayres, Thomas R.
2013giec.conf10202A Altcode:
UV spectra of normal red giants show many differences with the
Sun. The usual high-excitation, coronal-related emissions like
Si IV and C IV are weak or absent, but low-excitation species
like O I and Mg II are conspicuous and often carry signatures of
strong, chromospheric winds. In extreme cases, one even finds dusty
molecule-rich circumstellar envelopes that absorb strongly in the FUV
bands of CO. At higher energies -- X-rays -- the red giants are even
more feeble, inhabiting was has been called the "coronal graveyard." One
imagines that the general avoidance of high-energy emissions among
the red giants is a consequence of lack of magnetic activity due to
slow rotation. Indeed, if one considers tidally spun-up red giants
in short-period binaries, such objects are among the most coronally
active known. Still, even if the rotationally catalyzed "dynamo" is
suppressed in the normal red giants, they should have some residual
magnetic activity generated by surface convective processes. UV spectra
can provide clues to where these putative fields are hiding; and their
possible connection to the chromospheric winds.

---------------------------------------------------------
Title: Status of RAISE, the Rapid Acquisition Imaging Spectrograph
Experiment
Authors: Laurent, Glenn T.; Hassler, D. M.; DeForest, C.; Ayres,
T. R.; Davis, M.; De Pontieu, B.; Schuehle, U.; Warren, H.
2013SPD....44..145L Altcode:
The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) sounding
rocket payload is a high speed scanning-slit imaging spectrograph
designed to observe the dynamics and heating of the solar chromosphere
and corona on time scales as short as 100 ms, with 1 arcsec spatial
resolution and a velocity sensitivity of 1-2 km/s. The instrument is
based on a new class of UV/EUV imaging spectrometers that use only
two reflections to provide quasi-stigmatic performance simultaneously
over multiple wavelengths and spatial fields. The design uses an
off-axis parabolic telescope mirror to form a real image of the sun
on the spectrometer entrance aperture. A slit then selects a portion
of the solar image, passing its light onto a near-normal incidence
toroidal grating, which re-images the spectrally dispersed radiation
onto two array detectors. Two full spectral passbands over the same
one-dimensional spatial field are recorded simultaneously with no
scanning of the detectors or grating. The two different spectral
bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two
intensified Active Pixel Sensor (APS) detectors whose focal planes are
individually adjusted for optimized performance. The telescope and
grating are coated with B4C to enhance short wavelength (2nd order)
reflectance, enabling the instrument to record the brightest lines
between 602-622Å and 761-780Å at the same time. RAISE reads out the
full field of both detectors at 5-10 Hz, allowing us to record over
1,500 complete spectral observations in a single 5-minute rocket flight,
opening up a new domain of high time resolution spectral imaging and
spectroscopy. We present an overview of the project, a summary of the
maiden flight results, and an update on instrument status.Abstract
(2,250 Maximum Characters): The Rapid Acquisition Imaging Spectrograph
Experiment (RAISE) sounding rocket payload is a high speed scanning-slit
imaging spectrograph designed to observe the dynamics and heating of the
solar chromosphere and corona on time scales as short as 100 ms, with 1
arcsec spatial resolution and a velocity sensitivity of 1-2 km/s. The
instrument is based on a new class of UV/EUV imaging spectrometers
that use only two reflections to provide quasi-stigmatic performance
simultaneously over multiple wavelengths and spatial fields. The design
uses an off-axis parabolic telescope mirror to form a real image of
the sun on the spectrometer entrance aperture. A slit then selects
a portion of the solar image, passing its light onto a near-normal
incidence toroidal grating, which re-images the spectrally dispersed
radiation onto two array detectors. Two full spectral passbands over
the same one-dimensional spatial field are recorded simultaneously with
no scanning of the detectors or grating. The two different spectral
bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two
intensified Active Pixel Sensor (APS) detectors whose focal planes are
individually adjusted for optimized performance. The telescope and
grating are coated with B4C to enhance short wavelength (2nd order)
reflectance, enabling the instrument to record the brightest lines
between 602-622Å and 761-780Å at the same time. RAISE reads out the
full field of both detectors at 5-10 Hz, allowing us to record over
1,500 complete spectral observations in a single 5-minute rocket flight,
opening up a new domain of high time resolution spectral imaging and
spectroscopy. We present an overview of the project, a summary of the
maiden flight results, and an update on instrument status.

---------------------------------------------------------
Title: Computing Intrinsic LYα Fluxes of F5 V to M5 V Stars
Authors: Linsky, Jeffrey L.; France, Kevin; Ayres, Tom
2013ApJ...766...69L Altcode: 2013arXiv1301.5711L
The Lyα emission line dominates the far-ultraviolet spectra of
late-type stars and is a major source for photodissociation of important
molecules including H2O, CH4, and CO2
in exoplanet atmospheres. The incident flux in this line illuminating
an exoplanet's atmosphere cannot be measured directly as neutral
hydrogen in the interstellar medium (ISM) attenuates most of the flux
reaching the Earth. Reconstruction of the intrinsic Lyα line has been
accomplished for a limited number of nearby stars, but is not feasible
for distant or faint host stars. We identify correlations connecting
the intrinsic Lyα flux with the flux in other emission lines formed
in the stellar chromosphere, and find that these correlations depend
only gradually on the flux in the other lines. These correlations,
which are based on Hubble Space Telescope spectra, reconstructed
Lyα line fluxes, and irradiance spectra of the quiet and active Sun,
are required for photochemical models of exoplanet atmospheres when
intrinsic Lyα fluxes are not available. We find a tight correlation of
the intrinsic Lyα flux with stellar X-ray flux for F5 V to K5 V stars,
but much larger dispersion for M stars. We also show that knowledge
of the stellar effective temperature and rotation rate can provide
reasonably accurate estimates of the Lyα flux for G and K stars,
and less accurate estimates for cooler stars.

---------------------------------------------------------
Title: Absorbing Gas around the WASP-12 Planetary System
Authors: Fossati, L.; Ayres, T. R.; Haswell, C. A.; Bohlender, D.;
Kochukhov, O.; Flöer, L.
2013ApJ...766L..20F Altcode: 2013arXiv1303.3375F
Near-UV observations of the planet host star WASP-12 uncovered the
apparent absence of the normally conspicuous core emission of the
Mg II h and k resonance lines. This anomaly could be due either to
(1) a lack of stellar activity, which would be unprecedented for
a solar-like star of the imputed age of WASP-12 or (2) extrinsic
absorption, from the intervening interstellar medium (ISM) or from
material within the WASP-12 system itself, presumably ablated from the
extreme hot Jupiter WASP-12 b. HIRES archival spectra of the Ca II H
and K lines of WASP-12 show broad depressions in the line cores, deeper
than those of other inactive and similarly distant stars and similar to
WASP-12's Mg II h and k line profiles. We took high-resolution ESPaDOnS
and FIES spectra of three early-type stars within 20' of WASP-12 and
at similar distances, which show the ISM column is insufficient to
produce the broad Ca II depression observed in WASP-12. The EBHIS H I
column density map supports and strengthens this conclusion. Extrinsic
absorption by material local to the WASP-12 system is therefore the
most likely cause of the line core anomalies. Gas escaping from the
heavily irradiated planet could form a stable and thick circumstellar
disk/cloud. The anomalously low stellar activity index (log R^{{\prime
}}_{HK}) of WASP-12 is evidently a direct consequence of the extra core
absorption, so similar HK index deficiencies might signal the presence
of translucent circumstellar gas around other stars hosting evaporating
planets. Based on observations obtained at the Canada-France-Hawaii
Telescope (CFHT), which is operated by the National Research Council of
Canada, the Institut National des Sciences de l'Univers of the Centre
National de la Rechereche Scientifique of France, and the University of
Hawaii. Based on observations made with the Nordic Optical Telescope,
operated on the island of La Palma jointly by Denmark, Finland,
Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de
los Muchachos of the Instituto de Astrofisica de Canarias.

---------------------------------------------------------
Title: Is the Sun Lighter than the Earth? Isotopic CO in the
Photosphere, Viewed through the Lens of Three-dimensional Spectrum
Synthesis
Authors: Ayres, Thomas R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.;
Wedemeyer-Böhm, S.
2013ApJ...765...46A Altcode: 2013arXiv1301.5281A
We consider the formation of solar infrared (2-6 μm) rovibrational
bands of carbon monoxide (CO) in CO5BOLD 3D convection models,
with the aim of refining abundances of the heavy isotopes of carbon
(13C) and oxygen (18O, 17O), to
compare with direct capture measurements of solar wind light ions
by the Genesis Discovery Mission. We find that previous, mainly 1D,
analyses were systematically biased toward lower isotopic ratios (e.g.,
R 23 ≡ 12C/13C), suggesting an
isotopically "heavy" Sun contrary to accepted fractionation processes
that were thought to have operated in the primitive solar nebula. The
new 3D ratios for 13C and 18O are R 23
= 91.4 ± 1.3 (R ⊕ = 89.2) and R 68 =
511 ± 10 (R ⊕ = 499), where the uncertainties are
1σ and "optimistic." We also obtained R 67 = 2738 ±
118 (R ⊕ = 2632), but we caution that the observed
12C17O features are extremely weak. The new solar
ratios for the oxygen isotopes fall between the terrestrial values and
those reported by Genesis (R 68 = 530, R 67 =
2798), although including both within 2σ error flags, and go in the
direction favoring recent theories for the oxygen isotope composition
of Ca-Al inclusions in primitive meteorites. While not a major focus
of this work, we derive an oxygen abundance, epsilonO ~
603 ± 9 ppm (relative to hydrogen; log epsilon ~ 8.78 on the H =
12 scale). The fact that the Sun is likely lighter than the Earth,
isotopically speaking, removes the necessity of invoking exotic
fractionation processes during the early construction of the inner
solar system.

---------------------------------------------------------
Title: Isotopic CO in the Solar Photosphere, Viewed Through the Lens
of 3D Spectrum Synthesis
Authors: Ayres, T. R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.;
Wedemeyer-Bohm, S.
2013LPI....44.3038A Altcode: 2013LPICo1719.3038A
New analyses of CO isotopologue abundances in the solar photosphere
are now consistent with Genesis solar wind results, although ^17O
error bars are still large.

---------------------------------------------------------
Title: Advanced Spectral Library (ASTRAL): Cool stars edition
Authors: Ayres, T. R.
2013AN....334..105A Altcode: 2013csss...17..105A
ASTRAL is a project to create high-resolution, high-S/N UV (1150-3200
Å) atlases of bright stars utilizing {HST}/STIS. During Cycle 18
(2010-2011), eight cool star targets were observed, including key
objects like Procyon and Betelgeuse, churning through 146 orbits
in the process. The new spectral atlases are publically available
through the project website. Data were obtained with the Hubble
Space Telescope.

---------------------------------------------------------
Title: A Large Sample of Magnetically-Active Stars Observed With
Kepler
Authors: Wells, Mark; Neff, J. E.; Brown, A.; Ayres, T. R.; Basri,
G. S.; Berdyugina, S.; Harper, G.; Hawley, S. L.; Korhonen, H.;
Kowalski, A.; Micela, G.; Piskunov, N. E.; Ramsey, L. W.; Saar, S. H.;
Walkowicz, L. M.
2013AAS...22135415W Altcode:
We have observed about 325 stars in our Kepler Guest Observer
programs (Cycles 1 through 4). For most of these targets, we are
analyzing extremely high-precision light curves that have been
continuously sampled every 30 minutes for up to 3 years. Our sample
of candidate magnetically-active stars was selected primarily using
GALEX colors. Starspots, pulsations, and variations due to eclipsing
and contact binaries combine to produce a rich variety of light
curves. We have developed semi-automated procedures to characterize
this variability and thus to classify the targets and identify the
physical mechanisms that dominate their Kepler light curves. We will
describe these procedures and discuss the range of physical properties
covered by our final classification scheme. We are using this Kepler
database of variability over timescales of minutes to years to provide
diagnostics of flares, starspot formation, evolution, migration, and
ultimately of stellar cycles in general. This work contains results
obtained using the NASA Kepler satellite and from the Apache Point
Observatory, the MMT (using NOAO community access time), and the
Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants
NNX10AC51G, NNX11AC79G, and NNX12AC85G to the University of Colorado,
by NSF grant AST-1109695 to the College of Charleston, and by a grant
from the South Carolina Space Grant consortium.

---------------------------------------------------------
Title: Chromospheric thermal continuum millimetre emission from
non-dusty K and M red giants
Authors: Harper, G. M.; O'Riain, N.; Ayres, T. R.
2013MNRAS.428.2064H Altcode: 2012MNRAS.tmp..152H; 2012arXiv1210.2627H
We examine the thermal free-free millimetre fluxes expected from
non-dusty and non-pulsating K through mid-M giant stars based on our
limited understanding of their inhomogeneous chromospheres. We present
a semi-analytic model that provides estimates of the radio fluxes for
the mm wavelengths [e.g. Combined Array for Research in Millimetre-wave
Astronomy (CARMA), Atacama Large Millimetre/submillimetre Array (ALMA)
and Karl G. Jansky Very Large Array (JVLA) Q band] based on knowledge
of the effective temperatures, angular diameters and chromospheric Mg
ii h &amp; k emission fluxes. At 250 GHz, the chromospheric optical
depths are expected to be significantly less than unity, which means
that fluxes across the mm and submm range will have a contribution from
the chromospheric material that gives rise to the ultraviolet emission
spectrum, as well as the cool molecular material known to exist above
the photosphere. We predict a lower bound to the inferred brightness
temperature of red giants based on heating at the basal flux limit if
the upper chromospheres have filling factor ≃1. Multifrequency mm
observations should provide important new information on the structuring
of the inhomogeneous chromospheres, including the boundary layer, and
allow tests of competing theoretical models for atmospheric heating. We
comment on the suitability of these stars as mm flux calibrators.

---------------------------------------------------------
Title: Ultraviolet and Extreme Ultraviolet Emission of Host Stars
and Effects on Exoplanet Atmospheres
Authors: Linsky, Jeffrey; France, K.; Ayres, T. R.
2013AAS...22132105L Altcode:
The chemistry and mass-loss rates of exoplanet atmospheres are
controlled by the radiative and particle emission of their host
star. The host star's ultraviolet radiation, and especially the
Lyman-alpha emission, photodissociate important molecules in exoplanet
atmospheres including water, CO2, and methane. The intrinsic Lyman-alpha
emission cannot be observed because of attenuation by neutral hydrogen
in the interstellar medium and must therefore be reconstructed. We
describe a new reconstruction method based on correlations of
Lyman-alpha flux with the fluxes in other emission lines formed at
similar temperatures in the stellar chromosphere. Except for low metal
abundance stars, this technique provides estimates of the Lyman-alpha
flux within 20 percent of the values obtained by Wood et al. (2005)
for stars of spectral type F5 V to M5 V. We also show that the EUV flux
in 100 A wide spectral bands from 300 to 1170 A is well correlated
with the Lyman-alpha flux and therefore can be accurately estimated
for these stars. This work is based on observations with the COS and
STIS instruments on HST, and is supported by NASA grants to the Space
Telescope Science Institute and the University of Colorado.

---------------------------------------------------------
Title: Solar carbon monoxide: poster child for 3D effects .
Authors: Ayres, T. R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.;
Wedemeyer-Böhm, S.
2013MSAIS..24...85A Altcode:
Photospheric infrared (2-6 mu m) rovibrational bands of carbon
monoxide (CO) provide a tough test for 3D convection models such as
those calculated using CO5BOLD. The molecular formation is highly
temperature-sensitive, and thus responds in an exaggerated way to
thermal fluctuations in the dynamic atmosphere. CO, itself, is an
important tracer of the oxygen abundance, a still controversial
issue in solar physics; as well as the heavy isotopes of carbon
(13C) and oxygen (18O, 17O), which,
relative to terrestrial values, are fingerprints of fractionation
processes that operated in the primitive solar nebula. We show how 3D
models impact the CO line formation, and add in a second constraint
involving the near-UV Ca RIPTSIZE II line wings, which also are highly
temperature sensitive, but in the opposite sense to the molecules. We
find that our reference CO5BOLD snapshots appear to be slightly too
cool on average in the outer layers of the photosphere where the CO
absorptions and Ca RIPTSIZE II wing emissions arise. We show, further,
that previous 1D modeling was systematically biased toward higher
oxygen abundances and lower isotopic ratios (e.g., R23equiv
12C/13C), suggesting an isotopically “heavy”
Sun contrary to direct capture measurements of solar wind light ions
by the Genesis Discovery Mission. New 3D ratios for the oxygen isotopes
are much closer to those reported by Genesis, and the associated oxygen
abundance from CO now is consistent with the recent Caffau et al. study
of atomic oxygen. Some lingering discrepancies perhaps can be explained
by magnetic bright points. Solar CO demonstrates graphically the wide
gulf that can occur between a 3D analysis and 1D.

---------------------------------------------------------
Title: Mining the Advanced Spectral Library (ASTRAL): Characterizing
Winds of Evolved M-Stars
Authors: Nielsen, Krister E.; Carpenter, K. G.; Kober, G. V.; Cheng,
K.; Ayres, T. R.; Harper, G.
2013AAS...22135102N Altcode:
The HST/STIS treasury program Advanced Spectral Library (ASTRAL)
enables investigations of the character and dynamics of the wind and
chromosphere of cool stars, using high quality spectral data. This
paper present the analysis of the outflowing winds of the M3.4 giant
Gamma Cru and the M2Iab supergiant Alpha Ori. The outer atmospheres
of these objects show strong evidence for significant inhomogeneity
in their thermal and kinematic structure, and are in general not
well understood. The wind features are characterized by a strong
chromospheric emission suppressed by a overlying wind absorption,
for many transitions producing a double peak feature. The relative
strengths and wavelength shifts between the absorption and emission
components of the lines reflect the acceleration of the wind from the
base of the chromosphere, as the self-absorption is due to the overlying
wind absorption, whose velocity relative to the chromosphere varies
with height and thus line opacity. The wind profiles are sensitive to
the wind opacity, turbulence and flow velocity, and hence favorable
to analyze with the Sobolev source function with Exact Integration of
the transfer equation (SEI) code. This paper will show a velocity and
intensity analysis of the wind profiles and modeling with the SEI code
to derive an improved set of wind parameters, primarily, for Gamma Cru.

---------------------------------------------------------
Title: Young Star Populations in the Kepler Field
Authors: Brown, Alexander; Neff, J. E.; Wells, M.; Saar, S.; Furesz,
G.; Walkowicz, L. M.; Ayres, T. R.; Basri, G. S.; Berdyugina, S.;
Harper, G.; Hawley, S. L.; Korhonen, H.; Kowalski, A.; Micela, G.;
Piskunov, N. E.; Ramsey, L. W.
2013AAS...22135414B Altcode:
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that routinely
allow detailed studies of stellar magnetic activity on late-type stars
that were difficult previously. Kepler provides multi-year duration
light-curves that allow investigation of how activity phenomena --
such as the growth, migration, and decay of star-spots, differential
rotation, activity cycles, and flaring -- operate on a wide variety of
single and binary stars. The 105 square degree Kepler Field contains
tens of thousands of late-type stars showing rotational modulation due
to star-spots with periods ranging from one day to a “solar-like”
month. Short rotation periods and high levels of magnetic activity are
strongly correlated. However, there are only two basic reasons why stars
with rotation periods of a few days possess such high angular momentum
--- either they are close binaries or they are young stars. During
Kepler GO Cycles 1 through 4 we have been studying the Long-cadence
(30 minute sampling) photometry of hundreds of active late-type stars
and as an absolutely essential complement we have been obtaining high
resolution optical spectra to understand the physical properties of
these stars. We present results from a spectroscopic survey using the
MMT Hectochelle multi-object echelle of 4 square degrees of the Kepler
Field. We have discovered a significant population of young stars with
Li I absorption indicating ages of ~100 Myr or less at a spatial density
of at least 20 stars per square degree. Our detected young star sample
comprises at least 80 stars and represents a dramatic advance compared
to the previously known sample over the full Kepler Field of three
stars in this age range. Roughly one sixth of the stars observed are
young and a similar number short-period binaries based on 2-4 radial
velocities. We show how the rotational properties of the stars and their
physical properties are related. This work is based on data obtained
with the NASA Kepler satellite and the MMT Hectochelle spectrograph
using NOAO community access time. Support by NASA Kepler grants to the
University of Colorado and by NSF grant to the College of Charleston.

---------------------------------------------------------
Title: Mining the Advanced Spectral Library (ASTRAL): Fluorescence
in Evolved M-Stars
Authors: Carpenter, Kenneth G.; Nielsen, K. E.; Kober, G. V.; Cheng,
K.; Ayres, T. R.; Wahlgren, G. M.; Harper, G.
2013AAS...22135101C Altcode:
The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI =
T. Ayres) is an HST Cycle 18 Treasury Program designed to collect
a definitive set of representative, high-resolution ( 46,000 in the
FUV up to ~1700 Å, 30,000 for 1700-2150 Å, and 114,000 &gt;2150 Å)
and high signal/noise (S/N&gt;100) UV spectra of eight F-M evolved
cool stars. These extremely high-quality STIS UV echelle spectra are
available from the HST archive and through the University of Colorado
(http://casa.colorado.edu ayres/ASTRAL/) and will enable investigations
of a broad range of problems -- stellar, interstellar, and beyond -- for
many years. In this paper, we use the very rich emission-line spectra
of the two evolved M stars in the sample, the M3.4 giant Gamma Crucis
(GaCrux) and the M2Iab supergiant Alpha Orionis (Betelgeuse), to study
the fluorescence processes operating in their outer atmospheres. We
summarize the pumping transitions and fluorescent line products known
on the basis of previous work (e.g. Carpenter 1988 and references
therein) and newly identified in our current, on-going analysis and
provide some comments on their implications for the structure of the
outer atmospheres of these stars.

---------------------------------------------------------
Title: Near-ultraviolet Absorption, Chromospheric Activity, and
Star-Planet Interactions in the WASP-12 system
Authors: Haswell, C. A.; Fossati, L.; Ayres, T.; France, K.; Froning,
C. S.; Holmes, S.; Kolb, U. C.; Busuttil, R.; Street, R. A.; Hebb,
L.; Collier Cameron, A.; Enoch, B.; Burwitz, V.; Rodriguez, J.; West,
R. G.; Pollacco, D.; Wheatley, P. J.; Carter, A.
2012ApJ...760...79H Altcode: 2013arXiv1301.1860H
Extended gas clouds have been previously detected surrounding the
brightest known close-in transiting hot Jupiter exoplanets, HD 209458 b
and HD 189733 b we observed the distant but more extreme close-in hot
Jupiter system, WASP-12, with Hubble Space Telescope (HST). Near-UV
(NUV) transits up to three times deeper than the optical transit
of WASP-12 b reveal extensive diffuse gas, extending well beyond
the Roche lobe. The distribution of absorbing gas varies between
visits. The deepest NUV transits are at wavelength ranges with strong
stellar photospheric absorption, implying that the absorbing gas may
have temperature and composition similar to those of the stellar
photosphere. Our spectra reveal significantly enhanced absorption
(greater than 3σ below the median) at ~200 individual wavelengths
on each of two HST visits; 65 of these wavelengths are consistent
between the two visits, using a strict criterion for velocity
matching that excludes matches with velocity shifts exceeding ~20 km
s-1. Excess transit depths are robustly detected throughout
the inner wings of the Mg II resonance lines independently on both
HST visits. We detected absorption in Fe II λ2586, the heaviest
species yet detected in an exoplanet transit. The Mg II line cores
have zero flux, emission cores exhibited by every other observed star
of similar age and spectral type are conspicuously absent. WASP-12
probably produces normal Mg II profiles, but the inner portions of these
strong resonance lines are likely affected by extrinsic absorption. The
required Mg+ column is an order of magnitude greater than
expected from the interstellar medium, though we cannot completely
dismiss that possibility. A more plausible source of absorption is
gas lost by WASP-12 b. We show that planetary mass loss can produce
the required column. Our Visit 2 NUV light curves show evidence for a
stellar flare. We show that some of the possible transit detections in
resonance lines of rare elements may be due instead to non-resonant
transitions in common species. We present optical observations and
update the transit ephemeris. Based on observations made with
the NASA/ESA Hubble Space Telescope, obtained from MAST at the Space
Telescope Science Institute, which is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract
NAS 5-26555. These observations are associated with programs 11651
and 11673.

---------------------------------------------------------
Title: Alpha Cen: Climbing out of a Coronal Recession? {year 2
continuation}
Authors: Ayres, Thomas
2012hst..prop13060A Altcode:
Nearby Alpha Centauri contains the two best characterized G and K
dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved
angular diameters, and well understood co-evolutionary state. Alpha Cen
A &amp; B also have the best studied stellar X-ray activity cycles,
extending back to the 1970â??s. Present proposal is to continue
tracking the evolving multi-decadal high-energy narrative of Alpha
Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin
A is expected to be rising to cycle maximum from an extended coronal
recession. STIS E140M spectra will support and leverage the broad-band
X-ray measurements by probing subcoronal dynamics and providing a
low-T boundary condition for DEM modeling, with connection to HRC
through the FUV Fe XII coronal forbidden line.

---------------------------------------------------------
Title: Ultraviolet Spectroscopy of Rapidly Rotating Solar-Mass Stars:
Emission-line Redshifts as a Test of the Solar-Stellar Connection
Authors: Linsky, Jeffrey L.; Bushinsky, Rachel; Ayres, Tom; France,
Kevin
2012ApJ...754...69L Altcode: 2012arXiv1205.6498L
We compare high-resolution ultraviolet spectra of the Sun and
thirteen solar-mass main-sequence stars with different rotational
periods that serve as proxies for their different ages and magnetic
field structures. In this, the second paper in the series, we study
the dependence of ultraviolet emission-line centroid velocities on
stellar rotation period, as rotation rates decrease from that of the
Pleiades star HII314 (P rot = 1.47 days) to α Cen A (P
rot = 28 days). Our stellar sample of F9 V to G5 V stars
consists of six stars observed with the Cosmic Origins Spectrograph
on the Hubble Space Telescope (HST) and eight stars observed with the
Space Telescope Imaging Spectrograph on HST. We find a systematic
trend of increasing redshift with more rapid rotation (decreasing
rotation period) that is similar to the increase in line redshift
between quiet and plage regions on the Sun. The fastest-rotating
solar-mass star in our study, HII314, shows significantly enhanced
redshifts at all temperatures above log T = 4.6, including the corona,
which is very different from the redshift pattern observed in the
more slowly rotating stars. This difference in the redshift pattern
suggests that a qualitative change in the magnetic-heating process
occurs near P rot = 2 days. We propose that HII314 is an
example of a solar-mass star with a magnetic heating rate too large
for the physical processes responsible for the redshift pattern to
operate in the same way as for the more slowly rotating stars. HII314
may therefore lie above the high activity end of the set of solar-like
phenomena that is often called the "solar-stellar connection."

---------------------------------------------------------
Title: The Old Feeble Transition Regions and Coronae of Solar-like
Dwarf Stars in the Arcturus Moving Group
Authors: Brown, Alexander; Hodges-Kluck, E. J.; Ayres, T. R.; Harper,
G. M.
2012AAS...22032804B Altcode:
Old dwarf stars have generally spun down significantly thus
dampening one of the main contributors (rotation) to solar-like
alpha-omega magnetic dynamo activity. Studying how stellar
activity on stars older than the Sun changes in terms of the
chromospheric/transition-region/coronal temperature structure and
how much energy is radiated as a function of temperature provides
important constraints on how solar-like dynamos work. Stars with
different metallicities provide information on how the radiative
cooling channels control the temperature structure. We have
measured fluxes and profiles of FUV emission lines using the HST COS
spectrograph and the broad-band X-ray fluxes using Chandra ACIS-S for a
sample of old inactive dwarfs. Our sample comprises five members of the
7-8 Gyr Arcturus Moving Group --- HD90508/LHS2266 (F9 V/M4 V, [Fe/H] =
-0.4), HD65583 (G8 V, Fe/H]=-0.7), and HD145417 (K0 V, [Fe/H]=-1.4)
--- plus three well-studied comparison stars -- HD103095 (G8 V,
[Fe/H]=-1.4), Tau Ceti (G8 V, [Fe/H]=-0.4), and the Quiet Sun (G2 V,
[Fe/H]=0.0). In this poster we provide estimates of atmospheric
radiative losses as a function of temperature and metallicity. The
atmospheres of these low-metallicity stars are more heavily weighted
towards cooler temperatures than those of more active stars or even the
Sun. Chromospheric emission lines, e.g. C I lines, are far stronger
relative transition region lines, e.g C IV. Similarly the X-ray data
provide detections for all the targets but with primarily very soft
(0.3-0.5 keV) photons and imply "coronal" temperatures of less than
1 MK. While the temperature distributions are cooler, the overall
integrated X-ray and FUV luminosities are similar to those of the
"Quiet Sun" -- implying that similar amounts of non-radiative energy
input are being dissipated. This work is supported by NASA GALEX
grant NNX06AB46G, HST grants GO-11555 and GO-11829, and Chandra grants
GO6-7018X, GO7-8020X, and GO9-0021X to the University of Colorado.

---------------------------------------------------------
Title: Using Kepler Data to Characterize the Flare Properties of
GK Stars
Authors: Kowalski, Adam F.; Deitrick, Russell J.; Brown, Alex;
Davenport, Jim R. A.; Hawley, Suzanne L.; Hilton, Eric J.; Ayres,
Thomas R.; Berdyugina, Svetlana V.; Harper, Graham M.; Korhonen,
Heidi; Walkowicz, Lucianne M.
2012decs.confE.120K Altcode:
Due to their high occurrence rate and large contrast against the
background stellar emission, white-light flares on a handful of
very active low-mass M stars have been the primary source for our
understanding of optical flare emission. Kepler's high-precision, long
baseline light curves have opened up the characterization of white-light
emission to new domains of stars, including active G dwarfs. We present
the properties of white-light flares on GALEX-selected solar-type stars
from GO data in Q1-Q7. The flares are discussed in relation to intrinsic
stellar properties, which are constrained by a vast amount of follow-up
characterization of the sample. We compare the flare properties to
large white-light flares observed on the Sun. These high-precision
state-of-the-art observations will provide important constraints for
models of internal magnetic dynamos and NLTE radiative-hydrodynamic
simulations of energy deposition in the lower atmospheric layers.

---------------------------------------------------------
Title: The Solar Oxygen Crisis, Revisited
Authors: Ayres, Thomas R.
2012AAS...21914408A Altcode:
For years, controversy has raged over what seemingly should
be a well-established property of our Sun, the solar oxygen
abundance. Spectroscopic estimates early last decade based on
advanced 3D time-dependent photospheric convection simulations,
suggested that the true oxygen abundance was almost 40% lower than
the value (680 ppm relative to hydrogen) recommended only a few years
prior. The unexpectedly low value sparked what has come to be called
the “Solar Oxygen Crisis,” because the previous higher abundance was
almost exactly what was required by helioseismology to reproduce the
interior sound speed profile, well-characterized from surface p-mode
measurements. Although in most other parts of Astronomy, agreement to
within a factor of two is cause for celebration, in this case -- despite
intense efforts on both sides -- there did not seem to be an easy way
to reconcile the disparate results from the inside and outside of the
Sun. In this study, I examine the surface spectroscopy side of the
issue, bringing to bear additional diagnostics, such as center-to-limb
behavior, on the one hand to validate the thermal properties of the 3D
convection models, and on the other to provide additional leverage on
the abundance issue. The main conclusion is that existing 3D models can
reproduce the key continuum center-limb effect in the visible, showing
that the mean thermal gradient in the deep atmosphere is accurate,
but the same models misunderestimate intensities in the inner wings of
the H and K resonance lines of ionized calcium, a signature of too-low
temperatures in the middle photosphere (where key oxygen bearing CO
and OH reside). Implications for a unified description of the oxygen
abundance from atomic and molecular species are discussed. This work
supported by NSF.

---------------------------------------------------------
Title: Far-ultraviolet Continuum Emission: Applying This Diagnostic
to the Chromospheres of Solar-mass Stars
Authors: Linsky, Jeffrey L.; Bushinsky, Rachel; Ayres, Tom; Fontenla,
Juan; France, Kevin
2012ApJ...745...25L Altcode: 2011arXiv1109.5653L
The far-ultraviolet (FUV) continuum flux is recognized as a very
sensitive diagnostic of the temperature structure of the Sun's
lower chromosphere. Until now analysis of the available stellar FUV
data has shown that solar-type stars must also have chromospheres,
but quantitative analyses of stellar FUV continua require far higher
quality spectra and comparison with new non-LTE chromosphere models. We
present accurate far-ultraviolet (FUV, 1150-1500 Å) continuum flux
measurements for solar-mass stars, made feasible by the high throughput
and very low detector background of the Cosmic Origins Spectrograph on
the Hubbble Space Telescope. We show that the continuum flux can be
measured above the detector background even for the faintest star in
our sample. We find a clear trend of increasing continuum brightness
temperature at all FUV wavelengths with decreasing rotational period,
which provides an important measure of magnetic heating rates in stellar
chromospheres. Comparison with semiempirical solar flux models shows
that the most rapidly rotating solar-mass stars have FUV continuum
brightness temperatures similar to the brightest faculae seen on the
Sun. The thermal structure of the brightest solar faculae therefore
provides a first-order estimate of the thermal structure and heating
rate for the most rapidly rotating solar-mass stars in our sample.

---------------------------------------------------------
Title: The Amazing COS FUV (1320 - 1460 Å) Spectrum of λ Vel
(K4Ib-II)1
Authors: Carpenter, K. G.; Ayres, T.; Brown, A.; Harper, G. M.;
Wahlgren, G. M.
2011ASPC..448.1083C Altcode: 2011csss...16.1083C
The FUV spectrum (1320-1460 Å) of the K4 Ib-II supergiant λ Vel
was observed with the Cosmic Origins Spectrograph (COS) on HST, as
part of the Ayres and Redfield Cycle 17 SNAP program "SNAPing Coronal
Iron." This spectrum covers a region not previously recorded in λ
Vel at high resolution and, in a mere 20 minutes of exposure, reveals
an amazing treasure trove of information. It shows a wide variety of
strong emission lines and multiple absorption lines, superposed on a
bright chromospheric continuum, with contributions from both atomic
and molecular species. These features provide diagnostics of the
chromosphere and wind of the star, and by comparison with spectra of
stars of similar Teff and/or geff, will improve
our knowledge of the heating processes in the chromospheres and the
forces driving the stellar wind in cool evolved stars. We present
the details of this spectrum, in comparison with stars of similar
temperature or luminosity, and discuss our initial interpretation of
the data.

---------------------------------------------------------
Title: Bridging STIS's Neutral Density Desert
Authors: Ayres, Thomas
2011hst..prop12567A Altcode:
This is a calibration proposal focused on a set of unsupported
ND-filtered long slits {31X0.05NDA,B,C} that can be used with the
STIS echelles, and which provide attenuations intermediate between
the standard spectroscopic slits {0.2X0.06, 0.2X0.09, or 0.1X0.03}
and the {only two} supported ND slits: 0.2X0.05ND {ND=2} and 0.3X0.05ND
{ND=3}. These intermediate NDs {0.6-1.4} potentially are valuable for
bright continuum sources, mainly hot stars, for which currently the
supported ND slits must be used to mitigate MAMA global count rate
violations. Because there is such a large jump from the normal clear
spectroscopic slits {ND 0} to the next supported ND step {ND=2}, there
are many cases where an observation just barely exceeds the global rate
with a clear aperture, and therefore must shift to the ND=2 slit, but
now requires something like 100 times the exposure duration to achieve
a target S/N. Adding the currently unsupported slits to STIS's toolkit
will pave the way for more efficient future projects involving echelle
spectroscopy, especially for the top tier of bright hot stars not yet
observed by this powerful instrument.To qualify the 31X0.05ND slit set,
HST standard G191B2B {DA} will be measured to determine wavelength
dependent throughputs across the FUV+NUV range, and across the full
field of each MAMA camera. Pole-on rapid rotator Vega {A0V} - well-known
visible photometric standard, and which has a bright, rich, and complex
FUV spectrum - will provide a test for any lineshape degradation by
the long slits in the high-res echelle configuration. The high-S/N
Vega FUV echelle spectra will have unique scientific value as well.

---------------------------------------------------------
Title: Alpha Cen: Climbing out of a Coronal Recession?
Authors: Ayres, Thomas
2011hst..prop12758A Altcode:
Nearby Alpha Centauri contains the two best characterized G and K
dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved
angular diameters, and well understood co-evolutionary state. Alpha Cen
A &amp; B also have the best studied stellar X-ray activity cycles,
extending back to the 1970A?s. Present proposal is to continue
tracking the evolving multi-decadal high-energy narrative of Alpha
Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin
A is expected to be rising to cycle maximum from an extended coronal
recession. STIS E140M spectra will support and leverage the broad-band
X-ray measurements by probing subcoronal dynamics and providing a
low-T boundary condition for DEM modeling, with connection to HRC
through the FUV Fe XII coronal forbidden line.

---------------------------------------------------------
Title: EK Draconis: Warm Coronal Rain?
Authors: Ayres, Thomas
2011hst..prop12566A Altcode:
A remarkable FUV spectrum of young solar analog EK Draconis {G1.5V}
was taken by COS in Cycle 17. The mere 20-min SNAPshot captured two
distinct Si IV flares {T 60,000 K}; very broad profiles of Si IV and C
II {T 30,000 K}; and prominent Fe XXI coronal forbidden line emission
{T 10 MK}. Curiously, the bright Si IV features were significantly
redshifted, suggesting that warm gas must be continually accreting onto
the lower atmosphere. This possibly meshes with a new understanding
of the solar "coronal heating paradox," whereby the lacy loop-like
magnetic structures that define the Sun's "quiet" corona {away from
active regions} are very close to potential, and thus cannot carry
enough magnetic free energy to heat themselves: the heating must come
from elsewhere. That elsewhere possibly has been discovered recently:
needle-like jets of hot gas, called Type II Spicules, have been observed
blasting from deep in the chromosphere out into the corona, where the
ambient magnetic loops trap the upward streaming hot gas, which then
cools and eventually falls back to the surface. Ironically, then,
the corona was the wrong place to seek the roots of coronal heating:
the chromosphere is where the action really is. The EK Dra redshifts
perhaps are a glimpse of a super-sized version of the cooling phase
of the solar process. The purpose of this proposal is to utilize STIS
and COS to solidify the observational basis for the apparent coronal
downdrafts on EK Dra. If the "coronal rain" hypothesis is borne out,
it will be an important step toward resolving the long-standing mystery
of coronal heating in the Sun and stars.

---------------------------------------------------------
Title: Alpha Cen: Climbing out of a Coronal Recession?
Authors: Ayres, Thomas
2011cxo..prop.3466A Altcode:
Nearby Alpha Centauri contains the two best characterized G and
K dwarfs, next to the Sun itself, thanks to the accurate orbit,
resolved angular diameters, and well understood co-evolutionary
state. Alpha Cen A &amp; B also have the best studied stellar X-ray
activity cycles, extending back to the 1970's. Present proposal is to
continue tracking the evolving multi-decadal high-energy narrative of
Alpha Cen with semiannual HRC-I pointings in Cycles 13-15, as solar
twin A is expected to be rising to cycle maximum from an extended
coronal recession. STIS E140M spectra will support and leverage
the broad-band X-ray measurements by probing subcoronal dynamics and
providing a low-T boundary condition for DEM modeling, with connection
to HRC through the FUV Fe XII coronal forbidden line.

---------------------------------------------------------
Title: The Curious Case of the Alpha Persei Corona: A Dwarf in
Supergiant's Clothing?
Authors: Ayres, Thomas R.
2011ApJ...738..120A Altcode:
Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant
located at the blue edge of the Cepheid instability strip. It is one of
the brightest coronal X-ray sources in the young open cluster bearing
its name, yet warm supergiants as a class generally avoid conspicuous
high-energy activity. The Cosmic Origins Spectrograph on the Hubble
Space Telescope has recently uncovered additional oddities. The
1290-1430 Å far-ultraviolet (FUV) spectrum of α Per is dominated by
photospheric continuum emission, with numerous superposed absorption
features, mainly stellar. However, the normal proxies of coronal
activity, such as the Si IV 1400 Å doublet (T ~ 8 × 104
K), are very weak, as are the chromospheric C II 1335 Å multiplet
(T ~ 3 × 104 K) and O I 1305 Å triplet. In fact, the
Si IV features of α Per are not only narrower than those of later,
G-type supergiants of similar L X/L bol, but are
also fainter (in L Si IV /L bol) by two orders
of magnitude. Further, a reanalysis of the ROSAT pointing on α Per
finds the X-ray centroid offset from the stellar position by 9”,
at a moderate level of significance. The FUV and X-ray discrepancies
raise the possibility that the coronal source might be unrelated to
the supergiant, perhaps an accidentally close dwarf cluster member;
heretofore unrecognized in the optical, lost in the glare of the
bright star.

---------------------------------------------------------
Title: FK Com Multi-wavelength Campaign
Authors: Kashyap, Vinay; Ayres, T.; Korhonen, H.; Saar, S.; Drake,
J.; Garcia-Alvarez, D.; Huenemoerder, D.
2011HEAD...12.1004K Altcode:
FK Com (G5 III) is an ultrafast-rotating single yellow giant. It is
the eponymous member of its class, and is suspected to have been a
coalesced binary that has spun up. Here we present preliminary results
from a multi-wavelength campaign we have carried out in April-May
2011. We observe the corona with X-rays with the high-resolution
HETG spectrometer on Chandra, the corona and chromosphere FUV with
HST/COS, and obtain surface magnetic information via Zeeman Doppler and
Doppler Imaging with ground-based observations. The X-ray light curve
exhibits significant variability, but unlike previous observations,
is not dominated by large flares. The FUV lines show broad profiles,
and considerable jitter. This study has been supported by Chandra
and HST grants.

---------------------------------------------------------
Title: Starspot variability and evolution from modeling Kepler
photometry of active late-type stars
Authors: Brown, Alexander; Korhonen, Heidi; Berdyugina, Svetlana;
Tofany, Barton; Ayres, Thomas R.; Kowalski, Adam; Hawley, Suzanne;
Harper, Graham; Piskunov, Nikolai
2011IAUS..273...78B Altcode:
The Kepler satellite provides a unique opportunity to study the detailed
optical photometric variability of late-type stars with unprecedentedly
long (several year) continuous monitoring and sensitivity to very
small-scale variations. We are studying a sample of over two hundred
cool (mid-A - late-K spectral type) stars using Kepler long-cadence
(30 minute sampling) observations. These stars show a remarkable
range of photometric variability, but in this paper we concentrate on
rotational modulation due to starspots and flaring. Modulation at the
0.1% level is readily discernable. We highlight the rapid timescales
of starspot evolution seen on solar-like stars with rotational periods
between 2 and 7 days.

---------------------------------------------------------
Title: Kepler Observations of Starspot Evolution, Differential
Rotation, and Flares on Late-Type Stars
Authors: Brown, Alexander; Korhonen, H.; Berdyugina, S.; Walkowicz,
L.; Kowalski, A.; Hawley, S.; Neff, J.; Ramsey, L.; Redman, S.; Saar,
S.; Furesz, G.; Piskunov, N.; Harper, G.; Ayres, T.; Tofany, B.
2011AAS...21820502B Altcode: 2011BAAS..43G20502B
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that
routinely allow detailed studies of stellar magnetic activity on
late-type stars that were difficult, if not impossible, to attempt
previously. Rotational modulation due to starspots is commonly seen
in the Kepler light-curves of late-type stars, allowing detailed
study of the surface distribution of their photospheric magnetic
activity. Kepler is providing multi-year duration light-curves that
allow us to investigate how activity phenomena -- such as the growth,
migration, and decay of starspots, differential rotation, activity
cycles, and flaring -- operate on single and binary stars with a
wide range of mass and convection zone depth. We present the
first results from detailed starspot modeling using newly-developed
light-curve inversion codes for a range of GALEX-selected stars with
typical rotation periods of a few days, that we have observed as part of
our 200 target Kepler Cycle 1/2 Guest Observer programs. The physical
properties of the stars have been measured using high resolution
optical spectroscopy, which allows the Kepler results to be placed
within the existing framework of knowledge regarding stellar magnetic
activity. These results demonstrate the powerful diagnostic capability
provided by tracking starspot evolution essentially continuously for
more than 16 months. The starspots are clearly sampling the stellar
rotation rate at different latitudes, enabling us to measure the
differential rotation and starspot lifetimes. As would be expected,
stars with few day rotation show frequent flaring that is easily seen
as "white-light" flares in Kepler light-curves. We compare the observed
flare rates and occurrence with the starspot properties. This work
contains results obtained using the NASA Kepler satellite and from the
Apache Point Observatory, the MMT (using NOAO community access time),
and the Hobby-Eberly Telescope. Funding is provided by NASA Kepler
grants NNX10AC51G and NNX11AC79G.

---------------------------------------------------------
Title: Advanced Spectral Library (ASTRAL): Cool Stars
Authors: Ayres, Thomas R.; Co-Investigators, ASTRAL
2011AAS...21832814A Altcode: 2011BAAS..43G32814A
The Advanced Spectral Library (ASTRAL) is a Hubble Space Telescope (HST)
Cycle 18 (2010-2011) Large Treasury Project, whose aim is to collect
high-quality ultraviolet echelle spectra of bright stars utilizing
the high-performance Space Telescope Imaging Spectrograph (STIS). In
Cycle 18, ASTRAL focuses on eight iconic late-type objects -- all
well-known bright stars with vaguely unpronounceable names like Procyon
and Betelgeuse -- and will devote 146 HST orbits for the purpose. The
objective is to record each of the targets with broad uninterrupted
UV coverage (1150-3100 Angstroms) at the highest signal-to-noise
and highest spectral resolution achievable within the available
spacecraft time, and given a variety of observing constraints. The
broad ultraviolet coverage will be achieved by splicing together
echellegrams taken in multiple FUV and NUV prime echelle settings of
STIS. The observing strategy was designed to maximize S/N, ensure
accurate wavelength scales, and preserve the radiometric level of
the UV spectral energy distribution. This is a progress report on the
observational status of ASTRAL. Up-to-date information can be found
at the project website:http://casa.colorado.edu/ ayres/ASTRAL/. Supported by grants from the Space Telescope Science Institute,
operated by AURA for NASA.

---------------------------------------------------------
Title: Wavelength Calibration Accuracy for the STIS CCD and MAMA Modes
Authors: Pascucci, Ilaria; Hodge, Phil; Proffitt, Charles R.; Ayres, T.
2011stis.rept....1P Altcode:
Two calibration programs were carried out to determine the accuracy
of the wavelength solutions for the most used STIS CCD and MAMA modes
after Servicing Mission 4. We report here on the analysis of this
dataset and show that the STIS wavelength solution has not changed after
SM4. We also show that a typical accuracy for the absolute wavelength
zero-points is 0.1 pixels while the relative wavelength accuracy is
0.2 pixels.

---------------------------------------------------------
Title: The Discovery of a Photoevaporation-Driven Molecular Outflow
from the T Tauri Transitional Disk GM Aur
Authors: Hornbeck, Jeremy; Grady, C. A.; Brown, A.; Ayres, T.; Apai,
D.; Brittain, S.; Brown, J. M.; Hamaguchi, K.; Henning, T.; Herczeg,
G.; Kamp, I.; Perrin, M.; Petre, R.; Schneider, G.; Sitko, M.; Walter,
F.; Williger, G.; Wisniewski, J.; Woodgate, B.
2011AAS...21734029H Altcode: 2011BAAS...4334029H
Circumstellar disks are not only a byproduct of star formation, but are
also the place where planets form and migrate. The dominant gas-phase
constituent of disks early in their evolution is H2, and its lifetime
in the disk limits the time available for gas giant planet formation
and migration. A number of mechanisms have been proposed to remove gas,
including photoevaporation in the presence of the stellar X-ray, EUV,
and FUV radiation field, but the relative importance of these different
components and the point in disk evolution where they become significant
remain uncertain. Some models predict enhanced evaporation of gas in the
outer disk once the inner portions of the disk have begun to clear. One
such system is the T Tauri star GM Aur which hosts a large disk with an
r=20 AU central cavity. We have carried out the first high-contrast FUV
imaging of this star+disk using HST ACS/SBC and report the detection
of the inner 1" (140 AU) of the disk in the FUV and the discovery of
a roughly cylindrical structure 90 AU in radius and extending 200 AU
orthogonal to the disk, aligned with the previously reported red,
polar lobes. The structure is brightest at wavelengths where there
are numerous fluorescent molecular hydrogen transitions, both in our
imagery and in an archival HST/STIS long-slit spectrum. The cylinder is
marginally detected in the ACS/SBC F165LP band indicating that there is
some sub-0.2 micron-sized dust entrained in it, but is not detected in
ACS/SBC F122M imagery. The radial scale of the footprint of the cylinder
on the disk and the absence of atomic emission lines associated with
the structure exclude a conventional jet, but are consistent with a
photoevaporation-driven outflow. We compare the properties of this
outflow with predictions of X-ray, EUV, and FUV-driven disk winds.

---------------------------------------------------------
Title: λ Vel (K4 Ib-II): Fluorescence on a PAR with Other Luminaries
Authors: Wahlgren, G. M.; Carpenter, K. G.; Ayres, T. R.; Brown, A.;
Harper, G. M.
2011AAS...21715406W Altcode: 2011BAAS...4315406W
The ultraviolet spectral region of cool, luminous stars contains
emission features that originate from fluorescent mechanisms via PAR
(photo-excitation by accidental resonance). These mechanisms can account
for numerous emission lines, downward transitions from upper energy
levels pumped by strong transitions, such as H Ly-α, O I 1302, C II
1335, and Mg II h&amp;k. A new, high S/N observation of the cool giant
star λ Vel (K4 Ib-II) was obtained with the HST/COS instrument at a
resolving power of R 20000 and covers the wavelength region from 132 nm
to 147 nm. High-quality spectra (COS and GHRS) are now available from
128 nm to 147 nm, and at 12 moderate and high resolution observations
from the HST/GHRS, the latter covering approximately a third of the
wavelength interval from 189 nm to 285 nm. Using these data, together
with observations from FUSE and IUE, we investigate PAR processes in the
spectra of Cr II and Fe II and make comparisons with other stars. The
presence of additional atomic (O I, S I, and Cl I) and molecular (H2,
CO) PAR processes in the spectrum of λ Vel is briefly discussed.

---------------------------------------------------------
Title: The Potential of High Angular Resolution and Contrast FUV
Imagery for Studies of Star and Planetary System Formation
Authors: Grady, C. A.; Brown, A.; Woodgate, B.; Hornbeck, J.; Williger,
G.; Herczeg, G.; Brown, J.; Brittain, S.; Wisniewski, J.; Perrin,
M.; Hamaguchi, K.; Henning, T.; Kamp, I.; Petre, R.; Schneider, G.;
Sitko, M.; Walter, F.; Apai, D.; Ayres, T.
2011AAS...21734019G Altcode: 2011BAAS...4334019G
High contrast and high angular resolution imagery has opened new
viewpoints on the formation and early evolution of planetary systems,
revealing features of protoplanetary and young planetary systems which
would go undetected in the integrated measures of the systems. Much
of the power of such studies has resulted from pan-chromatic data, but
the majority of studies to date have been limited to optical and longer
wavelengths, despite the wealth of atomic, ionic, and molecular tracers
of circumstellar material in the FUV. As with high-contrast imaging
at longer wavelengths, realizing the full potential of FUV imagery
of young stars requires subtraction of PSF template data, which are
now available for 3 of the HST ACS/SBC bandpasses. Such imagery has
resulted in the first imagery of the circumstellar disk around the
Herbig Ae star PDS 144S and can trace the geometry of the molecular
gas disk for T Tauri stars. FUV imaging data also provide exquisite
detail for molecular outflows for systems like T Tauri, complementing
studies in the FIR with Herschel. Such data can also reveal the presence
of previously unsuspected disk winds, as seen in GM Aur. Since FUV
imagery is sensitive to extinction, FUV data preferentially detect
circumstellar material on the near side of disks and the approaching
components of outflows, removing ambiguities in disk viewing geometry,
and can map, at the highest angular resolution achievable with HST,
where disks are shadowed. This is a capability which future UV/Optical
telescopes optimized for studies of planetary system formation should
not be without. This study is based on data obtained with the
Hubble Space Telescope under GO programs 10864, 11336, and 12016.

---------------------------------------------------------
Title: FUV Spectroscopy Of Outflows And Disks Around The Intermediate
Mass Pre-main-sequence Stars HD135344B And HD104237
Authors: Brown, Alexander; Herczeg, G.; Brown, J. M.; Walter, F. M.;
Ayres, T. R.; DAOof TAU Team
2011AAS...21734034B Altcode: 2011BAAS...4334034B
The intermediate-mass, pre-main-sequence (Herbig Ae/Fe) stars HD135344B
(F4) and HD104237 (A8 IV-V) are both still surrounded by almost face-on
circumstellar disks. The disk around HD135344B is a “transitional”
disk with a 25 AU radius cleared inner hole but still with some gas
and dust very close to the star. We have obtained FUV spectra of these
stars using the HST COS and STIS spectrographs that show that both
stars have dramatic high-velocity (terminal velocity = 300-400 km/s)
outflows and rich fluorescently-excited molecular hydrogen emission,
originating primarily from warm gas in their disks. We present these
FUV spectra and outline the outflow and disk properties implied by
the observed emission and absorption line profiles. The profiles and
widths of the molecular hydrogen lines provide strong constraints on
the location of the emitting regions. This work is supported by
HST grants for GO projects 11828 and 11616, and Chandra grant GO9-0015X
to the University of Colorado.

---------------------------------------------------------
Title: The Chromospheric Structure and Wind of the K-Supergiant
Lambda Velorum
Authors: Carpenter, Kenneth G.; Ayres, T. R.; Brown, A.; Harper,
G. M.; Wahlgren, G. M.
2011AAS...21715407C Altcode: 2011BAAS...4315407C
Recently, the 1326-1466 Å region of the FUV spectrum of the K4 Ib-II
supergiant Lambda Vel was observed with the Cosmic Origins Spectrograph
(COS) on HST, as part of the Ayres and Redfield Cycle 17 SNAP program
"SNAPing Coronal Iron.” This spectrum covers a region not previously
recorded in Lambda Vel at high resolution and, in a mere 20 minutes
of exposure, reveals an amazing treasure trove of information. It
shows a wide variety of strong atomic and molecular emission lines
formed in the chromosphere and multiple atomic absorption lines
formed in the stellar wind, both superposed on a bright chromospheric
continuum. Further evidence of the stellar wind is seen in the P Cygni
profiles presented by the C II (UV 1) lines near 1335 Å. We combine
this COS data with archival GHRS spectra of other selected FUV and NUV
regions to better characterize the outer atmospheric structure of the
star and its massive, outflowing wind.

---------------------------------------------------------
Title: Warm Coronal Rain on Young Solar Analog EK Draconis?
Authors: Ayres, Thomas; France, Kevin
2010ApJ...723L..38A Altcode:
We report a moderate-resolution, 1290-1430 Å spectrum of young solar
analog EK Draconis (HD 129333: G1.5 V), obtained by Cosmic Origins
Spectrograph on Hubble Space Telescope. The 20 minute observation,
remarkably, captured two distinct "flares" in the Si IV 1400 Å doublet
(T ~ 6 × 104 K); very broad profiles of Si IV and the C II
1335 Å multiplet (T ~ 3 × 104 K); and prominent Fe XXI
λ1354 coronal forbidden line emission (T ~ 10 MK). The bright Si IV
features are significantly redshifted compared to the milder, although
still redshifted, equivalent components of solar-twin α1
Cen (HD 128620: G2 V). The broad, shifted, flaring hot-line profiles
of EK Dra indicate not only that the subcoronal plasma of the young
sun is highly dynamic, but also that the Si IV-bearing gas must be
continually accreting onto the lower atmosphere, perhaps the stellar
equivalent of warm "coronal rain."

---------------------------------------------------------
Title: SpS1-Digging in the solar COmosphere with NAC
Authors: Ayres, Thomas R.
2010HiA....15..547A Altcode:
The solar “COmosphere” is an enigmatic region of cold gas
(temperatures as low as ~3500 K) coexisting in the low chromosphere
with plasma much hotter (~7000 K). This zone probably consists of
patchy clouds of cool gas, seen readily in off-limb emissions of CO
4667 nm lines, threaded by hot gas entrained in long-lived magnetic
filaments as well as transient shock fronts. The COmosphere was not
anticipated in classical 1D models of the solar outer atmosphere,
but is quite at home in the contemporary 3D highly dynamic view,
which one might call the Magnetic Complexity Zone.

---------------------------------------------------------
Title: Alpha Cen to the Max
Authors: Ayres, Thomas
2010cxo..prop.3047A Altcode:
Nearby Alpha Centauri contains the two best characterized G and K
dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved
angular diameters, and well understood co-evolutionary state. Alpha Cen
A &amp; B also have the best studied stellar X-ray activity cycles,
extending back to the 1970's. In fact, Chandra LETGS spectra of the
double star are superior to any existing solar material in the crucial
2-20 nm band, accounting for bulk of Sun's XUV emission (relevant to
Space Weather). Present proposal is to continue the evolving coronal
narrative with dual HRC-I pointings in Cycle 12, and an LETGS spectrum
of the sun-like pair close to the peaks of their X-ray cycles. STIS
FUV spectra will leverage the coronal line measurements (e.g., dynamics
and low-T B.C. for DEM modeling).

---------------------------------------------------------
Title: Deep Lamp Too
Authors: Ayres, Thomas
2010hst..prop12280A Altcode:
This is a calibration proposal that addresses a significant obstacle
to ongoing efforts to enhance the quality of the dispersion solutions
implemented in the STIS echelle pipeline. Namely, the wavecal
material representing many of the secondary grating "tilts" is in
relatively poor shape. With solid lamp calibrations in all 37 supported
high-res {E140H and E230H} settings, STIS itself can be exploited to
bootstrap {by means of an empirical wavelength distortion correction} a
"laboratory calibration" to the many lines emitted by the STIS lamps,
mainly chromium, that were missing from the GHRS flight-spare units
originally measured at NIST in the 1990's, and more recent work with
STIS-type lamps that unfortunately only covers the FUV band. The
prototype distortion correction significantly improves the quality
of the pipeline spectra, to the great benefit of the many types of
GO programs that require accurate velocity measurements - stellar,
interstellar, and even intergalactic - and thus have turned to STIS
in the past. {And now again, during its "second life."} The proposed
exposure depth enhancements for the 28 {of 44} tilts require seven
orbits, with no impact on science time. The total exposure duration
{10 hours} is only 1/4 that already expended on "deep" wavecals
{texp&gt;60 s}, and essentially would complete the fundamental
wavelength calibration of this enormously valuable spectroscopic
machine. The program should have negligible impact on lamp life,
which is measured in many hundreds of hours.

---------------------------------------------------------
Title: FK Comae, King of Spin: the Movie
Authors: Ayres, Thomas
2010hst..prop12279A Altcode:
FK Comae is an ultra-fast rotating, single yellow giant, product of
a recent W UMa merger. Extraordinary levels of FUV and X-ray emission
rate FK Comae a coronal powerhouse on par with the most extreme of the
better known activity heavyweights: short-period RS CVn binaries. As a
single star, FK Comae has clear advantages as a laboratory for exploring
the outer limits of magnetospheric activity among the coronal cool
stars. FK Comae has a long history of attention at optical and X-ray
wavelengths, thanks to its generously spotted surface, and proclivity
to flare regularly at high energies. FUSE discovered ultra-broad,
redshifted profiles of O VI and C III, but unfortunately the singular
observation could not be repeated, thanks to the satellite's flaky
attitude system. The remarkable FUV spectrum was taken just a few
months before STIS failed in 2004, so there was no opportunity to
turn the more powerful gaze of Hubble to the task. Now, finally, the
amazing sensitivity of Cosmic Origins Spectrograph can be brought to
bear: a single orbit can capture an FUV spectrum of FK Comae with S/N
at instrumental limits for bright lines, and digging down to faint Fe
XXI 1354 {bridge to the coordinated Chandra HETGS pointing we also are
proposing}.We will trace how the bright FUV regions relate spatially
to the photospheric dark spots, to inform ideas of coronal structure
and heating in these advanced objects. We will probe whether a global
magnetosphere exists, and whether the field lines are loaded with hot
coronal gas {&gt;10 MK}, as well as the cooler 0.3 MK material already
suggested by highly broadened FUSE O VI. Further, we will test whether
the striking 100 km/s redshifts of the FUV lines, and similar shifts
seen in Ne X by Chandra HETGS, are caused by a massive coronal outflow
{perhaps implicated in magnetic braking}. Our method is to exploit, on
the one hand, emission-line "Doppler imaging," whereby bright surface
regions are mapped onto specific locations in the global profile,
according to the line-of-sight rotational velocity. On the other
hand, we compare features of different opacity and excitation {e.g.,
Si III 1206 and Si IV 1393} to deduce whether, say, a red asymmetry
is caused by blueshifted absorption, or alternatively by infall of the
entire feature. Multiple epochs spaced over two rotation periods break
the degeneracy between profile distortions caused by disk passage of
hot patches {Doppler imaging part}, and those caused by large-scale
flows. Contemporaneous spot maps from the ground will provide a
fundamental magnetic context for the coordinated FUV and X-ray "movies."

---------------------------------------------------------
Title: FK Comae, King of Spin: the Movie
Authors: Ayres, Thomas
2010cxo..prop.3035A Altcode:
FK Comae is an ultra-fast rotating, single yellow giant, product of a
recent W UMa merger. Extraordinary levels of FUV and X-ray emission rate
FK Comae a coronal powerhouse on par with the most extreme short-period
RS CVn binaries. As a single star, FK Comae has clear advantages as a
laboratory for exploring high-energy activity. We will bring to bear
Hubble's powerful Cosmic Origins Spectrograph, together with Chandra
HETGS and groundbased Zeeman Doppler Imaging, to trace -- over two
stellar rotations -- spatial relationships between bright FUV patches,
extended X-ray emission zones, and the photospheric dark spots, to
inform ideas of coronal structure and heating at the outer limits of
magnetospheric activity among the coronal cool stars.

---------------------------------------------------------
Title: Advanced Spectral Library Project: Cool Stars
Authors: Ayres, Thomas
2010hst..prop12278A Altcode:
Stars are the luminous backbone of the Universe, and without them, it
would be a dull and dreary place indeed: no light, no heavy elements, no
planets, no life. It also is safe to say that stellar spectroscopy is a
cornerstone of astrophysics, providing much of what we know concerning
temperatures and masses of stars, their compositions, planets, and
the dynamics and evolution of the galaxies they inhabit. The proper
interpretation of stellar spectra thus is fundamental to modern
astronomy. This is especially true for the satellite ultraviolet,
owing to the rich collection of atomic and ionic transitions found
there. Unfortunately, the existing archive of Space Telescope Imaging
Spectrograph rarely achieves the high S/N of the best ground-based
spectra, and relatively few objects have the full wavelength coverage
for which the powerful, highly multiplexed, second generation Hubble
instrument was designed. With UVES at ESO and ESPaDOnS at CFHT,
for example, astronomers routinely are obtaining broad-coverage
optical spectra with S/N &gt; 100 and resolving power of 100,000 to
fuel ground-breaking analyses. Our objective is to collect comparable
STIS UV echelle spectra for a diverse sample of representative stars,
to build an Advanced Spectral Library; a foundation for astrophysical
exploration: stellar, interstellar, and beyond. Our first effort
involves cool stars, whose main contribution to the UV is through
magnetic activity, an enigmatic phenomenon subject to close scrutiny
on the Sun, and of undeniable importance to a broad range of cosmic
situations: Space Weather, T-Tauri disk winds, red dwarf flares,
erosion of exoplanet atmospheres, and so forth.The main product of our
Treasury program will be detailed stellar "atlases," based on advanced
processing of the STIS echellegrams. Members of our broad collaboration
will analyze these data for specific purposes, such as detection of
rare species in sharp-lined F stars, properties and kinematics of
local interstellar clouds, and dynamics of chromospheres, coronae, and
winds of cool stars; but rapid public release {based on the "StarCAT"
model} will enable many other investigations by a much wider community,
for decades to come.

---------------------------------------------------------
Title: Alpha Cen to the Max
Authors: Ayres, Thomas
2010hst..prop12374A Altcode:
This is the HST part of a joint Chandra/HST observing program. The
objective for HST is to obtain new UV spectra of both components of the
Alpha Centauri binary: the primary {"Alpha Cen A"} is a near twin of
the Sun, while the companion {"B"} is an early K dwarf, slightly less
massive, smaller and less luminous than the Sun {but coronally more
active}. The orbital period is 80 yr, and the two stars currently are
separated by about 7". The Alpha Cen system has been the subject of long
term coronal X-ray monitoring by four successive generations of space
observatories, and extensive UV measurements were obtained periodically
during the IUE era, from the late 1970's to late 1990's. The present
program will obtain new STIS echelle spectra of both stars, which each
were observed in selected wavelength windows by GHRS in the mid-1990's,
and Alpha Cen A later by STIS in an extensive high-res program in
1999, then both stars this past HST Cycle 17 with STIS, as a part of
a previous joint Chandra-HST program with similar objectives.

---------------------------------------------------------
Title: Ironing Out the Wrinkles in STIS
Authors: Ayres, Thomas R.
2010hstc.workE...7A Altcode:
The echelle wavelength scales of Space Telescope Imaging Spectrograph
were evaluated based on a novel high-density line list for the on-board
Pt/Cr-Ne emission lamps. The new reference wavelengths were obtained
by a bootstrapping technique that exploited the space-borne instrument
as its own laboratory spectrometer. A number of strategies were
explored to mitigate subtle wavelength scale deviations identified
in the process (known from earlier work), either by modifying the
pipeline dispersion relations directly, or by a post-facto distortion
correction. The main conclusion is that the STIS echelle wavelengths
can be significantly improved with only modest changes to the current
dispersion model.

---------------------------------------------------------
Title: The solar photospheric abundance of carbon. Analysis of atomic
carbon lines with the CO5BOLD solar model
Authors: Caffau, E.; Ludwig, H. -G.; Bonifacio, P.; Faraggiana, R.;
Steffen, M.; Freytag, B.; Kamp, I.; Ayres, T. R.
2010A&A...514A..92C Altcode: 2010arXiv1002.2628C
Context. The analysis of the solar spectra using hydrodynamical
simulations, with a specific selection of lines, atomic data, and method
for computing deviations from local thermodynamical equilibrium, has
led to a downward revision of the solar metallicity, Z. We are using
the latest simulations computed with the CO5BOLD code to reassess
the solar chemical composition. Our previous analyses of the key
elements, oxygen and nitrogen, have not confirmed any extreme downward
revision of Z, as derived in other works based on hydrodynamical
models. Aims: We determine the solar photospheric carbon
abundance with a radiation-hydrodynamical CO5BOLD model and compute
the departures from local thermodynamical equilibrium by using the
Kiel code. Methods: We measured equivalent widths of atomic C
I lines on high-resolution, high signal-to-noise ratio solar atlases
of disc-centre intensity and integrated disc flux. These equivalent
widths were analysed with our latest solar 3D hydrodynamical simulation
computed with CO5BOLD. Deviations from local thermodynamic equilibrium
we computed in 1D with the Kiel code, using the average temperature
structure of the hydrodynamical simulation as a background model. 
Results: Our recommended value for the solar carbon abundance relies
on 98 independent measurements of observed lines and is A(C)=8.50
± 0.06. The quoted error is the sum of statistical and systematic
errors. Combined with our recent results for the solar oxygen and
nitrogen abundances, this implies a solar metallicity of Z = 0.0154
and Z/X = 0.0211. Conclusions: Our analysis implies a solar
carbon abundance that is about 0.1 dex higher than what was found in
previous analyses based on different 3D hydrodynamical computations. The
difference is partly driven by our equivalent width measurements
(we measure, on average, larger equivalent widths than the other work
based on a 3D model), in part because of the different properties of
the hydrodynamical simulations and the spectrum synthesis code. The
solar metallicity we obtain from the CO5BOLD analyses is in slightly
better agreement with the constraints of helioseismology than the
previous 3D abundance results.

---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Asplund, Martin; Puls, Joachim; Landstreet, John; Allende
Prieto, Carlos; Ayres, Thomas; Berdyugina, Svetlana; Gustafsson,
Bengt; Hubeny, Ivan; Ludwig, Hans Günter; Mashonkina, Lyudmila;
Randich, Sofia
2010IAUTB..27..197A Altcode:
The members of the Commission 36 Organizing Committee attending the IAU
General Assembly in Rio de Janeiro met for a business session on August
7. Both members from the previous (2006-2009) and the new (2009-2012)
Organizing Committee partook in the discussions. Past president John
Landstreet described the work he had done over the past three years
in terms of supporting proposed conferences on the topic. He has
also spent significant amount of time establishing an updated mailing
list of all &gt;350 members of the commission, which is unfortunately
not provided automatically by the IAU. Such a list is critical for a
rapid dissemination of information to the commission members and for
a correct and smooth running of elections of IAU officials. Everyone
present thanked John effusively for all of his hard work over the past
three years to stimulate a high level of activity within the discipline.

---------------------------------------------------------
Title: A Fresh Hubble Perspective on Sun-Like Dwarfs, Young and Old
Authors: Ayres, Thomas R.; Redfield, S.
2010AAS...21640013A Altcode: 2010BAAS...41..856A
Far-ultraviolet spectra of three sun-like stars have been obtained
recently by HST, utilizing its two powerful UV spectrographs: STIS
and COS. A 3.6 ks STIS E140M echellegram of nearby, bright Alpha
Cen A was taken as part of a joint Chandra-HST program to study the
coronal cycles of the solar twin, which has been mired in an activity
low-state the past several years, much like the Sun (although recovery
for our star apparently is imminent). As part of an HST Cycle 17 Guest
Observer program ("SNAPing Coronal Iron"), COS acquired short (20M)
G130M snapshots of two young-sun analogs: Hyades G star HD25825 and
Pi1 UMa, an early-G dwarf in the Ursa Major Stream, comparable in
age to the Hyades. The COS pointing on HD25825 represents the first
high-resolution (R=20,000) FUV spectrum of such a faint solar-type
dwarf, albeit a hyperactive one befitting its youth (600 Myr). The COS
spectra are spectacular, given the brief integrations, rivaling previous
STIS efforts (on brighter objects) that required equivalently 20X the
exposure depth. A comparison of these spectra show the evolution of
chromospheric, transition zone, and even coronal (FeXII 1349 and FeXXI
1354) line profiles from the pinnacles to the depths of activity. This work supported by grants HST-GO-11687.01 and HST-GO-11839.01
from STScI.

---------------------------------------------------------
Title: VizieR Online Data Catalog: StarCAT: STIS UV echelle spectra
of stars (Ayres, 2010)
Authors: Ayres, T. R.
2010yCat..21870149A Altcode:
StarCAT is a Cycle 14 Legacy Archival project supported by the Guest
Investigator program of Hubble Space Telescope (HST). The objective of
StarCAT was to create an easily accessible catalog of high resolution
spectral observations of targets broadly identified as "stars,"
collected by Space Telescope Imaging Spectrograph (STIS) from the
time of its installation in 1997, during Hubble Servicing Mission
2, to its shutdown in 2004 August. StarCAT is available through an
interface maintained at the Multimission Archive at Space Telescope
(MAST): http://archive.stsci.edu/prepds/starcat (3 data files).

---------------------------------------------------------
Title: Chandra and HST Observations of the High Energy (X-ray/UV)
Radiation Fields for an Evolutionary Sequence of Pre-Main-Sequence
Stars
Authors: Brown, Alexander; Herczeg, G. J.; Brown, J. M.; Walter,
F. M.; Valenti, J.; Ardila, D.; Hillenbrand, L. A.; Edwards, S.;
Johns-Krull, C. M.; Alexander, R.; Bergin, E. A.; Calvet, N.; Bethell,
T. J.; Ingleby, L.; Bary, J. S.; Audard, M.; Baldovin, C.; Roueff,
E.; Abgrall, H.; Gregory, S. G.; Ayres, T. R.; Linsky, J. L.
2010HEAD...11.1709B Altcode: 2010BAAS...42..684B
Pre-main-sequence (PMS) stars are strong X-ray and UV emitters and the
high energy radiation from the central stars directly influences the
physical and chemical processes in their protoplanetary disks. Gas
and dust in protoplanetary systems are excited by these photons,
which are the dominant ionization source for hundreds of AU around the
star. X-rays penetrate deep into disks and power complex chemistry on
grain surfaces. “Transitional disks” are an important short-lived
evolutionary stage for PMS stars and protoplanetary systems. These disks
have transformed most of the dust and gas in their inner regions into
planetesimals or larger solid bodies. As dust disks disappear after ages
of roughly 5 Myr high levels of stellar magnetic activity persist and
continue to bathe the newly-forming protoplanetary systems with intense
high energy radiation. We present new X-ray and UV spectra for
a sample of PMS stars at a variety of evolutionary stages, including
the classical T Tauri stars DE Tau and DK Tau, the transitional
disk stars GM Aur and HD135344B, the Herbig Ae star HD104237, and
the weak-lined T Tauri star LkCa4, the Eta Cha cluster [age 7 Myr]
members RECX1, RECX-11, and RECX-15, and TW Hya association [age 8 Myr]
member TWA-2. These include the first results from our 111 orbit HST
Large project and associated X-ray data. New and archival Chandra, XMM,
and Swift X-ray spectra and HST COS+STIS FUV spectra are being used to
reconstruct the full high energy (X-ray/EUV/FUV/NUV) spectra of these
stars, thus allowing detailed modeling of the physics and chemistry
of their circumstellar environments. The UV spectra provide improved
emission line profiles revealing details of the magnetically-heated
plasma and accretion and outflow processes. This work is supported
by Chandra grants GO8-9024X, GO9-0015X and GO9-0020B and proposal
11200754 and HST GO grants 11336, 11616, and 11828.

---------------------------------------------------------
Title: StarCAT: A Catalog of Space Telescope Imaging Spectrograph
Ultraviolet Echelle Spectra of Stars
Authors: Ayres, Thomas R.
2010ApJS..187..149A Altcode:
StarCAT is a catalog of high resolution ultraviolet spectra of objects
classified as "stars," recorded by Space Telescope Imaging Spectrograph
(STIS) during its initial seven years of operations (1997-2004). StarCAT
is based on 3184 echelle observations of 545 distinct targets,
with a total exposure duration of 5.2 Ms. For many of the objects,
broad ultraviolet coverage has been achieved by splicing echellegrams
taken in two or more FUV (1150-1700 Å) and/or NUV (1600-3100 Å)
settings. In cases of multiple pointings on conspicuously variable
sources, spectra were separated into independent epochs. Otherwise,
different epochs were combined to enhance the signal-to-noise ratio
(S/N). A post-facto correction to the calstis pipeline data sets
compensated for subtle wavelength distortions identified in a previous
study of the STIS calibration lamps. An internal "fluxing" procedure
yielded coherent spectral energy distributions (SEDs) for objects with
broadly overlapping wavelength coverage. The best StarCAT material
achieves 300 m s-1 internal velocity precision; absolute
accuracy at the 1 km s-1 level; photometric accuracy of order
4%; and relative flux precision several times better (limited mainly
by knowledge of SEDs of UV standard stars). While StarCAT represents
a milestone in the large-scale post-processing of STIS echellegrams,
a number of potential improvements in the underlying "final" pipeline
are identified.

---------------------------------------------------------
Title: The Cycles of Alpha Centauri
Authors: Ayres, Thomas R.
2010IAUS..264..146A Altcode:
The main AB pair of the nearby Alpha Centauri triple system has one
of the most extensive X-ray records of any cosmic object, stretching
over three decades. The primary, α Cen A (G2V), is a near twin of
the Sun, with a similarly soft (1-2 MK) corona. The secondary, α
Cen B (K1V), is more active than the Sun, with a generally harder
coronal spectrum. Here, spatially resolved measurements of the pair
by Chandra's High Resolution Camera are compared, on a common basis,
with previous pointings from ROSAT and XMM-Newton.

---------------------------------------------------------
Title: High Energy (X-ray/UV) Radiation Fields of Young, Low-Mass
Stars Observed with Chandra and HST
Authors: Brown, Alexander; Brown, J. M.; Herczeg, G.; Bary, J.;
Walter, F. M.; Ayres, T. R.
2010AAS...21542928B Altcode: 2010BAAS...42R.354B
Pre-main-sequence (PMS) stars are strong UV and X-ray emitters and
the high energy (UV/X-ray) radiation from the central stars directly
influences the physical and chemical processes in their protoplanetary
disks. Gas and dust in protoplanetary systems are excited by these
photons, which are the dominant ionization source for hundreds of AU
around the star. X-rays penetrate deep into disks and power complex
chemistry on grain surfaces. “Transitional disks” are a crucial
and important evolutionary stage for PMS stars and protoplanetary
systems. These disks have transformed most of the dust and gas in their
inner regions into planetesimals or larger solid bodies. The disks show
clear inner “holes” that almost certainly harbor infant planetary
systems, given the very sharp gap boundaries inferred. Transitional
disks are rare and represent a short-lived phase of PMS disk
evolution. We have observed a sample of PMS stars at a variety of
evolutionary stages, including the transitional disk stars GM Aur (K5)
and HD135344B (F4). Chandra ACIS CCD-resolution X-ray spectra and HST
STIS and COS FUV spectra are being used to reconstruct the full high
energy (X-ray/EUV/FUV/NUV) spectra of these young stars, so as to allow
detailed modeling of the physics and chemistry of their circumstellar
environments, thereby providing constraints on the formation process
of planetary systems. This work is supported by Chandra grants
GO8-9024X, GO9-0015X and GO9-0020B and HST grants for GO projects 11336,
11828, and 11616 to the University of Colorado.

---------------------------------------------------------
Title: A stellar perspective on chromospheres.
Authors: Ayres, T.
2010MmSAI..81..553A Altcode:
The Sun is not alone in hosting a chromosphere: virtually all convective
stars (F-types and later) possess them. Properties can vary wildly
from object to object. Historically, three key systemic behaviors were
recognized. First is the strong preference of chromospheres for the cool
half of the H-R diagram. Second is the so-called rotation-age-activity
connection (“Skumanich law”). Third is the Ca II H &amp; K emission
width-luminosity relation (“Wilson-Bappu effect”). In the modern era
of ultraviolet and X-ray telescopes in space, additional phenomenology
has been recognized; mainly concerning energetic relationships
between chromosphere and corona, importance of atmospheric dynamics,
and the curious “buried coronae” of red giant stars. Collectively,
these pieces of evidence hint that “relentlessly dynamic” stellar
chromospheres are the rule, not the exception.

---------------------------------------------------------
Title: The Cycles of Alpha Centauri
Authors: Ayres, Thomas
2009cfdd.confE..64A Altcode:
The main AB pair of the nearby Alpha Centauri triple system has an
extensive X-ray history, covering three decades. Alpha Cen A (G2V) is
a near twin of the Sun, with a similarly soft (1-2 MK) corona. Alpha
Cen B (K1V) is more active than the Sun, with a generally harder X-ray
spectrum. Here, spatially resolved measurements from ROSAT, XMM-Newton,
and Chandra are compared on a common basis. In the combined time series,
Alpha Cen B shows a distinct X-ray modulation with a period of about
eight years and a factor of 5 cycle depth (the latter is similar
to the Sun's). Alpha Cen A showed minimal variability 1995-2000,
a decrease in the initial XMM epoch 2003-2005, and nearly constant
behavior in the subsequent Chandra segment (late-2005 to present),
although down a factor of 2 from the mid-1990's level. A remarkable
“smoking gun” LETGS spectrum in mid-2007 emphasized that much of the
coronal luminosity of solar-activity objects falls at longer wavelengths
than recorded efficiently by contemporary instruments. This makes cycle
depth strongly dependent on the energy bandpass of the measurement (here
0.2-2 keV), and complicates assessments of coronal heating requirements.

---------------------------------------------------------
Title: The Ups and Downs of Alpha Centauri
Authors: Ayres, Thomas
2009cxo..prop.2756A Altcode:
Nearby Alpha Centauri hosts two of the best characterized late-type
dwarfs, besides the Sun itself; thanks to the accurate orbit, resolved
angular diameters, and well understood co-evolutionary state. The G
and K components of the system have X-ray measurements extending back
to the late-1970's; in some sense superior to the solar high-energy
irradiance. The latter is not routinely measured in the normal cosmic
energy bands, and must be reconstructed from proxies. The present
proposal is to continue this ongoing twin coronal narrative with
additional HRC-I pointings in Cycle 11, including an attempt to assess
the importance of rotational modulation effects. FUV spectroscopy by
HST-COS will leverage the unique coronal activity record.

---------------------------------------------------------
Title: Ironing Out the Wrinkles
Authors: Ayres, Thomas
2009hst..prop11743A Altcode:
This is a Calibration Archival proposal to develop, implement, and
test enhancements to the pipeline wavelength scales of STIS echelle
spectra, to take full advantage of the extremely high performance of
which the instrument is capable. The motivation is a recent extensive
investigation--The Deep Lamp Project--which identified systematic
wavelength distortions in all 44 primary and secondary settings of the
four STIS echelle modes: E140M, E140H, E230M, and E230H. The method
was to process deep exposures of the onboard Pt/Cr-Ne calibration
source as if they were science images, and measure deviations of
the lamp lines from their laboratory wavelengths. An approach has
been developed to correct the distortions post facto, but it would be
preferable to implement a more robust dispersion model in the pipeline
itself. The proposed study will examine a more extensive set of WAVECALs
than in the exploratory Deep Lamp effort, and will benefit from a new
laboratory line list specifically for the STIS lamps. Ironing out the
wrinkles in the STIS wavelength scales will impact many diverse science
investigations, especially the Legacy Archival project "StarCAT."

---------------------------------------------------------
Title: The Cycles of Alpha Centauri
Authors: Ayres, Thomas
2009hst..prop11839A Altcode:
This is the HST part of a joint Chandra/HST observing program. The
objective of the HST part is to obtain new UV spectra of both components
of the Alpha Centauri binary: the primary {"Alpha Cen A"} is a near
twin of the Sun, while the companion {"B"} is an early K dwarf,
slightly less massive, smaller and less luminous than the Sun. The
orbital period is 80 yr, and the two stars currently are separated by
about 8". The Alpha Cen system has been the subject of long term coronal
X-ray monitoring by four successive generations of space observatories,
and extensive UV measurements were obtained periodically during the
IUE era, from thelate 1970's to late 1990's. The present program
will obtain new STIS echelle spectra of both stars, which each were
observed in selected wavelength windows by GHRS in the mid-1990's,
and Alpha Cen A later by STIS in an extensive high-res program in 1999,
although B unfortunately never was recorded by STIS.

---------------------------------------------------------
Title: SNAPing Coronal Iron
Authors: Ayres, Thomas
2009hst..prop11687A Altcode:
This is a Snapshot Survey to explore two forbidden lines of highly
ionized iron in late-type coronal sources. Fe XII 1349 {T 2 MK}
and Fe XXI 1354 {T 10 MK} - well known to Solar Physics - have been
detected in about a dozen cool stars, mainly with HST/STIS. The UV
coronal forbidden lines are important because they can be observed
with velocity resolution of better than 15 km/s, whereas even the
state-of-the-art X-ray spectrometers on Chandra can manage only 300
km/s in the kilovolt band where lines of highly ionized iron more
commonly are found. The kinematic properties of hot coronal plasmas,
which are of great interest to theorists and modelers, thus only
are accessible in the UV at present. The bad news is that the UV
coronal forbidden lines are faint, and were captured only in very
deep observations with STIS. The good news is that 3rd-generation
Cosmic Origins Spectrograph, slated for installation in HST by SM4,
in a mere 25 minute exposure with its G130M mode can duplicate the
sensitivity of a landmark 25-orbit STIS E140M observation of AD Leo,
easily the deepest such exposure of a late-type star so far. Our
goal is to build up understanding of the properties of Fe XII and Fe
XXI in additional objects beyond the current limited sample: how the
lineshapes depend on activity, whether large scale velocity shifts can
be detected, and whether the dynamical content of the lines can be
inverted to map the spatial morphology of the stellar corona {as in
"Doppler Imaging”}. In other words, we want to bring to bear in the
coronal venue all the powerful tricks of spectroscopic remote sensing,
well in advance of the time that this will be possible exploiting the
corona's native X-ray radiation. The 1290-1430 band captured by side A
of G130M also contains a wide range of key plasma diagnostics that form
at temperatures from below 10,000 K {neutral lines of CNO}, to above
200,000 K {semi-permitted O V 1371}, including the important bright
multiplets of C II at 1335 and Si IV at 1400; yielding a diagnostic
gold mine for the subcoronal atmosphere. Because of the broad value
of the SNAP spectra, beyond the coronal iron project, we waive the
normal proprietary rights.

---------------------------------------------------------
Title: The Cycles of α Centauri
Authors: Ayres, Thomas R.
2009ApJ...696.1931A Altcode:
The main AB pair of the nearby α Centauri triple system has one of
the most extensive X-ray records of any cosmic object, stretching
over 30 years. The primary, α Cen A (G2 V), is a near twin of the
Sun, with a similarly soft (1-2 MK) corona. The secondary, α Cen B
(K1 V), is more active than the Sun, with a generally harder coronal
spectrum. Here, more than a decade of spatially resolved measurements
from ROSAT, XMM-Newton, and Chandra are compared on a common basis,
with careful attention to conversion factors that translate count rates
of the different instruments into absolute energy fluxes. For the latter
purpose, two epochs of Chandra transmission grating spectra, which fully
resolve the binary, were modeled using a differential emission measure
formalism. The aggregate time series suggests that α Cen B was near
X-ray maximum in the mid-1990s, minimum in the late-1990s, then peaked
again in 2004-2005, and more recently has been declining toward another
minimum. Meanwhile, α Cen A showed minimal variability 1995-2000,
and like the secondary presently is mired in an activity lull (in fact,
as seen by XMM-Newton, the primary "fainted" from view in the 2005 time
frame). Comparisons between X-ray luminosities in the 0.2-2 keV (6-60
Å) ROSAT "WGACAT" band and a softer counterpart 0.06-1.2 keV (10-200
Å) reinforce the idea that cycle depth is strongly dependent on the
energy span of the measurement, and that much of the coronal luminosity
of cool-corona objects like the Sun falls at longer wavelengths than
are recorded efficiently by contemporary instruments. Consequently,
one must be careful in discussing X-ray cycles, their amplitudes, and
coronal heating requirements unless one can demonstrate good control
over the out-of-band component.

---------------------------------------------------------
Title: Chandra and GALEX Observations of Stellar Activity on the 7
Gyr Old Arcturus Moving Group Dwarfs
Authors: Brown, Alexander; Hodges-Kluck, Edmund; Harper, Graham M.;
Ayres, Thomas R.
2009AIPC.1094..908B Altcode: 2009csss...15..908B
We present observations of the X-ray and ultraviolet emission from
a sample of dwarf stars in the Arcturus Moving Group. The Arcturus
Moving Group is very likely a remnant of the merger of a dwarf galaxy
with the Milky Way Galaxy in the distant past. This kinematically
distinct group has members located very close to the Sun, allowing
study of stellar activity on very old (7-8 Gyr), low metallicity stars
that would typically not be possible. Our sample has metallicities
between 0.4 and 0.04 solar, spectral types F9-mid-M, and distances
less than 25 pc from the Sun. We have detected X-ray emission
from five AMG dwarfs with the Chandra ACIS-S S3 back-illuminated
detector and for four stars have measured or placed upper limits on
the C IV UV1 emission flux using GALEX GRISM spectra. The measured
X-ray luminosities are comparable to the minimum solar Lx
(range 6-20 1026 erg s-1 for 0.24-2.0 keV) and
for the late G/early K stars are also similar to that of the inactive,
more metal rich ([Fe/H] = -0.42] G8 dwarf Tau Cet. However, a major
difference from the Sun and Tau Cet is that the soft X-ray emitting
plasma is far cooler. The detected source X-rays are generally very
soft with energies of 0.2-0.3 keV, and the bulk of this emission
originates from upper transition region emission lines, such as C V,
rather than a conventional solar-like corona.

---------------------------------------------------------
Title: Mass-Loss and Magnetic Fields as Revealed Through Stellar
X-ray Spectroscopy
Authors: Osten, Rachel A.; Audard, Marc; Ayres, Tom; Brown, Alex;
Drake, Jeremy; Drake, Steve; Gagné, Marc; Huenemoerder, Dave; Kashyap,
Vinay; Leutenegger, Maurice; Linsky, Jeff; Oskinova, Lidia; Schulz,
Norbert; Schmitt, Jurgen; Sciortino, Salvatore; Stelzer, Beate;
Tuellmann, Ralph; Waldron, Wayne; Wolk, Scott
2009astro2010S.228O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Chromosphere: Old Challenges, New Frontiers
Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger,
T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White,
S.; Solanki, S.
2009astro2010S...9A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamos and magnetic fields of the Sun and other cool stars,
and their role in the formation and evolution of stars and in the
habitability of planets
Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres,
Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen;
Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov,
Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier,
Klaus; Walter, Fred
2009astro2010S.262S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Chandra's Darkest Bright Star: not so Dark after All?
Authors: Ayres, Thomas R.
2008AJ....136.1810A Altcode:
The Chandra High Resolution camera (HRC) has obtained numerous short
exposures of the ultraviolet (UV)-bright star Vega (α Lyrae; HD
172167: A0 V), to calibrate the response of the detector to out-of-band
(non-X-ray) radiation. A new analysis uncovered a stronger "blue leak"
in the imaging section (HRC-I) than reported in an earlier study of Vega
based on a subset of the pointings. The higher count rate—a factor of
nearly 2 above prelaunch estimates—raised the possibility that genuine
coronal X-rays might lurk among the out-of-band events. Exploiting the
broader point-spread function of the UV leak compared with soft X-rays
identified an excess of counts centered on the target, technically at
3σ significance. A number of uncertainties, however, prevent a clear
declaration of a Vegan corona. A more secure result would be within
reach of a deep uninterrupted HRC-I pointing.

---------------------------------------------------------
Title: Solar Forbidden Oxygen, Revisited
Authors: Ayres, Thomas R.
2008ApJ...686..731A Altcode:
Recent large reductions in the solar oxygen abundance, based on
synthesis of photospheric O I, OH, and CO absorptions with 3D convection
models, have provoked consternation in the helioseismology community:
the previous excellent agreement between measured p-mode oscillation
frequencies and predictions based on the recommended epsilonO
of a decade ago (680 parts per million [ppm] relative to hydrogen)
unravels at the new low value (460 ppm). In an attempt to reconcile
these conflicting results, the formation of pivotal [O I] λ6300, which
is blended with a weak Ni I line, has been reconsidered, exploiting an
alternative 3D model (albeit only a single temporal snapshot). And while
there are several areas of agreement with the earlier [O I] studies
of Allende Prieto, Asplund, and others, there is one crucial point of
disagreement: the epsilonO derived here is significantly
larger, 650 +/- 65 ppm (although at the expense of a ~30% weaker
Ni I line than expected from the recommended nickel abundance). One
innovation is a more robust treatment of the solar wavelengths: the
balance between the components of the [O I] + Ni I blend is sensitive
to velocity errors of only a few hundred m s-1. A second
improvement is enforcement of a "continuum calibration" to ensure a
self-consistent 3D temperature scale. Because of the renewed agreement
between the linchpin tracer [O I] and seismic oxygen, the proposed
downward slump of the solar metallicity and the perceived "oxygen
crisis" now can be said to rest on less secure footings.

---------------------------------------------------------
Title: A New Era in Solar Thermal-IR Astronomy: the NSO Array Camera
(NAC) on the McMath-Pierce Telescope
Authors: Ayres, T.; Penn, M.; Plymate, C.; Keller, C.
2008ESPM...12.2.74A Altcode:
The U.S. National Solar Observatory Array Camera (NAC) is a
cryogenically cooled 1Kx1K InSb “Aladdin" array that recently became
operational at the McMath-Pierce facility on Kitt Peak, a high dry site
in the southwest U.S. (Arizona). The new camera is similar to those
already incorporated into instruments on nighttime telescopes, and has
unprecedented sensitivity, low noise, and excellent cosmetics compared
with the Amber Engineering (AE) device it replaces. (The latter was
scavenged from a commercial surveillance camera in the 1990's: only
256X256 format, high noise, and annoying flatfield structure). The
NAC focal plane is maintained at 30 K by a mechanical closed-cycle
helium cooler, dispensing with the cumbersome pumped--solid-N2 40 K
system used previously with the AE camera. The NAC linearity has been
verified for exposures as short as 1 ms, although latency in the data
recording holds the maximum frame rate to about 8 Hz (in "streaming
mode"). The camera is run in tandem with the Infrared Adaptive
Optics (IRAO) system. Utilizing a 37-actuator deformable mirror, IRAO
can--under moderate seeing conditions--correct the telescope image to
the diffraction limit longward of 2.3 mu (if a suitable high contrast
target is available: the IR granulation has proven too bland to reliably
track). IRAO also provides fine control over the solar image for spatial
scanning in long-slit mode with the 14 m vertical "Main" spectrograph
(MS). A 1'X1' area scan, with 0.5" steps orthogonal to the slit
direction, requires less than half a minute, much shorter than p-mode
and granulation evolution time scales. A recent engineering test run,
in April 2008, utilized NAC/IRAO/MS to capture the fundamental (4.6 mu)
and first-overtone (2.3 mu) rovibrational bands of CO, including maps
of quiet regions, drift scans along the equatorial limbs (to measure
the off-limb molecular emissions), and imaging of a fortuitous small
sunspot pair, a final gasp, perhaps, of Cycle 23. Future work with
the NAC will emphasize pathfinding toward the next generation of IR
imaging spectrometers for the Advanced Technology Solar Telescope,
whose 4 m aperture finally will bring sorely needed high spatial
resolution to daytime infrared astronomy. In the meantime, the NAC
is available to qualified solar physicists from around the world to
conduct forefront research in the 1-5 mu region, on the venerable--but
infrared friendly--McMath-Pierce telescope.

---------------------------------------------------------
Title: The Cycles of Alpha Centauri
Authors: Ayres, T.
2008ESPM...12..4.1A Altcode:
As the nearest system of Sun-like stars, ? Centauri (G2 V + K1 V) is
a "poster child" of the solar-stellar connection. This is especially
true in coronal soft X-rays, where a parade of successive high-energy
observatories has imaged the binary over the past three decades. I
report a new analysis of ROSAT, XMM-Newton, and Chandra pointings
covering 1995-2008. Although XMM-Newton found a dramatic decline in the
coronal luminosity of first A in 2005, then more recently B in 2007,
the "Fainting of ? Cen" now is recognized as an instrument calibration
issue. Nevertheless, cycles of both stars clearly are evident in the
long term record, surprisingly synchronized in the current epoch.

---------------------------------------------------------
Title: The photospheric solar oxygen project. I. Abundance analysis
of atomic lines and influence of atmospheric models
Authors: Caffau, E.; Ludwig, H. -G.; Steffen, M.; Ayres, T. R.;
Bonifacio, P.; Cayrel, R.; Freytag, B.; Plez, B.
2008A&A...488.1031C Altcode: 2008arXiv0805.4398C
Context: The solar oxygen abundance has undergone a major downward
revision in the past decade, the most noticeable one being the
update including 3D hydrodynamical simulations to model the solar
photosphere. Up to now, such an analysis has only been carried out
by one group using one radiation-hydrodynamics code. Aims:
We investigate the photospheric oxygen abundance considering lines
from atomic transitions. We also consider the relationship between
the solar model used and the resulting solar oxygen abundance, to
understand whether the downward abundance revision is specifically
related to 3D hydrodynamical effects. Methods: We performed
a new determination of the solar photospheric oxygen abundance by
analysing different high-resolution high signal-to-noise ratio atlases
of the solar flux and disc-centre intensity, making use of the latest
generation of CO5BOLD 3D solar model atmospheres. Results: We
find 8.73 ≤ log (N_O/N_H) +12 ≤ 8.79. The lower and upper values
represent extreme assumptions on the role of collisional excitation
and ionisation by neutral hydrogen for the NLTE level populations
of neutral oxygen. The error of our analysis is ± (0.04± 0.03)
dex, the last being related to NLTE corrections, the first error
to any other effect. The 3D “granulation effects” do not play a
decisive role in lowering the oxygen abundance. Conclusions:
Our recommended value is log (N_O/N_H) = 8.76 ± 0.07, considering our
present ignorance of the role of collisions with hydrogen atoms on the
NLTE level populations of oxygen. The reasons for lower O abundances in
the past are identified as (1) the lower equivalent widths adopted and
(2) the choice of neglecting collisions with hydrogen atoms in the
statistical equilibrium calculations for oxygen. This paper is
dedicated to the memory of Hartmut Holweger.

---------------------------------------------------------
Title: The Cycles of Alpha Centauri
Authors: Ayres, Thomas
2008cxo..prop.2547A Altcode:
Alpha Centauri (G2V + K1V) is the nearest system of Sun-like stars;
the primary long regarded a solar twin. The binary has been a popular
target for previous X-ray missions, although the shrinking orbit now
is resolvable only by Chandra. The 25 year X-ray record has revealed
striking long term changes in the Alpha Cen coronae, including a deep
X-ray minimum of the primary spotted by XMM in 2004-05. A recent LETGS
pointing showed that the G star had become quite deficient in &gt;2
MK emissions, but the softer 1 MK spectrum was little changed. Two
additional 10 ks HRC-I snapshots in 2009 will continue this remarkable
coronal narrative. We also propose key HST FUV spectra of the pair,
to constrain emission measures and probe subcoronal dynamics.

---------------------------------------------------------
Title: The Deep Lamp Project: An Investigation of the Precision
and Accuracy of the Echelle Wavelength Scales of Space Telescope
Imaging Spectrograph
Authors: Ayres, Thomas R.
2008ApJS..177..626A Altcode:
The precision and absolute accuracy of the echelle mode wavelength
scales of Space Telescope Imaging Spectrograph (STIS) are
investigated. The method is to measure deep exposures of the onboard
Pt/Cr-Ne hollow cathode calibration lamp. The standard deviation of
emission spots from their laboratory wavelengths in a single image
is a measure of the internal precision of the pipeline-assigned
scales. The average shift of the image as a whole is a measure of
the absolute accuracy. While systematic patterns can be identified in
all four echelle modes (E140M, E140M, E230M, and E230H), the overall
precision (even without compensating for long-range trends with λ) is
excellent: of order one-tenth of the resolution element (σ ~ 600 and
300 m s-1, for medium- [M] and high- [H] resolution modes,
respectively). Furthermore, the absolute accuracy and its repeatability
(assessed in a time series of WAVECAL images) is of order a remarkable
100 m s-1, aside from one of the E230M modes (secondary
tilt λ2269) that shows a systematic offset 10 times larger. The
excellent precision of the STIS echelle wavelengths could be improved
by adding higher order terms to the biquadratic polynomial currently
implemented in the CALSTIS pipeline. On the other hand, the existing
small distortions might be resolved more naturally by a "physical
instrument model," currently under development by the Space Telescope
European Coordinating Facility's STIS Calibration Enhancement Project.

---------------------------------------------------------
Title: The Fainting of α Centauri A, Resolved
Authors: Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt,
Jürgen H. M. M.
2008ApJ...678L.121A Altcode:
Beginning in 2003, XMM-Newton snapshot monitoring of α Centauri (HD
128620, 128621: G2 V, K1 V) documented a steady fading of the primary's
X-ray corona, which had all but disappeared by early 2005. The steep
decline in LX was at odds with the previous two decades
of high-energy measurements, which showed only modest variability of
the Sun-like star. A Chandra LETGS spectrum in 2007 June, however,
fully resolved the source of the curious X-ray darkening: a depletion
of plasma above ~2 MK had substantially depressed the line spectrum
where the XMM-Newton response peaks (λ lesssim 30 Å), even though the
overall coronal luminosity, dominated by longer wavelength emissions,
had declined only slightly. This is reminiscent of the Sun's magnetic
activity cycle, where the 2-3 MK active regions of sunspot maximum
give way to the spatially pervasive, but cycle-independent, 1 MK
"quiet corona" at minimum. This emphasizes that any discussion of
cyclic coronal variability in low-activity stars will depend crucially
on the energy coverage of the measurements.

---------------------------------------------------------
Title: The Solar Oxygen Problem: Crisis, Catastrophe, or Opportunity?
Authors: Ayres, T. R.
2008ASPC..384...52A Altcode: 2008csss...14...52A
A proposed large reduction in the solar oxygen abundance--motivated by
spectral synthesis of weak forbidden O I absorptions using 3D convection
models--has provoked consternation in the helioseismology community:
the spectacular agreement between measured interior sound speed profiles
and predictions based on the historical ɛ_{O} completely unravels at
the new lower value. In an effort to validate low-O, two generic tests
of the 3D models are outlined. A snapshot from the CO^5BOLD class of
convection simulations is shown to meet some of the requirements,
but fail others. Implications for the solar carbon monoxide (CO)
spectrum--alternative O tracer--are discussed.

---------------------------------------------------------
Title: Instruments: HRC
Authors: Kraft, Ralph; Kenter, Almus; Ayres, Thomas R.; Judge, Philip
G.; Saar, Steven H.; Schmitt, Jurgen H. M. M.; Anderson, Gemma;
Gaensler, Bryan; Chicago Team
2008ChNew..15...13K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Spite, Monique; Landstreet, John D.; Asplund, Martin; Ayres,
Thomas R.; Balachandran, Suchitra C.; Dravins, Dainis; Hauschildt,
Peter H.; Kiselman, Dan; Nagendra, K. N.; Sneden, Christopher;
Tautvaišiené, Grazina; Werner, Klaus
2007IAUTB..26..160S Altcode:
The business meeting of Commission 36 was held during the General
Assembly in Prague on 16 August. It was attended by about 15
members. The issues presented included a review of the work made
by members of Commission 36, and the election of the new Organising
Committee. We note that a comprehensive report on the activities of
the commission during the last triennium has been published in Reports
on Astronomy, Transactions IAU Volume XXVIA. The scientific activity
of the members of the commission has been very intense, and has led
to the publication of a large number of papers.

---------------------------------------------------------
Title: The Solar Oxygen Crisis: a Goldilocks Solution
Authors: Ayres, Thomas R.
2007AAS...211.5908A Altcode: 2007BAAS...39..842A
The recent recommended large reduction in the solar oxygen
abundance--mainly motivated by spectral synthesis of a weak forbidden
O I absorption (6300 A) using 3D convection models---has provoked
consternation in the helioseismology community: the spectacular
agreement between measured interior sound speed profiles and
predictions based on the historical abundance (850 ppm relative to
hydrogen) completely unravels at the new lower value (450 ppm). At
the same time, molecular tracers of the oxygen abundance, such as CO,
indicate a value closer to 700 ppm, when the photospheric temperatures
in the region of peak molecular concentration are carefully adjusted to
match the temperature sensitive wings of the Ca II H and K lines. (One
does derive 450 ppm when the unaltered 3D models are used, but these
simulations are too cool in the upper photosphere where the molecular
diagnostics arise.) In order to reconcile these disparate results,
I have reconsidered the formation of the [O I] 6300 feature using
an alternative 3D convection model that matches key observational
constraints such as the visible continuum center-limb behavior, and
calibrated continuum intensities at disk center. As compared with the
previous work of Allende Prieto, Asplund, and collaborators, I find that
the so-called "1D-to-3D abundance correction" not only is very small,
contrary to their study, but also goes in the opposite direction. The
consequence is an oxygen abundance of about 650 ppm from 3D [O I]: not
too high, not too low, but just right (in the middle). This work was
supported by NSF. I thank the CO5BOLD collaboration for making available
snapshots from their 3D time dependent solar convection simulations.

---------------------------------------------------------
Title: The Further Fainting of Alpha Cen A
Authors: Ayres, Thomas
2007cxo..prop.2330A Altcode: 2007cxo..prop.2286A
Alpha Centauri (G2V + K1V) is the nearest system of solar-like
stars. The primary has long been regarded a solar twin. Previous X-ray
missions have been able to separate the coronal point sources (14"
apart in Y2000), although the orbit now is closing rapidly and beyond
2006 can only be resolved easily by Chandra. The 25 year X-ray record
has revealed striking long term changes in the Alpha Cen coronae, likely
related to analogs of the still mysterious solar sunspot cycle. Recent
work suggests that the K star is falling into a cycle minimum, while the
G star is relapsing following a brief recovery from an unprecedented
deep X-ray minimum in 2005 (that fully challenges our understanding
of stellar dynamos). Two 10 ks HRC-I snapshots in 2008 will build on
this remarkable coronal narrative.

---------------------------------------------------------
Title: Filling in the Coronal Graveyard
Authors: Ayres, Thomas
2007cxo..prop.2333A Altcode: 2007cxo..prop.2289A
20 ks Chandra HRC-I pointings on 5 late-type G/K supergiants in
the depths of the "coronal graveyard" will complete a survey of the
limits of X-ray activity in evolved cool stars. Our ambition is to gain
insight into magnetic generation in the absence of sensible rotation,
and the disposition of hot coronal structures in the extended outer
envelopes of these objects, possibly partially smothered under a "cool
absorber." Such buried activity might be the long sought initiator
of chromospheric winds in the giant branch. Coronal activity is
important to the Sun-Earth connection, the fate of primitive planetary
atmospheres, and a broad reaching set of magnetic phenomena in diverse
cosmic environments. Understanding the activity, and its evolution,
is a key objective of stellar astrophysics.

---------------------------------------------------------
Title: X-Ray and Ultraviolet Spectroscopy of Intermediate-Mass,
First Crossing Giants
Authors: Ayres, Thomas R.; Hodges-Kluck, Edmund; Brown, Alexander
2007ApJS..171..304A Altcode:
Chandra, FUSE, and HST STIS jointly have obtained spectra of four
intermediate-mass giants (&lt;~3 Msolar) crossing the
Hertzsprung gap for the first time, passing through a “rapid braking
phase” analogous to, but much briefer than, the more gradual prolonged
decay of magnetic activity experienced by single low-mass stars like
the Sun. All four giants display hot, dense coronal plasmas (6-30 MK,
~1012 cm-3), with near solar abundances. The
UV spectra show a remarkable congruence of shapes of the 0.06-0.2
MK lines of Si IV, C IV, and N V, which further can be decomposed
into narrow and broad Doppler components. The profile isomorphism
extends to the yellow dwarf α1 Cen (G2 V), utilized as a
solar surrogate. The broad component fraction of the total increases
with LX/Lbol and is suggestive of persistent
“microflaring.” Indeed, the most active of the targets, HR 9024 (G1
III), experienced a macroflare during the Chandra pointing, reaching a
remarkable 100 MK. In prebraking phase 31 Com (G0 III) and solar proxy
α1 Cen emission levels in the 0.03-0.3 MK “transition
zone” regime are very similar to those of the 1-10 MK corona, but
in the three cooler giants, the hotter plasma is dominant. The high
coronal densities of all four giants contrast to much lower values
(~1010 cm-3) at 0.15 MK from O IV line ratios,
contrary to expectations for isobaric magnetic loops, but possibly
analogous to the bimodal pressure behavior of certain solar impulsive
flares.

---------------------------------------------------------
Title: α TrA Junior
Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M.
2007ApJ...658L.107A Altcode:
The “hybrid chromosphere” star α Trianguli Australis (K2 Ib-IIa)
displays atypical coronal properties for its class: elevated soft X-ray
emission, flare outbursts, and a superhot (T~10 MK) spectrum. The Wide
Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope
(HST) now has found a faint object close to the red supergiant, 0.4"
nearly due south and about 1% its intensity in the F160BW ultraviolet
filter, consistent with a G0 dwarf. Potentially, the “young sun”
companion to the massive primary could completely dominate the
coronal luminosity. The X-ray centroid in a contemporaneous Chandra
High-Resolution Camera (HRC) pointing is offset in the direction of
the faint UV secondary, but measurements of the radio counterpart of a
serendipitous X-ray source 12" southeast (SE) of α TrA, obtained with
the Australia Telescope Compact Array (ATCA), suggest a conflicting
offset.

---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Spite, Monique; Landstreet, John; Asplund, M.; Ayres, T.;
Balachandran, S.; Dravins, D.; Hauschildt, P.; Kiselman, D.; Nagendra,
K. N.; Sneden, C.; Tautvaišiené, G.; Werner, K.
2007IAUTA..26..215S Altcode:
Commission 36 covers all the physics of stellar atmospheres. The
scientific activity in this large field has been very intense during
the last triennium and led to the publication of a large number of
papers which makes an exhaustive report practically not feasible. As
a consequence we decided to keep the format of the preceding report:
first a list of areas of current research, then web links for obtaining
further information.

---------------------------------------------------------
Title: Deep GRISM Survey of the Hyades Cluster. Ii.
Authors: Ayres, Thomas
2007galx.prop...65A Altcode:
The nearby, young (600 Myr) Hyades cluster is an important testing
ground for theories of stellar activity and flares, whose associated
chromospheric and coronal emissions are particularly conspicuous at high
energies. The Hyades region has been imaged numerous times by soft X-ray
observatories, beginning a quarter century ago with Einstein, continuing
with ROSAT, and more recently Chandra and XMM-Newton. However, FUV
observations -- particularly of key energy balance and flare tracer
C IV 1550 -- have been hampered by faintness of the cluster members
and the usual limitation to observe them one at a time. Here, we
propose to continue our Cycle 3 program by imaging three rich fields
in the Hyades with the GALEX grisms to capture C IV (and Mg II 2800)
in 30, or more, cluster members of late spectral type (F-K), mostly
main sequence stars. The controlled sample will strongly leverage our
understanding of high energy processes and flare outbursts in Sun-like
stars, especially in the crucial age range of our own solar system when
primitive planetary atmospheres were strongly eroded by coronal ionizing
radiations and mass ejections. The spatial multiplex advantage, high
sensitivity, spectral isolation, and long stare capability of GALEX
are ideally suited to the project."

---------------------------------------------------------
Title: The Old Feeble Coronae of Solar-like Dwarf Stars in the
Arcturus Moving Group
Authors: Brown, Alexander; Hodges-Kluck, E.; Ayres, T. R.; Harper,
G. M.
2006AAS...209.8905B Altcode: 2006BAAS...38Q1025B
The Arcturus Moving Group (AMG) is very likely a remnant of the merger
of a dwarf galaxy with the Milky Way Galaxy in the distant past. This
kinematically distinct group has members located very close to the
Sun, allowing study of coronal activity on very old stars that would
typically not be possible. We are investigating a sample of nearby
AGM dwarfs to study the properties of stellar magnetic activity on
old (7-8 Gyr), low metallicity stars. Our sample has metallicities
between 0.4 and 0.04 solar, spectral types F9 K0, and distances
less than 35 pc from the Sun. We have detected X-ray emission from
two AMG dwarfs with the Chandra ACIS-S S3 BI detector during Cycle
7 and two further stars have been approved for observation in Cycle
8. The detected stars are HD199288 (G0 V, V=6.6, d = 21.6 pc, [Fe/H]
= -0.68) and HD65583 (G8 V, V=6.9, d = 16.8 pc, [Fe/H] = -0.68) and
their derived X-ray luminosities are 4.4 and 1.9 1026 erg
s-1 respectively. These X-ray luminosities are somewhat less
than the minimum solar Lx (range 6 -20 1026 erg
s-1 ) but are comparable with that of the inactive, more
metal rich ([Fe/H] = -0.42] G8 dwarf Tau Cet. All the detected source
X-rays are very soft with energies of 0.2-0.3 keV, indicating very cool
(∼ 1 MK) coronal temperatures. These results were obtained and
funded by CXO project 7200977.

---------------------------------------------------------
Title: The Coronae of γ Draconis
Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M.
2006ApJ...651.1126A Altcode:
The Chandra X-Ray Observatory has detected coronal (T&gt;~106
K) emission from the red giant γ Draconis (HD 164058: K5 III;
d=45 pc), now fully resolved from a stronger source 21" to the
SE that had confused earlier measurements by Röntgensatellit
(ROSAT). The second source is coincident with the 13th magnitude
visual component ADS 10923B (γ Dra B), possibly a dM star in a wide
orbit around the red giant. The 0.2-2 keV luminosity of γ Dra is
LX~1.2+0.4-0.2×1027
ergs s-1 (1 σ confidence interval), assuming
log(Tcor)&gt;~6.5 K, while that of the faint optical
companion is 3.2+0.7-0.5×1027
ergs s-1, assuming the same distance. Both sources have an
intermediate spectral hardness within the range displayed by coronal
stars. γ Dra has LX/Lbol an order of magnitude brighter than the other
red giants previously imaged by Chandra, Arcturus (α Boo: K1.5 III)
and Aldebaran (α Tau: K5 III), despite having an only 2 × elevated
LC IV/Lbol (T~105 K).

---------------------------------------------------------
Title: Strip-Mining the Coronal Graveyard
Authors: Ayres, Thomas
2006xmm..prop...95A Altcode:
XMM-Newton pointings on 5 late-type G/K supergiants in the outskirts
of the coronal graveyard will explore the midrange of X-ray activity
in evolved late-type stars. Our ambition is to gain insight into
magnetic field generation in the absence of sensible rotation,
and the disposition of hot coronal structures in the extended outer
envelopes of these objects, possibly partially smothered beneath a cool
absorber. Such buried activity might be the long sought initiator of
chromospheric winds in the giant branch. The project will capture the
remaining most promising candidates from UV and X-ray flux limited
samples identified in the ROSAT era. Understanding the broad reaches
of coronal activity, and its evolution, are key objectives of cool
star astrophysics.

---------------------------------------------------------
Title: The Fainting of Alpha Cen A
Authors: Ayres, Thomas
2006cxo..prop.2108A Altcode:
Alpha Centauri (G2V+K1V) is the nearest system of solar-like stars;
the primary has long been regarded a solar twin. Historical X-ray
missions have been able to separate the coronal point sources (14"
apart in Y2000), although the orbit now is closing rapidly and beyond
2006 can only be resolved by Chandra. The 35 year X-ray record has
revealed striking long term changes in the Alpha Cen coronae, likely
related to analogs of the still mysterious solar sunspot cycle. Recent
work suggests that the K star is rising out of a cycle minimum,
while the G star has experienced a startling, unprecedented plunge
in its X-ray luminosity that calls into question our understanding of
stellar dynamos. A deep LETGS spectrum, and two short HRC-I snapshots,
will build on this remarkable coronal narrative.

---------------------------------------------------------
Title: Solar Carbon Monoxide, Thermal Profiling, and the Abundances
of C, O, and Their Isotopes
Authors: Ayres, Thomas R.; Plymate, Claude; Keller, Christoph U.
2006ApJS..165..618A Altcode: 2006astro.ph..6153A
A solar photospheric “thermal profiling” analysis is presented,
exploiting the infrared (2.3-4.6 μm) rovibrational bands of carbon
monoxide (CO) as observed with the McMath-Pierce Fourier transform
spectrometer (FTS) at Kitt Peak, and from above the Earth's atmosphere
by the Shuttle-borne ATMOS experiment. Visible continuum intensities
and center-limb behavior constrained the temperature profile of the deep
photosphere, while CO center-limb behavior defined the thermal structure
at higher altitudes. The oxygen abundance was self-consistently
determined from weak CO absorptions (for C/O≡0.5). Our analysis
was meant to complement recent studies based on three-dimensional
(3D) convection models, which, among other things, have revised the
historical solar oxygen (and carbon) abundance downward by a factor
of nearly 2, although in fact our conclusions do not support such a
revision. Based on various considerations, an ɛO=700+/-100
ppm (parts per million relative to hydrogen) is recommended; the large
uncertainty reflects the model sensitivity of CO. New solar isotopic
ratios also are reported: 12C/13C=80+/-1,
16O/17O=1700+/-220, and
16O/18O=440+/-6-all significantly lower than
terrestrial. CO synthesis experiments utilizing a stripped down
version of the 3D model-which has large temperature fluctuations in the
middle photosphere, possibly inconsistent with CO “movies” from the
Infrared Imaging Spectrometer (IRIS), and a steeper mean temperature
gradient than matches visible continuum center-limb measurements-point
to a lower oxygen abundance (~500 ppm) and isotopic ratios closer
to terrestrial. A low oxygen abundance from CO-and other molecules
like OH-thus hinges on the reality of the theoretically predicted
midphotospheric convective properties.

---------------------------------------------------------
Title: Those Cool Stars...So Hot Right Now
Authors: Ayres, T. R.
2006ASPC..348..145A Altcode:
I offer four (out of many possible) examples of FUSE programs focussing
on late-type ("cool") stars: (1) a survey of coronal forbidden lines;
(2) the buried coronae of red giants; (3) super-rotational UV line
broadening in Hertzsprung gap stars; and (4) FUV time series as a
gauge of activity.

---------------------------------------------------------
Title: A Cycle-4 Survey of RS CVn Binary Systems
Authors: Redfield, S.; Linsky, J. L.; Ayres, T. R.; Brown, A.; Herczeg,
G. J.
2006ASPC..348..269R Altcode:
RS CVn systems are detached late-type binaries that are very active as
a result of their tidally enforced rapid rotation. They are actively
studied and bright at X-ray and ultraviolet (UV) wavelengths, but very
few have been observed in the far-UV. We present multiple orbital
phase observations of RS CVn systems taken by the Far Ultraviolet
Spectroscopic Explorer (FUSE) through a survey program in Cycle
4. Located in the FUSE spectral range are emission lines formed in
plasma at 50,000--300,000 K (e.g., C III and O VI). We present an
analysis of the strong emission line profiles. By monitoring the
change in the profile shape over the course of an orbital period
we can measure the fractional contributions of each star in the RS
CVn binary system at different plasma temperatures. In addition,
the spectral resolution and wavelength scale of FUSE permit us to
measure the width and velocity shift of the O VI and C III lines,
providing a new window on stellar atmospheric dynamics and structure.

---------------------------------------------------------
Title: The Remarkable Far-Ultraviolet Spectrum of FK Comae Berenices:
King of Spin
Authors: Ayres, Thomas R.; Harper, Graham M.; Brown, Alexander;
Korhonen, Heidi; Ilyin, Ilya V.; Redfield, Seth; Wood, Brian E.
2006ApJ...644..464A Altcode:
A Far Ultraviolet Spectroscopic Explorer (FUSE) pointing on the
ultrafast rotating yellow giant FK Comae Berenices (HD 117555;
vsini~163 km s-1) recorded emission profiles of C III
λ977 (T~8×104 K) and O VI λ1031 (T~3×105
K) that are exceptionally broad and asymmetric, but nearly identical
in shape, aside from a blueward absorption component in the latter
(identified as interstellar O I, rather than, say, a C III outflow
feature). The FWHMs exceed 500 km s-1, twice the broadest
far-UV line shape of any normal late-type star observed to date, but
similar to the Hα profiles of FK Com, and following the trend of other
fast spinning early G giants that often display “superrotational”
broadening of their UV “hot” lines. Although the red-asymmetric O
VI λ1031 profile is suggestive of an outflow at ~3×105
K, the weaker member of the doublet, λ1037, does not display the
differential absorption pattern expected from a warm wind. Furthermore,
at times the chromospheric Mg II λ2796 + λ2803 composite profile,
from a collection of International Ultraviolet Explorer (IUE)
echellegrams obtained two decades earlier, is nearly identical in shape
to red-asymmetric O VI λ1031. A contemporaneous optical Doppler map
places the photospheric dark spots mainly in the polar regions of the
approaching hemisphere. The dominantly redward biased profiles of C
III and O VI could be explained if the associated emission zones were
leading the starspots in phase and partially rooted in lower latitudes.

---------------------------------------------------------
Title: Key problems in cool-star astrophysics
Authors: Pagano, Isabella; Ayres, Thomas R.; Lanzafame, Alessandro C.;
Linsky, Jeffrey L.; Montesinos, Benjamín; Marcello-Rodonò
2006Ap&SS.303...17P Altcode:
Selected key problems in cool-star astrophysics are reviewed, with
emphasis on the importance of new ultraviolet missions to tackle the
unresolved issues. UV spectral signatures are an essential probe of
critical physical processes related to the production and transport
of magnetic energy in astrophysical plasmas ranging, for example, from
stellar coronae, to the magnetospheres of magnetars, and the accretion
disks of protostars and Active Galactic Nuclei. From an historical
point of view, our comprehension of such processes has been closely
tied to our understanding of solar/stellar magnetic activity, which
has its origins in a poorly understood convection-powered internal
magnetic dynamo. The evolution of the Sun's dynamo, and associated
magnetic activity, affected the development of planetary atmospheres
in the early solar system, and the conditions in which life arose on
the primitive Earth. The gradual fading of magnetic activity as the
Sun grows old likewise will have profound consequences for the future
heliospheric environment. Beyond the Sun, the magnetic activity of
stars can influence their close-in companions, and vice versa. Cool
star outer atmospheres thus represent an important laboratory in which
magnetic activity phenomena can be studied under a wide variety of
conditions, allowing us to gain insight into the fundamental processes
involved. The UV range is especially useful for such studies because it
contains powerful diagnostics extending from warm (∼ 104 K)
chromospheres out to hot (1 10 MK) coronae, and very high-resolution
spectroscopy in the UV has been demonstrated by the GHRS and STIS
instruments on HST but has not yet been demonstrated in the higher
energy EUV and X-ray bands. A recent example is the use of the hydrogen
Lyα resonance line—at 110 000 resolution with HST STIS—study,
for the first time, coronal winds from cool stars through their
interaction with the interstellar gas. These winds cannot be detected
from the ground, for lack of suitable diagnostics; or in the X-rays,
because the outflowing gas is too thin. A 2m class UV space telescope
with high resolution spectroscopy and monitoring capabilities would
enable important new discoveries in cool-star astronomy among the
stars of the solar neighborhood out to about 150 pc. A larger aperture
facility (4 6 m) would reach beyond the 150 pc horizon to fainter
objects including young brown dwarfs and pre-main sequence stars in
star-forming regions like Orion, and magnetic active stars in distant
clusters beyond the Pleiades and α Persei. This would be essential,
as well, to characterize the outer atmospheres of stars with planets,
that will be discovered by future space missions like COROT, Kepler,
and Darwin.

---------------------------------------------------------
Title: Stellar Activity on Young Stars in the Local Association:
FUSE Observations of the Beta Pic and Tucana-horologium Moving Groups
Authors: Brown, Alexander; Harper, G. M.; Ayres, T. R.
2006AAS...208.1003B Altcode: 2006BAAS...38...89B
A significant number of the nearby single active dwarf stars are members
of the Local Association, which is a widespread aggregate of young
stars related to star formation in the Sco-Cen association. The ages
of stars within the Local Association span a range of 8-150 Myr, but
the subgroups have much narrower age spreads. The older portions of the
Local Association include the Pleiades and Alpha Per clusters. Younger
subgroupings of the Local Association include the Beta Pic [age 12Myr]
and Tucana-Horologium [age 30Myr] moving groups. By ages of 12 Myr,
circumstellar disks and associated protoplanetary systems are at an
extremely interesting stage of evolution with gas giant formation
well under way and terrestrial planets starting to form. The high
energy radiation and particle (wind+flare) emission from the central
star plays an important role in the evolution of these disks. The
crucial EUV radiation field that photoioizes protoplanetary disks
and atmospheres is dominated by transition region ( 105
K) emission lines, such as He I 584, 537 A, He II 304 A, N III 686 A,
O III 600, 703 A, O IV 556, 610, 790 A, O V 630, 760 A, Ne VIII 780 A,
and sub-coronal emissions such as Mg IX 368 A and Mg X 610, 625 A. These
emission lines are unobservable because of strong absorption by the
interstellar medium and their strengths must be estimated from UV
observations of other emission lines from the same ions or ions formed
at similar temperatures. We are currently undertaking a FUSE Cycle 6/7
Legacy project to study the Beta Pic moving group and a large Cycle 7
Survey project to investigate the Tucana-Horologium moving group. We
present the current status of these projects and discuss the O VI and
C III emission line properties observed.

---------------------------------------------------------
Title: Exploring High Time Resolution Coronal Dynamics with the
Rapid Acquisition Imaging Spectrograph (RAISE) Sounding Rocket Program
Authors: Hassler, Donald W.; DeForest, C. E.; McIntosh, S.; Slater,
D.; Ayres, T.; Thomas, R.; Scheuhle, U.; Michaelis, H.; Mason, H.
2006SPD....37.3706H Altcode:
The Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation
high resolution imaging spectrograph to study the dynamics of the
solar chromosphere and corona on time scales as short as 100 ms. High
speed imaging from TRACE has shown that rapid motions and reconnection
are central to the physics of the transition region and corona, but
cannot resolve the differences between propagating phenomena and bulk
motion. SoHO/CDS and SoHO/SUMER have yielded intriguing measurements
of motion and heating in the solar atmosphere, and Solar-B/EIS will
capture EUV spectra of flares in progress; but no currently planned
instrument can capture spectral information in the chromosphere,
transition region, or cool corona on the 1-10 Hz time scale required for
few-second cadence spectral imaging or rapid wave motion studies. RAISE
is uniquely suited to exploring this hard-to-reach domain.The first
flight of RAISE is scheduled for October 24, 2006 (Flight 36.219 US)
and will focus on the study of high frequency, small-scale dynamics
of active region structures and the high frequency wave structure
associated with these active regions.

---------------------------------------------------------
Title: Deep Grism Survey of the Hyades Cluster
Authors: Ayres, Thomas
2006galx.prop...81A Altcode:
The nearby, young (600 Myr) Hyades cluster is an important testing
ground for theories of stellar activity and flares, whose associated
chromospheric and coronal emissions are particularly conspicuous at high
energies. The Hyades region has been imaged numerous times by soft X-ray
observatories, beginning a quarter century ago with Einstein, continuing
with ROSAT, and more recently Chandra and XMM-Newton. However, FUV
observations--particularly of key energy balance and flare tracer C
IV 1550--have been limited by faintness of the cluster members and
the usual limitation (of slit spectrographs) to observe them one at
a time. Here, we propose to image four rich fields in the Hyades with
the GALEX grisms to capture C IV (and Mg II 2800) in about 30 cluster
members of late spectral type (F-K), mostly main sequence stars. The
highly controlled sample will strongly leverage our understanding of
high energy processes and flare outbursts in Sun-like stars, especially
in the crucial age range of the young Sun relevant to the erosion
of primitive planetary atmospheres by coronal ionizing radiations
and mass ejections. The spatial multiplex advantage, sensitivity,
spectral isolation, and long stare capability of GALEX are ideally
suited to the project.

---------------------------------------------------------
Title: Seven Days in the Life of AR Lac
Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Korhonen, H.;
Redfield, S.; Hawley, S. L.; Optical Support Team
2005AAS...20717505A Altcode: 2005BAAS...37.1445A
A week-long pointing on the short-period eclipsing RS CVn binary AR Lac
(K0IV+G4IV; P=2d) by the Far-Ultraviolet Spectroscopic Explorer was
coordinated with groundbased optical Doppler mapping, to provide an
unprecedented view of structure, energetics, and dynamics of subcoronal
activity, through time-resolved measurements of FUV diagnostics like
C III λ 977, O VI λ 1031, and (coronal forbidden line) Fe XVIII
λ 974. The observation was carried out over the period 29 November
to 7 December 2004, with a total exposure of 225 ks, covering four
revolutions of the binary. Three large flares were captured during
this period, and numerous smaller ones, mainly on the K subgiant
primary. We discuss the appearance of the FUV activity on the surfaces
of the two hyperactive companions, with special emphasis on the eclipse
intervals. This work was supported by a FUSE Guest Investigator
grant.

---------------------------------------------------------
Title: Anomalous Coronae of Yellow Giants and Supergiants
Authors: Ayres, Thomas
2005xmm..prop...47A Altcode:
EPIC-pn spectra of "X-ray deficient" yellow giants and supergiants will
explore why these stars display anomalous coronal behavior compared with
cooler giants only slightly further advanced in their evolution. Among
the class-III objects, the sharp transition in coronal properties on
the way to helium flash might be caused by disruption of a "fossil"
magnetosphere by a newly born solar-like dynamo. But, the class-I
supergiants are post-flash, and a second deficiency mechanism likely
applies, perhaps highly extended chromospheric envelopes obscuring
X-rays from submerged magnetic loops. A key discriminator is the
coronal energy distribution, especially the presence of enhanced
soft absorption.

---------------------------------------------------------
Title: Further Resolving the Puzzle of Hybrid Star X-rays
Authors: Ayres, Thomas
2005cxo..prop.1897A Altcode: 2005chan.prop.1829A; 2005cxo..prop.1829A
Do Alpha TrA (K2II) and Beta Ind (K1II) have previously unrecognized
X-ray active dwarf companions, leading us astray concerning the coronal
properties of the "hybrid-chromosphere" class? Establishing the true
X-ray luminosities of the hybrids is a basis for understanding magnetic
field generation in evolved supergiants, the driving of their winds, and
the seeding of coronal conditions in their extended outer envelopes. It
also bears on the issue of late-type dwarfs orbiting main sequence B
stars, the evolutionary predecessors of K bright giants. We propose
to directly image the putative hybrid companions using Chandra, with
supporting observations from HST/WFPC2. We also propose to obtain
a coronal temperature for the archetype hybrid Alpha Aqr (G2Ib),
recently detected by HRC-I.

---------------------------------------------------------
Title: Chandra Observations of Coronal Emission from the Early G
Supergiants α and β Aquarii
Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M.
2005ApJ...627L..53A Altcode:
We report Chandra detections of coronal X-rays from the early G
supergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD 204867:
G0 Ib). Previous ROSAT observations of these archetypical “hybrid
chromosphere” stars were inconclusive, in the case of α Aqr owing
to a 38' mispointing, and for β Aqr because of a small positional
discrepancy of the apparent source. The Chandra High Resolution Camera
(HRC-I), with its superior spatial resolution and sensitivity, has
obtained a positive detection of α Aqr and recovered faint emission
at the location of β Aqr, now well separated from the stronger source
to the southeast that dominated the earlier ROSAT image. The coronal
LX/LC IV luminosity ratios of both supergiants are extremely
depressed relative to early G main-sequence stars, continuing the
“X-ray deficiency syndrome” originally identified in late F/early
G luminosity class III giants of the Hertzsprung gap.

---------------------------------------------------------
Title: StarCAT
Authors: Ayres, Thomas
2005hst..prop10638A Altcode:
StarCAT is a two-year Legacy Archival project to assemble all of the
STIS ultraviolet echelle exposures of normal stars into a broad-ranging
UV spectral library. The STIS echelle collection will be unique
for the decade, or more, that it will take to reproduce the lost UV
high-resolution capability in space. Consequently, StarCAT will be an
important resource for a wide variety of investigations, for years
to come. It follows-on an earlier Cycle 11 effort-CoolCAT-focussing
on late-type stars, which stands as a successful demonstration
project. But, StarCAT will capture as many as 300 targets and 2000
individual spectra {6X CoolCAT}, so it will have much further reach
and impact. Equally important, we can improve upon the CoolCAT
post-processing procedures and employ the definitive version of the
STIS pipeline when it becomes available. StarCAT will serve a broad
cross-section of the community beyond the familiar stellar enterprises,
supporting work on the interstellar medium, asterospheres, circumstellar
environments, exoplanets, and more. Now, at the end of STIS operations,
is the time to undertake such a UV preservation effort for the benefit
of future researchers, before the current expertise with the instrument
inevitably fades away.

---------------------------------------------------------
Title: Further Resolving the Puzzle of Hybrid Star X-rays
Authors: Ayres, Thomas
2005hst..prop10767A Altcode:
Do Alpha TrA {K2II} and Beta Ind {K1II} have previously unrecognized
X-ray active dwarf companions, leading us astray concerning the coronal
properties of the "hybrid-chromosphere" class? Establishing the true
X-ray luminosities of the hybrids is a basis for understanding magnetic
field generation in evolved supergiants, the driving of their winds, and
the seeding of coronal conditions in their extended outer envelopes. It
also bears on the issue of late-type dwarfs orbiting main sequence B
stars, the evolutionary predecessors of K bright giants. We propose
to directly image the putative hybrid companions using Chandra, with
supporting observations from HST/WFPC2.

---------------------------------------------------------
Title: The Solar Oxygen Abundance, and the Rare Isotopes of C and O,
Derived from Infrared Spectra of Carbon Monoxide
Authors: Ayres, T. R.; Plymate, C.; Keller, C.; Kurucz, R. L.
2005AGUSMSP41B..09A Altcode:
A detailed abundance analysis is presented for solar oxygen based on
the ΔV=1 fundamental (4.6~μm) and ΔV=2 (2.3~μm) first-overtone
rovibrational bands of carbon monoxide observed above the Earth's
atmosphere at very high spectral resolution and high signal-to-noise by
the Shuttle-borne ATMOS Fourier transform spectrometer (FTS). Additional
observations to define the reference photospheric thermal structure
were taken of the CO fundamental bands in an atmospheric window at
2145~cm-1 (4.6~μm) using the 1~m FTS of the McMath-Pierce telescope
at Kitt Peak and a fast tip/tilt image stabilization system. The latter
allowed measurements at the extreme limb where the highly slanted rays
probe into the outer layers of the photosphere. High spatial resolution
"movies" of weak CO lines at disk center taken under excellent seeing
conditions with the Infrared Imaging Spectrometer (IRIS), also on
the McMath-Pierce telescope, further constrained thermal and velocity
fluctuations in the layers in which the abundance-sensitive CO lines
form. This work is meant to complement a series of recent studies
which have revised the previously recommended solar oxygen abundance
downward by nearly a factor of two; although in fact our conclusions
do not support such a revision. The oxygen abundance recovered in the
present work is 700±70~ppm (parts per million relative to hydrogen)
compared with the proposed downward revision to 460±60~ppm, and the
recommended value of 650±100~ppm of a decade ago. In our analysis,
a fixed C/O ratio of 0.5, derived in independent work, was assumed;
so the associated carbon abundance is 350~ppm. New accurate values
for the solar abundance ratios of the rare isotopes of C and O also
are reported: 12C/13C= 70, 16O/17O= 400, and 16O/18O= 2000. All three
ratios are lower than terrestrial or meteoritic values (indicating
higher isotopic abundances). We find no evidence in the ATMOS3 spectra
for measurable 14C16O lines.

---------------------------------------------------------
Title: XMM-Newton observations of Pleiades-age K dwarfs
Authors: Brown, A.; Day, F.; Ayres, T. R.; Ambruster, C.
2005ESASP.560..465B Altcode: 2005csss...13..465B
No abstract at ADS

---------------------------------------------------------
Title: CoolCAT
Authors: Ayres, T. R.
2005ESASP.560..419A Altcode: 2005csss...13..419A
No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet Atlas of the Arcturus Spectrum, 1150-3800 A
Authors: Hinkle, Kenneth; Wallace, Lloyd; Valenti, Jeff; Ayres, Thomas
2005uaas.book.....H Altcode: 2005ASPMP...3.....H
The third volume of a set of atlases covering the infrared through
ultraviolet spectrum of the K giant Arcturus. This volume covers the
ultraviolet spectrum observed from the ground as well as moderate and
high resolution ultraviolet spectra observed with STIS on the HST. The
wavelength coverage of this volume is 1150 to 3800 A. In addition to
the spectrum of Arcturus, the solar spectrum or the spectrum of the
solar proxy alpha Cen A are shown. Each atlas page covers 10 to 15
A of spectrum with line identifications shown. Tables are included
summarizing the line identifications.

---------------------------------------------------------
Title: COmospheres and Beyond
Authors: Ayres, Thomas
2005hris.conf..353A Altcode:
There is an unexpectedly cool atmospheric layer on top of the Sun’s
photosphere, likely present in virtually all stars of solar temperature
and cooler. The main diagnostic of this mysterious layer is the = 1
(fundamental) rovibrational band system of carbon monoxide in the
thermal infrared, near 5 μm. It is thought that strong radiative
cooling by the CO bands, themselves, is directly responsible for
the depressed thermal structure of the cold layer, thus the moniker
“COmosphere.” Here, three different views of stellar COmospheres
are presented: a survey of the 5 μm CO bands in late-type stars
with the PHOENIX cryogenic echelle spectrometer at the Kitt Peak 2.1
m telescope; recent studies of the off-limb CO emissions in the Sun
exploiting the McMath-Pierce Fourier transform spectrometer (FTS); and
time-resolved integral field spectroscopy of solar surface dynamics
using the Imaging Infrared Spectrograph (IRIS) and a new IR adaptive
optics system, also on the McMath-Pierce at Kitt Peak.

---------------------------------------------------------
Title: X-Rays from Hybrid Stars
Authors: Ayres, Thomas R.
2005ApJ...618..493A Altcode:
The late-type giants and supergiants of the “hybrid chromosphere”
class display signatures of cool (T&lt;~2×104 K)
winds together with hot emission lines from species like C IV
(T~105 K). A survey of such stars by Reimers et al. using
ROSAT reported numerous X-ray detections (T~106 K),
strengthening the (then heretical) idea that hot coronae and cool
winds can coexist in luminous giants. However, several of the candidate
sources were offset from the predicted stellar coordinates, calling into
question the identifications. In an effort to secure better knowledge of
the X-ray luminosities of the hybrids, the ROSAT fields from the Reimers
et al. survey were reexamined, exploiting the USNO-A2.0 astrometric
catalog to register the pointings to a few arcseconds accuracy. On
the basis of positional mismatches, at least two of the previously
reported detections of key hybrid stars-γ Dra (K5 III) and β Aqr
(G0 Ib)-must be rejected. The new X-ray upper limits for these stars,
combined with the remaining candidate detections (and nondetections)
from the original survey, place the hybrids into the same “X-ray
deficient” category as the “noncoronal” red giants like Arcturus (α
Boo: K1.5 III) and Aldebaran (α Tau: K5 III). A few of the hybrid X-ray
sources are exceptional, however. The archetype α TrA (K2 II-III), in
particular, is securely detected in terms of positional coincidence, but
its anomalous, contradictory coronal properties suggest that an unseen
companion-a young hyperactive G dwarf-might dominate the X-ray emission.

---------------------------------------------------------
Title: The Soho-Stellar Re-Connection
Authors: Ayres, T. R.
2004ESASP.575..279A Altcode: 2004soho...15..279A
No abstract at ADS

---------------------------------------------------------
Title: FK Comae: King of Spin
Authors: Ayres, T. R.; Korhonen, H.; Harper, G. M.; Brown, A.;
Redfield, S.
2004AAS...205.1202A Altcode: 2004BAAS...36.1356A
Fast-rotating early-G giants often display ultraviolet profiles of
“hot lines,” like O VI (3×105 K), up to twice as broad
as anticipated from the photospheric υsin {i}. This peculiar behavior
has been attributed to highly extended coronal outer atmospheres. FUSE recently has contributed fundamentally to the exploration of
these “super-rotational” effects by observing the fascinating object
FK Comae Berenices (G5 III). It is prototype of a class of rapidly
rotating single giants which display spectacular emission activity
from X-rays to radio. FK Com has a spin period of only 2.4 d, and a
remarkable υsin {i} of 160 km s-1. The origins of such
ultra-fast--rotating stars are controversial. They might result from a
coalesced contact binary, cannibalism of a “hot Jupiter,” or simply
represent the top of the natural spin distribution of moderate-mass
Hertzsprung gap giants. In February 2004, FUSE obtained a 13 ks
exposure of FK Com in the 920--1180 Å range, the first UV observation
of this unusual object since the IUE era a decade ago, and by far
the best quality spectrum to date. The FUV emissions of O VI λ
1031 and C III λ 977 are enormously broad, asymmetric, but nearly
identical in shape, aside from a blue-shifted absorption component
in the latter. The FHWM's are a remarkable 600 km s-1,
about twice the broadest FUV profile of any late-type star observed
up to that point. The blueshifted C III feature might represent
a wind at ∼ 3×104 K, or alternatively a scattering
structure in the highly extended coronal envelope, something like the
“prominences” seen already in Hα . The asymmetric O VI profile might
indicate an outflow at higher ∼ 3× 105 K temperatures;
or simply reflects a skewed distribution of high-altitude activity
in the equatorial zones of FK Com. The relationship between the hot
lines and photospheric active regions---deduced from contemporaneous
optical Doppler mapping---also will be discussed. This work was
supported by FUSE Guest Investigator grant NNG04GH25G.

---------------------------------------------------------
Title: HRC Imaging of the `Fainted' Primary of the Alpha Centauri
System
Authors: Ayres, Thomas
2004cxo..prop.1874A Altcode:
The famous Alpha Centauri binary (G2V+K1V) has been regularly
observed in X-rays since first resolved by Einstein 25 years ago,
later by ROSAT/HRI, and more recently by XMM. The latest EPIC-pn
imaging uncovered an extremely odd result: solar twin Alp Cen A has
nearly disappeared in X-rays. This behavior had not been encountered
in the previous quarter century of X-ray work on the system, and is
quite unlike anything ever seen on the Sun, except perhaps the curious
18th-century "Maunder minimum," when sunspots vanished from the solar
disk for decades at a time, and coronal activity likely was severely
depressed; although, of course, we don't have any X-ray observations
from then to confirm the true coronal behavior. The AB orbit now has
closed below the resolution of EPIC, although still is easy for Chandra
to separate. I therefore propose to continue the crucial X-ray time
series on this important solar analog using Chandra's HRC-I.

---------------------------------------------------------
Title: Resolving the Puzzle of Hybrid Star Coronal X-rays
Authors: Ayres, Thomas
2004cxo..prop.1644A Altcode:
We propose 20 ks HRC-I pointings to detect 3 members of the so-called
"hybrid star" class, and 50 ks to confirm a previous HRC-I detection of
the archetype noncoronal giant Arcturus. Coronal activity, mirrored
in X-ray emission, is important to the Sun-Earth connection, the
fate of primitive planetary atmospheres, and a broad reaching set of
magnetic phenomena in diverse cosmic environments. Our program will
explore the limits of X-ray activity across the "coronal dividing
line," focussing on targets for which ROSAT-era detections have been
challenged recently. Assessing the true levels of coronal activity
in these objects has important implications for understanding the
initiation of chromospheric winds in red giants, a key phenomenon
whose origins remain elusive.

---------------------------------------------------------
Title: A Multiwavelength Perspective of Flares on HR 1099: 4 Years
of Coordinated Campaigns
Authors: Osten, Rachel A.; Brown, Alexander; Ayres, Thomas R.; Drake,
Stephen A.; Franciosini, Elena; Pallavicini, Roberto; Tagliaferri,
Gianpiero; Stewart, Ron T.; Skinner, Stephen L.; Linsky, Jeffrey L.
2004ApJS..153..317O Altcode: 2004astro.ph..2613O
We report on four years of multiple wavelength observations of the RS
CVn system V711 Tau (HR 1099) from 1993, 1994, 1996, and 1998. This
combination of radio, ultraviolet, extreme ultraviolet, and X-ray
observations allows us to view, in the most comprehensive manner
currently possible, the coronal and upper atmospheric variability of
this active binary system. We report on the changing activity state
of the system as recorded in the EUV and radio across the four years
of the observations, and study the high energy variability using an
assemblage of X-ray telescopes. (Longer abstract in paper).

---------------------------------------------------------
Title: The Deep Lamp Project
Authors: Ayres, Thomas
2004hst..prop10203A Altcode:
Space Telescope Imaging Spectrograph is the most sophisticated
space-borne spectrometer ever built, probably the last of its kind
for some time to come. A key virtue of STIS is that its medium-
and high-resolution echelle modes provide access to broad intervals
of the vacuum ultraviolet spectrum in a single shot. Another virtue
is the validation of the wavelength scales by periodic observations
of an onboard hollow-cathode emission line source. Tying together the
different echelle orders by means of the accurately known lamp spectrum
enables a wide range of studies that exploit differential comparisons
of velocity diagnostics in stellar, interstellar, and even extragalactic
spectra. Despite the importance of the wavelength calibrations, however,
they are done only infrequently {once a year}. While STIS undoubtedly
must be one of the most stable orbiting spectrographs ever designed,
possible thermal distortions of the instrument might cause small
nonlinear deviations of the wavelength scales and thereby impact the
velocity precision. The existing wavecal data sets are separated too
far apart in time to isolate short-term thermal fluctuations from
long-term secular behavior, and the routine WAVELINEs taken with
every grating switch are too underexposed to reveal any differential
behavior across the spectrum, aside from a simple zero-point offset. I
therefore propose to obtain a series of deep lamp exposures in a
few representative modes of the NUV and FUV MAMAs to search for
and characterize short-term differential distortions of the echelle
formats. This work also will provide an important dataset to test
new approaches to derive the basic dispersion relations, such as the
effort underway by the Physical Modeling Group at ESA's ST-ECF. The
calibration campaign can be scheduled in pure parallel mode with no
loss of orbits from the Cycle 13 science program.

---------------------------------------------------------
Title: A Comparison of the Outer Atmosphere of the “Flat Activity”
Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A (G2 V)
Authors: Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres,
Thomas R.
2004ApJ...609..392J Altcode:
Driven by the desire to understand the roles of acoustic and
magnetic mechanisms in heating the outer atmospheres of Sun-like
stars, we compare solar UV spectra with archival STIS spectra from
the Hubble Space Telescope of α Cen A (G2 V) and new STIS spectra
of the extremely inactive dwarf star τ Cet (G8 V, V=3.5). The
activity of τ Cet shows occasional rotational modulations but no
long-term cyclic variation. It may be in a phase analogous to the
solar Maunder minimum. Solar disk center intensities from both the
HRTS instrument and the SUMER instrument on SOHO were converted to
Sun-as-a-star fluxes by using center-to-limb data from Dammasch and
colleagues. The derived solar flux spectrum represents conditions
near the minimum of the solar magnetic activity cycle. We find that
the τ Cet line profiles differ systematically from those of the Sun
and α Cen A. While lines formed in the middle chromospheres appear
similar, the entire emission from the upper chromosphere to the middle
transition region of τ Cet has lower flux densities by factors of
~2, the line widths are significantly narrower, and, uniquely, the
transition region lines are not significantly redshifted. The soft
X-ray surface flux of τ Cet, measured between 0.1 and 2.4 keV, is
~9×103 ergs cm-2 s-1, several times
smaller than the median solar value. We also find that the UV spectrum
of α Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun
is in an intermediate phase of its activity cycle but that its coronal
emission may be somewhat smaller. We discuss the implications of these
results for magnetic fields and heating mechanisms in the stars and
speculate that τ Cet's UV spectrum might represent the solar spectrum
during a grand minimum phase.

---------------------------------------------------------
Title: Fossil Magnetospheres Confront Newborn Dynamos in the Rapid
Braking Zone
Authors: Ayres, T. R.
2004IAUS..215..280A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Positional Uncertainties and Detection Limits of ROSAT
X-Ray Sources
Authors: Ayres, Thomas R.
2004ApJ...608..957A Altcode:
This study addresses, primarily, positional uncertainties of
sources imaged by the X-ray cameras on the Röntgensatellit
(ROSAT). Monte Carlo simulations are exploited to estimate the
precision of centroiding point-source “photon clouds” in ROSAT
event lists. Measurements of bright coronal stars demonstrate that
the design specification 6" accuracy of a ROSAT pointing center was
achieved in practice. Furthermore, the accuracy often can be improved
to 2" or better by matching serendipitous X-ray sources to an optical
catalog like the US Naval Observatory A2. Even a low signal-to-noise
detection usually can be localized well enough to obtain a unique
identification with a cataloged object or to establish that no bright
optical counterpart is present. Secondarily, and in a more general
context, the study addresses detection significance and flux limits in
the sparse counting regime. Building on previous work by Gehrels and
Kraft, Burrows, &amp; Nousek, scaling laws are developed to estimate
detection thresholds and lower and upper bounds on possible source
fluxes. Although the specific application of ROSAT was in mind,
the flux limit approximations apply to other situations governed by
Poisson statistics; including ultraviolet and X-ray spectra with low
source counts and nonnegligible backgrounds.

---------------------------------------------------------
Title: Coronal Activity on Rapidly-Rotating Solar-Like Stars:
Chandra Observations of ER Vul
Authors: Brown, A.; Brown, J. M.; Osten, R. A.; Ayres, T. R.;
Guinan, E.
2004IAUS..215..334B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High Time Cadence Observations with the Rapid Acquisition
Imaging Spectrograph (RAISE) Rocket Program
Authors: Ayres, T. R.; Hassler, D. M.; Slater, D.; DeForest, C. E.;
Mason, H.; McIntosh, S.; Thomas, R. J.
2004AAS...204.9704A Altcode: 2004BAAS...36..828A
The Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation
high resolution imaging spectrograph scheduled to fly on a NASA sounding
rocket in 2006 to study the dynamics of the solar chromosphere and
corona on time scales as short as 100 ms. High speed imaging from
TRACE has shown that rapid motions and reconnection are central to the
physics of the transition region and corona, but cannot resolve the
differences between propagating phenomena and bulk motion. SoHO/CDS and
SoHO/SUMER have yielded intriguing measurements of motion and heating
in the solar atmosphere, and Solar-B/EIS will capture EUV spectra of
flares in progress; but no currently planned instrument can capture
spectral information in the chromosphere, transition region, or cool
corona on the ∼ 1-10 Hz time scale required for few-second cadence
spectral imaging or rapid wave motion studies. RAISE is uniquely suited
to exploring this hard-to-reach domain. This work is supported
by NASA Grant NNG04WC01G to the Southwest Research Institute.

---------------------------------------------------------
Title: The Stellar-Solar Connection
Authors: Ayres, T. R.
2004AAS...204.3601A Altcode: 2004BAAS...36..707A
Many solar-stellar astronomers believe that the solar-stellar connection
primarily is a one-way street: the exquisitely detailed studies of
the solar surface, interior, and heliosphere strongly mold our views
of the distant, unresolved stars. Perhaps many solar physicists have
gone so far as to adopt the myopic view that stellar astronomy, by and
large, is merely sponging up the fabulous insights from ever deeper
examinations of our local star, but the “dark side” is not really
capable of returning the favor. What could we possibly learn from
the stars, that we don't already know from much better observations
of the Sun? In my Introduction to this Topical Session, I will
discuss two broad issues: (1) the present divergence between solar
and stellar physics (driven by the different goals and tools of the
two disciplines); and (2) the diversity of stars in the H-R diagram,
to help inform our understanding of solar processes. Today, there are
observations of stars that greatly exceed the quality of analogous
solar measurements: e.g., HST/STIS UV echelle spectra of Alpha Cen A;
Chandra transmission grating spectra of solar-type stars; and only
recently have we obtained a definitive understanding of the Sun's soft
X-ray luminosity in the key ROSAT/PSPC band. The lack of equivalent
solar observations hinders practical applications of the solar-stellar
connection. On the more informative side, the evolutionary paths of
other stars can be quite different from the Sun's, with potentially
dramatic influences on phenomena such as magnetic activity. Equally
important, examples of Sun-like stars can be found at all stages of
evolution, from proplyds to red giants, in the volume of nearby space
out to 500 pc. In short, the solar-stellar connection need not be a
one-way street, but rather a powerful tool to explore solar processes
within the broader context of stars and stellar evolution. This
work was supported by NASA grant NAG5-13058.

---------------------------------------------------------
Title: A New Spin on FK Comae
Authors: Ayres, T.
2004fuse.prop.D075A Altcode:
FUSE observations of the ultra-fast rotating Hertzsprung gap giant
FK Comae (G5 III; v-sin-i= 160 km/s) will exploit the phenomenon of
super-rotational broadening to test whether such stars have extended
co-rotating regions of 100,000 K subcoronal gas. Extended emission
zones are expected in a magnetospheric scenario that describes a
possible fundamental dramatic change in magnetic activity as rapidly
evolving moderate-mass giants first enter the convective part of the
H-R diagram. A 15 ks exposure will obtain moderate S/N profiles of O
VI 1032 and C III 977, suitable to test the super-rotation hypothesis.

---------------------------------------------------------
Title: The Giant Star Ca II Ionization Problem: Mass Loss Revisited
Authors: Harper, G. M.; Brown, A.; Ayres, T.; Sim, S. A.
2004IAUS..219..651H Altcode: 2003IAUS..219E.143H
Pioneering studies of winds from non-coronal evolved late-type stars
were plagued by uncertainties in the Ca ionization balance that
resulted in very large uncertainties in derived mass-loss rates. Here
we re-examine the Ca II ionization balance in these stellar winds
using FUSE spectra which reveal for the first time the flux from the
photoionizing radiation field shortward of 1045 Angstroms. We
present a FUSE 912-1185 Angstrom spectroscopic survey of evolved late-K
and M stars; including the M giants alpha Cet (M1.5 III) gamma Cru (M3.5
III) beta Gru (M4.5 III) and R Dor (M8e III). Trends are presented
of the high excitation emission of C III fluorescent Fe II pumped
by H Lyman alpha and continuum fluxes with spectral-type. Using FUSE
spectra of alpha Tau (K5 III) supplemented with partial redistribution
calculations of H Lyman alpha and beta together with UV and radio data
we present a detailed study of alpha Tau's wind ionization balance
and derive new limits on its mass-loss rate

---------------------------------------------------------
Title: Future Observations with the Rapid Acquisition Imaging
Spectrograph (RAISE)
Authors: Hassler, D. M.; Deforest, C. E.; Slater, D.; Ayres, T.;
Mason, H.; McIntosh, S.; Thomas, R.
2004cosp...35.2280H Altcode: 2004cosp.meet.2280H
The Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation
high resolution imaging spectrograph scheduled to fly on a NASA sounding
rocket in 2006 to study the dynamics of the solar chromosphere and
corona on time scales as short as 100 ms. High speed imaging from TRACE
has shown that rapid motions and reconnection are central to the physics
of the transition region and corona, but cannot resolve the differences
between propagating phenomena and bulk motion. SoHO/CDS and SoHO/SUMER
have yielded intriguing measurements of motion and heating in the
solar atmosphere, and Solar-B/EIS will capture EUV spectra of flares
in progress; but no currently planned instrument can capture spectral
information in the chromosphere, transition region, or cool corona
on the ~1-10 Hz time scale required for few-second cadence spectral
imaging or rapid wave motion studies. RAISE is uniquely suited to
exploring this hard-to-reach domain.

---------------------------------------------------------
Title: Multi-Wavelength Observations of EV Lacertae
Authors: Osten, R. A.; Hawley, S. L.; Allred, J.; Johns-Krull, C. M.;
Roark, C.; Ambruster, C.; Brown, A.; Ayres, T. R.; Linsky, J. L.
2004IAUS..219..249O Altcode: 2003IAUS..219E.207O
We present an analysis of simultaneous radio optical UV and
X-ray observations of the dMe flare star EV Lacertae taken in 2001
September. The analysis is time-resolved and concentrates on determining
flare-related changes in each spectral region. Temporal correlations
in different wavelength regions are examined. Numerous X-ray flares
were observed; two X-ray flares are accompanied by UV enhancements
in a pattern reminiscent of the Neupert effect seen in solar flares
where UV bursts are interpreted as a product of nonthermal heat input
to the lower atmosphere and soft X-ray emission occurs as a result of
the heating. An extemely large radio flare seen at two frequencies
and representing a factor of 100 increase in quiescent radio flux
density has an optical counterpart with an enhancement of about 3
magnitudes in the U filter. There is no corresponding increase in
soft X-ray flux. We investigate scenarios which could give rise to the
observed multi-wavelength correlations. The run of electron density with
temperature in the outer atmosphere (transition region through corona)
is investigated and implications for coronal structure are given.

---------------------------------------------------------
Title: COmospheric Waves
Authors: Ayres, T. R.
2004ESASP.547..119A Altcode: 2004soho...13..119A
The puzzling cool "COmosphere" is an important interface between the
radiatively controlled outer photosphere and the dynamics-dominated
chromosphere. Highresolution spectroscopy of the thermal infrared
rovibrational bands of carbon monoxide is a key tool to elucidate
the physical properties of the cool gas, and to search for dynamical
signatures of the waves that shock at higher altitudes to excite the Ca
II "K grains" and other phenomena. An adaptive optics system developed
for the McMath-Pierce telescope has shown exceptional promise for
improving thermal infrared observations, particularly with the very
high-resolution Fourier transform spectrometer. At the same time,
AO and integral field units now are allowing high-quality imaging
spectroscopy (albeit at lower spectral resolution) of the CO lines over
10 × 10 areas with high enough cadence to measure the wave field down
to periods of about 10 s.

---------------------------------------------------------
Title: Seven Days in the Life of AR Lac
Authors: Ayres, T.
2004fuse.prop.E542A Altcode:
A week-long FUSE stare at short-period eclipsing RS CVn binary AR Lac
K0IV+G4IV; P2d), coordinated with groundbased radio imaging and optical
Doppler mapping, will provide an unprecedented view of structure,
energetics, and dynamics of hot-gas activity, through time-resolved
measurements of FUV diagnostics like C III 977, O VI 1031, and (coronal
forbidden line) Fe XVIII 974. As a class, RS CVns are notorious for
extreme high-energy emissions even during quiescent periods, but are
most spectacular during flare outbursts. Our project is the cool star
equivalent of a Hubble Deep Field, in the time domain; a new window on
magnetic activity in extreme environments ubiquitous in the Cosmos,
but only now beginning to be characterized and understood. (Although
the FUSE program is stand-alone, we plan to broaden and enhance the
campaign by requesting Chandra HETGS and HST STIS time to be coordinated
with the FUV spectroscopy.)

---------------------------------------------------------
Title: The Holely Coronal Graveyard
Authors: Ayres, T.
2004fuse.prop.D115A Altcode:
A 100 ks FUSE pointing will probe the O VI and C III emissions of an
archetype denizen of the coronal graveyard--Aldebaran (Alpha Tauri;
K5 III). HST spectra suggest the possible--surprising--presence of
solar-like magnetic activity on the old, spun-down red giant. But,
many of the characteristic 1150-1500 A UV emissions apparently
are extinguished by a cool absorber overlying the hot (100,000 K)
structures. Detection of O VI by FUSE suggests that the cool absorber
opacity thins out just above the LyC edge, so O VI 1032 (and C III 977)
could be a sensitive probe of the submerged activity through the far-UV
opacity hole. The deep pointing will achieve high S/N, to search for
discrete absorption structure in the hot lines, impressed on them by
the cool absorber; and will allow an assessment of temporal variability
due to the heating process, which might be convective-acoustic but
probably is magnetic. If the latter, the buried magnetic activity
on red giants possibly plays a key role in driving their winds--a
long-standing astrophysical mystery, and a crucial component of galactic
chemical evolution. The existing FUSE spectrum is too low in S/N to
unambiguously measure discrete absorption components, and its singular
nature precludes any variability analysis.

---------------------------------------------------------
Title: A Far-Ultraviolet Spectroscopic Survey of RS CVn Binary Systems
Authors: Redfield, S.; Linsky, J. L.; Ayres, T. R.; Brown, A.; Herczeg,
G. J.
2003AAS...203.1218R Altcode: 2003BAAS...35.1224R
RS CVn systems are detached late-type binaries that are very active as
a result of their tidally-enforced rapid rotation. They are actively
studied and bright at X-ray and ultraviolet (UV) wavelengths, but very
few have been observed in the far-UV. We present multiple orbital
phase observations of RS CVn systems taken by the Far Ultraviolet
Spectroscopic Explorer (FUSE). Located in the FUSE spectral range are
emission lines formed in plasma at 50,000-300,000 K (e.g., C III and
O VI). We present an analysis of the strong emission line profiles. By
monitoring the change in the profile shape over the course of an orbital
period we can measure the fractional contributions of each star in the
RS CVn binary system at different plasma temperatures. In addition,
the spectral resolution and wavelength scale of FUSE permit us to
measure the width and velocity shift of the O VI and C III lines,
providing a new window on stellar atmospheric dynamics and structure.

---------------------------------------------------------
Title: Hybrid-Star Coronal X-ray Sources
Authors: Ayres, T. R.
2003AAS...203.4805A Altcode: 2004BAAS...36R.580A
“Hybrid chromosphere” stars show evidence of cool winds together
with hot emission lines like C 4 λ 1548 (T ∼ 105 K),
originally thought to be mutually exclusive in “noncoronal” giants and
supergiants to the red of the Linsky-Haisch coronal dividing line near
K1 III. Several surveys of such stars by the Roentgensatellit (ROSAT )
reported numerous X-ray detections and concluded that the hybrids as a
class are legitimate coronal sources, in some cases strong. However,
several of the detected sources were displaced from the predicted
stellar positions, calling into question the identifications. I have
reexamined the issue, using the U.S. Naval Observatory A2 Catalog to
astrometrically register deep pointings by the ROSAT Position Sensitive
Proportional Counter (PSPC) and High-Resolution Imager (HRI) to ∼few
arcsecond accuracy. At least two of the previously proposed detections
of key hybrid stars---γ Draconis (K5 III) and β Aquarii (G0 Ib)---must
be rejected on the basis of lack of positional coincidence. (Together
with HR 4289 [K5 III] whose identification originally was challenged by
Huensch, Reimers, &amp; Schmitt [1996, A&amp;A, 313, 755], who found
that the ∼ 30” displaced X-ray source coincided with a
faint, previously unknown galaxy.) Given that many of the original
survey sample were not even detected by ROSAT in the first place,
and that several of the secure detections plausibly can be attributed
to low-mass active MS companions, the conclusion is that hybrid stars
generally are very weak coronal sources, at best. The hybrids possibly
fall into the same category as the “noncoronal” red giants like α Boo
(K1 III) and α Tau (K5 III) whose hot-line emitting regions appear
to be buried deep in their X-ray opaque chromospheres. [-3mm]
This work was supported by grant NAG5-13058 from NASA to the
University of Colorado. The study made extensive use of the ROSAT
public archive at the HEASARC of NASA's Goddard Space Flight Center,
and the USNO-A2 astrometric catalog, as accessed from the Catalogue
Server of the ESO/ST-ECF Archive.

---------------------------------------------------------
Title: Buried Alive in the Coronal Graveyard
Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M.
2003ApJ...598..610A Altcode:
We have used the High Resolution Camera (HRC-I) of the Chandra
X-Ray Observatory to search for coronal (T~106 K)
emission from the archetype “noncoronal” red giants Arcturus
(α Bootis=HD 124897, K1 III) and Aldebaran (α Tauri=HD 29139, K5
III). Our program follows up previous detections of ultraviolet
coronal proxies such as C IV λ1548 (T~1×105 K)
and O VI λ1031 (T~3×105 K). The deep (~19 ks) HRC-I
pointings obtained a tentative 3 σ detection of Arcturus, with
fX(0.2-2keV)=1.0+1.8-0.8×10-15
ergs cm-2 s-1 (95% confidence limits
[CLs]), but failed to record Aldebaran, with an upper limit of
&lt;~1.5×10-15 ergs cm-2 s-1
(also at 95% CL). The corresponding LX/Lbol
ratios are a factor of ten thousand less than the Sun, a low-activity
coronal dwarf. At the same time, Hubble Space Telescope Imaging
Spectrograph far-ultraviolet spectra suggest the presence of a “cool
absorber,” probably near the base of the red giant chromosphere,
imprinting discrete low-excitation absorptions on top of highly
ionized features such as Si IV λ1393. The hot emission zones thus
are at least partially buried under a large column of chromospheric
material, which would severely attenuate any soft X-rays that might
be emitted. The submerged hot structures presumably are magnetic
because of their high temperatures and broad C IV profiles (FWHM~130 km
s-1). Perhaps these structures are analogous to small-scale
ephemeral bipolar regions seen ubiquitously on the Sun throughout
the sunspot cycle and thought to be of direct convective origin. If
small-scale magnetic fields indeed are present in the lower atmospheres
of red giants such as Arcturus and Aldebaran, they might play a role
in initiating the cool winds of such stars, perhaps through a mechanism
similar to solar spicules.

---------------------------------------------------------
Title: High Resolution Infrared, Visible and Ultraviolet Spectral
Atlases of the Sun and Arcturus
Authors: Hinkle, K.; Wallace, L.; Livingston, W.; Ayres, T.; Harmer,
D.; Valenti, J.
2003csss...12..851H Altcode:
Various groups of the co-authors have produced series of solar and
stellar atlases. Some atlases are listed below and the most recent
products described.

---------------------------------------------------------
Title: Dynamics of Coronal Iron Lines in Cool Stars based on FUSE
and HST/STIS Observations
Authors: Redfield, S.; Ayres, T. R.; Linsky, J. L.; Guinan, E. F.
2003csss...12..863R Altcode:
We present UV observations of coronal forbidden lines of highly
ionized iron. Fe XXI λ1354 and Fe XII λ1242 have been observed
by spectrographs on board the Hubble Space Telescope (HST), and Fe
XVIII λ975 recently has been identified in spectra taken by the Far
Ultraviolet Spectroscopic Explorer (FUSE). Mass motions of hot gas in
the corona provide information on the heating mechanism and magnetic
field strength in the corona. Observations of forbidden iron lines
with these moderate to high resolution spectrographs provide a unique
opportunity to study high temperature dynamics of the hot coronal
plasmas. We positively detect the forbidden iron line of Fe XVIII
λ975 in five stars. β Ceti shows the strongest Fe XVIII emission,
and since it is a single star system, it is an ideal target to study
stellar coronal dynamics. We find that the hot coronal plasma is
confined, in contrast to observed downflows at the temperatures where
the 105 K lines like C III λ977 form.

---------------------------------------------------------
Title: The Future of Cool-Star Astrophysics
Authors: Brown, A.; Harper, G. M.; Ayres, T. R.
2003csss...12.....B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: An Estimate of the Sun's ROSAT-PSPC X-Ray Luminosities Using
SNOE-SXP Measurements
Authors: Judge, Philip G.; Solomon, Stanley C.; Ayres, Thomas R.
2003ApJ...593..534J Altcode:
Using solar soft X-ray irradiance measurements from the SXP instrument
on the SNOE satellite, we relate the solar surface flux densities and
their variability to those of stars as measured with the PSPC instrument
on ROSAT. We translate SNOE-SXP measurements into equivalent ROSAT-PSPC
counts using model spectra calculated from the CHIANTI package. Using
the SNOE-SXP measurements has significant advantages over earlier
studies: the absolute calibration is known to +/-25%, SNOE measures the
Sun as if it were an unresolved star, it has operated over a significant
fraction of the solar cycle, and its three wavelength channels overlap
substantially with that of the ROSAT-PSPC instrument. The predicted
solar X-ray luminosities and surface flux densities are compared with
measurements from the ROSAT database. We find that we can estimate
the luminosity of the Sun as seen in the 0.1-2.4 keV (“RASS”)
passband of ROSAT-PSPC to within +/-50%, not counting sources of
systematic uncertainty mentioned in an appendix: the result lies
between 1027.1 and 1027.75 ergs s-1
(measured in the existing data set, only partially covering a full
solar cycle) and between 1026.8 and 1027.9
ergs s-1 (extrapolated to the full activity range of a
typical solar cycle). The solar luminosities lie close to the median
behavior found for a volume-limited (d&lt;13 pc) sample of G stars
studied in 1997 by Schmitt, revealing the Sun to be a normal or
slightly inactive G dwarf. A factor of 1.5 peak-to-peak variation in
the RASS passband is predicted due simply to rotational modulations
(i.e., those filtered to include periods P&lt;81 days). The ratio of
maximum/minimum RASS luminosities from the magnetic activity cycle
(filtered to include periods P&gt;81 days) are estimated to be 0.7-0.8
in log10LRASS, a ratio of 5 or 6. These variations are much
smaller than both recent estimates of solar X-ray variability and
the range of X-ray luminosities seen within Schmitt's sample. It is
suggested that the reported absence of “solar-like” cyclic emission
in stellar X-rays might partly arise because the Sun is less variable
than assumed in some earlier work. Repeated ROSAT observations of
α Cen A during 1995-1998 show X-ray behavior reminiscent of the Sun
during activity minimum conditions.

---------------------------------------------------------
Title: The Outer Atmosphere of Canopus: Detection of a Fast Stellar
Wind from an F Supergiant
Authors: Brown, A.; Harper, G. M.; Ayres, T. R.; Brown, J. M.
2003AAS...202.3211B Altcode: 2003BAAS...35..745B
We have investigated the outer atmospheric structure of the F0 Ib
supergiant Canopus using HST, Chandra and FUSE and have discovered a
number of unexpected properties, including the presence of an unusually
fast stellar wind from this post-M supergiant. Our observations
consist of 96 ksec of Chandra HETGS spectroscopy obtained on 2000
July 21, a set of HST-STIS (E140M, E230M, E230H) UV spectra obtained
on 2002 June 11, and three FUSE FUV spectra obtained in 2000 December
and 2001 October. The STIS and FUSE spectra provide full coverage of
the 900-3000 Å spectrum and the first UV emission line profiles from
the transition region of an F supergiant. These high signal-to-noise
profiles allow detailed study of the physical conditions in Canopus'
outer atmosphere from photospheric temperatures up to 5 105
K. Of particular interest is the hydrogen Lyman alpha line at 1215
Å ; this line shows clear evidence of high velocity (up to 400 km
s-1) wind absorption, which is a surprisingly high value
for a cool star wind. Investigating the winds from F supergiants, lying
between the fast (thousands km s-1) hot star winds and the
slow (tens km s-1) red supergiant winds, is particularly
important because the wind structure and driving mechanisms for such
stars is currently unknown. We see no evidence for wind absorptions
in any other UV emission lines observed by STIS or FUSE. The Chandra
spectrum shows the presence of a corona whose emission measure peaks at
7 MK and contains temperatures up to 20 MK. Other coronal properties
including elemental abundances are presented. No coronal variability
was seen. This work was supported by HST grant GO-06783.01-A,
SAO Chandra grant GO0-1087X, and NASA grant NAG5-4804 to the University
of Colorado.

---------------------------------------------------------
Title: CoolCAT
Authors: Ayres, T. R.
2003AAS...202.2504A Altcode: 2003BAAS...35..732A
CoolCAT is a cool-star UV spectral catalog derived from the rich
stellar archive of STIS E140M/H and E230M/H exposures. There are
approximately 50 more-or-less normal late-type stars in the HST
STIS archive with at least one E140M spectrogram, providing full UV
wavelength coverage from 1150--1700 Å at a resolution of R≡ λ
/Δ λ ∼ 4*E4. About 70% of these stars also have one
or more E230M/H exposures, covering all, or part, of the interval
1700--3000 Å. Approximately 150 E140M exposures have been reduced
for CoolCAT, and a comparable number of E230's, split nearly equally
between the medium-res (M: R ∼ 3*E4) and high-res (H: R
∼ 1*E5) modes. CoolCAT consists of a collection of digital
spectral atlases---echellograms processed to the same uniform standard,
multiple observations graded and coadded, and adjacent wavelength
regions concatenated---and a supporting catalog of line identifications,
wavelengths, widths, and fluxes. Semiautonomous line fitting procedures
ensure a homogeneous and uniform treatment of the diverse spectral
material. A wide range of investigations---from the photochemical
evolution of primitive planetary atmospheres, the dynamics of cool
star atmospheres, to galactic population synthesis---will be enabled
by CoolCAT. The database will reside at the Multimission Archive at
Space Telescope (MAST). [-3mm] This work was supported by
grant HST--AR--09550.01--A from STScI to the University of Colorado.

---------------------------------------------------------
Title: A Far Ultraviolet Spectroscopic Explorer Survey of Coronal
Forbidden Lines in Late-Type Stars
Authors: Redfield, Seth; Ayres, Thomas R.; Linsky, Jeffrey L.; Ake,
Thomas B.; Dupree, A. K.; Robinson, Richard D.; Young, Peter R.
2003ApJ...585..993R Altcode: 2002astro.ph.11363R
We present a survey of coronal forbidden lines detected in Far
Ultraviolet Spectroscopic Explorer (FUSE) spectra of nearby stars. Two
strong coronal features, Fe XVIII λ974 and Fe XIX λ1118, are
observed in 10 of the 26 stars in our sample. Various other coronal
forbidden lines, observed in solar flares, also were sought but
not detected. The Fe XVIII feature, formed at logT=6.8 K, appears
to be free of blends, whereas the Fe XIX line can be corrupted by
a C I multiplet. FUSE observations of these forbidden iron lines at
spectral resolution λ/Δλ~15,000 provides the opportunity to study
dynamics of hot coronal plasmas. We find that the velocity centroid
of the Fe XVIII feature deviates little from the stellar rest frame,
confirming that the hot coronal plasma is confined. The observed line
widths generally are consistent with thermal broadening at the high
temperatures of formation and show little indication of additional
turbulent broadening. The fastest rotating stars, 31 Com, α Aur Ab,
and AB Dor, show evidence for excess broadening beyond the thermal
component and the photospheric vsini. The anomalously large widths in
these fast-rotating targets may be evidence for enhanced rotational
broadening, consistent with emission from coronal regions extending
an additional ΔR~0.4-1.3R* above the stellar photosphere,
or represent the turbulent broadening caused by flows along magnetic
loop structures. For the stars in which Fe XVIII is detected, there is
an excellent correlation between the observed Röntgensatellit (ROSAT)
0.2-2.0 keV soft X-ray flux and the coronal forbidden line flux. As
a result, Fe XVIII is a powerful new diagnostic of coronal thermal
conditions and dynamics that can be utilized to study high-temperature
plasma processes in late-type stars. In particular, FUSE provides the
opportunity to obtain observations of important transition region
lines in the far-UV, as well as simultaneous measurements of soft
X-ray coronal emission, using the Fe XVIII coronal forbidden line.

---------------------------------------------------------
Title: XMM-Newton Proposal 02015603
Authors: Ayres, Thomas
2003xmm..prop...86A Altcode:
Objectives of the proposal are twofold: (1) obtain EPIC-pn spectra
of three key "X-ray deficient" Hertzsprung gap stars, to explore why
these F2-G0 giants display anomalous coronal behavior compared with
G/K dwarfs; and (2) record deep RGS spectra of four other gap giants,
3 of which were observed previously by Chandra, to capture the O VII
He-like triplet and other faint, but important, diagnostics beyond
the reach of H/LETGS. Interpretations will be based on comparisons
of derived emission measure distributions, and FIP, MAD, inverse-FIP
abundance behavior, with RGS and H/LETGS X-ray spectra of stars
previously collected. A sharp transition in coronal properties on the
way to He-flash might be due to disruption of a "fossil" magnetosphere
by a nascent solar-like dynamo.

---------------------------------------------------------
Title: Space Telescope Imaging Spectrograph Survey of Far-Ultraviolet
Coronal Forbidden Lines in Late-Type Stars
Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M.; Osten,
Rachel A.; Linsky, Jeffrey L.; Wood, Brian E.; Redfield, Seth
2003ApJ...583..963A Altcode:
We describe an extensive search with the Space Telescope Imaging
Spectrograph (STIS) for ultraviolet coronal (T&gt;106
K) forbidden lines in a sample of 29 F-M dwarfs, giants, and
supergiants. Measuring coronal lines in the 1150-1700 Å band with
STIS has important advantages of superior velocity resolution and an
absolute wavelength calibration compared with using the Chandra or
XMM-Newton grating spectrometers to observe permitted transitions of
the same ion stages in the kilovolt X-ray region. Fe XII λλ1242, 1349
(T~2×106 K) and Fe XXI λ1354 (107 K) are well
known from solar studies and have been reported in previous stellar
work. A search for other coronal forbidden lines in the 1200-1600 Å
region was largely negative. The few candidate identifications (e.g.,
Ar XIII λ1330 and Ca XV λ1375) are too faint to be diagnostically
useful. We add new dwarfs to the list of Fe XII detections, including
the nearby solar twin α Cen A (G2 V). Clear detections of Fe XXI were
obtained in dMe stars, active giants, a short-period RS CVn binary,
and possibly in active solar-type dwarfs. We developed a semiempirical
method for removing the C I blend that partially affects the Fe XXI
λ1354 profile. As discussed recently by Johnson et al., Capella (α
Aur; G8 III+G1 III) displays clear Fe XXI variability between Goddard
High-Resolution Spectograph (GHRS) and STIS observations 4 yr apart,
which is apparently due to a substantial decline in the contribution
from the G8 primary. We present an alternative model of the GHRS and
STIS era profiles using information in the two sets of line shapes
jointly, as well as knowledge of the behavior of Fe XXI profiles of
other late-G “clump” giants similar to Capella G8. The full survey
sample also provides a context for the apparent variability: the Fe
XXI flux of the G8 star in the GHRS spectrum is nearly identical (in
LFeXXI/Lbol) to other clump giants of similar
LX/Lbol, but it had dropped at least a factor
of 6 in the STIS measurement. The He II λ1640 Bα feature-which is
thought to be responsive to coronal irradiation-also showed significant
changes between the GHRS and STIS epochs, but the decrease in the
G8 star was much smaller than Fe XXI. The Fe XII flux displays a
correlation with the ROSAT 0.2-2 keV X-ray flux that can be described
by an α=0.5 power law. Fe XXI exhibits a steeper, perhaps linear
(α=1), correlation with the ROSAT flux down to an activity level of
LX/Lbol~10-5, below which detections
of the coronal forbidden line are rare. There is no evidence of large,
systematic Doppler shifts in either Fe XII λ1242 or Fe XXI λ1354. This
suggests that the emissions arise dominantly in confined structures,
analogous to magnetic loops on the Sun, rather than, say, in a hot
wind. The Fe XII and Fe XXI line widths generally are close to thermal
(FWHM~40-90 km s-1 at T~106.2-107.0
K), except for the Hertzsprung-gap giants 31 Comae (G0 III) and Capella
G1 and the K1 subgiant primary of HR 1099, all of which show evidence
for excess broadening in Fe XXI (Fe XII is obscured in these objects by
broad N V λ1242 features). If the excess broadening is rotational, it
implies that the hot coronae of “X-ray-deficient” 31 Com and Capella
G1 are highly extended, contrary to the compact structures suggested
by recent density estimates in a number of active coronal sources.

---------------------------------------------------------
Title: Accuracy and Precision of Measuring Emission Line Velocities
with the Space Telescope Imaging Spectrograph
Authors: Ayres, T. R.
2003hstc.conf..170A Altcode:
I describe some of the issues connected with measurements of emission
line velocities in STIS spectra, primarily in the key E140M band. These
issues are important not only in studies of the magnetodynamics
of stellar outer atmospheres, but also to gain insight into ways of
bootstrapping calibrations onto solar FUV instruments, which typically
have avoided internal wavecal lamps (like those flown in all of the
HST spectrometers) in favor of using in situ spectral "standards"
(such as the average velocity of weak chromospheric emission lines to
set the zero point offset). I address the issue of accuracy by comparing
apparent emission line radial velocities, as measured by STIS in the
FUV, with high-quality optical measurements of photospheric spectra, for
a large sample of late-type stars. I address the issue of precision by
conducting a series of numerical experiments to simulate Gaussian line
fitting in the presence of Poisson noise. I also discuss generalization
of these principles to the next generation HST spectrometer, the Cosmic
Origins Spectrograph.

---------------------------------------------------------
Title: Resolution of the COmosphere Controversy
Authors: Ayres, T. R.
2003ASPC..286..431A Altcode: 2003ctmf.conf..431A
No abstract at ADS

---------------------------------------------------------
Title: Chandra, Extreme Ultraviolet Explorer, and Very Large Array
Observations of the Active Binary System σ2 Coronae
Borealis
Authors: Osten, Rachel A.; Ayres, Thomas R.; Brown, Alexander; Linsky,
Jeffrey L.; Krishnamurthi, Anita
2003ApJ...582.1073O Altcode:
We present the results of a coordinated observing campaign on the
short-period RS CVn binary σ2 Coronae Borealis (F6V+G0V
Porb=1.14 days) with the Very Large Array, the Extreme
Ultraviolet Explorer, and the Chandra X-Ray Observatory High-Energy
Transmission Grating Spectrometer. The radio emission is consistent with
previously determined quiescent gyrosynchrotron properties. Multiple
flares were seen with Extreme Ultraviolet Explorer, five occurring
within two consecutive orbital periods. The first of these flares
was observed with Chandra. The Chandra observations of σ2
CrB showed no systematic variations of line fluxes, widths, or Doppler
shifts with orbital phase, nor any response in line width or offset
due to the flare. This is consistent with both stars being equally
active coronal emitters. We have developed a self-consistent method of
spectral analysis to derive information from the line and continuum
emissions concerning the distribution of plasma with temperature and
elemental abundances. A bimodal temperature distribution is appropriate
for both quiescent and flare intervals, with a stable peak at 6-8 MK and
another variable enhancement at higher temperatures, with evidence for
significant contribution from temperatures up to 50 MK during the flare,
compared to 30 MK during quiescence. The iron abundance is subsolar
during quiescence but is enriched by about a factor of 2 during a
large flare seen with Chandra. The noble gas elements neon and argon
show elevated abundances with respect to iron, but there is no clear
evidence for any first ionization potential-based abundance pattern
during quiescence or the flare. We have determined coronal electron
densities from the helium-like ions O VII, Ne IX, Mg XI, and Si XIII,
which imply densities &gt;=1010 cm-3. There is
a small enhancement in the electron densities derived for the flare,
but it is not statistically significant. We call attention to electron
temperature constraints provided by the ratios of 1s2
1S0-1snp 1P1 transitions
of the helium-like ions O VII, Ne IX, Mg XI, and Si XIII. The derived
coronal electron pressures change by 1-2 orders of magnitude over a 25%
change in temperature, implying nonisobaric coronal conditions. We
find no evidence for significant departures from the effectively
thin coronal assumption. The electron densities inferred from the
soft X-ray spectra are inconsistent with cospatial gyrosynchrotron
emission; further observations are necessary to discriminate the
relative locations of the radio and soft X-ray-emitting plasma.

---------------------------------------------------------
Title: A Far Ultraviolet Spectroscopic Explorer Survey of Late-Type
Dwarf Stars
Authors: Redfield, Seth; Linsky, Jeffrey L.; Ake, Thomas B.; Ayres,
Thomas R.; Dupree, A. K.; Robinson, Richard D.; Wood, Brian E.; Young,
Peter R.
2002ApJ...581..626R Altcode:
We describe the 910-1180 Å spectra of seven late-type dwarf stars
obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE)
satellite. The stars include Altair (A7 IV), Procyon (F5 IV-V), α
Cen A (G2 V), AB Dor (K1 V), α Cen B (K2 V), ɛ Eri (K2 V), and AU
Mic (M0 V). We present line identifications, fluxes, Doppler shifts,
and widths. Doppler shifts are measured with respect to heliocentric
wavelength scales determined from interstellar absorption lines, and
are compared with transition region line shifts seen in Hubble Space
Telescope (HST) ultraviolet spectra. For the warmer stars the O VI lines
extend the trend of increasing redshift with line formation temperature,
but for the cooler stars the O VI line redshifts are essentially
zero. The C III and O VI lines of most stars in the sample are best
fit with two Gaussians, and we confirm the correlation of increasing
importance of the broad component with increasing stellar activity. The
nonthermal velocities of the narrow component are subsonic and exhibit
a trend toward larger velocities with decreasing surface gravity, while
the nonthermal velocities of the broad components show no obvious trend
with stellar gravity. The C III and O VI lines of Altair show unique
broad horned profiles. Two flares were observed on AU Mic. One shows
increasing continuum flux to shorter wavelengths, which we interpret as
free-free emission from hot plasma, and relatively narrow, redshifted
C III and O VI emission. The other shows very broad line profiles.

---------------------------------------------------------
Title: The Quiescent and Flaring Atmosphere of the dMe Flare Star
EV Lacertae
Authors: Osten, R. A.; Hawley, S. L.; Johns-Krull, C. M.; Brown, A.;
Ayres, T. R.; Ambruster, C.
2002AAS...201.1207O Altcode: 2002BAAS...34.1113O
We report on a multi-wavelength campaign to observe flares on the dM4.5e
flare star, EV Lac, in 2001 September. The campaign utilized the Chandra
ACIS-HETGS, HST-STIS, VLA, and optical photometry and spectroscopy
with the McDonald Observatory's 2.1 and 2.7m telescopes. The goal of
the campaign was to characterize EV Lac's dynamic outer atmosphere
and study the characteristics of magnetic energy release processes in
a completely convective star. X-ray grating observations confirm the
quiescent underabundance of iron deduced from previous low spectral
resolution observations and show evidence of enhanced and variable
Ne/Fe abundance ratios. Numerous flares were observed in the 100
ksec X-ray pointing; UV observations overlap one impulsive event,
while radio and optical observations reveal impulsive flare signatures
during a moderate X-ray flare. Preliminary results from a time-resolved
spectroscopic analysis of the X-ray data will be presented, including
determination of changing abundances, density, and temperature structure
of the coronal plasma in EV Lac. The timing of flares in radio, UV,
and optical will be compared against X-ray variations. A discussion
of the observed multi-wavelength temporal trends will be given, and
comparison made to solar flares. RAO acknowledges support from Chandra
grant G01-2014A and HST grant GO-08880.04-A, as well as support from
NRAO through a Jansky fellowship.

---------------------------------------------------------
Title: Buried Alive in the Coronal Graveyard
Authors: Ayres, T. R.; Brown, A.; Harper, G. M.
2002AAS...201.1204A Altcode: 2002BAAS...34Q1113A
We have used the highly sensitive “solar-blind” Chandra High
Resolution Camera (HRC-I) to search for 0.2--10 keV coronal X-ray
emission from the key “noncoronal” red giants Arcturus (α Boo: K1
III) and Aldebaran (α Tauri: K5 III). Our program follows up previous
detections of subcoronal (T ~ 105 K) emission lines, such
as C 4 λ 1548, by HST STIS, and its predecessor GHRS. The two deep
(19 ks) HRC-I pointings failed to detect either red giant, however,
with 3 σ upper limits of 1x 10-4 cnts s-1
and 2x 10-4 cnts s-1 for Arcturus and Aldebaran,
respectively. The corresponding 0.2--2.0 keV L X/L
bol levels are a factor of a thousand lower than the Sun (itself
already an inconspicuous coronal object), establishing new limits
of coronal futility among late-type stars. At the same time, STIS
far-ultraviolet spectra suggest the presence of a “cool absorber”
in the red giant atmosphere capable of selectively extinguishing
the subcoronal spectrum shortward of ~ 1500 Å. The cool absorber
must lie beneath the extensive chromospheric (T ~ 7000 K) envelope,
because the chromospheric lines lack absorption signatures from the
cool layer. As a result, the hot-line structures must be doubly buried
under a large column of neutral hydrogen, undoubtedly smothering any
soft X-ray emission that might be present. If small-scale magnetic
active regions indeed exist in the lower atmospheres of red giants
like Arcturus and Aldebaran, they might in some way be responsible
for initiating and sustaining the cool outflows of such stars. The
source of the near surface magnetism could be analogous to that of
the small-scale ephemeral bipolar regions seen ubiquitously on the Sun
throughout the sunspot cycle, and thought to be of direct convective
origin. [-3mm] This work was supported by Chandra grant G02-3014X and
HST grant GO-09273.01--A to the University of Colorado.

---------------------------------------------------------
Title: Coordinated Chandra HETGS and VLA Radio Observations of the
Active Coronae on the Short-Period Binary ER Vul (G0 V + G5 V)
Authors: Brown, A.; Osten, R. A.; Ayres, T. R.; Harper, G.; Guinan, E.
2002ASPC..277..223B Altcode: 2002sccx.conf..223B
No abstract at ADS

---------------------------------------------------------
Title: Chandra HETGS Observations of the Active Binary σ2
Coronae Borealis
Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Linsky, J. L.
2002ASPC..277..239O Altcode: 2002sccx.conf..239O
No abstract at ADS

---------------------------------------------------------
Title: Limits on Chromospheres and Convection among the Main-Sequence
A Stars
Authors: Simon, Theodore; Ayres, Thomas R.; Redfield, Seth; Linsky,
Jeffrey L.
2002ApJ...579..800S Altcode:
In deeply convective stars, the nonthermal energy required
to heat the chromosphere ultimately is supplied by turbulent
magnetoconvection. Because the early and middle A stars have very
shallow convective layers, they are not expected to produce enough
magnetoconvective power to sustain luminous chromospheres or hot
coronae. Here we describe a search for chromospheric emission in the
far-ultraviolet (905-1185 Å) spectra of seven main-sequence A stars,
based on observations from the Far Ultraviolet Spectroscopic Explorer
(FUSE) telescope. Our survey spans the interval in effective temperature
along the main sequence over which powerful subsurface convection zones
and hence chromospheric emission are expected to vanish. The presence
or absence of high-temperature emissions in our FUSE spectra therefore
can be used to identify the locus for the transition from convective to
radiative envelopes-a change in stellar structure that is difficult to
assess by other means. We present our observations and analysis of the
subcoronal emission lines of C III λλ977, 1175 and O VI λλ1032,
1037, which bracket a range in formation temperatures from 50,000
to 300,000 K. To supplement our FUSE observations, we also report
Goddard High Resolution Spectrograph measurements of Si III λ1206 and
H I Lyα λ1215, obtained from archival observations of the Hubble
Space Telescope, as well as X-ray measurements from previous ROSAT
survey and pointed observations. We detected C III and O VI emission
features in the FUSE spectra of the coolest stars of our sample,
at Teff&lt;~8200 K. When normalized to the bolometric
luminosities, the detected emission-line fluxes are comparable to
solar values. We detected none of the hotter stars in our survey at
Teff&gt;=8300 K. Upper limits on the normalized flux in some
instances approach 40 times less than solar. Within an uncertainty in
the effective temperature scale of up to several hundred kelvins, our
FUSE observations indicate that the transition between convective and
radiative stellar envelopes takes place at, or very near, the point
along the main sequence where stellar structure models predict and,
moreover, that the changeover occurs very abruptly, over a temperature
interval no greater than ~100 K in width. Our FUSE sample also includes
two binary stars. In both cases, the narrow UV line profiles we have
observed suggest that the high-temperature emission is most likely
associated with the late-type companions rather than the A stars
themselves. Based on observations made with the NASA-CNES-CSA Far
Ultraviolet Spectroscopic Explorer, operated for NASA by Johns Hopkins
University under NASA contract NAS5-32985.

---------------------------------------------------------
Title: Does the Sun Have a Full-Time COmosphere?
Authors: Ayres, Thomas R.
2002ApJ...575.1104A Altcode:
Off-limb emissions of solar 4.7 μm rovibrational bands of carbon
monoxide, recorded under excellent observing conditions with the
Infrared Imaging Spectrograph at the McMath-Pierce telescope, are
compared with theoretical translimb CO simulations based on time slices
from the Carlsson &amp; Stein dynamical model of chromospheric “K
grains.” In the Carlsson-Stein view, the solar outer atmosphere-in
nonmagnetic internetwork regions-is a spatially and temporally
intermittent wave-driven phenomenon, yielding an average thermal
profile in the classical low chromosphere that is cool, not hot. Recent
papers by Kalkofen and collaborators have criticized the dynamical
model in favor of traditional “layered” stratifications, in which
temperatures vary smoothly with altitude and are warm throughout the
chromosphere. The present work sharpens the controversy by reiterating
that traditional models with warm thermal profiles in the altitude range
500-1000 km fail two key “infrared CO” tests. The same tests reveal
that the Carlsson-Stein dynamical model-which Kalkofen et al. argue
is too cool in the low chromosphere-is not cold enough. Equally
important, there need not be any contradiction between the existence
of cool gas above the classical temperature minimum and observations
of ubiquitous ultraviolet emission from the solar outer atmosphere,
a central criticism by Kalkofen and collaborators of a full-time cold
“COmosphere.”

---------------------------------------------------------
Title: CoolCAT
Authors: Ayres, Thomas
2002hst..prop.9550A Altcode: 2002hst..prop.5895A
A cool-star UV spectral catalog--CoolCAT-- will improve dramatically
the accessibility and utility of the rich stellar archive of STIS
E140M/H and E230M/H exposures. CoolCAT will contain digital spectral
atlases--echellograms processed to the same uniform standard, multiple
observations graded and coadded, and adjacent wavelength regions
concatenated--and a supporting catalog of line identifications,
wavelengths, widths, and fluxes. Semiautonomous line fitting
procedures will ensure a homogeneous and uniform treatment of the
diverse spectral material. Valuable experience already has been
gained with cycle 8 project 8280, which obtained full UV echelle
coverage {1150-3000 Angstrom} of 13 representative late-type stars. My
personal interest in these data involves studies of gas dynamics in
stellar outer atmospheres, traced by emission line Doppler widths
and shifts. However, a wide range of other investigations--from the
photochemical evolution of primitive planetary atmospheres to galactic
population synthesis--will be enabled by CoolCAT.

---------------------------------------------------------
Title: Comparison of the spectrum of a sunspot-like star with
a sunspot
Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Osten, R. A.
2002AN....323..321L Altcode:
A typical sunspot umbra has an effective temperature, gravity,
and strong magnetic field strength similar to the dM1e star AU
Microscopii. We compare STIS, Chandra, EUVE, and FUSE spectra of AU Mic
with typical spectra of sunspots to characterize the major differences
and then compare models of AU Mic with sunspot models. We find that the
emission, heating rates, and differential emission measure distributions
are very different for AU Mic and sunspots, and conclude that the root
cause of the difference lies in the very different geometries of the
two magnetic fields.

---------------------------------------------------------
Title: Chandra HETGS Observes Tortured Coronae in the Rapid Braking
Zone
Authors: Ayres, T. R.; Osten, R. A.; Brown, A.; Gagne, M.; Linsky,
J. L.
2002AAS...200.7419A Altcode: 2002BAAS...34..773A
We have obtained Chandra High Energy Transmission Grating Spectrometer
observations of five moderate mass (2--3 Msun) giants
straddling the portion of the Hertzsprung gap where early-G III
stars---evolving rapidly toward the red giant branch---suffer strong
rotational braking and dramatic changes in their X-ray emitting
coronae. G0 III giants prior to the braking epoch are fast rotators
(υ rot ~ 50-100 km s-1) and display very hot
(T&gt; 107 K) coronae, but nevertheless have curiously
depressed X-ray luminosities. The post-braking giants are slow rotators
(υ rot&lt; 10 km s-1) with cooler coronae (T ~
106.8 K), but nevertheless manage a healthy level of X-ray
emission. We believe the differences reflect the violent replacement
of a “fossil” magnetosphere---inherited from the late-B or early-A
MS progenitor---by a solar-like regenerative magnetic dynamo. The
latter becomes dominant when the initially shallow surface convection
in yellow giants at the blue edge of the Hertzsprung gap gives way to
deep convective layers as the stars evolve to the red edge. Three of
the targets were observed in Cycle 2: 31 Com (G0 III) on 2001-03-12
[132.0 ks]; HR 9024 (G1 III) on 2001-08-11 [96.9 ks]; and μ Vel (G5
III) on 2001-09-24 [19.9 ks], 2001-10-29 [58.1 ks], and 2001-12-18
[57.7 ks]. (The first μ Vel observation was scheduled for 80 ks,
but was cut short by a solar flare. The second pointing was intended
to complete the exposure, but was affected by “threshold crossing
plane” latchup in the ACIS CCDs, and was repeated two months later,
accounting for the third pointing.) The remaining two stars are: Cycle 3
target 24 UMa (G4 III; ~50 ks pointings on 2002-03-26 and 2002-03-29);
and GTO target β Ceti (K0 III) observed on 2001-06-29 [87.5 ks]. We
describe the HETGS spectra and our efforts to infer plasma conditions
(temperature/density models), chemical fractionation, gas dynamics
(through emission line Doppler shifts), and coronal variability. [-3mm]
This work was supported by Chandra grant GO1-2018X to the University
of Colorado.

---------------------------------------------------------
Title: Four Years of Multi-Wavelength Observations of the RS CVn
System HR 1099 (V711 Tau)
Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Linsky, J. L.
2002ASPC..264..156O Altcode: 2002ccea.conf..156O
No abstract at ADS

---------------------------------------------------------
Title: Glimmers of Life in the Coronal Graveyard
Authors: Ayres, Thomas R.
2002fuse.prop.C106A Altcode:
Red giants represent the final stage in the life cycle of normal
stars. Those evolving from low-mass dwarfs like the Sun were
magnetically active for most of their main sequence phase, thanks to
a spin-catalyzed convective dynamo. At the same time, such stars also
experienced significant rotational braking by their coronal winds. Once
they expanded into red giants, their spins further plummeted, and they
should have become magnetically dead; an expectation seemingly confirmed
by a conspicuous lack of coronal X-ray detections. However, reports of
the deaths of red giant coronae were premature - far-UV C IV emissions
(an important coronal proxy) have been detected in archetype members
of the class by HST, and now O VI has been seen by FUSE in at least
one case. Curiously, however, features formed at similar temperatures
-- Si IV and N V -- are absent, apparently removed by a mysterious
cool absorber. Our objective is to obtain additional detections of
the O VI doublet in key red giants, to help address the question of
the nature of the cool absorber, and the implications for smothering
any coronal X-ray emission. If we can show that there is lingering
magnetic activity on the red giants, we might have found a possible
link to the acceleration of their chromospheric winds, which chemically
enrich the ISM and themselves are a long-standing astrophysical puzzle.

---------------------------------------------------------
Title: Coronal Iron Survey The Yellow Giants
Authors: Ayres, Thomas R.
2002fuse.prop.C107A Altcode:
We propose a small survey of yellow giants to study the Fe XVIII lambda
974 coronal forbidden line, discovered recently in several late-type
stars by FUSE. We selected candidate targets from an extensive HST
STIS survey of the analogous Fe XXI lambda 1354 feature. Active yellow
giant stars (G0--G9 III) are the best choice, because their coronal
emission measures narrowly peak at approx. 6x106 K, where Fe
L-shell species -- such as Fe XVIII -- are most prominent. Measurements
of Doppler widths and shifts of the lambda 974 feature, at the high
velocity resolution afforded by FUSE, will revolutionize the study
of stellar coronal dynamics in ways that the current generation of
orbiting X-ray observatories cannot. A novel aspect of our program is
use of the interstellar absorption feature in the adjacent bright C
III lambda 977 emission core to calibrate the velocity scale.

---------------------------------------------------------
Title: X-ray coronae of stars: recent results from Chandra
Authors: Linsky, J.; Ayres, T.; Brown, A.; Osten, R.
2002cosp...34E1302L Altcode: 2002cosp.meetE1302L
The Chandra X-ray Observatory has opened up the new field of
astronomical X-ray spectroscopy and has also provided beautiful X-ray
images of young star clusters with unprecedented angular resolution. We
will summarize some of the important discoveries coming from the
HETG and LETG observations of many active stars and binary systems
as well as early-type stars. For the active late-type stars, we
will intercompare derived differential emission measures and coronal
electron densities of stars with different properties and consider
the main uncertainties that enter such analyses. We will also discuss
whether coronae are geometrically extended and how coronae change when
a star flares. Chandra has also provided important new information on
differences between coronal and photospheric abundances. For early-type
stars we will summarize the evidence for and against coronal vs wind
emission mechanisms. The final topic will be the question of how the
coronae of pre-main sequence stars differ from older but still active
stars as a result of the presence of magnetic disks and accretion
flows. Deep ACIS images of young star clusters like the Trapezium in
Orion and M16 are providing insights on this topic.

---------------------------------------------------------
Title: \it HST STIS Observations of Fluoresced Molecular Hydrogen
Emission in Diverse Stellar Environments
Authors: Ayres, T. R.; Wood, B. E.; Herczeg, G. J.; Linsky, J. L.
2001AAS...19915805A Altcode: 2002BAAS...34..567A
The broad coverage, high sensitivity, and precise wavelength calibration
of the Space Telescope Imaging Spectrograph's E140M medium-resolution
echelle mode make it ideal for studies of broadly dispersed spectral
features, such as molecular band systems, in the 1150--1700 Å far-UV
interval. The present work focuses on the B--X electronic rovibration
bands of H 2, which can be radiatively pumped by H I
λ 1215 Lyα resonance emission in stellar environments where cold
molecular gas (T&lt; 4000 K) is irradiated by hotter, chromospheric
(T ~ 104 K) material. We compare three very different
stellar objects whose only common feature appears to be extensive
fluoresced H 2 bands: The 10 Gyr old red giant Arcturus
(α Bootis; K2 III); the 10 Myr young T-Tauri star TW Hya; and
the enigmatic accretion/wind source Mira B, which apparently was
caught in a low state during the 1999 August STIS observations. We
discuss implications of spectral differences among these objects
concerning physical properties (temperatures and column densities)
in the different environments where the molecular hydrogen is pumped
(stellar “COmosphere,” PMS accretion disk, and wind-shock interaction
zone), as well as intrinsic profiles of the Lyα irradiation field,
which can be deduced free from the usual strong interstellar absorption
that affects the H I emission core. This work was supported by STScI
grant GO-08614.02-02A to the University of Colorado, and NASA grant
S-56500-D to NIST and CU. Observations were from the NASA/ESA HST,
collected at the STScI, operated by AURA, under contract NAS5-26555.

---------------------------------------------------------
Title: 3 Ms in the Life of β Ceti: Sustained Flare Activity on a
Clump Giant Detected by the Extreme Ultraviolet Explorer
Authors: Ayres, Thomas R.; Osten, Rachel A.; Brown, Alexander
2001ApJ...562L..83A Altcode:
A 34 day Extreme Ultraviolet Explorer (EUVE) pointing on the “clump”
giant β Ceti (HD 4128; K0 III) recorded a series of striking coronal
flare events, reminiscent of a singular outburst seen previously from μ
Velorum (HD 93497; G6 III + dF). The recent flaring episode contrasts
with a more placid behavior in a 6 day EUVE observation of β Cet 6
years earlier. The average 70-180 Å Deep Survey count rate in the new
observation is twice as high, and the 75-150 Å spectrum displays a
distinct hardening. The discovery of sustained flare activity on β
Cet raises the possibility that such episodes are more common than
suspected among the core helium-burning giants and sharpens the puzzle
of the survival of magnetic activity beyond helium flash.

---------------------------------------------------------
Title: Long-Slit Observations of Extended C II λ1335 Emission around
V854 Centauri and RY Sagittarii
Authors: Clayton, G. C.; Ayres, T. R.
2001ApJ...560..986C Altcode: 2001astro.ph..6529C
We have obtained long-slit far-ultraviolet (1150-1730 Å) spectra
of the R Coronae Borealis (RCB) stars V854 Cen and RY Sgr near
maximum light and pulsational phase zero with the Space Telescope
Imaging Spectrograph on board the Hubble Space Telescope. The far-UV
spectrum of each star shows a photospheric continuum rising steeply
toward longer wavelengths and a prominent emission feature at C II
λ1335. RY Sgr displays a second, but fainter, emission attributed
to Cl I λ1351 (which is radiatively fluoresced by C II λ1335),
but Cl I is weak or absent in V854 Cen. Most surprisingly, the C
II emission of V854 Cen is significantly extended along the slit by
+/-2.5", about 6×103 AU at the distance of the star. The C
II feature of RY Sgr exhibits no such gross extension. Nevertheless,
subtle broadenings of the C II emissions beyond the point response
profile suggest inner clouds of radius ~0.1" (250 AU) around both
stars. V854 Cen is only the third RCB star after R CrB and UW Cen
known to have a resolved shell. Based on observations obtained with
the NASA/ESA Hubble Space Telescope, which is operated by STScI for
the Association of Universities for Research in Astronomy, Inc.,
under NASA contract NAS 5-26555.

---------------------------------------------------------
Title: a tale of Two G Stars
Authors: Ayres, Thomas
2001cxo..prop..767A Altcode: 2001chan.prop..723A; 2001cxo..prop..723A
High-quality HETGS exposures of key coronal stars are presenting a
unique, novel view of some of the most ubiquitous high-energy phenomena
in the galaxy; and taking crucial steps toward making X-ray spectroscopy
an indispensable remote-sensing tool for Astronomy. We will focus on the
influence of stellar surface gravity by adding to our ongoing program
the active G dwarf Chi1 Orionis (G0V) and the active G giant 24 Ursae
Majoris (G4III). Chandra transmission grating spectroscopy offers
a new way to determine temperatures and densities in the hot outer
atmospheres of cool stars, probe chemical fractionation processes, and
explore plasma dynamics. Our program will add to the Chandra Emission
Line Project and help interpret lower-res XMM-Newton/RGS spectra of
fainter stars.

---------------------------------------------------------
Title: Buried Alive in the Coronal GRAVEYARD?!
Authors: Ayres, Thomas
2001cxo..prop..759A Altcode: 2001cxo..prop..713A; 2001chan.prop..713A
We propose 20 ks pointings with Chandra HRC-I to obtain detections of
3 red giants in the depths of the "coronal graveyard." Stellar coronal
activity is important to the Sun-Earth connection, to the fate of
primitive planetary atmospheres, and to a broad reaching set of magnetic
phenomena in many cosmic environments. Understanding the activity,
and its evolution, therefore is a key objective in astrophysics. The
birth of magnetic activity in young stars is well-studied; the death of
coronae in highly evolved stars is not. Our program ultimately will test
the hypothesis that significant coronal activity persists on the red
giants, but smothered beneath a "cool absorber" in the chromospheric
envelope. Such activity might be the long-sought initiator of red
giant winds.

---------------------------------------------------------
Title: Chandra HETGS and VLA Radio Observations of the Active Coronae
on the Short-Period Binary ER Vul (G0 V + G5 V)
Authors: Brown, Alexander; Osten, Rachel A.; Ayres, Thomas R.;
Harper, Graham
2001tysc.confE..46B Altcode:
We present results from a long (114 ksec) Chandra HETGS observation
of the short period (Porb = 0.69 d) active binary ER Vul,
which consists of two solar-like dwarfs with rotation rates ~ 40 times
that of the Sun. X-ray spectra were obtained on 2001 March 29-30 along
with 12 hours of simultaneous VLA monitoring at 3.6 and 20 cm. The
Chandra Medium Energy Grating (MEG) covers the wavelength range 1.8
- 25 Å in first order, while the High Energy Grating (HEG) covers
1.8-18 Å. ER Vul showed continuous low-level variability throughout
the observation with the largest flare peaking at slightly more than
twice the “quiescent” level. Contrary to the behaviour of most longer
period active binaries, no large, long-duration flares were detected,
consistent with previous X-ray observations of this binary. The largest
flare detected has a duration of only ~ 30 minutes, and appears to be
very “solar-like”. Unfortunately this flare was not observed in the
radio. The 20 cm radio emission does show a highly polarized (LCP)
flare that has at best only a weak X-ray resonse. We characterise
the flare-related variability seen in the coronal line and continuum
emission, place limits on any orbital phase-related variability, and
quantify the quiescent coronal temperature and density distributions.

---------------------------------------------------------
Title: Buried Alive in the Coronal Graveyard?
Authors: Ayres, Thomas
2001hst..prop.9273A Altcode:
We propose 20 ks pointings with Chandra HRC-I to obtain detections
of two red giants in the depths of the "coronal graveyard." Our
program will test the hypothesis that significant coronal activity
persits on the red giants, but smothered beneath a "cool absorber"
in the chromospheric envelope. Such activity might be the long-sought
initiator of red giant winds. HST/STIS E140M spectra are proposed for
one of the targets-alpha Tau {K5 III}; to help probe conditions in
the cool absorber. High-S/N STIS spectra already are available for
the other target, alpha Boo {K2 III}.

---------------------------------------------------------
Title: HST STIS Coronal Iron Survey
Authors: Ayres, T. R.; Brown, A.; Linsky, J. L.
2001AAS...198.4404A Altcode: 2001BAAS...33..845A
The broad coverage, high sensitivity, and precise wavelength calibration
of the Space Telescope Imaging Spectrograph's medium-resolution echelle
mode, coupled with the growing collection of GO and GTO E140M exposures,
are ideal for surveys of specific spectral diagnostics across a
diversity of stellar types, luminosities, and activity levels. Of great
current interest are the weak coronal forbidden lines that appear in the
far-UV, which are well known from solar flare work. Measuring coronal
lines with STIS in the 1150--1700 Å band has significant advantages
over using, say, Chandra HETGS or XMM-Newton RGS in the 1 keV range,
because the STIS velocity resolution is 40x, or more, higher; STIS has
an absolute wavelength calibration established by an onboard emission
lamp; and the large effective area of the HST telescope compensates
for the faintness of the forbidden lines. Here, we report a survey of
Fe XXI λ 1354 in a sample of ~25 stars. The forbidden iron feature
forms at a temperature of about 107 K, characteristic of
very active or flaring coronal conditions. Clear detections of the
coronal iron line are made in active M dwarfs (AU Mic, AD Leo), active
giants (α Aur, β Cet, ι Cap, 24 UMa, HR 9024), short-period RS CVn
binaries (e.g., HR 1099), and possibly in active solar-type dwarfs
(ζ Dor, χ1 Ori). We describe our semi-empirical method
for removing the C I blend that partially corrupts the Fe XXI profile,
and our measurements of coronal line widths and Doppler shifts. Although
α Aur displays clear variability between Fe XXI profiles obtained at
the same orbital phase, but four years apart; the hyperactive HR 1099
system showed virtually no change in its coronal iron feature during
a sequence of 14 spectra taken over a 7 hr period in 1999 September,
despite the occurrence of two large flares in far-UV lines such as
Si IV and C IV. This work was supported by grant GO-08280.01-97A
from STScI. Observations were from the NASA/ESA HST, collected at the
STScI, operated by AURA, under contract NAS5-26555. We thank the other
collaborators in HST program 8280 for their help in carrying out the
STIS stellar survey upon which the present study is based.

---------------------------------------------------------
Title: Chandra, EUVE, HST, and VLA Multiwavelength Campaign on HR
1099: Instrumental Capabilities, Data Reduction, and Initial Results
Authors: Ayres, Thomas R.; Brown, Alexander; Osten, Rachel A.;
Huenemoerder, David P.; Drake, Jeremy J.; Brickhouse, Nancy S.;
Linsky, Jeffrey L.
2001ApJ...549..554A Altcode:
In mid-September of 1999, a multiwavelength campaign was carried out
on the coronally active RS Canum Venaticorum binary HR 1099 (K1 IV+G5
V P=2.84 days), during commissioning of the High Energy Transmission
Grating Spectrometer (HETGS) of the Chandra X-ray Observatory (CXO). The
coordinated program involved the Extreme Ultraviolet Explorer (EUVE),
the Hubble Space Telescope Imaging Spectrograph (STIS), and the Very
Large Array (VLA). The objective was to study the system in quiescence,
across as much of the electromagnetic spectrum as practical, and to
catch any flares that might occur. The EUVE 80-180 Å light curve of
HR 1099, covering the period September 13-22, showed only a single
impulsive outburst, which occurred at the very end of the 9 day
pointing. The 3-25 Å bremsstrahlung continuum displayed an overall
decay during the 1.5 day Chandra observation on September 14-16,
with a few superimposed mild enhancements. The VLA 3.5 cm and 20 cm
radio light curves, obtained during a 10 hr period on September 15
immediately before the HST pointing, similarly revealed normal quiescent
gyrosynchrotron emission and an absence of impulsive events. In
contrast, the 7 hr STIS time series later on September 15 contained
two distinct flares. The first was accompanied by intensification of
the preexisting broad wings of the medium excitation species (e.g.,
Si IV λ1393 and C IV λ1548), while the second involved primarily
the narrow cores of the lines, and even cooler temperatures. The
Fe XXI λ1354 forbidden line showed little response to either flare,
consistent with the contemporaneous soft X-ray and EUV light curves. The
lack of coronal counterparts to the ultraviolet flares is unusual and
suggests that they belong to a separate class of outbursts, sharing
some similarities with the “transition zone explosive events”
seen on the Sun. The density sensitive O IV λ1400 multiplet was
not affected by either flare. The density sensitive Si III λ1300
multiplet showed little response to the first flare, but a dramatic
brightening in the second, likely due to the lower peak temperature
of that event. The O IV line ratios were near their low-density
limits and suggest ne~1010 cm-3
for the duration of the HST observations. The Si III ratios during
the second flare rise indicate ne~7×1010
cm-3. The far-UV diagnostics jointly imply electron pressures
of neT~2×1015 K cm-3, if formed
close to their respective ionization equilibrium temperatures. The
helium-like triplets of O VII, Ne IX, and Mg XI in the HETGS spectra
have forbidden-to-intercombination line ratios consistent with average
coronal electron densities of &lt;~1011 cm-3
at T~0.3-1×107 K over the duration of the Chandra
pointing. Fe XXI λ102/λ128 and λ142/λ128 ratios from EUVE suggest
ne&lt;~1012-1013 cm-3,
near 107 K. Thus, the coronal electron pressures could be
as much as several orders of magnitude larger than those of the lower
atmosphere. We constructed time-resolved spectra from the HETGS event
lists and measured the centroids of the three brightest X-ray lines of
HR 1099 in 60 minute bins. In high-S/N Ne X λ12.1, we believe that we
can see the changing radial velocity of the K1 IV star over the half
an orbital cycle recorded by Chandra. The amplitude of the velocity
change is only ~100 km s-1 over the 1.5 day interval,
a small fraction of the 300-500 km s-1 resolution of the
HETGS at 12 Å. Ne X λ12.1 also displayed a transient blueshift
of ~60 km s-1 immediately prior to the first STIS flare,
during which the far-UV lines briefly exhibited blueshifts of similar
magnitude. The apparent displacement of Ne X appears independently in
the -1 and +1 orders of the medium energy band (MEG), but there was no
confirmation in the redundant high energy band (HEG), nor in other X-ray
lines. Fe XXI λ1354 showed a blueshift about 30 minutes later at the
beginning of the second HST orbit, but only at the 20 km s-1
level. Analogous HETGS time series of the brightest lines of comparison
star Capella (α Aurigae G8 III+G1 III) exhibited steady behavior,
consistent with measurement uncertainties, without the transient
Doppler “bursts” seen in HR 1099. Although the reality of the Ne
X Lyα blueshift is in doubt, there is no question that the Chandra
HETGS velocity scales are stable and free from large systematic errors.

---------------------------------------------------------
Title: Stellar Coronae: New Insights into Fundamental Questions
(Invited)
Authors: Linsky, Jeffrey L.; Ayres, Tom; Brown, Alec; Osten, Rachel;
Skinner, Steve; Gagne, Marc
2001ASPC..251...22L Altcode: 2001ncxa.conf...22L
No abstract at ADS

---------------------------------------------------------
Title: Cool Flares on HR 1099 (A Saga of Joint Observations with
Chandra and HST)
Authors: Ayres, T. R.
2001ASPC..234...93A Altcode: 2001xras.conf...93A
No abstract at ADS

---------------------------------------------------------
Title: Far-UV Echelle Spectroscopy of Arcturus with HST STIS (CD-ROM
Directory: contribs/ayres)
Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.;
Linsky, J. L.; Carpenter, K. G.; Robinson, R. D.
2001ASPC..223.1079A Altcode: 2001csss...11.1079A
No abstract at ADS

---------------------------------------------------------
Title: Cool Star Chromospheres and the Sun
Authors: Linsky, J.; Redfield, S.; Ayres, T.; Brown, A.; Harper, G.
2001ASPC..242..247L Altcode: 2001ecom.conf..247L
No abstract at ADS

---------------------------------------------------------
Title: STIS Observations of the Transition Region of ζ Doradus
(CD-ROM Directory: contribs/redfield)
Authors: Redfield, S.; Linsky, J. L.; Ayres, T. R.; STIS Cycle 8 Cool
Star Survey Team
2001ASPC..223.1045R Altcode: 2001csss...11.1045R
No abstract at ADS

---------------------------------------------------------
Title: STIS Observations of the Hybrid-Chromosphere Star alpha TrA
(CD-ROM Directory: contribs/linsky2)
Authors: Linsky, J. L.; Redfield, S.; Harper, G.; Ayres, T.; Brown, A.
2001ASPC..223.1626L Altcode: 2001csss...11.1626L
No abstract at ADS

---------------------------------------------------------
Title: Magnetospheres and Winds in the Rapid Braking Zone
Authors: Ayres, Thomas
2001fuse.prop.B072A Altcode:
FUSE exposures of five late-Fearly-G giants will probe fundamental
plasma dynamics in their hot magnetized outer atmospheres; as encoded
in spectral line widths, Doppler shifts, broad components, asymmetries,
and wind-induced circumstellar absorptions. The giants lie in or near
the Rapid Braking Zone where moderate mass stars undergo a radical
transformation of their coronal outer atmospheres. We also will explore
the even more extreme extension of the RBZ to higher masses two G0
supergiants in the so-called hybrid region where hot coronae mix
freely with cool stellar winds. FUSE spectra of the key O VI λ1032
and CIII λ977 features will allow us to separate the influences of
temperature and opacity on the super-rotational broadening of the RBZ
subcoronal emissions; and will strongly complement an ongoing HST STIS
(1150--3100 A) survey of late-type stars. Our ultimate objective is
to understand stellar magnetic activity; crucial to solar-terrestrial
relations, the early evolution of solar system, and one face of a myriad
of hydromagnetic phenomena that occur in many cosmic environments
protostellar envelopes, neutron star magnetospheres, the accretion
disks of cataclysmics, and those of AGN. The dramatic, rapid magnetic
evolution of the RBZ stars allows us to view many fundamental aspects of
stellar activity---coronal structuring, heating, and angular momentum
loss---from an entirely different perspective than afforded by the
highly accessible---but singular---case of our Sun. It is through these
different perspectives that we can hope to gain new insights into the
underlying physical processes.

---------------------------------------------------------
Title: "Coronal" vs. "Noncoronal" Giants: A Spectral Comparison of
α Boo and β Gem (CD-ROM Directory: contribs/osten)
Authors: Osten, R. A.; Ayres, T. R.; Brown, A.; Linsky, J. L.
2001ASPC..223.1102O Altcode: 2001csss...11.1102O
No abstract at ADS

---------------------------------------------------------
Title: On the Temperature Structure of α TrA's Wind
Authors: Harper, G. M.; Brown, A.; Ayres, T. R.; Osten, R. A. .;
Bennett, P. D.; Linsky, J. L.; Skinner, S. L.; Redfield, S.; Baade,
R.; Reimers, D.; Andersson, B. -G.
2000AAS...197.0803H Altcode: 2000BAAS...32.1406H; 2000AAS...197..803H
We present new constraints on the wind temperature structure of the
hybrid bright-giant α TrA (K2 II) based on multi-wavelength datasets
(ATCA, HST/GHRS &amp; STIS, FUSE, ASCA). A previous study by Dupree
&amp; Brickhouse (1998), based on an ORFEUS-SPAS II spectrum, suggested
that α TrA's wind temperature was 3 x 105 K but this appears
inconsistent with the line profile shapes of lower excitation species
observed in GHRS spectra. The GHRS profiles indicate an ionization
temperature at the base of the wind of Tion &lt;= 20,000 K
(Harper 2001). We present new high sensitivity and R ~ 20,000 spectral
resolution FUSE spectra which allow us to examine the C III 977Å and
O VI line profiles in detail. Contrary to the ORFEUS-SPAS II spectra,
the O VI lines show no evidence that they are physically associated
with the stellar wind. To within the inherent uncertainties in the FUSE
wavelength scale, the O VI 1031.9Å line is symmetric when centered on
the photospheric rest frame. This indicates that (i) O VI photons are
not created within a 3 x 105 K outflow, and (ii) there is
no significant material at this temperature to scatter photons within
the wind. We also investigate the suggestion by Ayres &amp; Kashyap
(1994) that the large asymmetry observed in the H Lyα line, which is
also observed in the FUSE Lyβ profile, is a result of trace neutral
hydrogen in a high velocity (400\&gt;km\&gt;s-1) coronal
wind. This research is funded by NASA grants NAG5-9010 &amp; NAG5-3226.

---------------------------------------------------------
Title: Radio, X-Ray, and Extreme-Ultraviolet Coronal Variability
of the Short-Period RS Canum Venaticorum Binary σ2
Coronae Borealis
Authors: Osten, Rachel A.; Brown, Alexander; Ayres, Thomas R.; Linsky,
Jeffrey L.; Drake, Stephen A.; Gagné, Marc; Stern, Robert A.
2000ApJ...544..953O Altcode:
We present the results of a coordinated observing campaign on the
short-period (1.14 days) RS CVn binary σ2 Coronae Borealis
with the VLA, ASCA, and RXTE. We also discuss earlier observations
of the same system obtained by the Extreme Ultraviolet Explorer
(EUVE). Dramatic coronal variability is present in all of these
observations across the electromagnetic spectrum. σ2
CrB undergoes frequent large flares that occur close together in
time. Radio flares are unambiguously correlated with X-ray flares;
the X-ray flares peak as much as 1.4 hr before the corresponding
radio maxima. Response to flares is more rapid in higher energy
X-ray bandpasses, signaling an increase in temperature during the
course of the flare. Flares are seen more frequently in the harder
RXTE bandpass than in simultaneously taken ASCA observations. There
is greater contrast between flaring and nonflaring conditions in the
RXTE light curve. Complex flaring is seen in the radio at 3 and 6 cm,
consistent with optically thin nonthermal gyrosynchrotron emission for
most of the duration of the observation. Bursts of left-circularly
polarized emission at 20 cm lasting &lt;=15 minutes appear to be
due to a coherent emission process. EUVE spectra reveal coronal
material at ne&lt;=1012 cm-3, with
no discernible density differences between flaring and quiescent time
intervals. Quiescent ASCA spectra show lower than solar photospheric
abundances with iron depleted by a factor of 4 from the solar
photospheric value. The abundances increase during a large flare
observed with ASCA, with iron enhanced to the solar photospheric
value during the rise phase of the flare. Two-temperature fits to
extracted spectra show a low-temperature quiescent value of 8 MK and a
high-temperature component that varies from 22 MK during quiescence to
50 MK at the peak of the flare. Emission measure distributions measured
from the ASCA observations are consistent with the temperatures derived
from the discrete two-temperature fits and indicate the presence
of very hot (&gt;100 MK) plasma during the rise phase of the ASCA
flare. Many of the flares observed with EUVE, ASCA, and RXTE show a
double exponential decay phase, further highlighting the importance of
this phenomenon in diagnosing flaring conditions. We also find that
the observed second decay timescale cannot be explained by some of
the currently used flare parameterizations.

---------------------------------------------------------
Title: Origins, Structure, and Evolution of Magnetic Activity in
the Cool Half of the H--R Diagram: Progress Report on a Major HST
STIS Stellar Survey
Authors: Ayres, T. R.; Brown, A.; Drake, S. A.; Dupree, A. K.; Guedel,
M.; Guinan, E.; Harper, G. M.; Jordan, C.; Linsky, J. L.; Reimers,
D.; Schmitt, J. H. M. M.; Simon, T.
2000AAS...197.4407A Altcode: 2000BAAS...32.1472A
In early October 2000, HST completed a year and a half long ultraviolet
spectral survey of late-type stars with its Space Telescope Imaging
Spectrograph (STIS). Thirteen stars were observed, ranging over
spectral types F7--K0 on the main sequence, F8--G8 in the giant branch,
and G0--G8 in the supergiants. A total of 72 observation sequences
were executed, some consisting of several independent exposures
(up to 13: in the case of HR 1099, recorded during a long grating
observation by Chandra ). Spectra were taken in the medium resolution
echelle modes (E140M, E230M: R ~ 30--40,000) below about 2500 Å,
and in the high-resolution echelle mode (E230H: R ~ 105)
between 2500--3000 Å. For each target, about 70% of the exposure
time was devoted to the key E140M interval (1150--1700 Å). Although
the observations were collected primarily to study the magnetically
disturbed outer atmospheres of late-type stars, they also are valuable
for investigating the local interstellar medium through UV absorptions
in H 1, O 1, Fe 2, and Mg 2, and for measuring the cosmologically
significant D/H ratio. We present examples of the superb spectra
resulting from the program, and discuss some of the new insights we
have gained concerning plasma dynamics in the 105 K layers
of the stellar “transition zone;” the super-rotational broadening
of the Si 4, C 4, and N 5 emissions in Hertzsprung gap giants; and the
spectral peculiarities of the “hybrid chromosphere” supergiants. This
work was supported by grant GO-08280.01-97A from STScI. Observations
were from the NASA/ESA HST, collected at the STScI, operated by AURA,
under contract NAS5-26555.

---------------------------------------------------------
Title: Solar Spectroscopy: Infrared Emission
Authors: Ayres, T.
2000eaa..bookE2231A Altcode:
The solar infrared spectrum extends from 1 μm to 1 mm, nestled between
the well-studied visible and radio bands. The infrared is rich in
spectral proxies of temperature, velocity and magnetic field. These
range from high-excitation He I 1.083 μm, to low-excitation molecules
like carbon monoxide, hydroxyl, and even water vapor (in sunspots),
to magnetically sensitive atomic iron absorptions near 1...

---------------------------------------------------------
Title: Chromosphere: Thermal Bifurcation
Authors: Ayres, T.
2000eaa..bookE2259A Altcode:
Thermal bifurcation refers to the existence of `cool clouds' of gas
(T&lt;3500 K) at high altitudes in the solar atmosphere, within what
was thought to be a uniformly hot (T∼7000 K) CHROMOSPHERE. It also
refers to a cooling instability, promoted by carbon monoxide molecules,
which operates in places where the chromospheric mechanical heating
is weak. The cool clouds were discovered through the anoma...

---------------------------------------------------------
Title: Capella
Authors: Ayres, T.
2000eaa..bookE2397A Altcode:
Capella—the `Goat Star' in the constellation Auriga, the
`Charioteer'—is the sixth brightest star in the sky, third in the
Northern hemisphere. It is a well-known spectroscopic binary of yellow
giants, appears to form a physical system with Capella HL, an outlying
pair of RED DWARFS, and is a member of the extended Hyades MOVING GROUP
(coeval with the nuclear region of the nearby young cluster)....

---------------------------------------------------------
Title: Chandra HETG Spectroscopy of the F0 Ib Supergiant Canopus
Authors: Brown, A.; Ayres, T. R.; Osten, R. A.; Harper, G. M.
2000HEAD....5.4216B Altcode: 2000BAAS...32.1257B
The F0 supergiant Canopus (α Car) was observed by the Chandra
X-ray Observatory on 2000 July 21 for 96 ksec using the High Energy
Transmission Grating (HETG) and the ACIS-S detector. Canopus is the
nearest supergiant star at a distance of only 96 pc and undergoing
He-burning, post-M-supergiant evolution. It has a hot (107 K)
corona with log Lx ~ 29.8 erg s-1, even though it
has only a thin convection zone. The HETG data show a coronal emission
line spectrum with the strongest lines being from Fe XVII, Ne X,
and O VIII. We shall present a detailed analysis of the HETG spectra
and the first accurate description of this star's coronal temperature
distribution. These coronal properties will be compared with those
implied by earlier ASCA, EUVE, ROSAT, and Einstein observations. This
work is supported by NASA LTSA grant NAG5-3226, NASA GSRP fellowship
NGT5-50241, and the Chandra Guest Observer program.

---------------------------------------------------------
Title: Coordinated Observations of the Active Binary σ 2
CrB with Chandra, EUVE, and the VLA
Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Krishnamurthi, A.;
Linsky, J. L.
2000HEAD....5.4214O Altcode: 2000BAAS...32.1257O
We report on coordinated observations of the short-period active
binary σ 2 CrB (F6V + G0V, P orb=1.14 d) taken
with the Chandra X-ray Observatory, the Extreme Ultraviolet Explorer,
and the Very Large Array. EUVE observations span more than 7 orbital
periods of the system. Centered in the middle of the nine day EUVE
observation is a Chandra ACIS-S+HETGS grating observation lasting
85 ks and an overlapping 12 hour multifrequency VLA observation. We
discuss the coronal variability, present high-resolution X-ray spectra
and preliminary analysis including the search for flares, and tie the
thermal high temperature emission together with nonthermal coronal
emission. RAO acknowledges funding from a NASA GSRP fellowship, grant
NGT5-50241. AB and TRA acknowledge funding from NASA grant NAG5-3226,
and JLL acknowledges support from NASA through grants S-56500-D and
H-04630D.

---------------------------------------------------------
Title: Tortured Coronae in the Rapid Braking Zone
Authors: Ayres, Thomas
2000cxo..prop..561A Altcode: 2000cxo..prop..430A; 2000chan.prop..430A
Deep HETGS exposures of four key G0-G5 giants will address fundamental
questions concerning their hot magnetized coronae by determining
temperatures and densities, probing chemical fractionation processes,
and exploring plasma dynamics. The giants lie in or near the "Rapid
Braking Zone" where moderate mass stars undergo a radical transformation
of their outer atmospheres, perhaps as a relic magnetosphere is
disrupted by the onset of a solar-like dynamo. ACIS-I CCD spectra of
five G/K supergiants will explore the even more extreme extension of the
RBZ to higher masses: where hot coronae mix freely with cool stellar
winds. These are ideal targets to exploit the experience gained in
the Emission Line Project studies of the active binaries Capella and
HR 1099.

---------------------------------------------------------
Title: 71 Tauri: Hyades Enigma Resolved?
Authors: Simon, Theodore; Ayres, Thomas R.
2000ApJ...539..325S Altcode:
71 Tauri (HD 28052; F0 IV-V) is an enigmatic object for two reasons:
(1) it is the second brightest X-ray source in the Hyades, yet early
F stars as a rule are not strong coronal emitters; and (2) it lies a
magnitude above the cluster main sequence, but radial velocity studies
and speckle imaging suggest that it is single. Recently, long-slit
ultraviolet spectra of the star, obtained with the Space Telescope
Imaging Spectrograph (STIS), serendipitously have revealed the presence
of a stellar companion at a distance of 0.1" directly south of the
primary. The companion is seen only in its far-UV chromospheric emission
lines. The nature of this object cannot be determined from our STIS
spectra alone, but its high emission levels are most readily explained
if it is a close binary of coronally active dG/dK stars. The presence
of the secondary can account for the striking X-ray properties of 71 Tau
but not its unusual location in the cluster color-magnitude diagram. It
is conceivable that the primary itself is a close double of nearly equal
stars, making 71 Tau a possible quadruple system. The alternative-that
71 Tau is ~150 Myr older than other members of the Hyades, approaching
the end of core hydrogen burning for a 2 Msolar star-would
challenge the presumed synchrony of star formation in the cluster.

---------------------------------------------------------
Title: Tortured Coronae in the Rapid Breaking Zone
Authors: Ayres, Thomas
2000hst..prop.8889A Altcode:
Deep Chandra X-ray Observatory high energy transmission grating {HETGS}
exposures of three key G0-G5 giants will address fundamental questions
concerning their hot magnetized coronae by determining temperatures
and densities, probing chemical fractionation processes, and exploring
plasma dynamics. The giants lie in or near the "Rapid Braking Zone"
where moderate mass stars undergo a radical transformation of their
outer atmospheres, perhaps as a relic magnetosphere is disrupted by the
onset of a solar-like dynamo. These are ideal targets to exploit the
experience gained in the CXO "Emission Line Project" studies of the
active binaries Capella and HR 1099. For two of the targets-31 Comae
and Mu Velorum-we will obtain contemporaneous medium-resolution far-UV
echelle spectra using the HST/STIS E140M mode for 3 orbits each. The
far-UV spectra will provide a snapshot of the physical state of the
subcoronal atmosphere during each long X-ray grating exposure, and
will tie directly into the 2-25 A HETGS spectra by recording the key
Fe XXI 1354 A coronal forbidden line.

---------------------------------------------------------
Title: Chandra Sees Its First Stellar Flares: Results from Coordinated
{Chandra, EUVE, HST} STIS, and VLA Observations of HR 1099
Authors: Osten, R. A.; Ayres, T. R.; Brown, A.; Huenemoerder, D.;
Drake, J. J.; Linsky, J. L.; Brickhouse, N.
2000AAS...19511214O Altcode: 1999BAAS...31.1541O; 2000BAAS...32..877O
On September 15, 1999, the Chandra X-ray Observatory began a 36 hour
pointing on the coronally active RS CVn binary system HR 1099 (V711
Tau; K1 IV {+} dG) as part of the Emission Line Project. The High
Energy Transmission Grating Spectrometer delivered time-tagged moderate
resolution (E/Δ {E} 500--1000) spectra between 2--18 Angstroms (HEG)
and 6--30 Angstroms (MEG). Other space-based and ground facilities
participated in the campaign -- the Extreme Ultraviolet Explorer
provided 10 days of 70--170 Angstroms Deep Survey photometry and
70--300 Angstroms spectroscopy beginning September 14; HST STIS
contributed five orbits of echelle-resolution spectroscopy in the
1150--1700 Angstroms region, beginning 16 UT September 15; and the
VLA recorded 9 1/2 hours of emission at 3, 6, and 20 cm just before
the HST window. The coordinated program represented an unprecedented
opportunity to study the energetics and kinematics of stellar flares,
a trademark of active binaries like HR 1099. Sporadic flaring activity
was recorded by all the observatories, from radio to X-ray. The Chandra
MEG light curves of hydrogenic Ne X λ 12.1 and O VIII λ 19.0, derived
from 15-minute-binned spectra, exhibit a number of impulsive rises and
decays. The bright Ne X feature follows an overall velocity pattern
consistent with the 50 km s-1 orbital motion of the active
primary star during the long Chandra observation, which covered half a
binary cycle. There are a few “bursts” of Ne X velocity, including
a sustained 45 minute period of apparent 150--200 km s-1
blueshifts; immediately prior to the detection by HST STIS of a
dramatic hypersonic event in Si IV λ 1393 and C IV λ 1548, with
Doppler broadening up to +/-500 km s-1. Chandra's ability
to measure directly plasma motions in stellar coronal flare events
is a key diagnostic advance. Highlights of our initial studies of
the campaign data sets will be presented. [2mm] {Supported by NASA
(NAG5-3226) and STScI (GO-08280.01-97A).}

---------------------------------------------------------
Title: Probing the Multi-Wavelength Nature of Stellar Flares
Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Linsky, J. L.
2000AAS...196.1304O Altcode: 2000BAAS...32..691O
The Extreme Ultraviolet Explorer has been instrumental in advancing
our understanding of flares on late-type stars. Its long observations
of coronal sources for &gt; 100 ks are perfectly matched for studying
flaring variability on active binary systems, whose flaring time
scales can last for tens of hours. This ability makes EUVE an ideal
companion for multi-wavelength observations of flares, as it can
place the shorter observations of other satellites and telescopes in
perspective of the coronal variability. For example, EUVE recently
participated in a campaign to observe the RS CVn binary HR 1099
(V711 Tau) during a calibration observation with the Chandra X-ray
Observatory, with accompanying high-resolution UV coverage from HST/STIS
and radio coverage from the VLA. I will discuss the results of this
campaign as well as earlier multi-wavelength observations involving
EUVE and other satellites such as ASCA, RXTE, and BeppoSAX of flaring
variability on active binary systems. RAO acknowledges funding from a
NASA GSRP fellowship, grant number NGT5-50241. AB and TRA acknowledge
funding from NASA grant NAG5-3226 and JLL acknowledges support from
NASA through grants S-56500-D and H-04630D.

---------------------------------------------------------
Title: Stellar Activity and Outer Atmospheric Structure of Yellow
Supergiants from HST STIS and GHRS Spectroscopy
Authors: Brown, A.; Ayres, T. R.; Harper, G. M.; Osten, R. A.; Linsky,
J. L.; Dupree, A. K.; Jordan, C.
2000AAS...196.4013B Altcode: 2000BAAS...32..739B
Yellow supergiants with spectral types F-G show a complex pattern of
outer atmospheric structure with stellar wind and activity indicators
varying significantly for stars with similar positions in the H-R
diagram. The efficiency of the processes driving their stellar winds and
heating their atmospheres is critically dependent on the evolutionary
position and surface gravity of each star. We present high-resolution
ultraviolet HST/STIS and HST/GHRS spectra for a range of intermediate
mass F and G supergiants, including Alpha Car (F0 Ib), Beta Cam (G0 Ib),
Beta Dra (G2 Ib), and Epsilon Gem (G8 Ib), and compare the atmospheric
properties of these stars with lower luminosity giants and bright
giants. We provide a systematic overview of the supergiant atmospheric
properties dealing particularly with activity levels, the presence
of hot “transition region” plasma, signatures of wind outflow, and
the role of overlying cool absorbing plasma that becomes increasingly
prominent for the cooler stars like Epsilon Gem. This work is supported
by HST grants for program GO-08280 and by NASA grant NAG5-3226.

---------------------------------------------------------
Title: Does the Sun have a Full Time COmosphere?
Authors: Ayres, T. R.
2000SPD....31.1104A Altcode: 2000BAAS...32R.843A
Strong lines of the 5 μ m bands of carbon monoxide display surprisingly
cool brightness temperatures at the extreme edge of the solar disk,
and curious off-limb emissions protruding hundreds of kilometers
into the supposedly hot chromosphere, an environment too hostile for
molecules to exist. A straightforward---but controversial---proposal is
that the low chromosphere is not pervasively hot at all, but instead
is permeated by cool clouds, a “COmosphere” if you will (because
the formation mechanism originally envisioned was a CO-inspired
autocatalytic “molecular cooling catastrophe”). More recently,
Carlsson &amp; Stein have invoked a purely dynamical process to explain
the existence of molecule-laden gas at high altitudes. In their view,
the solar chromosphere is a spatially and temporally intermittent
wave-driven phenomenon; the time average thermal structure in the
classical chromospheric layers is cool, not hot. Nevertheless,
Kalkofen, Ulmschneider, &amp; Avrett have criticized several of the
key assumptions of the dynamical simulation, calling into question
the existence of a cool “part time” COmosphere. The cause of the
supraphotospheric molecular gas thus remains controversial. Here, I will
describe measurements of the off-limb emissions of CO, obtained under
exceptional observing conditions in May 1996 with the Infrared Imaging
Spectrometer (IRIS) on the 1.5-m McMath-Pierce telescope at Kitt Peak. I
will compare these data with theoretical off-limb CO simulations based
on time slices from the Carlsson-Stein dynamical model. Finally, I will
demonstrate through simple UV continuum formation models that there
need not be any contradiction between the existence of substantial
amounts of cool gas well above the classical temperature minimum,
and the observation of ubiquitous ultraviolet line and continuum
emission from the solar outer atmosphere. This work was supported by
NSF grant AST-9618505.

---------------------------------------------------------
Title: The SOHO-Stellar Connection
Authors: Ayres, Thomas R.
2000SoPh..193..273A Altcode:
The `solar- stellar connection' bridges the daytime and nighttime
communities; an essential link between the singular, but detailed,
views of our Sun, and the broad, but coarse, glimpses of the distant
stars. One area in particular - magnetic activity - has profited
greatly from the two way traffic in ideas. In that spirit, I present
an evolutionary context for coronal activity, focusing on the very
different circumstances of low-mass main-sequence stars like the Sun,
compared with more massive stars. The former are active mainly very
early in their lives, whereas the latter become coronal only near
the end of theirs, during the brief incursion into the cool half
of the Hertzsprung-Russell diagram as yellow, then red, giants. I
describe tools at the disposal of the stellar astronomer; especially
spectroscopy in the ultraviolet and X-ray bands where coronae leave
their most obvious imprints. I compare HST STIS spectra of solar-type
dwarfs - ζ Dor (F7 V), an active coronal source, and α Cen A (G2
V), near twin of the Sun - to the SOHO SUMER UV solar atlas. I also
compare the STIS line profiles of the active coronal dwarf to the
corresponding features in the mixed activity `hybrid chromosphere'
bright giant α TrA (K2 II) and the archetype `non-coronal' red giant
Arcturus (α Boo; K2 III). The latter shows dramatic evidence for a
`cool absorber' in its outer atmosphere that is extinguishing the
`hot lines' (like Si iv λ1393 and N v λ1238) below about 1500
Å; the corona of the red giant seems to lie beneath its extended
chromosphere, rather than outside as in the Sun. I present an early
taste of the moderate resolution spectra we can expect from the recently
launched Chandra X-ray Observatory (CXO), and contemporaneous STIS
high resolution UV measurements of the CXO calibration star Capella
(α Aur; G8 III + G1 III). Last, I describe preliminary results from
a May 1999 observing campaign involving SOHO SUMER, TRACE, and the
Kitt Peak Infrared Imaging Spectrometer (IRIS). The purpose was to
explore the dynamics of the quiet solar atmosphere through the key
`magnetic transition zone' that separates the kinetically dominated deep
photosphere from the magnetically dominated coronal regime. Linking
spatially and temporally resolved solar phenomena to properties of
the average line shapes (widths, asymmetries, intensity ratios, and
Doppler shifts) is a crucial step in carrying physical insights from
the solar setting to the realm of the distant stars.

---------------------------------------------------------
Title: High Resolution IR, Visible, and UV Spectroscopy of the Sun
and Arcturus
Authors: Hinkle, K.; Wallace, L.; Harmer, D.; Ayres, T.; Valenti, J.
2000IAUJD...1E..26H Altcode:
As part of our series of solar and stellar atlases, we have produced
high-resolution atlases in the infrared and visible for both the sun
and Arcturus. Samples of the spectra will be shown and information
provided on obtaining the spectra in both electronic and printed
formats. We are currently extending the spectral coverage of both
atlases into the 1200-3000 Å region of the ultraviolet. In this region
line identification can be difficult due to both unidentified spectral
features, some of which are modestly strong, and the transition of the
spectrum from absorption to emission. Selected segments from the UV
atlas will be shown. We will present a summary of atomic and molecular
features identified in cool star spectra as well as suggestions for
atomic and molecular species that need additional laboratory work.

---------------------------------------------------------
Title: The Fundamental Physical Processes Producing and Controlling
Stellar Coronal/Transition Region/Chromospheric Activity and Structure
Authors: Ayres, T. R.; Brown, A.
2000STIN...0269131A Altcode:
Our LTSA (Long Term Space Astrophysics) research has utilized
current NASA and ESA spacecraft, supporting ground-based IR, radio,
and sub-mm telescopes, and the extensive archives of HST (Hubble
Space Telescope), IUE (International Ultraviolet Explorer), ROSAT,
EUVE (Extreme Ultraviolet Explorer), and other missions. Our research
effort has included observational work (with a nonnegligible groundbased
component), specialized processing techniques for imaging and spectral
data, and semiempirical modelling, ranging from optically thin emission
measure studies to simulations of optically thick resonance lines. In
our previous LTSA efforts, we have had a number of major successes,
including most recently: organizing and carrying out an extensive
cool star UV survey in HST cycle eight; obtaining observing time
with new instruments, such as Chandra and XMM (X-ray Multi-Mirror)
in their first cycles; collaborating with the Chandra GTO program and
participating with the Chandra Emission Line Project on multi-wavelength
observations of HR 1099 and Capella. These are the main broad-brush
themes of our previous investigation: a) Where do Coronae Occur in the
Hertzsprung-Russell Diagram? b) Winds of Coronal and Noncoronal Stars;
c) Activity, Age, Rotation Relations; d) Atmospheric Inhomogeneities;
e) Heating Mechanisms, Subcoronal Flows, and Flares; f) Development
of Analysis and Modelling Tools.

---------------------------------------------------------
Title: Origins, Structure, and Evolution of Magnetic Activity in
the Cool Half of the H--R Diagram: an HST STIS Survey
Authors: Ayres, T. R.; Brown, A.; Drake, S. A.; Dupree, A. K.; Guedel,
M.; Guinan, E.; Harper, G. M.; Jordan, C.; Linsky, J. L.; Reimers,
D.; Schmitt, J. H. M. M.; Simon, T.
1999AAS...195.5013A Altcode: 1999BAAS...31Q1449A
In HST's cycle 8, we are carrying out a major ultraviolet spectral
survey of late-type stars using the powerful capabilities of the
Space Telescope Imaging Spectrograph (STIS). The origin of the hot
UV emissions of otherwise cool stars is a fundamental puzzle in
astrophysics. Magnetic phenomena---at the heart of chromospheric and
coronal activity, and perhaps wind driving as well---play a central
role in many cosmic settings. Our objective is to obtain high-quality
ultraviolet spectra of a diverse collection of F--K stars, of all
luminosity classes. Such a major project was unthinkable before
STIS, but now is practical given the high resolution, broad spectral
coverage, and sensitivity of the second generation spectrograph. Here,
we discuss our choice of the thirteen targets; the observing strategy
(which captures the entire UV spectrum between 1150--3000 Angstroms
at resolutions λ /δ λ 30--100*E3 with good S/N); and
preliminary results for the several targets observed to date (ζ Dor, F7
V, 1 May 1999, 2 CVZ orbits; V711 Tau, K1 IV+G5 IV, 15 September 1999, 5
orbits; β Cam, G0 I, 19 September 1999, 4 CVZ orbits). The observation
of V711 Tau (HR 1099) was carried out during a long transmission grating
pointing by the Chandra X-ray Observatory, in support of its “Emission
Line Project.” This work was supported by grant GO-08280.01-97A from
STScI. Observations were from the NASA/ESA HST, collected at the STScI,
operated by AURA, under contract NAS5-26555.

---------------------------------------------------------
Title: Detections of CO in the Circumstellar Shells of R Coronae
Borealis Stars
Authors: Clayton, G. C.; Hanson, M. M.; Gordon, K. D.; Ayres, T. R.
1999AAS...195.4513C Altcode: 1999BAAS...31Q1438C
It has been known for 60 years that the declines of R Coronae Borealis
(RCB) stars are caused by circumstellar dust formation. The declines
occur suddenly and without warning. No spectroscopic changes have yet
been noted near the beginning of the decline, which might be linked to
the cooling gas that must be condensing to form the dust. The mechanism
of mass loss and dust formation is still a mystery. New observational
evidence along with models of the carbon chemistry around RCB stars
suggest that dust may condense close to the star. Shocks propagating
through the outer atmospheres encourage non-equilibrium conditions
where the conditions for carbon nucleation may be present. CO is thought
to be a critical gas coolant in this process. We report detections of
the CO 4th positive system lines in STIS UV spectra of two RCB stars
and of the CO v=2 bands in the near-IR for several RCB stars. These
observations are being used to model the temperature and density of
condensing gas around these stars.

---------------------------------------------------------
Title: The Rise and Fall of μ Velorum: A Remarkable Flare on a
Yellow Giant Star Observed with the Extreme Ultraviolet Explorer
Authors: Ayres, Thomas R.; Osten, Rachel A.; Brown, Alexander
1999ApJ...526..445A Altcode:
The close visual double μ Velorum (HD 93497; G6 III+dF) consists of
a yellow giant and a fainter companion currently 2" apart. Recently μ
Vel was the source of a large flare recorded by the Extreme Ultraviolet
Explorer. The long 1.5 day decay phase was like the extremes seen
on hyperactive RS CVn-type binaries. The primary, μ Vel A is a 3
Msolar star, in the “rapid braking zone” redward of G0
III. Yellow giants are not commonly reported as flare stars, perhaps
because the first-crossers are relatively rare and not well represented
in the observational samples. The secondary star is classified G2 V, but
the 1700 Å energy distribution places it earlier on the main sequence,
probably F4 or F5 V, in a class also not usually known for coronal
variability. The long duration of the μ Vel event suggests that it
occurred in a significantly elongated structure of moderate density,
ne&lt;~109 cm-3. If it was a magnetic
plasmoid, like a coronal mass ejection on the Sun, then such events
might play a role in shedding angular momentum from active evolved
stars. The associated spin-down could control the activity survival time
of red giants (in later stages of evolution than the first-crosser μ
Vel) whose dynamos were rejunvenated by dredge-up of angular momentum
from the interior, or more exotic sources, such as cannibalism of
close-in substellar companions during the first or second ascent.

---------------------------------------------------------
Title: Sleuthing the Dynamo. II. Hubble Space Telescope Goddard High
Resolution Spectrograph Observations of Solar-Type Dwarfs in Young
Galactic Clusters
Authors: Ayres, Thomas R.
1999ApJ...525..240A Altcode:
Far-ultraviolet (1150-1670 Å) spectra of three solar-type dwarfs in
the young galactic clusters α Persei and the Pleiades were obtained
with the Hubble Space Telescope Goddard High-Resolution Spectrograph
(G140L mode). Time series of Si IV λ1393 show erratic variability on
timescales of tens of minutes. An X-ray/C IV flux-flux diagram displays
a power-law slope of ~2, up to the level of the most active cluster
stars. These fall systematically below the extrapolation owing to X-ray
“saturation.” In rotation-activity diagrams, the X-rays plateau above
~15 km s-1 (P~3 days), while C IV continues to rise until
~35-50 km s-1 (P~1-1.5 days). Such behavior is significant
for understanding the magnetic “dynamo” at high rotational velocities
and is relevant for predicting the ionizing environment bathing newly
formed planets around low-mass main-sequence stars.

---------------------------------------------------------
Title: Digging Deeper in the Coronal Graveyard: Postscript
Authors: Ayres, Thomas R.
1999ApJ...525.1009A Altcode:
An X-ray upper limit--from the ROSAT High Resolution Imager--is
presented for ɛ Corvi (HD 105707), a K2 giant that lies in the
“noncoronal” zone of the Hertzsprung-Russell diagram, but which
previously was detected by the Hubble Space Telescope Goddard High
Resolution Spectrograph in far-ultraviolet coronal proxies. The new
measurement strengthens the anticorrelation between coronal X-rays
and λ1380 carbon monoxide emission among the red giants.

---------------------------------------------------------
Title: Origins, Structure and Evolution of Magnetic Activity in the
Cool Half of the H-R Diagram: A STIS Survey
Authors: Ayres, Thomas
1999hst..prop.8280A Altcode: 1999hst..prop.4614A
We propose to carry out a major ultraviolet spectral survey of "coronal"
late-type stars using the powerful capabilities of STIS. The origin of
the hot UV emissions of otherwise cool stars is a fundamental puzzle in
astrophysics, and is linked closely with another long-standing mystery,
that of late-type winds. Stars are the powerhouses and chemical
factories of galaxies. The source of their ionizing radiations and
the driving of their mass loss are of paramount importance in studies
ranging from population synthesis, galactic chemical evolution,
and cosmic rays to planetary atmospheres and terrestrial "space
weather." Magnetic phenomena--at the heart of coronal activity and
perhaps wind driving as well--are crucial in many cosmic settings,
particularly dynamic environments such as associated with accretion
and mass-transfer. Stars are accessible "laboratories without walls"
in which to study the interplay of magnetic and plasma processes, and
seek a unification with the h ig hly refined--but singular--portrait
of the Sun painted by an array of recent orbiting observatories. The
missing link: high-quality ultraviolet spectra of a diverse collection
of late-type stars. Such a major project was unthinkable before STIS,
but the high resolution, broad spectral coverage, and sensitivity of
the second generation spectrograph can capture the stellar equivalent
of a Hubble Deep Field.

---------------------------------------------------------
Title: STIS UV Atlas of the Red Giant Arcturus(1)
Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.;
Linsky, J. L.; Carpenter, K. G.; Robinson, R. D.
1999AAS...194.6701A Altcode: 1999BAAS...31..930A
The Space Telescope Imaging Spectrograph (STIS) conducted a series
of observations of the archetype “noncoronal” red giant Arcturus
(HD 124897; alpha Boo; K1 III) on 24 August 1998, 17--23 UT. The STIS
program was the result of a failed cycle 5 pointing, which could not
be rescheduled during the abbreviated cycle 6, and was carried over
to cycle 7. Three grating settings---E230H (t_exp= 1340 s), E230M
(2493 s), and E140M (5208 s)---covered the ultraviolet spectrum
from 1150--2850 Angstroms, at resolutions between R ~ 4*E(4) -
1*E(5) , with essentially no gaps. The resulting spectrograms are
stunning. The resolution is very high, as is the S/N; the spectral
coverage is broad and comprehensive. The far-UV interval (1150--1700
Angstroms) is a rich emission line spectrum, dominated by the broad
resonance transitions of atomic hydrogen (lambda 1215) and oxygen
(lambda 1305 triplet). There are numerous narrow emissions, mostly
from low-excitation species such as Si I, Fe II, and fluoresced bands
of carbon monoxide. Surprisingly, high-excitation species---Si IV
(lambda 1393: 6*E(4) K) and C IV (lambda 1548: 1*E(5) K)---are present
as well (as seen in the earlier “failed” GHRS spectra). The mid-UV
(1700--2600 Angstroms) shows additional emission lines, particularly [C
II] and [Si II] in the 2325 Angstroms region; the photospheric continuum
rises strongly toward the longer wavelengths. The 2600--2850 Angstroms
interval is mostly a photospheric absorption spectrum, although the
bright chromospheric emission doublet of Mg II lords over the 2800
Angstroms region. We present a comprehensive spectral atlas based on
our reductions of the STIS echellograms. We discuss the processing
strategies, line identifications, and some of the preliminary results
from our analysis of this windy, noncoronal giant. (1) This work was
supported by grants GO-06066.01-94A from STScI, and NAG5-3226 from
NASA. Observations were from the NASA/ESA HST, collected at the STScI,
operated by AURA, under contract NAS5-26555.

---------------------------------------------------------
Title: The Magnetic Lives of Giant Stars
Authors: Ayres, T. R.; Brown, A.
1999HEAD....4.0904A Altcode: 1999BAAS...31..705A
After two decades of study by high-energy missions---beginning with
HEAO-1 and Einstein, and extending more recently to ROSAT, EUVE,
ASCA and BeppoSAX---the evolution of coronal magnetic activity of
evolved stars has come into sharper focus. We present a synthesis
of ideas advanced to explain the various coronal peculiarities of
late-type giants, ranging from the “X-ray deficiency” of the F--G0
III Hertzsprung gap stars, the “rapid braking zone” in the yellow
giants (mid-G), and the “coronal graveyard” redward of K0 III. The
main source of the diversity of coronal behavior among the giant
stars is the wide range of main sequence progenitors whose post-MS
evolution converges in the relatively small region of the H--R diagram
appropriately called the red giant “clump.” Common threads are:
relic magnetospheres from hot-star predecessors; the tension between
direct convectively generated magnetic flux (the so-called “magnetic
carpet” fields on the Sun) and the large scale rotation-catalyzed
“dynamo;” activity-assisted mass loss and spindown; and coronal
rejuvenation (through spin-up via internal redistribution of angular
momentum, or engulfment of a substellar companion). The new generation
of X-ray missions---AXAF and XMM---can test many of these ideas through
moderate-resolution spectroscopy of the coronal plasmas, to complement
ongoing high-resolution dissection of the subcoronal layers by HST
(earlier GHRS, now STIS) and soon FUSE. This work was supported by
grant NAG5-3226 from NASA to the University of Colorado.

---------------------------------------------------------
Title: First Observations of an R Coronae Borealis Star with the
Space Telescope Imaging Spectrograph: RY Sagittarii near Maximum Light
Authors: Clayton, Geoffrey C.; Ayres, T. R.; Lawson, Warrick A.;
Drilling, John S.; Woitke, P.; Asplund, Martin
1999ApJ...515..351C Altcode:
We describe the far-UV (1140-1740 Å) spectrum of the hydrogen-deficient
R Coronae Borealis (RCB) star RY Sgr, obtained near maximum light
(pulsational phase ~0.1) by the Space Telescope Imaging Spectrograph
(STIS) on Hubble Space Telescope. The far-UV spectrum shows a
photospheric continuum rising steeply toward longer wavelengths and
two prominent emission features at the shorter wavelengths: C II λ1335
and Cl I λ1351 (the latter is radiatively fluoresced by the 10 times
stronger C II multiplet). We also find evidence for CO A-X 4th-positive
system absorption band heads and possible weak CO fluorescent emissions
pumped by C II λ1335, but the inferred column densities are low (~few
times 1016 cm-2), consistent with formation in
a warm (~5000 K) atmospheric layer. The detection of CO molecules,
if confirmed, would be significant, because they are thought to
play a key role in the dust ejection episodes of RCB stars through
the initiation of “molecular cooling catastrophes.” Based on
observations obtained with the NASA/ESA Hubble Space Telescope, which
is operated by STScI for the Association of Universities for Research
in Astronomy Inc. under NASA contract NAS 5-26555.

---------------------------------------------------------
Title: High-Resolution Thermal Infrared Imaging of the Sun: A
Pipe Dream?
Authors: Ayres, T.
1999ASPC..183..186A Altcode: 1999hrsp.conf..186A
No abstract at ADS

---------------------------------------------------------
Title: The SOHO-Stellar Connection
Authors: Ayres, Thomas R.
1999STIN...9914314A Altcode:
I discusses practical aspects of the so-called "solar-stellar"
connection; namely, the fundamental principles, the tools at the
disposal of the stellar astronomer, and a few recent examples of the
connection in action. I provide an overall evolutionary context for
coronal activity, calling attention to the very different circumstances
of low mass main sequence stars like the Sun, which are active mainly
early in their lives; compared with more massive stars, whose coronally
active phase occurs near the end of their lives, during their brief
incursion into the cool half of the Hertzsprung-Russell diagram as
yellow and then red giants. On the instrumental slide, I concentrate
primarily on spectroscopy, in the ultraviolet and X-ray bands where
coronae leave their most obvious signatures. I present an early glimpse
of the type of moderate resolution spectra we can expect from the
recently launched Chandra observatory, and contemporaneous HST STIS
high-resolution UV measurements of the CXO calibration star Capella
(alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type
dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A
(G2 V), a near twin of the Sun-to a trace obtained with the SOHO
SUMER imaging UV spectrometer. I also compare STIS line profiles of the
active coronal dwarf to the corresponding features in the mixed-activity
"hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype
"noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows
dramatic evidence for a "cool absorber" in its outer atmosphere
that is extinguishing the "hot lines" (like Si IV lambda1393 and
N V lambda1238) below about 1500 A, probably through absorption in
the Si I lambda1525 and C I lambda1240 photoionization continua. The
disappearance of coronae across the "Linsky-Haisch" dividing line near
K1 III thus apparently is promoted by a dramatic overturning in the
outer atmospheric structure, namely the coronae of the red giants seem
to lie beneath their extended chromospheres, rather than outside as in
the Sun. I then discuss an intriguing long-slit STIS low-resolution
observation of an X-ray active late-A dwarf in the nearby Hyades
cluster: the spatially resolved UV spectroscopy clearly shows that a
previously unseen close companion (a dKe or dMe) likely is responsible
for the coronal activity, rather than some unexplained departure of the
A dwarf from its expected state of X-ray dormancy. Finally, I describe
early results from a joint observing campaign involving SOHO SUMER,
TRACE, and the Kitt Peak Infrared Imaging Spectrometer, conducted May
1999, to explore the dynamics of the quiet solar atmosphere through
the key "magnetic transition zone" that separates the kinetically
dominated deep photosphere from the magnetically dominated coronal
regime. Linking spatially and temporally resolved solar properties to
aspects of the averaged lineshapes (for example: widths, asymmetries,
intensity ratios, and Doppler shifts) is a crucial step in carrying any
physical wisdom we develop in the solar setting to the distant stars.

---------------------------------------------------------
Title: The SOHO-Stellar Connection
Authors: Ayres, Thomas R.
1999STIN...9914301A Altcode:
Objective was to conduct a variety of observing programs with the
SUMER spectrometer on SOHO, in order to further the understanding of
the solar-stellar connection. The program was a continuation of SOHO
GO program NAG5-6124 of the previous year.

---------------------------------------------------------
Title: A Search for an Emission-Line Region in the Hydrogen-deficient
Carbon Star HD 182040
Authors: Brunner, Andrew R.; Clayton, Geoffrey C.; Ayres, T. R.
1998PASP..110.1412B Altcode:
A long-exposure short-wavelength IUE spectrum of the hydrogen-deficient
carbon (HdC) star HD 182040 does not show any detectable emission in
the C II lambda1335 line. It is not certain whether this absence of
emission is intrinsic or due to the large uncertainties in the distance,
absolute luminosity, and reddening toward HD 182040. If intrinsic,
this absence of emission along with the absence of an IR excess from
circumstellar dust imply that little or no mass loss is occurring at
present from this star even though it is very similar spectroscopically
to the R Coronae Borealis (RCB) stars. This result also suggests that
the emission-line gas and the circumstellar dust may result from the
same mass-loss mechanism in the RCB stars.

---------------------------------------------------------
Title: The Rise and Fall of MU Velorum
Authors: Ayres, T. R.; Osten, R. A.; Brown, A.
1998AAS...193.4602A Altcode: 1998BAAS...30.1320A
Mu Velorum (HD 93497) is a close visual pair consisting of a G5 III
primary and a fainter companion, currently 2” apart, with an orbital
period of about 140 yr. The distance to the system is 36 pc. Mu Vel
A is a 3 Msun giant, in the Hertzsprung gap beyond the
“rapid braking zone” just redward of G0 III. Mu Vel recently was
the source of a giant EUV flare, caught during a 12-day pointing in
March 1998 by the Deep Survey telescope of the Extreme Ultraviolet
Explorer. The outburst rose in less than half a day, and decayed with
an e-folding time of several days. The peak flux, ~ 0.3 cnts s(-1) in
the DS band 80--180 Angstroms, was approximately twice the quiescent
level recorded during the previous ten days of observation. The size
and long duration of the event are very unusual for a mid-G giant;
in fact, more typical of the extremes seen among the hyperactive
short-period RS Canum Venaticorum binaries. Although the secondary
star is classified as a G2 V, published visual magnitude differences,
and the enhanced 1900 Angstroms continuum (mu Vel was detected by IUE,
but AB were not resolved), suggest that it falls earlier on the MS
(perhaps F5 V) and indeed itself might be a pair. If mu Vel B is a
short-period double, then arguably it could be the source of the
giant flare. Unfortunately, little is known about the secondary
owing to the small separation of the visual components of mu Vel,
and their large difference in brightness. We discuss the flare event,
EUV spectra obtained in quiescence and during the flare decay, and
the nature of the puzzling secondary. [2mm] This work was supported
by NASA grant NAG5-3226.

---------------------------------------------------------
Title: High-Excitation Emission Lines in the Far-Ultraviolet Spectrum
of the Late A Star α Cephei
Authors: Simon, Theodore; Ayres, Thomas R.
1998ApJ...500L..37S Altcode:
The A7 V star α Cephei lies in a region of the Hertzsprung-Russell
diagram that is generally thought to be devoid of solar-like
magnetic activity. The far-ultraviolet spectrum of this star was
observed with the Berkeley spectrograph during the 1996 ORFEUS-SPAS
II mission. We detected emission lines of Si III, C III, and O VI
in the 900-1200 Å interval, spanning formation temperatures of
2×104-3×105 K. The normalized strengths of
these lines, \RscrL≡fL/fbol,
are within a factor of 2 of solar values. Lines of two C III
multiplets in the ORFEUS spectrum yield an electron density
estimate, ne~109.4+/-0.3, at a temperature
of ~6×104 K. The corresponding electron pressure,
p≡neT~1014.2+/-0.3, is similar to that of the
average Sun, but several times smaller than previous estimates made
for other late-type G-K stars. At higher temperatures, the normalized
flux ratio for coronal soft X-rays is 20 times less for α Cep than it
is for the Sun. This greatly reduced X-ray brightness suggests that
the outer atmosphere of α Cep differs strikingly from that of the
average Sun, being more akin to a low-density “coronal hole.”

---------------------------------------------------------
Title: PHOENIX IR Spectra of CO in the Sun and the Stars
Authors: Ayres, T. R.; Valenti, J. A.; Hinkle, K. H.; Johns-Krull,
C. M.; Wiedemann, G. R.
1998AAS...192.6709A Altcode: 1998BAAS...30..918A
We report high-resolution (R ~ 5*E(4) ) spectra of the 2143 cm(-1)
(4.7 mu m) interval---containing lines from the fundamental (Delta v
=1) bands of carbon monoxide---in the Sun and other late-type stars,
obtained with the PHOENIX cryogenic infrared spectrometer. The solar
work was conducted at the McMath-Pierce telescope during the period
21--26 April 1997, while the stellar observations were obtained on
the night of 6 December 1997 at the Kitt Peak 2.1-m. Comparisons of
spatially-averaged spectra from the long-slit observations of the
Sun with very high-resolution Fourier transform spectrometer scans
permitted an evalution of the PHOENIX instrumental profile (affected
by flexing of the grating owing to unequal thermal coefficients of
the epoxy replica and the silicon substrate). The profile information
subsequently was applied in comparisons of the stellar data sets
with CO spectra synthesized using a variety of prototype thermal
structure models. On the stellar side, we concentrated on bright
K-type giants whose broad CO profiles are fully resolved at PHOENIX
resolution. Our intent was to test the degree of thermal heterogeneity
in the outer layers of the red giant atmospheres; analogous to the
“thermal bifurcation” effects deduced in the solar context (namely,
the dichotomy between classical hot chromosphere and the controversial
cool “COmosphere”). Our spectral analyses provide a preview of the
power of PHOENIX for high-resolution infrared spectroscopy of stars; to
be realized in the coming months when the original grating is replaced
with an improved version. [-2mm] The observations were obtained at
the National Optical Astronomy Observatories, which is operated by
AURA, Inc., under a cooperative agreement with the National Science
Foundation. This work was supported by NSF grant AST-9618505.

---------------------------------------------------------
Title: The Coronae of Moderate-Mass Giants in the Hertzsprung Gap
and the Clump
Authors: Ayres, Thomas R.; Simon, Theodore; Stern, Robert A.; Drake,
Stephen A.; Wood, Brian E.; Brown, Alexander
1998ApJ...496..428A Altcode:
We have used the Röentgensatellit (ROSAT), the Extreme Ultraviolet
Explorer (EUVE), and the Hubble Space Telescope (HST) to measure X-ray
and ultraviolet emissions of moderate-mass (~2-3 M⊙)
giants in the Hertzsprung gap (spectral types early F to mid-G)
and the post-helium flash “clump” (~G8-K0). Our motivation was to
document the evolution of hot coronae (T &gt; 106 K) along
the post-main-sequence trajectories traveled by such stars in order to
gain insight concerning the “X-ray deficiency” of the F-G0 giants
and the strong braking of stellar rotation at the red edge of the
Hertzsprung gap. With few exceptions, Hertzsprung gap and clump
giants observed by ROSAT PSPC show hot (T ~ 107 K) coronal
energy distributions, regardless of any X-ray deficiency. EUVE spectra
of gap star 31 Com (G0 III) indicate a broad coronal emission measure
hump at ~107.2 K, while the active clump giant β Ceti (K0
III) displays a sharp peak at ~106.8 K, as seen previously
in the mixed clump/gap binary Capella (α Aur: G8 III + G0 III). The
gap giants υ Peg (F8 III) and 24 UMa (G4 III) have EUV emissions of
intermediate temperature (~107.0 K). The stars 31 Com,
ψ3 Psc (G0 III), and β Cet exhibit redshifted transition
zone (TZ: ~105 K) lines in HST GHRS spectra, as reported
earlier in Procyon (α CMi: F5 IV-V) and Capella G0. Such redshifts
on the Sun are thought to signify flows in magnetic loops. β Cas
(F2 III)--a rare soft coronal source among the gap stars--displays
blueshifts of C IV and O IV], although emissions at cooler and hotter
temperatures are near the photospheric velocity. The remarkably broad
line profiles of the fastest rotating gap giants suggest that the
105 K “subcoronal” emission zones extend to h~R*
above the photosphere, about 50 scale heights. In contrast
to the TZ line redshifts, the upper chromospheric emissions (e.g.,
Mg II and Si III) of 31 Com and ψ3 Psc have blueshifted
cores. Blue-asymmetric peaks in the solar Mg II lines are thought
to indicate dynamical heating in the chromosphere. Observations of
the H I Lyα feature of 31 Com taken 9 months apart reveal striking
profile changes, reminiscent of those noted previously in the Lyα
blue peak of the Capella G0 star. We used the far-ultraviolet
diagnostics, in combination with ROSAT X-ray photometry and EUVE
high-excitation line strengths, to constrain physical models of the
stellar outer atmospheres. Quasi-static magnetic loops can simulate
the empirical coronal emission measures of the giant stars, but the
inferred pressures for sensible loop lengths conflict with direct
measurements of subcoronal densities. Furthermore, the high rate of
emission at ~105 K cannot be explained by thermal conduction
down the legs of hot quasi-static loops. On the other hand, the
possible existence of elongated (l ~ R*) emission structures
on the gap giants leads to a speculative scenario to explain the X-ray
deficiency. It is based on the increased importance of the dynamical
filling phase (“explosive evaporation”) of the loop life cycle;
conductive cooling, yielding TZ emissions at the footpoints, when the
heating is interrupted; and the possibility for transitions between
“hot” and “cool” energy balance solutions owing to dynamical
suspension and centrifugal trapping of the cooling gas. The long
loops might represent a vestigial global “magnetosphere” inherited
from the main-sequence phase, which ultimately is disrupted near ~G0
by the deepening convective envelope and growth of a more solar-like
dynamo. Coronal emissions might be boosted temporarily as the X-ray
deficiency is removed but soon would be quenched by wind braking
previously inhibited by the magnetospheric “dead zone.”

---------------------------------------------------------
Title: Flaring on RS CVn systems: Results from EUVE Photometry
Authors: Osten, R. A.; Brown, A.; Ayres, T. R.
1998ASPC..154.1540O Altcode: 1998csss...10.1540O
We present broadband EUV photometry for a sample of RS CVn systems
observed with the Deep Survey Spectrometer and Right Angle Program (RAP)
Scanners on the Extreme Ultraviolet Explorer (EUVE). We have developed
robust data analysis and light curve software for the interpretation
of these data. Large-scale flaring activity is seen on 15 of the 18
systems studied. These binaries cover a range in orbital period of
0.7 days to 21 days and include a mixture of giant, subgiant, and
dwarf luminosity classes. For many systems the photometric coverage
extends over several orbital periods and flaring is unambiguously
characterized. We present statistics on the distribution of variability
in the survey. Correlations of flaring with binary properties are
examined.

---------------------------------------------------------
Title: Chromospheric Structure and Dynamics-Observations
Authors: Ayres, Thomas R.
1998ASPC..140..209A Altcode: 1998ssp..conf..209A
No abstract at ADS

---------------------------------------------------------
Title: CO and the temperature structure of the solar atmosphere
Authors: Ayres, T. R.
1998IAUS..185..403A Altcode:
The surface layers of the Sun provide a crucial boundary condition
for many of the processes that occur in the deep interior. The
stratification of the outer solar atmosphere once was thought to be
well understood. However, studies of thermally sensitive molecular
absorptions in the infrared revealed puzzling anomalies. Strong lines
of the CO fundamental vibration-rotation bands near 5 microns showed
very cool temperatures at the extreme limb, and remarkable off-limb
emissions extending well into the supposedly hot chromosphere. The
conflicting pictures of the photosphere/chromosphere interface, from
the widely separated wavelength regimes, has raised suspicions that
those “layers” of the atmosphere are much more inhomogeneous than
previously suspected. One proposal is that the low chromosphere is
dominated by cool gas---the “COmosphere,” if you will---which is
threaded by a network of persistent small-scale hot magnetic filaments
and occasionally disrupted by localized acoustic disturbances. The
COmosphere is capped by the merged fields of the network elements in
the chromospheric “canopy.” I will describe the evidence in favor of
that model, including recent work at the NSO McMath-Pierce telescope
(including use of the new “Phoenix” spectrometer) and translimb
far-UV spectroscopy by SOHO/SUMER.

---------------------------------------------------------
Title: Why Solar Analogs?
Authors: Ayres, Thomas R.
1998saco.conf..155A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thirty Days in the Life of Beta Ceti
Authors: Ayres, Thomas R.
1998euve.prop...23A Altcode:
Coronal flares are common among short-period RS CVn-type binaries;
easy and valuable targets for EUVE. Less well known, but equally
enigmatic, are flares on normal single stars; particularly G/K giants,
whose coronal variability has been poorly documented. For such stars,
flare-associated mass ejections might promote angular momentum loss,
thereby controlling the lifetime of their magnetic activity (which
possibly can be rejuvenated by cannibalism of hot Jupiters!). We
propose to obtain an unprecedented 30-day history of the EUV behavior
of the archetype active single K0 III giant, Beta Ceti. DS photometry
will enable an inventory of flare sizes and frequencies, while the
spectrometers will secure high-S/N emission line diagnostics during
the quiescent periods, and hopefully also flare decays, for use in
semiempirical modeling. The ability to record high-quality spectra over
usefully-long time intervals is a unique, vital advantage of EUVE that
should be exploited to the fullest extent possible during its final
cycle. The study of magnetic activity, and its natural variability,
impacts diverse fields of research including: stellar evolution,
Sun-Earth relations, and ionizing radiation environments of evolving
planetary systems.

---------------------------------------------------------
Title: Digging Deeper in the Coronal Graveyard
Authors: Ayres, Thomas R.; Brown, Alexander; Harper, G. M.; Bennett,
P. D.; Linsky, J. L.; Carpenter, K. G.; Robinson, R. D.
1997ApJ...491..876A Altcode:
Soft X-ray detections of stellar coronae (T ~ 106 K) are
rare in the giant branch redward of ~K1 III. We have conducted a less
direct--but more sensitive--search using the Hubble Space Telescope
Goddard High-Resolution Spectrograph to probe for far-ultraviolet
proxies of the hot coronal gas in representative “noncoronal”
red giants. In every target so far examined, we find weak but
statistically significant Si IV emission, as well as, commonly,
C IV and, in some cases, N V. Si IV is not affected by the CNO
anomalies produced by the first dredge-up, which can deplete the
carbon abundance and weaken C IV. In the low-activity giants,
the λ1393 component of the Si IV doublet must be corrected
for sharp absorptions, which we believe are caused by carbon
monoxide in overlying cool material. The normalized flux ratios
(\Rscr≡f/fbol) of Si IV and X-rays among the “coronal”
yellow giants (lying just blueward of the “noncoronal” zone) fall on a
uniform track, \RscrX~\Rscr2SiIV. In
the noncoronal zone, however, the Si IV index is nearly constant
(\RscrSiIV~10-8), independent of \RscrX
(which ranges from ~10-8 to &lt;~10-10). The
mechanism that diminishes X-ray activity in the red giants is highly
sensitive to an as yet unidentified stellar property. Photoelectric
absorption by cool gas might play a more important role than previously
suspected, particularly if hot magnetic loops are partly or completely
buried in the chromosphere.

---------------------------------------------------------
Title: Far-UV Spectra of Solar Proxies in Young Galactic Clusters
Authors: Ayres, T. R.
1997AAS...191.1307A Altcode: 1997BAAS...29.1230A
Solar magnetic activity is of special interest to solar-system
physicists who study its influence on planetary atmospheres, and to
stellar astronomers who study its analogs on other stars. The stars,
in particular, tell us what solar activity might have been like
in the Sun's youth, or its distant future; and provide insights
into the fundamental stellar parameters---and underlying physical
mechanisms---that drive it. I describe recent HST GHRS low-resolution
( ~ 1 Angstroms) far-ultraviolet spectra, and archival ROSAT X-ray
photometry, of two G-type dwarf stars in the young open cluster alpha
Persei (t ~ 50 Myr), and of the Pleiades G dwarf H II 314 (t ~ 70
Myr). The young galactic cluster stars provide convenient surrogates
for the hyperactive neonatal Sun, corresponding to the Hadean era
when planetary surfaces were forming. I compare the new results
with previous measurements of field and cluster stars of a range of
activity levels, including earlier FOS spectra of alpha Per, Pleiades,
and Hyades members. The solar-type stars follow a nonlinear (alpha
=2 power law) relation in an X-ray/C IV flux-flux diagram, although
the most active members of the sample fall away from the main trend,
showing a saturation in X-rays. Stellar rotation is a key factor setting
the activity level, presumably via the dynamo. The decline of rotation
with advancing age in single stars (owing to wind-induced spindown)
leads to the age--activity relation. The subcoronal f_C IV/f_bol flux
ratio apparently follows a simple power law up to v_rot ~ 50 km s(-1)
, and only the very fast rotating alpha Per star HE 699 appears to
deviate. In contrast, saturation (away from the alpha ~ 3 power law)
occurs in the X-ray diagram at only ~ 20 km s(-1) , affecting all
of the alpha Per stars, and the Pleiad H II 314. Unlike the previous
FOS measurements of H II 314, there did not appear to be any dramatic
flare activity during the more recent GHRS exposures. This work was
supported by grant GO-06795.01-95A from STScI.

---------------------------------------------------------
Title: Steps toward Determination of the Size and Structure of the
Broad-Line Region in Active Galactic Nuclei. XI. Intensive Monitoring
of the Ultraviolet Spectrum of NGC 7469
Authors: Wanders, I.; Peterson, B. M.; Alloin, D.; Ayres, T. R.;
Clavel, J.; Crenshaw, D. M.; Horne, K.; Kriss, G. A.; Krolik,
J. H.; Malkan, M. A.; Netzer, H.; O'Brien, P. T.; Reichert, G. A.;
Rodríguez-Pascual, P. M.; Wamsteker, W.; Alexander, T.; Anderson,
K. S. J.; Benitez, E.; Bochkarev, N. G.; Burenkov, A. N.; Cheng,
F. -Z.; Collier, S. J.; Comastri, A.; Dietrich, M.; Dultzin-Hacyan,
D.; Espey, B. R.; Filippenko, A. V.; Gaskell, C. M.; George, I. M.;
Goad, M. R.; Ho, L. C.; Kaspi, S.; Kollatschny, W.; Korista, K. T.;
Laor, A.; MacAlpine, G. M.; Mignoli, M.; Morris, S. L.; Nandra, K.;
Penton, S.; Pogge, R. W.; Ptak, R. L.; Rodríguez-Espinoza, J. M.;
Santos-Lleó, M.; Shapovalova, A. I.; Shull, J. M.; Snedden, S. A.;
Sparke, L. S.; Stirpe, G. M.; Sun, W. -H.; Turner, T. J.; Ulrich,
M. -H.; Wang, T. -G.; Wei, C.; Welsh, W. F.; Xue, S. -J.; Zou, Z. -L.
1997ApJS..113...69W Altcode:
From 1996 June 10 to July 29, the International Ultraviolet Explorer
monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to
measure time delays between the continuum and emission-line fluxes. From
the time delays, one can estimate the size of the region dominating
the production of the UV emission lines in this source. We find the
strong UV emission lines to respond to continuum variations with time
delays of about 2.3d-3.1d for Lyα, 2.7d for C IV λ1549, 1.9d-2.4d
for N V λ1240, 1.7d-1.8d for Si IV λ1400, and 0.7d-1.0d for He
II λ1640. The most remarkable result, however, is the detection of
apparent time delays between the different UV continuum bands. With
respect to the UV continuum flux at 1315 Å, the flux at 1485 Å,
1740 Å, and 1825 Å lags with time delays of 0.21d, 0.35d, and 0.28d,
respectively. Determination of the significance of this detection
is somewhat problematic since it depends on accurate estimation of
the uncertainties in the lag measurements, which are difficult to
assess. We attempt to estimate the uncertainties in the time delays
through Monte Carlo simulations, and these yield estimates of ~0.07d for
the 1 σ uncertainties in the interband continuum time delays. Possible
explanations for the delays include the existence of a continuum-flux
reprocessing region close to the central source and/or a contamination
of the continuum flux with a very broad time-delayed emission feature
such as the Balmer continuum or merged Fe II multiplets.

---------------------------------------------------------
Title: Distant Futures of Solar Activity
Authors: Ayres, Thomas
1997hst..prop.7733A Altcode: 1997hst..prop.4070A
We will explore possible future fates of solar magnetic activity
through high-S/N ultraviolet spectra of the ancient Sun analog,
Arcturus {K2 III}. The fundamental mechanisms that drive the hot
{T&gt;10^6 K} coronae of cool stars remain elusive. Solving the
mystery is a central theme of the “solar-stellar connection;” whose
importance extends beyond astronomy to areas ranging from basic plasma
physics to solar-terrestrial relations. A significant property of the
activity is that it subsides with age: G dwarfs in young clusters are
intense coronal sources, whereas old low mass K giants are so feable
in soft X-rays that most are below current detection limits. For that
reason, historical studies of activity have been biased towards the
younger stars. Now HST/STIS easily can record faint coronal proxies
{like Si IV and C IV} in nearby cool subgiants and giants, thereby
mitigating the de facto age discrimination. In the solar neighborhood
the brightest single star of advanced age {9-11 Gyr} is Alpha Bootis
{K2 III}. Previous studies have placed the archetype red giant firmly
in the “coronal graveyard.” Our project focuses on understanding the
“basal” chromosphere; molecular cooling catastrophes and the structure
of the passive “COmosphere;” the dynamics and energy balance of the
residual subcoronal gas; and mass loss mechanisms. {This program is
a carryover from a failed Cycle 5 GHRS observation.}

---------------------------------------------------------
Title: Translimb Spectroscopy with SOHO/SUMER
Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi,
I.; Solanki, S.
1997SPD....28.0104A Altcode: 1997BAAS...29..879A
We have used SUMER to obtain deep exposures of the 1300--1400 Angstroms
spectrum, at the extreme limb and off-limb. Previous “translimb”
studies in the thermal infrared had revealed remarkable extensions
of cold material (T ~ 3000 K)---traced by carbon monoxide emission
lines---into the heart of the hot chromosphere. A main objective of
our program was to search for corresponding far-UV signatures of the
“thermally-bifurcated” low chromosphere; for example, radiatively
fluoresced emissions of the CO A--X 4th-positive system (collisional
excitation would be negligible in cold gas). We conducted two separate
observing programs with SUMER. Both made use of the 1(”) -diameter
circular aperture, translated across the limb in the minimum motor
step increments of 0.(”) 375, along the central meridian in the
Northern polar coronal hole. The first program executed for nine hours
beginning 19UT 25 Oct 1996. The full wavelength range was 1340--1400
Angstroms. It was recorded in two overlapping segments, placing key
regions of the spectrum alternately on the KBr and bare parts of
the detector, to help isolate 2nd-order features. Each segment was
integrated for 500 s, and 32 pairs were obtained to span a 12(”)
swath centered on the optical limb. The second program was conducted
00--09UT 01 Dec 1996. It consisted of a single wavelength setting
(1300--1340 Angstroms) with exposure time 500 s, but twice the spatial
coverage of the earlier series: 64 steps, for a total displacement
of 24(”) . The strong chromospheric resonance lines of atomic oxygen
(1302--1305 Angstroms) and ionized carbon (1334--1335 Angstroms) were
observed on the bare part of the MCP camera. We report our progress
in cataloging the rich, diverse translimb emission spectrum; and our
efforts to deduce fundamental properties of the thermally heterogeneous
chromosphere. [-3mm] SOHO is a project of international cooperation;
the participation of TRA was supported by NASA grant NAG5-3226.

---------------------------------------------------------
Title: Multiwavelength Coronal Studies of the RS CVn Binaries sigma
(2) CrB and HR1099
Authors: Brown, A.; Osten, R. A.; Ayres, T. R.; Drake, S. A.
1997AAS...190.2509B Altcode: 1997BAAS...29..807B
We have used the ASCA, XTE, and EUVE satellites and the VLA radio
array to study the coronal emission from the RS CVn binaries sigma
(2) CrB, observed 1997 March 11-13, and HR1099 (V711 Tau), observed
1996 September 1-11 with additional, more limited, observations during
the period 1996 October 9-22. We present time-resolved analyses of the
variable coronal emission, including flares, from these systems. sigma
(2) CrB was observed simultaneously by ASCA, XTE, and VLA, while
simultaneous observations of HR1099 were obtained by XTE, EUVE, and
VLA. During these observations HR1099 underwent a very large flare
lasting 3 days. In addition we present a synopsis of the coronal
variability seen for HR1099 from a total EUVE coverage lasting 34 days
obtained between 1992 and 1996. This work is supported by NASA Grants
NAG5-2259, NAG5-2530, &amp; NAG5-3226 to the University of Colorado.

---------------------------------------------------------
Title: Evaluating Possible Heating Mechanisms Using the Transition
Region Line Profiles of Late-Type Stars
Authors: Wood, Brian E.; Linsky, Jeffrey L.; Ayres, Thomas R.
1997ApJ...478..745W Altcode:
Our analysis of high-resolution Goddard High-Resolution Spectrograph
(GHRS) spectra of late-type stars shows that the Si IV and C IV lines
formed near 105 K can be decomposed into the sum of two
Gaussians, a broad component and a narrow component. We find that
the flux contribution of the broad components is correlated with
both the C IV and X-ray surface fluxes. For main-sequence stars,
the widths of the narrow components suggest subsonic nonthermal
velocities, and there appears to be a tight correlation between these
nonthermal velocities and stellar surface gravity (ξNC
~ g-0.68+/-0.07). For evolved stars with lower surface
gravities, the nonthermal velocities suggested by the narrow components
are at or just above the sound speed. Nonthermal velocities computed
from the widths of the broad components are always highly supersonic. We
propose that the broad components are diagnostics for microflare
heating. Turbulent dissipation and Alfvén waves are both viable
candidates for the narrow component heating mechanism. A solar
analog for the broad components might be the “explosive events”
detected by the High-Resolution Telescope and Spectrograph (HRTS)
experiment. The broad component we observe for the Si IV λ1394
line of α Cen A, a star that is nearly identical to the Sun, has
a FWHM of 109 +/- 10 km s-1 and is blueshifted by 9 +/-
3 km s-1 relative to the narrow component. Both of these
properties are consistent with the properties of the solar explosive
events. However, the α Cen A broad component accounts for 25% +/-
4% of the total Si IV line flux, while solar explosive events are
currently thought to account for no more than 5% of the Sun's total
transition region emission. This discrepancy must be resolved before
the connection between broad components and explosive events can be
positively established. In addition to our analysis of the Si IV
and C IV lines of many stars, we also provide a more thorough analysis
of all of the available GHRS data for α Cen A (G2 V) and α Cen B
(K1 V). We find that the transition region lines of both stars have
redshifts almost identical to those observed on the Sun: showing an
increase with line formation temperature up to about log T = 5.2 and
then a rapid decrease. Using the O IV] lines as density diagnostics,
we compute electron densities of log ne = 9.65 +/- 0.20
and log ne = 9.50 +/- 0.30 for α Cen A and α Cen B,
respectively. Based on observations with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy Inc., under NASA Contract NAS5-26555.

---------------------------------------------------------
Title: CO and the Temperature Structure of the Solar Atmosphere
Authors: Ayres, Thomas R.
1997STIN...9914335A Altcode:
The surface layers of the Sun provide a crucial boundary condition
for many of the processes that occur in the deep interior. The
stratification of the outer solar atmosphere once was thought to be
well understood. However, studies of thermally sensitive molecular
absorptions in the infrared revealed puzzling anomalies. Strong lines
of the CO fundamental vibration-rotation bands near 5 microns showed
very cool temperatures at the extreme limb, and remarkable off-limb
emissions extending well into the supposedly hot chromosphere. The
conflicting pictures of the photosphere/chromosphere interface, from the
widely separated wavelength regimes, has raised suspicions that those
"layers" of the atmosphere are much more inhomogeneous than previously
suspected. One proposal is that the low chromosphere is dominated by
cool gas--the "COmosphere," if you will--which is threaded by a network
of persistent small-scale hot magnetic filaments and occasionally
disrupted by localized acoustic disturbances. The COmosphere is capped
by the merged fields of the network elements in the chromospheric
"canopy." I will describe the evidence in favor of that model, including
recent work at the NSO McMath-Pierce telescope (including use of the new
"Phoenix" spectrometer) and translimb far-UV spectroscopy by SOHO/SUMER.

---------------------------------------------------------
Title: Chromospheric Structure and Dynamics--Observations
Authors: Ayres, Thomas R.
1997STIN...9914312A Altcode:
The chromosphere is a highly structured dynamic 'layer' of
the solar outer atmosphere. Here, not only are the effects of
mechanical heating first evident (moving upward in altitude from
the deep photosphere), but also the amount of nonradiative energy
deposited is far greater than in the albeit much hotter overlying
transition region and corona. Further, the chromosphere is by
far the thickest zone of the solar atmosphere with respect to the
pressure scale height. A major goal of stellar astrophysics is to
understand how the chromosphere is heated and why it adopts its
peculiar structure. A cursory examination of solar filtergrams and
high-resolution movies demonstrates that much of the chromospheric
"action" must be occurring on fine spatial scales and short times;
particularly in the cell interior transient brightenings, but also
in the longer-lived network fragments. That regime of investigation
is far removed from what one usually associates with "synoptic"
measurements. Nevertheless, synoptic observations of chromospheric
indices, filtergrams, and globally-averaged profile parameters (e.g.,
for Ca II) not only can provide important insight concerning the crucial
role of the cycle-variable part of the solar magnetic field; but they
also can forge a key link with analogous measurements of the stars,
where often the phenomena can be significantly exaggerated from the
solar case, but high spatial resolution reconnaissance is not even a
remote possibility. In addition to discussing the synoptic aspects of
chromospheric structure and dynamics, I will summarize new insights
into the general problem of the solar chromosphere that have been
obtained recently with the SUMER far-ultraviolet spectrometer on SOHO.

---------------------------------------------------------
Title: The Solar-Stellar Connection (NAG5-6124: SOHO Guest
Investigator Program)
Authors: Ayres, Thomas R.
1997STIN...9932584A Altcode:
The following is a final report from the SOHO Guest Investigator program
to use the SUMER far-UV spectrometer to obtain imaging spectroscopy in
support of the goals of the so-called "solar-stellar connection." In
particular, a major emphasis was utilization of the long-slit
time-resolved maps of the solar surface in bright far-UV emission
lines to deduce how particular aspects of the temporally and spatially
averaged line profiles trace back to individual structural features
of the magnetically disturbed outer atmosphere; to help interpret the
unresolved line profiles from high quality stellar observations (say,
with the Space Telescope Imaging Spectrograph). The researchers served
two tours of duty in the SOHO Operations Center as SUMER planners,
during which time we conducted an extensive series of observing
programs. These can be divided into three general categories: surface
mapping, translimb spectroscopy, and active region diagnostics. We have
analyzed some of the large volumes of data to the point where we have
presented them in poster papers, and in invited papers at national and
international meetings. Listed below are the titles of the preliminary
publications we have written, including brief abstracts to indicate the
main results. (1) Chromospheric structure and Dynamics-- Observations --
The chromosphere is a highly structured dynamic 'layer' of the solar
outer atmosphere. Here, not only are the effects of mechanical heating
first evident (moving upward in altitude from the deep photosphere),
but also the amount of nonradiative energy deposited is far greater
than in the albeit much hotter overlying transition region and
corona. Further, the chromosphere is by far the thickest zone of the
solar atmosphere with respect to the pressure scale height. A major
goal of stellar astrophysics is to understand how the chromosphere is
heated and why it adopts its peculiar structure. A cursory examination
of solar filtergrams and high-resolution movies demonstrates that
much of the chromospheric "action" must be occurring on fine spatial
scales and short times; particularly in the cell interior transient
brightenings, but also in the longer-lived network fragments. That
regime of investigation is far removed from what one usually associates
with "synoptic" measurements. Nevertheless, synoptic observations
of chromospheric indices, filtergrams, and globally-averaged profile
parameters not only can provide important insight concerning the crucial
role of the cycle-variable part of the solar magnetic field; but they
also can forge a key link with analogous measurements of the stars,
where often the phenomena can be significantly exaggerated from the
solar case, but high spatial resolution reconnaissance is not even a
remote possibility. In addition to discussing the synoptic aspects of
chromospheric structure and dynamics, I summarized new insights into
the general problem of the solar chromosphere that have been obtained
recently with the SUMER far-ultraviolet spectrometer on SOHO. (2) CO
and the Temperature Structure of the Solar Atmosphere -- The surface
layers of the Sun provide a crucial boundary condition for many of the
processes that occur in the deep interior. The stratification of the
outer solar atmosphere once was thought to be well understood. However,
studies of thermally sensitive molecular absorptions in the infrared
revealed puzzling anomalies. Strong lines of the CO fundamental
vibration-rotation bands near 5 microns showed very cool temperatures
at the extreme limb, and remarkable off-limb emissions extending
well into the supposedly hot chromosphere. The conflicting pictures
of the photosphere/chromosphere interface, from the widely separated
wavelength regimes, has raised suspicions that those "layers" of the
atmosphere are much more inhomogeneous than previously suspected. One
proposal is that the low chromosphere is dominated by cool gas,
the "COmosphere," which is threaded by a network of persistent
small-scale hot magnetic filaments and occasionally disrupted by
localized acoustic disturbances. The COmosphere is capped by the merged
fields of the network elements in the chromospheric "canopy." (3)
Translimb Spectroscopy with SOHO/SUMER -- We have used SUMER to obtain
deep exposures of the 1300-1400 A spectrum, at the extreme limb and
off-limb. Previous "translimb" studies in the thermal infrared had
revealed remarkable extensions of cold material (T is approximately
equal to 3000 K)-traced by carbon monoxide emission lines-into the heart
of the hot chromosphere. A main objective of our program was to search
for corresponding far-UV signatures of the "thermally-bifurcated" low
chromosphere; for example, radiatively fluoresced emissions of the CO
A-X 4th-positive system (collisional excitation would be negligible in
cold gas). We conducted two separate observing programs with SUMER. Both
made use of the 1 inch-diameter circular aperture, translated across the
limb in the minimum motor step increments of 0."375, along the central
meridian in the Northern polar coronal hole. The first program executed
for nine hours beginning 19UT 25 Oct 1996. The full wavelength range
was 1340-1400 A. It was recorded in two overlapping segments, placing
key regions of the spectrum alternately on the KBr and bare parts of
the detector, to help isolate 2nd-order features. Each segment was
integrated for 500 s, and 32 pairs were obtained to span a 12" swath
centered on the optical limb. The second program was conducted 00-09UT
01 Dec 1996. It consisted of a single wavelength setting (1300-1340
A) with exposure time 500 s, but twice the spatial coverage of the
earlier series: 64 steps, for a total displacement of 24". The strong
chromospheric resonance lines of atomic oxygen (1302-1305 A) and ionized
carbon (1334-1335 A) were observed on the bare part of the MCP camera.

---------------------------------------------------------
Title: A Final Look at the Gap and Clump Giants
Authors: Ayres, Thomas R.
1997euve.prop...51A Altcode:
Our objective is to develop insight into the X-ray deficiency of stars
at the blue edge of the Hertzsprung gap, possibly a result of fossil
magnetospheres preserved from the main sequence phase. EUVE spectra
of representative stars in, and beyond, the Hertzsprung gap will
be utilized to test models of the hot coronae. Several targets were
observed by EUVE previously. We propose in Cycle 6 to revisit the two
brightest single stars of our sample, 31 Com (G0 III) and Beta Cet
(K0 III). Long pointings (500 ks) not only would improve existing
spectral material, attaining sufficient S/N to detect weak density
diagnostic lines, but also would secure unique medium-term records of
coronal variability.

---------------------------------------------------------
Title: Hertzsprung Gap Coronae: ASCA Guest Investigator Program
Authors: Ayres, Thomas R.
1997cub..rept.....A Altcode:
The objective was a deep (40 ks) SIS/GIS pointing on the bright stellar
X-ray source 31 Comae (G0 III) to record the 1-10 keV spectrum and
obtain a lightcurve over the approx. 1 day duration of the observation.

---------------------------------------------------------
Title: Evolution of the solar ionizing flux
Authors: Ayres, Thomas R.
1997JGR...102.1641A Altcode:
A young magnetically active Sun, with enhanced ionizing radiations
and an elevated solar wind, might have contributed to erosion of
the primordial atmosphere of Mars (which is particularly vulnerable
to dissociative recombination and sputtering by solar wind pickup
ions). Spacecraft and ground based observations of solar-type dwarfs
in young galactic clusters have yielded a unified view of the early
evolution and subsequent systematic decline of magnetic activity with
age. Rotational braking by the coronal wind ultimately quenches the
spin-catalyzed “dynamo” at the heart of stellar magnetism. Decay
of the 106-107K corona is much faster than
the 104K chromosphere, but XUV emissions of both can be
predicted reliably, and photoionization of key planetary atmospheric
constituents can be modeled. The early Martian atmosphere (age ~1Gyr)
probably was subjected to photoionization rates ~5 times contemporary
peak values (sunspot maximum), possibly more if the ages of galactic
clusters have been underestimated.

---------------------------------------------------------
Title: Ultraviolet variability in active galaxies: a systematic
survey of the IUE archives.
Authors: Edelson, R.; Penton, S.; Shull, J. M.; Ayres, T. R.; Pike, G.
1996BAAS...28.1287E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Sleuthing the Dynamo: Hubble Space Telescope Faint Object
Spectrograph Observations of Solar-Type Dwarfs in Young Galactic
Clusters
Authors: Ayres, Thomas R.; Simon, Theodore; Stauffer, J. R.; Stern,
R. A.; Pye, J. P.; Brown, Alexander
1996ApJ...473..279A Altcode:
We have used the Faint Object Spectrograph of the Hubble Space Telescope
to record the ultraviolet emissions of solar-type [(B - V)0
∼0.6 mag] dwarf stars in young galactic clusters: five in the Hyades
(t 600 Myr); three in the Pleiades (t ∼ 70 Myr); and two in αPersei
(t ∼ 50 Myr). Despite high levels of scattered light in the G130H
(1140-1606 Å) spectra, the key C IV λ1549 blend was detected in all
of the targets. The 105 K emission displays a dramatic
decline from the youngest to the oldest stars of the sample, well
correlated with rotational velocity; evidence of flaring in the most
active of the G dwarfs; a wide spread in intensity among the Pleiades
stars; but a small dispersion among the Hyades stars. The Mg II λ2800
emission is strongly enhanced in the younger stars, and the 2000 Å
continuum is significantly elevated in the Hyades stars compared with
the Sun. The hyperactive stars of the sample show an apparent saturation
of their C IV emission at high rotational velocities, analogous to
that seen in X-rays. The rotation-activity relations possibly exhibit
mild curvature, in addition to the saturation, which nevertheless
maps onto a simple power law in fX/fbol
versus fCIV/fbol. The Sun apparently tracks
a similar power law over the course of its magnetic activity
cycle. We discuss these results in terms of simple magnetic
loop models. We show that the nonlinear power- law variation of
CIV/fbol with rotational velocity (slope ∼1.5,
contrary to the suspected linear dependence of the magnetic filling
factor) very likely arises from a systematic increase in the base
pressures of the dominant coronal loops compared with their counterparts
on the Sun. The nonlinear X-ray/C IV power law (slope ∼1.7) separately
indicates a significant increase in the mean apex temperature of
the dominant coronal loops. We argue that the distribution of loop
structures might change character from inactive stars like the Sun
(dominated by X-ray-bright points and Active Region loops) to the
hyperactive cluster stars (dominated by interregion large-scale
structures or postflare loops).

---------------------------------------------------------
Title: Ultraviolet Variability in Active Galaxies: A Systematic
Survey of the IUE Archives
Authors: Edelson, R.; Penton, S.; Shull, J. M.; Ayres, T.; Pike, G.
1996AAS...189.1101E Altcode: 1996BAAS...28R1287E
Now that the mission of IUE has been completed, the Colorado IUEAGN
group is using the TOMSIPS software to systematically re-extract
all of the AGN data in the archives. The spectra are then fitted
with a multi-parameter model in order to measure continuum and line
fluxes. We then compile a database of fluxes in a number of bands
for each observation. In this talk, we present continuum variability
data for all AGN with at least 12 SWP observations. These data are
generally sensitive to long-term variations, as the IUE satellite
was operational for almost 20 yr. For certain objects that were the
subjects of intensive monitoring campaigns (e.g., NGC 5548, NGC 4151,
etc.), shorter time scale data also exist. We will report the results
of a number of studies. First, for individual well-observed objects,
we determine the relation between variability amplitude and wavelength,
on both long and short time scales. Second, for entire classes of
objects (e.g., Seyfert 1s or BL Lacs), we measure the correlation
between mean object luminosity and variability amplitude. Finally,
we compare the variability properties of different classes of objects.

---------------------------------------------------------
Title: Fishing in the Coronal Graveyard
Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.;
Linsky, J. L.; Carpenter, K. G.; Robinson, R. D.
1996AAS...189.7815A Altcode: 1996BAAS...28.1379A
Hot coronae (T ~ 10(6) K) are thought to be rare among single giant
stars to the right of the “Linsky--Haisch dividing line” near K0 in
the H--R diagram. K and M giants are such slow rotators that absence of
dynamo generated magnetic activity would be natural. Nevertheless,
gamma Dra (K5 III) unexpectedly was detected in FUV coronal
proxies---hot lines Si IV lambda 1393 and C IV lambda 1548---by HST
/GHRS during Science Verification, and subsequently was discovered
as a faint X-ray source in a deep ROSAT /PSPC pointing. Is gamma Dra
anomalous, or is the lack of coronal detections among the K giants
simply a matter of insufficient sensitivity? We have used the GHRS
low resolution mode to search for additional examples of hot lines
among inactive single red giants. Si IV provides a clean diagnostic
of subcoronal material because it falls near the peak sensitivity
of the G140L mode and does not suffer from abundance depletions that
can affect C IV in red giants. X-ray/Si IV ratios are such that HST
can reach to much fainter limiting “coronal” magnitudes than even
very deep ROSAT pointings. In every target so far examined, we find
weak---but statistically significant---Si IV emission. These include:
the ancient red giant Arcturus (alpha Boo: K1 III), recorded at the
end of Cycle 5; and epsilon Crv (K2.5 III) and epsilon Sco (K2 III)
observed in Cycle 6. X-ray/Si IV ratios of red giants (for which
measurements, or upper limits, of both diagnostics are available)
fall on a uniform track, extending downward from active K0 “Clump”
giants like beta Ceti all the way to Arcturus itself, in the depths of
the “coronal graveyard.” The systematic behavior argues that magnetic
dynamo action continues even when long term angular momentum loss has
slowed the stellar spin to a crawl. This work was supported by grant
GO-06066.01-94A from STScI.

---------------------------------------------------------
Title: Mg Emission from Hybrid-Chromosphere Stars: 1.5 Decades of
Chromospheric Variability Monitoring
Authors: Brown, Alexander; Deeney, Bryan D.; Ayres, Thomas R.; Veale,
Anthony; Bennett, Philip D.
1996ApJS..107..263B Altcode:
We present an analysis of the available long-wavelength,
high-dispersion spectra of seven hybrid-chromosphere stars obtained
with the International Ultraviolet Explorer between 1978 and 1993. Our
investigation of the variability of the Mg II h and k resonance doublet
demonstrates that the emission- line fluxes are not rotationally
modulated with the periods previously suggested by Brosius, Mullan,
&amp; Stencel. Furthermore, we find no evidence in the Mg II data
to corroborate the multiple periodicities reported in the Ca II
emissions of hybrid stars by Rao et al. Examination of 40 pairs of
closely spaced Mg II observations failed to reveal the presence of any
strong chromospheric flaring on the sample stars. Significant (20%-40%)
nonperiodic Mg II flux variability, on time scales of days to years,
is observed in six of the seven stars. The flux variations occasionally
are accompanied by dramatic changes in the morphology of the Mg II
profiles, indicating variable stellar-wind absorption. We argue that the
variability observed is consistent with stochastic changes associated
with the slow growth and decay of chromospheric active regions and
the gradual evolution of the physical conditions in the winds. It is
our opinion that no compelling argument has yet been made for periodic
variability in the chromospheric diagnostics of hybrid stars.

---------------------------------------------------------
Title: Multiwavelength Observations of Short-Timescale Variability
in NGC 4151. IV. Analysis of Multiwavelength Continuum Variability
Authors: Edelson, R. A.; Alexander, T.; Crenshaw, D. M.; Kaspi,
S.; Malkan, M. A.; Peterson, B. M.; Warwick, R. S.; Clavel, J.;
Filippenko, A. V.; Horne, K.; Korista, K. T.; Kriss, G. A.; Krolik,
J. H.; Maoz, D.; Nandra, K.; O'Brien, P. T.; Penton, S. V.; Yaqoob,
T.; Albrecht, P.; Alloin, D.; Ayres, T. R.; Balonek, T. J.; Barr,
P.; Barth, A. J.; Bertram, R.; Bromage, G. E.; Carini, M.; Carone,
T. E.; Cheng, F. -Z.; Chuvaev, K. K.; Dietrich, M.; Dultzin-Hacyan,
D.; Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hemar, S.; Ho, L. C.;
Huchra, J. P.; Hutchings, J.; Johnson, W. N.; Kazanas, D.; Kollatschny,
W.; Koratkar, A. P.; Kovo, O.; Laor, A.; MacAlpine, G. M.; Magdziarz,
P.; Martin, P. G.; Matheson, T.; McCollum, B.; Miller, H. R.; Morris,
S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.; Pike,
G.; Pogge, R. W.; Ptak, R. L.; Qian, B. -C.; Recondo-Gonzalez, M. C.;
Reichert, G. A.; Rodriguez-Espinoza, J. M.; Rodriguez-Pascual, P. M.;
Rokaki, E. L.; Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo,
M.; Shields, J. C.; Shull, J. M.; Smith, D. A.; Smith, S. M.; Snijders,
M. A. J.; Stirpe, G. M.; Stoner, R. E.; Sun, W. -H.; Ulrich, M. -H.;
van Groningen, E.; Wagner, R. M.; Wagner, S.; Wanders, I.; Welsh,
W. F.; Weymann, R. J.; Wilkes, B. J.; Wu, H.; Wurster, J.; Xue,
S. -J.; Zdziarski, A. A.; Zheng, W.; Zou, Z. -L.
1996ApJ...470..364E Altcode: 1996astro.ph..5082A; 1996astro.ph..5082E
This paper combines data from the three preceding papers in order
to analyze the multi-wave-band variability and spectral energy
distribution of the Seyfert I galaxy NGC 4151 during the 1993
December monitoring campaign. The source, which was near its peak
historical brightness, showed strong, correlated variability at X-ray,
ultraviolet, and optical wavelengths; The strongest variatIons were
seen in medium-energy (~1.5 keV) X-rays, with a normalized variability
amplitude (NVA) of 24%. Weaker (NVA = 6%) variations (uncorrelated
with those at lower energies) were seen at soft gamma ray energies of
~100 keV. No significant variability was seen in softer (0.1-1 keV)
X-ray bands. In the ultraviolet/optical regime the NVA decreased from
9% to 1% as the wavelength increased from 1275 to 6900 A. These data
do not probe extreme ultraviolet (1200 A to 0.1 keV) or hard X ray
(2-50 keV) variability. The phase differences between variations in
different bands were consistent with zero lag, with upper limits
of &lt;~ 0.15 day between 1275 A and the other ultraviolet bands,
&lt;~0.3 day between 1275 A and 1.5 keV, and &lt;~1 day between
1275 and 512 A. These tight limits represent more than an order of
magnitude improvement over those determined in previous multi wave
band AGN monitoring campaigns. The ultraviolet fluctuation power
spectra showed no evidence for periodicity, but were instead well
fitted with a very steep, red power law (a &lt;= -2.5). If photons
emitted at a "primary" wave band are absorbed by nearby material
and "reprocessed" to produce emission at a secondary wave band,
causality arguments require that variations in the secondary band
follow those in the primary band. The tight interband correlation and
limits on the ultraviolet and medium-energy X-ray lags indicate that
the reprocessing region is smaller than ~0.15 lt-day in size. After
correcting for strong (a factor of ~&gt; 15) line-of-sight absorption,
the medium-energy X-ray luminosity variations appear adequate to drive
the ultraviolet/optical variations. However the medium-energy X-ray NVA
is 2- 4 times that in the ultraviolet, and the single-epoch absorption-
corrected X-ray/gamma ray luminosity is only about one third of that
of the ultraviolet optical/infrared, suggesting that at most about a
third of the total low energy flux could be reprocessed high-energy
emission. The strong wavelength dependence of the ultraviolet NVAs
is consistent with an origin in an accretion disk, with the variable
emission coming from the hotter inner regions and nonvariable emission
from the cooler outer regions. These data, when combined with the
results of disk fits indicate a boundary between these regions near a
radius of order R ~ 0.07 lt-day. No interband lag would be expected,
as reprocessing (and thus propagation between regions) need not occur,
and the orbital timescale of 1 day is consistent with the observed
variability timescale. However, such a model does not immediately
explain the good correlation between ultraviolet and X-ray variations.

---------------------------------------------------------
Title: Multiwavelength Observations of Short-Timescale Variability
in NGC 4151. I. Ultraviolet Observations
Authors: Crenshaw, D. M.; Rodriguez-Pascual, P. M.; Penton, S. V.;
Edelson, R. A.; Alloin, D.; Ayres, T. R.; Clavel, J.; Horne, K.;
Johnson, W. N.; Kaspi, S.; Korista, K. T.; Kriss, G. A.; Krolik,
J. H.; Malkan, M. A.; Maoz, D.; Netzer, H.; O'Brien, P. T.; Peterson,
B. M.; Reichert, G. A.; Shull, J. M.; Ulrich, M. -H.; Wamsteker, W.;
Warwick, R. S.; Yaqoob, T.; Balonek, T. J.; Barr, P.; Bromage, G. E.;
Carini, M.; Carone, T. E.; Cheng, F. -Z.; Chuvaev, K. K.; Dietrich,
M.; Doroshenko, V. T.; Dultzin-Hacyan, D.; Filippenko, A. V.;
Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hutchings, J.; Kazanas,
D.; Kollatschny, W.; Koratkar, A. P.; Laor, A.; Leighly, K.; Lyutyi,
V. M.; MacAlpine, G. M.; Malkov, Yu. F.; Martin, P. G.; McCollum, B.;
Merkulova, N. I.; Metik, L.; Metlov, V. G.; Miller, H. R.; Morris,
S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.;
Pike, G.; Pogge, R. W.; Pronik, I.; Pronik, V. I.; Ptak, R. L.;
Recondo-Gonzalez, M. C.; Rodriguez-Espinoza, J. M.; Rokaki, E. L.;
Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo, M.; Sergeev,
S. G.; Smith, S. M.; Snijders, M. A. J.; Sparke, L. S.; Stirpe, G. M.;
Stoner, R. E.; Sun, W. -H.; van Groningen, E.; Wagner, R. M.; Wagner,
S.; Wanders, I.; Welsh, W. F.; Weymann, R. J.; Wilkes, B. J.; Zheng, W.
1996ApJ...470..322C Altcode: 1996astro.ph..5079A; 1996astro.ph..5079C
We present the results of an intensive ultraviolet monitoring campaign
on the Seyfert I galaxy NGC 4151, as part of an effort to study its
short-timescale variability over a broad range in wavelength. The
nucleus of NGC 4151 was observed continuously With the International
Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP
spectra every ~70 minutes, and during 4 hr periods for 4 days Prior
to and 5 days after the continuous-monitoring period. The sampling
frequency of the observations is an order of magnitude higher than
that of any previous UV monitoring campaign on a Seyfert galaxy. The
continuum fluxes in bands from 1275 to 2688 A went through four
significant and well-defined events of duration 2-3 days during
the continuous-monitoring period. We find that the amplitudes of
the continuum variations decrease with increasing wavelength, which
extends a general trend for this and other Seyfert galaxies to smaller
timescales (i.e., a few days). The continuum variations in all the UV
bands are simultaneous to within an accuracy of ~0.15 days, providing
a strict constraint on continuum models. The emission-line light
curves show only one major event during the continuous monitoring
(a slow rise followed by a shallow dip) and do not correlate well
with continuum light curves over the short duration of the campaign,
because the timescale for continuum variations is apparently smaller
than the response times of the emission lines.

---------------------------------------------------------
Title: Teaching materials: stellar atmospheres/radiative transfer.
Authors: Hawley, S. L.; Ayres, T. R.
1996BAAS...28Q.883H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Fishing in the Coronal Graveyard
Authors: Ayres, Thomas
1996hst..prop.6551A Altcode: 1996hst..prop.2962A
We propose a far-UV spectroscopic survey of K2-K4 giants. Hotcoronae
(T&gt; 10^6 K) are rare or absent in single giant starsto the right
of a boundary in the H-R diagram near K0(“Linsky-Haisch dividing
line”). The early-K giants aresuch slow rotators that the absence
of Dynamo-generatedmagnetic activity is natural. Nevertheless, Gamma
Draconis(K5 III) unexpectedly was detected in the coronal proxy
C IVby HST/GHRS, and subsequently was discovered as a faintX-ray
source in a deep ROSAT pointing. The basis for thecoronal emission
is unknown, given the presumed lack of Dynamoaction. However,
the X-ray/C IV ratio of Gamma Dra falls on acontinuum of values;
extending from the active K0 “Clump”giants like Beta Ceti, down to
the old red giant Alpha Boo (K1III) in the depths of the “coronal
graveyard.” GHRS/G140Lreconnaissance of high-excitation FUV emissions
(Si IV, C IV,and N V) can be conducted at sensitivity levels orders
ofmagnitude better than possible prior to HST. Such a surveyof single
red giants would provide a unique perspective on thebreadth of activity
to the right of the L-H boundary. Italso would record the fluoresced
4th-positive system of CO,a key tracer of thermal inhomogeneities in
late-typeatmospheres. Seven candidates fall in the magnitude rangeV
&lt; 3. Three--Beta UMi, Epsilon Sco, and Epsilon Crv--willbe observed,
consistent with the TAC allocation.

---------------------------------------------------------
Title: Sleuthing the Dynamo: the Final Frontier
Authors: Ayres, Thomas
1996hst..prop.6795A Altcode: 1996hst..prop.3206A
Innovative technologies are opening new windows into the Sun;from its
hidden interior to the far reaches of its turbulentouter envelope:
rare-earth detectors for solar neutrinos; theGONG project for
helioseismology; SOHO for high-resolutionXUV spectroscopy, and
YOHKOH for coronal X-ray imaging. Atthe same time, a fleet of space
observatories--ROSAT, EUVE,ASCA, and HST itself--are providing
unprecedented views ofthe vacuum-UV and X-ray emissions of stars
in our Galacticneighborhood. These seemingly unrelated developments
are infact deeply connected. A central issue of solar-stellarphysics
is the nature and origin of magnetic activity: thelink between the
interior dynamics of a late-type star and theviolent state of its
outermost coronal layers. As solarphysicists are unlocking the secrets
of the hydromagneticDynamo deep inside the Sun, we and others have
beendocumenting the early evolution of the Dynamo and itsassociated
external gas-dynamic activity. In particular, wehave obtained HST/FOS
spectra of ten young solar-type starsin three nearby open clusters--the
Hyades, Pleiades, andAlpha Persei--ranging in age from 50 Myr to 600
Myr. We havesupplemented the HST spectroscopy with deep ROSAT pointings,
and ground-based studies. Here, we will continue the HSTside of our
project by obtaining FUV spectra of two AlphaPerseids from our original
program (but not yet observed),and high-S/N follow-up measurements of
the hyperactive PleiadH II 314.

---------------------------------------------------------
Title: Teaching Materials: Stellar Atmospheres/Radiative Transfer
Authors: Hawley, S. L.; Ayres, T. R.
1996AAS...188.3905H Altcode: 1996BAAS...28..883H
We will present a selection of modern teaching materials for courses
in Stellar Atmospheres and Radiative Transfer that have been collected
from a wide variety of sources. We will provide brief synopses of each
book, or set of of notes, and endeavor to compare and contrast the
different presentations of the material. One of the newer additions
to the literature is “Radiative Transfer in Stellar Atmospheres,”
lecture notes from R.J. Rutten based on courses taught at Utrecht
University. In addition, I. Hubeny and D. Mihalas presently are writing
a new edition of Mihalas' famous “Stellar Atmospheres.” Other books
we are aware of range from the planning stages to near completion. We
will emphasize the diversity of styles and presentation techniques, but
will try to make clear the central themes around which any successful
Stellar Atmospheres/Radiative Transfer course must be built.

---------------------------------------------------------
Title: 2-D Inhomogeneous Modeling of the Solar CO Bands
Authors: Ayres, T. R.
1996AAS...188.3904A Altcode: 1996BAAS...28R.882A
The recent discovery of off-limb emissions in the mid-IR ( ~ 5 mu m)
vibration-rotation bands of solar carbon monoxide (CO) has sparked new
interest in the formation of the molecular lines, and their ability to
diagnose thermal conditions at high altitudes. The off-limb extensions
of the strong CO lines indicate the penetration of cool material
(T ~ 3500 K) several hundred kilometers into the otherwise hot (T ~
6000 K) chromosphere. The origin of the cool gas, and its role in
the thermal energy balance, remain controversial. The interpretation
of the CO observations must rely heavily upon numerical modeling, in
particular highly-inhomogeneous thermal structures arrayed in a 2-D
scheme that can properly treat the geometry of the grazing rays at the
solar limb. The radiation transport, itself, is especially simple for
the CO off-limb emissions, because the fundamental bands form quite
close to LTE (high collision rates; low spontaneous decay rates) and
the background continuum is purely thermal as well (f--f transitions
in H(-) and H). Thus, the geometrical aspects of the problem can be
treated in considerably more detail than would be practical for typical
NLTE scattering lines. I describe the recent modeling efforts, and the
diagnostic potential of the CO bands for future observational studies
of inhomogeneous surface structure on the Sun, and on other stars of
late spectral type. This work was supported by NSF grant AST-9218063
to the University of Colorado.

---------------------------------------------------------
Title: Observations of Solar Carbon Monoxide with an Imaging Infrared
Spectrograph. I. Thermal Bifurcation Revisited
Authors: Ayres, Thomas R.; Rabin, Douglas
1996ApJ...460.1042A Altcode:
We describe long-slit spectroscopy of the solar 4.7 μm carbon monoxide
(CO) Δυ = 1 bands at the Main spectrograph of the NSO McMath-Pierce
telescope. We utilized stigmatic imaging of the temperature-
and velocity-sensitive CO absorptions to map quiet regions near
disk center and at the extreme limb. At Sun center the dominant
long-lived spatial structures are small-scale hot spots associated
with fragments of the supergranulation network seen in cotemporal Ca
II filtergrams. Oscillatory thermal and velocity fluctuations of the
global p-mode interference pattern are a pervasive feature of the
maps, but the rms amplitudes (≍70 K and ≍240 m s-1)
are perturbations on a relatively unstructured outer photosphere. We
occasionally see small-scale transient cooling episodes longer lived
than the p-mode wavepackets that might be overshooting granules
or rising magnetic flux ropes. The events are too rare, however,
to influence the global properties of the CO fundamental bands. Seeing-selected frames of the off-limb CO emissions show a typical
extension of 0".6 for the strongest lines, with little variation along
the limb. The off-limb extensions indicate the presence of cool gas
up to 350 km above the "Tmin" of popular reference models
of the solar chromosphere. We carried out two-dimensional model
atmosphere simulations to study the effects of thermal inhomogeneities
on the disk-center, extreme-limb, and off-limb behavior of the CO
lines. The models are spherically symmetric, static, and in LTE. Our
data favor a scenario in which the bulk of the low chromosphere
below the base of the magnetic "canopy" is in reality a "COmosphere"
dominated by gas colder than the minimum temperature in conventional
models. The moderate-scale (≍5"), mild thermal perturbations
of the p-mode pattern have little influence on the CO Δυ = 1
spectra. Small-scale (≍1") hot regions embedded in a cool average
atmosphere are strongly "shadowed" at the extreme limb. The shadowing
is of little consequence, however, because the atmosphere already is
dominated by the cool component. The opposite scenario-small-scale
cold regions in a warm average produce effective shadowing at the
limb for granule-size (≍1"-2") dark points only if the covering
fraction is relatively large (f &amp;#8819 0.2). That scenario is
ruled out: it predicts high-contrast dark spots at disk center,
contrary to our observations. We also argue against the possibility
of shadowing by even smaller, subresolution (≍0"3) cold spots with
f &amp;#8819 0.1. We show that multistep reactions, rather than
direct radiative associations, dominate the gas-phase chemistry of
CO molecules under conditions typical of the outer photosphere. The
CO formation and radiative cooling timescales are fast enough that
low-temperature plasma conditions can be restored following disruption
by a localized heating event such as a Ca II K2v "flash." In
cool giant stars, the chemical formation timescales are much longer than
in dwarfs like the Sun. Nevertheless, the density dependence is such
that the molecular cooling proceeds proportionately more rapidly than
the gas dynamics, ensuring an even more important role for autocatalyzed
"thermal bifurcation."

---------------------------------------------------------
Title: Evolution of the Solar EUV Radiation and Its Impact on Martian
Exospheric Constituents Over Time
Authors: Ayres, T. R.
1996emv..work....2A Altcode: 1995LPITR9504....2A
No abstract at ADS

---------------------------------------------------------
Title: Hot Times in the Hertzsprung Gap
Authors: Ayres, Thomas R.
1996aeu..conf..113A Altcode: 1996IAUCo.152..113A
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Structures and Giant Flares in HR1099
Authors: Foing, B. H.; Char, S.; Ayres, T.; Catala, C.; Zhai, D. S.;
Jiang, S.; Huang, L.; Hao, J. X.; Houdebine, E.; Jankov, S.; Baudrand,
J.; Czarny, J.; Donati, J. F.; Felenbok, P.; Catalano, S.; Cutispoto,
G.; Frasca, A.; Rodono, M.; Neff, J. E.; Simon, T.; Collier-Cameron,
A.; Butler, C. J.; MUSICOS 1989 Campaign Collaboration
1996mpsa.conf..283F Altcode: 1996IAUCo.153..283F
No abstract at ADS

---------------------------------------------------------
Title: Stellar spectroscopy with HST
Authors: Ayres, T. R.
1996ASPC..109..215A Altcode: 1996csss....9..215A
No abstract at ADS

---------------------------------------------------------
Title: How Hot - and Variable - are the Coronae of Hertzsprung-Gap
Giants?
Authors: Ayres, Thomas
1996rxte.prop10001A Altcode:
Hertzsprung-gap giants (F0-G1) are "hyperactive" late-type stars whose
X-ray coronae are among the hottest known (&gt;1 keV); reminiscent
of flaring gas in solar active regions, or on RS CVn binaries and dMe
stars. Yet, the H-gap giants as a class so far have shown no evidence
for flare-like outbursts (at least in the UV or soft X-rays). The
paradox - flare-temperature gas but lack of overt flaring behavior -
bears on the nature of late-type magnetic activity and the elusive
coronal heating mechanism. XTE can add crucial insight by directly
detecting the highest excitation coronal gas, and possible transient
variability of the multi-keV X-rays. 31 Comae (G0 III), a single star,
and the nearby binary Capella (G8 III + G1 III) are the most promising
targets.

---------------------------------------------------------
Title: Thermal bifurcation as a driver of stellar surface
inhomogeneities (review)
Authors: Ayres, T. R.
1996IAUS..176..371A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Digging for Fossils in the Hertzsprung Gap
Authors: Ayres, Thomas R.
1996euve.prop...37A Altcode:
Something remarkable happens to moderate-mass giants during their
post-MS evolution through the Hertzsprung gap (F-G5), on their way
to the core helium burning Clump (G8-K0). The subcoronal fluxes of
such stars (traced by Mg II and Si IV) appear normal for fast rotating
giants, but their coronal X-rays are depressed an order of magnitude or
more. The nearby binary Capella is the archetype: the G0 secondary has
a Si IV flux ten times that of the G8 primary, and rotates faster by
a similar margin. Yet, evidence suggests near equality of the coronal
X-ray fluxes. I, and my colleagues, have been conducting a study of
the dichotomy (and its implications for coronal heating, structure,
and the evolution of magnetic dynamo action) through EUVE spectra of
key stars on post-MS trajectories connecting the Hertzsprung gap and
the Clump. Recent work points to a possibly pivotal role played by a
fossil magnetosphere inherited from the upper-MS phase. We propose to
pursue the idea further through observations of Beta Cassiopeia (F2 III)
and Mu Velorum (G5 III), at the crucial blue and red edges of the gap.

---------------------------------------------------------
Title: Outer atmospheric structures of high-luminosity G/K stars
Authors: Deeney, B. D.; Brown, A.; Ayres, T. R.
1996ASPC..109..519D Altcode: 1996csss....9..519D
No abstract at ADS

---------------------------------------------------------
Title: The Transition Region, Corona, Chromosphere, and Wind of the
K5 Giant gamma Draconis
Authors: Brown, A.; Carpenter, K. G.; Robinson, R. D.; Harper, G. M.;
Deeney, B. D.; Ayres, T. R.
1995AAS...18710303B Altcode: 1995BAAS...27.1430B
Gamma Draconis (K5 III) is the first single, normal late K giant
located on the red side of the coronal “dividing line” known to
show conclusive evidence for both hot ( ~ 10(5) K) transition \
region (TR) and coronal (&gt; 10(6) K) plasma. We present HST GHRS
ultraviolet spectra of gamma Dra obtained on 1995 July 20 and 1991
April 6/18. These observations include spectra obtained at low, medium,
and echelle resolution that provide a full set of chromospheric and
TR emission line fluxes and profiles. These are combined with ROSAT
PSPC observations to measure the TR and coronal properties, such
as emission measure distribution, electron density, and nonthermal
velocity fields, of this star. The high temperature emissions of gamma
Dra are compared to those of a sample of hybrid-chromosphere bright
giants and supergiants. This work is supported by Space Telescope
Science Institute grant GO-06068.01-94A and NASA grants NAG5-1792 and
NAGW-4529 to the University of Colorado.

---------------------------------------------------------
Title: A Semiempirical Determination of the Wind Velocity Structure
for the Hybrid-Chromosphere Star alpha Trianguli Australis
Authors: Harper, Graham M.; Wood, Brian E.; Linsky, Jeffrey L.;
Bennett, Philip D.; Ayres, Thomas R.; Brown, Alexander
1995ApJ...452..407H Altcode:
We have used the Goddard High-Resolution Spectrograph (GHRS) on the
Hubble Space Telescope to study the wind of the hybrid-chromosphere
star α TrA (K4 II). The stellar wind produces significant
absorption at negative radial velocities in the chromospheric Mg II
resonance lines (h and k). Spectra obtained with the GHRS echelle
high-resolution grating (4A 85,000) on 1993 February 10 and 1994
May 1 reveal complex interstellar absorption in the Mg II emission
lines and a high-velocity wind absorption feature centered near -95
km s-1. The 1993 February observation shows an asymmetry
of the Mg II emission cores, corresponding to an apparent redshift
of 6.0±1.5 km s-1. We construct a simple wind model that
explains several of the key observational features. The scattering of
the Mg II h and k photons in a geometrically extended region dominates
the observed flux near line center, which supports the assignment
of the low-velocity absorption components to interstellar absorption
rather than to a chromospheric self-reversal. For the 1993 February
observation, the parameters for our simple wind model are as follows:
terminal velocity V(∞) = 100 km s-1, turbulent velocity
Vturb = 24 km s-1, Mṡ ∼ 1.8 ×
1010 Msun yr-1, for a fixed value
of the velocity-law parameter β = 1 and fixed stellar radius of
R* = 97 Rsun, assuming Mg II is the dominant
ionization state in the flow. Our analysis of the 1994 May observation
resulted in similar values for these parameters, and the mass-loss
rate could be as small as Mṡ ∼ 1.6 × 10-10
Msun yr-1. The value of β is uncertain (≥
0.3) and if β ∼ 3.5 as found from the recent analysis of the ζ
Aurigae systems, Mṡ could be larger by a factor of 3-4. A
comparison of our result with numerical solutions to the momentum and
conservation equations reveals that the derived velocity distribution
lies within a limited region of parameter space where there is a
large nonthermal pressure on the plasma close to the base of the wind
consistent with previous wind models for α TrA. Our best model fit to
the two interstellar absorption components indicates a total hydrogen
column density toward α TrA of NHI = 2 × 1019
cm-2.

---------------------------------------------------------
Title: Deuterium and the Local Interstellar Medium Properties for
the Procyon and Capella Lines of Sight
Authors: Linsky, Jeffrey L.; Diplas, Athanassios; Wood, Brian E.;
Brown, Alexander; Ayres, Thomas R.; Savage, Blair D.
1995ApJ...451..335L Altcode:
We present Goddard High-Resolution Spectrograph observations of the
interstellar H I and D I Lyα lines and the Mg II and Fe II resonance
lines formed along the lines of sight toward the nearby stars Procyon
(3.5 pc, l = 214°, b = 13°) and Capella (12.5 pc, l = 163°, b =
5°). New observations of Capella were obtained at orbital phase 0.80,
when the radial velocities of the intrinsic Lyα emission lines of each
star were nearly reversed from those of the previous observations at
phase 0.26 (analyzed by Linsky et al.). Since the intrinsic Lyα line
of the Capella system the "continuum" against which the interstellar
absorption is measured has different shapes at phases 0.26 and 0.80,
we can derive both the intrinsic stellar profiles and the interstellar
absorption lines more precisely by jointly analyzing the two data
sets. We derive interstellar parameters from the simultaneous analysis
of the two data sets as follows: (D/H)LISM = (1.60±0.09
[+0.05, - 0.10 systematic error]) × 10-5, temperature T =
7000±500 [±400 systematic error] K, and microturbulence ξ = 1.6±0.4
[and ±0.2 systematic error] km s-1. (All random errors
determined in this paper are ±2 σ.) For the analysis of the
Procyon line of sight, we first assumed that the intrinsic Lyα line
profile is a broadened solar profile, but this assumption does not
lead to a good fit to the observed D I line profile for any value of
D/H. We then assumed that (D/H)LISM = 1.6 × 10-5,
the same value as for the Capella line of sight, and we modified the
broadened solar profile to achieve agreement between the simulated and
observed line profiles. The resulting asymmetric intrinsic stellar
line profile is consistent with the shapes of the scaled Mg II line
profiles. We believe therefore that the Procyon data are consistent with
(D/H)LISM = 1.6 × 10-5, but the uncertainty
in the intrinsic Lyα emission-line profile does not permit us to
conclude that the D/H ratio is constant in the local interstellar medium
(LISM). The temperature and turbulence in the Procyon line of sight
are T = 6900±80 (±300 systematic error) K and ξ = 1.21±0.27 km
s-1. These properties are similar to those of Capella, except
that the gas toward Procyon is divided into two velocity components
separated by 2.6 km s-1 and the Procyon line of sight has a
mean neutral hydrogen density that is a factor of 2.4 larger than that
of the Capella line of sight. This suggests that the first 5.3 pc along
the Capella line of sight lies within the local cloud and the remaining
7.2 pc lies in the hot gas surrounding the local cloud. We propose
that nHI = 0.1065±0.0028 cm-2 be adopted for
the neutral hydrogen density within the local cloud and that ξ =
1.21±0.27 km s-1 be adopted for the nonthermal motions. The
existence of different second velocity components toward the nearby
stars Procyon and Sirius provides the first glimpse of a turbulent
cloudlet boundary layer between the local cloud and the surrounding hot
interstellar gas. We speculate that what is often called "turbulence"
may instead be velocity shear within the local cloud that is not a rigid
comoving structure. We also derive gas phase abundances of iron and
magnesium in the Procyon line of sight and the abundance of oxygen in
the Capella line of sight. Within the context of standard big bang
nucleosynthesis, our observed value of (D/H)LISM leads to
0.042 ≤ ΩBh250 ≤ 0.09, depending
on the assumed model for Galactic chemical evolution of deuterium. Our
lower limit (D/H)LISM &gt; 1.41 × 10-5 provides
a hard lower limit to the primordial D abundance and thus a hard upper
limit on ΩBh250 ≤ 0.125. These
limits are independent of Galactic chemical evolution models and only
assume that D is destroyed with time.

---------------------------------------------------------
Title: Hot Times in the Hertzsprung Gap
Authors: Ayres, Thomas
1995hst..prop.6067A Altcode: 1995hst..prop.2540A
I propose to explore the early evolution of magnetic activity in F-G0
giants crossing the Hertzsprung gap. The giant branch evolution of 2-4
solar mass stars provides a vital test of our understanding of magnetic
Dynamo action, coronal heating, and winds. The “X-ray deficiency”
of the F-G0 giants represents a clear distinction compared to cooler
Main Sequence stars. Possibly connected with the deficiency is the
newly recognized warm wind of the G0 secondary of Capella, as well
as indications for a previously unrecognized “broad component”
in its high excitation emissions like C IV 1548. The mass loss rate
of the Capella wind is low, but could be quite important in braking
the fast stellar rotation. The broad components might be associated
with the wind, but more likely are due to highly dynamic phenomena in
the subcoronal atmosphere; perhaps the stellar equivalent of solar
“transition zone explosive events.” These new aspects of stellar
activity warrant detailed consideration. My strategy is to use the
HST/GHRS to record key FUV emissions -- spanning the broad temperature
range 10,000 K - 200,000 K -- with high S/N in archetype Hertzsprung gap
stars. The objective is to measure line widths, profile asymmetries,
circumstellar absorptions, systematic Doppler shifts, and density
sensitive line ratios. Such diagnostics will be used to constrain
existing physical models, and develop new ones. The HST spectra will
strongly complement ongoing ROSAT &amp; EUVE work.

---------------------------------------------------------
Title: A Reanalysis of the SWP-HI IUE Observations of Capella
Authors: Wood, Brian E.; Ayres, T. R.
1995ApJ...443..329W Altcode:
We have reanalyzed the numerous high-resolution, far-ultraviolet
observations of Capella made by the International Ultraviolet Explorer
(IUE) in its 16 yr lifetime. Our purpose was to search for long-term
profile variations in Capella's ultraviolet emission lines and to
complement the analysis of Goddard High Resolution Spectrograph
(GHRS) observations of Capella, discussed in a companion paper
(Linsky et al. 1995). We implemented a state-of-the-art photometric
correction and spectral extraction procedure to improve S/N and control
potential sources for systematic errors. Nevertheless, we were unable
to find compelling evidence for any significant long-term profile
variations. Previous work has shown that the G8 primary star is only a
minor contributor to the high-excitation transition region lines but is
a significant contributor to the low-excitation chromospheric lines. We
have found exceptions to this rule, however. We find that the G8 star
is responsible for a significant portion of Capella's N V lambda lambda
1239, 1243 emission, but is not a large contributor to the S I lambda
1296, Cl I lambda 1352, and O lambda 1356 lines. We suggest possible
explanations for these behaviors. We also find evidence that the He II
lambda 1640 emission from the G1 star is from the transition region,
while the He II lambda 1640 emission from the G8 star is chromospheric,
consistent with the findings of Linsky et al. (1994). The C II lambda
1336 line shows a weak central reversal. It is blueshifted by about
9 km/s with respect to the centroid of the emission from the G1
star. While the central reversal of the C II line is blueshifted by
about 9 km/s with respect to the centroid of the emission from the
G1 star. While the central reversal of the C II line is blueshifted,
the central reversal of the Si III lambda 1207 line discussed by Linsky
et al. (1994) is not.

---------------------------------------------------------
Title: The Transition Regions of Capella
Authors: Linsky, Jeffrey L.; Wood, Brian E.; Judge, Philip; Brown,
Alexander; Andrulis, Catherine; Ayres, Thomas R.
1995ApJ...442..381L Altcode:
We have used the Goddard High Resolution Spectrometer (GHRS) to observe
the spectoscopic binary system Capella (G8 III + G1 III). Exposures
with the G140L, G140M, G160M, G200M, and echelle gratings provide
emission line profiles with unprecedented signal-to-noise and spectral
resolving power (lambda/Delta-lambda) up to 92,000. Multi-Gaussin fits
to the line profiles show that the hotter star contributes 60%-70% of
the total flux in the chromospheric O I and Mg II resonance lines, but
about 90% of the flux in the Si III, Si IV, and C IV lines formed in the
transition region at T less than or = 105 K. We find clear
evidence that the emission lines from the hotter star are systemtically
redshifted relative to the photosphere with Doppler shifts of 5 +/-
1 km/s for the +9 +/- 3 km/s in the chromospheric Mg II and O I lines,
respectively, increasing to +24 +/- 5 km/s for the transition region Si
IV 1393.8A line. The multi-Gaussian fits to permitted transition region
lines of SI III, Si IV, C IV, and N V indicate the presence of three
components: moderately broad lines formed in the transition region of
the hotter star (component H), narrow lines formed in the transition
region of the cooler star (component C), and very broad lines that we
think are formed in microflares on the hotter star (component B). The
He II 1640.4 A feature has an broad profile, which indicates that it
is formed by collisional excitation primarily from the hotter star,
and a weak narrow component that we interpret as due to radiative
recombination on the cooler star. We observed spin-forbidden emission
lines of C III), O III), Si III), O IV), O V), and S IV) that are
sensitive to electron density. Fainter members of the O IV) multiplet
and all of the S IV) lines have never before been seen in any star than
the Sun. We determine electron densities in the transition regions
of the Capella stars using lines ratios of O IV) lines and emission
measure analysis. The emission measures are self-consistent only when
the fluxes from each emitting component are considered separately. In
particular, the transition region abundance distributions appear to
be different on the two stars, and the spin-forbidden lines were not
detected in the B component. The emission measures for component
H (the G1 star) are consistent with a constant electron pressure
(or hydrostatic equilibrium) transition region with Pe =
1015 + 0.1/cu cm K and possibly solar 'coronal' abundances.

---------------------------------------------------------
Title: The Hydrogen Hole at the North Galactic Pole
Authors: Ayres, T. R.; Linsky, J. L.; Diplas, A.
1995AAS...186.3508A Altcode: 1995BAAS...27..860A
The yellow giant 31 Comae (HD111812: G0 III) lies near the North Galatic
Pole (b(II) = +89{fdg }6; l(II) = 114{fdg }9). Although 80 pc distant in
the Coma Berenices open cluster, 31 Com is a strong EUV source. Recent
HST/GHRS spectra of the star show surprisingly weak Mg II lambda2800 and
H I lambda1215 interstellar absorptions. The neutral hydrogen column
in that direction must be quite low, reminiscent of the interstellar
“void” toward epsilon CMa discovered by the EUVE. Indeed, previous
EUVE observations have shown that the lines of sight to the hot white
dwarfs HZ 43 (b(II) = +84deg ; l(II) = 54deg ) and GD 153 (b(II) =
+85deg ; l(II) = 317deg ) have very low columns, NH &lt;
1*E(18) cm(-2) , suggesting another “tunnel” near the NGP. We modeled
the GHRS spectra of 31 Com to determine whether there is a further
northward extension of the HZ 43/GD 153 void. [-3mm] The interstellar
Mg II h and k absorptions in the 31 Com spectrum are quite sharp,
suggesting only a single velocity component along the line of sight
(compared with several distinct clouds in the direction of epsilon
CMa). Our preliminary modeling of the Mg II, H I, and D I ISM features
indicates that xi_t , T, and [D/H] are similar to the values measured
previously for the lines of sight toward the nearby stars Capella and
Procyon. Furthermore, the bulk velocity (-2 km s(-1) , heliocentric) is
the same as predicted for the local cloud. The inferred neutral hydrogen
column, NH ~ 8*E(17) cm(-2) , is one of the smallest ever
measured directly from the Lyalpha absorption. We speculate that the
majority of the neutral gas in the direction of 31 Com lies very close
to the Sun in a few pc extension of the local “fluff”, and that the
remainder of the sightline is quite rarified and probably hot. In all
likelihood the HZ 43/GD 153 void is considerably larger than suspected
previously. [-2mm] This work was supported by NASA grants GO-5323.01-93A
(HST), S-56460-D (HST), and NAG5-2274 (EUVE).

---------------------------------------------------------
Title: Hubble Observations of D/H in the Local ISM and Consequences
for
Authors: Linsky, J. L.; Diplas, A.; Ayres, T. R.; Wood, B.; Brown, A.
1995lea..conf..215L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The RIASS Coronathon: Joint X-Ray and Ultraviolet Observations
of Normal F--K Stars
Authors: Ayres, Thomas R.; Fleming, T. A.; Simon, T.; Haisch, B. M.;
Brown, A.; Lenz, D.; Wamsteker, W.; de Martino, D.; Gonzalez, C.;
Bonnell, J.; Mas-Hesse, J. M.; Rosso, C.; Schmitt, J. H. M. M.;
Truemper, J.; Voges, W.; Pye, J.; Dempsey, R. C.; Linsky, J. L.;
Guinan, E. F.; Harper, G. M.; Jordan, C.; Montesinos, B. M.; Pagano,
I.; Rodono, M.
1995ApJS...96..223A Altcode:
Between 1990 August and 1991 January the ROSAT/IUE All Sky Survey
(RIASS) coordinated pointings by the International Ultraviolet Explorer
(IUE) with the continuous X-ray/EUV mapping by the Roentgensatellit
(ROSAT). The campaign provided an unprecedented multiwavelength
view of a wide variety of cosmic sources. We report findings for
F-K stars, a large proportion of the RIASS targets. Forty-eight of
our 91 'Coronathon' candidates were observed by the IUE during the
campaign. For stars missed by the IUE, we supplemented the ROSAT survey
fluxes with archival UV spectra and/or follow-on observations.

---------------------------------------------------------
Title: Surface structures and white-light flares on HR 1099: review
of MUSICOS 1989 results.
Authors: Foing, B. H.; Catala, C.; Baudrand, J.; Böhm, T.; Hubert,
A. M.; Cuby, J. G.; Czarny, J.; Dreux, M.; Felenbok, P.; Zhai, D.;
Jiang, S.; Huang, L.; Hao, J.; Char, S.; Jankov, S.; Ayres, T.;
Neff, J. E.; Simon, T.; Houdebine, E. R.; Butler, C. J.; Beust, H.;
Lagrange, A. -M.; Ferlet, R.; Vidal-Madjar, A.; Vitry, R.; Cutispoto,
G.; Catalano, S.; Frasca, A.; Rodonò, M.
1995mscs.conf..131F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Gappers and Clumpers: Finale
Authors: Ayres, Thomas R.
1995euve.prop...45A Altcode:
Something remarkable happens to moderate-mass giants during their
post-MS evolution through the Hertzsprung gap (F-G1), on their way
ultimately to the core-helium-burning Clump (G8-K0). The subcoronal
emissions of such stars (traced by Mg II and C IV) appear to be normal
for fast-rotating giants, but their coronal X-ray luminosities are
depressed by an order of magnitude or more. The nearby binary Capella is
the archetype: the G1 secondary has a C IV flux ten times that of the G8
primary, and rotates faster by a similar margin. Yet, evidence points
to near equality of the coronal X-ray fluxes. I, and my colleagues,
have been conducting a study of the dichotomy (and its implications
for coronal heating, structure, and the evolution of Dynamo action)
through EUVE spectroscopy of key stars along the post-MS trajectories
connecting the Hertzsprung gap and the Clump. The remaining candidate
for the program is the G5 giant, Mu Velorum. It is intermediate in its
properties to the previous targets, and is a bright source in the 100A
EUVE Survey band.

---------------------------------------------------------
Title: Thermal Bifurcation Revisited
Authors: Ayres, T. R.
1995itsa.conf..289A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: EUVE guest investigator program
Authors: Ayres, Thomas R.
1995cub..rept.....A Altcode:
The purpose of the grant was to obtain and analyze data from the EUVE
mission: specifically to investigate the 'coronal X-ray deficiency
syndrome.' This refers to the fact that late-F/early-G giants in
the Hertzsprung gap tend to show high levels of X-ray activity, but
curiously depressed relative to their emissions of coronal proxies
like C IV (lambda)1549. Later, when such stars have evolved through
the red-giant branch to the post-flash 'Clump,' their X-ray levels
decline dramatically, but their X-ray/C IV ratios return to 'normal'
values. The origin of the dichotomy is thought to bear strongly on the
nature of the elusive coronal heating mechanism, and its evolution
in time. The observations undertaken here include: ROSAT and ASCA
(specifically, 31 Com, a gap star; and beta Cet, an active Clump
giant) to probe the high-temperature material; HST/GHRS spectroscopy
to measure TZ flows and densities; and EUVE (31 Com observed in AO-1,
re-observed in AO-3; beta Cet and v Peg (a gap giant) in AO-2).

---------------------------------------------------------
Title: HST/GHRS and EUVE Spectra of the Active Clump Giant beta Ceti
(K0 III)
Authors: Ayres, T. R.; Brown, A.; Drake, S.; Simon, T.; Stern, R. A.;
Wood, B. E.
1994AAS...185.4510A Altcode: 1994BAAS...26.1381A
The nearby red giant beta Ceti (HD 4128: K0 III; d= 16 pc) is in
the postflash core helium burning phase. It is a member of a class
of coronally active “Clump” giants that includes the G8 primary of
Capella (alpha Aur: G8 III + G1 III) and the Hyad theta (1) Tauri (K0
III). Prior to the first ascent of the giant branch, such stars very
likely were hyperactive Hertzsprung-gap giants, like the G0 secondary of
Capella and 31 Comae (G0 III). HST/GHRS obtained spectra of beta Ceti
on 1994 June 2, in five intervals using both the SSA and LSA. Exposure
times ranged from 5.4 minutes (ECH-B/2800 Angstroms) to 43.5 minutes
(G160M/1400 Angstroms). Strong emissions of H I, Mg II, Si III, Si IV,
C IV, and N V were recorded with high S/N. Fainter lines of N I, C I,
Si I, O IV], and O V] also were seen. After correction for systematic
effects, we find that emissions which form below about 3*E(4) K are
close to the rest frame of the star, but higher excitation species are
systematically redshifted (as had been suggested previously on the basis
of lower S/N IUE echelle spectra). The redshifts are 10+/-2 km s(-1)
at N V/O IV temperatures (2*E(5) K); 16+/-1 at C IV (1*E(5) K); and
7+/-1 at Si IV (6*E(4) K). The strong high-excitation emissions have
nearly uniform FWHM's (~ 90 km s(-1) ), but show evidence for “broad
components” (FWHM ~ 150 km s(-1) ) at the bases of their profiles which
are slightly more redshifted than the parent lines. We see no evidence
for wind absorptions in the very high S/N (&gt;50:1) profiles of Mg II
k or H I Lyalpha , although the former displays a clear chromospheric
central reversal outside of the sharp ISM feature. We will compare
the HST/GHRS spectra with a 140 ks pointing on beta Ceti by the EUVE,
conducted during the six day period beginning 1994 September 30. This
work was supported by NASA grants GO-5323.01-93A (HST) and NAG5-2274
(EUVE).

---------------------------------------------------------
Title: Multi-site continuous spectroscopy. II. Spectrophotometry
and energy budget of exceptional white-light flares on HR1099 from
the MUSICOS 89 campaign.
Authors: Foing, B. H.; Char, S.; Ayres, T.; Catala, C.; Neff, J. E.;
Zhai, D. S.; Catalano, S.; Cutispoto, G.; Jankov, S.; Rodono, M.;
Simon, T.; Akan, C.; Aslanov, A.; Avellar, P.; Baudrand, J.; Beust,
H.; Cao, H.; Chatzichristou, H.; Cuby, J. G.; Czarny, J.; de La Reza,
R.; Dreux, M.; Felenbok, P.; Ferlet, R.; Frasca, A.; Floquet, M.;
Ghosh, K.; Guo, Z.; Guerin, J.; Hao, J. X.; Houdebine, E. R.; Huang,
L.; Hubert, A. M.; Hubert, H.; Huovelin, J.; Hron, J.; Ibanoglu, C.;
Jiang, S.; Keskin, V.; Lagrange-Henri, A. M.; Lecontel, J. M.; Li,
Q.; Mavridis, L.; Nolthenius, R.; Petrov, P.; Savanov, I.; Scherbakov,
A.; Tuominen, I.; Vidal-Madjar, A.; Zhang, R.; Zhang, X.
1994A&A...292..543F Altcode:
We report results from the December 89 multi-site continuous observing
campaign (MUSICOS 89) dedicated to the study of surface active
structures and flares on the RS CVn-type system HR1099 (=V711 Tau). This
system has been observed by up to 17 telescopes around the globe during
this campaign. We obtained complete phase coverage for Doppler imaging
of photospheric spots. Quasi-simultaneously, we observed the modulation
of Ca II K line profile due to chromospheric plage regions. At least
two exceptional white-light flares on 14 Dec. 15:00 UT and 15 Dec. 1:00
UT (the largest such optical flare episode ever reported in a RS CVn
system) were detected photometrically with typical rise and decay
times of 60-90 min, and with remarkable spectral dynamic signatures
in Hα, with longer decay time scale. Equivalent colours, temperature
excesses and projected flare areas (0.55 and 0.89 solar disc areas)
were derived for the two optical flares. We estimate the energy budget
for these two events, with respective peak intensities of radiative
losses of 1.65 and 1410^33^erg/s and integrated losses over the
white-light event duration of a few hours of 8.10^36^ and 10^38^ergs
(in the 3100-5900A range), indicating a total energy balance several
times these values. The emission was also measured in the Hα and
Hβ lines during these flares with a ratio of flare optical emission
over Balmer emission 3-4 times larger compared to other flares on
dwarfs. More than one day after the last white-light flare, part of
the flare decay phase was also measured with IUE in UV lines of low
and high excitation; the extrapolated transition region EUV losses are
found similar to the derived Balmer line losses. Both flares were shown
to occur near the limb. We derive their physical area, and estimate
their densities, column mass, and penetration depth. From Balmer line
broadening and flows, we derive a kinetic energy budget comparable to
the radiative losses. We discuss a possible magnetic energy budget
and the interpretation in terms of filament ejection occurring over
a magnetic arcade. These observations bring a new understanding and
questions about energy transport mechanisms in stellar flares.

---------------------------------------------------------
Title: A reanalysis of the IUE high resolution observations of
Capella.
Authors: Wood, B. E.; Ayres, T. R.
1994BAAS...26..864W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Flare-Ona of 31 Comae
Authors: Ayres, T. R.; Brown, A.
1994AAS...184.0503A Altcode: 1994BAAS...26..863A
31 Comae (HD111812: G0 III) is a rapidly rotating moderate mass giant
in the middle of the Hertzsprung gap. It is a luminous source of soft
X-rays and C IV lambda 1549, although it is a member of the “X-ray
deficient” class of F/G giants (and early-F dwarfs) identified
by Simon &amp; Drake (1989, ApJ, 346, 303). We discuss the nature
of the corona of 31 Com based on an 80 ks pointing by the Extreme
Ultraviolet Explorer (EUVE), and historical FUV and X-ray exposures
from IUE and ROSAT, respectively. We provide a context for the 31 Com
energy distribution by applying an identical analysis to archival EUVE,
IUE, and ROSAT/PSPC spectra of the evolved stars alpha CMi (F5 IV),
alpha Aur (G8 III + G0 III), and HR1099 (K0 IV [+ G5 V]). 31 Com shows
a remarkably hot coronal energy distribution that rivals that of the
hyperactive RS CVn system HR1099 (and the dMe flare star AU Mic). It
is decidedly different from soft coronal sources like the Sun and
alpha CMi. The hot coronal structure is reminiscent of a continuously
flaring plasma. However, the overt signatures of impulsive outbursts
-- common on RS CVn's and dMe flare stars -- are absent. We propose
that the G0 III giants at the red edge of the Simon &amp; Drake X-ray
deficiency boundary are undergoing a transient evolutionary episode of
intense magnetic activity. We believe that the surface manifestations
include widespread compact flaring “bright points” commensurate with
the shallow unstable envelopes of these newly convective stars. The
“flare-ona” of 31 Com suggested by the EUVE allows us to interpret
the peculiar 80--300 Angstroms spectrum of alpha Aur reported by Dupree
and collaborators (1993, ApJL, 418, L41). The enhanced emission measure
at and above 10(7) K very likely is from the active G0 III secondary,
while the pronounced peak in EM near 5*E(6) K is from the more evolved
(post helium flash) G8 III primary. Our work was supported by EUVE
Guest Observer grants from NASA.

---------------------------------------------------------
Title: A Reanalysis of the IUE High Resolution Observations of Capella
Authors: Wood, B. E.; Ayres, T. R.
1994AAS...184.0509W Altcode: 1994BAAS...26Q.864W
We have reanalyzed the numerous high resolution observations of
Capella (G8 III + G0 III) made by the SWP camera of the International
Ultraviolet Explorer (IUE) in its 16 year lifetime. One of our goals
was to search for long term profile variations in Capella's ultraviolet
emission lines, but we were unable to find any compelling evidence for
any significant variations. Another goal is to compare the line profiles
observed by the IUE with those observed by the Goddard High Resolution
Spectrograph aboard the Hubble Space Telescope. Previous authors
have shown that the G8 star is only a minor contributor to the high
excitation transition region lines, but is a significant contributor
to the low excitation chromospheric lines. We have found exceptions
to this rule, however. We find that the G8 star is responsible for
a large portion of Capella's N V lambda lambda 1238, 1242 emission,
but is not a large contributor to the chromospheric S I lambda 1295,
Cl I lambda 1351, and O I] lambda 1355 lines, and we suggest possible
explanations for this. We also find evidence that the He II lambda
1640 emission from the G0 star is from the transition region, while
the He II lambda 1640 emission from the G8 star is chromospheric. The
C II lambda 1335 line shows a weak central reversal. We have modeled
this line with Gaussians, and we find that the Gaussian representing
the central reversal is blueshifted by about 9 km s(-1) with respect
to the Gaussian representing the emission from the G0 star, similar
to the central reversal observed in the solar C II lambda 1335 line.

---------------------------------------------------------
Title: Carbon Monoxide Fundamental Bands in Late-Type
Stars. III. Chromosphere or CO-mosphere?
Authors: Wiedemann, G.; Ayres, T. R.; Jennings, D. E.; Saar, S. H.
1994ApJ...423..806W Altcode:
The strong vibration-rotation lines of CO at 4.6 microns (Δυ = 1)
are unique diagnostics for the thermal conditions in the atmospheric
altitude range of late-type stars near and above the temperature
minimum in chromospheric models. Exploiting recent improvements in IR
instrumentation, we observed a number of cool stars with high spectral
resolution (R ≍ 100,000). The analysis of the spectra was based on
an earlier theoretical study which had established CO Δυ = 1 non-LTE
spectra as useful probes for stars of spectral type F, G, and K with
log g ≥ 1. No direct chromospheric indicators were detected
in the CO spectra. Stellar boundary (CO) temperatures were determined
for the program stars and temperature profiles were constructed for α
Tau, α Boo, β Gem and β Dra. The CO-based models feature a steady
decrease in temperature at the height where the temperature increases in
chromospheric models. Further comparison with chromospheric indicators
shows an increasing discrepancy between the temperatures determined
from CO measurements and those predicted from radiative equilibrium
models, respectively, with increasing chromospheric activity. Thermal
bifurcation of the stellar surfaces is proposed to reconcile the
contradicting scenarios derived based on different spectral diagnostics.

---------------------------------------------------------
Title: Sleuthing the Dynamo: HST/FOS Observations of UV Emissions
of Solar-Type Stars in Young Clusters
Authors: Ayres, T.; Basri, G.; Simon, T.; Stauffer, J.; Stern, R.;
Antiochos, S.; Bookbinder, J.; Brown, A.; Doschek, G.; Linsky, J.;
Ramsey, L.; Walter, F.
1994ASPC...64...53A Altcode: 1994csss....8...53A
No abstract at ADS

---------------------------------------------------------
Title: The Corona of the K5 Giant γ Dra, and its Relation to the
HybridChromosphere Stars
Authors: Brown, A.; Linsky, J. L.; Ayres, T. R.
1994AIPC..313...36B Altcode: 1994sxrc.conf...36B
Gamma Draconis is the first, normal, single late K giant located on
the red side of the coronal “dividing line” known to show conclusive
evidence for hot (∼105 K) transition region (TR) and
coronal plasma. We present ROSAT PSPC data and HST GHRS spectra of
γ Dra and describe the coronal and TR properties of this K5 III
star. The high temperature emissions of γ Dra are compared to those
of a sample of hybrid-chromosphere bright giants and supergiants. New
PSPC detections of the K3 giant α Hya and the G supergiant β Aqr are
presented. Upper limits are found for the hybrid-chromosphere stars
θ Her and α Aqr. These new measurements extend the X-ray to C IV
flux-flux relations to significantly lower activity levels.

---------------------------------------------------------
Title: A Far-Ultraviolet Flare on a Pleiades G Dwarf
Authors: Ayres, T. R.; Stauffer, J. R.; Simon, Theodore; Stern, R. A.;
Antiochos, S. K.; Basri, G. S.; Bookbinder, J. A.; Brown, A.; Doschek,
G. A.; Linsky, J. L.; Ramsey, L. W.; Walter, F. M.
1994ApJ...420L..33A Altcode:
The Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) recorded
a remarkable transient brightening in the C IV lambda lambda 1548,50
emissions of the rapidly rotating Pleiades G dwarf H II 314. On the one
hand the 'flare' might be a rare event luckily observed; on the other
hand it might be a bellwether of the coronal heating in very young
solar-mass stars. If the latter, flaring provides a natural spin-down
mechanism through associated sporadic magnetospheric mass loss.

---------------------------------------------------------
Title: The Transition Regions of Capella
Authors: Linsky, J. L.; Wood, B. E.; Brown, A.; Andrulis, C.; Judge,
P.; Ayres, T. R.
1994ASPC...64...62L Altcode: 1994csss....8...62L
No abstract at ADS

---------------------------------------------------------
Title: COmospheres and Coronae
Authors: Ayres, T. R.
1994ASPC...57..124A Altcode: 1994scsa.conf..124A
No abstract at ADS

---------------------------------------------------------
Title: New Light on the Heart of Darkness of the Solar Chromosphere
Authors: Solanki, S. K.; Livingston, W.; Ayres, T.
1994Sci...263...64S Altcode:
Solar carbon monoxide spectra indicate the existence of a cool (less
than 4000 kelvin) component to the solar chromosphere coexisting with
the hot, bright gas at 6000 to 7000 kelvin. However, both the existence
and the location of the cool component have been controversial. New
high-resolution spectra show that carbon monoxide goes into emission
just beyond the limb, allowing it to be probed without photospheric
contamination. The cool component has temperatures as low as 3000 to
3500 kelvin and appears to cover 50 to 85 percent of the quiet solar
surface. There is a steep temperature rise to normal chromospheric
temperatures at a height of 900 to 1100 kilometers. Large horizontal
velocities are seen, suggesting that the cool component is maintained
by the supersonic adiabatic expansion of upwelling gas in overshooting
granules.

---------------------------------------------------------
Title: Gappers and Clumpers, Cont'd
Authors: Ayres, Thomas R.
1994euve.prop...27A Altcode:
Something remarkable happens to moderate mass stars during their post-MS
evolution through the Hertzsprung gap (F-G0), on their way ultimately
to the post-helium-flash Clump (G8-K0). The subcoronal emissions of
the H-gap stars (traced by Mg II and C IV) appear to be normal for
fast-rotating giants, but their coronal X-ray luminosities are depressed
by an order of magnitude or more. The nearby binary Capella is the
archetype: the G0 secondary has a C IV flux ten times that of the G8
primary, and rotates faster by a similar factor. Yet, evidence points
to near equality of the coronal X-ray fluxes. I propose to continue
a broad-reaching exploration of the dichotomy (and its implications
for coronal heating, structure, and the evolution of Dynamo action)
through EUVE spectroscopy of key stars along the post-Main-Sequence
trajectories connecting the Hertzsprung gap and the Clump. Part of the
program is a re-observation of the prime target from AO-1: 31 Comae
(G0 III). The SW spectrum is faint but remarkable. It exhibits almost
exclusively very hot (T = 1 keV) lines. A three times deeper exposure
can almost triple the S/N owing to the reduced detector background in
recent observations. Key coronal density diagnostic lines might then
become accessible.

---------------------------------------------------------
Title: The Shocking Truth about Beta Cassiopeia
Authors: Ayres, T. R.
1994ASPC...64..351A Altcode: 1994csss....8..351A
No abstract at ADS

---------------------------------------------------------
Title: The Spectral Variability of BP Tauri
Authors: Simon, Theodore; Imhoff, C. L.; Basri, G. S.; Ayres, T. R.
1994ASPC...64..729S Altcode: 1994csss....8..729S
No abstract at ADS

---------------------------------------------------------
Title: The MUSICOS Network for Multi-Site Continuous Spectroscopy
Authors: Foing, B. H.; MUSICOS Collaboration; Catala, C.; Baudrand,
J.; Boehm, T.; Hubert, A. M.; Jankov, S.; Cutispoto, G.; Catalano,
S.; Pagano, I.; Rodono, M.; Umana, G.; Zhai, D. S.; Jiang, S.; Huang,
L.; Hao, J. X.; Char, S.; Houdebine, E. R.; Ayres, T.; Neff, J. E.;
Simon, T.; Butler, C. J.; Collier-Cameron, A.; Kennelly, T.; Walker,
G.; Talavera, A.
1994ASPC...64..699F Altcode: 1994csss....8..699F
No abstract at ADS

---------------------------------------------------------
Title: The Relationship Between Radiative and Magnetic Fluxes on
Three Active Solar-type Dwarfs
Authors: Linsky, J. L.; Andrulis, C.; Saar, S. H.; Ayres, T. R.;
Giampapa, M. S.
1994ASPC...64..438L Altcode: 1994csss....8..438L
We present some preliminary results from our coordinated campaign of
IUE and McMath Telescope magnetic field measurements of three active
solar-type dwarf stars: 59 Vir, xi Boo A, and HD 131511. We observed
the three stars nearly every day from May 9 to May 25, 1993, covering
between 1 and 3 rotations. We explore the functional and spatial
relationship between magnetic and radiative fluxes.

---------------------------------------------------------
Title: The upper photosphere and lower chromosphere of small-scale
magnetic features
Authors: Solanki, S. K.; Bruls, J. H. M. J.; Steiner, O.; Ayres, T.;
Livingston, W.; Uitenbroek, H.
1994ASIC..433...91S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Atmospheric Dynamics and Mass Loss in Gappers, Clumpers,
and Hybrids CYC4 - Medium
Authors: Ayres, Thomas
1994hst..prop.5323A Altcode: 1994hst..prop.1771A
The giant branch evolution of moderate-mass stars provides a
vital test of our understanding of magnetic dynamo action, coronal
energization, and winds. The blatant“X-ray deficiency” of the
Hertzsprung-gap giants appears to be genuine, while that of many
“hybrid-chromosphere” supergiants appears to be due to absorption
by a previously unrecognized warm or hot component of their winds;
not apparent in the Mg II circumstellar features but quite evident in
the H I Lyman-alpha profile (of at least one case). There also is new
evidence for a warm wind on the G0 secondary of Capella -- a “gap”
star. The mass-loss rate is low, but dynamically quite significant in
braking the fast stellar rotation. Outflows of some kind probably exist
on post-helium-flash Clump giants, as well, although “antiwinds”
are the hallmark of the archetype, Beta Ceti. I propose to clarify
the subcoronal properties of the Hertzsprung-gap, active Clump, and
Hybrid stars through a spectral dissection of one representative of each
class. My strategy is to use the HST/GHRS to record key FUV emissions --
spanning the broad temperature range 10,000-250,000 K -- with high S/N
to measure line widths, profile asymmetries, circumstellar absorptions,
systematic Doppler shifts, and density-sensitive line ratios. Such
diagnostics will be used to constrain existing physical models, and
develop new ones. The HST spectra will strongly complement ongoing
X-ray work with ROSAT and recent EUVE spectroscopy.

---------------------------------------------------------
Title: The Cold Heart of the Solar Chromosphere
Authors: Ayres, T. R.
1994IAUS..154...11A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Topology
Authors: Ayres, Thomas
1994iue..prop.4749A Altcode:
The coronal morphology of the RS Canum Venaticorum binaries has been
the subject of considerable debate over the past decade. Are the UV and
X-ray bright structures of the subgiant primaries relatively compact,
surface-hugging features analogous to the magnetic arcades of solar
active regions? Or, do they extend to great altitudes, possibly
interacting with their counterparts from the MS secondary? Given
the practical difficulties of directly resolving the high-excitation
'surface' of a distant star, one must resort to proxies: (1) spectral
imaging; and (2) rotational modulations of inhomogeneous brightness
distributions. The techniques are best suited to the fastest-rotating
objects, which conveniently also are the most active owing to the
catalyzing effect of rotation on the generation of magnetic flux in
cool stars. We propose to obtain a unique one-month sampling of the
UV emissions of three bright RS CVn variables in concert with the
near-continuous record of coronal intensities provided by the ALEXIS
EUV sky-monitor. We currently are undertaking such a campaign for
the bright RS CVn II Peg and the distantly-related object alpha Aur
(Capella: sometimes called a "long-period RS CVn"). Our objective is
to study the 3-D structure of hyperactive atmospheres in their most
favorable light.

---------------------------------------------------------
Title: Rapid Ultraviolet Variability in NGC 4151
Authors: Edelson, R.; Fenton, S.; Crenshaw, D. M.; Reichert, G. A.;
Peterson, B. M.; Clavel, J.; Rodriguez-Pascual, P.; Warwick, R.;
Smith, D.; Ayres, T.; Shull, J. M.
1994ASPC...69..171E Altcode: 1994rmbl.conf..171E
No abstract at ADS

---------------------------------------------------------
Title: Coronal Winds from Giants and Supergiants
Authors: Ayres, T. R.; Kashyap, V.
1994ASPC...64..681A Altcode: 1994csss....8..681A
No abstract at ADS

---------------------------------------------------------
Title: A Reanalysis of the Interstellar Medium along the Capella
Line of Sight
Authors: Linsky, J. L.; Diplas, A.; Ayres, T.; Wood, B.; Brown, A.
1993AAS...18311413L Altcode: 1993BAAS...25.1464L
We report on new GHRS/HST observations of the interstellar HI and DI
Lyman-alpha lines and the FeII and MgII resonance lines along the line
of sight toward the nearby (12.5 pc) star Capella. These observations
were obtained at orbital phase 0.80 when the combined stellar emission
lines had different shapes compared to those obtained in earlier
observations at phase 0.26 and analyzed by Linsky et al. (ApJ 402,
694 (1993)). By reversing the radial velocities of the two stars we
are better able to derive the intrinsic stellar profiles, especially
for the Lyman alpha line, and therefore to determine the interstellar
absorption lines more precisely. We compare the derived properties
of the local interstellar medium (D/H ratio, temperature, turbulent
velocity, hydrogen column density, and gas phase abundances) for Capella
at the two phases with the properties derived for the line of sight to
another nearby (3.5 pc) star Procyon. This work is supported by NASA
grant S-56460-D to the National Institute of Standards and Technology.

---------------------------------------------------------
Title: Visualization techniques to aid in the analysis of
multi-spectral astrophysical data sets
Authors: Brugel, Edward W.; Domik, Gitta O.; Ayres, Thomas R.
1993colo.reptQ....B Altcode:
The goal of this project was to support the scientific analysis
of multi-spectral astrophysical data by means of scientific
visualization. Scientific visualization offers its greatest value
if it is not used as a method separate or alternative to other data
analysis methods but rather in addition to these methods. Together
with quantitative analysis of data, such as offered by statistical
analysis, image or signal processing, visualization attempts to
explore all information inherent in astrophysical data in the most
effective way. Data visualization is one aspect of data analysis. Our
taxonomy as developed in Section 2 includes identification and access to
existing information, preprocessing and quantitative analysis of data,
visual representation and the user interface as major components to
the software environment of astrophysical data analysis. In pursuing
our goal to provide methods and tools for scientific visualization of
multi-spectral astrophysical data, we therefore looked at scientific
data analysis as one whole process, adding visualization tools to an
already existing environment and integrating the various components
that define a scientific data analysis environment. As long as the
software development process of each component is separate from
all other components, users of data analysis software are constantly
interrupted in their scientific work in order to convert from one data
format to another, or to move from one storage medium to another, or
to switch from one user interface to another. We also took an in-depth
look at scientific visualization and its underlying concepts, current
visualization systems, their contributions, and their shortcomings. The
role of data visualization is to stimulate mental processes different
from quantitative data analysis, such as the perception of spatial
relationships or the discovery of patterns or anomalies while browsing
through large data sets. Visualization often leads to an intuitive
understanding of the meaning of data values and their relationships by
sacrificing accuracy in interpreting the data values. In order to be
accurate in the interpretation, data values need to be measured,
computed on, and compared to theoretical or empirical models
(quantitative analysis). If visualization software hampers quantitative
analysis (which happens with some commercial visualization products),
its use is greatly diminished for astrophysical data analysis. The
software system STAR (Scientific Toolkit for Astrophysical Research)
was developed as a prototype during the course of the project to better
understand the pragmatic concerns raised in the project. STAR led
to a better understanding on the importance of collaboration between
astrophysicists and computer scientists.

---------------------------------------------------------
Title: Visualization techniques to aid in the analysis of
multispectral astrophysical data sets
Authors: Brugel, E. W.; Domik, Gitta O.; Ayres, T. R.
1993colo.reptS....B Altcode:
The goal of this project was to support the scientific analysis
of multi-spectral astrophysical data by means of scientific
visualization. Scientific visualization offers its greatest value
if it is not used as a method separate or alternative to other data
analysis methods but rather in addition to these methods. Together
with quantitative analysis of data, such as offered by statistical
analysis, image or signal processing, visualization attempts to
explore all information inherent in astrophysical data in the most
effective way. Data visualization is one aspect of data analysis. Our
taxonomy as developed in Section 2 includes identification and access to
existing information, preprocessing and quantitative analysis of data,
visual representation and the user interface as major components to
the software environment of astrophysical data analysis. In pursuing
our goal to provide methods and tools for scientific visualization of
multi-spectral astrophysical data, we therefore looked at scientific
data analysis as one whole process, adding visualization tools to an
already existing environment and integrating the various components
that define a scientific data analysis environment. As long as the
software development process of each component is separate from
all other components, users of data analysis software are constantly
interrupted in their scientific work in order to convert from one data
format to another, or to move from one storage medium to another, or
to switch from one user interface to another. We also took an in-depth
look at scientific visualization and its underlying concepts, current
visualization systems, their contributions and their shortcomings. The
role of data visualization is to stimulate mental processes different
from quantitative data analysis, such as the perception of spatial
relationships or the discovery of patterns or anomalies while browsing
through large data sets. Visualization often leads to an intuitive
understanding of the meaning of data values and their relationships by
sacrificing accuracy in interpreting the data values. In order to be
accurate in the interpretation, data values need to be measured,
computed on, and compared to theoretical or empirical models
(quantitative analysis). If visualization software hampers quantitative
analysis (which happens with some commercial visualization products),
its use is greatly diminished for astrophysical data analysis. The
software system STAR (Scientific Toolkit for Astrophysical Research)
was developed as a prototype during the course of the project to
better understand the pragmatic concerns raised in the project. STAR
led to a better understanding on the importance of collaboration
between astrophysicists and computer scientists. Twenty-one examples
of the use of visualization for astrophysical data are included with
this report. Sixteen publications related to efforts performed during
or initiated through work on this project are listed at the end of
this report.

---------------------------------------------------------
Title: Signal-to-Noise Ratios in IUE Low-Dispersion
Spectra. II. Photometrically-Corrected Images
Authors: Ayres, Thomas R.
1993PASP..105..538A Altcode:
The character of detector noise is explored in photometrically-corrected
images from the shortwavelength and longwavelength prime intensified
vidicon cameras of the International Ultraviolet Explorer. A
protocol is proposed for deriving realistic "noise models"--crucial
to the application of Optimal extraction algorithms like that of
Kinney, Bohlin, and Neill (1991)--from the available collections of
UV-Flood calibration images. The protocol includes evaluation of the
"noise-filtering" properties of the SWP and LWP cameras through 2-D
spatial power spectrum analysis. (SECTION: Instrumentation and Data
Analysis)

---------------------------------------------------------
Title: The Hydrogen Lyman-Alpha Emission of Capella
Authors: Ayres, Thomas R.; Brown, A.; Gayley, K. G.; Linsky, Jeffrey L.
1993ApJ...402..710A Altcode:
We describe the hydrogen Ly-alpha emission of the spectroscopic
binary Capella (G8 III + GO III) recorded at 0.1 A resolution by the
International Ultraviolet Explorer. The overt changes in the composite
line shape with orbital phase are controlled by the active GO III
star and permit a dissection of the stellar components despite the
obliteration of the central portion of the profile by atomic hydrogen
and deuterium absorption along the 12.5 pc sightline. The Ly-alpha line
shape of the active GO III star is surprisingly asymmetric and possibly
is variable. Both characteristics suggest a stellar wind of moderate
excitation (20,000-100,000 K), a key component of the coronal evolution
scenario of Simon and Drake (1989) for the Hertzsprung-gap giants.

---------------------------------------------------------
Title: The Coronal X-ray Deficiency Syndrome
Authors: Ayres, Thomas R.
1993euve.prop...38A Altcode:
Something strange happens to M ~ 3 M(sun) stars during their post-MS
evolution through the Hertzsprung gap (F--G0), on their way ultimately
to the post-helium-flash “Clump (G8--K0). The subcoronal emissions
of the H-gap stars (traced by Mg II and C IV) appear to be normal
for fast-rotating giants, but their coronal X-ray luminosities are
depressed by an order of magnitude or more. The nearby binary Capella
is the archetype: the G0 secondary has a C IV flux 10 times that of
the G8 primary, and rotates faster by a similar factor. Yet, evidence
points to near equality of the coronal X-ray fluxes. We propose to
continue our broad-reaching exploration of the dichotomy (and its
implications for coronal heating and the evolution of Dynamo action)
through EUVE spectroscopy of key stars along the post-Main-Sequence
trajectories connecting the Hertzsprung gap and the Clump.

---------------------------------------------------------
Title: Coronal Topology
Authors: Ayres, Thomas R.
1993iue..prop.4481A Altcode:
The coronal morphology of the RS Canum Venaticorum binaries has been
the subject of considerable debate over the past decade. Are the
UV and X-ray bright structures of the subgiant primaries relatively
compact, surface-hugging features analogous to the magnetic arcades of
solar active regions? Or, do they extend to great altitudes, possibly
interacting with their counterparts from the MS secondary star? Given
the practical difficulties of directly resolving the high-excitation
'surface' of a distant star, one must resort to proxies. The most
useful are: (1) spectral imaging; and (2) "rotational modulations"
of inhomogeneous brightness distributions. The techniques are best
suited to the fastest-rotating objects, which conveniently also
are the most "active" owing to the catalyzing effect of rotation on
the generation of magnetic flux in cool stars. We propose to obtain
a unique medium-term (months) sampling of the UV emissions of four
bright RS CVn variables, and the related object alpha Aur, in concert
with the near-continuous record of coronal intensities provided by the
ALEXIS EUV sky-monitor. Our objective is to study the three-dimensional
structure of hyperactive atmospheres in their most favorable light. [Our
proposal is substantially identical to an approved 15th-Episode program
of the same title. Our current target-of-opportunity program cannot,
however, be implemented in the present episode because the launch of
ALEXIS has slipped into spring 1993, and the five prime targets will
not be available until the fall. Thus, we are renewing our request.]

---------------------------------------------------------
Title: The Cool-Star Spectral Catalog: A Uniform Collection of
IUE SWP-LOs
Authors: Ayres, T.; Lenz, D.; Burton, R.; Bennett, J.
1993ASPC...52...51A Altcode: 1993adass...2...51A
We have assembled an extensive electronically-accessible catalog of
low-dispersion far-ultraviolet spectra of chromospheric emission-line
stars observed with the International Ultraviolet Explorer.

---------------------------------------------------------
Title: Goddard High-Resolution Spectrograph Observations of the Local
Interstellar Medium and the Deuterium/Hydrogen Ratio along the Line
of Sight toward Capella
Authors: Linsky, Jeffrey L.; Brown, Alexander; Gayley, Ken; Diplas,
Athanassios; Savage, Blair D.; Ayres, Thomas R.; Landsman, Wayne;
Shore, Steven N.; Heap, Sara R.
1993ApJ...402..694L Altcode:
HST Goddard High-Resolution Spectrograph observations of the 1216,
2600, and 2800 A spectral regions are analyzed for the spectroscopic
binary system Capella, obtained at orbital phase 0.26 with 3.27-3.57
km/s resolution and high SNR. The column densities of H I, D I, Mg II,
and Fe II for the local interstellar medium along this 12.5 pc line
of sight, together with estimates of the temperature and turbulent
velocity are inferred. It is inferred that the atomic deuterium/hydrogen
ratio by number is 1.65(+0.07, -0.18) x 10 exp -5 for this line of
sight. Galactic evolution calculations indicate that the primordial
D/H ratio probably lies in the range of (1.5-3) x (D/H)LISM. If H0 =
80 km/s Mpc, as recent evidence suggests, then the baryonic density in
units of the Einstein-de Sitter closure density is 0.023-0.031. Thus
the universe is argued to expand forever, unless nonbaryonic matter
greatly exceeds the amount of baryonic matter.

---------------------------------------------------------
Title: The Distant Future of Solar Activity: A Case Study of beta
Hydri. III. Transition Region, Corona, and Stellar Wind
Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Linsky, J. L.;
Monsignori-Fossi, B.; Simon, T.; Wallinder, F.
1993ApJ...403..412D Altcode:
The paper investigates the secular decay of solar-type activity
through a detailed comparison of the present sun with the very old
solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses
of successive atmospheric layers are presented, with emphasis of the
outermost parts. The FUV emission lines for the transition zone are
among the faintest so far seen in any solar-type star. The coronal soft
X-ray spectrum was measured through different filters on EXOSAT and
compared to simulated X-ray observations of the sun seen as a star. The
flux from Beta Hyi is weaker than that from the solar corona and has
a different spectrum. It is inferred that a thermally driven stellar
wind can no longer be supported, which removes the mechanism from
further rotational braking of the star through a magnetic stellar wind.

---------------------------------------------------------
Title: Errors Associated with Fitting Gaussian Profiles to Noisy
Emission-Line Spectra
Authors: Lenz, Dawn D.; Ayres, Thomas R.
1992PASP..104.1104L Altcode:
Landman, Roussel-Dupre, and Tanigawa developed prescriptions to predict
profile fitting errors for Gaussian emission lines perturbed by white
noise. We show that their scaling laws can be generalized to more
complicated signal-dependent "noise models" of common astronomical
detector systems. (SECTION: Instrumentation and Data Analysis)

---------------------------------------------------------
Title: Extreme Ultraviolet Spectroscopy of Capella
Authors: Green, James C.; Wilkinson, Erik; Ayres, Thomas R.; Cash,
Webster C.
1992ApJ...397L..99G Altcode:
The X-ray active binary system Capella was observed with a
moderate-resolution extreme ultraviolet spectrograph from 200 to 330
A. Two low-level emission features were detected. One most likely is
geocoronal He II 304 A emission, while the other probably originates
from the corona of Capella. The weak stellar emission at 304 A is
in direct conflict with predictions of the intrinsic stellar He II
flux based on standard scaling arguments but is consistent with the
only previous observation of Capella in the EUV. The most plausible
explanation for the lack of stellar 304 A emission is a warm wind from
the active G0 III star.

---------------------------------------------------------
Title: The Capella Dichotomy: Paradigm Lost?
Authors: Ayres, Thomas R.
1992euve.prop...82A Altcode:
Recent studies of the soft X-ray and C IV emissions of M &lt; 3 M(sun)
giants have shown that those in the post helium flash Clump (near
K0) sit on a R(X) ~ R(C IV)^3/2 power law like the F-K dwarfs, while
the early-F/early-G Hertzsprung-gap giants tend to lie on a separate
parallel relation. The nearby binary Capella (G8III + G0III) is the
archtype: the G0 secondary has a C IV flux 10x that of the G8 primary,
and rotates faster by a similar factor. Yet, evidence points to near
equality of the coronal X-ray fluxes. The latter facet of the Capella
dichotomy is at odds with the central paradigm of cool-star coronae:
the rotation-activity connection. I propose to explore the differences
between the coronal properties of the Hertzsprung-gap and active Clump
giants through measurements of the T(cor)s and EM distributions of 3
representative members of each class.

---------------------------------------------------------
Title: The Shocking Truth About Beta Cassiopeiae
Authors: Ayres, Thomas R.
1992iue..prop.4192A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The distant future of solar activity: a case study of beta
Hydri (abstract)
Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.;
Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, Å.;
Simon, T.; Vandenberg, D.; Wallinder, F.
1992sccw.conf..105D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Colorado scale-model solar system
Authors: Bennett, Jeffrey O.; Ayres, Thomas R.; Center, Kenneth B.;
Carter, Matthew F.; Bass, Ronald S.
1991PhTea..29..371B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Digging in the Coronal Graveyard: A ROSAT Observation of the
Red Giant Arcturus
Authors: Ayres, Thomas R.; Fleming, Thomas A.; Schmitt, Juergen
H. M. M.
1991ApJ...376L..45A Altcode:
A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with
the Roentgensatellit (Rosat) failed to detect soft X-ray emission from
the archetype 'noncoronal' red giant. The 3-sigma upper limit in the
energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than
3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density
of less than 0.0001 solar. The nondetection safely eliminates coronal
irradiation as a possible mechanism to produce the highly variable He
I 10830 feature and emphasizes the sharp decline in solarlike coronal
activity that accompanies the evolution of low-mass single stars away
from the main sequence. While the most conspicuous object in the Rosat
field of view was not visible in X-rays, at least one fainter star is
among the about 60 sources recorded: the Sigma Sct variable CN Boo,
an A8 giant in the UMa Stream.

---------------------------------------------------------
Title: The Many Faces of F Stars: A Rotational Modulation Study of
Capella, Procyon, and Caph with the International Ultraviolet Explorer
Authors: Ayres, Thomas R.
1991ApJ...375..704A Altcode:
Far-UV spectroscopy of the F stars Capella, Procyon, and Caph is
reported. Although all three stars are regard as chromospherically
'active', none exhibited any sensible rotational modulations, indicating
a smooth surface distribution of chromospheric emission. Balancing
this nonsolar behavior are a variety of puzzling differences among the
three stars. On the one hand, the C IV features of Procyon are narrow,
while that of the Capella secondary and Caph are broad; differences
in v sin i alone cannot explain the dichotomy. On the other hand, the
high-excitation emissions of the Capella secondary and Procyon, but
not Caph, exhibit statistically significant redshifts. The significance
of these results is discussed in the light of the speculation by Simon
and Drake (1989) that the X-ray deficient coronae of the early F dwarfs
are produced by classical acoustic heating.

---------------------------------------------------------
Title: Sleuthing the Dynamo: Cycle 2 Continuation
Authors: Ayres, Thomas
1991hst..prop.3908A Altcode:
Innovative technologies of the 1990s will open new windows to the
interior of the Sun and its hidden dynamics: the GONG project for
helioseismology; rare-earth detectors for solar neutrinos; and SOLAR
PROBE for high-order moments of the mass distribution. At the same
time, newly-commissioned space observatories will provide unprecedented
views of the vacuum-UV and X-ray emissions of stars in our Galactic
neighborhood. These seemingly unrelated developments are in fact deeply
connected. A central issue of solar-stellar physics is the nature and
origin of magnetic activity: the profound link between the interior
dynamics of a late-type star and the violent state of its outermost
million-degree coronal layers. As solar physicists are unlocking the
secrets of the hydromagnetic dynamo deep inside the Sun, we will apply
one of the powerful new astronomical tools of the decade -- the HST
-- to document the early evolution of the dynamo and its associated
external gas-dynamic activity. In particular, we will obtain high-S/N
FUV spectra of solar-type stars in young galactic clusters ranging in
age from 1/10-th to 1/100-th that of the Sun.

---------------------------------------------------------
Title: IUE Far Ultraviolet Spectra of Capella and Gamma-Draconis
for Comparison to Hst/ghrs / Hubble Space Telescope / Goddard High
Resolution Spectroscopy GTO Observations
Authors: Ayres, T. R.
1991fyho.conf..216A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: CO Fundamental Bands in Late-Type Stars. II. Spectrum
Simulations for F--K Stars
Authors: Wiedemann, Guenter; Ayres, Thomas R.
1991ApJ...366..277W Altcode:
The procedure of Ayres and Wiedemann (1989) was applied to a range of
stellar-atmosphere models to study the CO Delta-v = 1 spectrum and to
establish its use as a remote sensor of thermal conditions in late-type
stars. Spectra were computed to examine the sensitivity of the CO
Delta-v = 1 to fundamental stellar parameters and to assess the errors
introduced into the spectrum intepretation by uncertain input parameters
and non-LTE effects. Results of the sensitivity study demonstrate that
CO fundamental spectra are useful probes for the temperature structure
of the outer layers of cool stellar atmospheres, but that their value
is limited by the uncertainties introduced by non-LTE effects. However,
in stars with surface gravities of log g of about 1.5 and greater,
the values of these uncertainties are reasonably small.

---------------------------------------------------------
Title: An Infrared Perspective on Chromospheres (With 3 Figures)
Authors: Ayres, T. R.
1991mcch.conf..228A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronathon Follow-On
Authors: Ayres, Thomas R.
1991iue..prop.3917A Altcode:
RIASS is a campaign to coordinate IUE spectroscopy of selected
high-excitation celestial sources with the ROSAT all-sky survey (8/90
- 1/91). 1 and collaborators responded to that unique opportunity
in the 13th Episode with a carefully-chosen sample of approx 80 F-K
stars. Studies of the magnetically-engendered chromospheres and coronae
of such stars particularly benefit from joint observations of far-UV
emission lines (Tex approx 10^4 - 10^5 K) and broad-band soft X-ray
fluxes (0.1-2 keV: Tex &gt; 101 K). Ultimately, half of our "Coronathon"
targets were observed during RIASS. Here, I request additional IUE time
to record far-UV spectra of two groups of stars from the original sample
which were not observed during the campaign either: (1) because the
target had not previously been observed by the IUE (thereby violating
one of the central requirements of RIASS); or, (2) the star was too
faint (at C IV 1549) given the limited observing time. Far-UV spectra
of these two groups will complete (in a statistical sense) the IUE
archival collection of specific key classes of late-type stars, thereby
permitting a broad range of statistical studies of stellar coronae which
heretofore have been frustrated by incomplete or highly-biased samples.

---------------------------------------------------------
Title: Signal-to-Noise Ratios in IUE SWP-LO Spectra of Chromospheric
Emission-Line Sources
Authors: Ayres, Thomas R.
1990PASP..102.1420A Altcode:
The short-wavelength-prime (SWP) detector of the International
Ultraviolet Explorer should operate near the photon-counting
limit, but the noise levels in flat-field images are several times
higher. The exaggerated noise can be traced to the incomplete removal
of the pixel-to-pixel granularity of the television frames by the
prevailing spectral image processing system. An empirical noise model
for the current-epoch photometric linearization strategy and one for
a hypothetical processing system that achieves complete flat fielding
of the raw images are derived. A formula is then proposed to predict
the signal-to-noise ratio in the measured flux of an emission line
(possibly superimposed on a smooth continuum) in an IUE low-dispersion
(5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded
with the SWP camera. For illustration, the formula is specialized to the
important C IV 1549 A feature of F-K stars. The S/N relation permits
one to determine sensitivity limits, upper limits in faint exposures,
and optimum exposure times.

---------------------------------------------------------
Title: Sleuthing the Dynamo: Cycle 1 Observations
Authors: Ayres, Thomas
1990hst..prop.2485A Altcode:
Innovative technologies of the 1990s will open new windows to the
interior of the Sun and its hidden dynamics: the GONG project for
helioseismology; rare-earth detectors for solar neutrinos; and SOLAR
PROBE for high-order moments of the mass distribution. At the same
time, newly-commissioned space observatories will provide unprecedented
views of the vacuum-UV and X-ray emissions of stars in our Galactic
neighborhood. These seemingly unrelated developments are in fact deeply
connected. A central issue of solar-stellar physics is the nature and
origin of magnetic activity: the profound link between the interior
dynamics of a late-type star and the violent state of its outermost
million-degree coronal layers. As solar physicists are unlocking the
secrets of the hydromagnetic dynamo deep inside the Sun, we will apply
one of the powerful new astronomical tools of the decade -- the HST
-- to document the early evolution of the dynamo and its associated
external gas-dynamic activity. In particular, we will obtain high-S/N
FUV spectra of solar-type stars in young galactic clusters ranging in
age from 1/10-th to 1/100-th that of the Sun.

---------------------------------------------------------
Title: Fourier Transform Spectrometer Observations of Solar Carbon
Monoxide. III. Time-resolved Spectroscopy of the Delta V = 1 Bands
Authors: Ayres, Thomas R.; Brault, James W.
1990ApJ...363..705A Altcode:
Time series of the 2100/cm Delta v = 1 absorption bands of CO at the
center of the solar disk and at the extreme limb have been recorded by
Fourier transform spectrometer. The photospheric 5-min oscillation
appears prominently at sun center. The peak-to-peak brightness
temperature amplitude is roughly 300 K, and the peak-to-peak Doppler
shift is roughly 1100 m/s. The 70 deg phase lag of maximum core
intensity with respect to maximum redshift for the strongest Delta
v = 1 absorptions is less than the 90 deg expected in the adiabatic
limit. No dominant four-minute signal in the line intensity like
that reported by Deming et al. (1984, 1986, and 1987) is found,
nor is evidence for extreme fluctuations on short time scales like
those proposed by Kalkofen et al. (1984). The strong Delta v = 1
lines exhibit systematic Doppler shifts of less than about 1 km/s,
contrary to the predictions of transonic redshifts if the CO 'clouds'
are associated with a dynamic cooling phase of the Ca II 'cell flashes.'

---------------------------------------------------------
Title: A Case Study: Multi-Sensor Data Analysis of HH Objects Via
STAR: A Scientific Toolkit for Astrophysical Research
Authors: Mickus, K. D.; Brugel, E. W.; Domik, G. O.; Ayres, T. R.
1990BAAS...22R1259M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The distant future of solar activity - A case study of
Beta Hydri
Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.;
Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, A.;
Simon, T.; Vandenberg, D.; Wallinder, F.
1990ESASP.310..323D Altcode: 1990eaia.conf..323D
No abstract at ADS

---------------------------------------------------------
Title: STAR - A Scientific Toolkit for Astrophysical Research
Authors: Mickus, K. D.; Domik, G. O.; Brugel, E. W.; Ayres, T. R.
1990BAAS...22..828M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thermal Bifurcation of the Outer Photosphere
Authors: Ayres, T. R.
1990IAUS..138...23A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Sleuthing the Dynamo II
Authors: Ayres, Thomas R.
1990iue..prop.3641A Altcode:
A key puzzle in modern astrophysics is the nature of the solar
hydromagnetic dynamo: the direct cause of the 11-year sunspot cycle,
and indirect source of the ebb and flow of chromospheric and coronal
activity. New clues have come with the discovery of analogous long-term
cycles on a number of other late-type dwarfs through systematic
monitoring-surveys of Ca II K. However, the low-excitation Ca II
emission does not form exclusively in areas disturbed by magnetic flux,
and thus provides an incomplete proxy view of the dynamogenerated
fields. In contrast, high-excitation vacuum-ultraviolet emissions -
like Si IV 1400 and C IV 1550 - form entirely in the regions most
strongly affected by concentrated magnetic flux (spots, plage, and
network). The modulations of these emissions over a stellar cycle
directly mirror the changing face of the dynamo. We believe that the
development of a complete theory of the dynamo requires a comprehensive
database concerning the superficial manifestations of activity cycles,
Particularly critical are far-UV spectra from the cycle maxima and
minima of representative near-solar stars. We have received time
in previous episodes to collect far-UV spectra of a small sample of
key stars for that purpose. In addition, we calibrated and measured
2,500 SWP-LOs of late-type stars from the Archives, and published
preliminary emission histories for 10 stars. Since the IUE continues
to function well, it would be a tragic scientific oversight not to
continue systematic monitoring of at least a few late-type stars for
as long as the satellite remains healthy. Owing to the long-term nature
of the program, we are requesting two-year status for it.

---------------------------------------------------------
Title: The distant future of solar activity - a case study of
Beta Hydri.
Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.;
Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, Å.;
Simon, T.; Vandenberg, D.; Wallinder, F.
1990apsu.conf...17D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Chilling Truth about the Solar Chromosphere
Authors: Ayres, Thomas R.
1990ASPC....9..106A Altcode: 1990csss....6..106A
The notion that much of the solar gas in the low chromosphere is cool
is discussed in terms of its validity. The dark CO absorption cores
recorded at the extreme limb of the sun are described, including the 3-2
R14 line with a core-brightness temperature of 3620 K. A bifurcation
in the plasma energy balance described to explain the high altitude
cold gas is reviewed in terms of recent investigations. Spectral
simulations of CO are described which examine the range of thermal
profiles allowed by CO observations with low spatial resolution and
limb darkening. Weak emission shoulders in the K line demonstrate
that a cool chromosphere with Ca II emission is feasible, although
the cold gas requires a surface coverage of as little as 20 percent
to reproduce the limb darkening. To distinguish between the thermal
bifurcation notion and the neophotosphere concept, observations of
the high spatial resolution spectra of the CO bands are required.

---------------------------------------------------------
Title: CO Fundamental Lines - Indicators for Inhomogeneous Atmospheres
in Cool Stars
Authors: Wiedemann, Guenter; Ayres, Thomas R.
1990ASPC....9..158W Altcode: 1990csss....6..158W
Carbon monoxide fundamental lines near 4.7 microns are employed to
probe the thermal structure of the atmospheres of cool stars. A new
non-LTE radiation transfer code is used to analyze high-resolution
infrared CO line spectra and derive observation-based stellar atmosphere
models. The main results are: (1) the CO-based models developed here
deviate strongly from previously published models based on UV/visible
observations; (2) varying degrees of agreement between the CO empirical
models and predictions based on theoretical radiative-equilibrium
atmosphere models are found; and (3) the parameter used to quantify
this agreement is anticorrelated with the magnitude of chromospheric
activity in the observed stars. These results suggest thermally
bifurcated upper atmospheres as the standard case for cool stars.

---------------------------------------------------------
Title: How deep can one see into the Sun?
Authors: Ayres, Thomas R.
1989SoPh..124...15A Altcode:
Conventional wisdom dictates that the 1.642 μm H−
`opacity minimum' is the best window to the depths of the solar
photosphere. However, the violet continuum near 0.4 μm exhibits a
larger intensity response to small thermal perturbations at depth,
and thus might offer an even better view of the subsurface roots of
granulation cells and magnetic flux tubes.

---------------------------------------------------------
Title: Non--LTE CO Revisited
Authors: Ayres, Thomas R.; Wiedemann, Gunter R.
1989ApJ...338.1033A Altcode:
A more extensive and detailed non-LTE simulation of the Delta v =
1 bands of CO than attempted previously is reported. The equations of
statistical equilibrium are formulated for a model molecule containing
10 bound vibrational levels, each split into 121 rotational substates
and connected by more than 1000 radiative transitions. Solutions
are obtained for self-consistent populations and radiation fields
by iterative application of the 'Lambda-operator' to an initial LTE
distribution. The formalism is used to illustrate models of the sun
and Arcturus. For the sun, negligible departures from LTE are found in
either a theoretical radiative-equilibrium photosphere with outwardly
falling temperatures in its highest layers or in a semiempirical hot
chromosphere that reproduces the spatially averaged emission cores
of Ca II H and K. The simulations demonstrate that the puzzling 'cool
cores' of the CO Delta V = 1 bands observed in limb spectra of the sun
and in flux spectra of Arcturus cannot be explained simply by non-LTE
scattering effects.

---------------------------------------------------------
Title: FTS observation of CO fundamental bands in cool stellar
atmospheres.
Authors: Wiedemann, G.; Ayres, T. R.; Jennings, D. E.
1989hrft.conf...23W Altcode:
CO fundamental lines are important diagnostics for cool star upper
atmospheres. High resolution FTS observations at 4.7 μm provide an
independent way to study inhomogeneous chromospheres.

---------------------------------------------------------
Title: Cool-Star Betathon
Authors: Ayres, Thomas R.
1989iue..prop.3362A Altcode:
As the IUE becomes firmly entrenched in the second decade of its
mission, it is time to move away from the dominant focus of the first
decade: broad-brush surveys of as many objects as possible regardless of
how weak the resulting spectra might be. Continuing to add an increasing
number of increasingly-marginal detections to the Archives is not the
way to achieve fundamental understanding of, for example, physical
processes in the high-excitation (10^4- 10^6 K) outer atmospheres of
magnetically-active F-M stars. While such survey work was absolutely
vital in the early years of the IUE, its continuation must fall to
the next generation of instruments. The HST will will be capable of
recording 1-A-resolution far-UV spectra of latetype stars a thousand
times fainter than the IUE limit. Since the IUE cannot compete with
the HST in faint-object spectroscopy, a better future course for
the IUE lies in doing what it does best: taking diagnostic-quality
SWP-HI spectra (0.15 A resolution; 1150-2000 A) of bright stars. The
SWP echellograms represent a unique scientific resource that will
not be duplicated by the HST spectrographs (owing to the minimal free
spectral range of the HRS). The SWP-HIs have proved to be essential in
exploring the properties of magnetic activity among late-type stars,
particularly concerning the dynarnics and energy balance of the 10'
K subcoronal transition zone. Unfortunately, the existing database
of images is rather spotty, with only a few stars represented by more
than one deep exposure. In the spirit of our exploratory SWP-HI work
in the first decade of the IUE, we propose to invest a significant
amount of observing time - both NASA and ESA - to acquire additional
long-duration exposures of key stars. We will conduct the observations
using newly-developed strategies designed to significantly enhance the
quality of the spectra compared with previous work. The stars that
will most benefit from new deep SWPIlls are betaAqr (G0 Ib), beta
Cet (K0 III), beta Dra (G2 Ib-IIa), beta Gem (K0 III), and alpha Boo
(K1 III). Owing to the nature of the targets, and the long durations
of the proposed exposures, we call our project the "BETATHON" (with
apologies to Arcturus).

---------------------------------------------------------
Title: Sleuthing the Dynamo II
Authors: Ayres, Thomas R.
1989iue..prop.3359A Altcode:
A key puzzle in modern astrophysics is the nature of the solar
hydromagnetic dynamo: the direct cause of the 11-year sunspot cycle,
and indirect source of the ebb and flow of chromospheric and coronal
activity. New clues have come with the discovery of analogous
long-term cycles on a number of other late-type dwarfs through
systematic monitoringsurveys of Ca II K. However, the low-excitation
Ca II emission does not form exclusively in areas disturbed by magnetic
flux, and thus provides an incomplete proxy view of the dynamogenerated
fields. In contrast, high-excitation vacuum-ultraviolet emissions -
like Si IV 1400 and C IV 1550 - form entirely in the regions most
strongly affected by concentrated magnetic flux (spots, plage,
and network). The modulations of these emissions over a stellar
cycle directly mirror the changing face of the dynamo. We believe
that the development of a complete theory of the dynamo requires a
comprehensive database concerning the superficial manifestations of
activity cycles. Particularly critical are far-UV spectra from the
cycle maxima and minima of representative near-solar stars. We have
received time in previous episodes to collect far-UV spectra of a
small sample of key stars for that purpose. In addition, we calibrated
and measured 2,500 SWP-LOs of late-type stars from the Archives, and
published preliminary emission histories for 10 stars. Since the IUE
continues to function well, it would be a tragic scientific oversight
not to continue systematic monitoring of at least a few late-type stars
for as long as the satellite remains healthy. Owing to the long-term
nature of the program, we are requesting two-year status for it.

---------------------------------------------------------
Title: Sleuthing the Dynamo
Authors: Ayres, Thomas R.
1989iue..prop.3358A Altcode:
Long-term cycles of "activity", analogous to the 11-year sunspot cycle,
have been discovered on a number of late-type dwarf stars through
systematic groundbased surveys of the Ca II HK "S-index". The Ca
II emission forms over a diverse range of chromospheric structures,
and thus provides a broad view of the areas of the stellar surface
disturbed by magnetic activity. In contrast, spectral signatures of
activity in the vacuum ultraviolet - like Si IV 1400 and C IV 1550 -
form exclusively in the high-excitation layers of the stellar outer
atmosphere: the modulation of these emissions over a stellar cycle
mirror the changing area of the regions most strongly affected by
concentrated fields. Thus, comparisons between low-excitation,
chromospheric diagnostics - like Ca II and high-excitation,
transition-zone emissions - like Si IV and C IV - provide insight into
the relative surface distributions of large scale plage and network
compared with small-scale, concentrated active regions. We believe
that the development of a complete theory of the stellar magnetic
"dynamo" requires a comprehensive understanding of the surface
distributions of magnetic regions throughout activity cycles. Thus,
we propose to continue a program we began in the Ninth Episode to
study the properties of far-UV spectra of representative late-type
stars over their cycles. Our objective is not to measure the cycle
periods, themselves; that is better done with Ca II photometry from
the ground. Instead, we wish to record representative emission levels
of each star throughout at least one complete cycle: our goal is
to compare chromospheric and transition-zone emissions in flux-flux
diagrams; in particular, the trajectory followed by a star over its
cycle relative to the slope defined by the broad behavior of many
stars of different mean activity levels. Differences in the slopes are
signatures of 'nonlinear' behavior in the dynamo; important clues to
confront theoretical models of dynamo action.

---------------------------------------------------------
Title: CO Fundamental Bands: Diagnostic for Inhomogeneities in Cool
Stellar Atmospheres
Authors: Wiedemann, G.; Ayres, T. R.
1988BAAS...20..998W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Empirical Continuum Modeling for IUE Low-Dispersion Spectra
Authors: Bennett, Jeffrey O.; Ayres, Thomas R.
1988PASP..100.1129B Altcode:
The authors describe a numerical procedure for empirically determining
a "continuum" level in low-dispersion spectra from the International
Ultraviolet Explorer. They developed the technique for the automated
fitting of SWP-LO (1150 Å - 2000 Å) spectra of stars of late spectral
type, but it is more widely applicable.

---------------------------------------------------------
Title: A Spectral Dissection of the Ultraviolet Emissions of Capella
Authors: Ayres, Thomas R.
1988ApJ...331..467A Altcode:
Phase-resolved observations of Capella (α Aurigae A: G5 III+G0 III)
were conducted with the IUE in order to separate the spectrum of the
core-helium-burning (CHeB) primary (Aa) from that of the fast-rotating,
chromospherically active secondary (Ab). The ultraviolet emissions of
the primary were compared to those of the four K0 giants of the Hyades
and the field K giants β Cet and β Gem. In terms of C IV emission,
the six reference CHeB giants fall into two distinct groups: the
more active β Cet type; and the less active β Gem type. Capella Aa
clearly belongs in the β Cet group. The similarity between the Capella
primary and the two active Hyads - γ Tauri and θ1 Tauri
- is striking. If Capella truly is coeval with the Hyades nucleus,
then the age of the cluster might be less than half that commonly
assumed. The UV spectra of the Capella secondary show evidence of mass
outflow in the upper chromosphere, although the flow very likely is
part of a circulation system like that thought to operate in magnetic
active regions on the Sun.

---------------------------------------------------------
Title: Ultraviolet emission lines and optical photometry of the
flare star AT Microscopii.
Authors: Elgaroy, O.; Joras, P.; Engvold, O.; Jensen, E.; Pettersen,
B. R.; Ayres, T. R.; Ambruster, C.; Linsky, J. L.; Clark, M.; Kunkel,
W.; Marang, F.
1988A&A...193..211E Altcode:
Ultraviolet spectra of the dwarf flare star binary AT Mic (dM 4.5e+dM
4.5e) were obtained with the IUE spacecraft on three days in September
1985. A high-resolution short-wavelength spectrum was exposed for 25
hours. Simultaneous optical monitoring in the U-band was performed
during part of the IUE observations. At the time of observation AT
Mic was flaring at an average rate of 1.3 flares per hour. On the
average 9% of the energy in the U-band was due to the detected flare
activity. From the observed high resolution spectra, line wavelengths,
widths and fluxes were derived, and the effects of the binary structure
of AT Mic on the spectral lines were evaluated. The ultraviolet emission
line spectrum is similar in character to that of flare regions on the
Sun and other stars.

---------------------------------------------------------
Title: Far-ultraviolet and X-ray emission of the long period RS CVn
star sigma Geminorum.
Authors: Engvold, O.; Ayres, T. R.; Elgaroy, O.; Jensen, E.; Joras,
P. B.; Kjeldseth-Moe, O.; Linsky, J. L.; Schnopper, H. W.; Westergaard,
N. J.
1988A&A...192..234E Altcode:
The new UV and X-ray observations of σ Gem support the theory that
large active regions associated with starspots are responsible for the
enhanced line emission commonly seen in RS CVn systems. The rotational
modulation of the UV line fluxes increases with temperature of the
line-forming region. The X-ray emission from the stellar corona, on the
other hand, shows only a barely detectable variation with rotational
phase. One may infer that the coronal active regions of the system
are not co-spatial with the activity in the transition region below,
and/or occupy a significantly larger surface area. An equally probable
explanation, however, is that the X-ray emission is emitted from huge,
stellar sized loops.

---------------------------------------------------------
Title: Redshifts of High Temperature Emission Lines in the
Far-Ultraviolet Spectra of Late-Type Stars. II. New, Precise
Measurements of Dwarfs and Giants
Authors: Ayres, Thomas R.; Jensen, Eberhard; Engvold, Oddbjorn
1988ApJS...66...51A Altcode:
Results are presented from an IUE SWP camera investigation of the
occurrence of gasdynamic flows, analogous to the downdrafts of 10
to the 5th K material observed over magnetic active regions of the
sun, among stars of late spectral type. The SWP calibration spectra
study conducted documents the existence of local, small, persistent
distortions of the echelle wavelength scales that are of unknown
origin. Attention is given to the enormous widths of the stellar
high-excitation emission lines in both the dwarfs and the giants,
with respect to the comparatively small, subsonic Doppler shifts; the
widths are typically an order of magnitude greater than the redshifts.

---------------------------------------------------------
Title: Doppler-Dissection of UX Arietis
Authors: Ayres, Thomas R.
1988iue..prop.3041A Altcode:
UX Arietis (K0 IV+G5 V) is a 6.4-day period RS CVn binary - near the
peak of magnetic "activity" among stars of late spectral type - that
recently was subjected to intense scrutiny with the IUE, including a
very-deep (1265-min exposure) SWP-HI spectrum. We wish to continue
our study of this hyperactive system by conducting a unique series
of LWP-HI measurements of Mg II A2800 at ten phases near consecutive
orbital velocity extrema. We intend to subject the spectra to "Doppler
dissection", a powerful technique to extract information concerning
spatial nonuniformities on the surfaces of rapidly-rotating stars
from recurring distortions in chromospheric emission profiles. Our
objective is to understand why the "hyperactive" chromospheres still
exhibit substantial spatial irregularities, instead of being completely
covered by intense, uniform magnetic plage as the solar analogy would
suggest. We will approach this question by identifying the typical
sizes and surface fluxes of chromospheric nonuniformities on UX Ari
(in addition to other representative close binaries we have observed
previously); and attempt to deduce, through numerical modelling,
the physical properties and total heating rates of the enhanced
regions. The derived physical quantities, in turn, can guide the
development of theories of the heating processes and thermal-instability
mechanisms that might lead to the natural formation of chromospheric
inhomogeneities. In order to take advantage of specialized algorithms
to filter camera defects from IUE spectrograms, we propose to acquire
a graded sequence, of echellograms at independent locations on the LWP
camera (by placing the target image at offcenter positions in the large
aperture). The scheme not only extends the dynamic range and improves
S/N, but it also mitigates the influence of any persistent artifacts
of the vidicon images that are not eliminated in the nominal IUESIPS
processing or by our spike- removal procedures.

---------------------------------------------------------
Title: Very-Deep SWP-HI of Aldebaran
Authors: Ayres, Thomas R.
1988iue..prop.3039A Altcode:
We propose to conduct the longest exposure ever attempted with the
IUE (&gt;25 hours) in order to obtain a high-quality recording of
the far-ultraviolet (1150-2000 A) emission line spectrum of the
bright red giant Aldebaran (alpha Tauri: K5 III), in high dispersion
(0.15 A). Our objectives include: the study of fluorescent phenomena;
the measurement of tracers of temperature and density in the possibly
highly-inhomogeous chromosphere; and the search for faint emissions
of high-excitation species, like Si IV and C IV, which are signatures
of hotter gas (101 K) usually not found in the low-gravity, evolved
stars. In addition, preceding and during the very long SWP exposure,
we propose to monitor the chromosphere and wind of Aldebaran, with
LWP echellograms exposed for the Mg II 2800 doublet. Our objective is
to document possible short-term variability like that identified in
optical studies of the redgiant Arcturus. Our proposal is intended to
carry forward a program - to explore the ultraviolet spectra of stars
of late spectral type - that we, and our collaborators at Oxford,
have been conducting since the early years of the IUE.

---------------------------------------------------------
Title: The Debit Side of the Chromospheric Energy Budget
Authors: Ayres, Thomas R.
1988iue..prop.3032A Altcode:
The chromosphere is a thick, hot (&lt; 10' K), nonradiatively
heated layer of the stellar outer atmosphere, immediately above the
photosphere, which is found in virtually all stars of late spectral
type. Despite considerable observational and theoretical effort in the
particularly favorable case of the Sun, the origin of the chromosphere -
and its wealth of fine structure largely remains a mystery. Small-scale
magnetic "flux tubes" are thought to play a significant role in imposing
physical structure on the chromosphere, and the heating of the gas is
believed to be associated with the deposition of wave energy - acoustic
or various magnetic modes propagating up from the deep convection zone;
however, there is considerably more speculation in the field than
hard facts, despite literally decades of work (in the solar case, at
least). A fundamental question in this regard is the relative importance
of various atomic and ionic species in cooling the chromospheric
gas. Not only is an understanding of the detailed constituents of the
plasma cooling function important to theoretical modelling efforts,
but also to observational efforts to measure the radiative losses of
stellar chromospheres across the HR diagram: identification of the most
important species, and their relative contributions, permits observers
to concentrate on a few critical spectral intervals, and correct
their measurements for the additional species that are not directly
detected. The present proposal seeks to assess the relative importance
of several species in the chromospheric energy budget by numerically
comparing the vacuumultraviolet energy distributions of pairs of stars
of similar spectral type and luminosity class, but widely different
"activity" levels. The ultimate goal is to examine the gross properties
of chromospheres as a function of fundamental stellar attributes like
spectral type and luminosity class: by moving away from the perhaps
too-familiar solar example, one might be able to develop new clues
into the nature of the elusive chromospheric heating processes.

---------------------------------------------------------
Title: Short-Term Variability of Arcturus
Authors: Ayres, Thomas R.
1988iue..prop.3036A Altcode:
Arcturus is the nearest and brightest of the low-mass red
giants; a paradigm of the "inactive" stars in the cool-half of the
Hertzsprung-Russell diagram. Nevertheless, recent optical studies have
reported unexpected periodicities in the global velocity of the red
giant on timescales of hours to days: the envelope pulsations share
some similarities with those of the RR Lyrae variables. Furthermore, the
B-band polarization and the Ca II "S-index" exhibit erratic variability
from day to day, as well as evidence for a 45-day periodicity. Finally,
a time-series of the 4.7 micron bands of CO has suggested significant
global changes in the coolest layers of the Arcturan chromosphere
on timescales of hours. The recent variability studies have raised
important questions concerning the structure and dynamics of the
outer atmosphere of Arcturus, and their relationship to the mass-loss
process. We, therefore, propose a program, in collaboration with
our colleagues at Oxford, to study the short-term (hours to days)
variability of important ultraviolet emission features that form in
the chromosphere and wind of the archetype red giant.

---------------------------------------------------------
Title: The Age of the Hyades
Authors: Ayres, Thomas R.
1988iue..prop.3038A Altcode:
Based on recent evidence, it is very likely that Capella (alpha
Aurigae: G6 III+F9 III) is the same age as the nucleus of the
nearby Hyades open cluster. Further, the evolutionary status of the
fast-rotating F9 secondary star is well-established (it is one of the
rare "HertzsprungGap" giants, in a transient, magnetically-active
phase of the first-crossing to the red giant branch). Thus, if one
can measure the mass of Capella "F", the age of the Hyades follows
directly. Unfortunately, previous attempts to record the diffuse,
rotationally-broadened absorption lines of the secondary spectrum in
the optical and near-IR have met with mixed success, presumably owing
to the confusing influence of the rich, sharp-line spectrum of the
cooler, more slowly-rotating primary. One study finds the secondary
about 7% less massive than the primary; and the inferred age is nearly
a factor of three less than commonly assumed for the Hyades based
on the cluster turnoff method. If that mass estimate is correct -
and Capella and the Hyades nucleus truly are coeval - then there is
a curious, inexplicable deficit of early-A main-sequence stars in
the cluster. A second study - based on extensive observations with a
CORAVEL-type radial velocity spectrometer - finds that the secondary is
less massive than the primary by almost 20%; an amount large enough to
stretch the credence of existing models of stellar evolution. Therefore,
I propose to apply a carefully-designed observing strategy to obtain the
highest SIN, highest-wavelength-precision observations ever attempted
with the IUE in order to: (1) establish, unambiguously, the radial
velocity semiamplitude of the secondary of Capella - by observing in
the 1800-2000 A region where the F9 photosphere is seen in its most
favorable light; and (2) record the faint emissions of the far-UV
spectra of the primary and secondary in order to study questions of
gas-dynamics, line-broadening, and densitysensitive line ratios at
the limits of the capabilities of the IUE.

---------------------------------------------------------
Title: The chromospheres and coronae of five G-K main-sequence stars.
Authors: Jordan, C.; Ayres, T. R.; Brown, A.; Linsky, J. L.; Simon, T.
1987MNRAS.225..903J Altcode:
Five main-sequence stars, χ1 Ori (G0 V), α Cen A (G2
V), ξ Boo A (G8 V), α Cen B (K0 V) and ɛ Eri (K2 V) have been
observed at low and high dispersion with the International Ultraviolet
Explorer (IUE) satellite. The data obtained and X-ray observations
reported in the literature are used to make models of the structure
of the atmospheres of these stars, from the high chromosphere to the
corona. The electron pressures and coronal temperatures in these stars
range from being similar to those in the quiet solar atmosphere (α Cen
A) to the higher values found more typically in solar active regions
(e.g. χ1 Ori, ξ Boo A). The models are used to examine
the energy lost by radiation and transferred by thermal conduction,
in order to establish the heating requirements. The results are similar
to those found for the solar atmosphere.

---------------------------------------------------------
Title: A Deep, Doppler-Compensated IUE SWP Echellogram of the KO
Primary of HR 1099
Authors: Bennett, J. O.; Ayres, T. R.; Jensen, E.; Engvold, O.
1987BAAS...19R.706B Altcode: 1987BAAS...19Z.706B
No abstract at ADS

---------------------------------------------------------
Title: The Colorado Scale Model Solar System
Authors: Bennett, J. O.; Ayres, T. R.; Center, K.; Bass, R.; Carter, M.
1987BAAS...19Q.750B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Deep SWP-HI of Lux Arietis
Authors: Ayres, Thomas R.
1987iue..prop.2725A Altcode:
In the Ninth Episode of the IUE, I and my collaborators applied
a novel observing technique to the 2.8-day RS CVn binary HR 1099
(KO IV+G5 V) the paradigm of magnetic activity among the nearby
stars of late spectral type - to record high S/N profiles of a
diverse range of chromospheric (6,000 K) and transition-zone (10^5 K)
emissions. The program involved a 19.5-hour highdispersion exposure of
the far-ultraviolet (1150-2000 A) spectrum in which the image of the
target periodically was stepped in the large aperture to compensate
for the changing orbital Doppler shifts of the active K0 primary. The
success of the observation has encouraged us to attempt the same
technique on another prototype RS CVn: the 6.4-day system UX Arietis
(K0 IV+G5 V), which is very similar in its properties to HR 1099,
aside from the longer orbital period (and hence slower synchronous
rotational velocities). The major objectives of the program are
to: search for evidence of gasdynamic flows in the high-excitation
emissions like C IV 1548; measure the profiles of weak, but important,
emissions like Si IV 1394 and O I 1305; evaluate the high-pressure
limit of chromospheric density diagnostics like C II] 2325; and measure
the relative "activity" of the G-type secondary star. A detailed
comparison of the high-dispersion spectra of UX Ari and HR 1099
should reveal, through any differences, important properties of the
magneticallydisturbed outer atmospheres of the "classical" RS CVn stars.

---------------------------------------------------------
Title: Further Studies of Beta Cassiopeiae
Authors: Ayres, Thomas R.
1987iue..prop.2721A Altcode:
In an exploratory IUE program two years ago, one of us (TRA) obtained
an intriguing series of far-ultraviolet spectra of beta Cassiopeiae:
the nearest and brightest of the delta Scuti variables. On the one hand,
a sequence of low-dispersion spectra recorded an abrupt, factorof-two
increase in the chromospheric Ly-alpha (1216 A) emission on a timescale
comparable to the 2.4-hour pulsation period. This behavior favors a
"pulsational" origin for the chromospheric heating as Schmidt and
Parsons have suggested for the more luminous Cepheids. On the other
hand, the C IV 1548 emission profile, though noisy, exhibits one of the
largest velocity widths known among "normal" stars of late spectral
type. The enhanced broadening, if due to the rapid rotation of the
star, implies that the atmospheric structures which are bright in the
C IV emission must reach to considerable heights above the limb of the
star. This behavior is more compatible with a conventional magnetic
origin for the high excitation emission. In the magnetic picture, the
abrupt brightening of the Ly-alpha emission might be due to a stellar
"flare", or to the rotation onto the visible hemisphere of a bright
"activity center". The purpose of the present proposal is to collect
additional low-dispersion SWP spectra, in conjunction with ground-based
Stromgren photometry and high-precision radial-velocity spectroscopy,
to monitor beta Cas on both rotational (few days) and pulsational (few
hours) timescales. Our objective is to to distinguish among the possible
chromospheric energization mechanisms at the important juncture in the
H-R diagram represented by early-F stars like beta Cas. We also propose
to take a deep high-dispersion SWP exposure to improve the profiles
of the C IV features and reach down to weaker emissions like the Si
IV doublet near 1400 A, in an effort to study gas-dynamic phenomena
in the outer atmosphere of this intensely active delta Sct variable.

---------------------------------------------------------
Title: Far-ultraviolet observations of the Delti-Scuti variable
Beta Cassiopeiae
Authors: Ayres, Thomas R.; Bennett, Jeffrey O.
1987LNP...274..127A Altcode: 1987stpu.conf..127A
FUV (115-200-nm) observations of Beta Cas, obtained at resolutions
5 and 0.15 A by the IUE during September 1984, are reported and
analyzed. The data are presented graphically and compared with results
for Procyon, a sharp-lined F star similar in temperature to Beta
Cas. A sharp factor-of-two increase in H I Ly-alpha flux on a time
scale comparable to its Delta Sct pulsation period was observed,
but the data were insufficient to determine whether the increase
was flarelike or pulsation-related. The outer edges of the Beta Cas
emission are shown to be significantly wider than those of Procyon.

---------------------------------------------------------
Title: Carbon Monoxide Fundamental Bands in Late Type Stars
Authors: Wiedemann, G.; Ayres, T.; Jennings, D.; Saar, S.
1987LNP...291..374W Altcode: 1987csss....5..374W; 1987LNP87.291..374W
No abstract at ADS

---------------------------------------------------------
Title: High-Dispersion Observations of Alpha Bootis (K1 III) with
the International Ultraviolet Explorer
Authors: Ayres, T. R.; Judge, P.; Jordan, C.; Brown, A.; Linsky, J. L.
1986ApJ...311..947A Altcode:
The authors have obtained very deeply exposed IUE echelle spectrograms
of the bright, early-K giant Arcturus. They did not detect significant
flux in the most prominent high-excitation species of a solar-like
transition zone, C IV λ1548.2. The presence of a weak feature of
Si III] λ1892.0, and possibly also Si IV λ1393.8, indicates the
existence of a small amount of plasma at temperatures as hot as
6×104K. Measurements of C II] multiplet UV0.01 near 2325
Å provide a lower limit of about 5×109cm-3 for
the electron density in the chromospheric layers. C II UV1 (1335 Å)
emission is very weak. These results confirm that the "coronal" activity
of the old red giants is considerably diminished from that of even the
"quietest" of their main-sequence predecessors, stars like the Sun.

---------------------------------------------------------
Title: Exploration of the CO Fundamental Bands in Late Type Stars
Authors: Wiedemann, G.; Ayres, T.; Jennings, D.; Saar, S.
1986BAAS...18..982W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Far-Ultraviolet Fluorescence of Carbon Monoxide in the Red
Giant Arcturus. II. Analysis of High-Dispersion IUE Spectra
Authors: Ayres, T. R.
1986ApJ...308..246A Altcode:
Faint, diffuse emissions near 1380 A in deeply exposed IUE spectrograms
of the red giant Arcturus very likely are associated with bands of
the A-X fourth-positive system of carbon monoxide, fluoresced by
multiplet UV2 of neutral oxygen near 1305 A. Numerical simulations
indicate that the strength of the CO bands is exceedingly sensitive,
in the best available one-dimensional model of the chromosphere of
Arcturus, to a delicate balance between the rapid inward attenuation
of the oxygen radiation field and the rapid outward decline of the
molecular absorptivity. The fortuitous character of the overlap region
in the single-component model argues that one should also consider
the possibility that the pumping occurs in a highly inhomogeneous
chromosphere, of the type proposed in previous studies of Arcturus
based on observations of the infrared absorption bands of CO.

---------------------------------------------------------
Title: UV and optical observations of AT Mic
Authors: Ayres, T. R.; Elgaroy, O.; Joras, P.
1986ESASP.263...91A Altcode: 1986NIA86.......91A; 1986niia.conf...91A
The red dwarf binary AT Mic was observed in 1985 by IUE in the UV and
optical wavelength regions. In the U-band flares were observed at a
rate of 1 per hour. In the UV region surface line fluxes are enhanced
compared to those of the quiet Sun and show closer relation to values
which are characteristic of very active regions on the Sun. Hot lines (C
IV, Si IV) show larger broadening and negative frequency shifts whereas
cooler lines (Fe II, Mg II) are less broadened and reveal small negative
or positive line shifts. Improved radial velocity determinations of
AT Mic are essential for the interpretation of the results.

---------------------------------------------------------
Title: Tz-Fornacis - an Eclipsing Capella-Like System Observed
with IUE
Authors: Eriksson, K.; Saxner, M.; Gustafsson, B.; Ayres, T. R.;
Linsky, J. L.; Anderson, J.
1986ESASP.263..225E Altcode: 1986niia.conf..225E; 1986NIA86......225E
The IUE observed TZ Fornacis at orbital phases 0.0, 0.25 and 0.79 in
1986. Most of the exposures were LWP-HI or SWP-LO. Results show that:
the surface fluxes for transition region emission lines are similar
to those for the Capella system while that of the Mg II emission is
smaller; the total flux in the Mg II emission lines is constant with
phase, whereas the flux in the C IV emission lines decreases by 1/3
during primary eclipse, indicating that most of the activity is due
to the hotter giant (F7 III), which is also the case for Capella.

---------------------------------------------------------
Title: Fourier Transform Spectrometer Observations of Solar Carbon
Monoxide. II. Simultaneous Cospatial Measurements of the Fundamental
and First-Overtone Bands, and CA II K, in Quiet and Active Regions
Authors: Ayres, T. R.; Testerman, L.; Brault, J. W.
1986ApJ...304..542A Altcode:
Fourier transform spectrometry has yielded simultaneous cospatial
measurements of important diagnostics of thermal structure in the high
solar photosphere and low chromosphere. It is noted that the anomalous
behavior of the fundamental bands of CO in quiet areas near the limb is
accentuated in an active region plage observed close to the limb. The
difference between the core temperatures of the CO fundamental bands
in a plage and a nearby quiet region at the limb is larger than the
corresponding brightness temperature differences in the inner wings
of the Ca II line measured in a quiet region and several plages
closer to the disk center. Numerical simulations indicate that the
disparate behavior of the CO bands with respect to Ca II K cannot be
reconciled with existing single component thermal structure models;
a two-component atmosphere is required.

---------------------------------------------------------
Title: Ultraviolet, Optical, Infrared, and Microwave Observations
of HR 5110
Authors: Little-Marenin, I. R.; Simon, Theodore; Ayres, T. R.; Cohen,
N. L.; Feldman, P. A.; Linsky, J. L.; Little, S. J.; Lyons, R.
1986ApJ...303..780L Altcode:
HR 5110 is a close binary system (P = 2d.6) with the
characteristics of an Algol system. Because the primary star is
relatively cool (F2 IV) and there is no apparent emission from
an accretion disk, the authors were able to detect in IUE spectra
the emission of an active chromosphere and transition region of the
cooler (K0 IV) secondary. The surface fluxes of the UV emission lines
of the K star are similar to those of active RS CVn binaries. The
line fluxes appear to vary with orbital phase and are interpreted as
emission from an active region on the K star. Two large radio flares
were detected. VLBI observations during one of these flares indicated
that half the emission came from a region more than 4 times the binary
separation.

---------------------------------------------------------
Title: A Deep, Doppler-Compensated, SWP Echellogram of HR 1099
Authors: Ayres, Thomas R.
1986iue..prop.2399A Altcode:
I, and my ESA collaborators, propose to apply a novel observing
technique to the classical shortperiod (2.8 d) RS CVn binary HR 1099
(K0 IV + G5 V) - the paradigm of magnetic activity among the nearby
stars of late spectral type. The program involves a long-duration
exposure (25 hours or more) of the far-ultraviolet (1150-2000 A)
spectrum in high dispersion (0.15 A resolution) in which the image
of the target is periodically stepped in the large aperture along the
dispersion axis in order to compensate for the orbital Doppler shifts
of the K0 primary, which largely by virtue of its size completely
dominates the ultraviolet emission of the system. We also propose to
obtain very high-quality maps of the middle-ultraviolet (2000-3200 A)
spectrum using graded sequences of LWP exposures obtained at nonstandard
positions in the large aperture, and combined by means of a filtering
technique that largely eliminates defects like reseau marks and
cosmic-ray hits. The major objectives of the program are to: Search
for persistent redshifts of the high-excitation (105 K) emissions,
above the smoothed background of "Doppler-imaged" surface structure;
identify weak blends near important diagnostic lines, which otherwise
might be misconstrued as Dopplerimaged features; measure the profiles
of weak, but important, emissions like the N V doublet (1240 A), 0 V]
(1218 A), and the O I triplet near 1305 A; attempt to detect coronal
forbidden lines like [Fe XII]; and evaluate the high-pressure limit of
chromospheric density diagnostics like C II] (2325 A). The observations
of HR 1099 also will be valuable for long-term monitoring programs
and efforts to construct a high-dispersion atlas of late type stars.

---------------------------------------------------------
Title: Activity on Both Components of HR 1099
Authors: Bennett, J. O.; Ayres, T. R.
1986LNP...254...37B Altcode: 1986csss....4...37B
No abstract at ADS

---------------------------------------------------------
Title: An IUE High-Dispersion Cool-Star Atlas
Authors: Ayres, T. R.; Brugel, E. W.; Linskyl, J. L.; Brown, A.;
Carpenter, K. G.
1986LNP...254..106A Altcode: 1986csss....4..106A
We are planning to compile a spectral atlas based on high-dispersion
images of representative late-type stars recorded by the International
Ultraviolet Explorer. We solicit advice from the ultraviolet community
concerning how best to present the spectral material.

---------------------------------------------------------
Title: The dichotomy between co absorptions and CA II emissions
in the sun and stars: an indirect diagnostic for gas disturbed by
magnetic fields?1
Authors: Ayres, T.
1986LNP...254..336A Altcode: 1986csss....4..336A
Spectra of the 4.7 um bands of carbon monoxide in absorption, and
spectra of the cores of the 0.4 um resonance lines of ionized calcium
in emission, might be used to diagnose the presence of atmospheric
inhomogeneities, caused by the action of surface magnetic fields,
on stars as diverse as the Sun and the red giant Arcturus.

---------------------------------------------------------
Title: The dichotomy between CO absorption and CA II emissions in
the sun and stars - an indirect diagnostic for gas disturbed by
magnetic fields?
Authors: Ayres, T.
1986HiA.....7..425A Altcode:
It has been found that the cores of the strongest of the CO transitions
in the solar disk do not exhibit limb-brightening, but continue to
darken toward the limb. The results of research are reviewed which
show that, to the extent that the hot regions of the solar atmosphere
are manifestations of magnetic 'activity' and the cool zones represent
the undisturbed state of the gas, simultaneous cospatial measurements
of the 4.7 micron absorption bands of CO and 0.4 micron emission cores
of the H and K lines of Ca(+) can be used to diagnose indirectly the
presence and scale of such activity on the solar surface. The finding
of a similar dichotomy between the absorptions of the fundamental CO
bands in the red giant Arcturus and chromospheric models based on the
prominent emission reversals of the Ca II lines is also discussed.

---------------------------------------------------------
Title: Long-Term Cycles in the Magnetic Active Regions of Cool Stars
Authors: Ayres, Thomas R.
1986iue..prop.2398A Altcode:
Long-term activity cycles, believed to be analogous to the 11 year
solar cycle, have been discovered on numerous late-type stars through
ground-based Ca II observations. The most valuable activity diagnostics,
however, are emission features found in the ultraviolet: UV emission
features available in IUE spectra are formed over a wide range of
physical conditions in the active layers of stellar atmospheres,
and are free of the photospheric contamination suffered by Ca II. We
therefore propose to search for and study stellar activity cycles
using data collected by the IUE. We have chosen a set of program stars
which are well-represented in the Archives, and propose a multiyear
program of continued monitoring of these stars. We believe that the
development of a complete theory of stellar activity will ultimately
require the compilation of a large data base concerning empirical
properties of activity cycles. Our proposed program will provide the
first extensive, ultraviolet data set of this type. The key to the
success of our project will be to analyze all data in a systematic and
consistent fashion. We therefore intend to reprocess relevant Archive
images using the latest calibrations and ITFs, and to measure line
fluxes in all new and existing images using automated software in
order to ensure homogeneity of the data analysis procedures.

---------------------------------------------------------
Title: Progress Report: Precise Measurements of Radial Velocities
of Far-Ultraviolet Emission Lines in Stars of Late Spectral Type
Authors: Ayres, T.; Engvold, O.; Jensen, E.; Linsky, J.
1986LNP...254...94A Altcode: 1986csss....4...94A
Recent high-dispersion, far-ultraviolet IUE spectra of the G-type
supergiant β Draconis contain evidence for organized, persistent
downflows of gas, apparently confined to a high-density component of
the stellar transition zone.

---------------------------------------------------------
Title: Hydrogen Lyman Alpha Fluxes for Late-Type Dwarf Stars
Authors: Neff, J. E.; Carpenter, K. G.; Ayres, T. R.
1985BAAS...17..879N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A physically realistic approximate form for the redistribution
function R(II-A)
Authors: Ayres, T. R.
1985ApJ...294..153A Altcode:
An approximation is proposed to the redistribution function R(II-A)
(coherent, isotropic scattering in the rest frame of the atom) which
is fast to compute and attains much higher accuracy than previous
approximations for the astrophysically important case of small Voigt
parameters. Further, the new approximation permits the diffusion in
frequency of wing photons ('Doppler drifting') which is lost in one
of the widely-used versions of the R(II-A) approximation schemes:
Kneer's normalization of the Jefferies-White formulation.

---------------------------------------------------------
Title: Alpha Trianguli Australis (K2 II-III) : hybrid or composite ?
Authors: Ayres, T. R.
1985ApJ...291L...7A Altcode:
The prototype "hybrid-spectrum" giant, α Trianguli Australis, exhibits
a far-ultraviolet continuum which is considerably bluer than would
be expected of a star of its optical colors, suggesting the presence
of a previously unrecognized companion. If the K type primary is
as luminous as indicated by the widths of its Ca II and Hα lines,
the companion could be an early F type dwarf that only recently has
arrived on the main sequence. Indeed, the flux of C IV from α TrA -
an important measure of "hybridness" - would not be inconsistent with
that expected from a very young, chromospherically active F star.

---------------------------------------------------------
Title: Cool plasma at the base of the solar chromosphere revealed
by infrared bands of carbon monoxide.
Authors: Ayres, T. R.
1985cdm..proc..259A Altcode:
The author describes empirical evidence - cool cores in strong,
middle-infrared carbon monoxide (CO) lines - for the existence of
low-temperature plasma (T &lt; 4000K) at the levels of the solar outer
atmosphere where conventional models place the chromosphere proper
(T ≈ 6000K). He also reports recent observational and interpretative
studies of CO, and Ca II K, in magnetic active regions which further
support the hypothesis of a highly inhomogeneous, thermally "bifurcated"
chromosphere.

---------------------------------------------------------
Title: A Deep SWP Echelle Exposure of a Red Dwarf Flare Star:
At Microscopii
Authors: Ayres, Thomas R.
1985iue..prop.2101A Altcode:
Among the late-type stars that exhibit prominent chromospheric and
coronal activity, the H-alpha emission-line red dwarfs (dMe) fall at the
extreme high end of Xray and C IV intensity levels. The extraordinary
emission strengths of the dMe stars almost certainly are related to
high rates of magnetic field production by the "dynamo" mechanism
owing to the extensive convective zones of the low-mass, main-sequence
stars. Despite the large intrinsic surface fluxes of the dMe stars in
high-excitation emissions like C IV, the observed fluxes at Earth are
too small for these objects to be studied with the high dispersion mode
of IUE, at least using conventional observing strategies. Nevertheless,
high-dispersion observations of other late-type single stars and
binary systems have provided a wealth of information concerning the
physical conditions and dynamics of the important "transition zone"
between the lowexcitation chromospheric layers and the overlying,
multimillion degree corona. We therefore propose an IUE observing
program to attempt high-dispersion, far-ultraviolet spectroscopy of
a prototype flare-star binary, AT Mic AR (dM4.5e + dM4.5e), using a
novel observing strategy. The goals of our program are threefold: -
To measure at high dispersion the line profiles of prominent emissions
in the far-ultraviolet spectrum of the main-sequence, M-type flare
star AT Mic B inside and outside of flares. - To separately determine
the emission levels of the two nearly identical components of the AT
Mic binary. - Test whether a novel observing technique can extend IUE
exposures to as long as 30 hours. Our program is designed to push IUE
to its observational limits, and, if successful, will pave the way
for much deeper IUE exposures than heretofore have been considered
practical. Furthermore, the program will provide high quality UV line
profile information for the latest-type main-sequence star(s) that
are accessible to the IUE in high dispersion, and will thereby fill
an important gap in the existing data base of echelle observations of
cool stars.

---------------------------------------------------------
Title: A Far-Ultraviolet Echelle Survey of Young F Stars in the URSa
Major Cluster
Authors: Ayres, Thomas R.
1985iue..prop.2099A Altcode:
Late-type stars nearly universally exhibit the spectroscopic
symptoms of solarlike chromospheric and coronal activity, while the
early-type stars are decidedly non-solar in their outer atmospheric
properties. The boundary between the solar-like and non-solar
behavior occurs among the F-type stars, where shallow convective
envelopes first develop. Within this critical boundary, the very
young, fast-rotating F-type stars are an important sub-class of
their own: It is among the fast rotating late-type stars that the
most intense chromospheric and coronal phenomena are observed,
presumably related to extremes of magnetic dynamo action. It is our
intent, therefore, to carry previous high-dispersion, farultraviolet
studies of late-type stars to the important sub-class represented by
the very young F-types. The region of the stellar outer atmosphere
that is perhaps most sensitive to the transition from non-solar to
solar-like behavior is the chromosphere-corona 'transition zone'
(TZ), with characteristic temperatures between 2XJ04 and a few x lO^5
K. High-dispersion observations of TZ lines in the far-UV spectra of
active G and K stars have revealed the existence of important dynamical
phenomena--systematic downflows and supersonic 'turbulence'-as well as
providing detailed information concerning TZ densities. However, even
the brightest of the young F stars (which are in the nearby Ursa Major
Cluster and Stream) are too faint to observe with high S/N at the most
prominent TZ emission -- C IV 1548 -- in high dispersion. Therefore, we
will focus our attention on the longwavelength end of the farultraviolet
spectrum: The SWP camera is most sensitive near 1900A, and the region
contains important emissions of Si III] and C III], as well as Si II
at somewhat shorter wavelengths, all of which are superimposed on a
bright photospheric continuum.

---------------------------------------------------------
Title: How Steady are the Far-Ultraviolet Emissions of the F Stars?
Authors: Ayres, Thomas R.
1985iue..prop.2100A Altcode:
A detailed monitoring of the ultraviolet spectrum of the active F-type
giant of Capella ( alpha Aur A: G6 III + F9 III) over the course
of two months in the Spring of 1981 revealed that fluctuations in
the high-excitation emissions like C IV 1548 were remarkably small,
in fact below the sensitivity limit of the IUE echelle images taken
during the program. The steadiness of the C IV flux of Capella
was quite surprising, given the rather dramatic variations of
highexcitation emissions seen in other stars of comparable C IV and
X-ray intensity levels, particularly the cool K0 subgiants of the RS
CVn-type binaries. Recently, M. Giampapa and R. Rosner have argued that
the F-stars should he comparatively steady in their chromospheric and
coronal emissions compared with the cooler late-type stars, because
the shallow convective envelopes of the Ftypes are not conducive to
the development of large, spatially-coherent structures of the internal
magnetic field. It is the eruption of the subsurface fields into large,
organized, long-lived active regions which is thought to be responsible
for the substantial "rotational modulations" of the ultraviolet
emissions of the cooler stars. If the Giampapa-Rosner mechanism is
correct, then steady far-ultraviolet emissions should be a trade-mark
of the F-stars. I propose to test that hypothesis by a very sensitive
monitoring of the C IV emission of three prototype F-stars: Procyon
(F5 IV-V), the secondary of Capella (F9 III), and a Cassiopeia (F2 IV).

---------------------------------------------------------
Title: A Critical Test of the SWP Wavelenght Scale
Authors: Ayres, Thomas R.
1985iue..prop.2102A Altcode:
Calibrations using the onboard platinum hollow-cathode lamps of the IUE
provide a high degree of internal consistency in the derived wavelengths
of SWP echelle images. However, it has been recognized recently that
SWP images suffer small, stable wavelength distortions on spatial
scales comparable to, or larger than, the size of the calibration
'spots'. Although the distortions are small enough that routine
observations are not appreciably affected, there are several programs
involving high-precision measurements of late-type chromospheric
emission-line stars where the presence of the wavelength distortions
might seriously compromise the scientific objectives. I propose,
therefore, to undertake a detailed study of small-scale wavelength
distortions in SWP echelle-mode images. The study will consist of two
parallel parts: - A detailed analysis of existing images of the onboard
calibration lamp based on very recent laboratory measurements of the
lamp spectrum. The new measurements increase by a factor of about
three the number of emission spots in the calibration images for which
reliable laboratory wavelengths are available. Accordingly, the spatial
extents of the wavelength distortions can be mapped significantly more
accurately than previously. - A critical empirical test of the fidelity
of the IUE wavelength scales for a typical chromospheric emission-line
star based on observations of the target at different locations in
the large aperture. By positioning the target at one end of the large
aperture, parallel to the dispersion direction, one should obtain the
same wavelength scale as for an aperture-center observation, aside from
the easily calculated shift owing to the physical translation of the
'image'. Any differences between relative line positions in apertureedge
and aperture-center observations therefore should reveal the extent of
the wavelength distortions. The chromospheric emission-line stars are
important for such a test because their high-excitation, far-ultraviolet
emission lines are much broader than the calibration lines, but are
narrow enough that comparatively subtle dynamical phenomena--like the
10-20 km s^-1 redshifts of the C IV and Si IV doublets of Capella--can
be measured at a significant level. Therefore, the broad lines of the
stellar sources might respond differently to the wavelength distortions
than the narrow lines of the calibration lamps: Gauging of the magnitude
of the effect is critically important to the study of the dynamics of
high-excitation plasma in the outer atmospheres of late-type stars.

---------------------------------------------------------
Title: Summary report for working group on line synthesis and
atmospheric modeling.
Authors: Ayres, T. R.
1985cdm..proc....3A Altcode:
Obstacles encountered in the fields of atmospheric modeling and line
synthesis are discussed with attention focused on the following:
(1) velocity fields, (2) thermal inhomogeneities, (3) geometry, and
(4) finite computing resources. It is noted that in some cases, such
as global P-mode oscillations, the velocity fields are indicative of
fundamental solar properties; in others, such as turbulence in the
upper chromosphere and lower transition zone, these fields signify the
operation of energy transport and dissipation mechanisms. With regard
to geometry, particular emphasis is placed on the vertical spreading
of magnetic flux tubes. It is concluded that in order to solve the
current problems in this field, high-quality ultraviolet, optical and
infrared observations of the sun from space must be obtained.

---------------------------------------------------------
Title: The solar stellar connection in the far ultraviolet.
Authors: Bennett, J. O.; Ayres, T. R.; Rottman, G. J.
1984NASCP2349..437B Altcode: 1984IUE84......437B; 1984fiue.rept..437B
The authors compare the far-ultraviolet "activity" of solar-type stars,
as measured with the IUE, to that of the Sun, as measured by the Solar
Irradiance Monitor of the Solar Mesosphere Explorer. The goal of the
study is to explore the relationships between the "ultraviolet activity"
at different levels of the atmospheres of solar type stars. Secondary
goals are to establish the strength of the solar ultraviolet activity
within the class of solar-type stars, and to examine the amplitudes of
rotational modulations of the solar emission lines during the declining
portion of the current sunspot cycle. A unique aspect of the study is
that the spectral resolution of the SME instrument (7.5 Å) compares
very favorably with that of the low dispersion model of the IUE (5 Å).

---------------------------------------------------------
Title: Three short-period binaries seen at high-dispersion: UX Ari,
Iota Triand HR 5110.
Authors: Little-Marenin, I. R.; Ayres, T. R.; Simon, T.
1984NASCP2349..404L Altcode: 1984IUE84......404L; 1984fiue.rept..404L
The three short-period binary systems UX Ari (P=6.43791 days),
iota Tri (P=14.732 days) and RH5110 (P=2.61328 days) represent three
different evolutionary stages: (1) an evolved subgiant primary with
a secondary still on the main sequence (UX Ari); (2) two evolved G
giants that appear to be crossing the Hertzsprung gap for the first
time together (iota Tri); and (3) an evolved subgiant that fills its
Roche lobe and has lost mass to the secondary to the point where the
original secondary is now about 3.5 times as massive as its evolved
KOIV companion (HR5110). All three systems show strong UV emission
lines indicative of plasmas ranging in temperature from 6000K to
20,000K. X-ray emission was detected from UX Ari and HR5110 indicating
hot coronae. The chromospheric, transition region and coronal activity
appears to be related primarily to the rotational velocity of the stars
(but also to other parameters such as the depth of the convection
zone). High-dispersion short-wavelength as well as long-wavelength
IUE spectra of all three systems were analyzed.

---------------------------------------------------------
Title: A progress report on the analysis of long exposure SWP high
resolution spectra of cool stars.
Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Carpenter, K.;
Jordan, C.; Judge, P.; Gustafsson, B.; Eriksson, K.; Saxner, M.;
Engvold, O.; Jensen, E.; Moe, O. K.; Simon, T.
1984NASCP2349..445L Altcode: 1984fiue.rept..445L; 1984IUE84......445L
The IUE is the first experiment with sufficient sensitivity to obtain
high resolution spectra (lambda/delta lambda is approximately 10,000)
of many cool stars in the vitally important 1200 to 2000 A spectral
region. These data provide qualitatively new information with
which to understand the properties of and structures in the outer
atmospheres of these stars. Also, these cool star spectra will be
extremely useful in planning for the Space Telescope High Resolution
Spectrograph, which will be 1000 times more sensitive than IUE but will
be hampered by limited observing time and limited spectral bandwidth
in each exposure. Very long exposure, high disperson SWP spectra of
many stars located throughout the cool half of the HR diagram were
obtained. These 12 to 21 hour exposures were obtained by combining
NASA and Vilspa shifts so as to obtain the longest possible exposures
at times of low background. Included are dwarf stars of spectral type
G0 V to M2 V, G9.5 III to M5 II giants, G2 Ib to M2 Iab supergiants,
a number of RS CVn-type systems, and Barium stars.

---------------------------------------------------------
Title: Precise measurements of radial velocities of emission lines
in the far-ultraviolet spectra of late-type stars.
Authors: Ayres, T. R.; Engvold, O.; Moe, D. K.; Simon, T.; Jordan,
C.; Judge, P.; Brown, A.; Linsky, J. L.
1984NASCP2349..468A Altcode: 1984fiue.rept..468A; 1984IUE84......468A
The radial velocities of emission lines in deep short wave prime camera
echelle exposures of several late-type dwarf and giant stars were
measured. The goal was to search for absolute and differential Doppler
shifts of emission lines formed at different temperatures in the stellar
outer atmospheres analogous to the redshifts of C IV lambda 1548 (10
to the 5th power K) which occur in the solar transition zone. Existing
images, taken without the precise radial velocity precautions, of five
dwarf stars, four giant stars, and three supergiants are reanalyzed.

---------------------------------------------------------
Title: Calibrations of wavelengths in SWP echelle spectra
Authors: Delapana, M. D.; Ayres, T. R.
1984NASCP2349..521D Altcode: 1984fiue.rept..521D
Sources of random and systematic errors in the echelle wavelength scales
that must be minimized in order to obtain high quality radial velocity
measurements of emission lines in the far UV with IUE are reviewed. The
problem of overexposure of the strongest Pt II emission lines at the
long wavelength end of the spectrum and the faintness of the remaining
Pt II emission features is also examined. Wavelength calibration
spectra from IUE archives were analyzed using an interactive procedure
incorporating a least squares Gaussian fitting algorithm. The standard
deviation of the PHCAL wavecals (+/- 1.1 km/sec using 1982 data only)
is less than was found for the 6 wavecals (+/- 3.1 km/sec) obtained
on consecutive days in December of 1982 in a previous study nearly
contemporaneous wavecals to register velocity scales of stellar high
dispersion observations. The standard deviation of the mean residuals
of the orders averaged over 1982 is 2.2 km/sec, which can be interpreted
as the internal consistency of the IUE SW wavelength scales.

---------------------------------------------------------
Title: IUE Observations of the RS CVn Binary - TZ Tri
Authors: Little-Marenin, I. R.; Ayres, T. R.; Young, A.
1984BAAS...16..912L Altcode: 1984BAAS...16S.912L
No abstract at ADS

---------------------------------------------------------
Title: New Insights into the Solar-Stellar Connection
Authors: Ayres, T. R.
1984BAAS...16.1011A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The many faces of Capella : a search for rotational
modulations and astudy of systematic velocities of emission lines
in the ultraviolet.
Authors: Ayres, T. R.
1984ApJ...284..784A Altcode:
The ultraviolet emission of the spectroscopic binary Capella has
been monitored with IUE over the course of half an orbital cycle (2
months). The first objective was to detect changes in the fluxes or
shapes of ultraviolet emission lines in response to the evolution of
large-scale active regions or their rotation onto and off the visible
hemisphere of the active F-type secondary star. Capella proved to be
surprisingly steady in its ultraviolet emissions. The second objective
was to investigate systematic velocities of the low-excitation
and high-excitation emission lines. It is found that the latter
are significantly redshifted with respect to the former. The author
concludes that the redshifts indicate true downflows of 105K
plasma in the stellar "transition zone", rather than the operation of a
"P Cygni" effect in an optically thick outflow.

---------------------------------------------------------
Title: The Many Faces of HR 1099
Authors: Ayres, T. R.; Bennett, J. O.; Linsky, J. L.; Simon, T.
1984BAAS...16..893A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-resolution, far-ultraviolet study of beta Draconis
(G2 Ib-II) : transition region structure and energy balance.
Authors: Brown, A.; Jordan, C.; Stencel, R. E.; Linsky, J. L.; Ayres,
T. R.
1984ApJ...283..731B Altcode:
High-resolution far ultraviolet spectra of the star Beta Draconis have
been obtained with the IUE satellite. The observations and emission
line data from the spectra are presented, the interpretation of the
emission line widths and shifts is discussed, and the implications
are given in terms of atmospheric properties. The emission measure
distribution is derived, and density diagnostics involving both line
ratios and line opacity arguments is investigated. The methods for
calculating spherically symmetric models of the atmospheric structure
are outlined, and several such models are presented. The extension of
these models to log T(e) greater than 5.3 using the observed X-ray flux
is addressed, the energy balance of an 'optimum' model is investigated,
and possible models of energy transport and deposition are discussed.

---------------------------------------------------------
Title: A Far-Ultraviolet Study of the Bright Delta Scuti Variable
Beta Cassiopeia
Authors: Ayres, Thomas R.
1984iue..prop.1747A Altcode:
Beta Cassiopeiae is a fast rotating early-F subgiant that exhibits
smallamplitude pulsations in optical light and radial velocity of
the delta Scuti class, and is a bright far-ultraviolet emission-line
source having surface fluxes in excess of thirty times those of
the quiet Sun. It is plausible that the fast rotation of a Cas, and
the recent development of a shallow convection zone as the star has
evolved into the blue edge of the Hertzsprung gap, have conspired
to produce substantial amounts of surface magnetic activity by
means of the dynamo mechanism. The strong chromospheric and higher
temperature emissions might then arise from processes analogous to
those operating in magnetic "active regions" on the Sun. However, it
certainly also is possible that the strong ultraviolet emissions are
a byproduct of the delta Sct phenomenon, itself, as in fact has been
suggested recently in the case of the Cepheids, which are similar in
temperature but more luminous than the delta Scuti stars. Accordingly,
I feel that beta Cas is a worthwhile subject for a detailed study with
IUE in order to investigate the properties of its chromospheric and
higher -temperature emission lines: High-dispersion, far-ultraviolet
measurements of beta Cas would extend previous studies of F-M dwarfs,
giants, and supergiants into the earliest spectral types where
solar-like chromospheric phenomena have been identified; and IUE is
sufficiently sensitive to test the hypothesis of pulsationinduced
chromospheric heating, through monitoring of the lowdispersion SWP
spectrum of beta Cas over several of the 2^h.4 cycles for evidence of
periodic behavior in the far-ultraviolet emissions.

---------------------------------------------------------
Title: Wind or Antiwinds
Authors: Ayres, Thomas R.
1984iue..prop.1752A Altcode:
One of the surprising discoveries by IUE is that of redshifted emission
lines of Si IV and C IV in the farultraviolet spectra of several
late-type giants and supergiants. In the solar atmosphere, redshifts of
high excitation emissions frequently are observed over magnetic active
regions, and are thought to be associated with downflows of 10^5 K
plasma in magnetic filaments. Nevertheless, the giants and supergiants
that exhibit redshifted Si IV and C IV emissions differ substantially
from dwarf stars like the Sun in terms of their fundamental stellar
properties. It is possible, therefore, that the redshifts of the giants
and supergiants have an entirely different origin than suggested by the
solar analogy. For example, the appearance of a redshifted emission
profile could result from an expanding, optically thick wind owing
to the "P-Cygni" mechanism. We propose to continue, in the 7th year
of IUE, the exploration of redshifts of high excitation emissions by
addressing the question of whether the phenomenon in the supergiants
is produced by an outflow of optically thick plasma (a "wind") or by a
downflow of material (an "antiwind"). The test requires observations,
using a precise radial velocity technique, of the intersystem lines
of Si III (1892) and C III (1909) in the spectrum of the most luminous
star, beta Draconis (G2 Ib-II), for which redshifts have been detected
previously. In particular, the intersystem lines are optically thin,
and therefore cannot exhibit a P-Cygni effect, whereas the Si IV and C
IV doublets might be optically thick and therefore susceptible to the
P-Cygni phenomenon. Furthermore, owing to different sensitivities to
density, the C III] emission will be more heavily weighted towards a
low-density, extended wind, while the Si III] emission will tend to be
formed in the higher density structures from which the permitted lines
of Si IV and C IV arise. Accordingly, the absolute velocity of Si III]
1892, and the difference in the velocities of 1892 and C III] 1909, can
be used to test the wind and antiwind hypotheses. The highest precision
in the measurement of the velocity differences can be achieved by taking
a minimum of four separate spectra of the 1900A region of Beta Dra. The
optimum exposures of the 1900 A region of Beta Ori are 7 hours, but the
precise measurement of radial velocities requires that the satellite
be thermally stable prior to the observations. The necessary stability
can be attained, and maintained, only by coordinating US2, Vilspa,
and US1 shifts on consecutive days. An important practical byproduct
of the requirement for thermal stability is the opportunity to take
Intensity Transfer Function calibrations in the LWR or LWP cameras
during the long SWP exposures.

---------------------------------------------------------
Title: Ultraviolet Observations of the Limb-Crossing of an Active
Region on Sigma Geminorum
Authors: Ayres, Thomas R.
1984iue..prop.1755A Altcode:
We propose to study, at high dispersion, the behavior of the ultraviolet
emission line spectrum of the RS CVn-type binary Sigma Geminorum (KI
III + ?) as an optically identified starspot group rotates over the
limb of the K giant and onto the visible hemisphere. The scientific
goal is to distinguish between the two most promising hypotheses to
explain the significant changes that were observed in a pair of IUE SWP
echelle images of Sigma Gem taken over consecutive days in May 1982: (1)
a flare which occurred near the receding limb of the giant (or near disk
center but accompanied by significant downflows of 10^5 K material); or
(2) the rotation off of the visible hemisphere of a small-scale, but
bright, active region associated with a previously identified optical
starspot group. We feel that the behavior of similar systems, like II
Peg, favors the second hypothesis. If so, a mechanism must operate
in the cool, fast rotating giants to produce a significant spatial
concentration of the decaying magnetic fields that are thought to be
responsible for the enormously enhanced far-ultraviolet emissions of
the RS CVn-type binaries. We believe that it is essential to understand
why the "activity" on the cool giants can become so concentrated and
intense. An important way to explore in detail the physical association
of high excitation active regions with photospheric starspot groups
is to use the technique of "Doppler, Imaging", developed by Vogt and
collaborators to study the changing profiles of absorption features
in the spectra of fast rotating late-type stars. We have applied the
emission-line analog of the approach previously to the shortperiod RS
CVn system, HR 1099, and propose to continue our work in the 7th-year
of IUE with a study of Sigma Gem. In addition, we intend to search for
the occurrence of flare activity in Si IV and C IV by monitoring the
farultraviolet spectrum of a Gem at low dispersion. As a novel twist to
the program, we intend to arrange simultaneous coverage with the Very
Large Array to explore the association of the microwave corona of a Gem
with the farultraviolet emission regions and optical starspots. [Note:
this program could be easily integrated into an ITF recalibration
effort for the LWP, LWR and SWP cameras: The optimum observing window
is in late February or early March, before Spring shadow season.]

---------------------------------------------------------
Title: Sigma Geminorum (K1 III + ?) : variability of the ultraviolet
emission lines near conjunction.
Authors: Ayres, T. R.; Simon, T.; Linsky, J. L.
1984ApJ...279..197A Altcode:
Far-ultraviolet IUE echelle spectra are reported of the moderate-period
RS CVn system σ Geminorum. Despite the location of the red giant
primary of σ Gem in a portion of the H-R diagram where cool stellar
winds are common, no evidence is found for circumstellar absorption
features or blueward asymmetries in the chromospheric O I emission
cores. However, observations on two consecutive days indicate
significant changes in the profiles of high-excitation species, such
as Si IV and C IV which probably were produced by the rotation off of
the visible hemisphere of the primary of a large-scale magnetic active
region identified in a previous photometric study.

---------------------------------------------------------
Title: Observing the Sun as a Star; Observing Stars as Suns
Authors: Ayres, T. R.
1984stp..conf....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Capella HL
Authors: Ayres, Thomas R.
1984LNP...193..202A Altcode: 1984csss....3..202A
No abstract at ADS

---------------------------------------------------------
Title: Outer atmospheres of cool stars. XV. High-dispersion
ultraviolet studies of active chromospheric G-K dwarfs.
Authors: Ayres, T. R.; Linsky, J. L.; Simon, T.; Jordan, C.; Brown, A.
1983ApJ...274..784A Altcode:
The authors have obtained IUE ultraviolet echelle spectra of the three
late-type active-chromosphere dwarf stars χ1 Ori, ξ Boo A
and ɛ Eri. These are compared with previously published observations
of the quiet chromosphere dwarfs α Cen A and α Cen B. The spectra
indicate a gross strengthening of chromospheric and transition-region
line fluxes from quiet to active dwarf stars without a fundamental
change in the line shapes. Qualitatively the same spectroscopic behavior
is seen in detail on the solar surface between regions of strong and
weak magnetic fields. They believe that the correspondence between
the stellar and solar behavior is not accidental, but instead affirms
that enhanced chromospheric and coronal emission on late-type main
sequence stars is a result of increased surface coverage of magnetic
active regions.

---------------------------------------------------------
Title: Redshifts of high-temperature emission lines in the
far-ultraviolet spectra of late-type stars.
Authors: Ayres, T. R.; Stencel, R. E.; Linsky, J. L.; Simon, T.;
Jordan, C.; Brown, A.; Engvold, O.
1983ApJ...274..801A Altcode:
High-dispersion IUE spectra of six late-type stars exhibit small but
statistically significant differential redshifts of high-temperature
emission lines, like Si IV and C IV, with respect to low-temperature
lines like S I and O I. A well-exposed, small-aperture spectrum of
the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9
III) establishes that the high-temperature lines are redshifted in an
absolute sense with respect to the accurately determined photospheric
velocity of the system at single-line phase 0.50. Several possible
explanations for the stellar redshifts are discused, including a warm
wind (100,000 K) in which aparent redshifts are produced in optically
thick lines by an accelerating outfow, and the downflowing component
of a vertical circulation system for which the up-leg portion of the
flow is too cool, too hot, or too tenuous to be visible in Si IV and C
IV. If the second scenario is true, the stellar redshifts may provide
an important phenomenological link to the downflows observed in 100,000
K species over magnetic active regions in the sun.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. XIII. Capella at critical
phases.
Authors: Ayres, T. R.; Schiffer, F. H., III; Linsky, J. L.
1983ApJ...272..223A Altcode:
The results are presented of a program of high-dispersion spectroscopy
of Capella at critical orbital phases utilizing the International
Ultraviolet Explorer. The considered program had the objective
to establish as carefully as possible the relative ultraviolet
emission levels of the Capella primary and secondary in order to
obtain an understanding regarding the nature of their chromospheres
and coronae. The results of the program confirm the earlier study
of the Capella by Ayres and Linsky (1980), which was limited to
orbital phases 0.50 and 0.75. Both programs found that the Capella
secondary is considerably brighter than the primary, in surface flux,
in all of the prominent far-ultraviolet emissions, particularly the
high-excitation CII-CIV lines. In addition, the present study has
revealed several puzzling aspects of the system. It is concluded that
the Capella primary is comparatively bright, for a yellow giant, in
far-ultraviolet and perhaps also in soft X-ray normalized fluxes. The
implications of this conclusion are evaluated.

---------------------------------------------------------
Title: The narrow ultraviolet emission lines of the red dwarf AU
Microscopii(dM1.6e).
Authors: Ayres, T. R.; Eriksson, K.; Linsky, J. L.; Stencel, R. E.
1983ApJ...270L..17A Altcode:
It is pointed out that the red dwarfs are the smallest, coolest,
faintest, least massive, but most common of normal main-sequence
stars. The dMe (H-alpha emission) subclass of the red dwarfs
exhibits the largest median soft X-ray to bolometric luminosity
ratio of any group of late-type stars. In connection with the present
investigation, attention is given to the first high-dispersion spectra
of the chromospheric (6000 K) and higher temperature (up to 100,000
K) emissions of a dMe star, AU Microscopii in the far-ultraviolet
(1150-2000 A) and middle-ultraviolet (2000-3000 A) bands accessible to
the International Ultraviolet Explorer (IUE). AU Mic is one of the most
luminous of lower main-sequence stars in C IV and soft X-ray emission.

---------------------------------------------------------
Title: High-Dispersion Observations of Alpha Bootis
Authors: Ayres, Thomas R.
1983iue..prop.1394A Altcode:
Investigating the late phases of the life of a star is central to an
understanding of stellar structure and evolution, and the aping of
stellar magnetic activity. For yellow dwarf stars like the Sun, the
advanced stages of their life cycle are represented by old red giants
like Arcturus (alpha Bootis, K2 III). I propose, therefore, to undertake
the most detailed spectroscopic study of Arcturus yet attempted with
the International Ultraviolet Explorer. The study includes a 24-hour
superexposure of the farultraviolet (1150-2000 A) region, obtained with
collaborators in the U.K., and a uniformly high signalto-noise map of
the 2750-2900 A region of the middle ultraviolet. The IUE observations
will be coordinated with ground-based high-resolution spectroscopy
of the Ca I, Ca II and H-alpha lines of the optical region. The SWP
superexposure will be utilized to search for bands of the carbon
monoxide 4th positive system, which have been identified in low
dispersion spectra but are not seen in the existing 8-hour SWP echelle
exposure, and to detect, or set harder upper limits on, highexcitation
emission lines like C II 1336, Si IV 1394, and C IV 1548, which are
diagnostics for the presence of hot plasma (T&gt;2_10^4 K) in the
outer atmosphere of the red giant. The strength of the farultraviolet
ionic emission lines can be used to constrain the competing models to
explain the structure of red giant chromospheres, coronae and winds,
while the fluoresced molecular features can be used to probe the
coolest layers of the red giant photosphere, which are radiatively
pumped from above by the strong chromospheric emissions of O I 1305
triplet) and C I (1657 multiplet). The high quality map of the middle
ultraviolet region can be utilized to study the strong chromospheric
emission cores and faint inner damping wings of the Mg II resonance
lines, and the weak emission core of the neutral magnesium resonance
line at 2852 A. These spectra can he applied to a number of problems
ranging from the properties of the circumstellar envelope and wind of
Arcturus, to the surface gravity and mass of the archetype red giant.

---------------------------------------------------------
Title: Capella HL
Authors: Ayres, Thomas R.
1983iue..prop.1393A Altcode:
The main component of the a Aurigae system, alpha Aurigae A (also
known simply as Capella), is a 104 day spectroscopic binary of evolved
yellow giants which is extraordinarily bright in the far-ultraviolet
region and accordingly has been the subject of a number of detailed
studies with IUE. These studies have revealed that the evolutionarily
less advanced F-type secondary of Capella is the dominant source of
highexcitation emissions from the system, and reinforce the notion
that evolutionary "youth" and enhanced chromospheric activity are
strongly associated. Capella HL is a faint binary of red dwarfs which
is an outlying member of the a Aurigae system. Although the dM stars
as a class are quite common in the solar neighborhood, Capella HL is
quite unusual among the red dwarfs since it is one of the very few for
which a reliable age is available. In particular, the well-determined
masses of Capella Aa and Ab and their evolutionary status imply
that the spectroscopic binary is about half the age of the Hyades
cluster. Since Capella HL is gravitationally bound to the main pair,
it very likely is coeval and therefore as young. There are surprisingly
few other dM stars whose ages are known as unambiguously as that of
Capella HL, an important exception being Proxima Centauri which is
bound to the solar-age alpha Centauri system. Accordingly, Capella HL
provides a unique opportunity to study the youthactivity connection
among stars of the lower main sequence. I therefore am requesting a
US1 low radiation shift to obtain wellexposed low-dispersion spectra
of the red dwarf pair in the farultraviolet and middle-ultraviolet
hands accessible to IUE. The objective of the program is to study the
strength of chromospheric and higher temperature emissions in one of
the very few red dwarfs whose age is known. The study is intended to
advance our understanding of the evolution of magnetic activity in
the cool half of the Hertzsprung-Russell diagram.

---------------------------------------------------------
Title: The Hydrogen Emission of Active Red Dwarfs
Authors: Ayres, Thomas R.
1983iue..prop.1390A Altcode:
A number of low-dispersion studies of the emission-line dwarf M stars
with IUE have revealed that their ultraviolet emissions share the
enormous enhancement over quiet Sun levels typical of their coronal soft
X-ray intensities. In fact, the visually very faint red dwarf AU Mic
(M1.6e) is so bright in the far-ultraviolet region that highdispersion
IUE spectra have been obtained successfully. These measurements
further corroborate the notion that the dMe stars are heavily covered
by intense magnetic activity, although the most pronounced effects
appear to be confined to the multi-million degree corona. Indeed, an
important new model for the lower atmospheres of the dMe stars proposed
by L. Cram suggests that the 6,000 K chromospheric layers in fact are
heated largely by XUV emission from the overlying corona, rather than
by hydrodynamical effects. If this model is correct, the red dwarfs
provide an opportunity to study a significant physical phenomenon that
is thought to operate on the Sun only during the most intense flares. In
this regard, the previous studies of the red dwarfs with IUE have
overlooked the most important feature of the far-ultraviolet spectrum
for elucidating the X-ray heating scenario: the Ly-alpha resonance
line of neutral hydrogen. Owing to the substantial recombination of
hydrogen throughout the XUV irradiated layers of the dMe chromosphere,
the Ly-alpha emission is anticipated to be considerably brighter than
ordinarily would be expected from a more solar-like star, where the H
I emission is governed largely by collisional excitation at conductive
interfaces between the chromosphere and corona. I therefore propose
a program to obtain short exposures of the farultraviolet Ly-alpha
emission of a representative sample of dMe stars in order to test the
Cram X-ray heating hypothesis. In fact, the predicted Ly-alpha exposure
times are so short that the program is suitable for NASA high radiation
time. Furthermore, I intend to coordinate the IUE observations with
ground-based measurements of Ca II, the H I Balmer series and other
chromospheric emission lines in the optical region. The main objective
is to obtain a complete set of chromospheric diagnostics to constrain
the numerical models that will he utilized to test the Cram hypothesis
or other possible mechanisms for energizing the red dwarf chromospheres.

---------------------------------------------------------
Title: Determination of Absolute Velocities for Emission Lines of
Late-Type Stars
Authors: Ayres, Thomas R.
1983iue..prop.1391A Altcode:
The recent discovery of redshifted emission lines like Si IV and C IV
in the far-ultraviolet spectra of active-chromosphere stars may be an
important link with the downflows of 10^5 K material seen commonly in
the magnetic loon structures of solar active regions. On the Sun, the
net redshifts of the hiqh-excitation species almost certainly result
from a continual exchange of plasma between the chromosphere and corona,
in which the upleg portion of the circulation is too cool (spicules, for
example) or too hot (explosive evaporation, for example) to be visible
in the intermediate temperature emissions. However, the differential
redshifts measured in the spectra of other late-type stars may result
from a net blueshift of the weak, lowexcitation emission features that
are used to provide -an ad hoc zero velocity reference. Furthermore,
even if the 10^5 K lines are redshifted in an absolute sense, an
outflowing wind at that temperature could absorb some of the emission
on the short-wavelength side of the line profile, and thereby give the
appearance of a net redshifted feature. According to the importance
of the redshift phenomenon with regard to winds and "antiwinds" in
late-type chromospheric emission-line stars, we propose to undertake
an extensive observational program with IUE to (1) establish whether
the high-excitation lines indeed are redshifted in an absolute sense,
(2) distinguish among the several competing hypotheses to explain
the redshifts, and (3) study the flow structure in a number of red
giants that are known to possess winds of moderate terminal velocity
but comparatively low excitation. The observational objectives of
the program can be met by obtaining long exposures in the SWP and LWR
regions of prototype bright stars whose spectra contain optically thin
forbidden and intersystem lines as well as strong permitted transitions
that probably are optically thick. The spectra will he taken according
to simple procedures that permit the assignment of a sufficiently
reliable absolute velocity scale. Finally, the absolute velocity
spectra that result from this program will be analyzed in the context
of detailed numerical simulations of geometrically extended, expanding
chromospheres, in order to elucidate the mechanisms responsible for
the winds and/or downflows.

---------------------------------------------------------
Title: The structure and energy balance in main sequence stars
Authors: Jordan, C.; Ayres, T. R.; Brown, A.
1983ASSL..102...61J Altcode: 1983ards.proc...61J; 1983IAUCo..71...61J
High-resolution spectra obtained with the IUE satellite have been
used to study the structure and energy balance in the main sequence
stars ξ Boo A, α Cen A, α Cen B and ɛ Eri. The EUV observations
are combined with X-ray fluxes to predict the coronal temperatures,
the electron pressures and energy lost or transferred by radiation
and thermal conduction.

---------------------------------------------------------
Title: Evolution of chromospheres and coronae in solar mass stars
: a far-ultraviolet and soft X-ray comparison of Arcturus (K2III)
and alf CEN A (G2V).
Authors: Ayres, T. R.; Simon, T.; Linsky, J. L.
1982ApJ...263..791A Altcode:
IUE far-UV and Einstein Observatory soft X-ray observations for the red
giant Arcturus and the nearby yellow dwarf Alpha-Centauri A, which are
archetypes of solar mass stars in different stages of evolution, are
compared. Evidence is found for neither coronal soft X-ray emission
from the red giant, at surface flux levels of only 0.0006 that
detected previously for the yellow dwarf, nor C II and IV resonance
line emission at surface flux levels of only 0.02 those of the yellow
dwarf. The resonance line upper limits and previous detections of the
C II intersystem UV multiplet 0.01 near 2325 A provide evidence for an
Arcturus outer atmosphere that is geometrically extended, tenuous and
cool. The red giant has, in addition, a prominent cool stellar wind. An
extensive tabulation of line identifications, widths and fluxes for
the IUE far-UV echelle spectra of the two stars is given, and two
competing explanations for the Wilson-Bappu effect are discussed.

---------------------------------------------------------
Title: Prospects for the Solar-Stellar Connection Outside the Optical
Band: A Matter of Resolution
Authors: Ayres, T. R.
1982BAAS...14..946A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Narrow Ultraviolet Emission Lines of the Red Dwarf AU
Microscopii (dM1.6e)
Authors: Ayres, T. R.; Eriksson, K.; Gustafsson, B.; Linsky, J. L.;
Saxner, M.; Stencel, R. E.
1982BAAS...14Q.865A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Appendix - Empirical Estimates of Noise Levels in IUE
Low-Dispersion Spectra
Authors: Ayres, T. R.
1982ApJ...257..243A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Outer atmospheric properties of beta Draconis (G2 Ib-II)
Authors: Brown, A.; Jordan, C.; Ayres, T. R.; Linsky, J. L.; Stencel,
R. E.
1982ESASP.176..142B Altcode: 1982IUE3r......142B; 1982iue..conf..142B
Observations of the supergiant Beta Draconis made by IUE are
discussed. Electron pressure is comparable with that found in the quiet
solar atmosphere. The X-ray fluxes from previous observations suggest
T = 10 to 20 million k, when combined with the analysis of the IUE
spectra; this would be greater than the proton escape velocity. The
radiation losses between 10,000 and 100,000 K exceed those from the
Sun by an order of magnitude, but in the absence of a stellar wind the
energy losses from the corona would be lower than in the Sun. The line
profile widths indicate substantial (M=2) nonthermal broadening. If
interpreted as energy associated with a wave flux, they would imply
more coronal energy than required by radiation and conduction losses,
suggesting an energetic mass loss. However, line asymmetries can also
be interpreted as motions within the atmosphere.

---------------------------------------------------------
Title: High resolution EUV spectroscopy of 56 Pegasi (K0II P + wd).
Authors: Jordan, C.; Brown, A.; Ayres, T. R.; Linsky, J. L.; Stencel,
R. E.
1982ESASP.176..161J Altcode: 1982iue..conf..161J; 1982IUE3r......161J
The hypothesis that X-ray and UV emission by 56 Pegasi (K0II p + wd)
originates in a conventional chromosphere, transition region and corona,
as opposed to Schindler's hypothesis of accretion of the cool stellar
wind onto the white dwarf companion, is discussed. Analysis of IUE data
indicates that within the uncertainties associated with determining the
stellar radius and abundances, the chromosphere, transition region, and
corona of 56 Peg are similar to that of Beta Draconis both in structure
and energy balance. The accretion hypothesis is not a unique explanation
of the observed spectral properties and the white dwarf companion may
not play a direct role. Furthermore, 56 Peg, according to current
values of V-R and luminosity class, is on the nonsolar side of the
Linsky-Haisch dividing line whereas Beta Draconis is on the solar side.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. XI. High-dispersion IUE
spectra of five late-type dwarfs and giants.
Authors: Ayres, T. R.; Linsky, J. L.; Basri, G. S.; Landsman, W.;
Henry, R. C.; Moos, H. W.; Stencel, R. E.
1982ApJ...256..550A Altcode:
We present high-dispersion, far-ultraviolet (1150-2000 Å) spectra
of five late-type dwarfs and giants obtained with the International
Ultraviolet Explorer. The chromospheric (T ≲104K)
emission lines in the giants tend to be about twice as broad as
the corresponding features of the dwarf star spectra, suggesting a
width-luminosity relation similar to the Wilson-Bappu effect for Ca
II H and K. The Si III λ1892 and C III λ1909 intercombination lines
formed in hotter layers (T ≍ 5 × 104K) also broaden
by a factor of 2 from the main-sequence stars to the evolved stars,
and the permitted resonance doublets of C II(3 × 104
K), Si IV (6 × 104 K), and C IV (105 K) are as much as
a factor of 4 broader in the giants than in the dwarfs. However, we
find no evidence for asymmetric or shifted emission profiles that
might indicate the presence of warm (T≪105K) stellar
winds. We conclude that broad C iv profiles, in particular, are typical
of active chromosphere giant stars and are unlikely to be a unique
signature of an extended, expanding warm wind. Since the resonance
lines tend to be wider than the intersystem lines formed at similar
temperatures in the chromosphere and in hotter layers, we conclude
that opacity must be an important broadening enhancement mechanism in
active chromosphere giant stars. Nevertheless, the intercombination
line widths do indicate a general increase in the outer atmosphere
Doppler motions from the dwarfs to the giants. Application of
the density sensitive line ratio C III λ1909/Si III λ1892 suggests
that the outer atmosphere pressures (T ≍ 5 × 104K)
are similar in the active chromosphere subgiant λ And and the quiet
chromosphere dwarfs, α Cen A and B. However, the pressures derived
for the Capella secondary and β Dra are factors of 3 or more lower
than the dwarfs, suggesting geometrically extended, low-density outer
atmosphere structures qualitatively different from the high-pressure,
compact structures typical of solar magnetic active regions. Finally, we have isolated the He II λ1640 emission component
from contaminant blends, and we find that the line strength is well
correlated with soft X-ray fluxes of the sample stars, as predicted
by photoionization-recombination models of the He II Bα formation.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. X. HR 1099 at quadrature.
Authors: Ayres, T. R.; Linsky, J. L.
1982ApJ...254..168A Altcode:
IUE high-dispersion, far-UV spectra of the active-chromosphere RS
CVn binary HR 1099 are reported. The emission features produced by
such high-temperature species as C II and C IV are found to be very
bright, to exhibit structure, change significantly in the one-week
interval separating the two exposures, and generally follow the radial
velocity motion of the K subgiant primary, while the less massive G
dwarf secondary appears only weakly in the composite spectrum. It is
concluded that chromospheric and transition region emission in RS CVn
binaries is a stellar rather than system phenomenon, and the structure
evident in some of the emission line shapes is interpreted as a patchy
brightness distribution on and above the K star surface that is spread
out in velocity by the rapid rotation.

---------------------------------------------------------
Title: High dispersion IUE spectra of active chromosphere G and
K dwarfs.
Authors: Ayres, T. R.; Linsky, J. L.; Brown, A.; Jordan, C.; Simon, T.
1982NASCP2238..281A Altcode: 1982auva.nasa..281A; 1982NASCP2338..281A; 1982IUE82......281A
IUE far ultraviolet echelle spectra of three active chromosphere
dwarf stars X1 Orionis (GO V), Bootis A (G8 V), and Eridani (K2 V),
are analyzed utilizing spectra of Alpha Cen A (G2 V) and Alpha Cen B
(K1 V) as quiet chromosphere comparisons.

---------------------------------------------------------
Title: The Many Faces of HR 1099
Authors: Ayres, Thomas R.
1982iue..prop.1045A Altcode:
We propose to monitor, in high-dispersion, the far-ultraviolet
emission of the archetype short-period RS Canum Venaticorum binary
system, HR 1099 = V711 Tauri (K0 IV + G5 V) through two complete
orbital revolutions. The tidally-locked RS CVn binaries have among
the brightest chromospheres (T = 6000 K) and coronae (T ~ 10^6
K) known, and are thought to suffer intense magnetic activity in
their surface layers. Accordingly, RS CVn binaries, as a class, are
valuable prototypes for investigating how magnetic flux is generated in
rapidly-rotating convective stars; the spatial scales associated with
structural expressions of the surface fields (magnetic active regions,
for example); and general questions concerning the physical response
of atmospheric plasma to embedded, intense magnetic activity. Our
objective in monitoring HR 1099 throughout its orbit is to study
the spatial distribution of far-ultraviolet emission on all faces of
the active K0 subgiant in that system. Previous exploratory spectra
obtained at critical orbital phases, namely the opposite quadratures,
indicate that the cool subgiant is quite variable in its far-ultraviolet
output, and suggests that the emission has a rather patchy surface
distribution. We propose to obtain further observations in order
to characterize the spatial scales and brightness levels of large,
coherent active regions on the stellar surface. Central to our study
is the issue of whether the dark "starspots", thought responsible
for the low-amplitude, periodic photometric fluctuations in such
systems, are sites of enhanced farultraviolet emission, as the solar
analogs--active regions--might tend to suggest. Since the emission
features from any large-scale activity center will be spread out in
velocity by the rapid rotation of the tidally synchronized subgiant,
high-dispersion spectroscopy can be utilized to diagnose what fraction
of the stellar surface is involved. Furthermore, a sequence of IUE
high-dispersion images with the long- and shortwavelength echelles
over the binary orbit can help establish more firmly the contribution
of the main-sequence component of HR 1099 to the composite emission
spectrum. The former observation is relevant to the mechanisms that
amplify magnetic fields in the stellar convection zone and impress
large-scale spatial coherence on emerging flux ropes. The latter
observation is relevant to the mechanisms that generate magnetic flux
(dynamo action for example), since the primary and secondary of HR
1099 have somewhat different stellar properties and linear rotation
rates. An investigation of these issues is central to understanding
the extremely energetic phenomena associated with the intense surface
magnetic activity of the RS CVn subgiants.

---------------------------------------------------------
Title: The Wilson-Bappu Effect &amp; Beyond
Authors: Ayres, Thomas R.
1982iue..prop.1043A Altcode:
The broad photospheric damping wings and bright chromospheric
emission cores of the resonance lines of ionized Magnesium (h and k)
and Calcium (H and K) contain an extraordinarily detailed picture of
the temperature-height profile of the stellar outer atmosphere. When
combined with the wing shapes of the neutral species resonance
lines, Mg I 2852 A and Ca I 4227 A, the Mg II h and k and Ca II
H and K wings provide an empirical measure of the stellar surface
gravity. Furthermore, the core intensities of the six resonance lines
indicate the overall rates of plasma radiative cooling at different,
but adjacent, levels of the chromosphere. Finally, the emission
cores of Mg II k and Ca II K are known to exhibit a remarkable
systematic broadening with increasing stellar luminosity--the
Wilson-Bappu effect--whose origin remains controversial despite
several decades of study. Further fueling that controversy are recent
highresolution, ground-based studies of the absorption profile of
H I Balmer alpha (6562 A), that demonstrate a general broadening of
the chromospheric core with increasing luminosity, although not in
a one-to-one correspondence with the Ca II K behavior. We propose
below an observing program to address these several issues by means
of coordinated IUE and ground-based observations of a small sample
of representative G-K dwarfs and giants. The ground-based side of the
study, in collaboration with the Australian National University, will
consist of high-resolution spectrograms of Ca II H and K, Ca I 4227 A,
H-alpha, and other Balmer lines utilizing the Coude echelle and PCA
detector of the Mt. Stromlo 74". supplemented with Cassegrain echelle
spectra from the Siding Spring 40". The IUE side of the study will
consist of graded sequences of long-wavelength echellograms to optimally
expose the bright emission features of Mg II (2800 A) as well as the
faint damping wings of Mg II h and k and the chromospheric absorption
core of Mg I 2852 A. Previous observational work in this region has
tended to concentrate on the Mg II k core itself. Consequently, the
low contrast wings are usually recorded at poor signal-to-noise and
thereby are useless for theoretical interpretations. Our proposed
program is novel in that we will obtain analogous high-resolution,
high signal-tonoise profiles of Ca II H and K, Ca I 4227 A and H-alpha
as close in time to the IUE spectra as is practical. Near simultaneity
is an important consideration since late-type stars are known to exhibit
profile changes in their chromospheric emission cores on time scales as
short as hours. We intend to provide, by our coordinated investigation,
a high-quality set of calibrated chromospheric emission and absorption
line profiles of representative G-K dwarfs and giants to serve as a
basis for subsequent detailed numerical simulation studies of radiative
cooling, gravity-sensitive wing ratios, and the Wilson-Bappu effect.

---------------------------------------------------------
Title: Far-Ultraviolet Echelle Spectra of RS CVN Giants
Authors: Ayres, Thomas R.
1982iue..prop.1049A Altcode:
RS Canum Venaticorum systems, containing late-type main-sequence and
subgiant stars, are tidally-synchronized binaries that are among the
brightest far-ultraviolet and x-ray sources known. Such systems very
likely owe their enhanced chromospheric and coronal emission to intense
surface magnetic activity driven, in turn, by the interaction of rapid
rotation with strong subsurface convection. The RS CVn binaries are
valuable prototypes for investigating how magnetic -flux is generated
in stars, how the surface magnetic fields are expressed structurally,
and how the atmospheres of cool stars respond physically to intense
magnetic activity. Of special importance among the RS CVn binaries
are the moderateperiod (P ~ 20 day) subclass containing evolved giant
stars. Such systems represent the extreme of low surface gravities,
and consequently are critically important in any effort to understand
how chromospheric activity might be modified by gross stellar
parameters. The RS CVn giants also are pivotal in the question of
how the development of strong stellar winds among the later giants
might affect the expression of magnetic activity: Does the wind
directly smother the formation of high-temperature coronal magnetic
loops? Does the wind, instead, merely play a secondary role, for example
shortcircuiting magnetic activity by spinning down the star and thereby
quenching dynamo action? We propose to extend our previous studies of
the classical shortperiod RS CVn systems HR 1099 and UX Arietis, and
that of the long period Capella system, to an investigation of moderate
period (20 day) RS CVn binaries that contain evolved giant stars. We
intend to search for the as yet unseen secondary stars, by observing
the systems at critical orbital phases; for massive stellar winds,
by detecting Doppler shifts of far-ultraviolet emission features or
absorption components in Mg II h and k; and for opacity broadening of
the hightemperature lines caused by significant geometrical extension of
the emitting structures. Such studies are central to understanding the
exotic and energetic phenomena associated with chromospheric and coronal
magnetic activity among late-type stars in the solar neighborhood.

---------------------------------------------------------
Title: High dispersion far ultraviolet spectra of cool stars.
Authors: Stencel, R. E.; Linsky, J. L.; Ayres, T. R.; Jordan, C.;
Brown, A.; Engvold, O.
1982NASCP2238..259S Altcode: 1982auva.nasa..259S; 1982IUE82......259S; 1982NASCP2338..259S
Recent far ultraviolet high dispersion spectra of two cool supergiant
stars, Beta Dra (G2 Ib) and Alpha Ori (M2 Iab) are examined in the
context of current questions regarding stellar chromospheres, coronae
and mass loss. These stars show very different outer atmosphere
structure. Beta Dra has a geometrically thin transition region with
bright emission lines of 100,000 K plasma that are red-shifted,
indicating downflow in magnetic flux tubes. By contrast, Alpha Ori
has a cool extended chromosphere and circumstellar envelope with large
mass loss.

---------------------------------------------------------
Title: Capella revisited.
Authors: Ayres, T. R.
1982NASCP2238..251A Altcode: 1982auva.nasa..251A; 1982NASCP2338..251A; 1982IUE82......251A
The highlights of two studies of Capella, a spectroscopic binary,
undertaken during the third and fourth years of the IUE are given. The
first program consists of high dispersion spectroscopy at critical
phases of the Capella orbit. The second program is a two month
monitoring effort to search for ultraviolet modulations induced by
the rotation of magnetic active regions onto and off of the visible
hemisphere of the Capella secondary.

---------------------------------------------------------
Title: The cool Half of the H-R diagram in soft X-rays.
Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.;
Rosner, R.
1981ApJ...250..293A Altcode:
The results of an Einstein Observatory program to map the occurrence
of hot coronae (T greater than 1 million K) in the cool half of the
Hertzsprung-Russell diagram are reported. F-M dwarfs, and late F
through early K star giants characterized by 10,000 K chromospheric
and 20,000-200,000 K FUV emission lines were studied in one region,
while a second region study included red giants later than K2 III and
supergiants later than G5 Ib with weaker chromospheric emission and
no high temperature species. Program goals comprised determination of
the C IV division as seen in soft X-rays, and identification of stellar
parameters which distinguish strong from weak coronal X-ray sources. A
summary of target stars, X-ray fluxes, and UV emission profiles
is provided, and coronal emissions, comparisons of C IV and wind
boundaries, hybrid-spectrum supergiants, the energy balance of stellar
outer atmospheres, stellar rotation and coronae, and evolutionary
considerations are discussed, along with lines of future research.

---------------------------------------------------------
Title: Far-ultraviolet fluorenscence of carbon monoxide in the red
giant Arcturus.
Authors: Ayres, T. R.; Moos, H. W.; Linsky, J. L.
1981ApJ...248L.137A Altcode:
Evidence is presented that many of the weak features observed with
International Ultraviolet Explorer (IUE) in the far-ultraviolet
(1150-2000 A) spectrum of the archetype red giant Arcturus (K2 III) are
A-X fourth positive bands of carbon monoxide excited by chromospheric
emissions of O I, C I, and H I. The appearance of fluorescent CO bands
near the wavelength of commonly used indicators of high-temperature
(T greater than 20,000 K) plasma, such as C II at wavelength 1335 and
C IV at wavelength 1548, introduces a serious ambiguity in diagnosing
the presence of hot material in the outer atmospheres of the cool
giants by means of low-dispersion IUE spectra.

---------------------------------------------------------
Title: Relations among stellar X-ray emission observed from Einstein,
stellar rotation and bolometric luminosity.
Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. S.; Ayres,
T.; Linsky, J. L.
1981ApJ...248..279P Altcode:
The correlation between observed stellar X-ray luminosities, bolometric
luminosities, and projected rotational velocities for stars of various
spectral types and luminosity classes are determined. Early type
stars (O3 to A5) have X-ray luminosities independent of rotational
velocities, and correlating with bolometric luminosities. Late type
stars of spectral type G to M have luminosities well correlated to
equatorial rotational velocities, and are independent of luminosity
class. The dependence of late type stars is found to be equivalent
to a relation between the X-ray surface flux and the stellar angular
velocity. F stars are intermediate with X-ray luminosities higher
than would be predicted on the basis of the early type star relation,
although lower than expected from the late type velocity dependence. The
location of RS CVn stars as a class is also discussed, and it is found
that the heating of late type stellar coronas does not result from
direct conversion of ratational energy.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. IX. A survey of ultraviolet
emission from F-K dwarfs and giants with the IUE.
Authors: Ayres, T. R.; Marstad, N. C.; Linsky, J. L.
1981ApJ...247..545A Altcode:
Low-dispersion ultraviolet spectra (1150-2000 A) of a representative
sample of cool stars, including dwarfs and giants of spectral types
F-K, obtained with the IUE, are examined. The observation and the
absolute calibration procedures are described. Correlation diagrams
are constructed that compare chromospheric and transition-region
emission line strengths and broadband coronal soft X-ray fluxes. The
transition-region and coronal emission in the G-K dwarfs and G
giants is well correlated with the Mg II (wavelength 2800) doublet
emission strength, which is symptomatic of chromospheric energy
losses. The power-law slopes are steeper than unity, particularly for
soft X-rays. The implications of the correlations are discussed with
respect to the weakening or disappearance of transition regions and
hot coronae in the cool half of the red-giant branch and possible
chromospheric and coronal heating mechanisms. It is proposed that
the weakness of outer atmospheres in the red giants compared with the
yellow giants can be understood as a consequence of stellar evolution,
since it is possible that stars of slightly different spectral type
in the giant branch have very different main-sequence progenitors.

---------------------------------------------------------
Title: Fourier Transform Spectrometer observations of solar carbon
monoxide. I - The fundamental and first overtone bands in the
quiet sun
Authors: Ayres, T. R.; Testerman, L.
1981ApJ...245.1124A Altcode:
Measurements of the 2200/cm fundamental and 4300/cm first overtone
vibration-rotation band systems of solar carbon monoxide, were obtained
with the Fourier Transform Spectrometer of the McMath telescope at
Kitt Peak. The overtone measurements were taken at the east, north,
and west heliocentric limbs, and at disk center. Observations of the
strong fundamental bands were obtained at disk center and near the
north limb. The low core brightness temperatures of the strongest
fundamental carbon monoxide lines near the limb, reported previously
by Noyes (1972) and Hall (1974), are confirmed. The possibility that
thermal inhomogeneities might be responsible for the unusual behavior of
the fundamental carbon dioxide lines have been examined. The somewhat
discordant behavior of the fundamental lines at disk center compared
with the north limb seems to favor a limb shadowing effect. The
first overtone limb equivalent widths and the best-fit thermal and
microvelocity models indicate a solar carbon abundance of 0.004 (on
the scale with AH = 1) for an oxygen-to-carbon abundance
ratio of 2.

---------------------------------------------------------
Title: The stars that do not obey the Wilson-Bappu relationship.
Authors: Ayres, T. R.
1981Obs...101...38A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-resolution spectra of five late-type dwarfs and giants
obtained with the IUE satellite.
Authors: Ayres, T. R.; Basri, G. S.; Henry, R. C.; Landsman, W.;
Linsky, J. L.; Moos, H. W.; Stencel, R. E.
1981BAAS...13..546A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thermal Bifurcation in Solar Calcium Plages
Authors: Ayres, T. R.; Linsky, J. L.; Testerman, L.; Brault, J.
1981BAAS...13..915A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Excitation of the Chlorine I Line at 1351Å
Authors: Shine, R. A.; Woodgate, B. E.; Ayres, T. R.
1981BAAS...13Q.830S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Far-Ultraviolet Fluorescence of Carbon Monoxide in the Red
Giant Arcturus
Authors: Ayres, T. R.; Moos, H. W.; Linsky, J. L.
1981BAAS...13..515A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-Resolution Studies of Arcturus with IUE &amp;Einstein:
A Sensitive Search for High-Temperature Emission
Authors: Ayres, T. R.; Simon, T.; Linsky, J. L.
1981BAAS...13..811A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thermal bifurcation in the solar outer atmosphere
Authors: Ayres, T. R.
1981ApJ...244.1064A Altcode:
It is suggested that two distinct plasma thermal states are possible
in the solar outer atmosphere because of the bifurcated character
of the low-temperature cooling function at small optical depths. In
radiative equilibrium, the plasma is strongly cooled to temperatures
well below 4000 K by surface emission in the Delta V = 1 fundamental
vibration-rotation bands of CO. However, when significant mechanical
energy deposition is present in addition to the radiative heating
component, the only effective cooling channel available to stabilize
the plasma is optically thin emission in the recombination continuum
of H(-). Consequently, thermal equilibrium in a mechanically heated
atmospheric zone can be attained only for temperatures above the
critical temperature of 4900 K because H(-) is itself a net radiative
heating agent for temperatures cooler than the critical temperature.

---------------------------------------------------------
Title: High-Resolution Spectra of Five Late-Type Dwarfs and Giants
Obtained with the IUE Satellite
Authors: Ayres, T. R.; Basri, G. S.; Henry, R. C.; Landsman, W.;
Linsky, J. L.; Moos, H. W.; Stencel, R. E.
1981BAAS...13R.545A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Mg II h and k lines in a sample of dMe and dM stars.
Authors: Giampapa, M. S.; Pornmann, P. L.; Ayres, T. R.; Linsky,
J. L.; Worden, S. P.
1981NASCP2171..279G Altcode: 1981uviu.nasa..279G; 1981NASCP3171..279G; 1980IUE80......279G
Both Mg II h and k line fluxes are presented for a sample of 4 dMe and
3 dM stars obtained with the IUE satellite in the long wavelength,
low dispersion mode. The observed fluxes are converted to stellar
surface flux units and the importance of chromospheric non radiative
heating in this sample of M dwarf stars is intercompared. In addition,
the net chromospheric radiative losses due to the Ca II H and K lines in
those stars in the sample for which calibrated Ca II H and K line data
exist are compared. Active region filling factors which likely give
rise to the observed optical and ultraviolet chromospheric emission
are estimated. The implications of the results for homogeneous, single
component stellar model chromospheres analyses are discussed.

---------------------------------------------------------
Title: Timing Capella in the Ultraviolet
Authors: Ayres, Thomas R.
1981iue..prop..719A Altcode:
The long-period RS CVn-type spectroscopic binary system Capella (alpha
Aur A: G6 III and F9 III) presents a unique opportunity to study the
medium-term time evolution of chromospheric activity on a star that is
considerably more active than our Sun. (Note: The rapidly rotating Ftype
secondary is responsible for virtually all of the line emission from
the Capella system in high excitation species, such as C IV 1548 A and
Si IV 1394 A, and for most of the emission in chromospheric species,
such as H I L-alpha and Si II 1808 A.) In particular, a recent study
of Capella at critical orbital phases has revealed that the ultraviolet
output of the system is comparatively steady over timescales of ~hours,
but appears to decline somewhat over the three observing sessions, which
were separated 26^d apart. Because ultraviolet changes are apparent over
month-long timescales, but not over hour-long intervals, it would be
extremely valuable to explore the intermediate timescales, namely days,
of variability in the Capella secondary's chromospheric output. One
expects, for instance, to see modulations of the ultraviolet emission
lines in the Capella spectrum owing to the ~10^d rotational period of
the secondary. One might also expect to find longer term modulations
(~l month) owing to the birth, evolution and decay of large, bright
activity centers. In fact, the amplitude of the rotational modulation
provides an indication of how patchy the brightness distribution might
be. The patchiness of the chromospheric emission in turn provides an
indication of the size-scale spectrum of the emerging magnetic flux
elements that are likely ultimately responsible for the chromospheric
activity itself. Finally, a monitoring program extending from one
quadrature in the Capella orbit to the othe (54 degrees) would be
quite valuable in searching for and characterizing weak interstellar
components in the prominent chromospheric emission features, the O
I triplet near 1305 A and Si II 1808 A for example. I outline below
an observing program to obtain a timing record, at high dispersion,
of the ultraviolet output of an active chromosphere star the Capella
secondary - that is very different from the better studied, but more
mundane, solar example. Such a comparison should prove invaluable in
exploring the mechanisms responsible for magnetic flux generation
in stars, and the ultimate expression of the magnetic fields in
chromospheric activity.

---------------------------------------------------------
Title: Calibration of the SWP Echelle Mode for Chromospheric Emission
Sources
Authors: Ayres, Thomas R.
1981iue..prop..716A Altcode:
I propose to establish an absolute calibration for the SWP echelle mode
of IUE that would be useful for chromospheric emission-line stars. In
addition propose to study and characterize apparent vidicon artifacts
that appear in and near some of the prominent emission features of the
1150-2000 A region, particularly C IV 1548 A. The calibration would
be accomplished by a graded sequence of alternating echelle-mode and
low-dispersion exposures of the bright, chromospheric emission-line
source Capella (alpha Aurigae A). Such a calibration is straightforward,
and quite timely in view of the increasing number of long-exposure,
SWP echelle-mode observations of cool-star chromospheres that have
been attempted in the past, and are contemplated for the future. For
aesthetic reasons, the calibration should be obtained during a single,
low-noise shift. However, for expediency, many of the objectives could
be accomplished satisfactorily during a US #2 shift.

---------------------------------------------------------
Title: The IUE's eye view of cool-star outer atmospheres.
Authors: Ayres, T. R.
1981NASCP2171..237A Altcode: 1981uviu.nasa..237A; 1980IUE80......237A; 1981NASCP3171..237A
Three topics are discussed which together demonstrate the power of the
IUE to probe the occurrences of chromospheres and coronas in the cool
half of the HR diagram. These are: (1) the complementary low dispersion
and echelle observing modes; (2) Mg II h and k: chromospheric cooling
and width luminosity correlation; and (3) empirical correlations among
chromospheric, transition region, and coronal emission. The spectra of
alpha Centauri (G2 V + K1 V) and Capella (G6 III + F9 III) are compared
with that of the Sun and recent low dispersion surveys of cool star
emission in the 1150 A to 2000 A short wavelength region are summarized.

---------------------------------------------------------
Title: SWP Echelle Spectra of Chromospherically Active Dwarf Stars
Authors: Ayres, Thomas R.
1981iue..prop..715A Altcode:
High resolution spectra of the 1150-2000 A region are enormously
valuable for probing outer- atmosphere structure in cool stars. For
example, such data can be used to separate blends, identify individual
emission components in short-period binary systems, determine intensity
ratios in close multiplets, estimate reliable emission strengths of
lines superimposed on bright stellar continua, and test for the presence
or absence of stellar winds at 105 K temperatures. These possibilities
are not practical with IUE low-dispersion spectra. However, one must
pay a steep-price to obtain useable high-dispersion IUE spectra and
the additional dimension of diagnostic information, namely only
a handful of the brightest UV sources are accessible even with
shift-long exposures. We propose below an observing program to
obtain echelle spectra of chromospherically active dwarf stars in
the 1150-2000 A shortwavelength region. This program is intended
to explore a particular class of objects that heretofore have not
been observed at high dispersion with the SWP camera. Futhermore,
this program complements previous SWP echelle studies by our group
at the University of Colorado of quiet-chromosphere dwarf stars
(alpha Cen A, alpha Cen B), active giants (alpha Aur A, lambda And,
beta Dra), and the extreme case of the very active RS CVn-type system
HR 1099. As described below, highdispersion spectra of these targets
have provided a critical interpretive dimension that was lacking in
previous low-dispersion studies. However, several fundamental questions
have been raised in the course of our exploratory SWP work on what,
in practice, are two distinct classes of chromospheric stars: the quiet
dwarfs and the active giants. We feel that many of these questions can
be answered by bridging the interpretive gap with a careful study of
the active dwarfs. Our recent experience with shift-long SWP echelle
exposures of chromospheric emission stars has suggested that our
previous estimates of feasibility were too pessimistic, and that a
larger sample of chromospherically bright stars is in fact accessible
to IUE. Accordingly, we propose five candidate stars that we believe
can be observed successfully with deep SWP echelle-mode exposures. If
our proposal is accepted, we intend to collaborate with the Oxford
(U-K) cool-star group to attempt a joint 14^h exposure of one of the
brighter targets -- xi Boo A -- to provide an active-dwarf spectrum
that is well exposed even at the weaker diagnostic features of the
short-wavelength region.

---------------------------------------------------------
Title: Does H− truly cool the solar chromosphere?
Authors: Ayres, T. R.
1980SoPh...68..125A Altcode:
I examine the controversial problem of H− radiative
cooling in the solar chromosphere. I find, in agreement with Praderie
and Thomas, that H− is a substantial source of radiative
heating in the outer atmosphere, especially when departures from LTE
are important. The role of H− as a chromospheric heating
agent must be considered carefully before net radiative cooling rates
can be assessed from empirical chromospheric models, or calculations
of nonradiative heating, for example by acoustic waves, can be pursued
meaningfully.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. V. IUE observations of
Capella: the rotation-activity connection.
Authors: Ayres, T. R.; Linsky, J. L.
1980ApJ...241..279A Altcode:
UV spectra of Capella (G6 III + F9 III) obtained with the IUE are
analyzed. High-resolution emission-line profiles taken near the
elongation at phase 78 days suggest that virtually all of the emission
in transition-region lines and most of the emission in chromospheric
lines comes from the late-F secondary of the system. It is suggested
that the origin of the extraordinary activity levels on these otherwise
very similar stars can be traced to the one property that is obviously
different, i.e., rotation. The Capella primary is a normal sharp-line
slow rotating giant, whereas the secondary has broader lines and is
a rapid rotator for a late-type giant.

---------------------------------------------------------
Title: The Cool Half of the HR Diagram in Soft X-Rays
Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.;
Rosner, R.
1980BAAS...12..870A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Dichotomies
Authors: Ayres, T.
1980SAOSR.389...65A Altcode: 1980csss....1...65A
No abstract at ADS

---------------------------------------------------------
Title: Outer atmospheres of cool stars. III. IUE spectra and
transition region models for alf CEN A and B.
Authors: Ayres, T. R.; Linsky, J. L.
1980ApJ...235...76A Altcode:
We describe lUE ultraviolet spectra of two nearby dwarf stars, α
Centauri A (G2 V) and B (K1 V). These data include high-resolution
profiles of the Mg II h and k features and lower- resolution integrated
fluxes of lines from the following species: H I, C I-IV, N V, O I, A1
II, Si II-IV, and Fe II. We find that surface fluxes in chromospheric
and transition-region lines of α Cen A and B are nearly identical
to those of the quiet Sun. In addition, the measured stellar line
fluxes are in good agreement with predictions of a transition-region
scaling law based on conductive heating and pressures estimated from
chromospheric models of α Cen A and B. While this agreement does
not verify the conductive heating hypothesis, it does suggest that
the basic physical processes that control the structure and energy
balance in the chromospheres and transition regions of α Cen A and
B and the Sun are, on a gross scale, very likely the same.

---------------------------------------------------------
Title: Effects of Flux Tubes on Conventional Chromospheric Diagnostics
Authors: Ayres, T. R.
1980LNP...114..299A Altcode: 1980sttu.coll..299A; 1980IAUCo..51..299A
No abstract at ADS

---------------------------------------------------------
Title: A search for coronal soft X-ray emission from cool stars with
HEAO 1.
Authors: Ayres, T. R.; Linsky, J. L.; Garmire, G. P.; Cordova, F.
1979ApJ...232L.117A Altcode:
A search of the HEAO 1 A-2 experiment all-sky survey for coronal soft
X-ray emission from a sample of active chromosphere G-M stars including
six dwarfs, eight giants, four supergiants, and 10 dMe flare stars is
summarized. Point sources were detected near the positions of several
of the stars considered. However, of these, only the flare stars BY
Draconis (dM0e) and AD Leonis (dM3.5e) appear to be likely candidates
for the detected X-rays.

---------------------------------------------------------
Title: Discovery of X-rays from the 40 Eridani system.
Authors: Cash, W.; Charles, P.; Bowyer, S.; Walter, F.; Ayres, T. R.;
Linsky, J. L.
1979ApJ...231L.137C Altcode:
The detection of a point source of soft X-rays (H0405-08) consistent
with the position of the nearby triple star system 40 Eridani is
reported. The source, which has a temperature near 10 million K,
has a flux of 3 x 10 to the -11th erg/sqcm-sec at earth, implying a
luminosity of 9(+ or -3) x 10 to the 28th erg/s at the distance of 40
Eridani. The likely source of the bulk of the X-rays is considered,
including the K1 dwarf, the DA white dwarf, the dwarf M4 flare star,
or accretion onto the white dwarf.

---------------------------------------------------------
Title: Chromospheric scaling laws, width-luminosity correlations,
and the Wilson-Bappu effect.
Authors: Ayres, T. R.
1979ApJ...228..509A Altcode:
Simple scaling laws for the thickness and mean electron density of
stellar chromospheres as functions of surface gravity and chromospheric
heating are proposed. These scaling laws are shown to be a consequence
of hydrostatic equilibrium, the influence of gas ionization on plasma
cooling functions, and the assumption that chromospheric heating is
relatively constant with height. It is argued that line width-luminosity
correlations similar to those observed in the Ca II K and Mg II k
resonance lines are implied by the chromospheric scaling laws if the
outer edges of the K and k emission cores are formed in the Lorentzian
wings of the absorption profile. The results are compared with the
Wilson-Bappu effect, empirical width-luminosity correlations for Ca
II K1 minimum features, and solar-plage profiles of the Ca II K and
Mg II k resonance lines.

---------------------------------------------------------
Title: Capella: 1/2 of an RS CVn?
Authors: Ayres, T. R.; Linsky, J. L.
1979BAAS...11..472A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The center-to-limb behavior of Ca i λ6573 and [Ca ii] λ7324
Authors: Ayres, T. R.; Testerman, L.
1978SoPh...60...19A Altcode: 1978SoPh...60...19.
Center-to-limb measurements of the Ca I λ6573 intercombination line and
the Ca II λ7324 forbidden line are compared with synthetic profiles
based on a simple representation of the non-LTE Ca-Ca+
ionization equilibrium. The effects of photoionizations from low
lying excited states of neutral calcium are found to reduce the
sensitivity of the λ6573 center-to-limb behavior as a thermal structure
diagnostic. The synthetic center-to-limb behavior is also sensitive to
uncertainties in the nonthermal broadening. Nevertheless, the measured
center-to-limb behavior of λ6573 favors a `cool' photospheric model
similar to the Vernazza, Avrett, and Loeser model M over hotter models
based on the Ca II K wings. The non-LTE calcium abundance obtained
from the disk center equivalent widths of λ6573 and λ7324 using
the best fit model is ACa≅2.1±0.2 × 10-6
(by number relative to hydrogen). Applications of these lines as
diagnostics of the Ca-Ca+ ionization equilibrium in other
stars are briefly discussed.

---------------------------------------------------------
Title: Upper limits on extreme ultraviolet radiation from nearby
main sequence and subgiant stars.
Authors: Ayres, T. R.; Linsky, J. L.; Margon, B.; Bowyer, S.
1978A&A....70..431A Altcode:
Flux upper limits for 44-800 A radiation were measured in a sample
of nearby main sequence stars and one subgiant star with the aid of
the Apollo-Soyuz grazing incidence telescope. Comparisons of emission
measure upper limits with three different methods for predicting coronal
properties cannot yet determine which, if any, are valid. Data for
Alpha Centauri A and B are consistent with recent HEAO-1 soft X-ray
measurements which suggest that the surface flux of coronal emission
from the Alpha Cen system is comparable to that of the 'normal' sun.

---------------------------------------------------------
Title: Center-to-limb behavior of first-overtone vibration-rotation
transitions of solar carbon monoxide.
Authors: Ayres, T. R.
1978ApJ...225..665A Altcode:
High-spectral-resolution measurements of the center-to-limb behavior
of weak transitions in the carbon monoxide first-overtone (A V = 2)
vibration-rotation bands (w 4300 cm -`) are compared with synthetic
line widths and equivalent widths for a range of single-component and
multicomponent models of the solar photosphere. The single-component
thermal structure in best quantitative agreement with the observed
properties of the solar CO spectrum is similar to the Vernazza, Avrett,
and Loeser model M. Multicomponent models consisting of Gaussian-
distributed temperature perturbations around the best-fit model do not
significantly affect the computed center-to-limb behavior of CO lines or
the solar carbon abundance derived from measured disk-center equivalent
widths. The equivalent width ratios of low- and high-excitation lines
within a given vibration-rotation band are found to be inconsistent
with "hot" upperphotosphere models, such as the Linsky and Ayres and
Holweger and semiempirical single-component models, as well as with the
two-stream thermal structure proposed by Tsuji. Excitation ratios and
center-to-limb behavior of CO lines require a solar carbon abundance
near 3 x 10- for an assumed oxygen abundance of 7 x 10- . This value
is consistent with carbon abundances obtained by Tsuji (CO) and Mount
and Linsky (CN), but is much smaller than the revised solar carbon
abundance recommended recently by Lambert. Subject headings: molecular
processes - Sun: abundances - Sun: atmosphere - Sun: spectra

---------------------------------------------------------
Title: IUE observations of cool stars : alf Aur, HR 1099, lam and
EPS Eri.
Authors: Linsky, J. L.; Ayres, T. R.; Basri, G. S.; Morrison, N. D.;
Boggess, A.; Schiffer, F. H., III; Holm, A.; Cassatella, A.; Heck,
A.; Macchetto, F.; Stickland, D.; Wilson, R.; Blanco, C.; Dupree,
A. K.; Jordan, C.; Wing, R. F.
1978Natur.275..389L Altcode:
Initial IUE observations of four cool stars are reported. Observed
fluxes and surface fluxes are given for several UV emission lines in
the spectral range 1175-2000 A, obtained at low and high dispersion with
the short-wavelength spectrograph and camera. These lines are formed in
the outer atmospheres of these stars, in regions presumably analogous to
the solar chromosphere and transition region. The surface fluxes in the
lines increase along the sequence: quiet sun, Epsilon Eri, Lambda And,
Alpha Aur, and HR1099. The 2.8-d RS CVn-type binary HR1099, observed on
1 March 1978 near the end of a major flaring episode, has line surface
fluxes roughly 100 times that of the quiet sun, similar to those seen in
solar flares. Line profiles and flux ratios in multiplets for Capella
are presented, and comments given on the opacity of the lines and on
a tendency of line width to increase with temperature of formation.

---------------------------------------------------------
Title: Evolution of the alpha Centauri system.
Authors: Flannery, B. P.; Ayres, T. R.
1978ApJ...221..175F Altcode:
Available astrometric and photometric data are examined and in some
cases reanalyzed in order to derive accurate estimates for the stellar
masses, luminosities, temperatures, and chemical compositions of the A
and B components of Alpha Centauri. Theoretical evolutionary sequences
for the A and B components are computed for two values of metallicity,
Z = 0.02 and 0.04; a reference solar model with Z = 0.02 is also
calculated. The observed abundances are partially reanalyzed on the
basis of the equivalent measurements of French and Powell (1971), which
provide a consistency check on the evolutionary models. The results
indicate that: (1) the system is partially evolved since component A is
30% brighter with respect to B than would be expected for an unevolved
system; (2) the system is somewhat metal-rich with respect to the sun;
(3) the age of Alpha Cen is 6 billion years and the helium abundance
is essentially solar for an evolutionary sequence with twice the solar
metals; and (4) the components of Alpha Cen are also similar to the
sun in terms of galactic orbits. The difference in Z between the sun
and Alpha Cen is shown to be consistent with the idea that there is a
substantial dispersion in the metallicity of the interstellar medium
at any one time.

---------------------------------------------------------
Title: IUE Observations of the RS CVn Stars HR 1099 and λ And
Authors: Ayres, T. R.; Linsky, J. L.; Morrison, N. D.
1978BAAS...10R.444A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A comparison of synthetic and measured solar continuum
intensities and limb darkening coefficients.
Authors: Ayres, T. R.
1978SoPh...57...19A Altcode:
Absolute continuum intensities and wavelength-dependent low-order
polynomial fits to optical and infrared continuum limb darkening
provide useful discriminants among single-component models of the solar
photosphere. The thermal structure in best quantitative agreement with
the recent center-limb measurements by Pierce and Slaughter (1977)
and by Pierce et. al. (1977) is the semi-empirical model by Vernazza,
Avrett and Loeser (VAL). However, the VAL model M temperatures must
be scaled upward by a factor of 1.015 ±0.005 to be consistent with
the Labs and Neckel absolute calibration of continuum high points in
the optical region 0.40-0.65 μm.

---------------------------------------------------------
Title: Stellar model chromospheres. VI. Empirical estimates of the
chromospheric radiative losses of late-type stars.
Authors: Linsky, J. L.; Ayres, T. R.
1978ApJ...220..619L Altcode:
A method is developed for estimating the nonradiative heating of
stellar chromospheres by measuring the net radiative losses in strong
Fraunhofer line cores. This method is applied to observations of the Mg
II resonance lines in a sample of 32 stars including the sun. At most
a small dependence of chromospheric nonradiative heating on stellar
surface gravity is found, which is contrary to the large effect
predicted by recent calculations based on acoustic-heating theories.

---------------------------------------------------------
Title: High Resolution IUE Observations of α AUR: Is the Outer
Atmosphere of Capella Similar to a Sunspot?
Authors: Ayres, T. R.; Linsky, J. L.
1978BAAS...10Q.444A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Search for Solar Global Oscillations in the CA Ii K-Line
Authors: Beckers, Jacques M.; Ayres, Thomas R.
1977ApJ...217L..69B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evolution of the α Centauri System.
Authors: Flannery, B. P.; Ayres, T. R.
1977BAAS....9..638F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Nonthermal broadening in the solar photosphere derived from
widths of weak absorption features in the Ca II H and K wings.
Authors: Ayres, T. R.
1977ApJ...214..905A Altcode:
The depth dependence of nonthermal broadening in the solar photosphere
is estimated using the widths of weak absorption features in spatially
averaged profiles of the Ca II H and K wings. The inferred vertical
component of the photospheric total-motion field does not show a
significant depth dependence in constrast to previously proposed
models which have sharply inward increasing velocities in the deep
photosphere. The mean Gaussian nonthermal broadening obtained is 1.6 +
or - 0.1 km/s (one-half full e-folding width). In addition, the inferred
nonthermal broadening is used to estimate thermal widths, and therefore
also atomic weights, for several weak features in the H and K wings
which are unidentified or have uncertain identifications. It is found
that the majority of these are consistent with rare-earth absorption.

---------------------------------------------------------
Title: The surface gravity and mass of Arcturus.
Authors: Ayres, T. R.; Johnson, H. R.
1977ApJ...214..410A Altcode:
The surface gravity of the K giant Arcturus is estimated by comparing
synthetic spectra based on model atmospheres with measured wing
shapes of the Ca I and Ca II resonance lines calibrated by absolute
photometry. The result, log g of approximately 1.6 cm/sec per sec, is
consistent with previous spectroscopic estimates based on weak-line
ionization ratios, with the exception of a recent determination by
Maeckle et al. (1975). A stellar mass of 1.1(+1.7, -0.7) solar masses
is obtained for a radius of 27 solar radii. This estimate suggests
that Arcturus has not suffered substantial mass loss during its
post-main-sequence evolution on the 'ascending red-giant branch'.

---------------------------------------------------------
Title: A reexamination of solar upper photosphere models, the calcium
abundance, and empirical damping parameters.
Authors: Ayres, T. R.
1977ApJ...213..296A Altcode:
A general iterative method is described for constructing thermal models
of the solar photosphere consistent with observed strong and weak
lines of Ca I and Ca II. Calibrations of the solar calcium abundance
and the van der Waals parameter for important Ca I and Ca II lines are
obtained using plane-parallel largely LTE model atmospheres, and these
thermal models are modified for better fits to the measured Ca II H and
K inner wing shapes. Possible sources of error in this semiempirical
approach are evaluated. The derived hydrogen van der Waals broadening
is compared with theoretical estimates of that broadening as well as
with experimental measurements of the helium broadening

---------------------------------------------------------
Title: Stellar model chromospheres. V. Alpha Centauri A (G2 V)
and Alpha Centauri B (K1 V).
Authors: Ayres, T. R.; Linsky, J. L.; Rodgers, A. W.; Kurucz, R. L.
1976ApJ...210..199A Altcode:
Models for the upper photospheres and lower chromospheres of Alpha
Centauri A and B are derived from high-dispersion spectrograms of the
Ca II K-line emission cores and damping wings. Effective temperatures,
surface gravities, and ages consistent with the measured broadband
colors, metallicities, and absolute magnitudes are estimated for the
two stars. The spectrograms are calibrated by fitting the far-wing K
profiles with synthetic fluxes based on radiative-equilibrium models,
and the model atmospheres are obtained through a partial-redistribution
analysis of the line cores and damping wings. These models are compared
with those previously proposed for Procyon, Arcturus, and the sun. Many
features in all the models are found to be quite similar, and some
evidence suggests that Alpha Cen A may be significantly older and
more evolved than the sun, even though both stars exhibit similar
chromospheric properties.

---------------------------------------------------------
Title: The MG II h and k lines. II. Comparison with synthesized
profiles and Ca II K.
Authors: Ayres, T. R.; Linsky, J. L.
1976ApJ...205..874A Altcode:
Measured high-dispersion center and limb profiles of the solar Mg
II h and k resonance lines are compared with synthetic spectra
computed with a partial-redistribution formalism and based on
several upper-photosphere and lower-chromosphere temperature
distributions. Profiles of the analogously formed Ca II K resonance
line are also synthesized for the same atmospheric models. The
spectrum-synthesis approach is outlined, and the collisional and fixed
radiative rates appropriate to the adopted model atoms and solar
atmosphere are discussed. It is found that the HSRA and VAL models
predict systematically lower intensities in the h, k, and K inner
wings than observed and that models with a somewhat higher minimum
temperature (about 4450 K) can reproduce the measured inner wings and
limb darkening. A 'Ca II' solar model with a minimum temperature of
4450 K is proposed as an alternative to the class of models based on
continuum observations.

---------------------------------------------------------
Title: The Mass of Arcturus
Authors: Ayres, T. R.; Johnson, H. R.
1976BAAS....8..303A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Semiempirical upper photosphere models: the sun (G2 V) and
Procyon (F5 IV-V).
Authors: Ayres, T. R.
1975ApJ...201..799A Altcode:
A description is presented of an approach for developing a model of
the average upper photosphere temperature structure of a late-type
star. The approach makes use of the frequency dependence of the damping
wing opacity of a strong resonance line. Difficulties related to a
dependence on uncertain constant and parameter values are to be overcome
with the aid of a 'calibration' relative to a solar photosphere model
obtained by an independent method.

---------------------------------------------------------
Title: Stellar model chromospheres. IV. The formation of the Hepsilon
feature in the sun (G2 V) and Arcturus (K2 III).
Authors: Ayres, T. R.; Linsky, J. L.
1975ApJ...201..212A Altcode:
The formation of the Balmer-series member H-epsilon in the near-red
wing of the Ca II H line is discussed for two cases: the sun
(H-epsilon absorption profile) and Arcturus (H-epsilon emission
profile). It is shown that although the H-epsilon source functions
in both stars are dominated by the Balmer-continuum radiation field
through photoionizations, the line-formation problems in the two stars
are quantitatively different, owing to a substantial difference in the
relative importance of the stellar chromosphere temperature inversion
as compared with the stellar photosphere.

---------------------------------------------------------
Title: Stellar model chromospheres. III. Arcturus (K2 III).
Authors: Ayres, T. R.; Linsky, J. L.
1975ApJ...200..660A Altcode:
Models are constructed for the upper photosphere and chromosphere of
Arcturus based on the H, K, and IR triplet lines of Ca II and the h
and k lines of Mg II. The chromosphere model is derived from complete
redistribution solutions for a five-level Ca II ion and a two-level
Mg II ion. A photospheric model is derived from the Ca II wings using
first the 'traditional' complete-redistribution limit and then the
more realistic partial-redistribution approximation. The temperature
and mass column densities for the temperature-minimum region and
the chromosphere-transition region boundary are computed, and the
pressure in the transition region and corona are estimated. It is
found that the ratio of minimum temperature to effective temperature
is approximately 0.77 for Arcturus, Procyon, and the sun, and that
mass tends to increase at the temperature minimum with decreasing
gravity. The pressure is found to be about 1 percent of the solar
value, and the surface brightness of the Arcturus transition region and
coronal spectrum is estimated to be much less than for the sun. The
partial-redistribution calculation for the Ca II K line indicates
that the emission width is at least partially determined by damping
rather than Doppler broadening, suggesting a reexamination of previous
explanations for the Wilson-Bappu effect.

---------------------------------------------------------
Title: A non-LTE analysis of the CN 3883 Å band head in the upper
photosphere of Arcturus.
Authors: Mount, G. H.; Ayres, T. R.; Linsky, J. L.
1975ApJ...200..383M Altcode:
A detailed non-LTE study of the CN(0,0) 3883 A band-head spectrum of
Arcturus (K2 iii) provides an accurate determination of the carbon,
nitrogen, and oxygen abundances in Arcturus. Non-LTE effects are
significant, and we find that the Ayres-Linsky model provides an
adequate fit to the observations for [C,N]* = 13[C,N]0 and [O]* =
0.60[0]o, or for [C,N,O]* = 16[C,N,O]0, but the latter abundances are
unlikely. The upper photospheric microturbulence is found to be 2.5
+ . Subject headings: abundances, stellar - atmospheres, stellar -
late-type stars - molecules - stars, individual (alpha Boo)

---------------------------------------------------------
Title: The MG II H and K lines. II. Comparison with synthesized
profiles and CA II K
Authors: Ayres, T. R.; Linsky, J. L.
1975STIN...7722038A Altcode:
The Mg II h and k resonance line data and profiles of the Ca II K
line are compared with synthetic profiles computed using a partial
redistribution formalism and several single-component solar upper
photosphere and lower chromosphere models. It is found that second
models predict systematically lower intensities in the h, k, and K inner
wings than are observed, but that models with a somewhat larger minimum
temperature (T(min) about 4450 K) can reproduce the measured inner
wing intensities and limb darkening of these resonance lines. A 'hot'
T(min) solar model, which is reasonably consistent with the empirical
emission cores and wing intensities of the Ca II and Mg II resonance
lines is proposed to serve as an alternative to the class of models,
such as the HSRA and VAL, based on continuum observations.

---------------------------------------------------------
Title: Resonance line transfer with partial redistribution. III. Mg
II resonance lines in solar-type stars.
Authors: Milkey, R. W.; Ayres, T. R.; Shine, R. A.
1975ApJ...197..143M Altcode:
We discuss the gravity dependence of the Mg II resonance lines
calculated with inclusion of effects of partial redistribution in
frequency. Using chromospheric models scaled from a solar model, we
demonstrate the increased decoupling of the radiation temperature of
the k1 feature from the minimum electron temperature in lower-gravity
models. The limb darkening of the k-line in the main-sequence model
is also discussed.

---------------------------------------------------------
Title: Stellar Upper Photosphere Models Based on the Ca II
K-wing. II. The Coherent Scattering Approximation
Authors: Ayres, T. R.; Linsky, J. L.; Shine, R. A.
1975BAAS....7..359A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A possible width-luminosity correlation of the Ca II
K1 and Mg II k1 features.
Authors: Ayres, T. R.; Linsky, J. L.; Shine, R. A.
1975ApJ...195L.121A Altcode:
Existing high resolution stellar profiles of the Ca II and Mg II
resonance lines suggest a possible width-luminosity correlation of the
K1 minimum features. It is shown that such a correlation can be simply
understood if the continuum optical depth of the stellar temperature
minimum is relatively independent of surface gravity as suggested by
three stars studied in detail.

---------------------------------------------------------
Title: The lower chromospheres and upper chromospheres of late-type
stars
Authors: Ayres, Thomas Russell Tom
1975PhDT........99A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Lower Chromospheres and Upper Photospheres of Late-Type
Stars.
Authors: Ayres, T. R.
1975PhDT.........3A Altcode:
High dispersion, well calibrated profiles of Ca 2 K, Mg 2 h and k,
and H are interpreted in five late-type stars, including the sun,
by constructing plane-parallel, hydrostatic atmospheric models and
synthesizing spectra using a partial redistribution formalism. In
the empirical data there is a strong correlation between the widths
of the K1 inner wing minimum features and luminosity,
analogous to the Wilson-Bappu effect obeyed by the Ca 2 and Mg 2
emission half-widths. It is shown qualitatively that this behavior of
the K1 features would be expected if the continuum optical
depth of the stellar temperature minimum is relatively independent of
surface gravity, and support this conjecture by detailed modeling of
the temperature minimum regions of the five program stars.

---------------------------------------------------------
Title: Stellar Model Chromospheres. H. Procyon (F5 Iv/v)
Authors: Ayres, Thomas R.; Linsky, Jeffrey L.; Shine, Richard A.
1974ApJ...192...93A Altcode: 1974ApJ...192...95A
No abstract at ADS

---------------------------------------------------------
Title: The Formation of the Hɛ Emission Feature in
Late-Type Stars.
Authors: Ayres, T. R.; Linsky, J. L.
1974BAAS....6..226A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Model for the Chromosphere of Arcturus.
Authors: Ayres, T. R.; Linsky, J. L.
1973BAAS....5Q.454A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Photospheric Models Based on the Wings of the Ca II Lines.
Authors: Shine, R. A.; Ayres, T. R.
1973BAAS....5..453S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A model for the chromosphere of Arcturus.
Authors: Ayres, T. R.; Linsky, J. L.
1973BAAS....5..336A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A simple explanation of the Wilson-Bappu effect.
Authors: Ayres, T. R.; Linsky, J. L.; Shine, R. A.; Chipman, E.
1973BAAS....5..364A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Model for the Chromosphere of Arcturus.
Authors: Ayres, T. R.; Linsky, J. L.
1973BAAS....5R.336A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar model chromospheres. I. On the temperature minima of
F,G, and K stars.
Authors: Linsky, J. L.; Ayres, T.
1973ApJ...180..473L Altcode:
Brightness temperatures are deduced for the Hiv and Kiv features of
the Ca ii resonance lines in Procyon (F5 IV-V), Arcturus (K2 IlIp),
and the Sun (G2 V). The brightness temperatures of Procyon and the
Sun are in the same ratio as their effective temperatures, suggesting
a simple scaling law for the temperature minima of F and early G
stars. Arcturus departs from this law in a way that can be explained
by CO line blanketing. Subject headings: Ca ii emission - chromosphere,
solar chromospheres, stellar - late-type stars

---------------------------------------------------------
Title: Equator-Pole Temperature Difference and the Solar Oblateness
Authors: Noyes, R. W.; Ayres, T. R.; Hall, D. N. B.
1973SoPh...28..343N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Discovery of upper photospheric temperature inversions or
chromospheres in early A stars.
Authors: Linsky, J. L.; Shine, R. A.; Ayres, T. R.; Praderie, F.
1973BAAS....5....3L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Discovery of Chromospheres in Early A Stars.
Authors: Linsky, J. L.; Shine, R. A.; Ayres, T. R.; Praderie, F.
1973BAAS....5R...3L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Model for the Chromosphere of Procyon.
Authors: Linsky, J. L.; Ayres, T. R.
1972BAAS....4..334L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Identification of ^{13}C^{16}O in the Infrared Sunspot
Spectrum and the Determination of the Solar ^{12}C/^{13}C Abundance
Ratio
Authors: Hall, Donald N. B.; Noyes, Robert W.; Ayres, Thomas R.
1972ApJ...171..615H Altcode:
The presence of the first-overtone vibration-rotation bands of 13C16O
in the infrared sunspot spectrum has been established on the basis of
wavenumber and relative intensity consistency of 30 weak lines. Nine
particularly clean lines have been used to obtain a solar 12C/13C
abundance ratio of 90 with a probable error of 15 percent.