Author name code: giampapa
ADS astronomy entries on 2022-09-14
author:"Giampapa, Mark"
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Title: Final Report for SAG 21: The Effect of Stellar Contamination
on Space-based Transmission Spectroscopy
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.;
Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas;
Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah
L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier,
Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg;
Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder,
Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh;
Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato,
Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson,
Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven;
Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.;
Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert,
Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik,
Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
Bibcode: 2022arXiv220109905R
Altcode:
Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program
Analysis Group (ExoPAG) was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method for
studying exoplanetary atmospheres by measuring the wavelength-dependent
radius of a planet as it transits its star. Transmission spectroscopy
relies on a precise understanding of the spectrum of the star being
occulted. However, stars are not homogeneous, constant light sources
but have temporally evolving photospheres and chromospheres with
inhomogeneities like spots, faculae, and plages. This SAG has brought
together an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar astrophysics,
planetary science, and exoplanetary atmosphere research communities,
to study the current needs that can be addressed in this context to
make the most of transit studies from current NASA facilities like
HST and JWST. The analysis produced 14 findings, which fall into
three Science Themes encompassing (1) how the Sun is used as our best
laboratory to calibrate our understanding of stellar heterogeneities
("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
extend our knowledge of heterogeneities ("Surface Heterogeneities of
Other Stars") and (3) how to incorporate information gathered for the
Sun and other stars into transit studies ("Mapping Stellar Knowledge
to Transit Studies").
Title: The GAPS programme at TNG. XXII. The GIARPS view of the
extended helium atmosphere of HD 189733 b accounting for stellar
activity
Authors: Guilluy, G.; Andretta, V.; Borsa, F.; Giacobbe, P.; Sozzetti,
A.; Covino, E.; Bourrier, V.; Fossati, L.; Bonomo, A. S.; Esposito,
M.; Giampapa, M. S.; Harutyunyan, A.; Rainer, M.; Brogi, M.; Bruno,
G.; Claudi, R.; Frustagli, G.; Lanza, A. F.; Mancini, L.; Pino, L.;
Poretti, E.; Scandariato, G.; Affer, L.; Baffa, C.; Baruffolo, A.;
Benatti, S.; Biazzo, K.; Bignamini, A.; Boschin, W.; Carleo, I.;
Cecconi, M.; Cosentino, R.; Damasso, M.; Desidera, S.; Falcini,
G.; Martinez Fiorenzano, A. F.; Ghedina, A.; González-Álvarez,
E.; Guerra, J.; Hernandez, N.; Leto, G.; Maggio, A.; Malavolta, L.;
Maldonado, J.; Micela, G.; Molinari, E.; Nascimbeni, V.; Pagano, I.;
Pedani, M.; Piotto, G.; Reiners, A.
Bibcode: 2020A&A...639A..49G
Altcode: 2020arXiv200505676G
Context. Exoplanets orbiting very close to their parent star are
strongly irradiated. This can lead the upper atmospheric layers to
expand and evaporate into space. The metastable helium (He I) triplet
at 1083.3 nm has recently been shown to be a powerful diagnostic
to probe extended and escaping exoplanetary atmospheres.
Aims: We perform high-resolution transmission spectroscopy of the
transiting hot Jupiter HD 189733 b with the GIARPS (GIANO-B + HARPS-N)
observing mode of the Telescopio Nazionale Galileo, taking advantage
of the simultaneous optical+near infrared spectral coverage to detect
He I in the planet's extended atmosphere and to gauge the impact of
stellar magnetic activity on the planetary absorption signal.
Methods: Observations were performed during five transit events of HD
189733 b. By comparison of the in-transit and out-of-transit GIANO-B
observations, we computed high-resolution transmission spectra. We
then used them to perform equivalent width measurements and carry
out light-curves analyses in order to consistently gauge the excess
in-transit absorption in correspondence with the He I triplet.
Results: We spectrally resolve the He I triplet and detect an absorption
signal during all five transits. The mean in-transit absorption depth
amounts to 0.75 ± 0.03% (25σ) in the core of the strongest helium
triplet component. We detect night-to-night variations in the He I
absorption signal likely due to the transit events occurring in the
presence of stellar surface inhomogeneities. We evaluate the impact of
stellar-activity pseudo-signals on the true planetary absorption using
a comparative analysis of the He I 1083.3 nm (in the near-infrared)
and the Hα (in the visible) lines. Using a 3D atmospheric code, we
interpret the time series of the He I absorption lines in the three
nights not affected by stellar contamination, which exhibit a mean
in-transit absorption depth of 0.77 ± 0.04% (19σ) in full agreement
with the one derived from the full dataset. In agreement with previous
results, our simulations suggest that the helium layers only fill part
of the Roche lobe. Observations can be explained with a thermosphere
heated to ~12 000 K, expanding up to ~1.2 planetary radii, and losing ~1
g s-1 of metastable helium.
Conclusions: Our results
reinforce the importance of simultaneous optical plus near infrared
monitoring when performing high-resolution transmission spectroscopy of
the extended and escaping atmospheres of hot planets in the presence
of stellar activity.
Based on observations made with the Italian
Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo
Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the
Observatorio del Roque de los Muchachos (La Palma, Canary Islands,
Spain).
Title: Towards Mitigating the Impact of Stellar Photospheric
Heterogeneity on Precise Exoplanet Transmission Spectra
Authors: Rackham, Benjamin; Apai, Dániel; Giampapa, Mark; Espinoza,
Néstor; Madhusudhan, Nikku; Zhou, Yifan
Bibcode: 2019EPSC...13..971R
Altcode:
Exoplanet transmission spectroscopy, the study of spectroscopic transit
depths, provides our best opportunity to characterize the atmospheres of
temperate, Earth-sized exoplanets in the next two decades. However, this
technique is subject to spurious signals introduced by the photospheric
heterogeneity of exoplanet host stars, which may mimic or mask real
exoplanetary signals. As the late-type hosts that provide the most
favorable planet-to-star radius ratios for studying small exoplanets
also tend to be more photospherically heterogeneous, our ability
to disentangle stellar and planetary signals represents a possible
limitation for precise transmission spectroscopy. Here we present
our recent work to understand the scale of TLS signals with forward
models and to characterize the photospheres of important exoplanet
host stars through (1) transit crossings of magnetic active regions,
(2) joint retrievals of stellar and exoplanetary properties from
transmission spectra, and (3) stellar photospheric decomposition with
moderate-resolution visual and near-infrared spectra. Constraining the
photospheric heterogeneity of exciting exoplanet host stars with these
approaches will be key to realizing the opportunity to characterize
Earth-sized exoplanets via transits.
Title: Constraining Stellar Photospheres as an Essential Step for
Transmission Spectroscopy of Small Exoplanets
Authors: Rackham, Benjamin; Pinhas, Arazi; Apai, Dániel; Haywood,
Raphaëlle; Cegla, Heather; Espinoza, Néstor; Teske, Johanna;
Gully-Santiago, Michael; Rau, Gioia; Morris, Brett M.; Angerhausen,
Daniel; Barclay, Thomas; Carone, Ludmila; Cauley, P. Wilson; de Wit,
Julien; Domagal-Goldman, Shawn; Dong, Chuanfei; Dragomir, Diana;
Giampapa, Mark S.; Hasegawa, Yasuhiro; Hinkel, Natalie R.; Hu, Renyu;
Jordán, Andrés; Kitiashvili, Irina; Kreidberg, Laura; Lisse,
Carey; Llama, Joe; López-Morales, Mercedes; Mennesson, Bertrand;
Molaverdikhani, Karan; Osip, David J.; Quintana, Elisa V.
Bibcode: 2019BAAS...51c.328R
Altcode: 2019astro2020T.328R; 2019arXiv190306152R
Transmission spectra probe the atmospheres of transiting exoplanets, but
these observations are also subject to signals introduced by magnetic
active regions on host stars. We outline scientific opportunities in
the next decade for providing useful constraints on stellar photospheres
for the purposes of exoplanet transmission spectroscopy.
Title: The Transit Light Source Effect. II. The Impact of Stellar
Heterogeneity on Transmission Spectra of Planets Orbiting Broadly
Sun-like Stars
Authors: Rackham, Benjamin V.; Apai, Dániel; Giampapa, Mark S.
Bibcode: 2019AJ....157...96R
Altcode: 2018arXiv181206184R
Transmission spectra probe exoplanetary atmospheres, but they can
also be strongly affected by heterogeneities in host star photospheres
through the transit light source effect. Here we build upon our recent
study of the effects of unocculted spots and faculae on M-dwarf
transmission spectra, extending the analysis to FGK dwarfs. Using
a suite of rotating model photospheres, we explore spot and facula
covering fractions for varying activity levels and the associated
stellar contamination spectra. Relative to M dwarfs, we find that the
typical variabilities of FGK dwarfs imply lower spot covering fractions,
though they generally increase with later spectral types, from ∼0.1%
for F dwarfs to 2%-4% for late-K dwarfs. While the stellar contamination
spectra are considerably weaker than those for typical M dwarfs,
we find that typically active G and K dwarfs produce visual slopes
that are detectable in high-precision transmission spectra. We examine
line offsets at Hα and the Na and K doublets and find that unocculted
faculae in K dwarfs can appreciably alter transit depths around the
Na D doublet. We find that band-averaged transit depth offsets at
molecular bands for CH4, CO, CO2, H2O,
N2O, O2, and O3 are not detectable
for typically active FGK dwarfs, though stellar TiO/VO features are
potentially detectable for typically active late-K dwarfs. Generally,
this analysis shows that inactive FGK dwarfs do not produce detectable
stellar contamination features in transmission spectra, though active
FGK host stars can produce such features, and care is warranted in
interpreting transmission spectra from these systems.
Title: The Transit Light Source Effect in F to M Dwarf Systems
Authors: Rackham, Benjamin V.; Apai, Dániel; Giampapa, Mark S.;
Zhang, Zhanbo; Zhou, Yifan
Bibcode: 2019AAS...23310302R
Altcode:
Transmission spectra are powerful probes of exoplanet atmospheres,
but they are also subject to spectral features introduced by the
transit light source (TLS) effect. This phenomenon imprints on transit
depths the contrast between the emergent spectrum of the transit
chord—the true light source for the transmission measurement—and the
out-of-transit disk-averaged stellar spectrum—the necessarily assumed
light source. Here we summarize a series of studies exploring the TLS
effect in F to M dwarfs. We use a suite of model rotating photospheres
to determine spot and faculae covering fractions for typical stellar
activity levels, with which we calculate the corresponding TLS signals
in transmission spectra. We find that transit depth changes due to the
TLS effect can be comparable to or even an order of magnitude larger
than those expected for transiting exoplanets. TLS signals are more
pronounced in smaller and cooler main sequence stars—the same stars
that have been the focus of many transit studies, given their favorable
planet-to-star radius ratios. The TLS effect can mimic or mute H2O
features from planetary atmospheres in M-dwarf systems and TiO/VO
features in active late-G- and K-dwarf systems. We will discuss the
spectral characteristics and scales of TLS signals for F to M spectral
types and present transmission spectra from two M-dwarf systems that
show evidence for TLS contamination: the GJ 1214 system (M4.5V) and
the TRAPPIST-1 system (M8V). Robust methods of disentangling stellar
and planetary features in transits will be crucial to interpretations
of high-precision transmission spectra from JWST and future missions.
Title: Enhanced Stellar Activity for Slow Antisolar Differential
Rotation?
Authors: Brandenburg, Axel; Giampapa, Mark S.
Bibcode: 2018ApJ...855L..22B
Altcode: 2018arXiv180208689B
High-precision photometry of solar-like members of the open cluster M67
with Kepler/K2 data has recently revealed enhanced activity for stars
with a large Rossby number, which is the ratio of rotation period
to the convective turnover time. Contrary to the well established
behavior for shorter rotation periods and smaller Rossby numbers,
the chromospheric activity of the more slowly rotating stars of M67
was found to increase with increasing Rossby number. Such behavior has
never been reported before, although it was theoretically predicted
to emerge as a consequence of antisolar differential rotation (DR)
for stars with Rossby numbers larger than that of the Sun, because in
those models the absolute value of the DR was found to exceed that for
solar-like DR. Using gyrochronological relations and an approximate
age of 4 Gyr for the members of M67, we compare with computed rotation
rates using just the B - V color. The resulting rotation-activity
relation is found to be compatible with that obtained by employing
the measured rotation rate. This provides additional support for the
unconventional enhancement of activity at comparatively low rotation
rates and the possible presence of antisolar differential rotation.
Title: Understanding Stellar Contamination in Exoplanet Transmission
Spectra as an Essential Step in Small Planet Characterization
Authors: Apai, Dániel; Rackham, Benjamin V.; Giampapa, Mark S.;
Angerhausen, Daniel; Teske, Johanna; Barstow, Joanna; Carone, Ludmila;
Cegla, Heather; Domagal-Goldman, Shawn D.; Espinoza, Néstor; Giles,
Helen; Gully-Santiago, Michael; Haywood, Raphaelle; Hu, Renyu; Jordan,
Andres; Kreidberg, Laura; Line, Michael; Llama, Joe; López-Morales,
Mercedes; Marley, Mark S.; de Wit, Julien
Bibcode: 2018arXiv180308708A
Altcode:
Transmission spectroscopy during planetary transits is expected to be a
major source of information on the atmospheres of small (approximately
Earth-sized) exoplanets in the next two decades. This technique,
however, is intrinsically affected by stellar spectral contamination
caused by the fact that stellar photo- and chromospheres are not
perfectly homogeneous. Such stellar contamination will often reach or
exceed the signal introduced by the planetary spectral features. Finding
effective methods to correct stellar contamination -- or at least to
quantify its possible range -- for the most important exoplanets is a
necessary step for our understanding of exoplanet atmospheres. This
will require significantly deepening our understanding of stellar
heterogeneity, which is currently limited by the available data.
Title: The Transit Light Source Effect: False Spectral Features and
Incorrect Densities for M-dwarf Transiting Planets
Authors: Rackham, Benjamin V.; Apai, Dániel; Giampapa, Mark S.
Bibcode: 2018ApJ...853..122R
Altcode: 2017arXiv171105691R
Transmission spectra are differential measurements that utilize stellar
illumination to probe transiting exoplanet atmospheres. Any spectral
difference between the illuminating light source and the disk-integrated
stellar spectrum due to starspots and faculae will be imprinted in the
observed transmission spectrum. However, few constraints exist for the
extent of photospheric heterogeneities in M dwarfs. Here we model spot
and faculae covering fractions consistent with observed photometric
variabilities for M dwarfs and the associated 0.3-5.5 μm stellar
contamination spectra. We find that large ranges of spot and faculae
covering fractions are consistent with observations and corrections
assuming a linear relation between variability amplitude, and covering
fractions generally underestimate the stellar contamination. Using
realistic estimates for spot and faculae covering fractions, we
find that stellar contamination can be more than 10× larger than
the transit depth changes expected for atmospheric features in rocky
exoplanets. We also find that stellar spectral contamination can lead to
systematic errors in radius and therefore the derived density of small
planets. In the case of the TRAPPIST-1 system, we show that TRAPPIST-1's
rotational variability is consistent with spot covering fractions
{f}{spot}={8}-7+18 % and faculae
covering fractions {f}{fac}={54}-46+16
% . The associated stellar contamination signals alter the transit
depths of the TRAPPIST-1 planets at wavelengths of interest for
planetary atmospheric species by roughly 1-15× the strength of
planetary features, significantly complicating JWST follow-up
observations of this system. Similarly, we find that stellar
contamination can lead to underestimates of the bulk densities of the
TRAPPIST-1 planets of {{Δ }}(ρ )=-{8}-20+7 %
, thus leading to overestimates of their volatile contents.
Title: Exoplanet Transits of Stellar Active Regions
Authors: Giampapa, Mark S.; Andretta, Vincenzo; Covino, Elvira;
Reiners, Ansgar; Esposito, Massimiliano
Bibcode: 2018AAS...23123402G
Altcode:
We report preliminary results of a program to obtain high spectral-
and temporal-resolution observations of the neutral helium triplet
line at 1083.0 nm in transiting exoplanet systems. The principal
objective of our program is to gain insight on the properties of
active regions, analogous to solar plages, on late-type dwarfs by
essentially using exoplanet transits as high spatial resolution
probes of the stellar surface within the transit chord. The 1083 nm
helium line is a particularly appropriate diagnostic of magnetized
areas since it is weak in the quiet photosphere of solar-type stars
but appears strongly in absorption in active regions. Therefore,
during an exoplanet transit over the stellar surface, variations in
its absorption equivalent width can arise that are functions of the
intrinsic strength of the feature in the active region and the known
relative size of the exoplanet. We utilized the Galileo Telescope and
the GIANO-B near-IR echelle spectrograph to obtain 1083 nm spectra
during transits in bright, well-known systems that include HD 189733,
HD 209458, and HD 147506 (HAT-P-2). We also obtained simultaneous
auxiliary data on the same telescope with the HARPS-N UV-Visible
echelle spectrograph. We will present preliminary results from our
analysis of the observed variability of the strength of the He I
1083 nm line during transits.Acknowledgements: Based on observations
made with the Italian Telescopio Nazionale Galileo (TNG) operated on
the island of La Palma by the Fundación Galileo Galilei of the INAF
(Istituto Nazionale di Astrofisica) at the Spanish Observatorio del
Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The
NSO is operated by AURA under a cooperative agreement with the NSF.
Title: The Light Source Problem: The Effect of Heterogeneous Stellar
Photospheres on Searches for Transiting Exoplanet Biosignatures
Authors: Rackham, B. V.; Apai, D.; Giampapa, M. S.
Bibcode: 2017LPICo2042.4032R
Altcode:
TESS will soon enable the study of terrestrial exoplanet
atmospheres. However, spots and faculae in stellar photospheres can
complicate these measurements by mimicking or masking atmospheric
features. We detail our work to constrain this effect.
Title: VizieR Online Data Catalog: HeI 5876 & 10830Å EWs of
solar-type stars (Andretta+, 2017)
Authors: Andretta, V.; Giampapa, M. S.; Covino, E.; Reiners, A.;
Beeck, B.
Bibcode: 2017yCat..18390097A
Altcode:
A total of 134 FEROS spectra (R=48000) of our targets (including
telluric standards) were acquired on the night of UT 2011 December
6-7; spectral coverage from 3500 to 9200Å. The Fiber Extended-range
Optical Spectrograph (FEROS) was mounted at the 2.2m Max-Planck
Gesellschaft/European Southern Observatory (MPG/ESO) telescope at La
Silla (Chile). The HeIλ10830 spectroscopic observations were
carried out on the same night as the FEROS D3 observations,
using the CRyogenic high-resolution InfraRed Echelle Spectrograph
(CRIRES), mounted at Unit Telescope 1 (Antu) of the VLT array at Cerro
Paranal. The details of the observations is given in table 1. (3 data files).
Title: The Effect of Stellar Contamination on Transmission Spectra
of Low-mass Exoplanets
Authors: Rackham, Benjamin V.; Apai, Daniel; Giampapa, Mark S.
Bibcode: 2017DPS....4941620R
Altcode:
Transmission spectroscopy offers the exciting possibility of studying
terrestrial exoplanet atmospheres in the near-term future. The
Transiting Exoplanet Survey Satellite (TESS), scheduled for launch
next year, is expected to discover thousands of transiting exoplanets
around bright host stars, including an estimated twenty habitable zone
super-Earths. The brightness of the TESS host stars, combined with
refined observational strategies and near-future facilities, will
enable searches for atmospheric signatures from smaller and cooler
exoplanets. These observations, however, will be increasingly subject
to noise introduced by heterogeneities in the host star photospheres,
such as star spots and faculae. In short, the transmission spectroscopy
method relies on the assumption that the spectrum of the transit
chord does not differ from that of the integrated stellar disk
or, if it does, the contribution of photospheric heterogeneities
to the transmission spectrum can be constrained by variability
monitoring. However, any axisymmetric populations of spots and faculae
will strongly affect transmission spectra, and their presence cannot be
deduced from monitoring efforts. A clear need exists for a more robust
understanding of stellar contamination on transmission spectra. Here we
summarize our work on the impact of heterogeneous stellar photospheres
on transmission spectra and detail implications for atmospheric
characterization efforts. By modeling spot and faculae distributions
in stellar photospheres, we find that spot-covering fractions
extrapolated from observed variability amplitudes are significantly
underestimated. Likewise, corrections based on variability monitoring
likely fall short of the actual stellar spectral contamination. We
provide examples of contamination spectra for typical levels of stellar
activity across a range of spectral types. For M dwarfs, molecular
absorption features in spots and faculae can imprint apparent features
in transmission spectra of small exoplanets, including those of the
TRAPPIST-1 system. Constraining stellar contamination will likely be
a limiting factor for detecting atmospheric features in transmission
spectra of low-mass exoplanets around late-type stars from TESS.
Title: Science-Driven Optimization of the LSST Observing Strategy
Authors: LSST Science Collaboration; Marshall, Phil; Anguita, Timo;
Bianco, Federica B.; Bellm, Eric C.; Brandt, Niel; Clarkson, Will;
Connolly, Andy; Gawiser, Eric; Ivezic, Zeljko; Jones, Lynne; Lochner,
Michelle; Lund, Michael B.; Mahabal, Ashish; Nidever, David; Olsen,
Knut; Ridgway, Stephen; Rhodes, Jason; Shemmer, Ohad; Trilling, David;
Vivas, Kathy; Walkowicz, Lucianne; Willman, Beth; Yoachim, Peter;
Anderson, Scott; Antilogus, Pierre; Angus, Ruth; Arcavi, Iair; Awan,
Humna; Biswas, Rahul; Bell, Keaton J.; Bennett, David; Britt, Chris;
Buzasi, Derek; Casetti-Dinescu, Dana I.; Chomiuk, Laura; Claver, Chuck;
Cook, Kem; Davenport, James; Debattista, Victor; Digel, Seth; Doctor,
Zoheyr; Firth, R. E.; Foley, Ryan; Fong, Wen-fai; Galbany, Lluis;
Giampapa, Mark; Gizis, John E.; Graham, Melissa L.; Grillmair, Carl;
Gris, Phillipe; Haiman, Zoltan; Hartigan, Patrick; Hawley, Suzanne;
Hlozek, Renee; Jha, Saurabh W.; Johns-Krull, C.; Kanbur, Shashi;
Kalogera, Vassiliki; Kashyap, Vinay; Kasliwal, Vishal; Kessler,
Richard; Kim, Alex; Kurczynski, Peter; Lahav, Ofer; Liu, Michael C.;
Malz, Alex; Margutti, Raffaella; Matheson, Tom; McEwen, Jason D.;
McGehee, Peregrine; Meibom, Soren; Meyers, Josh; Monet, Dave; Neilsen,
Eric; Newman, Jeffrey; O'Dowd, Matt; Peiris, Hiranya V.; Penny, Matthew
T.; Peters, Christina; Poleski, Radoslaw; Ponder, Kara; Richards,
Gordon; Rho, Jeonghee; Rubin, David; Schmidt, Samuel; Schuhmann,
Robert L.; Shporer, Avi; Slater, Colin; Smith, Nathan; Soares-Santos,
Marcelles; Stassun, Keivan; Strader, Jay; Strauss, Michael; Street,
Rachel; Stubbs, Christopher; Sullivan, Mark; Szkody, Paula; Trimble,
Virginia; Tyson, Tony; de Val-Borro, Miguel; Valenti, Stefano; Wagoner,
Robert; Wood-Vasey, W. Michael; Zauderer, Bevin Ashley
Bibcode: 2017arXiv170804058L
Altcode:
The Large Synoptic Survey Telescope is designed to provide an
unprecedented optical imaging dataset that will support investigations
of our Solar System, Galaxy and Universe, across half the sky and
over ten years of repeated observation. However, exactly how the LSST
observations will be taken (the observing strategy or "cadence")
is not yet finalized. In this dynamically-evolving community white
paper, we explore how the detailed performance of the anticipated
science investigations is expected to depend on small changes to
the LSST observing strategy. Using realistic simulations of the LSST
schedule and observation properties, we design and compute diagnostic
metrics and Figures of Merit that provide quantitative evaluations of
different observing strategies, analyzing their impact on a wide range
of proposed science projects. This is work in progress: we are using
this white paper to communicate to each other the relative merits
of the observing strategy choices that could be made, in an effort
to maximize the scientific value of the survey. The investigation of
some science cases leads to suggestions for new strategies that could
be simulated and potentially adopted. Notably, we find motivation for
exploring departures from a spatially uniform annual tiling of the sky:
focusing instead on different parts of the survey area in different
years in a "rolling cadence" is likely to have significant benefits
for a number of time domain and moving object astronomy projects. The
communal assembly of a suite of quantified and homogeneously coded
metrics is the vital first step towards an automated, systematic,
science-based assessment of any given cadence simulation, that will
enable the scheduling of the LSST to be as well-informed as possible.
Title: Estimates of Active Region Area Coverage through Simultaneous
Measurements of the He I λλ 5876 and 10830 Lines
Authors: Andretta, Vincenzo; Giampapa, Mark S.; Covino, Elvira;
Reiners, Ansgar; Beeck, Benjamin
Bibcode: 2017ApJ...839...97A
Altcode: 2017arXiv170310060A
Simultaneous, high-quality measurements of the neutral helium triplet
features at 5876 Å and 10830 Å in a sample of solar-type stars are
presented. The observations were made with ESO telescopes at the La
Silla Paranal Observatory under program ID 088.D-0028(A) and MPG Utility
Run for Fiber Extended-range Optical Spectrograph 088.A-9029(A). The
equivalent widths of these features combined with chromospheric models
are utilized to infer the fractional area coverage, or filling factor,
of magnetic regions outside of spots. We find that the majority of the
sample is characterized by filling factors less than unity. However,
discrepancies occur among the coolest K-type and the warmest and
most rapidly rotating F-type dwarf stars. We discuss these apparently
anomalous results and find that in the case of K-type stars, they are
an artifact of the application of chromospheric models best suited to
the Sun than to stars with significantly lower T eff. The
case of the F-type rapid rotators can be explained by the measurement
uncertainties of the equivalent widths, but they may also be due
to a non-magnetic heating component in their atmospheres. With the
exceptions noted above, preliminary results suggest that the average
heating rates in the active regions are the same from one star to
the other, differing in the spatially integrated, observed level of
activity due to the area coverage. Hence, differences in activity in
this sample are mainly due to the filling factor of active regions.
Title: The Photometric Variability of Solar-Type Stars
Authors: Giampapa, Mark S.
Bibcode: 2016IAUFM..29A.365G
Altcode:
The joint variability of chromospheric emission with the integrated
flux in the Kepler visible band for the Sun as a star is examined. No
correlation between our Ca II K line parameter and the Kepler passband
is seen, suggesting that visible-band variability in solar-like stars
is mostly independent of solar-like chromospheric activity. However,
the K-line parameter time series and the total solar flux in the
infrared K band appear weakly correlated, reflecting the wavelength
dependence of the relationship between magnetic activity and broadband
variability. We then apply a schematic, three-component model as a
framework for the discussion of stellar photometric variability as
observed by Kepler. The model confirms that spots tend to dominate
stellar photometric variability in the visible though interesting
cases do emerge where the facular disk coverage may become important
in determining the amplitude of broadband variability.
Title: Maximizing Science in the Era of LSST: A Community-Based
Study of Needed US Capabilities
Authors: Najita, Joan; Willman, Beth; Finkbeiner, Douglas P.; Foley,
Ryan J.; Hawley, Suzanne; Newman, Jeffrey A.; Rudnick, Gregory; Simon,
Joshua D.; Trilling, David; Street, Rachel; Bolton, Adam; Angus, Ruth;
Bell, Eric F.; Buzasi, Derek; Ciardi, David; Davenport, James R. A.;
Dawson, Will; Dickinson, Mark; Drlica-Wagner, Alex; Elias, Jay; Erb,
Dawn; Feaga, Lori; Fong, Wen-fai; Gawiser, Eric; Giampapa, Mark;
Guhathakurta, Puragra; Hoffman, Jennifer L.; Hsieh, Henry; Jennings,
Elise; Johnston, Kathryn V.; Kashyap, Vinay; Li, Ting S.; Linder,
Eric; Mandelbaum, Rachel; Marshall, Phil; Matheson, Thomas; Meibom,
Soren; Miller, Bryan W.; O'Meara, John; Reddy, Vishnu; Ridgway, Steve;
Rockosi, Constance M.; Sand, David J.; Schafer, Chad; Schmidt, Sam;
Sesar, Branimir; Sheppard, Scott S.; Thomas, Cristina A.; Tollerud,
Erik J.; Trump, Jon; von der Linden, Anja
Bibcode: 2016arXiv161001661N
Altcode:
The Large Synoptic Survey Telescope (LSST) will be a discovery machine
for the astronomy and physics communities, revealing astrophysical
phenomena from the Solar System to the outer reaches of the observable
Universe. While many discoveries will be made using LSST data alone,
taking full scientific advantage of LSST will require ground-based
optical-infrared (OIR) supporting capabilities, e.g., observing
time on telescopes, instrumentation, computing resources, and
other infrastructure. This community-based study identifies, from a
science-driven perspective, capabilities that are needed to maximize
LSST science. Expanding on the initial steps taken in the 2015 OIR
System Report, the study takes a detailed, quantitative look at the
capabilities needed to accomplish six representative LSST-enabled
science programs that connect closely with scientific priorities from
the 2010 decadal surveys. The study prioritizes the resources needed
to accomplish the science programs and highlights ways that existing,
planned, and future resources could be positioned to accomplish the
science goals.
Title: Maximizing Science in the Era of LSST, Stars Study Group
Report: Rotation and Magnetic Activity in the Galactic Field
Population and in Open Star Clusters
Authors: Hawley, Suzanne L.; Angus, Ruth; Buzasi, Derek; Davenport,
James R. A.; Giampapa, Mark; Kashyap, Vinay; Meibom, Soren
Bibcode: 2016arXiv160704302H
Altcode:
This is the stars chapter of the Kavli workshop report, which resulted
from the community-based study of needed US OIR capabilities in
the LSST era. The full report, which will include this chapter,
is anticipated to be available in Fall 2016. See NOAO website
(http://www.noao.edu/meetings/lsst-oir-study/) for more details.
Title: The solar-stellar connection
Authors: Giampapa, Mark S.
Bibcode: 2016AsJPh..25..411G
Altcode:
A review of some principal results achieved in the area of stellar
astrophysics with its origins in solar physics - the Solar-Stellar
Connection - is presented from the perspective of an observational
astronomer. The historical origins of the Solar-Stellar Connection
are discussed followed by a review of key results from observations
of stellar cycles analogous to the solar cycle in terms of parameters
relevant to dynamo theory. A review of facets of angular momentum
evolution and irradiance variations, each of which is determined
by emergent, dynamo-generated magnetic fields, is given. Recent
considerations of the impacts of stellar magnetic activity on the
ambient radiative and energetic particle environment of the habitable
zone of exoplanet systems are summarized. Some anticipated directions
of the Solar-Stellar Connection in the new era of astronomy as defined
by the advent of transformative facilities are presented.
Title: Variability of Kepler Solar-like Stars Harboring Small
Exoplanets
Authors: Howell, Steve B.; Ciardi, David R.; Giampapa, Mark S.;
Everett, Mark E.; Silva, David R.; Szkody, Paula
Bibcode: 2016AJ....151...43H
Altcode: 2015arXiv151203108H
We examine Kepler light-curve variability on habitable zone transit
timescales for a large uniform sample of spectroscopically studied
Kepler exoplanet host stars. The stars, taken from Everett et al.,
are solar-like in their properties and each harbors at least one
exoplanet (or candidate) of radius ≤2.5 {R}{{e}}. The
variability timescale examined is typical for habitable zone planets
orbiting solar-like stars and we note that the discovery of the
smallest exoplanets (≤1.2 {R}{{e}}) with corresponding
transit depths of less than ∼0.18 mmag occur for the brightest and
photometrically quietest stars. Thus, these detections are quite rare in
Kepler observations. Some brighter and more evolved stars (subgiants),
the latter of which often show large radial velocity jitter, are found
to be among the photometrically quietest solar-like stars in our sample
and the most likely small planet transit hunting grounds. The Sun is
discussed as a solar-like star proxy to provide insight into the nature
and cause of photometric variability. It is shown that Kepler’s broad,
visible light observations are insensitive to variability caused by
chromospheric activity that may be present in the observed stars.
Title: Photometric Variations In The Sun And Solar-Type Stars
Authors: Giampapa, Mark
Bibcode: 2016csss.confE...1G
Altcode:
The rich array of solar magnetic field-related phenomena we see occurs
not only on stellar counterparts of our Sun but in stars that represent
significant departures in their fundamental parameters from those of
the
Sun. Though these phenomena appear energetically negligible
when compared to the total luminosity of stars, they nevertheless
govern the angular momentum evolution and modulate the radiative
and particle output of the Sun and late-type stars. The term "The
Solar-Stellar Connection" has been coined to describe the solar-stellar
synergisms in the investigation of the generation, emergence and
coupling of magnetic fields with the outer solar-stellar atmosphere
to produce what we broadly refer to as magnetic activity. With the
discovery of literally thousands of planets beyond our solar system,
the Solar-Stellar-Planet Connection is quickly emerging as a new area
of investigation of the impacts of magnetic activity on exoplanet
atmospheres. In parallel with this rapid evolution in our perspectives
is the advent of transformative facilities for the study of the Sun and
the dynamic Universe. The primary focus of this invited talk will be on
photometric variations in solar-type stars and the Sun. These brightness
variations are associated with thermal homogeneities typically defined
by magnetic structures that are also spatially coincident with key
radiative proxies. Photometric variability in solar-type stars and the
Sun includes transient brightening, rotational modulation by cool spots
and cycle-related variability, each with a characteristic signature in
time and wavelength. The emphasis
of this presentation will be on
the relationship between broadband photometric variations and magnetic
field-related activity in solar-type stars and the Sun. Facets of this
topic will be discussed both retrospectively and prospectively as we
enter a revolutionary, new era for astronomy.
Title: Seeing SPOTS with SOFIA: Starspot Photometric Observations
of Transiting Systems
Authors: Giampapa, Mark
Bibcode: 2015sofi.prop...24G
Altcode:
We propose to utilize the unique capabilities provided by HIPO/FLITECAM
(FLIPO) and the FPI to obtain simultaneous, time-resolved multi-color
photometry extending from the visible to the near infrared of
magnetically active dwarf stars that are also the hosts of transiting
exoplanets. In this way, we can measure the fundamental properties of
starspots that are eclipsed by the transiting planet and thereby provide
much improved constraints for starspot models than has been possible
with the single-band data from Kepler and CoRoT. Since starspots are
the strongest concentrations of magnetic flux on the Sun and stars, an
understanding of their properties can yield critical constraints for
stellar dynamo models and influence our views of the role of stellar
magnetic activity in star-planet interactions.
Title: A Method for Measuring Active Region Filling Factors on
Solar-Type Stars
Authors: Giampapa, Mark Steven; Andretta, Vincenzo; Beeck, Benjamin;
Reiners, Ansgar; Schussler, Manfred
Bibcode: 2015TESS....120101G
Altcode:
Radiative diagnostics of “activity” in the Sun and solar-type stars
are spatially associated with sites of emergent magnetic flux. The
magnetic fields themselves are widely regarded as the surface
manifestations of a dynamo mechanism. The further development of
both dynamo theory and models of the non-radiative heating of outer
stellar atmospheres requires a knowledge of stellar magnetic field
properties. In this context, it becomes important to determine the
surface distribution, or at least the fractional coverage of, magnetic
active regions as one critical constraint for dynamo models. But,
while information on the spatial distribution of activity on stellar
surfaces can be gathered in some special cases (mostly rapid rotators),
such measurements have always been elusive in more solar-like stars. We
discuss the challenges and results obtained from a method that relies
on the non-linear response of the two principal He I triplet lines
(at 1083 nm and 587.6 nm) to infer useful constraints on the fractional
area coverage of magnetic active regions on solar-type stars.
Title: SOLIS: Reconciling Disk-integrated and Disk-resolved Spectra
from the Sun
Authors: Pevtsov, Alexei A.; Bertello, Luca; Harker, Brian; Giampapa,
Mark; Marble, Andrew R.
Bibcode: 2015csss...18..887P
Altcode: 2014arXiv1411.7266P
Unlike other stars, the surface of the Sun can be spatially resolved
to a high degree of detail . But the Sun can also be observed as if
it was a distant star. The availability of solar disk-resolved and
disk-integrated spectra offers an opportunity to devise methods to
derive information about the spatial distribution of solar features
from Sun-as-a-star measurements. Here, we present an update on work
done at the National Solar Observatory to reconcile disk-integrated
and disk-resolved solar spectra from the Synoptic Optical Long-term
Investigation of the Sun (SOLIS) station. The results of this work
will lead to a new approach to infer the information about the spatial
distribution of features on other stars, from the overall filling factor
of active regions to, possibly, the latitude/longitude distribution
of features.
Title: Line Bisector Variability in the Sun as a Star
Authors: Giampapa, Mark; Bertello, Luca
Bibcode: 2015csss...18..495G
Altcode:
We utilize spectra obtained with the Integrated Sunlight Spectrometer
(ISS) instrument of the NSO SOLIS facility on Kitt Peak, AZ to perform
a preliminary study of the variability of line asymmetries in the Mn I
line at 539.5 nm and the nearby Fe I line at 539.3 nm, respectively. We
derive the line bisector for these photospheric features from
daily spectra of the Sun as a star acquired since January 2007, and
characterize the variability of a measure of bisector amplitude with
the solar cycle. A simple two-component model of the solar magnetic
field is investigated as a possible origin for the variation in line
depth with time of the magnetically sensitive Mn I feature.
Title: Solar Cycle Dependency of Sun-as-a-Star Photospheric Spectral
Line Profiles
Authors: Bertello, Luca; Pevtsov, Alexei A.; Giampapa, Mark S.;
Marble, Andrew R.
Bibcode: 2015csss...18..693B
Altcode:
We investigate solar-cycle related changes in the profile of several
photospheric spectral lines taken with the Integrated Sunlight
Spectrometer (ISS) operating at the National Solar Observatory at Kitt
Peak (Arizona). ISS, which is one of three instruments comprising
the Synoptic Optical Long-term Investigations of the Sun (SOLIS)
facility, is designed to obtain high spectral resolution (R = 300,000)
observations of the Sun-as-a-star in a broad range of wavelengths
(350 nm - 1100 nm). Daily measurements were obtained since December
2006, covering the decline of solar cycle 23 and the rising phase of
cycle 24. We present time series of line parameters and discuss their
correlation to indices of solar magnetic activity. Because of their
different response to variations in the thermodynamic and magnetic
structures of the solar atmosphere, the measured line shape parameters
provide an excellent tool for disentangling thermal and magnetic effects
occurring during different phases of the solar cycle. The results of
this analysis may also help with developing a better understanding of
magnetic cycles of activity in other solar-like stars.
Title: Stellar Activity and Variability: Our Sun in a Stellar Context
Authors: Giampapa, M.
Bibcode: 2013ASPC..478..365G
Altcode:
The variability of the Sun in its chromospheric emission and associated
irradiance changes is compared with that of other solar-type stars. A
review of the results thus far obtained indicates that the Sun is not
atypical in its magnetic field-related variations when compared to
relatively homogeneous samples of stars that are also solar-like in
key parameters such as effective temperature, gravity, rotation rate,
and mean level of activity. In a comparison with more heterogeneous
samples of ostensibly solar-type stars, the Sun appears to reside
at a boundary between “active” and “quiet” chromosphere
stars, suggesting that the structure of the outer solar atmosphere as
delineated by emergent magnetic fields includes attributes of each of
these broad stellar categories.
Title: Stellar cycles: general properties and future directions
Authors: Giampapa, Mark S.
Bibcode: 2012IAUS..286..257G
Altcode:
We discuss the general properties of stellar cycles with emphasis on
their amplitudes as a function of stellar parameters, particularly
those stellar characteristics relevant to dynamo-driven magnetic
activity. We deduce an empirical scaling relation between cycle
frequency and differential rotation based on previously established
empirical relations. We also compare the recent Cycle 23 to cycles
in solar-type stars. We find that the extended minimum of Cycle 23
resembled in its Ca II H & K emission at minimum the mean levels
of activity seen in stars with no cycles.
Title: Joint Response of the Helium Lines to Chromospheric Heating
in Solar-type Stars
Authors: Giampapa, Mark S.; Andretta, V.; Beeck, B.; Reiners, A.;
Schussler, M.
Bibcode: 2012AAS...22020314G
Altcode:
We present a preliminary report on simultaneous observations of
the He I 5876 and 10830 triplet lines, respectively, in a sample of
solar-type stars. The near-IR spectra were obtained with the VLT and
CRIRES instrument while the visible spectra were acquired with the
MPG/ESO 2.2-m telescope in conjunction with the FEROS spectrograph. The
correlation of the observed strengths of these lines will be examined
and their potential as diagnostics of active region area coverage in
solar-type stars will be discussed. The NSO is operated by AURA
under a cooperative agreement with the National Science Foundation.
Title: Estimating the Fractional Area Coverage of Active Regions in
Dwarf Stars
Authors: Andretta, V.; Giampapa, M.
Bibcode: 2011ASPC..448.1111A
Altcode: 2011csss...16.1111A
It has been shown (Andretta & Giampapa 1995) that the two He I
triplet lines at 1.083 μm and 587.6 nm, respectively, can be utilized
to infer the area coverage of active (plage-like) regions on stellar
surfaces by exploiting their different responses to chromospheric
heating. This kind of information, which is very difficult to obtain
through other methods, can serve as a fundamental constraint for
the development of stellar dynamo theory. We discuss the application
and limitations of this approach to the interpretation of spatially
resolved solar data along with some preliminary stellar observations.
Title: Splinter Session "Solar and Stellar Flares"
Authors: Fletcher, L.; Hudson, H.; Cauzzi, G.; Getman, K. V.; Giampapa,
M.; Hawley, S. L.; Heinzel, P.; Johnstone, C.; Kowalski, A. F.; Osten,
R. A.; Pye, J.
Bibcode: 2011ASPC..448..441F
Altcode: 2011csss...16..441F; 2012arXiv1206.3997F
This summary reports on papers presented at the Cool Stars-16 meeting in
the splinter session "Solar and Stellar flares." Although many topics
were discussed, the main themes were the commonality of interests,
and of physics, between the solar and stellar flare communities,
and the opportunities for important new observations in the near future.
Title: The evolution of stellar surface activity and possible effects
on exoplanets
Authors: Giampapa, Mark S.
Bibcode: 2011IAUS..273...68G
Altcode:
The evolution of stellar activity involves a complex interplay
between the interior dynamo mechanism, the emergent magnetic field
configurations and their coupling with stellar winds, the subsequent
angular momentum evolution, and fundamental stellar parameters. The
discussion of the evolution of surface activity will emphasize the
main sequence phase, from the ZAMS to stars of solar-age. We will
focus particularly on the evolution of the fractional area coverages
of spots on the surfaces of solar-type stars. We fit an empirical
relation to the fractional mean spot area coverage as a function of age
for ages greater than the Pleiades of the form log(MeanSpotCoverage) =
0.90(+/-0.26) - 1.03(+/-0.10)log(Age), where Age is in Myr. In addition,
we summarize the relative evolution of radiative emissions in various
short wavelength bands that are associated with stellar magnetic
field-related activity. Possible effects on young planetary atmospheres
also are appropriate to consider given that stellar surface activity
is the origin of the high-energy component of the ambient radiation
and particle fields in which planetary atmosphere evolution occurs.
Title: Stellar Imager (SI): developing and testing a predictive
dynamo model for the Sun by imaging other stars
Authors: Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska,
Margarita; Kraemer, Steve; Lyon, Richard; Mozurkewich, David;
Airapetian, Vladimir; Adams, John C.; Allen, Ronald J.; Brown, Alex;
Bruhweiler, Fred; Conti, Alberto; Christensen-Dalsgaard, Joergen;
Cranmer, Steve; Cuntz, Manfred; Danchi, William; Dupree, Andrea; Elvis,
Martin; Evans, Nancy; Giampapa, Mark; Harper, Graham; Hartman, Kathy;
Labeyrie, Antoine; Leitner, Jesse; Lillie, Chuck; Linsky, Jeffrey L.;
Lo, Amy; Mighell, Ken; Miller, David; Noecker, Charlie; Parrish, Joe;
Phillips, Jim; Rimmele, Thomas; Saar, Steve; Sasselov, Dimitar; Stahl,
H. Philip; Stoneking, Eric; Strassmeier, Klaus; Walter, Frederick;
Windhorst, Rogier; Woodgate, Bruce; Woodruff, Robert
Bibcode: 2010arXiv1011.5214C
Altcode:
The Stellar Imager mission concept is a space-based UV/Optical
interferometer designed to resolve surface magnetic activity and
subsurface structure and flows of a population of Sun-like stars,
in order to accelerate the development and validation of a predictive
dynamo model for the Sun and enable accurate long-term forecasting of
solar/stellar magnetic activity.
Title: Photometric Variability of Solar-Type Stars in the Young
Pleiades Open Cluster
Authors: Giampapa, Mark S.; Sherry, W. H.; Craine, E. R.
Bibcode: 2010AAS...21640014G
Altcode: 2010BAAS...41..856G
We present some preliminary results from a program of intensive
photometric monitoring of four solar-type stars in the young Pleiades
cluster at an age of approximately 100 Myr utilizing a small-aperture
robotic telescope. The Pleiades targets and their spectral types
include hz 212 (K7), hz 253 (G1 V), hz 345 (G8 V) and hz 489 (G0
V). Photometry of the comparison stars and selected field stars included
in the CCD frame is also given. The monitoring program over 43 nights
of observations and 1500 frames yields information on the nature of
both long-term variability and any short-term, transient activity
such as flare outbursts. This investigation is part of a broad
effort to delineate the joint evolution of activity and irradiance
variability in solar-type stars that may be the hosts of planetary
systems. Understanding the nature of the joint variability of irradiance
and magnetic activity on sun-like stars spanning a range of ages will
provide crucial insight on how frequently earth-like atmospheres are
likely to form and survive, and how frequently exo-earths encounter
benign climatic variations. We acknowledge support by a grant from
the NASA Astrobiology Institute. The NSO and the NOAO are each operated
by AURA under separate cooperative agreements with the National Science
Foundation. This research was partially supported by a grant from
the American Astronomical Association.
Title: The Asteroseismic Potential of Kepler: First Results for
Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
Bibcode: 2010ApJ...713L.169C
Altcode: 2010arXiv1001.0506C
We present preliminary asteroseismic results from Kepler on three G-type
stars. The observations, made at one-minute cadence during the first
33.5 days of science operations, reveal high signal-to-noise solar-like
oscillation spectra in all three stars: about 20 modes of oscillation
may be clearly distinguished in each star. We discuss the appearance of
the oscillation spectra, use the frequencies and frequency separations
to provide first results on the radii, masses, and ages of the stars,
and comment in the light of these results on prospects for inference
on other solar-type stars that Kepler will observe.
Title: Simultaneous Multi-Wavelength Observations of Magnetic Activity
in Ultracool Dwarfs. III. X-ray, Radio, and Hα Activity Trends in
M and L dwarfs
Authors: Berger, E.; Basri, G.; Fleming, T. A.; Giampapa, M. S.;
Gizis, J. E.; Liebert, J.; Martín, E.; Phan-Bao, N.; Rutledge, R. E.
Bibcode: 2010ApJ...709..332B
Altcode: 2009arXiv0909.4783B
As part of our on-going investigation into the magnetic field
properties of ultracool dwarfs, we present simultaneous radio, X-ray,
and Hα observations of three M9.5-L2.5 dwarfs (BRI 0021-0214, LSR
060230.4+391059, and 2MASS J052338.2-140302). We do not detect X-ray
or radio emission from any of the three sources, despite previous
detections of radio emission from BRI 0021 and 2M0523-14. Steady
and variable Hα emission are detected from 2M0523-14 and BRI
0021, respectively, while no Hα emission is detected from LSR
0602+39. Overall, our survey of nine M8-L5 dwarfs doubles the number
of ultracool dwarfs observed in X-rays, and triples the number of
L dwarfs, providing in addition the deepest limits to date, log(L
X/L bol) lsim -5. With this larger sample we find
the first clear evidence for a substantial reduction in X-ray activity,
by about two orders of magnitude, from mid-M to mid-L dwarfs. We
find that the decline in Hα roughly follows L Hα/L
bol vprop 10-0.4×(SP-6) for SP >= 6, where SP
= 0 for spectral type M0. In the radio band, however, the luminosity
remains relatively unchanged from M0 to L4, leading to a substantial
increase in L rad/L bol. Our survey also
provides the first comprehensive set of simultaneous radio/X-ray/Hα
observations of ultracool dwarfs, and reveals a clear breakdown of the
radio/X-ray correlation beyond spectral type M7, evolving smoothly
from L ν,rad/L X ≈ 10-15.5 to
~10-11.5 Hz-1 over the narrow spectral-type range
M7-M9. This breakdown reflects the substantial reduction in X-ray
activity beyond M7, but its physical origin remains unclear since,
as evidenced by the uniform radio emission, there is no drop in the
field dissipation and particle acceleration efficiency. Based on the
results of our survey, we conclude that a further investigation of
magnetic activity in ultracool dwarfs will benefit from a two-pronged
approach: multi-rotation observations of nearby known active sources
and a snapshot survey of a large sample within ~50 pc to uncover rare
flaring objects.
Title: The Origin of Enhanced Activity in the Suns of M67
Authors: Reiners, A.; Giampapa, M. S.
Bibcode: 2009ApJ...707..852R
Altcode: 2009arXiv0911.0424R
We report the results of the analysis of high-resolution photospheric
line spectra obtained with the UVES instrument on the VLT for a sample
of 15 solar-type stars selected from a recent survey of the distribution
of H and K chromospheric line strengths in the solar-age open cluster
M67. We find upper limits to the projected rotation velocities that
are consistent with solar-like rotation (i.e., v sin ilsim 2-3 km
s-1) for objects with Ca II chromospheric activity within
the range of the contemporary solar cycle. Two solar-type stars in
our sample exhibit chromospheric emission well in excess of even
solar maximum values. In one case, Sanders 1452, we measure a minimum
rotational velocity of v sin i = 4 ± 0.5 km s-1, or over
twice the solar equatorial rotational velocity. The other star with
enhanced activity, Sanders 747, is a spectroscopic binary. We conclude
that high activity in solar-type stars in M67 that exceeds solar
levels is likely due to more rapid rotation rather than an excursion
in solar-like activity cycles to unusually high levels. We estimate
an upper limit of 0.2% for the range of brightness changes occurring
as a result of chromospheric activity in solar-type stars and, by
inference, in the Sun itself. We discuss possible implications for
our understanding of angular momentum evolution in solar-type stars,
and we tentatively attribute the rapid rotation in Sanders 1452 to a
reduced braking efficiency.
Title: Periodic Radio and Hα Emission from the L Dwarf Binary 2MASSW
J0746425+200032: Exploring the Magnetic Field Topology and Radius
Of An L Dwarf
Authors: Berger, E.; Rutledge, R. E.; Phan-Bao, N.; Basri, G.;
Giampapa, M. S.; Gizis, J. E.; Liebert, J.; Martín, E.; Fleming, T. A.
Bibcode: 2009ApJ...695..310B
Altcode: 2008arXiv0809.0001B
We present an 8.5 hr simultaneous radio, X-ray, UV, and optical
observation of the L dwarf binary 2MASSW J0746425+200032. We detect
strong radio emission, dominated by short-duration periodic pulses
at 4.86 GHz with P = 124.32 ± 0.11 min. The stability of the pulse
profiles and arrival times demonstrates that they are due to the
rotational modulation of a B ≈ 1.7 kG magnetic field. A quiescent
nonvariable component is also detected, likely due to emission from
a uniform large-scale field. The Hα emission exhibits identical
periodicity, but unlike the radio pulses it varies sinusoidally
and is offset by exactly 1/4 of a phase. The sinusoidal variations
require chromospheric emission from a large-scale field structure,
with the radio pulses likely emanating from the magnetic poles. While
both light curves can be explained by a rotating misaligned magnetic
field, the 1/4 phase lag rules out a symmetric dipole topology since it
would result in a phase lag of 1/2 (poloidal field) or zero (toroidal
field). We therefore conclude that either (1) the field is dominated
by a quadrupole configuration, which can naturally explain the 1/4
phase lag; or (2) the Hα and/or radio emission regions are not
trivially aligned with the field. Regardless of the field topology,
we use the measured period along with the known rotation velocity (v
sin i ≈ 27 km s-1), and the binary orbital inclination
(i ≈ 142°), to derive a radius for the primary star of 0.078 ±
0.010 R sun. This is the first measurement of the radius of
an L dwarf, and along with a mass of 0.085 ± 0.010 M sun
it provides a constraint on the mass-radius relation below 0.1 M
sun. We find that the radius is about 30% smaller than
expected from theoretical models, even for an age of a few Gyr. The
origin of this discrepancy is either a breakdown of the models at the
bottom of the main sequence, or a significant misalignment between
the rotational and orbital axes.
Title: Photometric variability of solar-type members of the Pleiades
open cluster
Authors: Giampapa, Mark; Sherry, William; Craine, Eric; Tucker, Roy
Bibcode: 2009AIPC.1094..648G
Altcode: 2009csss...15..648G
We present some preliminary results from a program utilizing a
small-aperture transit telescope for the photometric monitoring of
a set of solar-type stars in the young Pleiades cluster at an age of
approximately 100 Myr. The photometry sample includes 12 stars in the
(B-V)0 color range of 0.58-0.76, corresponding to a range
in spectral type of approximately F9 V-G9 V.
Title: The Lifetime of Magnetic Fields in Fully Convective Brown
Dwarfs
Authors: Berger, Edo; Giampapa, Mark; Sherry, William
Bibcode: 2009noao.prop...84B
Altcode:
Until recently theoretical expectation was that magnetic activity would
disappear in fully convective ultracool dwarfs (very low mass stars
and brown dwarfs). We now know that magnetic activity in fact exists,
but the origin, configuration, and lifetime of the field and dynamo
remain largely unconstrained. Numerical simulations cannot presently
accommodate the relevant conditions in the lowest mass objects, and
progress mainly relies on observational clues. Recently, we uncovered
the first examples of periodic and sinusoidal H(alpha) emission from two
ultracool dwarfs (with a period of 2 hours). The H(alpha) emission is
due to a large-scale magnetic hot spot that rigidly rotates with the
stars. Here we propose observations separated by 1 and 2 years from
the original discovery in order to assess the stability timescale of
the magnetic field, a crucial constraint on the nature of the dynamo
mechanism.
Title: The Stars as a Sun: Secular Variations of Cycling and
Non-Cycling Stars
Authors: Hall, Jeffrey C.; Giampapa, Mark S.; Henry, Gregory W.;
Lean, Judith L.; Saar, Steven H.; Soderblom, David R.
Bibcode: 2009astro2010S.111H
Altcode:
No abstract at ADS
Title: Causes of Solar Activity
Authors: Giampapa, Mark S.; Gibson, Sarah; Harvey, J. W.; Hill, Frank;
Norton, Aimee A.; Pevtsov, A.
Bibcode: 2009astro2010S..92G
Altcode:
No abstract at ADS
Title: Asteroseismology: The Next Frontier in Stellar Astrophysics
Authors: Giampapa, Mark S.; Aerts, Conny; Bedding, Tim; Bonanno,
Alfio; Brown, Timothy M.; Christensen-Dalsgaard, Jorgen; Dominik,
Martin; Ge, Jian; Gilliland, Ronald L.; Harvey, J. W.; Hill, Frank;
Kawaler, Steven D.; Kjeldsen, Hans; Kurtz, D. W.; Marcy, Geoffrey W.;
Matthews, Jaymie M.; Monteiro, Mario Joao P. F. G.; Schou, Jesper
Bibcode: 2009astro2010S..91G
Altcode:
No abstract at ADS
Title: A global SOLIS vector spectromagnetograph (VSM) network
Authors: Streander, K. V.; Giampapa, M. S.; Harvey, J. W.; Henney,
C. J.; Norton, A. A.
Bibcode: 2008SPIE.7014E..7PS
Altcode: 2008SPIE.7014E.251S
Understanding the Sun's magnetic field related activity is far
from complete as reflected in the limited ability to make accurate
predictions of solar variability. To advance our understanding of solar
magnetism, the National Solar Observatory (NSO) constructed the Synoptic
Optical Long-term Investigations of the Sun (SOLIS) suite of instruments
to conduct high precision optical measurements of processes on the Sun
whose study requires sustained observations over long time periods. The
Vector Spectromagnetograph (VSM), the principal SOLIS instrument,
has been in operation since 2003 and obtains photospheric vector data,
as well as photospheric and chromospheric longitudinal magnetic field
measurements. Instrument performance is being enhanced by employing
new, high-speed cameras that virtually freeze seeing, thus improving
sensitivity to measure the solar magnetic field configuration. A major
operational goal is to provide real-time and near-real-time data for
forecasting space weather and increase scientific yield from shorter
duration solar space missions and ground-based research projects. The
National Solar Observatory proposes to build two near-duplicates of
the VSM instrument and place them at international sites to form a
three-site global VSM network. Current electronic industry practice
of short lifetime cycles leads to improved performance and reduced
acquisition costs but also to redesign costs and engineering impacts
that must be minimized. The current VSM instrument status and experience
gained from working on the original instrument is presented herein and
used to demonstrate that one can dramatically reduce the estimated
cost and fabrication time required to duplicate and commission two
additional instruments.
Title: Ca II H & K Spectra From The National Solar Observatory
Authors: Livingston, W. C.; Giampapa, M. S.; Harvey, J. W.; Keil,
S. L.; Toussaint, R. M.
Bibcode: 2008AGUSMSP53B..04L
Altcode:
When the Sun is observed as a star (i.e., spatially integrated full
disk) the cores of the chronospheric H and K resonance lines of
singly ionized calcium show the greatest cycle variability (up to
40% peak-to-peak) accessible from the ground. Synoptic archives are
available at monthly intervals from 1974 (Kitt Peak) and for K only
at almost a daily cadence from 1984 (Sacramento Peak). We discuss
these time series and compare them with, for example, sunspot numbers
and magnetic fields. Less frequent are center disk observations in
which the activity cycle is found to be absent, implying the quiet
basal atmosphere is constant and not, say, heated by cycle magnetic
activity. New, near daily, spatially integrated full disk solar data
from the SOLIS Integrated Sunlight Spectrometer (ISS)agree well with
the older work. We now propose to produce calibrated (Houtgast 1970;
Solar Phys 15, 273, high points: 387.5, 395.3, and 402.0 nm), low
dispersion full disk spectra that may be directly compared with that
from solar-type stars.
Title: Simultaneous Multiwavelength Observations of Magnetic Activity
in Ultracool Dwarfs. II. Mixed Trends in VB 10 and LSR 1835+32 and
the Possible Role of Rotation
Authors: Berger, E.; Basri, G.; Gizis, J. E.; Giampapa, M. S.;
Rutledge, R. E.; Liebert, J.; Martín, E.; Fleming, T. A.; Johns-Krull,
C. M.; Phan-Bao, N.; Sherry, W. H.
Bibcode: 2008ApJ...676.1307B
Altcode: 2007arXiv0710.3383B
As part of our ongoing investigation of magnetic activity in
ultracool dwarfs we present simultaneous radio, X-ray, UV, and
optical observations of LSR1835+32 (M8.5), and simultaneous X-ray
and UV observations of VB10 (M8), both with a duration of about 9
hr. LSR1835+32 exhibits persistent radio emission, and Hα variability
on timescales of 0.5-2 hr. The detected UV flux is consistent with
photospheric emission, and no X-ray emission is detected to a deep
limit of LX/Lbollesssim 10-5.7. The
Hα and radio emission are temporally uncorrelated, and the ratio of
radio to X-ray luminosity exceeds the correlation seen in F-M6 stars
by >2 × 104. The lack of radio variability during
four rotations of LSR1835+32 requires a uniform stellar-scale field
of ~10 G, and indicates that the Hα variability is dominated by much
smaller scales, <10% of the chromospheric volume. VB10, on the other
hand, shows correlated flaring and quiescent X-ray and UV emission,
similar to the behavior of early M dwarfs. Delayed and densely sampled
optical spectra exhibit a similar range of variability amplitudes and
timescales. Along with our previous observations of the M8.5 dwarf
TVLM513-46546 we conclude that late M dwarfs exhibit a mix of activity
patterns, which points to a transition in the structure and heating
of the outer atmosphere by large-scale magnetic fields. We find that
rotation may play a role in generating the fields as evidenced by a
tentative correlation between radio activity and rotation velocity. The
X-ray emission, however, shows evidence for supersaturation at vsin
i > 25 km s-1, which could be the result of secondary
effects such as inefficient heating or centrifugal stripping of extended
coronal loops. These effects may underlie the severe violation of the
radio/X-ray correlation in ultracool dwarfs.
Title: Externally Induced or Internally Produced: What is the Source
of the Extreme Magnetic Activity Observed in Very Low Mass Stars?
Authors: Howell, Steve B.; Giampapa, Mark; Harrison, Thomas; Hawley,
Suzanne; Hill, Frank; Honeycutt, Kent; Kafka, Stella; Silvestri,
Nicole; Szkody, Paula; Walter, Fred; West, Andrew
Bibcode: 2008noao.prop...95H
Altcode:
Recent observations of the very low mass donor stars in short
period interacting binaries have revealed the presence of active
chromospheres. Our group has obtained initial spectra for five such
systems to date and found evidence of stellar activity in all of
them, including a brown dwarf mass (0.055 M-sun) donor star. The
Washington group has obtained a SDSS sample of a number of close, but
non-interacting white dwarf + red dwarf binaries and find H(alpha)
emission related to activity. We plan to perform the first detailed
phase-resolved spectroscopic study of the active chromospheres in
this set of rapidly rotating (<0.3 day), low mass (<0.25 M-sun),
fully convective late-type stars and brown dwarfs. Our observational
goals are to study the extent, nature and short-term changes of these
active chromospheres on the low mass stars of close binaries. Is
the extreme activity caused by the low mass star itself or externally
driven by tidal or magnetic forces? The long term goals are to complete
a large enough sample (~10 systems) to provide statistically useful
measurements and to use the extended time allocation to obtain long term
``coverage" spectra of each system to monitor, measure, and understand
the solar-type cycles likely to be present.
Title: Simultaneous Multiwavelength Observations of Magnetic
Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5
Dwarf TVLM 513-46546
Authors: Berger, E.; Gizis, J. E.; Giampapa, M. S.; Rutledge, R. E.;
Liebert, J.; Martín, E.; Basri, G.; Fleming, T. A.; Johns-Krull,
C. M.; Phan-Bao, N.; Sherry, W. H.
Bibcode: 2008ApJ...673.1080B
Altcode: 2007arXiv0708.1511B
We present the first simultaneous radio, X-ray, ultraviolet, and
optical spectroscopic observations of the M8.5 dwarf TVLM 513-46546,
with a duration of 9 hr. These observations are part of a program to
study the origin of magnetic activity in ultracool dwarfs, and its
impact on chromospheric and coronal emission. Here we detect steady
quiescent radio emission superposed with multiple short-duration, highly
polarized flares; there is no evidence for periodic bursts previously
reported for this object, indicating their transient nature. We also
detect soft X-ray emission, with LX/Lbol ≈
10-5.1, the faintest to date for any object later than M5,
and a possible X-ray flare. TVLM 513-46546 continues the trend of severe
violation of the radio/X-ray correlation in ultracool dwarfs, by nearly
4 orders of magnitude. From the optical spectroscopy we find that the
Balmer line luminosity exceeds the X-ray luminosity by a factor of a
few, ruling out chromospheric heating by coronal X-ray emission. More
importantly, we detect sinusoidal Hα and Hβ equivalent width light
curves with a period of 2 hr, matching the rotation period of TVLM
513-46546. This behavior points to a corotating chromospheric hot spot
or an extended magnetic structure, with a covering fraction of about
50%. This feature may be transitory based on the apparent decline in
light-curve peak during the four observed maxima. From the radio data
we infer a large-scale and steady magnetic field of ~102
G. A large-scale field is also required by the sinusoidal Balmer
line emission. The radio flares, on the other hand, are produced in a
component of the field with a strength of ~3 kG and a likely multipolar
configuration. The overall lack of correlation between the various
activity indicators suggests that the short-duration radio flares do
not have a strong influence on the chromosphere and corona, and that
the chromospheric emission is not the result of coronal heating.
Title: The First MOTESS-GNAT Variable-Star Survey
Authors: Kraus, Adam L.; Craine, Eric R.; Giampapa, Mark S.; Scharlach,
Werner W. G.; Tucker, Roy A.
Bibcode: 2007AJ....134.1488K
Altcode:
We present the results of the first MOTESS-GNAT variable-star survey,
a deep, wide-field variability survey conducted over 2 yr with a total
sky coverage of 300 deg2. In this survey, we identified
26,042 variable-star candidates with magnitudes R = 13-19, including
5271 that are periodic at the 99% confidence level. We recovered 59
out of 68 members of the General Catalogue of Variable Stars (GCVS)
that are in this brightness range. We discuss the implications for
completeness and accuracy for both this survey and the GCVS; the
implied completeness for distinctly classifiable variable stars in
our survey is ~85%-90%. We also discuss some of the caveats of our
survey results. We conclude that this instrument design is ideal for an
inexpensive, longitudinally distributed telescope network that could
be used to study faint or rare transient phenomena in a previously
unexplored regime of parameter space.
Title: Variability of Young Solar-Type Stars in the Pleiades Open
Cluster
Authors: Giampapa, Mark S.; Sherry, W. S.; Craine, E. R.; Tucker, R.
Bibcode: 2007AAS...210.2301G
Altcode: 2007BAAS...39..128G
We present a preliminary report on a program of photometric
monitoring of the solar-type stars in the young Pleiades open
cluster. Specifically, we report on the results for 37 nights of
observation in our survey region that includes 12 solar-type Pleiades
members. The goal of the program is to characterize the short- and
long-term brightness variability of young solar-type stars during
the epoch of the formation and early evolution of young planetary
atmospheres. This work is supported in part by a joint grant from
the NASA Astrobiology Institute to the University of Arizona and the
NOAO/NSO. The NSO is operated by AURA under a cooperative agreement
with the NSF.
Title: Sun-as-a-Star Spectrum Variations 1974-2006
Authors: Livingston, W.; Wallace, L.; White, O. R.; Giampapa, M. S.
Bibcode: 2007ApJ...657.1137L
Altcode: 2006astro.ph.12554L
We have observed selected Fraunhofer lines, both integrated over
the full disk and for a small circular region near the center of the
solar disk, on 1215 days over the past 30 years. Our full disk results
for the chromosphere show that Ca II K 3933 Å nicely tracks the 11
yr magnetic cycle based on sunspot number, with a peak amplitude in
central intensity of ~37%. The wavelength of the midline core absorption
feature, called K3, referenced to nearby photospheric Fe, displays
an activity cycle variation with an amplitude of 3 mÅ (6 mÅ center
disk). Other chromospheric lines, such as He I 10830 Å, Ca II 8542 Å,
Hα, and the CN 3883 Å bandhead, track Ca II K intensity with lower
relative amplitudes. In the low photosphere, temperature-sensitive C I
5380 Å appears constant in intensity to 0.2%. In the high photosphere,
the cores of strong Fe I lines, Na D1 and D2, and the Mg I b lines,
present a puzzling signal, perhaps indicating a role for the 22 yr Hale
cycle. Solar minimum around 1985 was clearly seen, but the following
minimum in 1996 was missing. Our center disk results show that both
Ca II K and C I 5380 Å intensities are constant, indicating that the
basal quiet atmosphere is unaffected by cycle magnetism within our
observational error. A lower limit to the Ca II K central intensity
atmosphere is 0.040. This possibly represents conditions as they were
during the Maunder minimum. Converted to the Mount Wilson S-index
(H+K index), the Sun center disk is at the lower activity limit for
solar-type stars. An appendix provides instructions for URL access to
both the raw and reduced data.
Title: A Survey of Chromospheric Activity in the Solar-Type Stars
in the Open Cluster M67
Authors: Giampapa, Mark S.; Hall, Jeffrey C.; Radick, Richard R.;
Baliunas, Sallie L.
Bibcode: 2006ApJ...651..444G
Altcode: 2006astro.ph..7313G
We present the results of a spectroscopic survey of the Ca II H and K
core strengths in a sample of 60 solar-type stars that are members of
the solar-age and solar-metallicity open cluster M67. We adopt the HK
index, defined as the summed H+K core strengths in 1 Å bandpasses
centered on the H and K lines, respectively, as a measure of the
chromospheric activity that is present. We compare the distribution of
mean HK index values for the M67 solar-type stars with the variation
of this index as measured for the Sun during the contemporary solar
cycle. We find that the stellar distribution in our HK index is broader
than that for the solar cycle. Approximately 17% of the M67 Sun-like
stars exhibit average HK indices that are less than solar minimum. About
7%-12% are characterized by relatively high activity in excess of solar
maximum values, while 72%-80% of the solar analogs exhibit Ca II H+K
strengths within the range of the modern solar cycle. The ranges given
reflect uncertainties in the most representative value of the maximum
in the HK index to adopt for the solar cycle variations observed
during the period AD 1976-2004. Thus, ~20%-30% of our homogeneous
sample of Sun-like stars have mean chromospheric H+K strengths that
are outside the range of the contemporary solar cycle. Any cycle-like
variability that is present in the M67 solar-type stars appears to be
characterized by periods greater than ~6 yr. Finally, we estimate a mean
chromospheric age for M67 in the range of 3.8-4.3 Gyr. The results
presented herein are based on data obtained at the WIYN telescope and
at the McMath-Pierce Solar Telescope. The WIYN Observatory is a joint
facility of the University of Wisconsin-Madison, Indiana University,
Yale University, and the National Optical Astronomy Observatory. The
McMath-Pierce Solar Telescope Facility is operated by the National
Solar Observatory for the National Science Foundation. This paper is
WIYN Open Cluster Study XXVIII in the series.
Title: Age-Activity Correlation at Young Stellar Ages
Authors: Giampapa, Mark; Sherry, William
Bibcode: 2006noao.prop..321G
Altcode:
We propose to utilize WIYN/Hydra to conduct a survey of the Ca II H
& K resonance line profiles in the solar-type stars in the young (~
100 Myr) Pleiades cluster. The results of this program will represent
the first comprehensive survey of chromospheric Ca II strengths and line
shapes in the young solar-type members of the Pleiades. We will use
the measured chromospheric Ca II H& K line strengths to establish
the empirical calibration between Ca II chromospheric emission and
stellar age at young ages ~ 100 Myr. We will also directly compare the
range of Ca II emission encountered in the young Pleiades sun-like
stars to the range in variation of Ca II core emission seen in the
contemporary Sun during the course of the modern solar cycle as well as
to the results of our prior WIYN/Hydra survey of the solar-type stars
in the solar-age cluster, M67. Finally, the results of the Pleiades
survey will be compared to that obtained in our proposed Ca II survey
of the solar-type stars in the intermediate- age cluster NGC 752 (1.8
Gyr). The combined results of these programs will yield an accurate
calibration of the age-activity correlation, including the dispersion
in this correlation due to the range of activity in sun-like stars at a
given age, extending from cluster ages ~ 0.1 Gyr to ~ 4.5 Gyr. Finally,
the intercomparison of the survey results for the Pleiades, NGC 752,
M67, and the Sun, will yield quantitative insight on the evolution of
the ranges in cycle-related chromospheric activity from ~ 100 Myr to
solar age.
Title: Collaborative Research Opportunities with the Global Network
of Astronomical Telescopes (GNAT): Variable Star Research
Authors: Craine, E. R.; Tucker, R. A.; Kraus, A. L.; Culver, R. B.;
Giampapa, M. S.
Bibcode: 2006SASS...25..111C
Altcode:
The Global Network of Astronomical Telescopes (GNAT) is modeling
its observing system on a network of scan-mode telescopes following
the designs of the Moving Object and Transient Event Search System
(MOTESS), implemented at Goodricke-Pigott Observatory in Tucson,
Arizona. GNAT has developed a comprehensive data pipeline for extracting
photometric measurements of all of the stars observed in each of the
discrete declination bands observed with the scan-mode system. This
enormous volume of observations is leading to an aggressive program
of discovery of objects that are in many cases of great interest in
terms of follow-up observations. GNAT is reaching out to both the
professional and amateur astronomy communities to identify potential
collaborators who are interested in participating in a wide variety
of follow-up research programs.
Title: Structure and Availability of the MOTESS-GNAT Variable
Star Surveys
Authors: Craine, E. R.; Kraus, A. L.; Giampapa, M. S.; Scharlach,
W. W. G.; Tucker, R. A.
Bibcode: 2005AAS...20712212C
Altcode: 2005BAAS...37.1365C
The Moving Object Transient Event Search System (MOTESS) has resulted
in hardware and data streams that are being used as prototypes for the
Global Network of Astronomical Telescopes (GNAT) photometric monitoring
systems. Multiple telescopes are operated in scan mode to collect CCD
imagery of the sky, which is subsequently processed through a prototype
GNAT data reduction pipeline. This process leads to large arrays of
differential time series photometry for all of the detectable stars in
the survey band. The first of several planned surveys is now complete,
resulting in the MOTESS-GNAT MG1 variable star catalog. The MG1 survey
is at a declination of 03d18m with a width of 48-arcmin. The survey
has been reduced to observations of approximately 1.6 million stars
with a detection limit of R=19; the MG1 variable star catalog contains
26,042 variable star candidates with R = 13-19, including 5,271 which
are periodic at the 99% confidence level. In this presentation we
describe the structure of the catalog and its components and provide
details on accessing these data. We conclude with a status report on
subsequent MOTESS GNAT variable star survey programs.
Title: Chromospheric Activity at Intermediate Ages
Authors: Giampapa, Mark; Stauffer, John; Deliyannis, Constantine;
Sherry, William
Bibcode: 2005noao.prop...84G
Altcode:
The calibration of the empirical relation between Ca II chromospheric
strength and stellar age between 0.6 Gyr (Hyades) and 4.0 - 5 Gyr
(M67 and the Sun) relies on the uncertain determination of ages
for individual field stars in the solar neighborhood. We therefore
propose to obtain WIYN/Hydra spectra of ~ 100 solar-type dwarf stars
in the 1.8 Gyr old open cluster, NGC 752. This cluster contains a
sample of solar-type dwarfs that is homogeneous in age and chemical
composition. Furthermore, NGC 752 is the nearest-and hence brightest-
cluster at an age ~ 2 Gyr. The results will yield an improved
calibration of the age-activity relation at intermediate ages. In
addition, we will determine if the chromospheric Ca II strengths for the
solar-type stars in NGC 752 lie in the so-called "Vaughan-Preston Gap''-
an apparent discontinuity in the Ca II H& K strength-(B-V) diagram
found for field stars in the solar neighborhood. Our data will yield
insight on the two proposed origins for the gap, namely, that it is a
result of two different modes of dynamo action or that it is actually
an artifact of a discontinuity in the local star formation rate. This
is a resubmission of a previously approved proposal that was allocated
two nights in 2004 November. The time was lost to instrument problems
(Hydra gripper malfunctions) and weather. No usable data were obtained.
Title: The Magnetic Properties of an L Dwarf Derived from Simultaneous
Radio, X-Ray, and Hα Observations
Authors: Berger, E.; Rutledge, R. E.; Reid, I. N.; Bildsten, L.;
Gizis, J. E.; Liebert, J.; Martín, E.; Basri, G.; Jayawardhana, R.;
Brandeker, A.; Fleming, T. A.; Johns-Krull, C. M.; Giampapa, M. S.;
Hawley, S. L.; Schmitt, J. H. M. M.
Bibcode: 2005ApJ...627..960B
Altcode: 2005astro.ph..2384B
We present the first simultaneous, multiwavelength observations of
an L dwarf, the L3.5 candidate brown dwarf 2MASS J00361617+1821104,
conducted with the Very Large Array, the Chandra X-Ray Observatory,
and the Kitt Peak 4 m telescope. We detect strongly variable
and periodic radio emission (P=3 hr) with a fraction of about
60% circular polarization. No X-ray emission is detected to a
limit of LX/Lbol<~2×10-5,
several hundred times below the saturation level observed in early
M dwarfs. Similarly, we do not detect Hα emission to a limit of
LHα/Lbol<~2×10-7, the deepest for
any L dwarf observed to date. The ratio of radio to X-ray luminosity
is at least 4 orders of magnitude in excess of that observed in a
wide range of active stars (including M dwarfs), providing the first
direct confirmation that late-M and L dwarfs violate the radio/X-ray
correlation. The radio emission is due to gyrosynchrotron radiation
in a large-scale magnetic field of about 175 G, which is maintained
on timescales longer than 3 yr. The detected 3 hr period may be due
to (1) the orbital motion of a companion at a separation of about 5
stellar radii, similar to the configuration of RS CVn systems, (2)
an equatorial rotation velocity of about 37 km s-1 and an
anchored, long-lived magnetic field, or (3) periodic release of magnetic
stresses in the form of weak flares. In the case of orbital motion, the
magnetic activity may be induced by the companion, possibly explaining
the unusual pattern of activity and the long-lived signal. We conclude
that fully convective stars can maintain a large-scale and stable
magnetic field, but the lack of X-ray and Hα emission indicates that
the atmospheric conditions are markedly different than in early-type
stars and even M dwarfs. Similar observations are therefore invaluable
for probing both the internal and external structure of low-mass stars
and substellar objects, and for providing constraints on dynamo models.
Title: The Sun, Solar Analogs and the Climate
Authors: Haigh, Joanna D.; Lockwood, Michael; Giampapa, Mark S.;
Rüedi, Isabelle; Güdel, Manuel; Schmutz, Werner
Bibcode: 2005ssac.conf.....H
Altcode: 2005SAAS...34.....H
This book presents the lecture notes of the 34th Saas-Fee Advanced
Course "The Sun, Solar Analogs and the Climate" given by leading
scientists in the field. Emphasis is on the observed variability of
the Sun and the present understanding of the variability's origin
as well as its impact on the Earth's climate. The solar variability
is then studied in the broader context of solar-type stars, allowing
for better understanding of the solar-activity cycle and the magnetic
activity in general. This book provides an accessible and up-to-date
introduction to the field for graduate students and serves as a modern
source of reference for active researchers in this field.
Title: Stellar analogs of solar activity: the Sun in a stellar context
Authors: Giampapa, Mark S.
Bibcode: 2005ssac.conf..307G
Altcode: 2005SAAS...34..307G
Contents: 1. Introduction. 2. Stellar cycles. 3. Brightness changes
in solar-type stars. 4. Activity in solar analogs. 5. Stellar surface
inhomogeneities. 6. The coronae of solar analogs, low mass stars,
and brown dwarfs. 7. The early Sun. 8. Stellar activity and extrasolar
planets.
Title: Photometric Precisions in the Prototype MOTESS-GNAT Surveys
Authors: Giampapa, M. S.; Kraus, A. L.; Craine, E. R.; Sherry, W. H.;
Tucker, R. A.
Bibcode: 2004AAS...205.1403G
Altcode: 2004BAAS...36.1360G
The MG1 and MG2 MOTESS-GNAT surveys were conducted as 48-arcmin
wide scan-mode CCD imaging surveys of selected areas of the sky in
an efficient and highly successful asteroid search program. The
images were reduced photometrically as a test of a prototype of
a longitudinally distributed network of photometric scan-mode
telescopes for the Global Network of Astronomical Telescopes,
Inc. (GNAT). The MG1 and MG2 surveys, which are unfiltered, are
centered at declinations +03o 18 m 20
s (MG1) and +02o 05 m 00 s (MG2),
respectively. Although the source data were originally intended for
astrometric use, they nonetheless have yielded a great deal of useful
stellar brightness data. As such, they serve as excellent test-beds
for both future GNAT photometry surveys and as valuable sources of
new scientific discovery and analysis. To assist in defining some of
the possible serendipitous programs using the MG1 and MG2 Surveys, we
present in this poster an analysis of the photometric precisions that
are attained in these data sets. This effort is supported in part
by the National Aeronautics and Space Administration through the NASA
Astrobiology Institute under Cooperative Agreement No. CAN-02-OSS-02
issued through the Office of Space Science. The NSO and the NOAO are
operated by AURA for the NSF.
Title: A Summary of Known Variable Stars in the MOTESS-GNAT MG1
Survey and the Status of Future Surveys
Authors: Craine, E. R.; Scharlach, W. G. G.; Kraus, A. L.; Giampapa,
M. S.; Tucker, R. A.
Bibcode: 2004AAS...205.1402C
Altcode: 2004BAAS...36Q1360C
The MG1 Survey is a two year unfiltered, scan-mode CCD imaging survey
of a 48-arcmin wide band centered at declination +03° 18m 20s. The
MG1 survey has yielded open channel photometry of about 2.1 million
stars, of which some 35,000 were identified as likely variable star
candidates. Of those 35,000 only about 200 are cataloged in the
GCVS. In this poster we summarize the statistics of the detections
of known variable stars which were made using the MG1 data. The
results will be used to improve the methods and techniques that will
be employed in future GNAT scan-mode surveys. We also indicate how
these data can be used to develop useful student projects. Six new
scan-mode telescopes are under construction for the Global Network of
Astronomical Telescopes, Inc. (GNAT), effective October 2004. Three of
these telescopes are expected to become operational during the winter of
2004-05 and will be sited in Southern Arizona as a coordinated triplet
of photometric CCD imaging instruments. Another existing telescope will
be operational before December 2004. All four of these telescopes will
be used primarily to gather low amplitude variability data on Solar-type
stars in the Pleiades and M67, respectively, in a study of parameters
that control the ambient radiative and particle environments of the
habitable zones around such stars. Because the telescopes will operate
nightly for several years there will be a huge collateral accumulation
of photometric data from 24-hour long strips of the sky approximately
48 arcmin wide. Nightly bandpass photometry will be obtained for an
estimated 4-6 million stars, hence yielding a large archive of data
for a wide variety of interesting research projects. We would like to
attract collaborators comprised of students, professional and amateur
astronomers. The next two surveys to be run are the G1 Survey, at a
declination of approximately +24° (one telescope and a single filter),
and the G2 survey, at a declination of approximately +12° (three
telescopes and two filters). The exact declinations will be chosen to
maximize the number of solar-type stars in the respective fields. We
outline in this poster several of the possible research projects that
offer opportunities for collaboration. This material is based
upon work supported in part by the National Aeronautics and Space
Administration through the NASA Astrobiology Institute under Cooperative
Agreement No. CAN-02-OSS-02 issued through the Office of Space Science.
Title: High Amplitude Variable Stars in the MOTESS-GNAT MG1 Survey
Authors: Culver, R. B.; Craine, E. R.; Kraus, A. L.; Giampapa, M. S.;
Tucker, R. A.
Bibcode: 2004AAS...205.1404C
Altcode: 2004BAAS...36R1360C
The Moving Object and Transient Event Search System (MOTESS) is
a triplet of scan-mode telescopes located in Tucson, Arizona, and
devised originally for high efficiency, unfiltered astrometric asteroid
searches. Recently, the hardware system has been adopted by the Global
Network of Astronomical Telescopes, Inc. (GNAT), as a prototype for a
much expanded network of longitudinally distributed telescopes operating
primarily as a high efficiency, high time frequency photometric survey
system. The original MOTESS asteroid survey was operated for just over
two years at a declination of +03° 18m 20s. We developed a photometric
data reduction pipeline to process the extensive archive of deep,
unfiltered digital images. As a result, we now have two years of open
channel photometry for about 2.1 million stars, of which some 35,000
are identified as likely variable star candidates. Of those 35,000,
only ∼ 200 are cataloged in the General Catalogue of Variable Stars
(GCVS). Our primary purpose has been to use this survey, which we call
the MG1 Survey, as a proof-of-principle test-bed of our data reduction
system. In the process, our work has serendipitously yielded an enormous
amount of useful data, including tens of thousands of new variable
star discoveries. In this presentation, we discuss specifically our
efforts to characterize the highest amplitude variables in the MG1
Variable Star Catalog. This work has been supported in part by
Walker & Company.
Title: Extragalactic Variable Objects in GNAT Image Archives
Authors: Craine, E. R.; Culver, R. B.; Giampapa, M. S.; Kraus, A. L.;
Tucker, R. A.
Bibcode: 2004AAS...204.4018C
Altcode: 2004BAAS...36..719C
The Global Network of Astronomical Telescopes (GNAT) has used the
image output of its prototype, the Moving Object and Transient Event
Search System (MOTESS), to create a photometric database of two years
observations of over 2.5 million celestial point sources. These
observations have been made through the full 24-hr range of Right
Ascension at a fixed declination of +3d18m, with a field of view
of 48 arcmin. The integration time in each field is 191 sec allowing
detection of objects as faint as 20 mag. This catalog has been searched
for variable objects at the 6-sigma level, resulting in a list of about
36,000 newly discovered variables. The majority of these objects are
stars of a wide range of types, however, some of the variables are
expected to be extragalactic objects. We report progress on a program
to identify known extragalactic sources in the observed region of the
sky and to develop light curves for these objects using the archived
GNAT images. We appreciate the support of Walker & Company
for this research program.
Title: Early Results from SOLIS
Authors: Harvey, J.; Giampapa, M.; Henney, C.; Keller, C.; Jones, H.
Bibcode: 2004AAS...204.3701H
Altcode: 2004BAAS...36..708H
SOLIS (Synoptic Optical Long-Term Investigations of the Sun)
is a project that is replacing antiquated synoptic observing
equipment at the National Solar Observatory. SOLIS consists of
a suite of three instruments on an equatorial mount that will be
installed on Kitt Peak in April 2004. The major SOLIS instrument
is a vector spectromagnetograph (VSM) that maps magnetic fields
across the full solar disk using a slit spectrograph and one arc
sec pixels. Limited daily observations started at a temporary site
in August, 2003 and include line-of-sight component magnetograms in
the photosphere and chromosphere and, for the first time, full-disk
vector magnetograms. At a medium scan speed ( ∼ 10 minutes for the
full disk) noise is less than 1 Mx/cm2. This low noise,
combined with negligible instrumental polarization and well resolved
spectral line profiles, yields moderate resolution magnetograms of
unprecedented quality. Observations show magnetic flux nearly everywhere
in the photosphere from the disk center to the solar limb. Weak,
intranetwork fields are now routinely observed and show a tendency to
be of opposite polarity to the stronger surrounding fields. Diffuse
fields surround decaying active regions and appear to be distinct from
canopy fields. Vector magnetograms easily show the radial orientation
of network fields, and the diffuse component surrounding decaying active
regions. Near the disk center, the transverse magnetic fields of network
elements change on a time scale of minutes. Detailed quantitative
calibration of the observations is in progress. Good results have been
obtained from the other SOLIS instruments: a full-disk filter imager at
several narrow wavelengths and a double-pass grating spectrograph that
provides high-accuracy line spectra of integrated sunlight. SOLIS data
are freely available via the Internet and users are invited to submit
observing time requests for special observations. The National Solar
Observatory is operated by AURA, Inc. under a cooperative agreement
with the National Science Foundation. Additional support for the
development of SOLIS from NASA and ONR is gratefully acknowledged.
Title: GNAT/MOTESS Data Pipeline and Variable Star Catalog
Authors: Kraus, A. L.; Craine, E. R.; Giampapa, M. S.; Tucker, R. A.
Bibcode: 2003AAS...203.0903K
Altcode: 2003BAAS...35.1218K
The Global Network of Astronomical Telescopes (GNAT) is testing a
prototype system of multiple scan-mode telescopes, the Moving Object
and Transient Event Search System (MOTESS), at the Goodricke-Pigott
Observatory in Tucson, Arizona. A primary goal of GNAT has been
to develop a data pipeline for reduction of sky survey CCD images
to extract photometric data for all of the stars detected in the
images. This effort is now complete and we describe here the structure
of the data reduction system as it has been applied to the first two
years of observations. The system relies on IRAF at its core, augmented
by several custom routines for handling of the raw photometry. To
date, the system has been applied to a single declination of scanning,
+3d18m20s, and has resulted in systematic photometric observations of
about 1.5-2.5 million stars. Processing of these data has yielded a
list of about 35,000 stars which are convincingly variable. All but
about 200 of these stars are new variable discoveries. Funding for
this project was provided by an NSF REU grant and an anonymous donor.
Title: Known Variable Stars in GNAT/MOTESS Data
Authors: Craine, E. R.; Kraus, A. L.; Giampapa, M. S.; Tucker, R. A.;
Scharlach, W.
Bibcode: 2003AAS...203.0904C
Altcode: 2003BAAS...35.1218C
The Global Network of Astronomical Telescopes (GNAT) is using as
a hardware prototype a system of multiple scan mode telescopes of
the Moving Object and Transient Event Search System (MOTESS) of the
Goodricke-Pigott Observatory in Tucson, Arizona. During the first two
years of operation of the system, approximately 35,000 variable stars
were observed of which approximately 200 were previously known. In this
paper we provide details of the GNAT observations of the previously
known variable stars, compare these results with previously published
data, and use the observational results to help characterize the
observational system. Funding for this project was provided by an
anonymous donor.
Title: First Results from SOLIS
Authors: Harvey, J.; Giampapa, M.; Henney, C.; Jones, H.; Keller, C.
Bibcode: 2003AGUFMSH42B0545H
Altcode:
SOLIS (Synoptic Optical Long-term Investigations of the Sun) is a
project to replace antiquated synoptic observing equipment at the
National Solar Observatory. SOLIS includes a suite of three instruments
on an equatorial mount originally installed at a site in Tucson and will
be moved to Kitt Peak before the end of 2003. The major SOLIS instrument
is a vector spectromagnetograph that maps magnetic fields across the
full solar disk using a slit spectrograph and one arc sec pixels. Daily
observations include several line-of-sight component magnetograms in the
photosphere and chromosphere and, for the first time, full-disk vector
magnetograms. At a medium scan speed ( ∼10 minutes for the full disk)
noise is less than 1 Mx/cm2. This low noise, combined with
negligible instrumental polarization and well resolved spectral line
profiles, yields moderate resolution magnetograms of unprecedented
quality. Sample observations show magnetic flux nearly everywhere
in the photosphere from the disk center to the solar limb. The flux
is organized in large scale patterns that heretofore had been visible
only in strong flux elements or after substantial spatial smearing. Good
results have been obtained from the other SOLIS instruments: a full-disk
filter imager at several narrow wavelengths and a grating spectrograph
that provides high-accuracy line spectra of integrated sunlight. SOLIS
data are freely available via the Internet and users may submit
observing time requests for special observations. The National Solar
Observatory is operated by AURA, Inc. under a cooperative agreement
with the National Science Foundation. Additional support for the
development of SOLIS from NASA and ONR is gratefully acknowledged.
Title: The Suns of M67
Authors: Giampapa, M.
Bibcode: 2003csss...12...91G
Altcode:
We discuss the methodology and some preliminary results of a survey
of the chromspheric Ca II H & K line strengths in a sample of
solar-type stars in the galactic open cluster M67. We compare the
distribution of H&K line strength among the solar counterparts in
this cluster with that seen in the contemporary Sun during the course
of its 11-year cycle.
Title: The Quiescent Corona of VB 10
Authors: Fleming, Thomas A.; Giampapa, Mark S.; Garza, David
Bibcode: 2003ApJ...594..982F
Altcode:
We present results from a Chandra ACIS observation of the M8 dwarf
star VB 10, a star near the hydrogen-burning mass limit. Until now,
VB 10 has only been detected to flare at X-ray wavelengths. We can now
report that nonflare, ``quiescent,'' X-ray emission has been detected
with a luminosity, LX=(2.4+/-0.05)×1025 ergs
s-1 and log(LX/Lbol)=-4.9. This is
consistent with the previous ROSAT nondetections of quiescent emission
from VB 10. We discuss the implications of this discovery for the
nature of coronae in ultracool dwarfs.
Title: Chromospheric Activity in Solar-Type Stars
Authors: Giampapa, M. S.; Hall, J. C.; Radick, R. R.; Baliunas, S. L.
Bibcode: 2003SPD....34.0710G
Altcode: 2003BAAS...35..821G
We present an update on the results of a survey of chromospheric
activity in the solar-age and solar-metallicity open cluster, M67. The
objective of the survey is to gain insight on the potential range of
amplitudes of the solar cycle through observations of solar analogs
that are presumably at random phases in their cycles of magnetic
activity. We find that there is a significant overlap of the levels
of Ca II H and K emission in the sun-like stars in M67 with the
range of activity seen in the contemporary solar cycle. However,
there are also stars that exhibit levels of activity outside of this
range, including stars that are "super-solar" in their Ca II H and
K emission. The implications of these results will be discussed. The data presented in this investigation were obtained with the
WIYN 3.5-m telescope on Kitt Peak. The WIYN Observatory is a joint
facility of the University of Wisconsin-Madison, Indiana University,
Yale University, and the NOAO. The NSO and the NOAO are operated by
AURA for the National Science Foundation.
Title: SOLIS: an innovative suite of synoptic instruments
Authors: Keller, Christoph U.; Harvey, John W.; Giampapa, Mark S.
Bibcode: 2003SPIE.4853..194K
Altcode:
SOLIS (Synoptic Optical Long-term Investigations of the Sun) is
a suite of three innovative instruments under construction that
will greatly improve ground-based synoptic solar observations. The
Vector Spectromagnetograph (VSM) is a compact, high-throughput
vector-polarimeter with an active secondary mirror, an actively
controlled grating spectrograph, and two high-speed cameras with
silicon-on-CMOS-multiplexer hybrid focal plane arrays. It will measure
the magnetic field strength and direction over the full solar disk
within 15 minutes. The Full-Disk Patrol (FDP) takes full-disk solar
intensity and Doppler images in various spectral lines and in the
continuum at a high cadence through liquid-crystal tuned birefringent
filters. The Integrated Sunlight Spectrometer (ISS) uses a fiber-fed
spectrograph to measure minute changes of the Sun-as-a-star in
many spectral lines. A high degree of automation and remote control
provides fast user access to data and flexible interaction with the
data-collection process. SOLIS is currently in the final assembly
phase and will become operational early in 2003.
Title: Emission line variability in a newly discovered 2MASS star
Authors: Giampapa, Mark; Liebert, James; Reid, Neil; Cruz, Kelle
Bibcode: 2003noao.prop..234G
Altcode:
We propose to utilize the HET/HRS to obtain spectra of the newly
discovered, low-mass star 2M075223.9+161215. The primary objectives
are to search for (1) variability in the strength and position of
the H(alpha) emission line profile and (2) determine if the Li I
(lambda)6707 feature is present to confirm whether this enigmatic object
is a field brown dwarf. Previous HET/HRS spectra of this object were
obtained on the night of UT 01 April 2002. However, the S/N in the Li
region was insufficient to arrive at a definitive conclusion concerning
the presence of lithium in 2M075223.9. The additional spectra will
be co-added to the previous spectra in order to examine the complex
(lambda)6707 region in more detail. Of equal importance, the detection
of either short- or long- term variability will yield insight on the
origin of the emission line mechanism. The two competing models for the
origin of the strong emission line spectrum involve either strongly
enhanced chromospheric activity driven by magnetic dynamo action or
accretion in a low mass binary system.
Title: Implementation of the GNAT Network Design and System
Configurations
Authors: Culver, R. B.; Craine, E. R.; Giampapa, M. S.; Tucker, R. A.;
Kraus, A. L.
Bibcode: 2002AAS...20112202C
Altcode: 2002BAAS...34.1304C
Following the successful deployment of the three-telescope Moving Object
Transient Event Search System (MOTESS), which is a model prototype of
the Global Network of Astronomical Telescopes (GNAT) system, we have
begun design of a geographically distributed network of 48 automated,
scan-mode telescopes. During the course of the design effort it has
become apparent that such a network offers great versatility by virtue
of a large number of possible telescope and network configurations. This
versatility allows us to modify such parameters as system limiting
magnitude, image signal-to-noise ratios, time and frequency of field
observation, and field of view, among others. In this paper we consider
some of the most interesting system configurations discussed to date,
provide a summary of the resultant system parameters and outline the
nature of the science which can be most efficiently done with each
configuration. We also discuss practical experience gained to date
which scales the nature of the effort involved in reconfiguring the
network to accommodate various types of observations.
Title: A Prototype Data Reduction Pipeline for the GNAT System
Authors: Kraus, A. L.; Giampapa, M. S.; Tucker, R. A.; Craine, E. R.
Bibcode: 2002AAS...20112203K
Altcode: 2002BAAS...34Q1304K
The Moving Object and Transient Event Search System (MOTESS) has
been operating for the past year as a prototype for the Global
Network of Astronomical Telescopes (GNAT). During this time, it has
produced approximately 200 nights of observations on a 48-arcminute
band of declination near the celestial equator. We have developed an
automated data reduction pipeline that performs aperture photometry
and differential photometry on the nightly data and then matches
the results to a standard catalog based on the United States Naval
Observatory catalog. Objects that match the catalog are added to the
data library, while unmatched objects are placed into a separate catalog
for analysis. One data analysis technique we have been exploring is to
search the new object catalog for transient events such as supernovae
and cataclysmic variables. We have also been optimizing the pipeline
so that it can be scaled as additional instruments are added to the
GNAT network.
Title: The Coronae of Low Mass Stars and Brown Dwarfs
Authors: Giampapa, M. S.; Fleming, T. A.
Bibcode: 2002ASPC..277..247G
Altcode: 2002sccx.conf..247G
No abstract at ADS
Title: Stellar Variability Observations with MOTESS, a GNAT System
Prototype
Authors: Craine, E. R.; Giampapa, M. S.; Kraus, A. L.; Tucker, R. A.;
Scharlach, W.
Bibcode: 2002AAS...20112201C
Altcode: 2002BAAS...34.1303C
The Moving Object Transient Event Search System (MOTESS) is a three
telescope, scan-mode system developed initially for near-Earth asteroid
detection, and since adopted as a prototype for a Global Network of
Astronomical Telescopes (GNAT) system. In this paper we summarize
photometric characteristics of the prototype telescope network and
discuss initial results of measurements of stellar variability
using data obtained during the first full year of operation of
the system. In the initial data set, 173 known variable stars were
observed, of which 19 exceeded the useful upper brightness limits of
the images. The remaining stars ranged down to about 17.5 mag with the
brightness distribution peak at about 14.5 mag. The most frequently
occurring types are Mira variables (52), eclipsing systems (33),
and semi-regulars (25); with the remainder distributed over a wide
range of variable types. We give examples of data for known variables,
discuss the likely discovery of new variables and outline a strategy
for using these data in screening stellar observations suggestive of
possible planetary transits.
Title: Stellar Chromospheres and the Sun
Authors: Giampapa, M.
Bibcode: 2002AAS...200.5301G
Altcode: 2002BAAS...34..729G
Observations combined with the development of semi-empirical models
show that stellar chromospheres and the solar chromosphere share many
of the same features. Nevertheless, are homogeneous, single-component
models of stellar chromospheres adequate representations of their
atmospheres in the light of observations that clearly indicate the
multi-component natures of both the solar and stellar chromospheres? Is
the distinction between "active" and "quiet" chromosphere stars mainly
due to the fractional area coverage of otherwise identical magnetic
active regions on their surfaces, or can the distinction be attributed
primarily to differing heating rates in a relatively homogeneous
atmosphere? Can single-component, static models successfully account
for the levels of emission in the dominant radiative coolants in
stellar chromospheres? How does the radiative energy balance between
the chromosphere and corona change with effective temperature and
gravity in the cool half of the H-R diagram? Is there evidence for
"cool chromospheres" in main sequence stars? These issues will be
addressed in an effort to compare and contrast stellar chromospheres
with that of the Sun. The National Solar Observatory is operated for
the National Science Foundation by the Association of Universities
for Research in Astronomy.
Title: Moving Object and Transient Event Search System (MOTESS):
An Evaluation of Photometric Properties/Low Amplitude Stellar
Variation Measurements
Authors: Craine, E. R.; Tucker, R. A.; Giampapa, M. S.; Scharlach,
W. W. G.
Bibcode: 2002AAS...200.6412C
Altcode: 2002BAAS...34R.750C
The Moving Object and Transient Event Search System (MOTESS) is being
expanded from its original task as an automated, moving object search
system (astrometric application) to add the transient event detection
capability (photometric application). In anticipation of this activity,
photometric reductions of MOTESS images have been systematically
undertaken to characterize the system in terms of photometric precision
during a night, light curve stability from night to night and long term
time series photometry. We discuss the data pipeline, characteristics
of the system images, and photometric precision as a function of
brightness of the object observed. We also present example light curves
of known variable objects as a demonstration of the capabilities of the
system. In this context we summarize key science programs of the Global
Network of Automatic Telescopes (GNAT) which are being undertaken with
the MOTESS facility, including extrasolar planetary transit searches,
supernovae monitoring and other stellar variability programs.
Title: Solar-stellar connections
Authors: Giampapa, M.
Bibcode: 2002cosp...34E.638G
Altcode: 2002cosp.meetE.638G
The observation of the solar cycle with the telescope extends over a few
centuries while its study at high precisions with modern instrumentation
is only a few decades old. In fact, the measurement of solar luminosity
variability at the level of 0.1%, and the correlation of brightness
changes with the solar cycle of magnetic activity, is less than two
decades old. Thus, our knowledge of the full range of solar variability
that may occur is extremely limited. We believe that a substantially
larger brightness variation occurred during the Maunder minimum from
AD 1645 to 1715. But, because individual solar cycles are different
in form, amplitude and length, and because accurate solar data have
been available only for the most recent cycles, there is no direct
way of understanding long-term solar variability. The observation of
solar-type stars, however, can overcome the temporal confines of the
solar data-base, thereby revealing the potential range and nature of
solar variability over time scales that are simply not accessible
to the modern data-base of only a few decades. I will discuss the
empirical properties of magnetic field-related activity variations in
solar-type stars and the associated luminosity variability, and compare
these properties to that of the Sun. In this way, we can gain insight
on the full range of variability that the Sun can potentially exhibit
over long time scales. The National Solar Observatory is operated for
the National Science Foundation by the Association of Universities
for Research in Astronomy.
Title: Limits on Line Bisector Variability for Stars with Extrasolar
Planets
Authors: Povich, M. S.; Giampapa, M. S.; Valenti, J. A.; Tilleman,
T.; Barden, S.; Deming, D.; Livingston, W. C.; Pilachowski, C.
Bibcode: 2001AJ....121.1136P
Altcode:
We present an analysis of high-resolution synoptic spectra of ten F-
and G-type stars, seven of which exhibit periodic radial velocity
variations due to the presence of one or more substellar companions. We
searched for subtle periodic variations in photospheric line asymmetry,
as characterized by line bisectors. In principle, periodic variations
in line asymmetry observed at lower spectral resolution could mimic the
radial velocity signature of a companion, but we find no significant
evidence of such behavior in our data. Observations were obtained
from 1998 March to 1999 February using the National Solar Observatory
(NSO) 1.52 m McMath-Pierce Solar Telescope Facility on Kitt Peak in
conjunction with the solar-stellar spectrograph, achieving a resolving
power of 1.2×105. To characterize line asymmetry, we
first measured line bisectors for the unblended Fe I photospheric
line at 625.26 nm. To improve sensitivity to small fluctuations, we
then combined points in each bisector to form a velocity displacement
with respect to the line core. We searched for periodic variations in
this displacement, finding no substantial difference between stars with
substellar companions and those without reported companions. We find no
correlation between bisector velocity displacement and the known orbital
phase of substellar companions around our target stars. Simulations of
a periodic signal with noise levels that mimic our measurement errors
suggest that we can exclude bisector variations with amplitudes greater
than about 20 m s-1. These results support the conclusion
that extrasolar planets best explain the observed periodic variations
in radial velocity.
Title: Photometric Monitoring of M67 with the GNAT 0.5-m Telescope
Authors: Roberts, J. H.; Craine, E. R.; Giampapa, M. S.
Bibcode: 2000AAS...197.4004R
Altcode: 2000BAAS...32.1459R
A long-term program of nightly observations of the solar-age and
solar-metallicity, galactic open cluster, M67, was initiated with
the prototype GNAT 0.5-m automated telescope in conjunction with a
SITe 512 x 512 thermoelectrically cooled CCD. The broad objective
of this program is to investigate the utilization of the GNAT
0.5-m telescope for long-term projects requiring high-precision
photometry. The specific, dual applications include (1) the monitoring
of low-amplitude luminosity variations in solar-type stars and (2)
the detection of extrasolar planets via photometric transits. These
science goals require that precisions of at least a few millimags be
consistently achieved and maintained. As a prelude to these kinds of
programs, we obtained a nightly time-series of automated photometric
observations of M67 on 24 nights during a two month period from
abbreviated JD51604-JD51679. Unfiltered photometry with an integration
time of 180 sec per CCD frame was performed. A total of 1,260 frames
were obtained. For those frames characterized by high signal-to-noise
ratios, precisions of 4-5 mmag were attained on both an intranight
and internight basis. No variations that could be attributed to a
photometric transit event were detected. Further preliminary results
from this program will be discussed. JR gratefully acknowledges the
support of the NSF through the NSO/REU program. The NSO is operated
by AURA under cooperative agreement with the NSF.
Title: Red Dwarfs/Flare Stars
Authors: Giampapa, M.
Bibcode: 2000eaa..bookE1866G
Altcode:
The red dwarf stars are main-sequence stars characterized by masses
in the approximate range from 0.51M⊙ to 0.08M⊙. The upper mass
limit corresponds to a spectral type of M0 V and the lower limit is
the critical mass for the onset of nuclear burning in the central cores
of stars with chemical abundances similar to the Sun. Below the range
of approximately (0.074-0.08)M⊙ is the realm of substellar...
Title: The Coronae of Inactive Low-Mass Dwarfs
Authors: Kashyap, V. L.; Giampapa, M.; Drake, J. J.
Bibcode: 2000HEAD....5.4217K
Altcode: 2000BAAS...32.1257K
We analyze deep EUVE/SW data of two inactive low-mass dM stars GJ 205
and GJ 411. The spectra do not show any spectral lines that can be
used for temperature or density diagnostics. We therefore model these
spectra with different types of Differential Emission Measure (DEM)
distributions and show that the peak temperature in the corona is
akin to the Quiet Sun. We also derive constraints on the metallicity
of the corona of GJ 205, and suggest that compared to its photosphere
the corona appears to be metal deficient.
Title: A Survey of Activity in the Solar-Type Stars in M67
Authors: Giampapa, M. S.; Radick, R. R.; Hall, J. C.; Baliunas, S. L.
Bibcode: 2000SPD....3102120G
Altcode: 2000BAAS...32..832G
We present an update on a long-term study of the solar-type stars in
the solar-age and solar-metallicity open cluster, M67. The primary
objective of this program is to gain insight on the possible range of
solar chromospheric activity and the associated, potential long-term
variability of the Sun through the observation of stellar analogs of
the Sun. Spectra in the Ca II H & K line region of over 100 stars
in M67, including 76 `solar-type' stars (with unreddened colors in
the range +0.60 <= B-V <= +0.76) and 21 `solar-twins' (+0.63
<= B-V <= +0.67), were obtained with the 3.5-m WIYN telescope
on Kitt Peak in conjunction with the Hydra multi-fiber positioner
to perform multi-object spectroscopy over a 1 degree field. We find
that the distribution of chromospheric H&K line strengths in
the solar-type stars is broader than the distribution of H&K line
emission recorded in modern observations of the Sun, suggesting that the
potential excursion in the amplitude of the solar cycle is greater than
what we have seen so far in the contemporary record. Approximately 30%
of the solar-type stars in M67 exhibit levels of activity that are
outside the present envelope of solar activity. We interpret this to
mean that the Sun can be in a state of magnetic activity---either
exceptional quiescence similar to the Maunder-minimum episode or
enhanced activity---about 30% of the time. The authors gratefully
acknowledge both the NOAO Telescope Allocation Committee and the
WIYN Queue Program for their support of this investigation. The WIYN
Observatory is a joint facility of the University of Wisconsin-Madison,
Indiana University, Yale University, and the NOAO. The NSO and NOAO are
operated by AURA, Inc., under cooperative agreement with the National
Science Foundation.
Title: An X-Ray Flare Detected on the M8 Dwarf VB 10
Authors: Fleming, Thomas A.; Giampapa, Mark S.; Schmitt, Jürgen
H. M. M.
Bibcode: 2000ApJ...533..372F
Altcode: 2000astro.ph..2065F
We have detected an X-ray flare on the very low mass star VB 10
(GL 752 B; M8V) using the ROSAT High Resolution Imager. VB 10 is
the latest type (lowest mass) main-sequence star known to exhibit
coronal activity. X-rays were detected from the star during a single
1.1 ks segment of an observation that lasted 22 ks in total. The
energy released by this flare is on the order of 1027 ergs
s-1. This is at least 2 orders of magnitude greater than the
quiescent X-ray luminosity of VB 10, which has yet to be measured. This
X-ray flare is very similar in nature to the far-ultraviolet flare
that was observed by Linsky et al. using the Goddard High Resolution
Spectrograph onboard the Hubble Space Telescope. We discuss reasons
for the extreme difference between the flare and quiescent X-ray
luminosities, including the possibility that VB 10 has no quiescent
(106 K) coronal plasma at all.
Title: Line Bisector Variations in Stars with Extrasolar Planets
Authors: Povich, M. S.; Giampapa, M. S.; Valenti, J. A.; Tilleman, T.
Bibcode: 1999AAS...19510901P
Altcode: 1999BAAS...31.1533P
We present the results from a high-resolution, synoptic spectroscopic
program of observation of ten F- and G-type stars, seven of which
exhibit periodic radial velocity variations attributed to the
presence of one or more substellar companions. The observations
were obtained from 1998 March to 1999 February using the 1.52-m NSO
McMath-Pierce Solar Telescope Facility on Kitt Peak in conjunction
with the solar-stellar spectrograph. The spectra were acquired with a
resolving power of approximately 1.2 x 105. The line bisector
was then derived from unblended photospheric features. In particular,
we define the velocity displacement of the spectral line bisector
and determine the bisector amplitude for the Fe I absorption line
at 625.26 nm in order to search for variations in the line asymmetry
over time. Such variations could mimic Doppler shifts in observations
with lower spectral resolution. Examination of the bisector velocity
displacement over the time span of our observations reveals no
substantial difference between stars with planetary companions and
those without reported companions. We find no correlation between the
bisector variations and the orbital phase of a substellar companion
in any of our target stars. Simulations of a periodic signal with
noise levels based on our measurement errors suggest that we can
exclude bisector variations with amplitudes greater than about 20 m
s-1. These results support the conclusion that extrasolar
planets best explain the observed periodic variations in radial
velocity. This work was supported by a NASA grant to the NOAO under
the auspices of the Origins of Solar Systems Program. MP gratefully
acknowledges support from the NSF-sponsored Research Experience for
Undergraduates (REU) program at the NOAO. The NOAO is operated by AURA,
Inc., under a cooperative agreement with the NSF.
Title: The Suns of M67
Authors: Giampapa, M. S.; Radick, R. R.; Baliunas, S. L.
Bibcode: 1999AAS...194.9212G
Altcode: 1999BAAS...31..988G
The results of our program to survey the level of chromospheric Ca II
H&K emission in ~ 100 solar analogs in the galactic cluster M67 are
discussed. This cluster is an appropriate target of observation for
the study of solar-type stars since it is approximately the same age
and has the same chemical composition as the Sun. The key objective
of our program is to investigate the nature of solar variability. In
particular, we interpret the range of Ca II H&K emission observed
in the sun-like stars in M67 as indicative of the possible amplitudes
of cycle-related variability that can occur in the Sun itself. In
this way, we can efficiently gain insights on the potential long-term
variability of the Sun that would not otherwise be possible with the
modern solar Ca II synoptic database of just a few decades. This is
especially important given that the amplitude of long-term solar
(and stellar) variations in brightness are correlated with cycle
variations in chromospheric emission. In view of the fact that the
Sun is the engine that drives climate on the Earth, any variation
in the solar ``constant" must be taken into account in the study of
the long-term behavior of the global climate. The NOAO is operated
by the Association of Universities for Research in Astronomy, Inc.,
under cooperative agreement with the National Science Foundation.
Title: Cycles and Long-Term Variability in Solar-Type Stars
Authors: Giampapa, Mark S.; Radick, Richard R.; Hall, Jeffrey C.;
Baliunas, Sallie L.
Bibcode: 1999noao.prop..226G
Altcode:
We propose a long-term extension of our current WIYN/Hydra program to
study chromospheric activity cycles in the `Suns of M67.' Our results
thus far have revealed that the distribution of activity among the
solar- type stars in M67 is broader than what would be expected from a
comparison with the solar cycle. The next step is to determine whether
our results arise from the cyclic modulation of activity alone or
if the relative amplitudes of cycles in solar-type stars and the Sun
are actually similar and the spread in M67 is due to differences in
the mean level of activity. Only a long-term monitoring program of
regular observations can address these questions. The results of this
program are expected to reveal all the potential modes and amplitudes
of magnetic cycles in sun-like stars and, by inference, in the Sun
itself, with important implications for dynamo models and models of
global climate change.
Title: Differential Photometry Using the GNAT 0. 5 m Prototype
Authors: Taylor, J. M.; Craine, E. R.; Giampapa, M. S.
Bibcode: 1999ASPC..189..238T
Altcode: 1999pcp..conf..238T
No abstract at ADS
Title: X-Ray Activity in the Open Cluster IC 4665
Authors: Giampapa, Mark S.; Prosser, Charles F.; Fleming, Thomas A.
Bibcode: 1998ApJ...501..624G
Altcode:
We present the results of a joint ROSAT High Resolution Imager (HRI)
and optical investigation of the open cluster IC 4665. The ROSAT data
contains detections for 28 stellar sources in the field, including 22
cluster members and candidate members spanning the color range -0.18
<= (B-V)0 <= 1.63 (~B3-M3). Upper limits are given for
the remaining members (or candidate members) in the HRI field. Keck
HIRES spectra have been obtained that yield radial and rotational
velocity measures, respectively, for faint, low-mass candidate members
located within the field of the ROSAT HRI observation. In addition,
photometry of possible optical counterparts to previously uncataloged
X-ray sources in the HRI field is presented. The trends in
X-ray properties with B-V color in IC 4665 are found to be quite
similar to that for other, more nearby young clusters such as the
Pleiades and α Persei. In particular a maximum in normalized X-ray
luminosity of log (LX/Lbol) ~= -3 is observed,
beginning in the color range of (B-V)0 = 0.7-0.8. This
is similar to the corresponding color range among Pleiades members,
in agreement with the earlier estimate by Prosser & Giampapa
that the age of IC 4665 is similar to the age of the Pleiades. The
correlation of rotation and X-ray emission levels is consistent with
that in other young clusters. Among the high-mass stars in IC
4665, five B stars are detected as X-ray sources. Of these, one is
a spectroscopic binary while the remaining objects are apparently
single stars. The level of intrinsic X-ray emission observed in the
rapidly rotating (v sin i > 200 km s-1), single B stars
is consistent with an origin due to shock heating of the ambient
medium by radiatively driven, rotationally enhanced winds. On the
basis of these observations and the results for other clusters, we
argue that observed levels of X-ray emission in high-mass stars of log
(LX/Lbol) > -6.0 are likely due to intrinsic
emission associated with the B star itself rather than emission from
a late-type secondary. Finally, our results suggest that the initial
angular momentum distributions and the subsequent evolution of rotation,
LX, and (LX/Lbol) occur in practically
identical fashions in clusters with ages <~100 Myr.
Title: A Joint X-ray and Optical Investigation of the Young Open
Cluster IC 4665
Authors: Giampapa, M. S.; Prosser, C. F.; Fleming, T. A.
Bibcode: 1998ASPC..154.2106G
Altcode: 1998csss...10.2106G
We summarize the results of a joint ROSAT High Resolution Imager (HRI)
and optical investigation of the open cluster IC 4665. The ROSAT
data-set contains detections for 28 stellar sources in the field,
including 22 cluster members and candidate members spanning the color
range -0.18 <= (B-V)_o \<= +1.63 (~B3 - M3). Keck HIRES spectra
have been obtained that yield radial and rotational velocity measures,
respectively, for faint, low mass candidate members located within
the field of the ROSAT HRI observation.
Title: A Survey of Chromospheric Activity in the Solar-Type Stars
in M67
Authors: Giampapa, Mark S.
Bibcode: 1998saco.conf...65G
Altcode:
No abstract at ADS
Title: The Procyon campaign: Observations from Kitt Peak
Authors: Pilachowski, C. A.; Barden, S.; Hill, F.; Harvey, J. W.;
Keller, C. U.; Giampapa, M. S.
Bibcode: 1998IAUS..185..319P
Altcode:
Time series spectra of the F5IV star Procyon (alpha CMi) were obtained
at the Kitt Peak National Observatory during a 35-night observing run
in January-February 1997. The observations were obtained as part of an
international collaboration to detect and study acoustic oscillations
in solar-type stars. Spectra covered the wavelength range from 4000
to 5300 AA , with a resolving power of approximately 3500 (1.3 AA
resolution). The sampling rate was one observation per minute, and
the typical S/N ratio per observation is in excess of 1000. At the
time of writing, we have obtained over 10,000 spectra. The spectra
will be analyzed to identify any periodic signals due to acoustic
oscillations in Procyon. In addition to measuring the equivalent widths
of the three Balmer lines (Kjeldsen et al. 1995) covered by our spectra
(Hβ, Hγ, and Hdelta) we will also examine the spectra for variations
in the average metal line strength. Preliminary power spectra will
be presented.
Title: Asteroseismology from equivalent widths: a test of the sun
Authors: Keller, C. U.; Harvey, J. W.; Barden, S. C.; Giampapa, M. S.;
Hill, F.; Pilachowski, C. A.
Bibcode: 1998IAUS..185..375K
Altcode:
Kjeldsen et al. (1995) reported a probable detection of solar-like,
low-amplitude, p-mode oscillations of eta Bootes using equivalent
width measurements from low-resolution spectra of the hydrogen Balmer
lines. We tested the usefulness of this technique using observations of
the Sun in integrated light. Despite the very high signal-to-noise ratio
of the data stretching over six continuous days, no solar oscillation
signal was found so far in the equivalent width of Hβ. Spatially
resolved observations of the Hβ equivalent width at solar disk center
reveal that the oscillation signal is suppressed in the wings of Hβ
as compared to the continuum. Extrapolation of the oscillation signal
seen in the spatially resolved data suggests an amplitude of about
1ppm for integrated light measurements, which is about a factor of
5 lower than expected from simple theoretical arguments. We explore
other methods to deduce an oscillation signal from all spectral lines
simultaneously. cont has: Deng, L. et al.; auths fixed below
Title: Rotational Velocities and Chromospheric/Coronal Activity of
Low-Mass Stars in the Young Open Clusters IC 2391 and IC 2602
Authors: Stauffer, John R.; Hartmann, Lee W.; Prosser, Charles F.;
Randich, Sofia; Balachandran, Suchitra; Patten, Brian M.; Simon,
Theodore; Giampapa, Mark
Bibcode: 1997ApJ...479..776S
Altcode:
We have obtained high-resolution, moderate signal-to-noise ratio spectra
for approximately 80 candidate low-mass members of the nearby, very
young open clusters IC 2391 and IC 2602. Most of the stars observed
are confirmed as cluster members based on a combination of photometric
and spectroscopic criteria. We provide radial velocities, rotational
velocities, and Hα equivalent widths for these stars. From comparison
to theoretical pre-main-sequence (PMS) evolutionary isochrones
from D'Antona and Mazzitelli, we derive an estimated age of the two
clusters of ~25 Myr. By contrast, the usually quoted upper main-sequence
turnoff age for the clusters is ~35 Myr. We do not believe that this
provides evidence for noncoeval star formation within these clusters,
but rather that the best age estimate for them given the uncertainties
is ~30 +/- 5 Myr. In principle, the scatter of stars about the PMS
isochrone provides a measure of the age spread among the low-mass
stars in these clusters; however, with the data presently available,
we are able to derive only a relatively uninteresting upper limit for
an age spread of order 20 Myr. We compare the rotational velocity
distribution for IC 2391/2602 to that observed for the Pleiades. For
the G dwarfs in the IC clusters, we resolve rotation in all but one of
the probable cluster members, and thus except for inclination effects,
our data provide the complete distribution of rotational velocities for
solar mass stars on their arrival on the ZAMS. The projected rotational
velocities (v sin i) of the G dwarfs in the two IC clusters span the
range from ~8 to ~200 km s-1. Comparison of the distribution
of rotational velocities for the G dwarfs of the Pleiades and the IC
clusters indicates that both the slow and the rapid rotators lose of
order half their angular momentum during the first ~35 Myr on the main
sequence if they rotate as solid bodies. The low-mass stars in
these two clusters exhibit a similar correlation between rotation and
coronal activity as is found in several other young open clusters. That
is, there is a large spread in coronal activity for stars with v sin
i < 25 km s-1, where we assume there is an intrinsic
link between increasing rotation and increasing activity superimposed
upon which are a variety of observational and physical mechanisms that
act to smear out this relation; above v sin i ~ 25 km s-1,
all of the low-mass stars have log (LX/Lbol) ~
-3.0, the canonical ``saturation'' limit. Our measurements of the Hα
equivalent widths are consistent with a similar relationship holding
for chromospheric activity. One and possibly two of our spectra for M
dwarf members of the IC clusters show broad wings for the Hα profile,
which we attribute to a flare event or to microflares. Since spectra
of a small sample of late-type M dwarfs in the Pleiades also showed
similarly broad Hα wings, this suggests that flare frequencies for
very young M dwarfs may be quite high.
Title: Preface
Authors: Jokipii, J. R.; Sonett, C. P.; Giampapa, M. S.
Bibcode: 1997cwh..confD..11J
Altcode: 2006mslp.confD..11J
No abstract at ADS
Title: Cosmic Winds and the Heliosphere
Authors: Jokipii, Jack R.; Sonett, Charles P.; Giampapa, Mark S.
Bibcode: 1997cwh..book.....J
Altcode:
No abstract at ADS
Title: Cosmic winds and the heliosphere.
Authors: Jokipii, J. R.; Sonett, C. P.; Giampapa, M. S.
Bibcode: 1997cwh..conf.....J
Altcode:
No abstract at ADS
Title: The Coronae of Low-Mass Dwarf Stars
Authors: Giampapa, M. S.; Rosner, R.; Kashyap, V.; Fleming, T. A.;
Schmitt, J. H. M. M.; Bookbinder, J. A.
Bibcode: 1996ApJ...463..707G
Altcode:
We report the results of our analysis of pointed X-ray observations
of nearby dMe and dM stars using the position sensitive proportional
counter (PSPC) on board the ROSA T satellite (Roentgensatellit). In the
cases of those M dwarf stars where PSPC pulse-height distributions of
sufficient quality for spectral fitting were obtained, we derive key
coronal plasma parameters in order to investigate stellar coronal
structure in more detail. In particular, we utilize temperatures
and emission measures inferred for one or more distinct components
as constraints for the development of semiempirical magnetic loop
models as representations of the coronae of low-mass stars. The
consistency of these static models as adequate descriptions of the
coronae of M dwarfs is then examined. We find that the coronae of
low-mass dwarfs consist of two distinct thermal components: a "soft"
component with T ∼ 2-4 x 106 K and a "hard" component
with T ∼ 107 K. We find that the pulse- height spectra
are systematically fitted better with "depleted" abundances compared to
solar; the high- temperature emission component on dMe stars appears to
contribute a systematically larger fraction of the total flux than the
corresponding component in dM stars; and the high-temperature emission
component on dMe stars is responsible for most of the observed variation
in the count rate. We have modeled the observed temperature
components with hydrostatic coronal loop models, and find that: the
low-temperature components can be modeled with loops of small size (l
≪ R*) and high pressure (Po ); and the high-temperature
components require solutions with either small filling factors (
0.1), large loops (1 > R*), and high base pressure (P0
≳ P0sun), or very small filling factors
(∼0.1), small loops (1 ≳ R*), and very high
pressure (P0 ≫ P0sun)). Based on
these observational and model results, we conclude that coronal emission
in dMe stars can be interpreted as arising from quiescent active regions
(a quiescent, low-temperature component) and compact flaring structures
(variable, high- temperature component). Our conclusion that the
coronal geometry for low-mass dwarf stars is dominated by a combination
of relatively compact, quiescent loop configurations and an unstable
flaring component has implications for both stellar dynamo theory and
for our understanding of stellar angular momentum evolution. With regard
to rotation in late-type stars, which has a direct bearing on dynamo
action, we know from observations that the lowest mass stars spin down
(via magnetic braking) more slowly than the more nearly solar-type
stars. The compact loops we find for the low-temperature component
suggests a natural explanation for the observed mass dependence of
angular momentum evolution in late-type, main-sequence stars.
Title: Asteroseismology via equivalent widths - tests on Procyon,
Eta Bootis, and Alpha Trianguli.
Authors: Harvey, J. W.; Pilachowski, C.; Barden, S.; Giampapa, M.;
Keller, C. U.; Hill, F.
Bibcode: 1996BAAS...28..917H
Altcode:
No abstract at ADS
Title: Asteroseismology via Equivalent Widths -- Tests on Procyon,
Eta Bootes, and Alpha Triangulum
Authors: Harvey, J.; Pilachowski, C.; Barden, S.; Giampapa, M.;
Keller, C.; Hill, F.
Bibcode: 1996AAS...188.5903H
Altcode: 1996BAAS...28S.917H
Recently, Kjeldsen et al. reported a probable detection of solar-like
low-amplitude p-mode oscillations of Eta Bootes using equivalent
width measurements from low-resolution spectra of the H Balmer
lines. This technique has the potential to provide stellar oscillation
measurements good enough to allow the asteroseismic inference of stellar
structure. Here we report on the preliminary analysis of data from three
observing runs with the Kitt Peak Coude Feed and 2.1-m telescope in
November 1995 (Alpha Triangulum), February 1996 (Procyon), and March
1996 (Eta Bootes). These runs are being used to develop observing
and data reduction techniques, such as a synchronized timing system
to maintain evenly spaced temporal samples, a continuous unshuttered
CCD readout to increase the duty cycle of the observations, and a
simulation of the probability of a detection as a function of observing
run length. We observed the region around the H beta, gamma, and delta
lines with a spectral dispersion of about 0.4 Angstroms per pixel,
extracted equivalent widths, and performed time series analysis. The
temporal spectrum of Alpha Triangulum contains a significant peak near
the theoretical prediction, however, we do not yet know the origin of
this peak.
Title: The Future of High Resolution Spectroscopy at Kitt Peak
National Observatory
Authors: Barden, S.; Pilachowski, C.; Giampapa, M.
Bibcode: 1996AAS...188.3902B
Altcode: 1996BAAS...28..882B
Many astronomical studies benefit from observations of celestial
objects at high spectral resolving power. Some of the facilities and
instrumentation for high dispersion spectroscopy, however, are coming
under the threat of closure or are reaching their limit of usefulness
due to the small aperture of the telescopes that feed them. Many of
the new facilities either don't have sufficient spectral resolution
or are located at observatories with very restricted access or
scheduling. KPNO has convened a committee to 1) examine the scientific
needs of high resolution spectroscopy, 2) evaluate the facilities which
are available to the general astronomical community, and 3) develop
and prioritize instrumentation goals for future KPNO facilities. The
Committee will also consider policies for scheduling KPNO telescopes
to maximize scientific return from high resolution spectrographs,
including possible changes to the TAC process and visitor and queue
observing modes. We desire community input and will formulate our
report and recommendations over the next seven months.
Title: Advances in solar-stellar physics: optical and infrared studies
Authors: Giampapa, M. S.
Bibcode: 1996ASPC..109...11G
Altcode: 1996csss....9...11G
No abstract at ADS
Title: Coronal Structwre in M Dwarf Stars
Authors: Giampapa, M. S.; Rosner, R.; Kashyap, V.; Fleming, T. A.;
Schmitt, J. H. M. M.; Bookbinder, J. A.
Bibcode: 1996mpsa.conf...81G
Altcode: 1996IAUCo.153...81G
No abstract at ADS
Title: The chromospheric activity of the many "suns" in M67.
Authors: Giampapa, M. S.; Baliunas, S. L.; Radick, R. R.
Bibcode: 1996BAAS...28.1197G
Altcode:
No abstract at ADS
Title: Stellar Activity at the End of the Main Sequence: GHRS
Observations of the M8 Ve Star VB 10
Authors: Linsky, Jeffrey L.; Wood, Brian E.; Brown, Alexander;
Giampapa, Mark S.; Ambruster, Carol
Bibcode: 1995ApJ...455..670L
Altcode:
We present Goddard High Resolution Spectrograph observations of the M8
Ve star VB 10 (= Gl 752B), located very near the end of the stellar
main sequence, and its dM3.5 binary companion Gl 752A. These coeval
stars provide a test bed for studying whether the outer atmospheres of
stars respond to changes in internal structure as stars become fully
convective near mass 0.3 Msun (about spectral type MS), where
the nature of the stellar magnetic dynamo presumably changes, and near
the transition from red to brown dwarfs near mass 0.08 Msun
(about spectral type M9), when hydrogen burning ceases at the end of
the main sequence. We obtain upper limits for the quiescent emission
of VB 10 but observe a transition region spectrum during a large flare,
which indicates that some type of magnetic dynamo must be present. Two
indirect lines of evidence scaling from the observed X-ray emission and
scaling from a time-resolved flare on AD Le suggest that the fraction of
the stellar bolometric luminosity that heats the transition region of
VB 10 outside of obvious flares is comparable to, or larger than, that
for Gl 752A. This suggests an increase in the magnetic heating rates,
as measured by Lline/Lbol ratios, across the
radiative/convective core boundary and as stars approach the red/brown
dwarf boundary. These results provide new constraints for dynamo models
and models of coronal and transition-region heating in late-type stars.
Title: The Photometric Method for the Detection of Extrasolar Planets
Authors: Giampapa, M. S.; Craine, E. R.; Hott, D. A.
Bibcode: 1995AAS...187.7017G
Altcode: 1995BAAS...27.1382G
We offer further perspectives on the application of the photometric
technique to the search for extrasolar planets. The principal
obstacles to this approach include (1) the ambiguous interpretation
of the photometric signature of a possible transit event arising
from the potential for confusion with stellar activity, and (2) the
observational intensity of the search technique. We emphasize that
the former issue can be addressed through multiband observations
combined with considerations of the characteristic time scales of
forms of stellar activity compared to that of a transit event. In the
case of the latter concern, the advent of modern, automated telescope
technologies offers the realistic prospect of meeting the demanding
observational requirements of this approach. We find that joint
visual and near infrared observations are necessary to immediately
distinguish between, for example, a planetary transit and a cool spot
on the stellar surface. However, these observations by themselves
do not appear sufficient to distinguish between a brown dwarf and a
Jovian-size planetary companion of a dwarf M star. In such cases,
other complementary observations will be necessary. We develop a
computer simulation to estimate the average number of transits per
year that would be presented for a stellar sample characterized by
realistic properties in terms of spectral type distribution, effective
temperatures, masses, and radii. A simple thermal model is adopted
to estimate star-planet separations. The simulation suggests that the
frequency of transit events will be dominated by M dwarf systems. This
is due to the large number of these objects combined with the relative
proximity to these cool stars within which planetary formation can
occur according to current models.
Title: Comments on the photometric method for the detection of
extrasolar planets.
Authors: Giampapa, Mark S.; Craine, Eric R.; Hott, Douglas A.
Bibcode: 1995Icar..118..199G
Altcode:
We offer further perspectives on the application of the photometric
technique to the search for extrasolar planets. The principal
obstacles to this approach include (1) the ambiguous interpretation
of the photometric signature of a possible transit event arising
from the potential for confusion with stellar activity and (2) the
observational intensity of the search technique. We emphasize that the
former issue can be addressed through multiband observations combined
with consideration of the characteristic time scales of forms of
stellar activity compared to the time scale of a transit event. In the
case of the latter concern, the advent of modern, automated telescope
technologies offers the realistic prospect of meeting the demanding
observational requirements of this approach. We find that joint
visual and near infrared observations are necessary to immediately
distinguish between, for example, a planetary transit and a cool spot
on the stellar surface. However, these observations by themselves
do not appear sufficient to distinguish between a brown dwarf and
a jovian-size planetary companion of a dwarf M star. In such cases,
other complementary observations will be necessary. We developed a
computer simulation to estimate the average number of transits per
year that would be presented for a stellar sample characterized by
realistic properties in terms of spectral type distribution, effective
temperatures, masses, and radii. A simple thermal model is adopted
to estimate star-planet separations. The simulation suggests that the
frequency of transit events will be dominated by M dwarf systems. This
is due to the large number of these objects combined with the relative
proximity to these cool stars within which planetary formation can
occur according to current models.
Title: The X-Ray View of the Low-Mass Stars in the Solar Neighborhood
Authors: Schmitt, Juergen H. M. M.; Fleming, Thomas A.; Giampapa,
Mark S.
Bibcode: 1995ApJ...450..392S
Altcode:
We present the results of a complete and sensitive X-ray survey
of all known stars of spectral type K and M in the immediate solar
vicinity with distances less than 7 pc. The X-ray data were obtained
primarily from the ROSA T all-sky survey (RASS); those program stars
not detected in the RASS data were subsequently studied with the ROSAT
pointed observation program. These new X-ray observations resulted
in a detection rate of almost 94% for all K and M stars within 6
pc around the Sun, and 87% for K and M dwarfs within 7 pc around
the Sun. The resulting X-ray luminosity distribution function can be
well described by a log-normal distribution; the largest and smallest
X-ray luminosities from our sample stars differ by almost four orders
of magnitude. We show the existence of a correlation between total
emitted X-ray luminosity and spectral hardness, such that more luminous
objects tend to have larger spectral hardness, thus implying higher
coronal temperatures. A comparison with Einstein data shows the lack of
significant variability in excess of a factor of 2 in our sample stars.
Title: Correlations of Coronal X-Ray Emission with Activity, Mass,
and Age of the Nearby K and M Dwarfs
Authors: Fleming, Thomas A.; Schmitt, Juergen H. M. M.; Giampapa,
Mark S.
Bibcode: 1995ApJ...450..401F
Altcode:
Using the ROSAT telescope, we have detected X-ray emission from 87%
of all known K and M dwarfs within 7 pc of the Sun. Analysis of this
volume-limited sample of K and M dwarfs reveals no evidence for a
decrease in coronal heating efficiency (as measured by Lx/L
bol) among the lowest mass, presumably fully convective,
late-M dwarfs. Furthermore, our results indicate that those stars which
exhibit little chromospheric activity (i.e., dM and dK stars) do indeed
have cooler and weaker coronae than the more active dMe stars. While
we also see a correlation between coronal temperature/strength and
metallicity (and presumably age), no such correlation is seen with
kinematic class. The latter result leads us to suggest that kinematic
class is a poor age indicator for the nearby stars.
Title: Helium in the Spectrum of the Sun and of Solar-Type Stars
Authors: Andretta, V.; Giampapa, M. S.; Jones, H. P.
Bibcode: 1995IrAJ...22..177A
Altcode:
We present results from detailed non-LTE radiative transfer calculations
of the He I spectrum in the Sun. Using an extended grid of model
chromospheres, we explore the relative importance of, respectively,
the coronal XUV illumination and the thermal structure of the lower
transition region. With reference to the He I lambda 587.6 and lambda
1083.0 triplet lines, we point out some implications for the study of
activity in solar-type stars.
Title: The Coronae of Quiescent M Dwarf Stars
Authors: Giampapa, Mark S.
Bibcode: 1995euve.prop....6G
Altcode:
We propose to obtain SW and MW EUVE spectrometer observations of
the quiescent M dwarf GL 205 (dM1). This non-dMe star in the solar
neighborhood is an X-ray source as seen with the ROSAT PSPC. The
infrared colors of GL 205 suggest that its photospheric abundances are
solar-like. Our proposed EUVE data will be used to determine if the
coronal structure is characterized by only two dominant components,
as suggested by our analysis of X-ray data for dM stars, or if dwarf M
coronae actually consist of multiple components with a distribution of
maximum loop temperatures. This will yield valuable inputs for models
of coronal heating and angular momentum evolution. A comparison between
the results for a quiet non-dMe star with those for active dMe stars
(available in the EUVE archives) will reveal if the difference in
their emission levels arises from a fundamental difference in coronal
structure or if it is merely a difference in scale (e.g., filling
factors of active regions). In summary, the EUVE data for a dM star
will be an important comparison for active dMe stars.
Title: A Method for Estimating the Fractional Area Coverage of Active
Regions on Dwarf F and G Stars
Authors: Andretta, Vincenzo; Giampapa, Mark S.
Bibcode: 1995ApJ...439..405A
Altcode:
The D3 (lambda 5876) and lambda 10830 lines arising from
triplet levels in neutral helium appear in absorption in active
(plage) regions on the Sun and, by implication, in the active
regions on Sun-like (F-early K) stars. These features either do not
occur, or appear only very weakly, in the quite solar (or stellar)
photosphere. Hence, these diagnostics are ideal tracers of magnetic
regions outside of cool spots. The appearance of D3 and
lambda 10830 in absorption immediately suggests that these lines can
be utilized to infer the fractional area coverage, or filling factor,
of active region on stellar surfaces if their intrinsic absorption
strengths in these regions are known. In particular, a meaningful
lower limit to the active filling factor can be deduced if the maximum
absorption equivalent width (Wmax) in D3 or
lambda 10830 as either appears in stellar analogs of solar plages
can be estimated. We develop this approach by constructing a grid
of model chromospheres based on the VAL C model of the quiet solar
chromosphere. This thermal structure is superposed on published models
for F and G dwarf photospheres. We solve for the non-LTE ionization of
hydrogen to infer chromospheric electron densities. We then perform
a multilevel, non-LTE computation of the helium triplet lines in the
sequence of model chromospheres, taking into account the potential
effects of coronal XUV back radiation on the line formation. We
conservatively estimate that Wmax approximately = 100-150
mA for D3 in both F and G dwarfs. The implied lower limits
to the filling factor of plagelike regions can be approximately 20%
among active solar-type stars. We extend this approach by investigating
a method by which the actual filling factor can be deduced through
a study of the joint response of D3 and lambda 10830 to
chromospheric nonradiative heating. We emphasize that our filling factor
estimates indicate the area coverage at the height of formation of
the helium triplet lines in the active chromosphere. Because of field
line spreading with height, filling factors based on chromospheric
lines are expected to exceed estimates based on purely photospheric
lines. Finally, we discuss the relative importance of collisional
and photoionization processes in the formation of these important
diagnostics.
Title: Radial Velocities of Very Low Mass Stars and Candidate Brown
Dwarf Members of the Hyades and Pleiades. II.
Authors: Stauffer, John R.; Liebert, James; Giampapa, Mark
Bibcode: 1995AJ....109..298S
Altcode:
We have determined H alpha equivalent widths and radial velocities
with 1 sigma accuracies of approximately 5 km/s for approximately 20
candidate very low mass members of the Pleiades cluster and for a few
proposed very low mass members of the Hyades. Most of the Pleiades
targets were selected from the recent Hambly, Hawkins, and Jameson
proper motion survey, where they were identified as probable Pleiades
brown dwarfs with an age spread from 3 to 70 Myr. Our spectroscopic
data and a reinterpretation of the photometric data confirm that these
objects are indeed likely Pleiades members; however, we believe that
they more likely have masses slightly above the hydrogen burning mass
limit and that there is no firm evidence for an age spread amongst
these stars. All of the very low mass Pleiades and Hyades members show
H alpha in emission. However, the ratio of H alpha flux to biometric
flux in the Pleiades shows a maximum near MBol approximately
equal to 9.5 (M approximately equal to 0.3 solar mass) and a sharp
decrease to lower masses. This break occurs at the approximate mass
where low mass stars are expected to become fully convective, and it
is tempting to assume that the decrease in H alpha flux is caused by
some change in the behavior of stellar dynamos at this mass. We do not
see a similar break in activity at this mass in the Hyades. We discuss
possible evolutionary explanations for this difference in the H alpha
activity between the two clusters.
Title: The β Pictoris phenomenon among young stars. I. The case of
the Herbig AE star UX Orionis.
Authors: Grinin, V. P.; The, P. S.; de Winter, D.; Giampapa, M.;
Rostopchina, A. N.; Tambovtseva, L. V.; van den Ancker, M. E.
Bibcode: 1994A&A...292..165G
Altcode:
In this paper we present the first results of the study of very
young stars having non-periodic Algol type brightness minima. It is
based on cooperative observations between the Crimean Astrophysical
Observatory (CAO), the European Southern Observatory (ESO) and
the National Solar Observatory (NSO). In August-September, 1992,
a very deep ({DELTA}V=2.5mag), long lasting minimum of the light of
the isolated Herbig Ae star UX Ori occurred. At this event the star
was observed photometrically (UBVRI) and polarimetrically at the
CAO, and spectroscopically (high resolution: Hα and NaiD) at the
ESO. The spectroscopic observations were continued at the NSO with
the McMath solar/stellar telescope in October-December, 1992, when
the star returned to maximum brightness and again at the ESO in July
and October, 1993, when the star was bright. The main results of our
observations can be briefly summarized as follows: 1) The photometric
and polarimetric results are in agreement with the model according
to which UX Ori is surrounded by an edge-on circumstellar disk-like
envelope, and its variability is caused by variable obscuration of
the star by opaque circumstellar dust clouds. 2) The double-peaked
Hα profile observed at maximum light changed to single-peaked at
deep minimum; obscuration of a part of the circumstellar gas by an
optically thick dust cloud is causing this variation, 3) The inverse P
Cygni profiles and variable redshifted absorption components have been
observed in the NaiD lines indicating the infall of cool gas onto the
star. We believe that, such as in the case of the star β Pictoris,
violent comet-like activity takes place in the young protoplanetary
disk of UX Ori which causes the observed variability.
Title: Coronal Loop Model Atmospheres for Low Mass Stars
Authors: Giampapa, M.; Rosner, R.; Kashyap, V.; Fleming, T.; Schmitt,
J.; Bookbinder, J.
Bibcode: 1994AAS...185.9807G
Altcode: 1994BAAS...26Q1480G
We have constructed semi-empirical loop models that best fit key
coronal parameters derived from ROSAT PSPC observations of selected
low mass stars. The X-ray pulse-height distributions are represented
by two dominant components. These include a soft component that is
characterized by compact loop configurations with loop lengths that are
one or more orders of magnitude smaller than the stellar radius. By
contrast, two types of stable solutions can be found for the hard
component, namely very long loops (much larger than a pressure scale
height) with large filling factors, and very compact loops with very
small filling factors. The ``long" solutions are physically excluded
since they violate stability criteria. We identify the ``small"
solutions with compact loop flares. The implications of these results
for coronal structure and angular momentum evolution in low mass dwarfs
will be discussed.
Title: A Radial Velocity Survey of the Open Cluster IC 4665
Authors: Prosser, Charles F.; Giampapa, Mark S.
Bibcode: 1994AJ....108..964P
Altcode:
A radial velocity survey of the open cluster IC 4665 is reported for a
group of candidate members previously identified on the basis of proper
motion and photometry. Of those candidates observed, 20 out of 42 have
radial velocities consistent with membership; these cluster members
populate the F5-K0 dwarf region and represent the first relatively
conclusive membership determinations for such solar-type stars in IC
4665. Three new spectroscopic binary members of the cluster have been
identified. Rotational velocities have also been derived; the v sin i
distribution among IC 4665 members reveals that most apparent G dwarf
members of IC 4665 are seen to exhibit substantial rotation (v sin i
greater than 10 km/s). When compared to evolutionary isochrones, the
current list of intermediate-mass members appears to support earlier
suggestions that IC 4665 has an age comparable to the Pleiades.
Title: Radial Velocities of Very Low mass Stars and Candidate Brown
Dwarf Members of the Hyades and Pleiades
Authors: Stauffer, John R.; Liebert, James; Giampapa, Mark; Macintosh,
Bruce; Reid, Neill; Hamilton, Donald
Bibcode: 1994AJ....108..160S
Altcode:
We have determined H alpha equivalent widths and radial velocities
with 1 sigma accuracies of approximately 5 km s-1 for
approximately 20 candidate very low mass members of the Hyades and
Pleiades clusters. The radial velocities for the Hyades sample suggest
that nearly all of these stars are indeed highly probable members of the
Hyades. The faintest stars in the Hyades sample have masses of order 0.1
solar mass. We also obtained radial velocities for four candidate very
low mass members of the Pleiades and two objects that are candidate BD
Pleiads. All of these stars have apparent V magnitudes fainter than the
Hyades stars we observed, and the resultant radial velocity accuracy
is worse. We believe that the three brighter stars are indeed likely
very low mass stellar members of the Pleiades, whereas the status of
the two brown dwarf candidates is uncertain. The Hyades stars we have
observed and the three Pleiades very low mass stars are the lowest
mass members of any open cluster whose membership has been confirmed by
radial velocities and whose chromospheric activity has been measured. We
see no change in chromospheric activity at the boundary where stars
are expected to become fully convective (M approximately equals 0.3
solar mass) in either cluster. In the Pleiades, however, there may be
a decrease in chromospheric activity for stars with (V-I)K
greater than 3.5 (M less than or equal to 0.1 solar mass).
Title: Upgrade of the McMath-Pierce stellar spectrograph
Authors: Giampapa, Mark S.; Simmons, Jorge E.; Jaksha, David B.;
Perkins, E. L.
Bibcode: 1994SPIE.2198..302G
Altcode:
We discuss a design for an echelle spectrograph based on three prisms
as the cross-dispersing optical elements. Since high throughput in our
particular system is achieved using an image slicer, obtaining adequate
order separation is a challenge. We find that the design described
herein yields good efficiencies throughout the visible wavelength
range while also providing adequate order separation in the red.
Title: Extrasolar planetary search using a network of automated
telescopes
Authors: Craine, Eric R.; Giampapa, Mark S.; Hott, Douglas A.
Bibcode: 1994SPIE.2198.1398C
Altcode:
Conventional search techniques for extrasolar planets have not yielded
indisputable evidence of such planets. The small sample sizes of
previously employed searches ensure that a null result provides little
or no information on the numbers or distributions of such planets. The
photometric technique, wherein monitoring is performed to detect
light curves distinctively characteristic of a planetary transit, has
been a tantalizing prospect, but has always been rejected because of
its observational intensity. Moderate aperture (0.5-1.0 m) automated
telescopes and multi- color CCD imaging arrays with image recognition
software form the instrumental foundation for a global network to
conduct such a search. Catalogs of cool dwarf stars provide a program
star list with the advantages of orbital geometries and photometric
properties enabling detection of planetary transits with a network
of modes proportions. We reaffirm the viability of the photometric
approach and outline the methodology of the search. Computer modelling
of various strategies of conducting such a planetary search has been
undertaken and we outline the resulting network configurations and
observing strategies suggested by this effort.
Title: Lithium in RS Canum Venaticorum binaries and related
chromospherically active stars. III. Northern RS CVn systems.
Authors: Randich, S.; Giampapa, M. S.; Pallavicini, R.
Bibcode: 1994A&A...283..893R
Altcode:
High-resolution spectra of Northern RS CVn binaries obtained at the
NSO-Kitt Peak are analyzed with a spectrum synthesis code to derive Li
abundances, metallicities and rotation rates. The data are then combined
with previous observations of Southern RS CVn binaries obtained at ESO,
yielding a total sample of 67 individual components in 54 catalogued
RS CVn binaries. We confirm the presence of substantial amounts of
Li in many chromospherically active stars in the sample, with no
significant difference between the Northern and Southern samples. We
specifically address the question of whether these relatively high
Li abundances are due to enhanced chromospheric activity or rather
are a consequence of evolutionary history in stars of sufficiently
high mass. We investigate the dependence of Li abundance on mass by
using mass determinations in binary systems as well as comparison
with theoretical evolutionary tracks. We show that while Li abundances
in subgiants and in the warmer stars of the sample may be consistent
with a dependence on mass, there is no clear indication in the data
that the cooler giants with larger Li abundances are also the more
massive ones. Uncertainties in the comparison with evolutionary tracks
may partially be responsible for this negative result. Alternatively,
Li depletion and dilution in evolved stars may be more complex than
predicted by standard evolutionary models.
Title: The Beta Pictoris phenomenon among young stars. I. The case
of Herbig AC star UX ORI
Authors: Grinin, V. P.; Rostopchina, A. N.; de Winter, D.; The, P. S.;
van den Ancker, V.; Giampapa, M.; Tambovtseva, L. V.
Bibcode: 1994ASPC...62..130G
Altcode: 1994nesh.conf..130G
No abstract at ADS
Title: Perspectives on the Relationship between Activity and
Fundamental Stellar Parameters (Invited Review)
Authors: Giampapa, M. S.
Bibcode: 1994ASPC...64..509G
Altcode: 1994csss....8..509G
No abstract at ADS
Title: The X-Ray Luminosity Function of the Nearby K and M Dwarfs:
Results from ROSAT
Authors: Fleming, Thomas A.; Schmitt, J. H. M. M.; Giampapa, Mark S.
Bibcode: 1994ASPC...64...77F
Altcode: 1994csss....8...77F
No abstract at ADS
Title: The Coronae of Low Mass Dwarf Stars
Authors: Giampapa, Mark S.
Bibcode: 1994euve.prop...63G
Altcode:
We propose to obtain SW and MW EUVE spectrometer observations of
selected M dwarfs for which we have ROSAT PSPC X-ray pulse-height
distributions. The EUVE data will be used to determine if the coronal
structure is characterized by only two dominant components, as suggested
by our analysis of the X-ray data, or if dwarf M coronae actually
consist of multiple components with a distribution of maximum loop
temperatures. We will use the potential constraints available with the
density diagnostics in the EUV spectra to improve the determination
of loop morphologies that thus far have been based solely on X-ray
photometric data. This will yield valuable inputs for models of coronal
heating (through the determination of heat dissipation scales) and
models of angular momentum evolution (via magnetic braking) in low
mass stars. A comparison of the results for the quiet dM star and
the active dMe stars will reveal if the difference in their emission
levels arises from a fundamental difference in coronal structure
or if it is merely a difference in scale (e.g., filling factors of
active regions). Finally, an inter-comparison of the results for the
dMe stars in our program may reveal whether dynamo-related properties
change across the boundary between partial and full interior convection.
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.
Bibcode: 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: A Synoptic Study of H alpha Line Profile Variability in the
T Tauri Star SU Aurigae
Authors: Giampapa, Mark S.; Basri, Gibor S.; Johns, Christopher M.;
Imhoff, Catherine
Bibcode: 1993ApJS...89..321G
Altcode:
We present a catalog of 106 high spectral resolution observations of the
H-alpha line profile in the T Tauri star SU Aurigae, obtained during
the period from 1986 October through 1990 November. The spectra were
acquired during joint synoptic programs to observe selected T Tauri
stars using the Hamilton Echelle Spectrometer of the Lick Observatory
and the solar-stellar spectrograph at the McMath telescope of the
National Solar Observatory on Kitt Peak. A restricted set of Mg II h
and k line profiles was also obtained in a coordinated program involving
the International Ultraviolet Explorer (IUE) satellite observatory and
the McMath solar-stellar facility. Striking variability is evident on
a nightly basis. A key result is that the relative intensity in the
blue wing of H-alpha spanning a range of velocities bear -150 km/s is
modulated at a period of 2.98 +/- 0.4 days. We identify the 2.98 day
period with the rotation period of the star. We also find that the
occurrence of the periodic modulation of the mass outflow is episodic
and most evident during a 2 week sequence of nightly observations. We
find two other intervals where the periodic spectroscopic variability
is likely present, although at a lower level of significance at a
lower level of significance. The variability is otherwise stochastic in
nature. The Mg II resonance lines exhibit clear variability that is most
pronounced in the blue wing of the k line. A comparison of the Mg II k
line profile with H-alpha profiles obtained nearly simultaneous yields
no apparent correlation between the variable features in each line. The
profile shapes of the Mg II h and k lines are generally indicative
of formation in a wind. An analysis of the principal features that
appear in the H-alpha profile set suggests that the line is composed of
contributions from an enhanced chromosphere; a relatively slow moving,
dense, optically thick component of a stellar wind formed relatively
close to the star; and an optically thin, high-velocity, expanding
stellar wind located further away from the star. An investigation of
possible correlations among the principal features in the series of
H-alpha profiles suggests that as the density in the wind increases,
the wind may become more unstable to large turbulence. This may lead to
a reduction in the wind bulk velocity, thus regulating the mass-loss
rate. We also find that the position of the main absorption feature
which is always present in the H-alpha profiles is not correlated
with its depth, indicating that optical depth and wind velocity are
not correlated in the denser portions of the wind.
Title: The Structure of the Coronae of dMe and dM Stars
Authors: Giampapa, M. S.; Schmitt, J. H. M. M.; Fleming, T. A.
Bibcode: 1993AAS...183.1507G
Altcode: 1993BAAS...25.1314G
We discuss results obtained from preliminary coronal loop model
atmospheres developed on the basis of x-ray pulse-height spectra
obtained with the ROSAT PSPC. The limited sample is comprised of both
active dMe stars and quiescent dM stars. An intercomparison of the
inferred coronal loop parameters for the active and the relatively quiet
objects will be presented. As reported earlier (Giampapa et al. 1993;
BAAS, 25, 824), two-temperature fits are required to adequately
represent the x-ray properties of the dMe stars. In the case of the
non-dMe stars, the coronal emission measure is dominated by a single,
relatively soft component. Preliminary estimates of densities, filling
factors and loop lengths that characterize these separate components
which define the coronae of low mass dwarf stars will be discussed.
Title: Lithium and chromospheric activity in the Alpha Persei cluster.
Authors: Stauffer, John R.; Prosser, Charles F.; Giampapa, Mark S.;
Soderblom, Mark S.; Simon, Theodore
Bibcode: 1993AJ....106..229S
Altcode:
We have obtained high resolution spectra of a set of proposed members
of the Alpha Persei open cluster which had previously been shown to
have anomalously low lithium abundances. We have used the new spectra
to derive Ca II emission strengths, radial velocities, and reddening
estimates in order to assess whether these stars truly are members
of the Alpha Per cluster. We conclude that most of the weak lithium
stars are indeed bonafide cluster members, and thus the problem of
explaining their anomalous lithium abundances remains. We have also
obtained spectra for another sample of stars for which the previous
membership data were relatively limited. Most of these stars do not
appear to be members of the cluster.
Title: Active Region Area Coverages on Solar-Type Stars
Authors: Giampapa, M. S.; Andretta, V.
Bibcode: 1993BAAS...25.1216G
Altcode:
No abstract at ADS
Title: Stellar Coronae at the End of the Main Sequence: A ROSAT
Survey of the Late M Dwarfs
Authors: Fleming, Thomas A.; Giampapa, Mark S.; Schmitt, J. H. M. M.;
Bookbinder, Jay A.
Bibcode: 1993ApJ...410..387F
Altcode:
We present X-ray data, both detections and upper limits, from the ROSAT
all-sky survey for most known M dwarfs later than type M5, as well as
from selected ROSAT pointed observations of some of these stars. We
compare these data with similar data for early M dwarfs in an attempt
to probe the nature of the magnetic dynamo and coronal heating mechanism
for the very late M dwarfs, which are presumably totally convective. Our
results indicate that late M dwarfs can have coronae which are just
as active as those for the early M dwarfs and that coronal heating
efficiency for 'saturated' stars does not drop at spectral type M6.
Title: Coronal Structure of Late M Dwarf Stars
Authors: Giampapa, M. S.; Fleming, T. A.; Schmitt, J. H. M. M.
Bibcode: 1993AAS...182.2205G
Altcode: 1993BAAS...25R.824G
We present preliminary results of the analysis of x-ray pulse-height
spectra of very late dwarf M stars as obtained with the ROSAT
PSPC. The majority of the data are derived from a program of pointed
observations. The limited sample is comprised of both active dMe
stars and quiescent dM stars. The basic cornal properties are derived
and compared among the dMe and dM stars in the sample. We find that
two-temperature fits are required to account for the x-ray emission of
dMe stars while single-temperature fits appear to adequately represent
the x-ray properties of the non-dMe objects. In addition, we estimate
emission measures and coronal loop parameters. The implications for
coronal structure will be discussed. In particular, we suggest on the
basis of these preliminary results that the coronae of low mass dwarfs
are highly geometrically extended relative to the stellar radius. This
may account for both the high absolute values of L_x and the high
relative values, i.e., L_x /Lbol , that characterize the
x-ray emission levels of the dMe stars as compared to that of more
nearly solar-type stars.
Title: Astronomy with the Deep UV Explorer observatory.
Authors: Ferguson, D. H.; Giampapa, M. S.
Bibcode: 1993uxrs.conf..309F
Altcode: 1993uxsa.conf..309F
Recent advances in control systems and sensors allow construction of
an inexpensive yet high-performance orbiting observatory to collect
data at ultraviolet wavelengths between 1150 Å and 3000 Å. The Deep
Ultraviolet Explorer satellite (DUVE) will obtain all-sky imagery at
various broad band wavelengths, high-resolution images, and spectra
across the UV region. The DUVE program offers substantial performance
advantages over current space-based observatories.
Title: Stellar coronae at the end of the main sequence: A ROSAT
survey of the late M dwarfs
Authors: Fleming, T. A.; Giampapa, M. S.; Schmitt, J. H. M. M.;
Bookbinder, J. A.
Bibcode: 1993STIN...9419794F
Altcode:
X-ray data, both detections and upper limits, from the Rosat
all sky survey for most known M dwarfs later than type M5 are
presented. Selected Rosat pointed observations of some of these stars
are included. These data are compared to similar data for early M dwarfs
in an attempt to probe the nature of the magnetic dynamo and coronal
heating mechanism for the very late M dwarfs, which are presumably
totally convective. The results indicate that late M dwarfs can have
coronae which are just as active as those for the early M dwarfs and
that coronal heating efficiency for 'saturated' stars does not drop
at spectral type M6.
Title: Next generation ultraviolet astronomy with the Deep Ultraviolet
Explorer observatory
Authors: Ferguson, Donald H.; Giampapa, Mark S.
Bibcode: 1992SPIE.1697..274F
Altcode:
The Deep Ultraviolet Explorer (DUVE) satellite, which is a space-based
observatory providing all-sky imagery and high-resolution spectroscopy
at wavelengths between 1150 and 3000 A, is discussed. Sky coverage,
resolution, and sensitivity of DUVE are each equal to or better than
available on existing spacecraft. Recent advances in controls, sensors,
and telescope lightweighting coupled with space-qualified designs
combine to make the DUVE project affordable within the guidelines of
the Medium Explorer-class mission scenario.
Title: Science with GNAT: An Extra-Solar System Planetary Search
Authors: Craine, E. R.; Giampapa, M. S.
Bibcode: 1992AAS...181.5702C
Altcode: 1992BAAS...24R1214C
No abstract at ADS
Title: Spectroscopic and Photometric Observations of a Five-Magnitude
Flare Event on UV CETI
Authors: Eason, Erik L. E.; Giampapa, M. S.; Radick, R. R.; Worden,
S. P.; Hege, E. K.
Bibcode: 1992AJ....104.1161E
Altcode:
Optical observations of a 5-mag flare in the U band on UV Ceti (dM5.6e)
at both spectral and temporal resolutions are presented. A strong
violet continuum which cannot be reproduced solely with a thermal
bremsstrahlung spectrum is seen. The energy emitted by the flare in the
U band is about 5.0 x 10 exp 31 ergs. The corresponding total flare
energy in white light is estimated to be 1.2 x 10 exp 32 ergs. This
estimate, combined with the 700-s duration of the U-band event, yields
an average white-light flare luminosity which is about 3 percent of
the quiescent stellar bolometric luminosity. Strong H-alpha wings
appeared after the impulsive phase. A discernible central reversal
is present in both the quiescent H-alpha profile and, significantly,
in the flare profile following the impulsive phase. It is suggested
that the site of H-alpha flare emission is not necessarily associated
with a compact, high pressure region. The flare-enhanced line emission
arises from large flare volumes that are, in turn, a distinguishing
feature of stellar flares of this magnitude.
Title: Book-Review - the Sun in Time
Authors: Sonett, C. P.; Giampapa, M. S.; Matthews, M. S.
Bibcode: 1992SciAm.266f.130S
Altcode: 1992SciAm.266..130S
No abstract at ADS
Title: Mg II Line Profiles in the T Tauri Stars
Authors: Imhoff, C. L.; Giampapa, M. S.; Basri, G.
Bibcode: 1992AAS...180.4310I
Altcode: 1992BAAS...24..798I
No abstract at ADS
Title: Using Helium Lines as a Probe for Estimating Surface Filling
Factors on Sun-Like Stars
Authors: Andretta, V.; Giampapa, M. S.
Bibcode: 1992ASPC...26..552A
Altcode: 1992csss....7..552A
No abstract at ADS
Title: Chromospheric Activity; Kinematics of Very Low Mass M Dwarfs
Authors: Liebert, J.; Saffer, R. A.; Norsworthy, J.; Giampapa, M. S.;
Stauffer, J. R.
Bibcode: 1992ASPC...26..282L
Altcode: 1992csss....7..282L
No abstract at ADS
Title: Synoptic Studies of the T Tauri Star SU AUR
Authors: Johns, C. M.; Basri, G. S.; Giampapa, M. S.; Defonso, E.
Bibcode: 1992ASPC...26..441J
Altcode: 1992csss....7..441J
No abstract at ADS
Title: Cool stars, stellar systems, and the sun : seventh Cambridge
workshop
Authors: Giampapa, Mark S.; Bookbinder, Jay A.
Bibcode: 1992ASPC...26.....G
Altcode: 1992csss....7.....G
Bibliographic codes for individual papers begin with "1992csss....7".
Title: Lithium in RS CVn binaries and related chromospherically
active stars. I.Observational results.
Authors: Pallavicini, R.; Randich, S.; Giampapa, M. S.
Bibcode: 1992A&A...253..185P
Altcode:
The present survey of the Li I 6708 A line in a sample of spectral type
G and K stars with luminosity classes III, IV, and V shows that many
K-type stars in the sample, including a large number of RS CVn binaries,
show an anomalously high Li abundance relative to typical inactive stars
of the same spectral type. Only a few stars in the sample are likely to
be premain sequence objects of stars which have recently arrived on the
main sequence. Mechanisms that could lead to the enhanced Li absorption
in chromospherically active stars are discussed; these encompass large
cool spots on the stellar surface, the production of Li in stellar
flares by spallation reactions, and the evolution from main-sequence
progenitors without, or with very shallow, outer convective zones.
Title: Proposed Upgrade of the McMath Solar/Stellar Telescope to a
4 m Aperture
Authors: Giampapa, M. S.; Livingston, W. C.; Rabin, D. R.
Bibcode: 1992LNP...397..279G
Altcode: 1992sils.conf..279G
No abstract at ADS
Title: Spectroscopic Signatures of Active Regions on Main Sequence
Stars
Authors: Giampapa, Mark S.
Bibcode: 1992LNP...397...90G
Altcode: 1992sils.conf...90G
The observed characteristics of Ha in M dwarf stars combined with a
consideration of chromospheric line formation in cool dwarfs suggests
that it is radial structure, rather than lateral inhomogeneities,
which is the predominant factor in controlling chromospheric activity
in low mass stars. This conclusion implies, in turn, that chromospheres
determined by a single heating rate are relatively widespread on the
stellar surface. The implications for magnetic field structures depend
upon whether there is a unique association between chromospheric heating
rate and specific kinds of magnetic field configurations. Synoptic
observations of the marginal BY Draconis stars revealed irregular
variability in the total strength and the positions of features in the
their unique chromospheric Ha line. Further work must be done in order
to ascertain the kind of chromospheric structures that yield the range
of observed profiles. The special, and apparently rare, conditions
that give rise to this subset of the low mass dwarfs remaim elusive.
Title: Lithium Abundances in Northern RS CVn Binaries
Authors: Randich, S.; Giampapa, M. S.; Pallavicini, R.
Bibcode: 1992ASPC...26..576R
Altcode: 1992csss....7..576R
No abstract at ADS
Title: Lithium in RS CVn Binaries and Related Chromospherically
Active Stars
Authors: Pallavicini, R.; Randich, S.; Giampapa, M. S.
Bibcode: 1992LNP...397..108P
Altcode: 1992sils.conf..108P
No abstract at ADS
Title: The Nature of the Dynamo at the End of the Main Sequence:
A ROSAT Survey of the Late M Dwarfs
Authors: Fleming, T. A.; Giampapa, M. S.; Schmitt, J. H. M. M.;
Bookbinder, J. A.
Bibcode: 1992ASPC...26...93F
Altcode: 1992csss....7...93F
No abstract at ADS
Title: Next Generation Ultraviolet Astronomy with the Deep Ultraviolet
Explorer Observatory
Authors: Ferguson, D. H.; Giampapa, M. S.
Bibcode: 1992ASPC...26..629F
Altcode: 1992csss....7..629F
No abstract at ADS
Title: The Chromospheric Activity of Low-Mass Stars in the Hyades
Authors: Stauffer, John R.; Giampapa, Mark S.; Herbst, William;
Vincent, James M.; Hartmann, Lee W.; Stern, Robert A.
Bibcode: 1991ApJ...374..142S
Altcode:
High-resolution spectra or narrow-band H-alpha photometry of 106 dwarf
K and M stars in the Hyades cluster have been used to determine H-alpha
equivalent widths. These data reveal a sequence of Hyades members with
H-alpha in absorption for photospheric temperatures hotter than about
3500 K. Within this sequence, the dispersion about the mean equivalent
width-color relation is only slightly larger than the measurement
errors. A second sequence of Hyades members, characterized by H-alpha
emission and significant scatter at a given color, appears at effective
temperatures cooler than about 4000 K. This bifurcation in H-alpha
properties at 4000 K coincides with a bifurcation in the rotational
characteristics of Hyades stars: the dispersion in the rotational
velocities of the hotter Hyades members at a given effective temperature
is small while the cooler stars exhibit significant scatter in their
rotational velocities. On the basis of these data, it is suggested
that low-mass stars spin down to rotational velocities dependent upon
mass and age, but independent of premain-sequence angular momentum.
Title: Magnetic Activity in Pre-Main Stars
Authors: Feigelson, Eric D.; Giampapa, Mark S.; Vrba, Frederick J.
Bibcode: 1991suti.conf..658F
Altcode:
The extensive new evidence for extremely high levels of magnetic
activity on the surface of premain-sequence stars is reviewed and
analyzed in the context of solar evolution. Most of these observations
concern 'weak' T Tauri stars, in which the surface properties of the
young stars are not dominated by circumstellar matter as in 'classical'
T Tauri stars. Optical photometry shows that weak T Tauria stars are
moderately rapid rotaters with cool starspots covering 5 to 40 percent
of the surface. Optical and ultraviolet spectroscopy indicates that
their chromospheres are enhanced about 50 times over contemporary solar
levels. X-ray and radio intensities are of order 1000 to 100,000 times
greater than peak solar levels, and they vary on time scales of days and
(in a few cases) hours or minutes. The variability can only be explained
in terms of some extremely powerful magnetic-flare model. The large
numbers of weak T Tauri stars, probably larger than the population of
classical T Tauri stars, strongly suggests that the sun was a weak
T Tauri star for at least part of its premain-sequence evolutionary
phase. These findings are summarized in a suggested portrait of the
sun as a 1 Myr old weak T Tauri star.
Title: The sun in time
Authors: Sonett, Charles P.; Giampapa, Mark S.; Matthews, Mildred S.
Bibcode: 1991suti.conf.....S
Altcode:
Various papers on solar science are presented. The optics considered
include: variability of solar irradiance, sunspot number, solar
diameter, and solar wind properties; theory of luminosity and radius
variations; standard solar models; the sun and the IMF; variations of
cosmic-ray flux with time; accelerated particles in solar flares; solar
cosmic ray fluxes during the last 10 million yrs; solar neutrinos and
solar history; time variations of Be-10 and solar activity; solar and
terrestrial components of the atmospheric C-14 variation spectrum; solar
flare heavy-ion tracks in extraterrestrial objects. Also addressed are:
the faint young sun problem; atmospheric responses to solar irradiation;
quaternary glaciations; solar-terrestrial relationships in recent sea
sediments; magnetic history of the sun; pre- and main-sequence evolution
of solar activity; magnetic activity in pre-main-sequence stars;
classical T Tauri stars; relict magnetism of meteorites; luminosity
variability of solar-type stars; evolution of angular momentum in
solar-mass stars; time evolution of magnetic fields on solarlike stars.
Title: The Sun in Time
Authors: Sonett, Charles P.; Giampapa, Mark S.; Matthews, Mildred
Shapley
Bibcode: 1991suti.book.....S
Altcode:
No abstract at ADS
Title: The solar-stellar connection
Authors: Giampapa, Mark S.
Bibcode: 1990Natur.348..488G
Altcode:
No abstract at ADS
Title: Chromospheric H alpha and CA II Lines in Late-Type Stars
Authors: Robinson, Richard D.; Cram, Lawrence E.; Giampapa, Mark S.
Bibcode: 1990ApJS...74..891R
Altcode:
Observations of H-alpha and Ca II H and K in the chromospheres of 50
main-sequence K and M stars are reported. The photospheric contribution
to the integrated core flux in these lines is found to be more important
than previously thought, and earlier estimates of the basal flux of cool
dwarf stars are revised. The H-alpha data confirm the presence of both
an upper and a lower limit to the H-alpha equivalent width attained
at any given spectral type. The maximum H-alpha absorption strength
decreases gradually toward cooler stars while the maximum 'saturated'
quiescent emission strength increases. The Ca II emission strength
is related to the strength of the emission or absorption feature at
H-alpha, but there is not a one-to-one correlation. The main results may
be explained in terms of photoionization and collisional control of the
non-LTE H-alpha source function. Several aspects of the structure and
heating of the outer atmospheres of dwarf K and M stars are discussed.
Title: Lithium in chromospherically active stars.
Authors: Pallavicini, R.; Randich, S.; Giampapa, M.; Cutispoto, G.
Bibcode: 1990Msngr..62...51P
Altcode:
No abstract at ADS
Title: Rotational modulation and flares on RS Canum Venaticorum and
BY Draconis-type stars. XV. Observations of Proxima Centauri and
solar calibration data.
Authors: Haisch, B. M.; Butler, C. J.; Foing, B.; Rodono, M.; Giampapa,
M. S.
Bibcode: 1990A&A...232..387H
Altcode:
Results are reported from simultaneous Exosat and IUE observations
of flaring in Proxima Cen on March 2, 1985. The data are presented in
extensive tables and sample spectra and discussed in detail. The peak
emission of the soft-X-ray flare is found to be about 3 x 10 to the 27th
erg/sec, with energy about 3 x 10 to the 30th erg and an associated
increase in Mg II flux to 17,000-67,000 erg/sq cm sec, or about an
order of magnitude lower than the solar value. The presence of flare-
and microflare-related processes heating the corona is inferred.
Title: Introduction - Sun in Time - Conference - Tucson - 1989MAR6-10
Authors: Sonett, Charles P.; Giampapa, Mark S.
Bibcode: 1990SoPh..127..295S
Altcode:
No abstract at ADS
Title: Book Review: The restless sun / Smithsonian Institution
Press, 1989
Authors: Giampapa, M. S.
Bibcode: 1989S&T....78..602G
Altcode: 1989S&T....78..602W
No abstract at ADS
Title: A Search for Chromospheres at Faint Magnitudes
Authors: Fleming, Thomas A.; Giampapa, Mark S.
Bibcode: 1989ApJ...346..299F
Altcode:
The preliminary results of a program to detect chromospheric Ca
II K line emission in the faintest dwarf stars yet observed at this
wavelength using high spectral resolution are reported. The star LHS 429
(VB 8; dM7e) exhibits K line emission in addition to H-alpha emission
while LHS 2 (dM5-5.5) shows K line emission although no apparent
H-alpha feature was seen in a spectrum obtained during the course
of an earlier study by Giampapa and Liebert. A further seven stars
observed did not exhibit any apparent feature at the position of the
K line. The upper limits estimated for the K line surface flux in the
case of the nondetections are still consistent with these stars having
chromospheres characterized by a level of K line emission similar to
that of LHS 2. The trend of the measured K line widths with absolute
visual magnitude is qualitatively in accord with that expected from
the Wilson-Bappu effect.
Title: The CA II resonance lines in M dwarf stars without H-alpha
emission.
Authors: Giampapa, Mark S.; Cram, Lawrence E.; Wild, Walter J.
Bibcode: 1989ApJ...345..536G
Altcode:
Spectra of the Ca II H and K lines in a sample of 31 M dwarf stars
without H-alpha emission are used to calculate chromospheric K
line radiative losses, F(k), and to study the joint response of Ca
II K and H-alpha to chromospheric heating in dwarf M stars. It is
suggested that the poor correlation found in the equivalent width
- log F(K) diagram may be due either to radial segregation of the
H-alpha and K line forming regions or to lateral inhomogeneities
in the chromospheres. The results confirm the existence of dM stars
with weak H-alpha absorption and K line emission only slightly weaker
than that of the dMe stars, and show that dM stars with weak H-alpha
but kinematics and metallicities representative of the young disk
population belong to a class characterized by a comparatively high
degree of chromospheric activity.
Title: Analysis of the Chromospheric Spectrum of "Marginal" BY
Draconis Stars
Authors: Giampapa, M. S.
Bibcode: 1989BAAS...21.1116G
Altcode:
No abstract at ADS
Title: Variability of Chromospheric Lines in Late-Type Dwarf Stars
Authors: Cutispoto, Giuseppe; Giampapa, Mark S.
Bibcode: 1988PASP..100.1452C
Altcode:
The results of a high-resolution spectroscopic synoptic program of
observations of key chromospheric diagnostics in a sample of dwarf
stars are reported. Low-level variability in the strength of the
chromospheric H-alpha absorption line is found. The nature of the
variability implies that the operative chromospheric heating mechanism
is partially characterized by a transient component. This fact, combined
with the detectability of the low-level variability, suggests that
magnetic field-related, nonradiative atmospheric heating is widespread
in the dM stars. High-amplitude variability in the H-alpha emission
strength of the active dMe star BY Dra was also observed. Synoptic
observations of the He I 5876 A absorption line in three solar-type
stars revealed low-level variability in the strength of this feature.
Title: The High Resolution Spectroscopic Synoptic Program at the
McMath Telescope
Authors: Jaksha, D.; Giampapa, M. S.
Bibcode: 1988BAAS...20..998J
Altcode:
No abstract at ADS
Title: Multiwavelength observations of magnetic fields and related
activity on Xi Bootis A.
Authors: Saar, S. H.; Huovelin, J.; Giampapa, M. S.; Linsky, J. L.;
Jordan, C.
Bibcode: 1988ASSL..143...45S
Altcode: 1988acse.conf...45S
The authors present preliminary results of coordinated observations
of magnetic fields and related activity on the active dwarf, ξ Boo
A. Combining the magnetic fluxes with the linear polarization data,
a simple map of the stellar active regions has been constructed.
Title: Evolutionary Changes in the UV and EUV Flux of the Sun
Authors: Giampapa, M.
Bibcode: 1988srov.proc..241G
Altcode:
No abstract at ADS
Title: Formation of Chromospheric Lines in Cool Dwarf Stars
Authors: Cram, L. E.; Giampapa, M. S.
Bibcode: 1987ApJ...323..316C
Altcode:
A simple theory of the formation of H-alpha and Ca II K in dwarf M
stars has been developed which relates the observed variations in the
emission strengths of Ca II K and the equivalent widths of H-alpha to
physical differences in the underlying chromospheric structure of the
stars. The theory implies that Ca II K line emission fluxes increase
monotonically with increasing chromospheric temperature or mass
loading. However, H-alpha equivalent widths may increase or decrease
with increasing chromospheric temperature or mass loading, depending
on the actual values of the chromospheric parameters and the effective
temperature. The theory is used to elucidate aspects of the available
observational data on H-alpha and Ca II K lines in late-type dwarfs.
Title: Simultaneous Observations of the Hα and Mg II Resonance Line
Profiles in the T Tauri Star SU Aurigae
Authors: Giampapa, M. S.; Imhoff, C. L.
Bibcode: 1987BAAS...19.1026G
Altcode:
No abstract at ADS
Title: The Solar-Stellar Connection
Authors: Giampapa, Mark S.
Bibcode: 1987S&T....74..142G
Altcode:
The role of magnetic fields in the relation between solar and stellar
theories is studied. The strength of a magnetic fields is related to the
structure of a star's outer convection zone and stellar parameter such
as rotation rate and surface gravity. The analyses of H and K emission
lines of calcium for the sun and stars reveal the presence of plages and
spots in both the sun and stars. The correlation between stellar winds,
and coronal and chromospheric activity is investigated. It is determined
that the magnetic field causes an interaction between a star's rotation
and violent convective motions in its atmosphere. The magnetoacoustic
hypothesis for heating the coronae is described. Research planned for
the study of the solar-stellar relationship is discussed.
Title: A Catalog of Mg II Emission Line Fluxes for T Tauri Stars
Authors: Imhoff, C. L.; Basri, G.; Giampapa, M. S.
Bibcode: 1987BAAS...19..728I
Altcode:
No abstract at ADS
Title: Status Report on the SYNOP Project to Monitor Stars with
High-Resolution Spectroscopy
Authors: Linsky, J. L.; Giampapa, M. S.
Bibcode: 1987BAAS...19..701L
Altcode:
No abstract at ADS
Title: The Spatial Distribution of Magnetic Fields on Xi Bootis A
Authors: Saar, S. H.; Huovelin, J.; Giampapa, M. S.
Bibcode: 1987BAAS...19..703S
Altcode:
No abstract at ADS
Title: Atmospheres of Stars in the Limit of Thin and Thick Convection
Zones: The M Dwarf Stars (Invited review)
Authors: Giampapa, Mark S.
Bibcode: 1987LNP...291..236G
Altcode: 1987csss....5..236G; 1987LNP87.291..236G
This review summarizes our present understanding of the properties of
M dwarf chromospheres and coronae determined from x-ray emission and
ultraviolet and optical emission lines. These data permit estimates
of the energy balance and heating rates for both dM and dMe stars and
the presence of active regions. Two important questions are whether
the dynamo is qualitatively different for the fully convective stars
and whether the outer layers of dM stars are heated acoustically.
Title: Magnetic Field Measurements on the Sun and Implications for
Stellar Magnetic Field Observations
Authors: Sun, Wei-Hsin; Giampapa, Mark S.; Worden, Simon P.
Bibcode: 1987ApJ...312..930S
Altcode:
Results of solar magnetic field measurements in plages, sunspot umbrae,
and sunspot penumbrae using high spectral resolution, unpolarized
infrared H band spectral data are presented. A Fourier deconvolution
analysis scheme similar to that utilized for stellar magnetic field
measurements is adopted. As an example, a field strength of 3240 + or -
450 G is determined in a sunspot umbra combined with a value of 2000 +
or - 180 G in the associated penumbra. These values are compared with a
direct measurement of the spot umbra and penumbra field strengths based
on the observed separation of the Zeeman components of the magnetically
sensitive lines. Possible origins for the discrepancy between the
results inferred by these two different techniques are discussed. The
Fourier analysis results confirm the widespread occurrence of kilogauss
level fields in the solar photosphere. The implications of the solar
results for stellar magnetic field measurements are considered.
Title: 4 meter FTS observations of photospheric magnetic fields on
M dwarfs.
Authors: Saar, Steven H.; Linsky, Jeffrey L.; Giampapa, Mark S.
Bibcode: 1987LIACo..27..103S
Altcode: 1987oahp.proc..103S
Much of the observed activity on M dwarfs (e.g., spots, flares,
chromospheric and coronal emission) has been attributed to the
interaction of magnetic fields with the stellar atmosphere. Since data
on the magnetic field parameters of M dwarfs can potentially reveal much
about the physical mechanisms behind these phenomena and, additionally,
about stellar dynamos and the evolution of stellar angular momentum,
the authors have begun a program to measure the mean magnetic field
strength in stellar active regions, and the surface filling factor of
these regions for a sample of M dwarfs. In this paper some preliminary
results of this survey are discussed.
Title: Non-Axisymmetric Winds in T Tauri Stars
Authors: Giampapa, Mark S.
Bibcode: 1987iue..prop.2782G
Altcode:
We propose to obtain high dispersion, large aperture LWP observations
of the Mg II h and k lines of a T Tauri star during the course of
its rotation period in order to determine the empirical relationship
between surface magnetic field regions and winds and mass loss in T
Tauri stars. More specifically, we propose to monitor the Mg II hand k
line profiles during the rotation period of a T Tauri star to search for
evidence of rotational modulation in the blue wings. Such modulation
(in both position and the intensity of the wind absorption) would be
expected if the wind regions are intimately linked to magnetic field
configurations, similar to solar coronal holes, on or near the stellar
surface. This phenomenon has recently been observed with the IUE by
Praderie at al. (1986) in the wind of AB Aur and thus constitutes
the first direct evidence of a non-axisymmetric wind in an A type
pre-main sequence star. Clearly, it would be extremely interesting
to determine if this phenomenon is present in the precursors of
late-type, solar-like stars, namely, the T Tauri stars. The detection
of a nonaxisymmetric wind component in a T Tauri star would strongly
support the hypothesis that mass loss in T Tauri stars is associated
with nonradiative heating. Magnetic field related mass loss mechanisms,
such as the Alfven wave driven winds, would consequently become more
applicable in the context of mass loss from T Tauri stars. Our previous
work indicates that the Mg II 2800 lines are the best diagnostics
of physical conditions in the wind acceleration region between the
lower chromosphere and the more extended regions in the wind. In
addition, we will supplement these IUE observations with simultaneous
ground-based observations of the H-alpha profile. In this way we can
discern the radial extent of magnetic-field-related variability in the
wind component of the profile as modulated by rotation. This additional
component of the proposed program may provide a valuable constraint on
the lower bound for the Alfven radius in a pre-main sequence star. We
propose to acquire high dispersion LWP observations of the Mg II h and
k lines in the T Tauri star SU Aurigae. The upper limit to its rotation
period is 3.8 days; hence, we request 4 shifts to completely cover a
rotation period. The choice of SU Aur is dictated by the fact that
this T Tauri star exhibits both strong X-ray emission and evidence
for strong mass loss that Is variable. Thus, both open and closed
magnetic field regions are likely present on the stellar surface if
the solar analogy is applicable. The feasibility of this IUE program
has been demonstrated by two previous high dispersion observations of
SU Aur. In order to obtain adequate signal-to-noise, an exposure of
7 hr is required. We must therefore request US1 shifts entirely. If
approved, this program would represent the first time a T Tauri star
has been monitored for line profile variations during a rotation period.
Title: MOST: Multiple Object Spectroscopic Telescope.
Authors: Pilachowski, C.; Giampapa, M.; Barden, S.; Green, R.;
Osmer, P.
Bibcode: 1987inco.conf...53P
Altcode:
MOST is a multiple object spectroscopic telescope based on the
anticipated available of a 4 m, f/1.5 mirror from the NNTT mirror
development program. The authors describe the MOST concept and give
examples of how it can be applied to cosmological problems.
Title: The McMath Solar-Stellar Synoptic Program
Authors: Smith, Myron A.; Giampapa, Mark S.
Bibcode: 1987LNP...291..477S
Altcode: 1987LNP87.291..477S; 1987csss....5..477S
No abstract at ADS
Title: Synoptic Observations of the He I λ5876 Line in Active,
Solar-Type Stars
Authors: Giampapa, M. S.
Bibcode: 1986BAAS...18..982G
Altcode:
No abstract at ADS
Title: IUE observations of the eruptive pre-main sequence object
FU Orionis.
Authors: Ewald, R.; Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1986ESASP.263..205E
Altcode: 1986NIA86......205E; 1986niia.conf..203E
IUE observations have been used to examine the nature of
the eruptive pre-main sequence object FU Orionis. The Mg II
emission line is quite strong, with a surface flux of about
1.8×108erg/cm2sec, and probably arises in a
wind and extended envelope. The Mg II h and k line profiles appear
to be P Cygni, indicating that a substantial wind persists 50 years
after the original outburst in the star. The ultraviolet spectrum,
aside from the Mg II emission, resembles F2 Ia standard star spectra.
Title: High-Resolution H alpha Observations of M Dwarf Stars:
Implications for Stellar Dynamo Models and Stellar Kinematic
Properties at Faint Magnitudes
Authors: Giampapa, M. S.; Liebert, J.
Bibcode: 1986ApJ...305..784G
Altcode:
We present high-dispersion observations of the Hα spectral region for a
sample of very late M dwarf stars, as obtained with the Multiple Mirror
Telescope echelle spectrograph and Reticon detector. Radial velocities
and total space motions are derived. The Hα emission line properties
of our sample are thereby examined according to membership in stellar
kinematic populations. We find that, contrary to previous assertions,
M dwarf stars exist later than spectral type M5.5 which do not exhibit
Hα line emission. In fact, there are comparable numbers showing and
not showing Hα emission for Mv > + 15 in this sample of
large proper motion stars. Thus, the onset of full convection along the
main sequence does not necessarily imply an enhanced level of magnetic
field related chromospheric activity. However, we do find for the small
and biased sample considered in this investigation that dMe stars are
the dominant class of objects for absolute magnitudes Mv
> + 17. The dMe stars tend to exhibit the small total space motions
and (U, V, W) velocity dispersions that are indicative of young disk
kinematics, while nearly all the M dwarfs lacking Hα emission are
members of either the old disk or halo kinematic populations. The
faintest subdwarf included in this investigation has Mv
≍ +14.8. The implications for stellar dynamo theory and for the
nature of the stellar luminosity function at faint magnitudes are
discussed. In particular, the results constitute corroborative evidence
for a rotation-dependent distributed dynamo as a viable model for the
generation of magnetic flux in the very low mass stars. Our results
also suggest no significant difference between the kinematic properties
of the stellar population that is brighter than the likely maximum in
the luminosity function and that which is fainter.
Title: The Surface Magnetic Fields of dM and dMe Stars
Authors: Saar, S. H.; Linsky, J. L.; Giampapa, M. S.
Bibcode: 1986BAAS...18..670S
Altcode:
No abstract at ADS
Title: The Nature of the Dynamo in the Very Late M Dwarf Stars
Authors: Giampapa, Mark S.; Liebert, James
Bibcode: 1986LNP...254...62G
Altcode: 1986csss....4...62G
The results demonstrate that there are non-dMe stars with spectral
types later than M5.5. We also confirm the occurrence of dMe stars
at very late spectral types that, on the basis of current models,
correspond to fully convective interiors. Hence, the results support
a rotation-dependent distributed dynamo (or some variation thereof)
as a viable model for the generation of magnetic flux in the very low
mass stars. Future work should include v sin i determinations in order
to further extend the investigation of the properties of dynamos,
the kinematics, and the occurrence of binaries in the very low mass
stars. The acquisition of Ca II H and K line data for the old disk and
halo population stars in order to verify if any chromospheric activity
is at all present would prove valuable. Many of the known low luminosity
M dwarfs should be targeted for observation with future X-ray satellite
observatories. A monitoring program to determine whether cycles occur
in the fully convective M dwarf stars would provide valuable input on
the location of dynamo processes in the stellar interior, as suggested
by Dr. P. Gilman during the course of this workshop.
Title: Prospects for a new synoptic high resolution spectroscopic
observing facility
Authors: Giampapa, Mark S.
Bibcode: 1986pnsh.conf.....G
Altcode:
No abstract at ADS
Title: Summary of the Synoptic Spectroscopic Facility Workshop
Authors: Giampapa, M. S.
Bibcode: 1986tswo.work..145G
Altcode:
No abstract at ADS
Title: SHIRSOG Workshop / National Solar Observatory, Tucson,AZ., 1986
Authors: Giampapa, Mark S.
Bibcode: 1986tswo.work.....G
Altcode:
No abstract at ADS
Title: T Tauri stars: flare characteristics and flare models.
Authors: Giampapa, M. S.
Bibcode: 1986RALR...85..232G
Altcode:
The author notes the results of some recent work concerning surface
magnetic activity on T Tauri stars. Then he discusses the flare
properties of T Tauri stars.
Title: The SHIRSOG Workshop. Proceedings of a workshop on prospects
for a new synoptic high resolution spectroscopic observing facility,
held at the National Solar Observatory, National Optical Astronomy
Observatories, Tucson, Arizona, USA, 3 September 1986.
Authors: Giampapa, M. S.; Jefferies, J. T.; Linsky, J. L.
Bibcode: 1986swpw.book.....G
Altcode:
No abstract at ADS
Title: Synoptic Studies of T-Tauri Stars
Authors: Giampapa, M. S.
Bibcode: 1986tswo.work...53G
Altcode:
The synoptic study of pre-main sequence stars at non-redundant
wavelengths throughout the electromagnetic spectrum can elucidate
critical problems in stellar evolution. Among these problems are:
(1) The process of star formation in molecular clouds. (2) The
redistribution of angular momentum as cloud collapse occurs. (3)
The evolution of stellar magnetic activity up to the ZAMS. (4) The
origin of chromospheres and coronae, including the operative heating
mechanisms in the atmosphere and the associated mass flows. These
processes may ultimately influence the structure of the star forming
region and thereby play a role in regulating star formation rates.
Title: Chromospheric and Coronal Emission in DM Stars
Authors: Giampapa, Mark S.
Bibcode: 1986iue..prop.2455G
Altcode:
We propose to obtain low dispersion, large aperture LWP spectra of the
Mg II h+k chromospheric resonance lines for a volume limited sample
of mainly single dM (i.e., nondMe) stars for which X-ray data are
available. The combination of the IUE data-set we propose herein to
obtain and the previously acquired X-ray data-set (Bookbinder 1985)
will yield further insights on the nature of chromospheric and coronal
heating in the ordinary, inactive (quiescent) dM stars. In particular,
if the X-ray heating hypothesis for the source of chromospheric heating
in the dMe stars, as advanced by Cram (1982), is also applicable to the
dM stars then we would expect to find a linear correlation between the
luminosity in the Mg II lines and the X-ray luminosity. In general, if a
common source of in situ heating in the chromospheres and coronae of the
dM stars is present then we would expect to find a linear relationship
between the observed Mg II emission and the X-ray emission. Conversely,
if the sources of chromospheric and coronal heating are different
between these atmospheric regions in the dM stars then we expect to
find a departure from a simple linear relationship. The results to be
obtained in this program will yield critical observational constraints
on the possible mechanisms for atmospheric heating in the dM stars.
Title: The filling factor of active regions on the surfaces of the
dM stars.
Authors: Giampapa, M. S.
Bibcode: 1985ApJ...299..781G
Altcode:
According to the appearance of the H-alpha line in their spectra, the M
dwarf stars are subdivided into two classes, including the dMe stars and
the dM stars. Arguments, based on the unique properties of H-alpha line
formation in the M dwarf stars, are presented to demonstrate that the
surfaces of the dM stars must be characterized by a significant areal
coverage (or 'filling factor') of presumably magnetic field-related
active regions. In addition, an estimate regarding the lower limit to
the filling factor of chromospheric regions on dM stars is obtained, and
an empirical relation is provided for the upper limit to the intrinsic
Ca II (and Mg II) emission in these stellar surface regions. The
discussion utilizes general model results obtained by Cram and Mullan
(1979) and Giampapa et al. (1982).
Title: Stellar magnetic field measurements utilizing infrared
spectral lines.
Authors: Gondoin, Ph.; Giampapa, M. S.; Bookbinder, J. A.
Bibcode: 1985ApJ...297..710G
Altcode:
High-resolution spectra obtained with the KPNO 4 m telescope and FTS
in the infrared H and K bands are examined in order to select spectral
lines suitable for measurements of stellar magnetic field strengths and
filling factors. Only four lines are found suitable for the magnetic
field measurement technique adopted in this study. The authors analyze
the co-added spectra of the active stars ξ Boo A (G8 V), 61 UMa
(G8 V) and λ And (G8 IV-III) as obtained during four consecutive
nights. The analysis technique involves the Fourier deconvolution
of magnetically sensitive and insensitive line profiles in a single
spectrum. No evidence for the presence of magnetic fields is detected
in the co-added spectra of either ξ Boo A or 61 UMa. The data for λ
And suggest magnetic fields of ≡600 G extending over at least 20%
of the visible hemisphere. However, these values are near the detection
limit for the spectrum of λ And.
Title: Synoptic Observations of the Li I λ6707 Line in a Sample of
Solar-Type Stars
Authors: Giampapa, M. S.
Bibcode: 1985BAAS...17..902G
Altcode:
No abstract at ADS
Title: Simultaneous observations of CA II K and MG II K in T TAuri
stars.
Authors: Calvet, N.; Basri, G.; Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1985ApJ...293..575C
Altcode:
The first simultaneous, calibrated observations of the Ca II K and
Mg II k resonance lines in T Tauri stars are presented. It is found
that for T Tauri stars with mass greater than 1.5 solar mass, which
have radiative cores and tend to be fast rotators, the k line seems to
arise in an extended region (probably also responsible for the H-alpha
emission), whereas the K line apparently originates closer to the highly
inhomogeneous stellar surface. The lower mass stars, which are fully
convective and tend to be slow rotators, are more easily described by
a largely chromospheric model, consistent with main-sequence activity
structures but at greater values of the nonradiative flux. The strongest
emission-line stars in the low-mass group, however, are also likely
to have extended k line regions.
Title: Closed coronal structures. VI. Far-ultraviolet and X-ray
emission from active late-type stars and the applicability of coronal
loop models.
Authors: Giampapa, M. S.; Golub, L.; Peres, G.; Serio, S.; Vaiana,
G. S.
Bibcode: 1985ApJ...289..203G
Altcode:
We present far-ultraviolet line fluxes of prominent transition region
emission lines, as obtained with the International Ultraviolet
Explorer satellite, for a sample of solar-type stars. We combine
the ultraviolet observations with existing soft X-ray measurements
obtained by the Einstein Observatory (HEAO 2). We utilize the resulting
data set and a new coronal loop model numerical code developed at the
Harvard-Smithsonian Center for Astrophysics to perform a preliminary
investigation of the applicability of coronal loop models to solar-type
stars. In a few cases, reasonable agreement between the predictions of
single-component, coronal loop model atmospheres and the observational
data is achieved for a relatively well-defined, plausible range
of values in the pressure-filling factor (p, f) plane. In general,
however, we find that the addition of non- simultaneous ultraviolet
observations to a previously acquired soft X-ray data set does
not provide a sufficient constraint on the range of possible loop
filling factors and pressures for loop model atmospheres that may
be producing the observed X-ray and transition region emissions. We
discuss the origins of the discrepancies between the model results
and the observations within the context of (1) stellar variability,
(2) multiple coronal components, and (3) the presence of relatively
low temperature loops that give rise to far-ultraviolet emission
but not to coronal X-ray emission. We suggest on the basis of the
results presented in this investigation that in order to verify the
applicability of coronal loop models to solar-type stars, simultaneous
far-ultraviolet and moderate spectral resolution X-ray observations
will eventually have to be obtained.
Title: The ambient radiation field of young solar systems: ultraviolet
and X-ray emission from T Tauri stars.
Authors: Giampapa, M. S.; Imhoff, C. L.
Bibcode: 1985prpl.conf..386G
Altcode:
The authors review the principal results that have emerged from
ultraviolet and X-ray observations of T Tauri stars. They emphasize
that, as seen in the ultraviolet, T Tauri stars are characterized by
strongly enhanced emission. The X-ray emission and its variability,
when detected, is also enhanced and indicate of the occurrence of
violent flare activity near the stellar surface. The authors discuss
possible effects of these enhanced emissions on conditions in early
solar systems and the chemical evolution of early planetary atmospheres.
Title: Profiles of the MG II H and K Lines in Selected Red Dwarfs
Authors: Giampapa, Mark S.
Bibcode: 1985iue..prop.2149G
Altcode:
We propose to obtain high dispersion, large aperture, flux-calibrated
LWP observations of the Mg II h and k resonance lines for a selected
sample of 8 red dwarf stars in the spectral range dK7 - dM4.5. The
sample includes 6 active chromosphere emission line stars and 1
quiet chromosphere comparison dwarf. Furthermore, we will apply to
arrange for simultaneous, high spectral resolution, flux-calibrated
observations of the Ca II H and K lines and the H-alpha line using
the KPNO 4m echelle spectrograph and CCD. The resulting data-set
will be used to (1) develop self-consistent, semi-empirical model
chromospheres with the eventual goal of gaining insight on the Possible
atmospheric heating mechanisms operative in the chromospheres of
these stars and the relative geometries of the line emitting regions,
(2) testing the applicability of specific chromospheric scaling laws
(Ayres 1979) to the Mg II lines in these stars, and (3) determine if
the Wilson-Bappu effect persists through these late spectral types as
seen in the Mg II lines as well as the Ca II and H-alpha lines. We will
utilize a fully general, non-LTE transfer code at Berkeley to develop
semi-empirical model chromospheres according to the techniques employed
by Giampapa et al. (1982). The Mg II resonance lines in M dwarfs are
particularly interesting since they are formed at a level between the
lower chromospheric Ca II h and k lines and the upper chromospheric
Balmer lines. Thus the Mg II lines represent a crucial "bridge" between
these diagnostics. Moreover, the Mg II lines are significantly more
optically thick than the Ca II lines by virtue of the greater (~ 10)
abundance of magnesium relative to calcium. Thus they are potentially
a more sensitive test of chromospheric scaling laws (Ayres 1979) for
optically thick lines. Finally, an active star and a quiet chromosphere
star of the same spectral types (dK7) are included in the observing
program as a further test of the applicability of the Wilson-Bappu law
to red dwarfs. According to this law, the widths should be identical
within errors. Significant differences would be investigated within
the context of differences in chromospheric structure which would,
in turn, lead to new insights on chromospheric line formation and
the Wilson-Bappu effect. The feasibility of this IUE program has been
demonstrated by high dispersion, LWR observations of AU Mic (dM1.6e)
of 4 hr duration during a US2 shift (Ayres et al. 1983). We use this
result and low resolution Mg II flux measurements tabulated by Linsky et
al. (1982) to obtain reliable LWP-high dispersion exposure estimates for
the targets in our sample. We will precede each LWP - high with a LWP
- low for accurate flux calibration purposes. In addition, we wish to
bracket all exposures with FES visual magnitude estimates to check for
flare activity. The LWP - high exposures for the more flare active stars
in our program will be obtained in segments bracketed by FES magnitudes.
Title: Stellar surface inhomogeneities and the interpretation of
stellar spectra.
Authors: Giampapa, M. S.
Bibcode: 1985ASIC..152..305G
Altcode: 1985pssl.proc..305G
The author discusses manifestations of stellar surface thermal
inhomogeneities in stellar spectra. He illustrates the effects
of multi-components in stellar atmospheres on the interpretation
of line diagnostics and single-component models as well as on the
treatment of line transfer problems. The examples offered involve
metal abundance determinations, chromospheric line diagnostics, the
realistic representation of pre-main sequence atmospheres and stellar
magnetic fields.
Title: Coordinated Magnetic and Chromospheric Observations of Stars
Authors: Giampapa, Mark S.
Bibcode: 1985iue..prop.2147G
Altcode:
We propose to obtain time-resolved, coordinated observations of
magnetic flux and the associated chromospheric and transition region
line emissions for selected active chromosphere stars. The unique
data to be obtained in this program will provide a crucial input to
theories that describe the heating of stellar atmospheres. In essence,
the results to be acquired through the observations will establish a
preliminary empirical relationship between stellar photospheric magnetic
field strengths and magnetic flux, and stellar outer atmospheric
line emission. We are presently utilizing demonstrated methods to
directly detect magnetic fields on stellar surfaces. Magnetic results
indicate the existence of strong (a few kilogauss) fields that may
cover up to 80% of the stellar surface. Moreover, these fields are
observed to rapidly (2-3 days) vary in surface coverage, suggesting
a single large magnetic spot complex on only one hemisphere of the
star. We therefore propose a coordinated IUE/ground-based synoptic
program to obtain chromospherictransition region data (with IUE),
and photospheric magnetic field and flux measurements (ground-based
observations) for several stars that exhibit rapidly varying surface
field coverages over their rotational periods. Our IUE observing
pattern will primarily consist of low dispersion, SWP observations
and high-dispersion, LWR exposures. These data will be obtained
simultaneously (or near simultaneously) with ground-based optical and
IR observations. The ground-based data will be used to infer magnetic
field strengths and flux in the photosphere. We also require that the
IUE shifts be scheduled every third day to insure that we examine the
entire stellar surface over 10-15 day rotational periods. We require
two separate observing periods in order to have access to all objects
in the target list from ground-based observing sites.
Title: Active late-type stars and the applicability of coronal
loop models.
Authors: Giampapa, M. S.; Golub, L.; Peres, G.; Serio, S.; Vaiana,
G. S.
Bibcode: 1984NASCP2349..454G
Altcode: 1984fiue.rept..454G; 1984IUE84......454G
Far ultraviolet IUE observations of a sample of solar type stars
were combined with existing soft X-ray measurements obtained by HEAO
B. The resulting data set was utilized and a new coronal loop model
numerical code was developed to perform a preliminary investigation of
the applicability of coronal loop models to solar-type stars. Reasonable
agreement was found to exist between the predictions of single-component
coronal loop model atmospheres. It was demonstrated that semi-empirical,
coronal loop models can be applied to account for observed stellar
transition region and coronal emission. This result is corroborative
evidence for the presence of magnetic field structures analogous to
solar coronal loops on the surfaces of solar-type stars. It is suggested
that stellar transition region emission arises predominantly from the
base of quiescent coronal loop configurations.
Title: The appearance of magnetic flux on the surfaces of the early
main-sequence F stars
Authors: Giampapa, M. S.; Rosner, R.
Bibcode: 1984ApJ...286L..19G
Altcode:
Available chromospheric, transition region, and coronal observations
of the early main-sequence F stars are examined in order to find that
while these objects exhibit enhanced levels of magnetic field-related
radiative emissions, significant inhomogeneities in surface activity
are not present. This phenomenon is discussed within the context of the
calculations published by Schmitt and Rosner (1983) for the production
of flux ropes of various spatial scales at a given rotation rate at
the bottom of a stellar convection zone. It is found that the spatial
scales and area contrast of emergent magnetic flux in these stars that,
as a class, are characterized by rapid rotation and thin convection
zones are substantially reduced relative to that of the sun.
Title: The Filling Factor of Active Regions on non-dMe Stars
Authors: Giampapa, M. S.
Bibcode: 1984BAAS...16..940G
Altcode:
No abstract at ADS
Title: A Transition from Chromosphere to Wind for MgII in T Tauri
Stars
Authors: Basri, G.; Calvet, N.; Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1984BAAS...16..938B
Altcode:
No abstract at ADS
Title: Ultraviolet Continuum and Mg II Emission Rotational Modulation
in Three Pre-Main Sequence Stars
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1984BAAS...16..997I
Altcode:
No abstract at ADS
Title: Simultaneous IUE, Voyager, and Optical Observation of Epsilon
Persei
Authors: Giampapa, Mark
Bibcode: 1984iue..prop.1947G
Altcode:
No abstract at ADS
Title: New spectrophotometry of the extremely cool proper motion
star LHS 2924.
Authors: Liebert, J.; Boroson, T. A.; Giampapa, M. S.
Bibcode: 1984ApJ...282..758L
Altcode:
Improved spectrophotometric scans are presented for this very faint,
red, large-proper motion star which has a peculiar spectrum. The
Palomar Observatory 5 meter CCD spectrum shows the clear presence
of VO λ7400 and λ7900. However, the TiO and hydride bands and
the Na I and K I lines appear relatively weaker over the spectrum
of LHS 2924 than they do in the benchmark low-luminosity star VB
10. A high-resolution observation with the MMT echelle spectrograph
shows very weak Hα emission, at best. These and other recent results
eliminate all previously considered explanations of the nature of LHS
2924 other than a very cool, main-sequence star or sub-stellar-mass
"brown dwarf." The weakness of Hα emission tends to indicate that
the star is an old, main-sequence object.
Title: The Transition Regions of X-Ray Emitting Main-Sequence A Stars
Authors: Giampapa, Mark S.
Bibcode: 1984iue..prop.1812G
Altcode:
We propose to obtain low dispersion, large aperture SWP and high
dispersion, large aperture LWR observations of two (2) X-ray emitting,
single main-sequence A stars:: HR 7160 (A8V, log Lx = 29) and HD 117721
(A3V, log Lx = 30.4). These stars were strongly detected by HEAO-B
(Golub et al. 1983) and, unlike many of the other A stars detected by
Einstein, these objects appear to be single stars. lie thus propose to
verify the presence of hot plasma in these stars by searching for the
occurrence of transition region and chromospheric line emission. The
detection of transition region line emission (i.e. C IV, N V, Si IV,
etc.) in main sequence A stars would have important implications for
(1) our understanding of the precise location on the main sequence
of the onset of convection, and (2) the role of convection zone depth
and surface turbulence in the generation of stellar chromospheric and
coronal activity.
Title: Photometric variations of solar-type stars: results of the
Cloudcroftsurvey.
Authors: Giampapa, M. S.
Bibcode: 1984NASCP2310..173G
Altcode: 1984siva.work..173G
The author summarizes the results of a synoptic program conducted
at the Cloudcroft Observatory to search for the occurrence of
photometric variability in solar-type stars as seen in continuum
band photometry. The survey disclosed the existence of photometric
variability in solar-type stars that is, in turn, related to the
presence of spots on the stellar surface. Moreover, the observed
variability detected in solar-type stars is at enhanced levels (≡1%)
compared to that observed for the Sun.
Title: Lithium abundances and chromospheric activity. I. Empirical
results.
Authors: Giampapa, M. S.
Bibcode: 1984ApJ...277..235G
Altcode:
An empirical analysis is presented of the effects of chromospheric
activity on lithium abundance determinations, as deduced from high
signal-to-noise, high spectral resolution solar observations of
the Li I resonance doublet at 6707.8 A. In particular, solar active
(plage) regions and quiet comparison regions were observed to find a
maximum relative change in the Li I 6707 equivalent width of -0.53
among the limited number of solar plage observations available for
this investigation. The relative weakening of the lithium resonance
doublet is attributed to the increased ionization of neutral lithium
due to the enhanced nonradiative heating that characterizes solar
plages. The strong enhancement of the 6707 line in sunspot umbrae is
confirmed and it is emphasized that the presence of stellar surface
thermal inhomogeneities analogous to solar plages and sunspots can
substantially alter the equivalent width of this feature in stellar
spectra. Thus the effects of stellar chromospheric activity will
introduce ambiguities into lithium abundance determinations that, in
turn, can contribute significantly to the scatter in investigations
that utilize this diagnostic.
Title: Results from Ultraviolet Observations of T Tauri Stars
Authors: Giampapa, Mark S.
Bibcode: 1984LNP...193...14G
Altcode: 1984csss....3...14G
No abstract at ADS
Title: The response of chromospheric emission lines to flares on YZ
Canis Minoris.
Authors: Worden, S. P.; Schneeberger, T. J.; Giampapa, M. S.; Deluca,
E. E.; Cram, L. E.
Bibcode: 1984ApJ...276..270W
Altcode:
Six flares of the dMe star YZ CMi have been observed with simultaneous
photometry and high-dispersion, time-resolved spectroscopy.The spectra
have temporal resolutions of 3 minutes with spectral resolutions
of 0.24 Å. The largest observed flare had a U band amplitude of
1.5 mag. Hα and Hβ line profiles did not broaden during any of the
observed flares, although the line center intensity increased by over a
factor of 2 during some flares. After the initial increase in intensity,
the emission line strength decreases but remains at enhanced levels
for hours following U band flares. The Hα flare luminosity and total
energy are compared to corresponding properties of solar flares.
Title: Direct and Indirect Methods of Measurement of Stellar
Magnetic Fields
Authors: Giampapa, M. S.
Bibcode: 1984srps.conf..309G
Altcode:
Standard polarization methods for measuring stellar magnetic fields are
inappropriate for solar-type field topologies. The author is therefore
utilizing a "white-light" method that involves the interpretation
of spectral line shapes as seen in high spectral resolution
data. Through the application of Fourier deconvolution techniques,
the field strength and area coverage on a stellar surface can be
ascertained. The applicability and results of this method for both
solar and stellar magnetic field measurements are discussed. Besides
the aforementioned direct method, there potentially exist complementary
indirect methods. They are less satisfactory than direct methods. They
require a knowledge of the underlying physics that relates on observable
radiative emission to the local magnetic field strength or flux.
Title: Some Relevant Topics in Solar-Stellar Physics
Authors: Giampapa, M. S.
Bibcode: 1984ssdp.conf..457G
Altcode:
No abstract at ADS
Title: Combined ultraviolet studies of astronomical sources
Authors: Dupree, A. K.; Giampapa, M. S.; Huchra, J. P.; Noyes,
R. W.; Hartmann, L. W.; Raymond, J. C.; Blair, W. P.; Bothun, G. D.;
Patterson, J. O.; Baliunas, S. L.
Bibcode: 1983sao..reptR....D
Altcode:
Ultraviolet spectra of non-radiataive shock waves grain destruction and
elemental abundances in interstellar shocks, carbon abundance in M33
and M31 from supernova remnants, determination of the mass function
in the large Magellanic cloud, UV spectra of white dwarf pulsars,
stellar flares, availability of the double quasar Q 0957 + 56' AB,
spectra of late-F dwarfs and their relation to rotation, dynamics of
hot gas surrounding hybrid stars, high resolution study of epsilon
coronae Austriual, active regions on solar-type dwarfs as a function of
rotation rate and age, coordinated chromospheric synoptic observations
of selected late-type stars, the two-component atmosphere of Lambda
Andromedae, and activity in Hyades giants are discussed.
Title: Magnetic Field Measurements on the Sun and Synthesis of
Stellar Spectrum from Solar Data
Authors: Sun, W.; Giampapa, M. S.; Worden, S. P.
Bibcode: 1983BAAS...15..952S
Altcode:
No abstract at ADS
Title: The UV Variability of RW Aur
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1983BAAS...15..928I
Altcode:
No abstract at ADS
Title: The Young Sun and The Atmosphere and Photochemistry of the
Early Earth
Authors: Giampapa, M. S.; Canuto, V. M.; et al.
Bibcode: 1983Natur.305..281G
Altcode:
No abstract at ADS
Title: Concerning Spot Formation in the Early Main Sequence F Stars
Authors: Giampapa, M. S.
Bibcode: 1983BAAS...15..947G
Altcode:
No abstract at ADS
Title: The young Sun and the atmosphere and photochemistry of the
early Earth
Authors: Canuto, V. M.; Levine, J. S.; Augustsson, T. R.; Imhoff,
C. L.; Giampapa, M. S.
Bibcode: 1983Natur.305..281C
Altcode:
The origin and evolution of the Earth's early atmosphere depend
crucially on the dissipation time tN of the primitive solar
nebula, SN. Using different theories of turbulence, we estimate that
for a 0.1 Msolar SN, tN is 2.5-8.3Myr. Because
accretion times are usually much longer, we conclude that most planetary
accretion must have occurred in a gas-free environment. Using new IUE
data, a wavelength-dependent UV flux is constructed for the young Sun
which is then used to study the photochemistry and concentrations
of O, O2, O3, OH, H, HCO and formaldehyde
H2CO in the Earth's early prebiological atmosphere.
Title: High Resolution Ultraviolet and Optical Observations of
T-Tauri Stars
Authors: Giampapa, M. S.
Bibcode: 1983RMxAA...7..195G
Altcode:
No abstract at ADS
Title: Ultraviolet Observations of the T-Tauri Stars - Inferences
Regarding Their Chromospheres Transition Regions and Coronae
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1983RMxAA...7..191I
Altcode:
No abstract at ADS
Title: Ultraviolet Observations of the T Tauri Stars: Inferences
Regarding their Chromospheres, Transition Regions, and Coronae
Authors: Giampapa, M. S.
Bibcode: 1983RMxAA...7..191G
Altcode:
No abstract at ADS
Title: New Spectrophotometry of the Extremely Red Proper-Motion
Star LHS2924
Authors: Liebert, J. W.; Boroson, T. A.; Giampapa, M. S.
Bibcode: 1983nssl.conf..361L
Altcode: 1983IAUCo..76..361L; 1983LDP.....4..361L
LHS 2924 (LP 271-25) is the uniquely-red, faint proper motion star
recently reported to have a peculiar spectrum and colors by Probst
and Liebert (1983). This paper reports briefly the results of two
follow-up observations: an excellent red spectrum covering 5000 -
9000 Å, and a high dispersion spectrum of the important Hα region.
Title: The photometric variability of solar-type stars. II. Stars
selected from Wilson's chromospheric activity survey.
Authors: Radick, R. R.; Wilkerson, M. S.; Worden, S. P.; Africano,
J. L.; Klimke, A.; Ruden, S.; Rogers, W.; Armandroff, T. E.; Giampapa,
M. S.
Bibcode: 1983PASP...95..300R
Altcode:
The authors have observed eleven solar-type main-sequence stars to
search for continuum variability. Stars were selected from Wilson's
chromospheric activity survey, and were observed for periods of three
to six months with intermediate-band Stroemgren uvby photometry. The
authors find evidence that two of these eleven stars are variable
and that one other may be. Comparison with contemporaneous Ca II H +
K emission flux measurements shows that the amplitude of photometric
variability correlates strongly with both the mean emission flux
and the amplitude of its variation. Variations in continuum light and
emission flux tend to correlate in time, as well, with continuum minima
coinciding with emission maxima and vice-versa. The authors infer that
the surface activity of these stars tends to be confined to localized
activity centers that include both emission plages and dark spots,
similar to the active regions observed on the sun.
Title: The magnetic field on the RS Canum Venaticorum star lambda
Andromeda.
Authors: Giampapa, M. S.; Golub, L.; Worden, S. P.
Bibcode: 1983ApJ...268L.121G
Altcode:
A program to detect and measure magnetic flux on the surfaces of
late-type stars is discussed. A technique is adopted to deconvolve
magnetically insensitive lines from similar, magnetically sensitive
lines to infer the degree of Zeeman splitting in the latter lines. These
measurements yield values for the magnetic field strength and filling
factor (flux). To illustrate the approach, observations of the RS
CVn star Lambda And are presented. At the epoch of observation, 1981
April 26, a field strength of 1290 + or - 320 gauss covering 48 + or -
7 percent of this star's surface is found. This measurement compares
with an estimate of coronal magnetic flux in the cooler component of
the stellar corona of 1110 gauss with a coronal volume filling factor
of 75 percent, based on X-ray data for Lambda And.
Title: Methods and results for detecting magnetic fields on late-type
stars.
Authors: Giampapa, M. S.; Worden, S. P.
Bibcode: 1983IAUS..102...29G
Altcode:
A program to detect and measure magnetic flux on the surfaces of
late-type stars is discussed. A novel technique is adopted to deconvolve
magnetically insensitive lines from similar, magnetically sensitive
lines to infer the degree of Zeeman splitting in the latter lines. These
measurements yield values for the magnetic field strength and filling
factor (flux). To illustrate the approach multiple observations are
presented of the RS CVn star Lambda And. At the epoch of observation
26 April 1981 a field strength of 1290 + or - 50 gauss covering 48 +
or - 2 percent of this stars's surface is found. Observations at other
epochs clearly demonstrate magnetic flux variability on Lambda And.
Title: Fractional stellar convection-zone depth and the generation
of magnetic flux - an empirical approach
Authors: Giampapa, M. S.
Bibcode: 1983IAUS..102..187G
Altcode:
Preliminary results of an observational investigation of very late
M dwarf stars utilizing the Multiple Mirror Telescope facility are
presented. It is found that dwarf stars later than spectral type M5 do
not necessarily exhibit H-alpha line emission, contrary to the assertion
by Joy and Abt (1974). The preliminary results tentatively suggest,
but do not prove, that the generation of significant magnetic fields
and magnetic flux is severely inhibited in fully convective stars.
Title: Observations of Flare Activity on Selected DME Flare Stars
Authors: Giampapa, Mark S.
Bibcode: 1983iue..prop.1442G
Altcode:
Optical and ultraviolet spectroscopy can enable the assessment of
the physical conditions characterizing a stellar flare atmosphere and
thereby potentially elucidate the possible radiative and hydrodynamic
transport mechanisms operative during stellar flares. Observations
of flares on M dwarf stars offers the opportunity to obtain detailed
information on a solar-like phenomenon as it presumably occurs on many
stars, but can presently only be observed on the cool dMe stars due
to the highly favorable contrast between the UV and near UV bright
flare emission and the faint quiescent background. We therefore
propose to acquire timeresolved, low dispersion, large aperture SWP
and LWR observations simultaneously with moderate resolution (3-4A)
spectrophotometric optical observations of stellar flare events. We
also will attempt to coordinate simultaneous VLA (radio corona)
observations. We intend to monitor two highly flare active systems;
the binary UV Ceti (GL65AB) system and the single flare star YZ CMi
(GL 285). We wish to ascertain the dominant radiative transport
mechanism that gives rise to the UV and optical continuum emission
during flares as well as assess the relative energy balance in these
wavelength regions. Furthermore, we will utilize density diagnostics and
emission mesure analysis techniques developed for solar observations. In
addition, we will infer flare X-ray luminosities from the enhancement
of the He II 1640 recombination line. The UV data and inferred X-ray
data will ultimately be used to determine the applicability of flare
loop models. All data obtained in this program will be used as input
for the construction of semiempirical flare atmospheres.
Title: Results from optical and UV stellar flare spectroscopy
Authors: Giampapa, M. S.
Bibcode: 1983ASSL..102..223G
Altcode: 1983ards.proc..223G; 1983IAUCo..71..223G
Optical and ultraviolet spectroscopy can enable the assessment of
the physical conditions characterizing a stellar flare atmosphere and
thereby potentially elucidate the possible radiative and hydrodynamic
transport mechanisms operative during stellar flares. In this review,
illustrative examples are presented of the spectroscopic diagnostic
techniques that can be applied to the analysis of stellar flare
spectroscopic data and the resulting inferences concerning stellar
flare properties for M dwarf flare events.
Title: Outer atmospheres of cool stars. XII. A survey of IUE
ultraviolet emission line spectra of cool dwarf stars.
Authors: Linsky, J. L.; Bornmann, P. L.; Carpenter, K. G.; Wing,
R. F.; Giampapa, M. S.; Worden, S. P.; Hege, E. K.
Bibcode: 1982ApJ...260..670L
Altcode:
Quantitative information is obtained on the chromospheres and
transition regions of M dwarf stars, in order to determine how the outer
atmospheres of dMe stars differ from dM stars and how they compare with
the outer atmospheres of quiet and active G and K type dwarfs. IUE
spectra of six dMe and four dM stars, together with ground-based
photometry and spectroscopy of the Balmer and Ca II H and K lines,
show no evidence of flares. It is concluded, regarding the quiescent
behavior of these stars, that emission-line spectra resemble that of
the sun and contain emission lines formed in regions with 4000-20,000 K
temperatures that are presumably analogous to the solar chromosphere,
as well as regions with temperatures of 20,000-200,000 K that are
presumably analogous to the solar transition region. Emission-line
surface fluxes are proportional to the emission measure over the range
of temperatures at which the lines are formed.
Title: Fractional Stellar Convection Zone Depth and the Generation
of Magnetic Flux
Authors: Giampapa, M. S.
Bibcode: 1982BAAS...14..865G
Altcode:
No abstract at ADS
Title: Stellar model chromospheres. XIII. M dwarf stars.
Authors: Giampapa, M. S.; Worden, S. P.; Linsky, J. L.
Bibcode: 1982ApJ...258..740G
Altcode:
Single-component, homogeneous model chromospheres that are consistent
with high-resolution profiles of the Ca II K line calibrated in surface
flux units for three dMe and 2 dM stars observed at quiescent times
are constructed. The models reveal several systematic trends. Large
values of the ratio of T(min) to T(eff) are derived, indicating a large
amount of nonradiative heating present in the upper photospheres of M
dwarf stars. It is also found that the lower chromospheric temperature
gradient is similar for all the M dwarf stars. Since for the models here
the chromospheric K line emission strength is most sensitive to the
total amount of chromospheric material present within the approximate
temperature range T(min)-6000 K, increasing the emission strength is not
simply due to increasing chromospheric temperature gradients. It is also
found that both the electron density and electron temperature at one
thermalization length in the K line below the top of the chromospheres
are greater in the dMe stars than in the dM stars. The M dwarf models
here have microturbulent velocities between 1 and 2 km/sec, which are
much smaller than for solar chromosphere models.
Title: Observations of rapid line profile variability in the spectra
of T Tau stars.
Authors: Mundt, R.; Giampapa, M. S.
Bibcode: 1982ApJ...256..156M
Altcode:
Observation of six T Tauri stars, having a spectral resolution
of 240,000 and temporal resolutions in the 300-900 sec range, are
presented. In addition to presenting evidence for the existence of rapid
line profile variability in the spectrum of RW Aurigae, this object's
line spectrum properties in the vicinity of the H-alpha, H-gamma, and
Na D lines are discussed in view of three high-quality spectra, with
the result that photospheric absorption features are identified and a
rotational velocity of about 25 km/sec is tentatively estimated. The
data set acquired for RW Aur also reveals the existence of mass motions
with antiparallel velocity components in the line-emitting region of
the object. A spectral type for this previously unclassified T Tauri
star of K1 + or - 2 subclasses is determined.
Title: Combined ultraviolet studies of astronomical sources
Authors: Dupree, A. K.; Giampapa, M. S.; Huchra, J. P.; Noyes, R. W.;
Hartmann, L. W.; Raymond, J. C.
Bibcode: 1982sao..reptQ....D
Altcode:
Ultraviolet studies of astronomical sources are discussed. Some studies
utilized IVE data. Non-radiative shock at the edge of the Cygnses Loop,
stellar flares, local interestellar medium, hot galaxies, stellar mass
ejection, contact binaries, double quasars, and stellar chromosphere
and coronae are discussed.
Title: A heating mechanism for the chromospheres of M dwarf stars.
Authors: Giampapa, M. S.; Golub, L.; Rosner, R.; Vaiana, G. S.;
Linsky, J. L.; Worden, S. P.
Bibcode: 1982SAOSR.392A..73G
Altcode: 1982csss....2...73G
The atmospheric structure of the dwarf M-stars which is especially
important to the general field of stellar chromospheres and coronae
was investigated. The M-dwarf stars constitute a class of objects
for which the discrepancy between the predictions of the acoustic
wave chromospheric/coronal heating hypothesis and the observations is
most vivid. It is assumed that they represent a class of stars where
alternative atmospheric heating mechanisms, presumably magnetically
related, are most clearly manifested. Ascertainment of the validity
of a hypothesis to account for the origin of the chromospheric and
transition region line emission in M-dwarf stars is proposed.
Title: Second Cambridge workshop on cool stars, stellar systems,
and the sun. Vol. 1. Proceedings of a workshop held at the
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, October
21 - 23, 1981.
Authors: Giampapa, M. S.; Golub, L.
Bibcode: 1982SAOSR.392A....G
Altcode: 1982csss....2A....G
No abstract at ADS
Title: Cool stars, stellar systems and the sun : 2 : 1981
Authors: Giampapa, M. S.; Golup, L.
Bibcode: 1982SAOSR.392B....G
Altcode: 1982csss....2B....G
No abstract at ADS
Title: Preface
Authors: Giampapa, Mark; Golub, Leon
Bibcode: 1982SAOSR.392D...9G
Altcode: 1982csss....2D...9G
No abstract at ADS
Title: Far-ultraviolet and X-ray evidence concerning the chromospheres
and coronae of the T Tauri stars.
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1982SAOSR.392B.175I
Altcode: 1982csss....2..175I
No abstract at ADS
Title: Coordinated X-ray, optical and radio observations of flaring
activityon YZ Canis Minoris.
Authors: Kahler, S.; Golub, L.; Harnden, F. R.; Liller, W.; Seward,
F.; Vaiana, G.; Lovell, B.; Davis, R. J.; Spencer, R. E.; Whitehouse,
D. R.; Feldman, P. A.; Viner, M. R.; Leslie, B.; Kahn, S. M.; Mason,
K. O.; Davis, M. M.; Crannell, C. J.; Hobbs, R. W.; Schneeberger,
T. J.; Worden, S. P.; Schommer, R. A.; Vogt, S. S.; Pettersen, B. R.;
Coleman, G. D.; Karpen, J. T.; Giampapa, M. S.; Hege, E. K.; Pazzani,
V.; Rodono, M.; Romeo, G.; Chugainov, P. F.
Bibcode: 1982ApJ...252..239K
Altcode:
The YZ Canis Minoris (Gliese 285), a late-type dwarf star with
Balmer emission (dM4.5e), is a member of the UV Ceti class of flare
stars. Obtaining good X-ray observations of a dMe star flare is
important not only for understanding the physics of flares but also for
testing current ideas regarding the similarity between stellar and solar
flares. The Einstein X-ray Observatory has made it possible to conduct
X-ray observations of dMe stars with unprecedented sensitivity. A
description is presented of the results of a program of ground-based
optical and radio observations of YZ CMi coordinated with those of
the Einstein Observatory. The observations were carried out as part
of a coordinated program on October 25, 26, and 27, 1979, when YZ CMi
was on the dawn side of the earth. Comprehensive observational data
were obtained of an event detected in all three wavelength regions on
October 25, 1979.
Title: The relevance of the IUE results on young stars for earth's
paleoatmosphere.
Authors: Canuto, V. M.; Levine, J. S.; Augustsson, T. R.; Imhoff,
C. L.; Giampapa, M. S.
Bibcode: 1982NASCP2238..293C
Altcode: 1982auva.nasa..293C; 1982NASCP2338..293C
Using the latest IUE results for seven T Tauri stars, which are believed
to represent the young Sun and a detailed photochemical chemical model
of the paleoatmosphere, the vertical distribution of Oxygen and Ozone
in the early atmosphere was calculated. The calculations indicate that
the surface Oxygen mixing ratio is as much as six orders of magnitude
larger than previously estimated, but appears low enough for the
formation of amino acids via the Urey-Miller type of experiments. It
is believed that the quantification of the oxygen level in the Earth's
paleoatmosphere presented can reconcile the demands of both biological
and geological considerations.
Title: Magnetic & Chromospheric Synoptic Observations of
Late-Type Stars
Authors: Giampapa, Mark S.
Bibcode: 1982iue..prop.1099G
Altcode:
We propose to obtain time-resolved, coordinated observations of
magnetic flux and the associated chromospheric and transition region
line emission for selected active chromosphere stars. The unique data
to be obtained in this program will provide a crucial input to theories
that describe the heating of stellar chromospheres and coronae. In
essence, the results to be acquired through the observations proposed
herein will (for the first time) establish a preliminary empirical
relationship between stellar magnetic field strengths and magnetic flux,
and stellar outer atmospheric line emission. We are presently utilizing
a now and successfully demonstrated method to directly detect magnetic
fields on stellar surfaces. These results indicate the existence of
strong (~ a few kilogauss) magnetic fields that may cover up to 80%
of the stellar surface. Moreover, these fields are observed to rapidly
(2-3 days) vary in surface coverage. We therefore propose a coordinated
IUE ground-based synoptic program to obtain chromospheric-transition
region data (with IUE) and magnetic field and flux measurements
(ground-based observations) for several stars that exhibit rapidly
varying surface field coverages over their rotational periods. Our
IUE observing pattern will primarily consist of low dispersion, SWP
observations and high-dispersion, LWR exposures. These data will be
obtained simultaneously (or near simultaneously) with groundbased
optical and infrared observations. The groundbased data will
Title: Chromospheres and coronae in the T Tauri stars.
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1982NASCP2238..456I
Altcode: 1982NASCP2338..456I; 1982auva.nasa..456I
The Tauri stars exhibit strong far ultraviolet emission lines of C
II, III, IV; OI; Si II, III; IV; and sometimes N V and He II. Surface
fluxes of the lines for several T Tauri stars were computed, drawing
upon both International Ultraviolet Explorer observations and published
spectra. The surface fluxes are quite high. The FUV lines together
account for 0.1% of the stellar luminosity. These results indicate the
presence of active relatively dense chromospheres. The Tauri stars
showing very strong visual emission spectra exhibit weakened high
temperature FUV lines of C IV and N V, as well as He II which may be
produced by X-rays. In the same stars, no X-ray emission was detected
with Einstein. Among all the T Tauri stars the X-ray luminosities are
deficient by factors of 100 to 1000 compared to the FUV lines. It
is argued that the X-ray flux has not been heavily absorbed by
circumstellar gas, as has been previously suggested, but that the
X-rays are truly underluminous, perhaps due to the stellar wind. It is
suggested that the birth and development of the chromosphere and corona
may be occurring during the T Tauri stage of protostellar evolution.
Title: A preflare diminution in the quiescent flux of EQ Pegasi.
Authors: Giampapa, M. S.; Africano, J. L.; Klimke, A.; Parks, J.;
Quigley, R. J.; Robinson, R. D.; Worden, S. P.
Bibcode: 1982ApJ...252L..39G
Altcode:
The occurrence of a remarkable flare event on EQ Peg is reported as
recorded by high speed photometry in the Johnson U band: a stellar
flare event is immediately preceded by a well-defined decline in
the quiescent flux of the star. The U band flux decays to a minimum
level that is 75% of the stellar quiescent flux, and the duration of
the so-called negative flare event is 2.7 minutes. A description of
the observation is presented and hypotheses are discussed that may
eventually account for this phenomenon.
Title: IUE observations of pre-main-sequence stars. I. MG II and CA
II resonance line fluxes for T Tau stars.
Authors: Giampapa, M. S.; Calvet, N.; Imhoff, C. L.; Kuhi, L. V.
Bibcode: 1981ApJ...251..113G
Altcode:
IUE satellite and Lick 3 m reflector image tube scanner measurements
of the Mg II and Ca II resonance lines in a sample of T Tauri stars
are the basis of a discussion of the Mg II h and k line emission
and the Ca II H and K line emission, within the context of stellar
chromospheres. Corroborative evidence is presented for the chromospheric
origin of these resonance lines, and chromospheric radiative loss rates
in the Mg II and Ca II resonance lines are derived. It is found that
the degree of nonradiative heating present in the outer atmospheres
of T Tauri stars generally exceeds that of the RS CVn systems, as
well as the dMe stars and other active chromospheric dwarfs, and it is
inferred that the surfaces of such pre-main sequence stars are covered
by regions similar to solar plages. The mean chromospheric electron
density of T Tauri stars is determined as 10 to the 11th/cu cm.
Title: High-resolution profiles of chromospheric lines in M dwarf
stars.
Authors: Worden, S. P.; Schneeberger, T. J.; Giampapa, M. S.
Bibcode: 1981ApJS...46..159W
Altcode:
Forty-six hydrogen and sodium line profiles are presented for 17
selected dwarf M and dwarf M emission line stars. These profiles,
derived from echelle spectrograms, typically have 0.25 A spectral
resolution. Most of the dMe stars show hydrogen emission lines with
central reversals. Central emission features in the cores of the Na D
lines are often observed, and the presence of these emission features
is strongly correlated with hydrogen line emission.
Title: Stellar model chromospheres. XII. High-resolution, absolute
flux profiles of the CaII H and K lines in dMe and non-dMe stars.
Authors: Giampapa, M. S.; Worden, S. P.; Schneeberger, T. J.; Cram,
L. E.
Bibcode: 1981ApJ...246..502G
Altcode:
We present 142 mÅ resolution spectra of the cores and wings of the
Ca II H and K lines in three dMe and four comparison dwarf M stars,
obtained with the KPNO 4 m echelle spectrograph and blue image
tube. The narrow-band photometry of Willstrop and the Barnes and
Evans relations for stellar angular diameters convert the observed
relative flux to absolute surface flux units with an estimated
uncertainty of ± 15 %. We derive chromospheric radiative loss rates
in the H and K lines and discuss trends in these loss rates with
effective temperature. Monochromatic surface fluxes are tabulated for
different features in the H and K lines, and radiation temperatures
are derived from the mean surface fluxes at K1 and
H1, respectively. We find TR(H1) >
TR(K1), consistent with partial redistribution
theory. The TR(K1)/Teff ratio
is higher in these M dwarfs than the giants studied in Paper X,
and it is anomalously high for the dMe flare star YZ CMi. If
TR(K1)/Teff is an empirical age
indicator, then the result for YZ CMi implies that flare activity
and youth are directly correlated, as has been suggested by other
investigators. Moreover, the result implies that a high degree of
nonradiative heating is present in the upper photospheres of dMe
stars. Measurements of line widths at H1 and K1
are presented together with FWHM data for the H and K lines. We find
that the scaling law proposed by Ayres generally agrees with the
observed trend exhibited by the K1 widths. We also discuss
chromospheric radiative loss rates in the Hɛ line compared with loss
rates in the H and K lines, and present corrected FWHM(K) widths and
compare them to the widths predicted by the Wilson-Bappu relation as
calibrated by Lutz.
Title: High Resolution, Absolute Flux Profiles of the Mg II h and
k Lines for T Tauri Stars
Authors: Giampapa, M. S.; Morossi, C.; Ramella, M.; Imhoff, C. L.
Bibcode: 1981BAAS...13..811G
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.
Bibcode: 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: The ultraviolet variability of the T Tauri star RW Aurigae.
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1981NASCP2171..185I
Altcode: 1981uviu.nasa..185I; 1980IUE80......185I; 1981NASCP3171..185I
Between 1978 and 1979 the visible brightness of RW Aurigae increased
by 0.9 mag. During this time (1) CIV and SiIV increased by factors
of 2 to 4 while the lower ionization lines remained unchanged; (2)
the fluorescent OI line increased by a factor of 8; (3) the shell
spectrum changed from emission to absorption; and (4) the ultraviolet
continuum brightened by 2.3 mag. On a time scale of a week the continuum
varied by as much as 0.8 mag., but the MgII emission lines showed no
variability over 10 percent. An active chromosphere, transition region,
and envelope cooled by mass loss are hypothesized in order to explain
the ultraviolet observations of RW Aur.
Title: The Transition Regions & Coronae of Solar-Type Stars
Authors: Giampapa, Mark S.
Bibcode: 1981iue..prop..751G
Altcode:
We propose to obtain low dispersion, high signal-to-noise, short
wavelength spectra for a sample of solar-type stars for which X-ray
data are available. The transition region pressures, as inferred from
the short wavelength spectra to be obtained with the IUE satellite,
will be compared to the values of the transition region pressures
predicted by the scaling laws advanced by Rosner, Tucker and Vaiana
(1978) and Golub et al. (1980) on the basis of HEAO-B soft X-ray
observations. In addition, we will assess the energy balance in the
outer atmospheres of solar-type stars by comparing the total transition
region and chromospheric line luminosities to the X-ray luminosities
for the stars considered in this proposal.
Title: UV chromospheric and circumstellar diagnostic features among
F supergiant stars.
Authors: Stencel, R. E.; Worden, S. P.; Giampapa, M. S.
Bibcode: 1981NASCP2171..311S
Altcode: 1981NASCP3171..311S; 1980IUE80......311S; 1981uviu.nasa..311S
A survey of F supergiant stars to evaluate the extension of
chromospheric and circumstellar characteristics commonly observed
in the slightly cooler G, K, and M supergiant is discussed. An
ultraviolet survey was elected since UV features of Mg II and Fe II
might persist in revealing outer atmosphere phenomena even among F
supergiants. The encompassed spectral types F0 to G0, and luminosity
classes Ib, Ia, and Ia-0. In addition, the usefulness of the emission
line width-to-luminosity correlation for the G-M stars in both the Ca
II and Mg II lines is examined.
Title: High Dispersion, Long Wavelength Studies of T Tauri Stars
Authors: Giampapa, Mark S.
Bibcode: 1981iue..prop..762G
Altcode:
We propose to obtain high dispersion, high quality, long wavelength
spectra as well as some low dispersion, short wavelength spectra for
a sample of T Tauri stars. The data to be obtained in this program
will be supplemented with ground-based, high spectral resolution
optical observations to be acquired simultaneously with the IUE
observations. These data will be used for a comprehensive study of the
structure, energy balance, velocity fields and mass loss rates that
characterize the atmospheres of T Tauri stars. More specifically,
we will develop semi-empirical models for the chromospheres and
transition regions of specific T Tauri stars in order to parameterize
the atmospheres Of these pre-main sequence objects and to attempt to
discover why the T Tauri stars do not obey the Wilson-Bappu relation.
Title: IUE observations of the Mg II emission lines in T Tauri stars.
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1980PASP...92..548I
Altcode:
No abstract at ADS
Title: The Chromospheres of M Dwarf Stars
Authors: Giampapa, M. S.; Worden, S. P.; Linsky, J. L.
Bibcode: 1980BAAS...12..807G
Altcode:
No abstract at ADS
Title: The ultraviolet spectrum of the T Tau star RW Aur.
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1980ApJ...239L.115I
Altcode:
Ultraviolet spectra of the T Tauri star RW Aurigae have been obtained
with the International Ultraviolet Explorer. Emission lines include
Mg II, Fe II, Cr II, Si I, Si II, Si III, Si IV, C II, C IV, and
L alpha. The spectrum roughly resembles the solar chromospheric
spectrum, but the surface fluxes are 200 times greater. N V and He
II appear to be absent, a possible indication of either an extended
chromosphere cooled by mass loss or an optically thick, hot shocked
region. The ultraviolet excess in RW Aur is strong, consistent with
Balmer continuum emission. The observed continuum may be used to set
limits on the type and amount of extinction affecting the star.
Title: Emission measures derived from far ultraviolet spectra of T
Tau stars.
Authors: Cram, L. E.; Giampapa, M. S.; Imhoff, C. L.
Bibcode: 1980ApJ...238..905C
Altcode:
Spectroscopic diagnostics based on UV emission line observations have
been developed to study the solar chromosphere, transition region,
and corona. The atmospheric properties that can be inferred from
observations of total line intensities include the temperature, by
identifying the ionic species present; the temperature distribution of
the emission measure, from the absolute intensities; and the electron
density of the source, from line intensity ratios sensitive to the
electron density. In the present paper, the temperature distribution of
the emission measure is estimated from observations of far UV emission
line fluxes of the T Tauri stars, RW Aurigae and RU Lupi, made on the
IUE. A crude estimate of the electron density of one star is obtained,
using density-sensitive line ratios.
Title: An Estimate of Active Region Filling Factors for Dme-Stars
and Dm-Stars
Authors: Giampapa, M. S.
Bibcode: 1980SAOSR.389..119G
Altcode: 1980csss....1..119G
No abstract at ADS
Title: The chromospheres of M dwarf stars
Authors: Giampapa, Mark Steven
Bibcode: 1980PhDT.......127G
Altcode:
No abstract at ADS
Title: The chromospheres of M Dwarf Stars
Authors: Giampapa, Mark S.
Bibcode: 1980cmds.book.....G
Altcode:
No abstract at ADS
Title: The Chromospheres of M Dwarf Stars.
Authors: Giampapa, M. S.
Bibcode: 1980PhDT.........5G
Altcode:
Single-component, homogeneous, quiescent semi-empirical model
chromospheres are constructed, based upon high resolution,
well-calibrated profiles of the Ca II K line in 3 dMe and 2 dM
stars. The results of the atmospheric models inferred from the
observed Ca II K line profiles reveal several systematic trends
which characterize the chromospheres of M dwarf stars. In particular,
high values of T min/Teff are deduced for the stars considered, thus
indicating an unusually large degree of nonradiative heating present in
the upper photospheres of M dwarf stars. Hence dissipation of mechanical
energy is an important parameter in the control of the energy balance
in the upper photospheres of M dwarf stars. The value of the lower
chromospheric temperature gradient, dT/d log m, is similar for the
M dwarf stars considered. Chromospheric K-line emission strength is
most sensitive to the total amount of chromospheric material present
within the approximate temperature range Tmin-6000K.
Title: The Evolution of the Chromospheres and Transition Regions in
Dwarf Stars
Authors: Giampapa, Mark S.
Bibcode: 1980iue..prop..445G
Altcode:
We propose to study the active chromosphere stars xi Boo A and 70
Oph A. These are solar type stars which exhibit much larger levels
of chromospheric activity than the sun. There are two complementary
aspects of this proposal. Our first objective is to obtain high spectral
resolution observations of upper chromospheric and transition region
spectral diagnostics. These data will be used to model the quiescent
states of these stars and compare their upper atmospheric structure to
the sun and other quiet chromosphere G dwarf stars. Our second objective
is to perform a coordinated optical, X-ray, radio, and IUE ultraviolet
spectral monitoring of these two stars to study flare events. In
particular we hope to observe flare events, model flare structure,
and compare the derived physical conditions in stellar flares to solar
events. We have recently observed extensive large magnetic fields
on these stars, and we believe they exhibit frequent flares. We are
confident that time resolved data needed to model the stellar flares is
obtainable in the required spectral bands, including the IUE ultraviolet
region. The results of these studies will improve our understanding
of solar and stellar chromospheric and non-radiative phenomena.
Title: IUE Observations of T. Tauri Stars
Authors: Imhoff, C. L.; Giampapa, M. S.
Bibcode: 1979BAAS...11..681I
Altcode:
No abstract at ADS
Title: High Resolution Spectra of Stellar Flares
Authors: Worden, S. P.; Schneeberger, T. J.; Deluca, E.; Giampapa, M.
Bibcode: 1979BAAS...11..628W
Altcode:
No abstract at ADS
Title: The Ca II H and K Lines in dMe and non-dMe Stars
Authors: Giampapa, M. S.; Worden, S. P.; Schneeberger, T. J.; Cram,
L. E.
Bibcode: 1979BAAS...11..625G
Altcode:
No abstract at ADS
Title: The effect of chromospheric activity on metallicity
measurements.
Authors: Giampapa, M. S.; Gilliam, L. B.; Worden, S. P.
Bibcode: 1979ApJ...229.1143G
Altcode:
The intermediate band uvby-beta photometric system is used to observe
solar active (plage) regions and quiescent regions in an effort
to determine the effect of chromospheric activity on photometric
metallicity measurements. It is found that the active regions appear
metal deficient with respect to the quiet sun by approximately 35%.
Title: Compact variable extragalactic objects and small-pitch-angle
synchrotron theory.
Authors: Cocke, W. J.; Giampapa, M. S.; Pacholczyk, A. G.
Bibcode: 1979ApJ...229..503C
Altcode:
A small-pitch-angle synchrotron radiation model of luminous compact
variable radio sources is applied to a large class of such objects. The
model consists of a massive spinning object endowed with an extended
magnetosphere. The electrons are accelerated near its surface by a
strong electric field, spiral along the field lines, and lose their
energy by the small-pitch-angle synchrotron process responsible for
the observed centimeter and infrared radiation. The model adequately
explains the observed variability of the majority of compact sources for
(rest frame) frequencies greater than about 10 GHz. The model is not
able to account for the variability of sources at lower frequencies,
indicating clearly that an investigation of alternative radiation
mechanisms or relativistic effects resulting from bulk motion is
necessary.
Title: A Survey of Astronomy Graduate Students
Authors: Giampapa, M. S.
Bibcode: 1979AstQ....3....5G
Altcode:
No abstract at ADS
Title: Chromospheric emission lines in the red spectrum of AD
Leonis. I. The nonflare spectrum.
Authors: Giampapa, M. S.; Linsky, J. L.; Schneeberger, T. J.; Worden,
S. P.
Bibcode: 1978ApJ...226..144G
Altcode:
High-resolution red (5300-7300 A) spectra of the flare star AD Leonis
were obtained with the Kitt Peak 4 m echelle spectrograph system
at a spectral resolution of 0.22 A at Ha. A series of time-trailed
plates with 5 hours integration in total were averaged together
to obtain a representation of the star's nonflaring spectrum with
high signal-to-noise ratio. The He i A5876 triplet line and A6678
singlet line appear in emission with measured equivalent widths of
0.312 + 0.016 A and 0.058 + 0.029 A, respectively. The corresponding
triplet-to-singlet line flux ratio is 3.7, close to the ratio of the
level statistical weights. We argue that the He i lines are not produced
by recombination and cascade following photoionization by A < 504
A coronal photons, but are instead collisionally excited. We suggest
that these lines are formed in a geometrically thin chromospheric layer
at 20,000-50,000 K with a column density of nel 6 x 1018 . The sodium
D emission lines (A5890, AS 896) are found to be stellar in origin,
with measured FWHM of 0.7 A for both lines, and the Ha line has a
FWHM of 1.4 A. No other chromospheric emission lines were found in
this spectral region. Subject headings: stars: chromospheres - stars:
emission-line - stars: flare - stars: individual
Title: The Effects of Stellar Chromospheric Activity on Metallicity
Measurements.
Authors: Giampapa, M. S.; Worden, S. P.
Bibcode: 1978BAAS...10..458G
Altcode:
No abstract at ADS
Title: Application of the Small-Pitch Angle Synchrotron Theory to
a Wide Class of Variable Compact Extragalactic Objects.
Authors: Cocke, W. J.; Giampapa, M. S.; Pacholczyk, A. G.
Bibcode: 1978BAAS...10R.404C
Altcode:
No abstract at ADS
Title: On the polarization and mass of BL Lac objects.
Authors: Angel, J. R. P.; Boroson, T. A.; Adams, M. T.; Duerr, R.;
Giampapa, M. S.; Gresham, M. S.; Gural, P. S.; Hubbard, E. N.; Kopriva,
D. A.; Moore, R. L.; Peterson, B. M.; Schmidt, G. D.; Turnshek, D. A.;
Wilkerson, M. S.; Zotov, N. V.; Maza, J.; Kinman, T. D.
Bibcode: 1978bllo.conf..117A
Altcode: 1978blo..conf..117A
Optical polarization measurements have been obtained for 12 BL Lac
objects, including many repeated observations during a night. It
is found that the shortest time scale for substantial changes in
polarization is about 10 hours. Fluctuations with a 1-day characteristic
time are common. This time is identified with the dynamical time
scale of the most luminous material close to a black hole. It follows
that the typical mass is about 2 billion solar masses. Observations
over several years show that five out of 12 objects have a preferred
orientation of position angle, perhaps defined by the angular-momentum
vector of accreted material.
Title: Chromospheric Emission Lines in the Quiescent Spectrum of
the Flare Star AD Leo
Authors: Giampapa, M. S.; Linsky, J. L.; Schneeberger, T. J.; Worden,
S. P.
Bibcode: 1977BAAS....9..593G
Altcode:
No abstract at ADS