testa

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Author name code: testa
ADS astronomy entries on 2022-09-14
author:"Testa, Paola"

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Title: NExtUP: The Normal-incidence Extreme Ultraviolet Photometer
Authors: Garraffo, Cecilia; Jeremy, Drake; Testa, Paola; Gladstone,
Randy; Cheimets, . Peter; Koskinen, Tommi; Wolk, Scott; Barstow,
Martin; Glocer, Alex; France, Kevin; Mason, James; Siegmund, Oswald;
Alvarado Gómez, Julián David; Cohen, Ofer; Kashyap, Vinay; Fleming,
Brian; Wargelin, Bradford; Gronoff, Guillaume; Cadwell, David;
Monsch, Kristina; Youngblood, Allison; Norton, Timothy; Lopez-Morales,
Mercedes; Soufli, Regina
2022cosp...44.1995G Altcode:
The evolution and loss of exoplanetary atmospheres depend critically
on the host stars' extreme ultraviolet (EUV) spectra and fluxes. EUV
radiation is absorbed at high altitude, in the exosphere and upper
thermosphere, where the gas can be readily heated to high temperatures
conducive to escape. EUV heating is thought to be a dominant atmospheric
loss mechanism during most of a planet's life. There are only a
handful of accurately measured EUV stellar fluxes, all dating from
Extreme Ultraviolet Explorer (EUVE) observations in the '90s. These
observations were mostly single snapshots of what are highly variable
and often flaring sources. Consequently, current models of stellar
EUV emission are uncertain by more than an order of magnitude and
are the largest uncertainty in planetary atmospheric loss models. The
Normal-incidence Extreme Ultraviolet Photometer (NExtUP) is a smallsat
mission concept designed to measure the EUV radiation conditions of
exoplanet host stars, and F-M type stars in general. NExtUP will use
periodic and aperiodic multilayers on off-axis parabolic mirrors and a
prime focus microchannel plate detector to image stars in 5 bandpasses
between 150 and 900 A, down to flux limits two orders of magnitude lower
than reached by EUVE. NExtUP may also accomplish a compelling array
of secondary science goals, including using line-of-sight absorption
measurements to understand the structure of the local interstellar
medium, and imaging EUV emission from energetic processes on solar
system objects at unprecedented spatial resolution. NExtUP is well
within smallsat weight limits, requires no special orbital conditions,
and would be flown on a spacecraft supplied by MOOG Industries. It
draws on decades of mission heritage expertise at SAO and LASP,
including similar instruments successfully launched and operated to
observe the Sun.

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Title: Diagnostics of non-Maxwellian electron distributions in solar
active regions from Fe XII lines observed by Hinode/EIS and IRIS
Authors: Del Zanna, G.; Polito, V.; Dudík, J.; Testa, P.; Mason,
H. E.; Dzifčáková, E.
2022arXiv220707026D Altcode:
We present joint Hinode/EIS and IRIS observations of Fe XII lines
in active regions, both on-disk and off-limb. We use an improved
calibration for the EIS data, and find that the 192.4 A / 1349 A
observed ratio is consistent with the values predicted by CHIANTI and
the coronal approximation in quiescent areas, but not in all active
region observations, where the ratio is often lower than expected
by up to a factor of about two. We investigate a number of physical
mechanisms that could affect this ratio, such as opacity and absorption
from cooler material. We find significant opacity in the EIS Fe XII
193 and 195 A lines, but not in the 192.4 A line, in agreement with
previous findings. As we cannot rule out possible EUV absorption by
H, He and He II in the on-disk observations, we focus on an off-limb
observation where such absorption is minimal. After considering these,
as well as possible non-equilibrium effects, we suggest that the most
likely explanation for the observed low Fe XII 192.4 A / 1349 A ratio
is the presence of non-Maxwellian electron distributions in the active
regions. This is in agreement with previous findings based on EIS and
IRIS observations independently.

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Title: Parallel Plasma Loops and the Energization of the Solar Corona
Authors: Peter, Hardi; Chitta, Lakshmi Pradeep; Chen, Feng; Pontin,
David I.; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Testa, Paola; Tiwari, Sanjiv K.; Walsh, Robert W.; Warren, Harry P.
2022ApJ...933..153P Altcode: 2022arXiv220515919P
The outer atmosphere of the Sun is composed of plasma heated to
temperatures well in excess of the visible surface. We investigate
short cool and warm (&lt;1 MK) loops seen in the core of an active
region to address the role of field-line braiding in energizing these
structures. We report observations from the High-resolution Coronal
imager (Hi-C) that have been acquired in a coordinated campaign with
the Interface Region Imaging Spectrograph (IRIS). In the core of the
active region, the 172 Å band of Hi-C and the 1400 Å channel of IRIS
show plasma loops at different temperatures that run in parallel. There
is a small but detectable spatial offset of less than 1″ between
the loops seen in the two bands. Most importantly, we do not see
observational signatures that these loops might be twisted around each
other. Considering the scenario of magnetic braiding, our observations
of parallel loops imply that the stresses put into the magnetic field
have to relax while the braiding is applied: the magnetic field never
reaches a highly braided state on these length scales comparable to
the separation of the loops. This supports recent numerical 3D models
of loop braiding in which the effective dissipation is sufficiently
large that it keeps the magnetic field from getting highly twisted
within a loop.

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Title: The Solar X-ray Corona
Authors: Testa, Paola; Reale, Fabio
2022arXiv220603530T Altcode:
The X-ray emission from the Sun reveals a very dynamic hot atmosphere,
the corona, which is characterized by a complex morphology and broad
range of timescales of variability and spatial structuring. The
solar magnetic fields play a fundamental role in the heating and
structuring of the solar corona. Increasingly higher quality X-ray
solar observations with high spatial (down to subarcsec) and temporal
resolution provide fundamental information to refine our understanding
of the solar magnetic activity and of the underlying physical processes
leading to the heating of the solar outer atmosphere. Here we provide a
brief historical overview of X-ray solar observations and we summarize
recent progress in our understanding of the solar corona as made
possible by state-of-the-art current X-ray observations.

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Title: Diagnostics of Non-Maxwellian Electron Distributions in
Solar Active Regions from Fe XII Lines Observed by the Hinode
Extreme Ultraviolet Imaging Spectrometer and Interface Region
Imaging Spectrograph
Authors: Del Zanna, G.; Polito, V.; Dudík, J.; Testa, P.; Mason,
H. E.; Dzifčáková, E.
2022ApJ...930...61D Altcode:
We present joint Hinode Extreme Ultraviolet Imaging Spectrometer
(EIS) and Interface Region Imaging Spectrograph (IRIS) observations
of Fe XII lines in active regions, both on-disk and off-limb. We use
an improved calibration for the EIS data, and find that the 192.4
Å/1349 Å observed ratio is consistent with the values predicted by
CHIANTI and the coronal approximation in quiescent areas, but not in
all active-region observations, where the ratio is often lower than
expected by up to a factor of about two. We investigate a number of
physical mechanisms that could affect this ratio, such as opacity and
absorption from cooler material. We find significant opacity in the EIS
Fe XII 193 and 195 Å lines, but not in the 192.4 Å line, in agreement
with previous findings. As we cannot rule out possible EUV absorption by
H, He, and He II in the on-disk observations, we focus on an off-limb
observation where such absorption is minimal. After considering these,
as well as possible nonequilibrium effects, we suggest that the most
likely explanation for the observed low Fe XII 192.4 Å/1349 Å ratio
is the presence of non-Maxwellian electron distributions in the active
regions. This is in agreement with previous findings based on EIS and
IRIS observations independently.

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Title: Chromospheric emission from nanoflare heating in RADYN
simulations
Authors: Bakke, H.; Carlsson, M.; Rouppe van der Voort, L.; Gudiksen,
B. V.; Polito, V.; Testa, P.; De Pontieu, B.
2022A&A...659A.186B Altcode: 2022arXiv220111961B
Context. Heating signatures from small-scale magnetic reconnection
events in the solar atmosphere have proven to be difficult to
detect through observations. Numerical models that reproduce flaring
conditions are essential in understanding how nanoflares may act as a
heating mechanism of the corona. Aims: We study the effects of
non-thermal electrons in synthetic spectra from 1D hydrodynamic RADYN
simulations of nanoflare heated loops to investigate the diagnostic
potential of chromospheric emission from small-scale events. 
Methods: The Mg II h and k, Ca II H and K, Ca II 854.2 nm, and Hα and
Hβ chromospheric lines were synthesised from various RADYN models of
coronal loops subject to electron beams of nanoflare energies. The
contribution function to the line intensity was computed to better
understand how the atmospheric response to the non-thermal electrons
affects the formation of spectral lines and the detailed shape of
their spectral profiles. Results: The spectral line signatures
arising from the electron beams highly depend on the density of the
loop and the lower cutoff energy of the electrons. Low-energy (5 keV)
electrons deposit their energy in the corona and transition region,
producing strong plasma flows that cause both redshifts and blueshifts
of the chromospheric spectra. Higher-energy (10 and 15 keV) electrons
deposit their energy in the lower transition region and chromosphere,
resulting in increased emission from local heating. Our results indicate
that effects from small-scale events can be observed with ground-based
telescopes, expanding the list of possible diagnostics for the presence
and properties of nanoflares.

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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). II. Flares and Eruptions
Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin,
Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick;
Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward;
Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul;
Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub,
Leon; The
2022ApJ...926...53C Altcode: 2021arXiv210615591C
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (subarcseconds) and temporal (less than a few tens of
seconds) scales of the coronal dynamics of solar flares and eruptive
phenomena. The highest-resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by the Interface Region Imaging
Spectrograph for the low solar atmosphere, we need high-resolution
spectroscopic measurements with simultaneous imaging to understand the
dominant processes. In this paper: (1) we introduce the Multi-slit Solar
Explorer (MUSE), a spaceborne observatory to fill this observational
gap by providing high-cadence (&lt;20 s), subarcsecond-resolution
spectroscopic rasters over an active region size of the solar transition
region and corona; (2) using advanced numerical models, we demonstrate
the unique diagnostic capabilities of MUSE for exploring solar coronal
dynamics and for constraining and discriminating models of solar flares
and eruptions; (3) we discuss the key contributions MUSE would make
in addressing the science objectives of the Next Generation Solar
Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme
Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope
(and other ground-based observatories) can operate as a distributed
implementation of the NGSPM. This is a companion paper to De Pontieu
et al., which focuses on investigating coronal heating with MUSE.

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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). I. Coronal Heating
Authors: De Pontieu, Bart; Testa, Paola; Martínez-Sykora, Juan;
Antolin, Patrick; Karampelas, Konstantinos; Hansteen, Viggo; Rempel,
Matthias; Cheung, Mark C. M.; Reale, Fabio; Danilovic, Sanja; Pagano,
Paolo; Polito, Vanessa; De Moortel, Ineke; Nóbrega-Siverio, Daniel;
Van Doorsselaere, Tom; Petralia, Antonino; Asgari-Targhi, Mahboubeh;
Boerner, Paul; Carlsson, Mats; Chintzoglou, Georgios; Daw, Adrian;
DeLuca, Edward; Golub, Leon; Matsumoto, Takuma; Ugarte-Urra, Ignacio;
McIntosh, Scott W.; the MUSE Team
2022ApJ...926...52D Altcode: 2021arXiv210615584D
The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of
a multislit extreme ultraviolet (EUV) spectrograph (in three spectral
bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in
two passbands around 195 Å and 304 Å). MUSE will provide unprecedented
spectral and imaging diagnostics of the solar corona at high spatial
(≤0.″5) and temporal resolution (down to ~0.5 s for sit-and-stare
observations), thanks to its innovative multislit design. By obtaining
spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX-Fe
XXI 108 Å) covering a wide range of transition regions and coronal
temperatures along 37 slits simultaneously, MUSE will, for the first
time, "freeze" (at a cadence as short as 10 s) with a spectroscopic
raster the evolution of the dynamic coronal plasma over a wide range of
scales: from the spatial scales on which energy is released (≤0.″5)
to the large-scale (~170″ × 170″) atmospheric response. We use
numerical modeling to showcase how MUSE will constrain the properties of
the solar atmosphere on spatiotemporal scales (≤0.″5, ≤20 s) and
the large field of view on which state-of-the-art models of the physical
processes that drive coronal heating, flares, and coronal mass ejections
(CMEs) make distinguishing and testable predictions. We describe the
synergy between MUSE, the single-slit, high-resolution Solar-C EUVST
spectrograph, and ground-based observatories (DKIST and others), and
the critical role MUSE plays because of the multiscale nature of the
physical processes involved. In this first paper, we focus on coronal
heating mechanisms. An accompanying paper focuses on flares and CMEs.

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Title: Observations of the solar atmosphere - constraints on models,
and understanding of the underlying physical processes
Authors: Testa, Paola
2021AGUFMSH42B..01T Altcode:
I will discuss how high resolution current (and future) oberservations
of the solar atmosphere (e.g., with SDO, Hinode, SST, IRIS, PSP),
help us advance our understanding of the complex physical processing
underlying the observed phenomena. In particular I will discuss the
crucial role of the synergy between observations and state-of-the-art
models.

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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE): II. Flares and Eruptions
Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin,
Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred,
Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope,
Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah;
Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon
2021AGUFMSH51A..08C Altcode:
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (sub-arcseconds) and temporal scales (less than a few tens
of seconds) of the coronal dynamics of solar flares and eruptive
phenomena. The highest resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by IRIS for the low solar atmosphere,
we need high-resolution spectroscopic measurements with simultaneous
imaging to understand the dominant processes. In this paper: (1)
we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne
observatory to fill this observational gap by providing high-cadence
(&lt;20 s), sub-arcsecond resolution spectroscopic rasters over an
active region size of the solar transition region and corona; (2)
using advanced numerical models, we demonstrate the unique diagnostic
capabilities of MUSE for exploring solar coronal dynamics, and for
constraining and discriminating models of solar flares and eruptions;
(3) we discuss the key contributions MUSE would make in addressing the
science objectives of the Next Generation Solar Physics Mission (NGSPM),
and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the
Daniel K Inouye Solar Telescope (and other ground-based observatories)
can operate as a distributed implementation of the NGSPM. This is a
companion paper to De Pontieu et al. (2021, also submitted to SH-17),
which focuses on investigating coronal heating with MUSE.

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Title: Preliminary Results from the Marshall Grazing Incidence X-ray
Spectrometer (MaGIXS)
Authors: Winebarger, Amy; Savage, Sabrina; Kobayashi, Ken; Champey,
Patrick; Golub, Leon; Walsh, Robert; Athiray, P. S.; Bradshaw, Stephen;
Cheimets, Peter; Cirtain, Jonathan; DeLuca, Edward; Del Zanna, Giulio;
Mason, Helen; McKenzie, David; Ramsey, Brian; Reeves, Katharine;
Testa, Paola; Vigil, Genevieve; Warren, Harry
2021AGUFMSH51A..06W Altcode:
Coronal heating mechanisms are notoriously difficult to constrain with
current observations. We present new observations from an instrument
designed to measure a critical diagnostic of the frequency heating
events in active regions. The Marshall Grazing Incidence X-ray
Spectrometer (MaGIXS) is a sounding rocket mission that aims to
observe the soft x-ray solar spectrum (0.6 2.5 nm) with both spatial
and spectral resolution. This wavelength range has several high
temperature and abundance diagnostics that can be used to infer the
coronal heating frequency. MaGIXS will observe the Sun through a 12
x 33 slot, producing “overlappograms, where the spatial and spectral
information are overlapped and must be unfolded. In this presentation,
I will report on the MaGIXS launch and data collection and provide
preliminary analysis of MaGIXS observations.

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Title: Probing the physics of coronal heating with the Multi-slit
Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Testa, Paola; Martinez-Sykora, Juan;
Cheung, Chun Ming Mark
2021AGUFMSH55B1836D Altcode:
The Multi-slit Solar Explorer (MUSE) is a proposed NASA MIDEX mission,
currently in Phase A, composed of a multi-slit EUV spectrograph (in
three narrow spectral bands centered around 171Å, 284Å, and 108Å)
and an EUV context imager (in two narrow passbands around 195Å and
304Å). MUSE will provide unprecedented spectral and imaging diagnostics
of the solar corona at high spatial (~0.5 arcseconds), and temporal
resolution (down to ~0.5 seconds) thanks to its innovative multi-slit
design. By obtaining spectra in 4 bright EUV lines (Fe IX 171Å,
Fe XV 284Å, Fe XIX-XXI 108Å) covering a wide range of transition
region and coronal temperatures along 37 slits simultaneously, MUSE
will for the first time be able to “freeze" (at a cadence as short as
10 seconds) with a spectroscopic raster the evolution of the dynamic
coronal plasma over a wide range of scales: from the spatial scales
on which energy is released (&lt;0.5 arcsec) to the large-scale often
active-region size (~ 170 arcsec x 170 arcsec) atmospheric response. We
use advanced numerical modeling to showcase how MUSE will constrain
the properties of the solar atmosphere on the spatio-temporal scales
(&lt;0.5 arcsec, &lt;20 seconds) and large field-of-view on which
various state-of-the-art models of the physical processes that drive
coronal heating, solar flares and coronal mass ejections (CMEs)
make distinguishing and testable predictions. We describe how the
synergy between MUSE, the single-slit, high-resolution Solar-C EUVST
spectrograph, and ground-based observatories (DKIST and others) can
address how the solar atmosphere is energized, and the critical role
MUSE plays because of the multi-scale nature of the physical processes
involved. We focus on how comparisons between MUSE observations and
theoretical models will significantly further our understanding of
coronal heating mechanisms. This is a companion paper to Cheung et
al. (2021), also submitted to SH-17.

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Title: NExtUP: the Normal-incidence Extreme Ultraviolet Photometer
Authors: Drake, Jeremy J.; Cheimets, Peter; Garraffo, Cecilia;
Wargelin, Bradford; Youngblood, Allison; Kashyap, Vinay L.; Testa,
Paola; Caldwell, David; Mason, James; Fleming, Brian; France, Kevin;
Wolk, Scott; Siegmund, Oswald; Koskinen, Tommi; Alvarado-Gomez, Julian;
Lopez-Morales, Maria Mercedes; Gronoff, Guillaume; Bookbinder, Jay;
Barstow, Martin; Windt, David; Gladstone, Randy; Loghry, Christopher;
Yarbrough, Rix
2021SPIE11821E..08D Altcode:
The Normal-incidence Extreme Ultraviolet Photometer (NExtUP) is
a smallsat mission concept designed to measure the EUV radiation
conditions of exoplanet host stars, and F-M type stars in general. EUV
radiation is absorbed at high altitude in a planetary atmosphere, in
the exosphere and upper thermosphere, where the gas can be readily
heated to escape temperatures. EUV heating and ionization are the
dominant atmospheric loss drivers during most of a planet's life. There
are only a handful of accurately measured EUV stellar fluxes, all
dating from Extreme Ultraviolet Explorer (EUVE) observations in
the `90s. Consequently, current models of stellar EUV emission are
uncertain by more than an order of magnitude and dominate uncertainties
in planetary atmospheric loss models. NExtUP will use periodic and
aperiodic multilayers on off-axis parabolic mirrors and a prime focus
microchannel plate detector to image stars in 5 bandpasses between
150 and 900°A down to flux limits two orders of magnitude lower
than reached by EUVE. NExtUP may also accomplish a compelling array
of secondary science goals, including using line-of-sight absorption
measurements to understand the structure of the local interstellar
medium, and imaging EUV emission from energetic processes on solar
system objects at unprecedented spatial resolution. NExtUP is well
within smallsat weight limits, requires no special orbital conditions,
and would be flown on a spacecraft supplied by MOOG Industries. It
draws on decades of mission heritage expertise at SAO and LASP,
including similar instruments successfully launched and operated to
observe the Sun.

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

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Title: A New View of the Solar Interface Region from the Interface
Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Polito, Vanessa; Hansteen, Viggo; Testa,
Paola; Reeves, Katharine K.; Antolin, Patrick; Nóbrega-Siverio,
Daniel Elias; Kowalski, Adam F.; Martinez-Sykora, Juan; Carlsson,
Mats; McIntosh, Scott W.; Liu, Wei; Daw, Adrian; Kankelborg, Charles C.
2021SoPh..296...84D Altcode: 2021arXiv210316109D
The Interface Region Imaging Spectrograph (IRIS) has been obtaining
near- and far-ultraviolet images and spectra of the solar atmosphere
since July 2013. IRIS is the highest resolution observatory to provide
seamless coverage of spectra and images from the photosphere into the
low corona. The unique combination of near- and far-ultraviolet spectra
and images at sub-arcsecond resolution and high cadence allows the
tracing of mass and energy through the critical interface between the
surface and the corona or solar wind. IRIS has enabled research into the
fundamental physical processes thought to play a role in the low solar
atmosphere such as ion-neutral interactions, magnetic reconnection, the
generation, propagation, and dissipation of waves, the acceleration of
non-thermal particles, and various small-scale instabilities. IRIS has
provided insights into a wide range of phenomena including the discovery
of non-thermal particles in coronal nano-flares, the formation and
impact of spicules and other jets, resonant absorption and dissipation
of Alfvénic waves, energy release and jet-like dynamics associated
with braiding of magnetic-field lines, the role of turbulence and the
tearing-mode instability in reconnection, the contribution of waves,
turbulence, and non-thermal particles in the energy deposition during
flares and smaller-scale events such as UV bursts, and the role of flux
ropes and various other mechanisms in triggering and driving CMEs. IRIS
observations have also been used to elucidate the physical mechanisms
driving the solar irradiance that impacts Earth's upper atmosphere,
and the connections between solar and stellar physics. Advances in
numerical modeling, inversion codes, and machine-learning techniques
have played a key role. With the advent of exciting new instrumentation
both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST)
and the Atacama Large Millimeter/submillimeter Array (ALMA), and
space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim
to review new insights based on IRIS observations or related modeling,
and highlight some of the outstanding challenges.

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Title: Reconnection nanojets in the solar corona
Authors: Antolin, Patrick; Pagano, Paolo; Testa, Paola; Petralia,
Antonino; Reale, Fabio
2021NatAs...5...54A Altcode: 2020NatAs.tmp..201A; 2020NatAs.tmp..186A
The solar corona is shaped and mysteriously heated to millions of
degrees by the Sun's magnetic field. It has long been hypothesized
that the heating results from a myriad of tiny magnetic energy
outbursts called nanoflares, driven by the fundamental process of
magnetic reconnection. Misaligned magnetic field lines can break and
reconnect, producing nanoflares in avalanche-like processes. However,
no direct and unique observations of such nanoflares exist to date,
and the lack of a smoking gun has cast doubt on the possibility of
solving the coronal heating problem. From coordinated multi-band
high-resolution observations, we report on the discovery of very fast
and bursty nanojets, the telltale signature of reconnection-based
nanoflares resulting in coronal heating. Using state-of-the-art
numerical simulations, we demonstrate that the nanojet is a consequence
of the slingshot effect from the magnetically tensed, curved magnetic
field lines reconnecting at small angles. Nanojets are therefore the
key signature of reconnection-based coronal heating in action.

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Title: Reconnection Nanojets in the Solar Corona
Authors: Antolin, Patrick; Reale, Fabio; Testa, Paola; Pagano, Paolo;
Petralia, Antonino
2021cosp...43E1798A Altcode:
The solar corona is shaped and mysteriously heated to millions of
degrees by the Sun's magnetic field. It has long been hypothesised that
the heating results from a myriad of tiny magnetic energy outbursts
called nanoflares driven by the fundamental process of magnetic
reconnection. Misaligned magnetic field lines can break and reconnect,
producing nanoflares in avalanche-like processes. However, no direct
and unique observations of such nanoflares exist to date, and the
lack of a smoking gun has cast doubt on the possibility of solving the
coronal heating problem. From coordinated multi-band high-resolution
observations here we report on the discovery of very fast and bursty
nanojets, the telltale signature of reconnection-based nanoflares
resulting in coronal heating. Isolated and clustered nanojets are
detected, and a myriad are observed in an avalanche-like progression,
leading to the formation of a coronal loop. Using state-of-the-art
numerical simulations we demonstrate that the nanojet is a consequence
of the slingshot effect from the magnetically tensed, curved magnetic
field lines reconnecting at small angles. Nanojets are therefore the
key signature to look for reconnection-based coronal heating in action.

---------------------------------------------------------
Title: Publisher Correction: Reconnection nanojets in the solar corona
Authors: Antolin, Patrick; Pagano, Paolo; Testa, Paola; Petralia,
Antonino; Reale, Fabio
2021NatAs...5..103A Altcode: 2020NatAs.tmp..204A
An amendment to this paper has been published and can be accessed via
a link at the top of the paper.

---------------------------------------------------------
Title: High Resolution Observations of the Low Atmospheric Response
to Small Heating Events in Active Regions
Authors: Testa, P.; Rouppe van der Voort, L.; De Pontieu, B.; Bakke, H.
2020AGUFMSH004..03T Altcode:
We investigate the low atmospheric response to small heating events
(nano/micro-flares) by analyzing coordinated active region observations
with IRIS and SST, and also using the simultaneous SDO/AIA observations
to study the coronal emission. The events we observe as intense
brightenings in the chromosphere and transition region are clearly
associated with heating of the overlying loops to high temperatures
(5-10MK), as is clear from the strong Fe XVIII emission observed in
the 94A SDO/AIA passband. Some of the chromospheric brightenings have
been observed with the SST with the CRISP instrument in Ca II 8542 and
H-alpha, as well as with the new CHROMIS instrument in Ca II K, which
provides unprecedented resolution. We will present the rich spectral
diagnostics offered by IRIS and SST for these events, including insights
we obtained by applying a k-means clustering analysis to the SST and
IRIS spectra during the heating events. Our observations will help
provide more stringent constraints on the properties of non-thermal
particles in nanoflares and microflares.

---------------------------------------------------------
Title: Chromospheric and TR diagnostics in a large scale numerical
simulation of flux emergence: Synthetic vs Real observables
Authors: Hansteen, V. H.; De Pontieu, B.; Testa, P.; Gosic, M.;
Martinez-Sykora, J.
2020AGUFMSH0010021H Altcode:
Field stored just below or rising to the photosphere will break through
the surface and enter the upper atmosphere once the gradient of the
subphotospheric field strength becomes sufficiently large. Opposite
polarity flux bundles will reconnect in the photosphere and above,
to form steadily longer loops that expand into the outer solar
atmosphere, forming the corona. Some of the emerging flux is likely
due to a local dynamo, but also the direct emergence of large scale
magnetic structures from below is important, even in the quiet Sun. A
significant proportion of this field likely reaches the chromosphere
and may leave imprint on chromospheric dynamics and energetics. Using
large scale numerical models (72x72x60) Mm and the high resolution
spectra and slit jaw images from IRIS, as well as photospheric data
from Hinode/SOT, and SDO/HMI we study the interactions between the
magnetic flux caught in the granular flow field and the chromosphere
and chromospheric field above. We will compare synthetic observables
of the photospheric Fe I 617.3 nm line, the chromospheric Mg II h&amp;k
lines, and the transition region Si IV lines, with their observational
counterparts. We will also generate synthetic ALMA band 3 images. The
comparison of synthetic observational data will let us draw conclusions
as to the validity of the numerical modeling and the importance of flux
emergence for the dynamics and energetics of the outer solar atmosphere.

---------------------------------------------------------
Title: IRIS Observations of the Low-atmosphere Counterparts of Active
Region Outflows
Authors: Polito, Vanessa; De Pontieu, Bart; Testa, Paola; Brooks,
David H.; Hansteen, Viggo
2020ApJ...903...68P Altcode: 2020arXiv201015945P
Active region (AR) outflows have been studied in detail since
the launch of Hinode/EIS and are believed to provide a possible
source of mass and energy to the slow solar wind. In this work, we
investigate the lower atmospheric counterpart of AR outflows using
observations from the Interface Region Imaging Spectrograph (IRIS). We
find that the IRIS Si IV, C II&gt; and Mg II transition region (TR)
and chromospheric lines exhibit different spectral features in the
outflows as compared to neighboring regions at the footpoints ("moss")
of hot AR loops. The average redshift of Si IV in the outflow region
(≍5.5 km s-1) is smaller than typical moss (≍12-13
km s-1) and quiet Sun (≍7.5 km s-1) values,
while the C II line is blueshifted (≍-1.1-1.5 km s-1),
in contrast to the moss where it is observed to be redshifted by
about ≍2.5 km s-1. Further, we observe that the low
atmosphere underneath the coronal outflows is highly structured, with
the presence of blueshifts in Si IV and positive Mg II k2 asymmetries
(which can be interpreted as signatures of chromospheric upflows)
which are mostly not observed in the moss. These observations show a
clear correlation between the coronal outflows and the chromosphere
and TR underneath, which has not been shown before. Our work strongly
suggests that these regions are not separate environments and should
be treated together, and that current leading theories of AR outflows,
such as the interchange reconnection model, need to take into account
the dynamics of the low atmosphere.

---------------------------------------------------------
Title: On the Coronal Temperature in Solar Microflares
Authors: Testa, Paola; Reale, Fabio
2020ApJ...902...31T Altcode:
We present a study of solar imaging and spectral observations of
a microflare, focusing on the temperature diagnostics provided by
the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory, and the Extreme-Ultraviolet Imaging Spectrometer (EIS)
on board Hinode. Our data analysis, in particular from the emission in
the 131 and 94 Å channels, indicates that the heated plasma reaches
temperatures of ≳10 MK, at odds with a previous analysis of the same
event, and we discuss the reason for the discrepancy. A particularly
interesting aspect is the likely presence of the Fe XXIII 263.76 Å
line, though weak, in EIS spectra in the early phases of the event,
supporting the presence of high temperature plasma. Hydrodynamic 1D
modeling of a single loop heated with a 3 minute pulse to 12-15 MK
reproduces well most observed features along one of the brightening
loops, including intensities in the AIA hot channels and their
temporal variability, as well as the intensity, Doppler shift, and
line width of the EIS Fe XXIII line, and its timing relative to the
AIA emission. Overall, we obtain a coherent scenario of a typical
microflaring loop system and provide constraints on the intensity of
the energy release as well as its spatial and temporal distribution,
both along and across the loop.

---------------------------------------------------------
Title: Observation and Modeling of High-temperature Solar Active
Region Emission during the High-resolution Coronal Imager Flight of
2018 May 29
Authors: Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.;
Ugarte-Urra, Ignacio; Brooks, David H.; Winebarger, Amy R.; Savage,
Sabrina; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
Leon; Kobayashi, Ken; McKenzie, David; Morton, Richard; Rachmeler,
Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
2020ApJ...896...51W Altcode:
Excellent coordinated observations of NOAA active region 12712 were
obtained during the flight of the High-resolution Coronal Imager (Hi-C)
sounding rocket on 2018 May 29. This region displayed a typical active
region core structure with relatively short, high-temperature loops
crossing the polarity inversion line and bright "moss" located at the
footpoints of these loops. The differential emission measure (DEM) in
the active region core is very sharply peaked at about 4 MK. Further,
there is little evidence for impulsive heating events in the moss, even
at the high spatial resolution and cadence of Hi-C. This suggests that
active region core heating is occurring at a high frequency and keeping
the loops close to equilibrium. To create a time-dependent simulation of
the active region core, we combine nonlinear force-free extrapolations
of the measured magnetic field with a heating rate that is dependent
on the field strength and loop length and has a Poisson waiting time
distribution. We use the approximate solutions to the hydrodynamic
loop equations to simulate the full ensemble of active region core
loops for a range of heating parameters. In all cases, we find that
high-frequency heating provides the best match to the observed DEM. For
selected field lines, we solve the full hydrodynamic loop equations,
including radiative transfer in the chromosphere, to simulate transition
region and chromospheric emission. We find that for heating scenarios
consistent with the DEM, classical signatures of energy release,
such as transition region brightenings and chromospheric evaporation,
are weak, suggesting that they would be difficult to detect.

---------------------------------------------------------
Title: The Drivers of Active Region Outflows into the Slow Solar Wind
Authors: Brooks, David H.; Winebarger, Amy R.; Savage, Sabrina; Warren,
Harry P.; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
Leon; Kobayashi, Ken; McIntosh, Scott W.; McKenzie, David; Morton,
Richard; Rachmeler, Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
2020ApJ...894..144B Altcode: 2020arXiv200407461B
Plasma outflows from the edges of active regions have been suggested as
a possible source of the slow solar wind. Spectroscopic measurements
show that these outflows have an enhanced elemental composition,
which is a distinct signature of the slow wind. Current spectroscopic
observations, however, do not have sufficient spatial resolution to
distinguish what structures are being measured or determine the driver
of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a
sounding rocket in 2018 May and observed areas of active region outflow
at the highest spatial resolution ever achieved (250 km). Here we use
the Hi-C data to disentangle the outflow composition signatures observed
with the Hinode satellite during the flight. We show that there are
two components to the outflow emission: a substantial contribution
from expanded plasma that appears to have been expelled from closed
loops in the active region core and a second contribution from dynamic
activity in active region plage, with a composition signature that
reflects solar photospheric abundances. The two competing drivers of the
outflows may explain the variable composition of the slow solar wind.

---------------------------------------------------------
Title: Is the High-Resolution Coronal Imager Resolving Coronal
Strands? Results from AR 12712
Authors: Williams, Thomas; Walsh, Robert W.; Winebarger, Amy R.;
Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; Golub,
Leon; Kobayashi, Ken; McKenzie, David E.; Morton, Richard J.; Peter,
Hardi; Rachmeler, Laurel A.; Savage, Sabrina L.; Testa, Paola; Tiwari,
Sanjiv K.; Warren, Harry P.; Watkinson, Benjamin J.
2020ApJ...892..134W Altcode: 2020arXiv200111254W
Following the success of the first mission, the High-Resolution
Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1)
on 2018 May 29 from the White Sands Missile Range, NM, USA. On this
occasion, 329 s of 17.2 nm data of target active region AR 12712 were
captured with a cadence of ≈4 s, and a plate scale of 0.129 arcsec
pixel-1. Using data captured by Hi-C 2.1 and co-aligned
observations from SDO/AIA 17.1 nm, we investigate the widths of 49
coronal strands. We search for evidence of substructure within the
strands that is not detected by AIA, and further consider whether these
strands are fully resolved by Hi-C 2.1. With the aid of multi-scale
Gaussian normalization, strands from a region of low emission that can
only be visualized against the contrast of the darker, underlying moss
are studied. A comparison is made between these low-emission strands
and those from regions of higher emission within the target active
region. It is found that Hi-C 2.1 can resolve individual strands as
small as ≈202 km, though the more typical strand widths seen are
≈513 km. For coronal strands within the region of low emission, the
most likely width is significantly narrower than the high-emission
strands at ≈388 km. This places the low-emission coronal strands
beneath the resolving capabilities of SDO/AIA, highlighting the need
for a permanent solar observatory with the resolving power of Hi-C.

---------------------------------------------------------
Title: IRIS Observations of Short-term Variability in Moss Associated
with Transient Hot Coronal Loops
Authors: Testa, Paola; Polito, Vanessa; De Pontieu, Bart
2020ApJ...889..124T Altcode: 2019arXiv191008201T
We observed rapid variability (≲60 s) at the footpoints of transient,
hot (∼8-10 MK) coronal loops in active region cores, with the
Interface Region Imaging Spectrograph (IRIS). The high spatial (∼0"33)
and temporal (≲5-10 s) resolution of IRIS is often crucial for the
detection of this variability. We show how, in combination with 1D RADYN
loop modeling, these IRIS spectral observations of the transition region
(TR) and chromosphere provide powerful diagnostics of the properties of
coronal heating and energy transport (thermal conduction or nonthermal
electrons, NTEs). Our simulations of nanoflare-heated loops indicate
that emission in the Mg II triplet can be used as a sensitive diagnostic
for nonthermal particles. In our events, we observe a large variety
of IRIS spectral properties (intensity, Doppler shifts, broadening,
chromospheric/TR line ratios, Mg II triplet emission) even for
different footpoints of the same coronal events. In several events,
we find spectroscopic evidence for NTEs (e.g., TR blueshifts and Mg
II triplet emission), suggesting that particle acceleration can occur
even for very small magnetic reconnection events, which are generally
below the detection threshold of hard X-ray instruments that provide
direct detection of emission of nonthermal particles.

---------------------------------------------------------
Title: The Multi-slit Approach to Coronal Spectroscopy with the
Multi-slit Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Martínez-Sykora, Juan; Testa, Paola;
Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo; Cheung, Mark C. M.;
Antolin, Patrick
2020ApJ...888....3D Altcode: 2019arXiv190908818D
The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed
at understanding the physical mechanisms driving the heating of the
solar corona and the eruptions that are at the foundation of space
weather. MUSE contains two instruments, a multi-slit extreme ultraviolet
(EUV) spectrograph and a context imager. It will simultaneously
obtain EUV spectra (along 37 slits) and context images with the
highest resolution in space (0.″33-0.″4) and time (1-4 s) ever
achieved for the transition region (TR) and corona. The MUSE science
investigation will exploit major advances in numerical modeling, and
observe at the spatial and temporal scales on which competing models
make testable and distinguishable predictions, thereby leading to a
breakthrough in our understanding of coronal heating and the drivers
of space weather. By obtaining spectra in four bright EUV lines (Fe
IX 171 Å, Fe XV 284 Å, Fe XIX 108Å, Fe XXI 108 Å) covering a wide
range of TR and coronal temperatures along 37 slits simultaneously,
MUSE will be able to “freeze” the evolution of the dynamic
coronal plasma. We describe MUSE’s multi-slit approach and show
that the optimization of the design minimizes the impact of spectral
lines from neighboring slits, generally allowing line parameters to
be accurately determined. We also describe a Spectral Disambiguation
Code to resolve multi-slit ambiguity in locations where secondary lines
are bright. We use simulations of the corona and eruptions to perform
validation tests and show that the multi-slit disambiguation approach
allows accurate determination of MUSE observables in locations where
significant multi-slit contamination occurs.

---------------------------------------------------------
Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar
Magnetic Network Lanes
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon
E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P.
2019ApJ...887L...8P Altcode: 2019arXiv191102331P
We present high-resolution, high-cadence observations of six,
fine-scale, on-disk jet-like events observed by the High-resolution
Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We
combine the Hi-C 2.1 images with images from the Solar Dynamics
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface
Region Imaging Spectrograph (IRIS), and investigate each event’s
magnetic setting with co-aligned line-of-sight magnetograms from the
SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six
events are jetlet-like (having apparent properties of jetlets), (ii)
all six are rooted at edges of magnetic network lanes, (iii) four of
the jetlet-like events stem from sites of flux cancelation between
majority-polarity network flux and merging minority-polarity flux, and
(iv) four of the jetlet-like events show brightenings at their bases
reminiscent of the base brightenings in coronal jets. The average
spire length of the six jetlet-like events (9000 ± 3000 km) is three
times shorter than that for IRIS jetlets (27,000 ± 8000 km). While
not ruling out other generation mechanisms, the observations suggest
that at least four of these events may be miniature versions of both
larger-scale coronal jets that are driven by minifilament eruptions
and still-larger-scale solar eruptions that are driven by filament
eruptions. Therefore, we propose that our Hi-C events are driven by
the eruption of a tiny sheared-field flux rope, and that the flux rope
field is built and triggered to erupt by flux cancelation.

---------------------------------------------------------
Title: Diagnostics of nanoflare heating in active region core loops
from chromospheric and transition region observations and modeling
Authors: Testa, P.; Polito, V.; De Pontieu, B.; Reale, F.; Graham, D.
2019AGUFMSH13B..07T Altcode:
Rapid variability at the footpoints of active region coronal loops
has been observed (Testa et al. 2013, 2014), and provides powerful
diagnostics of the properties of coronal heating and energy transport
(e.g., Testa et al. 2014, Polito et al. 2018, Reale et al. 2019, Testa
et al. 2019). We will present results of our detailed analysis of
a dozen of IRIS/AIA observations of footpoints brightenings associated
with coronal heating, and will present the distribution of the observed
properties (e.g., duration of brightenings, intensity ratios, Doppler
shifts, non-thermal broadening,..). We will discuss the properties
of coronal heating as inferred from the coupling of these high
spatial, spectral, and temporal resolution chromospheric/transition
region/coronal observations, with modeling. We will also
present results of a new algorithm we have developed for an automatic
detection of these footpoint brightenings in AIA observations (Graham
et al. 2019), which will allow us, in our next step, to significantly
expand the number of events detected, and build more robust statistics
of the properties of nanoflares in active region loops.

---------------------------------------------------------
Title: Fine-scale Explosive Energy Release at Sites of Prospective
Magnetic Flux Cancellation in the Core of the Solar Active Region
Observed by Hi-C 2.1, IRIS, and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.;
De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.;
Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Walsh, Robert W.
2019ApJ...887...56T Altcode: 2019arXiv191101424T
The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial
and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X
emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56
UT. Three morphologically different types (I: dot-like; II: loop-like;
III: surge/jet-like) of fine-scale sudden-brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is (not reported before) resemble
IRIS bombs (in size, and brightness with respect to surroundings),
our dot-like events are apparently much hotter and shorter in span
(70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI
magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw
images to examine, at the sites of these events, brightenings and
flows in the transition region and corona and evolution of magnetic
flux in the photosphere. Most, if not all, of the events are seated
at sites of opposite-polarity magnetic flux convergence (sometimes
driven by adjacent flux emergence), implying likely flux cancellation
at the microflare’s polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. In types
I and II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow. The light curves from Hi-C,
AIA, and IRIS peak nearly simultaneously for many of these events,
and none of the events display a systematic cooling sequence as seen in
typical coronal flares, suggesting that these tiny brightening events
have chromospheric/transition region origin.

---------------------------------------------------------
Title: Can superposition of evaporative flows explain broad IRIS Fe
XXI line profiles during flares?
Authors: Polito, V.; Testa, P.; De Pontieu, B.
2019AGUFMSH44A..07P Altcode:
The observation of the high-temperature (&gt;10MK) IRIS Fe XXI 1354A
line with the Interface Region Imaging Spectrograph (IRIS) has provided
significant insights into the chromospheric evaporation process in
flares. In particular, the line is often observed to be completely
blueshifted, in contrast to previous observations at lower spatial
and spectral resolution, and in agreement with predictions from
theoretical models. Interestingly, the line is also observed to be
mostly symmetric and significantly broader than expected from thermal
motions (assuming the peak formation temperature of the ion is in
equilibrium). One popular interpretation for the non-thermal broadening
is the superposition of flows from different loop strands. In this work,
we test this scenario by forward-modelling the Fe XXI line profile
assuming different possible observational scenarios using hydrodynamic
simulations of multi-thread flare loops with the 1D RADYN code. Our
results indicate that the superposition of flows alone cannot easily
reproduce both the symmetry and the significant broadening of the line
and that some other physical process, such as turbulence, or a much
larger ion temperature than previously expected, likely needs to be
invoked in order to explain the observed profiles.

---------------------------------------------------------
Title: The High-Resolution Coronal Imager, Flight 2.1
Authors: Rachmeler, Laurel A.; Winebarger, Amy R.; Savage, Sabrina L.;
Golub, Leon; Kobayashi, Ken; Vigil, Genevieve D.; Brooks, David H.;
Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Testa, Paola; Tiwari, Sanjiv K.; Walsh,
Robert W.; Warren, Harry P.; Alexander, Caroline; Ansell, Darren;
Beabout, Brent L.; Beabout, Dyana L.; Bethge, Christian W.; Champey,
Patrick R.; Cheimets, Peter N.; Cooper, Mark A.; Creel, Helen K.;
Gates, Richard; Gomez, Carlos; Guillory, Anthony; Haight, Harlan;
Hogue, William D.; Holloway, Todd; Hyde, David W.; Kenyon, Richard;
Marshall, Joseph N.; McCracken, Jeff E.; McCracken, Kenneth; Mitchell,
Karen O.; Ordway, Mark; Owen, Tim; Ranganathan, Jagan; Robertson,
Bryan A.; Payne, M. Janie; Podgorski, William; Pryor, Jonathan; Samra,
Jenna; Sloan, Mark D.; Soohoo, Howard A.; Steele, D. Brandon; Thompson,
Furman V.; Thornton, Gary S.; Watkinson, Benjamin; Windt, David
2019SoPh..294..174R Altcode: 2019arXiv190905942R
The third flight of the High-Resolution Coronal Imager (Hi-C 2.1)
occurred on May 29, 2018; the Sounding Rocket was launched from White
Sands Missile Range in New Mexico. The instrument has been modified
from its original configuration (Hi-C 1) to observe the solar corona
in a passband that peaks near 172 Å, and uses a new, custom-built
low-noise camera. The instrument targeted Active Region 12712, and
captured 78 images at a cadence of 4.4 s (18:56:22 - 19:01:57 UT; 5
min and 35 s observing time). The image spatial resolution varies due
to quasi-periodic motion blur from the rocket; sharp images contain
resolved features of at least 0.47 arcsec. There are coordinated
observations from multiple ground- and space-based telescopes providing
an unprecedented opportunity to observe the mass and energy coupling
between the chromosphere and the corona. Details of the instrument
and the data set are presented in this paper.

---------------------------------------------------------
Title: Unfolding Overlappogram Data: Preparing for the COOL-AID
instrument on Hi-C FLARE
Authors: Winebarger, A. R.; De Pontieu, B.; Cheung, C. M. M.;
Martinez-Sykora, J.; Hansteen, V. H.; Testa, P.; Golub, L.; Savage,
S. L.; Samra, J.; Reeves, K.
2019AGUFMSH33A..06W Altcode:
During a solar flare, energy released in the corona streams to the solar
chromosphere, where plasma is heated and then evaporated upward. The
magnitude of these velocities and their evolution as a function of time
can provide quantitative information on the magnitude of energy released
and the method by which it is transported in a solar flare. Measuring
these velocities, however, is quite challenging. Typically, they are
measured with single slit spectrometers, where light passing through
a long but narrow slit is dispersed and emission lines formed across
a range of temperatures are observed. The main issue with using
single slit spectrometers to make this measurement is that they are
rarely pointed at the right place at the right time. Additionally,
their fields of view are limited by narrow slit widths, and although
rastering can effectively expand the field of view, it does so at the
cost of time. This combination means that single slit spectrometers
cannot adequately capture the evolution of the flare velocities. On
the contrary, slitless spectrometers can make "overlappograms”,
which provide both imaging and spectral information over a large field
of view. However, spatial information from different spectral lines
can overlap in the dispersion direction, making the data difficult
to interpret. Furthermore, the spectral resolution of slitless
spectrometers are limited and typically worse than single-slit
spectrometers, since no line fitting (and hence sub-pixel sampling) is
possible. For the next generation of the High-resolution Coronal
Imager (Hi-C) Rocket Experiment, which we are proposing to launch during
a solar flare, we are including the COronal OverLapagram - Ancillary
Imaging Diagnostics (COOL-AID) instrument. COOL-AID is a slitless
spectrometer based on the COronal Spectrographic Imager in the EUV
(COSIE) design, but with a narrow passband coating around 12.9 nm (the
same passband as the primary Hi-C telescope), a spatial resolution of
~1"x2", and a velocity resolution of ~5 km/s. The goal of the COOL-AID
instrument is to determine the velocity associated with the Fe XXI
12.9 nm spectral line during a solar flare. In this talk, we will
demonstrate the unfolding method developed by Cheung et al (2019) to
determine the velocity information from a simulated COOL-AID data set.

---------------------------------------------------------
Title: A comprehensive three-dimensional radiative magnetohydrodynamic
simulation of a solar flare
Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.;
Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.;
Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen,
B.; McIntosh, S. W.
2019NatAs...3..160C Altcode: 2018NatAs...3..160C
Solar and stellar flares are the most intense emitters of X-rays and
extreme ultraviolet radiation in planetary systems1,2. On
the Sun, strong flares are usually found in newly emerging sunspot
regions3. The emergence of these magnetic sunspot groups
leads to the accumulation of magnetic energy in the corona. When
the magnetic field undergoes abrupt relaxation, the energy released
powers coronal mass ejections as well as heating plasma to temperatures
beyond tens of millions of kelvins. While recent work has shed light
on how magnetic energy and twist accumulate in the corona4
and on how three-dimensional magnetic reconnection allows for rapid
energy release5,6, a self-consistent model capturing how
such magnetic changes translate into observable diagnostics has remained
elusive. Here, we present a comprehensive radiative magnetohydrodynamics
simulation of a solar flare capturing the process from emergence to
eruption. The simulation has sufficient realism for the synthesis of
remote sensing measurements to compare with observations at visible,
ultraviolet and X-ray wavelengths. This unifying model allows us to
explain a number of well-known features of solar flares7,
including the time profile of the X-ray flux during flares, origin
and temporal evolution of chromospheric evaporation and condensation,
and sweeping of flare ribbons in the lower atmosphere. Furthermore,
the model reproduces the apparent non-thermal shape of coronal X-ray
spectra, which is the result of the superposition of multi-component
super-hot plasmas8 up to and beyond 100 million K.

---------------------------------------------------------
Title: Large-amplitude Quasiperiodic Pulsations as Evidence of
Impulsive Heating in Hot Transient Loop Systems Detected in the EUV
with SDO/AIA
Authors: Reale, Fabio; Testa, Paola; Petralia, Antonino; Kolotkov,
Dmitrii Y.
2019ApJ...884..131R Altcode: 2019arXiv190902847R
Short heat pulses can trigger plasma pressure fronts inside closed
magnetic tubes in the corona. The alternation of condensations and
rarefactions from the pressure modes drive large-amplitude pulsations in
the plasma emission. Here we show the detection of such pulsations along
magnetic tubes that brighten transiently in the hot 94 Å EUV channel
of the Solar Dynamics Observatory/AIA. The pulsations are consistent
with those predicted by hydrodynamic loop modeling, and confirm pulsed
heating in the loop system. The comparison of observations and model
provides constraints on the heat deposition: a good agreement requires
loop twisting and pulses deposited close to the footpoints with a
duration of 0.5 minutes in one loop, and deposited in the corona with
a duration of 2.5 minutes in another loop of the same loop system.

---------------------------------------------------------
Title: Impulsive Coronal Heating from Large-scale Magnetic
Rearrangements: From IRIS to SDO/AIA
Authors: Reale, Fabio; Testa, Paola; Petralia, Antonino; Graham,
David R.
2019ApJ...882....7R Altcode: 2019arXiv190702291R
The Interface Region Imaging Spectrograph (IRIS) has observed bright
spots at the transition region footpoints associated with heating in
the overlying loops, as observed by coronal imagers. Some of these
brightenings show significant blueshifts in the Si IV line at 1402.77
Å ({log}T[{{K}}]≈ 4.9). Such blueshifts cannot be reproduced by
coronal loop models assuming heating by thermal conduction only, but
are consistent with electron beam heating, highlighting for the first
time the possible importance of nonthermal electrons in the heating of
nonflaring active regions. Here we report on the coronal counterparts
of these brightenings observed in the hot channels of the Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory. We show that
the IRIS bright spots are the footpoints of very hot and transient
coronal loops that clearly experience strong magnetic interactions and
rearrangements, thus confirming the impulsive nature of the heating
and providing important constraints for their physical interpretation.

---------------------------------------------------------
Title: Multi-component Decomposition of Astronomical Spectra by
Compressed Sensing
Authors: Cheung, Mark C. M.; De Pontieu, Bart; Martínez-Sykora,
Juan; Testa, Paola; Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo;
Antolin, Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young,
Peter; MUSE Team
2019ApJ...882...13C Altcode: 2019arXiv190203890C
The signal measured by an astronomical spectrometer may be due to
radiation from a multi-component mixture of plasmas with a range of
physical properties (e.g., temperature, Doppler velocity). Confusion
between multiple components may be exacerbated if the spectrometer
sensor is illuminated by overlapping spectra dispersed from different
slits, with each slit being exposed to radiation from a different
portion of an extended astrophysical object. We use a compressed sensing
method to robustly retrieve the different components. This method can
be adopted for a variety of spectrometer configurations, including
single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer
mission), and slot spectrometers (which produce overlappograms).

---------------------------------------------------------
Title: Automated Detection of Rapid Variability of Moss Using SDO/AIA
and Its Connection to the Solar Corona
Authors: Graham, David R.; De Pontieu, Bart; Testa, Paola
2019ApJ...880L..12G Altcode:
Active region moss—the upper transition region of hot loops—was
observed exhibiting rapid intensity variability on timescales of order
15 s by Testa et al. in a short time series (∼150 s) data set from
Hi-C (High-resolution Coronal Imager). The intensity fluctuations in
the subarcsecond 193A images (∼1.5 MK plasma) were uncharacteristic
of steadily heated moss and were considered an indication of heating
events connected to the corona. Intriguingly, these brightenings
displayed a connection to the ends of transient hot loops seen in
the corona. Following the same active region, AR11520, for 6 days,
we demonstrate an algorithm designed to detect the same temporal
variability in lower resolution Atmospheric Imaging Assembly (AIA)
data, significantly expanding the number of events detected. Multiple
analogous regions to the Hi-C data are successfully detected, showing
moss that appears to “sparkle” prior to clear brightening of
connected high-temperature loops; this is confirmed by the hot AIA
channels and the isolated Fe XVIII emission. The result is illuminating,
as the same behavior has recently been shown by Polito et al. while
simulating nanoflares with a beam of electrons depositing their energy
in the lower atmosphere. Furthermore, the variability is localized
mostly to the hot core of the region, hence we reinforce the diagnostic
potential of moss variability as the driver of energy release in the
corona. The ubiquitous nature of this phenomenon, and the ability to
detect it in data with extended time series, and large fields of view,
opens a new window into investigating the coronal heating mechanism.

---------------------------------------------------------
Title: Can the Superposition of Evaporative Flows Explain Broad Fe
XXI Profiles during Solar Flares?
Authors: Polito, Vanessa; Testa, Paola; De Pontieu, Bart
2019ApJ...879L..17P Altcode:
The observation of the high-temperature (≳10 MK) Fe XXI 1354.1
Å line with the Interface Region Imaging Spectrograph has provided
significant insights into the chromospheric evaporation process in
flares. In particular, the line is often observed to be completely
blueshifted, in contrast to previous observations at lower spatial
and spectral resolution, and in agreement with predictions from
theoretical models. Interestingly, the line is also observed to be
mostly symmetric and significantly broader than expected from thermal
motions (assuming the peak formation temperature of the ion is in
equilibrium). One popular interpretation for the nonthermal broadening
is the superposition of flows from different loop strands. In this
work, we test this scenario by forward-modeling the Fe XXI line profile
assuming different possible observational scenarios using hydrodynamic
simulations of multi-thread flare loops with the 1D RADYN code. Our
results indicate that the superposition of flows alone cannot easily
reproduce both the symmetry and the significant broadening of the line
and that some other physical process, such as turbulence, or a much
larger ion temperature than previously expected, likely needs to be
invoked in order to explain the observed profiles.

---------------------------------------------------------
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of the solar active region observed
by HiC2.1, IRIS and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep; Moore, Ronald L.;
De Pontieu, Bart; Testa, Paola; Winebarger, Amy R.
2019AAS...23411702T Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(HiC2.1) provided unprecedentedly-high spatial and temporal resolution
(150 km, 4.5 s) coronal EUV images of Fe IX/X emission at 172 Å, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &amp;
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament
system in the core of the AR. We complement the 5-minute-duration
HiC2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and
IRIS UV spectra and slit-jaw images to examine, at the sites of these
events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. These
outflows from both ends of the arch filament system are seen as
bi-directional flows in the arch filament system, suggesting that the
well-known counter-streaming flows in large classical filaments could be
driven in the same way as in this arch filament system: by fine-scale
jet-like explosions from fine-scale sites of mixed-polarity field in
the feet of the sheared field that threads the filament. Plausibly,
the flux cancellation at these sites prepares and triggers a fine scale
core-magnetic-field structure (a small sheared/twisted core field or
flux rope along and above the cancellation line) to explode. In types
I &amp; II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow in the manner of larger jets
in coronal holes, quiet regions, and active regions.

---------------------------------------------------------
Title: Radiative MHD Simulation of a Solar Flare
Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats;
De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W.
2019AAS...23431005C Altcode:
We present a radiative MHD simulation of a solar flare. The
computational domain captures the near-surface layers of the convection
zone and overlying atmosphere. Inspired by the observed evolution of
NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed
to emerge in the vicinity of a pre-existing sunspot. The emergence of
twisted magnetic flux generates shear flows that create a pre-existing
flux rope underneath the canopy field of the sunspot. Following erosion
of the overlying bootstrapping field, the flux rope erupts. Rapid
release of magnetic energy results in multi-wavelength synthetic
observables (including X-ray spectra, narrowband EUV images, Doppler
shifts of EUV lines) that are consistent with flare observations. This
works suggests the super-position of multi-thermal, superhot (up
to 100 MK) plasma may be partially responsible for the apparent
non-thermal shape of coronal X-ray sources in flares. Implications
for remote sensing observations of other astrophysical objects is also
discussed. This work is an important stepping stone toward high-fidelity
data-driven MHD models.

---------------------------------------------------------
Title: Multi-component Decomposition of Astronomical Spectra by
Compressed Sensing
Authors: Cheung, Mark; De Pontieu, Bart; Martinez-Sykora, Juan; Testa,
Paola; Winebarger, Amy R.; Daw, Adrian N.; Hansteen, Viggo; Antolin,
Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young, Peter R.
2019AAS...23411603C Altcode:
The signal measured by an astronomical spectrometer may be due to
radiation from a multi-component mixture of plasmas with a range of
physical properties (e.g. temperature, Doppler velocity). Confusion
between multiple components may be exacerbated if the spectrometer
sensor is illuminated by overlapping spectra dispersed from different
slits, with each slit being exposed to radiation from a different
portion of an extended astrophysical object. We use a compressed sensing
method to robustly retrieve the different components. This method can
be adopted for a variety of spectrometer configurations, including
single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer
mission; MUSE) and slot spectrometers (which produce overlappograms).

---------------------------------------------------------
Title: A stellar flare-coronal mass ejection event revealed by X-ray
plasma motions
Authors: Argiroffi, C.; Reale, F.; Drake, J. J.; Ciaravella, A.;
Testa, P.; Bonito, R.; Miceli, M.; Orlando, S.; Peres, G.
2019NatAs...3..742A Altcode: 2019NatAs.tmp..328A; 2019arXiv190511325A
Coronal mass ejections (CMEs), often associated with
flares1-3, are the most powerful magnetic phenomena occurring
on the Sun. Stars show magnetic activity levels up to ten thousand times
higher4, and CME effects on stellar physics and circumstellar
environments are predicted to be substantial5-9. However,
stellar CMEs remain observationally unexplored. Using time-resolved
high-resolution X-ray spectroscopy of a stellar flare on the
active star HR 9024 observed with the High Energy Transmission
Grating Spectrometer onboard the Chandra X-ray Observatory space
telescope, we distinctly detected Doppler shifts in S xvi, Si xiv
and Mg xii lines that indicate upward and downward motions of hot
plasmas (around 10-25 MK) within the flaring loop, with velocities
of 100-400 km s-1, in agreement with a model of a flaring
magnetic tube. Most notably, we also detected a later blueshift in
the O viii line that reveals an upward motion, with velocity 90 ± 30
km s-1, of cool plasma (about 4 MK), that we ascribe to a
CME coupled to the flare. From this evidence we were able to derive
a CME mass of 1 .2-0.8+2.6×1 021
g and a CME kinetic energy of 5 .2-3.6+27.7×1
034 erg. These values provide clues in the extrapolation of
the solar case to higher activity levels in other stars, suggesting that
CMEs could indeed be a major cause of mass and angular momentum loss.

---------------------------------------------------------
Title: Quantifying the Influence of Key Physical Processes on the
Formation of Emission Lines Observed by IRIS. I. Non-equilibrium
Ionization and Density-dependent Rates
Authors: Bradshaw, Stephen J.; Testa, Paola
2019ApJ...872..123B Altcode: 2019arXiv190103935B
In the work described here, we investigate atomic processes leading to
the formation of emission lines within the Interface Region Imaging
Spectrograph wavelength range at temperatures near 105
K. We focus on (1) non-equilibrium and (2) density-dependent effects
influencing the formation and radiative properties of S IV and O
IV. These two effects have significant impacts on spectroscopic
diagnostic measurements of quantities associated with the plasma
that emission lines from S IV and O IV provide. We demonstrate this
by examining nanoflare-based coronal heating to determine what the
detectable signatures are in transition region emission. A detailed
comparison between predictions from numerical experiments and
several sets of observational data is presented to show how one can
ascertain when non-equilibrium ionization and/or density-dependent
atomic processes are important for diagnosing nanoflare properties,
the magnitude of their contribution, and what information can be
reliably extracted from the spectral data. Our key findings are the
following. (1) The S/O intensity ratio is a powerful diagnostic of
non-equilibrium ionization. (2) Non-equilibrium ionization has a
strong effect on the observed line intensities even in the case of
relatively weak nanoflare heating. (3) The density dependence of atomic
rate coefficients is only important when the ion population is out
of equilibrium. (4) In the sample of active regions we examined, weak
nanoflares coupled with non-equilibrium ionization and density-dependent
atomic rates were required to explain the observed properties (e.g.,
the S/O intensity ratios). (5) Enhanced S/O intensity ratios cannot be
due solely to the heating strength and must depend on other processes
(e.g., heating frequency, non-Maxwellian distributions).

---------------------------------------------------------
Title: Instrument Calibration of the Interface Region Imaging
Spectrograph (IRIS) Mission
Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell,
T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.;
Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.;
Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M.
2018SoPh..293..149W Altcode:
The Interface Region Imaging Spectrograph (IRIS) is a NASA small
explorer mission that provides high-resolution spectra and images of
the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The
IRIS data are archived in calibrated form and made available to the
public within seven days of observing. The calibrations applied to
the data include dark correction, scattered light and background
correction, flat fielding, geometric distortion correction, and
wavelength calibration. In addition, the IRIS team has calibrated the
IRIS absolute throughput as a function of wavelength and has been
tracking throughput changes over the course of the mission. As a
resource for the IRIS data user, this article describes the details
of these calibrations as they have evolved over the first few years
of the mission. References to online documentation provide access to
additional information and future updates.

---------------------------------------------------------
Title: Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive
Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EIS
Authors: Polito, Vanessa; Dudík, Jaroslav; Kašparová, Jana;
Dzifčáková, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin
2018ApJ...864...63P Altcode: 2018arXiv180709361P
We analyze the spectra of high-temperature Fe XXIV lines observed by
the Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) during the
impulsive phase of the X8.3-class flare on 2017 September 10. The
line profiles are broad, show pronounced wings, and clearly depart
from a single-Gaussian shape. The lines can be well fitted with κ
distributions, with values of κ varying between ≈1.7 and 3. The
regions where we observe the non-Gaussian profiles coincide with
the location of high-energy (≈100-300 keV) hard X-ray (HXR) sources
observed by RHESSI, suggesting the presence of particle acceleration or
turbulence, also confirmed by the observations of nonthermal microwave
sources with the Expanded Owens Valley Solar Array at and above the HXR
loop-top source. We also investigate the effect of taking into account
κ distributions in the temperature diagnostics based on the ratio of
the Fe XXIII λ263.76 and Fe XXIV λ255.1 EIS lines. We found that
these lines can be formed at much higher temperatures than expected
(up to log(T[K]) ≈ 7.8) if departures from Maxwellian distributions
are taken into account. Although larger line widths are expected because
of these higher formation temperatures, the observed line widths still
imply nonthermal broadening in excess of 200 km s-1. The
nonthermal broadening related to HXR emission is better interpreted
by turbulence than by chromospheric evaporation.

---------------------------------------------------------
Title: Broad Non-Gaussian fe XXIV Line Profiles in the Impulsive
Phase of the 2017 September 10 X8.3-CLASS Flare Observed by Hinode/eis
Authors: Polito, Vanessa; Dudik, Jaroslav; Kasparova, Jana; Dzifcakova,
Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin
2018shin.confE.212P Altcode:
We analyze the spectra of high temperature Fe XXIV lines observed by
Hinode/EIS during the impulsive phase the X8.3-class flare on September
10, 2017. The line profiles are broad, show pronounced wings, and
clearly depart from a single Gaussian shape. The lines can be well
fitted with the ? distributions, with values of ? varying between
?1.7 to 3. The region where we observe the non-Gaussian profiles
coincides with the location of high-energy (?100-300 keV) HXR sources
observed by RHESSI, suggesting the presence of particle acceleration
or turbulence, also confirmed by the observations of a non-thermal
microwave sources with EOVSA at and above the HXR looptop source. We
also investigate the effect of taking into account ? distributions in
the temperature diagnostics based on the ratio of the Fe XXIII 263.76
?A and Fe XXIV 255.1 ?A EIS lines. We found that these lines can be
formed at much higher temperatures than expected (up to log(T [K])
? 7.8), if departures from Maxwellian distributions are taken into
account. Although larger line widths are expected because of these
higher formation temperatures, the observed line widths still imply
non-thermal broadening in excess of 200kms?1.

---------------------------------------------------------
Title: Investigating the Response of Loop Plasma to Nanoflare Heating
Using RADYN Simulations
Authors: Polito, V.; Testa, P.; Allred, J.; De Pontieu, B.; Carlsson,
M.; Pereira, T. M. D.; Gošić, Milan; Reale, Fabio
2018ApJ...856..178P Altcode: 2018arXiv180405970P
We present the results of 1D hydrodynamic simulations of coronal
loops that are subject to nanoflares, caused by either in situ
thermal heating or nonthermal electron (NTE) beams. The synthesized
intensity and Doppler shifts can be directly compared with Interface
Region Imaging Spectrograph (IRIS) and Atmospheric Imaging Assembly
(AIA) observations of rapid variability in the transition region (TR)
of coronal loops, associated with transient coronal heating. We find
that NTEs with high enough low-energy cutoff ({E}{{C}})
deposit energy in the lower TR and chromosphere, causing blueshifts
(up to ∼20 km s-1) in the IRIS Si IV lines, which
thermal conduction cannot reproduce. The {E}{{C}} threshold
value for the blueshifts depends on the total energy of the events
(≈5 keV for 1024 erg, up to 15 keV for 1025
erg). The observed footpoint emission intensity and flows, combined
with the simulations, can provide constraints on both the energy of the
heating event and {E}{{C}}. The response of the loop plasma
to nanoflares depends crucially on the electron density: significant
Si IV intensity enhancements and flows are observed only for initially
low-density loops (&lt;109 cm-3). This provides
a possible explanation of the relative scarcity of observations of
significant moss variability. While the TR response to single heating
episodes can be clearly observed, the predicted coronal emission (AIA
94 Å) for single strands is below current detectability and can only
be observed when several strands are heated closely in time. Finally,
we show that the analysis of the IRIS Mg II chromospheric lines can
help further constrain the properties of the heating mechanisms.

---------------------------------------------------------
Title: Guided flows in coronal magnetic flux tubes
Authors: Petralia, A.; Reale, F.; Testa, P.
2018A&A...609A..18P Altcode: 2017arXiv171104641P; 2017A&A...609A..18P
Context. There is evidence that coronal plasma flows break down into
fragments and become laminar. Aims: We investigate this effect
by modelling flows confined along magnetic channels. Methods: We
consider a full magnetohydrodynamic (MHD) model of a solar atmosphere
box with a dipole magnetic field. We compare the propagation of a
cylindrical flow perfectly aligned with the field to that of another
flow with a slight misalignment. We assume a flow speed of 200 km
s-1 and an ambient magnetic field of 30 G. Results: We
find that although the aligned flow maintains its cylindrical symmetry
while it travels along the magnetic tube, the misaligned one is rapidly
squashed on one side, becoming laminar and eventually fragmented because
of the interaction and back-reaction of the magnetic field. This model
could explain an observation made by the Atmospheric Imaging Assembly
on board the Solar Dynamics Observatory of erupted fragments that fall
back onto the solar surface as thin and elongated strands and end up in
a hedge-like configuration. Conclusions: The initial alignment
of plasma flow plays an important role in determining the possible
laminar structure and fragmentation of flows while they travel along
magnetic channels. Movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201731827/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)
Authors: Winebarger, A. R.; Savage, S. L.; Kobayashi, K.; Champey,
P. R.; McKenzie, D. E.; Golub, L.; Testa, P.; Reeves, K.; Cheimets,
P.; Cirtain, J. W.; Walsh, R. W.; Bradshaw, S. J.; Warren, H.; Mason,
H. E.; Del Zanna, G.
2017AGUFMSH44A..06W Altcode:
For over four decades, X-ray, EUV, and UV spectral observations have
been used to measure physical properties of the solar atmosphere. At
wavelengths below 10 nm, however, observations of the solar corona
with simultaneous spatial and spectral resolution are limited,
and not since the late 1970's have spatially resolved solar X-ray
spectra been measured. Because the soft X-ray regime is dominated
by emission lines formed at high temperatures, X-ray spectroscopic
techniques yield insights to fundamental physical processes that are
not accessible by any other means. Using a novel implementation of
corrective optics, the Marshall Grazing Incidence X-ray Spectrometer
(MaGIXS) will measure, for the first time, the solar spectrum from 0.6-
2.4 nm with a 6 arcsec resolution over an 8 arcmin slit. The MaGIXS
mission will address on of the fundamental problems of coronal physics:
the nature of coronal heating. There are several observables in the
MaGIXS wavelength range that will constrain the heating frequency and
hence discriminate between competing coronal heating theories. In this
presentation, we will present the MaGIXS scientific motivation and
provide an update on instrument development. MaGIXS will be launched
from White Sands Missile Range in the summer of 2019.

---------------------------------------------------------
Title: Observation and modelling of the Fe XXI line profile observed
by IRIS during the impulsive phase of flares
Authors: Polito, V.; Testa, P.; De Pontieu, B.; Allred, J. C.
2017AGUFMSH41A2741P Altcode:
The observation of the high temperature (above 10 MK) Fe XXI 1354.1 A
line with the Interface Region Imaging Spectrograph (IRIS) has provided
significant insights into the chromospheric evaporation process in
flares. In particular, the line is often observed to be completely
blueshifted, in contrast to previous observations at lower spatial
and spectral resolution, and in agreement with predictions from
theoretical models. Interestingly, the line is also observed to be
mostly symmetric and with a large excess above the thermal width. One
popular interpretation for the excess broadening is given by assuming
a superposition of flows from different loop strands. In this work,
we perform a statistical analysis of Fe XXI line profiles observed
by IRIS during the impulsive phase of flares and compare our results
with hydrodynamic simulations of multi-thread flare loops performed
with the 1D RADYN code. Our results indicate that the multi-thread
models cannot easily reproduce the symmetry of the line and that some
other physical process might need to be invoked in order to explain
the observed profiles.

---------------------------------------------------------
Title: Constraints on active region coronal heating properties
from observations and modeling of chromospheric, transition region,
and coronal emission
Authors: Testa, P.; Polito, V.; De Pontieu, B.; Carlsson, M.; Reale,
F.; Allred, J. C.; Hansteen, V. H.
2017AGUFMSH43A2804T Altcode:
We investigate coronal heating properties in active region cores in
non-flaring conditions, using high spatial, spectral, and temporal
resolution chromospheric/transition region/coronal observations coupled
with detailed modeling. We will focus, in particular, on observations
with the Interface Region Imaging Spectrograph (IRIS), joint with
observations with Hinode (XRT and EIS) and SDO/AIA. We will discuss
how these observations and models (1D HD and 3D MHD, with the RADYN
and Bifrost codes) provide useful diagnostics of the coronal heating
processes and mechanisms of energy transport.

---------------------------------------------------------
Title: Spectroscopy of Very Hot Plasma in Non-flaring Parts of a
Solar Limb Active Region: Spatial and Temporal Properties
Authors: Parenti, Susanna; del Zanna, Giulio; Petralia, Antonino;
Reale, Fabio; Teriaca, Luca; Testa, Paola; Mason, Helen E.
2017ApJ...846...25P Altcode: 2017arXiv170708445P
In this work we investigate the thermal structure of an off-limb
active region (AR) in various non-flaring areas, as it provides key
information on the way these structures are heated. In particular,
we concentrate on the very hot component (&gt; 3 {MK}) as it is a
crucial element to distinguish between different heating mechanisms. We
present an analysis using Fe and Ca emission lines from both the
Solar Ultraviolet Measurement of Emitted Radiation (SUMER) on board
the Solar and Heliospheric Observatory (SOHO) and the EUV Imaging
Spectrometer (EIS) on board Hinode. A data set covering all ionization
stages from Fe x to Fe xix has been used for the thermal analysis
(both differential emission measure and emission measure, EM). Ca
xiv is used for the SUMER-EIS radiometric cross calibration. We show
that the very hot plasma is present and persistent almost everywhere
in the core of the limb AR. The off-limb AR is clearly structured in
Fe xviii. Almost everywhere, the EM analysis reveals plasma at 10 MK
(visible in Fe xix emission), which is down to 0.1% of EM of the main
3 {MK} plasma. We estimate the power-law index of the hot tail of
the EM to be between -8.5 and -4.4. However, the question about the
possible existence of a small minor peak at around 10 {MK} remains
open. The absence in some part of the AR of the Fe xix and Fe xxiii
lines (which fall into our spectral range) enables us to determine
an upper limit on the EM at these temperatures. Our results include
a new Ca xiv 943.59 Å atomic model.

---------------------------------------------------------
Title: Realistic radiative MHD simulation of a solar flare
Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.;
De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W.
2017SPD....4840001R Altcode:
We present a recently developed version of the MURaM radiative
MHD code that includes coronal physics in terms of optically thin
radiative loss and field aligned heat conduction. The code employs
the "Boris correction" (semi-relativistic MHD with a reduced speed
of light) and a hyperbolic treatment of heat conduction, which allow
for efficient simulations of the photosphere/corona system by avoiding
the severe time-step constraints arising from Alfven wave propagation
and heat conduction. We demonstrate that this approach can be used
even in dynamic phases such as a flare. We consider a setup in which
a flare is triggered by flux emergence into a pre-existing bipolar
active region. After the coronal energy release, efficient transport
of energy along field lines leads to the formation of flare ribbons
within seconds. In the flare ribbons we find downflows for temperatures
lower than ~5 MK and upflows at higher temperatures. The resulting
soft X-ray emission shows a fast rise and slow decay, reaching a peak
corresponding to a mid C-class flare. The post reconnection energy
release in the corona leads to average particle energies reaching 50
keV (500 MK under the assumption of a thermal plasma). We show that
hard X-ray emission from the corona computed under the assumption of
thermal bremsstrahlung can produce a power-law spectrum due to the
multi-thermal nature of the plasma. The electron energy flux into the
flare ribbons (classic heat conduction with free streaming limit) is
highly inhomogeneous and reaches peak values of about 3x1011
erg/cm2/s in a small fraction of the ribbons, indicating
regions that could potentially produce hard X-ray footpoint sources. We
demonstrate that these findings are robust by comparing simulations
computed with different values of the saturation heat flux as well as
the "reduced speed of light".

---------------------------------------------------------
Title: Non-Maxwellian Analysis of the Transition-region Line Profiles
Observed by the Interface Region Imaging Spectrograph
Authors: Dudík, Jaroslav; Polito, Vanessa; Dzifčáková, Elena;
Del Zanna, Giulio; Testa, Paola
2017ApJ...842...19D Altcode: 2017arXiv170502104D
We investigate the nature of the spectral line profiles for
transition-region (TR) ions observed with the Interface Region Imaging
Spectrograph (IRIS). In this context, we analyzed an active-region
observation performed by IRIS in its 1400 Å spectral window. The TR
lines are found to exhibit significant wings in their spectral profiles,
which can be well fitted with a non-Maxwellian κ distribution. The fit
with a κ distribution can perform better than a double-Gaussian fit,
especially for the strongest line, Si IV 1402.8 Å. Typical values of κ
found are about 2, occurring in a majority of spatial pixels where the
TR lines are symmetric, I.e., the fit can be performed. Furthermore,
all five spectral lines studied (from Si IV, O IV, and S IV) appear
to have the same full-width at half-maximum irrespective of whether
the line is an allowed or an intercombination transition. A similar
value of κ is obtained for the electron distribution by the fitting
of the line intensities relative to Si IV 1402.8 Å, if photospheric
abundances are assumed. The κ distributions, however, do not remove
the presence of non-thermal broadening. Instead, they actually increase
the non-thermal width. This is because, for κ distributions, TR ions
are formed at lower temperatures. The large observed non-thermal width
lowers the opacity of the Si IV line sufficiently enough for this line
to become optically thin.

---------------------------------------------------------
Title: Coronal Heating Properties in the Core of Solar Active Regions
Authors: Testa, P.; Reale, F.; De Pontieu, B.
2016AGUFMSH33A..02T Altcode:
The Interface Region Imaging Spectrograph (IRIS) provides unprecedented
high spatial, temporal and spectral resolution observations of the
chromosphere and transition region. Joint with coronal observations
with Hinode (XRT and EIS), and SDO/AIA, these data cover from the
upper photosphere to the corona. I will discuss how IRIS observations
of footpoints of hot active region loops in non-flaring conditions,
coupled with detailed HD and MHD modeling including chromosphere,
transition region and corona, provide tight constraints on the coronal
heating mechanisms in the core of active regions.

---------------------------------------------------------
Title: The importance of high-resolution observations of the solar
corona
Authors: Winebarger, A. R.; Cirtain, J. W.; Golub, L.; Walsh, R. W.;
De Pontieu, B.; Savage, S. L.; Rachmeler, L.; Kobayashi, K.; Testa,
P.; Brooks, D.; Warren, H.; Mcintosh, S. W.; Peter, H.; Morton, R. J.;
Alexander, C. E.; Tiwari, S. K.
2016AGUFMSH31B2577W Altcode:
The spatial and temporal resolutions of the available coronal
observatories are inadequate to resolve the signatures of coronal
heating. High-resolution and high-cadence observations available with
the Interface Region Imaging Spectrograph (IRIS) and the High-resolution
Coronal Imager (Hi-C) instrument hint that 0.3 arcsec resolution images
and &lt; 10 s cadence provide the necessary resolution to detect
heating events. Hi-C was launched from White Sands Missile Range on
July 11, 2012 (before the launch with IRIS) and obtained images of
a solar active region in the 19.3 nm passband. In this presentation,
I will discuss the potential of combining a flight in Hi-C with a 17.1
nm passband, in conjunction with IRIS. This combination will provide,
for the first time, a definitive method of tracing the energy flow
between the chromosphere and corona and vice versa.

---------------------------------------------------------
Title: Bright Hot Impacts by Erupted Fragments Falling Back on the
Sun: Magnetic Channelling
Authors: Petralia, A.; Reale, F.; Orlando, S.; Testa, P.
2016ApJ...832....2P Altcode: 2016arXiv160904634P
Dense plasma fragments were observed to fall back on the solar surface
by the Solar Dynamics Observatory after an eruption on 2011 June 7,
producing strong extreme-ultraviolet brightenings. Previous studies
investigated impacts in regions of weak magnetic field. Here we
model the ∼ 300 km s-1 impact of fragments channelled by
the magnetic field close to active regions. In the observations, the
magnetic channel brightens before the fragment impact. We use a 3D-MHD
model of spherical blobs downfalling in a magnetized atmosphere. The
blob parameters are constrained from the observation. We run numerical
simulations with different ambient densitie and magnetic field
intensities. We compare the model emission in the 171 Å channel of
the Atmospheric Imaging Assembly with the observed one. We find that
a model of downfall channelled in an ∼1 MK coronal loop confined
by a magnetic field of ∼10-20 G, best explains qualitatively and
quantitatively the observed evolution. The blobs are highly deformed
and further fragmented when the ram pressure becomes comparable to
the local magnetic pressure, and they are deviated to be channelled by
the field because of the differential stress applied by the perturbed
magnetic field. Ahead of them, in the relatively dense coronal medium,
shock fronts propagate, heat, and brighten the channel between the
cold falling plasma and the solar surface. This study shows a new
mechanism that brightens downflows channelled by the magnetic field,
such as in accreting young stars, and also works as a probe of the
ambient atmosphere, providing information about the local plasma
density and magnetic field.

---------------------------------------------------------
Title: High Spatial Resolution Fe XII Observations of Solar Active
Regions
Authors: Testa, Paola; De Pontieu, Bart; Hansteen, Viggo
2016ApJ...827...99T Altcode: 2016arXiv160604603T
We use UV spectral observations of active regions with the Interface
Region Imaging Spectrograph (IRIS) to investigate the properties of
the coronal Fe xii 1349.4 Å emission at unprecedented high spatial
resolution (∼0.33″). We find that by using appropriate observational
strategies (I.e., long exposures, lossless compression), Fe xii emission
can be studied with IRIS at high spatial and spectral resolution, at
least for high-density plasma (e.g., post-flare loops and active region
moss). We find that upper transition region (TR; moss) Fe xii emission
shows very small average Doppler redshifts ({v}{{D}} ∼ 3
km s-1) as well as modest non-thermal velocities (with an
average of ∼24 km s-1 and the peak of the distribution at
∼15 km s-1). The observed distribution of Doppler shifts
appears to be compatible with advanced three-dimensional radiative
MHD simulations in which impulsive heating is concentrated at the TR
footpoints of a hot corona. While the non-thermal broadening of Fe
xii 1349.4 Å peaks at similar values as lower resolution simultaneous
Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) measurements of
Fe xii 195 Å, IRIS observations show a previously undetected tail
of increased non-thermal broadening that might be suggestive of the
presence of subarcsecond heating events. We find that IRIS and EIS
non-thermal line broadening measurements are affected by instrumental
effects that can only be removed through careful analysis. Our results
also reveal an unexplained discrepancy between observed 195.1/1349.4
Å Fe xii intensity ratios and those predicted by the CHIANTI atomic
database.

---------------------------------------------------------
Title: Physics &amp; Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
2016SPD....47.0607C Altcode:
We provide an update on our NASA Heliophysics Grand Challenges Research
(HGCR) project on the ‘Physics &amp; Diagnostics of the Drivers of
Solar Eruptions’. This presentation will focus on results from a
data-inspired, 3D radiative MHD model of a solar flare. The model
flare results from the interaction of newly emerging flux with a
pre-existing active region. Synthetic observables from the model
reproduce observational features compatible with actual flares. These
include signatures of coronal magnetic reconnection, chromospheric
evaporation, EUV flare arcades, sweeping motion of flare ribbons
and sunquakes.

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

---------------------------------------------------------
Title: EUV Flickering of Solar Coronal Loops: A New Diagnostic of
Coronal Heating
Authors: Tajfirouze, E.; Reale, F.; Peres, G.; Testa, P.
2016ApJ...817L..11T Altcode: 2016arXiv160103935T
A previous work of ours found the best agreement between EUV light
curves observed in an active region core (with evidence of super-hot
plasma) and those predicted from a model with a random combination
of many pulse-heated strands with a power-law energy distribution. We
extend that work by including spatially resolved strand modeling and
by studying the evolution of emission along the loops in the EUV 94 Å
and 335 Å channels of the Atmospheric Imaging Assembly on board the
Solar Dynamics Observatory. Using the best parameters of the previous
work as the input of the present one, we find that the amplitude of the
random fluctuations driven by the random heat pulses increases from the
bottom to the top of the loop in the 94 Å channel and from the top
to the bottom in the 335 Å channel. This prediction is confirmed by
the observation of a set of aligned neighboring pixels along a bright
arc of an active region core. Maps of pixel fluctuations may therefore
provide easy diagnostics of nanoflaring regions.

---------------------------------------------------------
Title: Time-resolved Emission from Bright Hot Pixels of an Active
Region Observed in the EUV Band with SDO/AIA and Multi-stranded
Loop Modeling
Authors: Tajfirouze, E.; Reale, F.; Petralia, A.; Testa, P.
2016ApJ...816...12T Altcode: 2015arXiv151007524T
Evidence of small amounts of very hot plasma has been found in active
regions and might be an indication of impulsive heating released at
spatial scales smaller than the cross-section of a single loop. We
investigate the heating and substructure of coronal loops in the
core of one such active region by analyzing the light curves in
the smallest resolution elements of solar observations in two EUV
channels (94 and 335 Å) from the Atmospheric Imaging Assembly on
board the Solar Dynamics Observatory. We model the evolution of
a bundle of strands heated by a storm of nanoflares by means of a
hydrodynamic 0D loop model (EBTEL). The light curves obtained from
a random combination of those of single strands are compared to the
observed light curves either in a single pixel or in a row of pixels,
simultaneously in the two channels, and using two independent methods:
an artificial intelligent system (Probabilistic Neural Network)
and a simple cross-correlation technique. We explore the space of
the parameters to constrain the distribution of the heat pulses,
their duration, their spatial size, and, as a feedback on the data,
their signatures on the light curves. From both methods the best
agreement is obtained for a relatively large population of events
(1000) with a short duration (less than 1 minute) and a relatively
shallow distribution (power law with index 1.5) in a limited energy
range (1.5 decades). The feedback on the data indicates that bumps in
the light curves, especially in the 94 Å channel, are signatures of
a heating excess that occurred a few minutes before.

---------------------------------------------------------
Title: Properties of moss emission from joint FeXII IRIS and Hinode
observations of active region plasma
Authors: Testa, P.; De Pontieu, B.; Hansteen, V. H.
2015AGUFMSH31D..06T Altcode:
IRIS provides unprecedented high resolution observations of the solar
chromosphere and transition region. Joint with Hinode XRT and EIS,
and SDO/AIA, these observations cover from the upper photosphere to
the corona and provide tight constraints on the mechanisms of energy
transport and heating of the plasma to coronal temperatures. We present
new IRIS and Hinode coronal studies of the corona in non-flaring
conditions, and compare the spectral line properties of FeXII emission
observed with EIS and IRIS in active region moss. We will discuss
the implications for the heating of hot coronal loops in the core of
active regions.

---------------------------------------------------------
Title: X-Ray Properties of Low-mass Pre-main Sequence Stars in the
Orion Trapezium Cluster
Authors: Schulz, Norbert S.; Huenemoerder, David P.; Günther, Moritz;
Testa, Paola; Canizares, Claude R.
2015ApJ...810...55S Altcode: 2015arXiv150304366S
The Chandra HETG Orion Legacy Project (HOLP) is the first comprehensive
set of observations of a very young massive stellar cluster that
provides high-resolution X-ray spectra of very young stars over a wide
mass range (0.7-2.3 {M}⊙ ). In this paper, we focus on
the six brightest X-ray sources with T Tauri stellar counterparts that
are well-characterized at optical and infrared wavelengths. All stars
show column densities which are substantially smaller than expected
from optical extinction, indicating that the sources are located on
the near side of the cluster with respect to the observer as well
as that these stars are embedded in more dusty environments. Stellar
X-ray luminosities are well above 1031 erg s-1,
in some cases exceeding 1032 erg s-1 for a
substantial amount of time. The stars during these observations show
no flares but are persistently bright. The spectra can be well fit
with two temperature plasma components of 10 MK and 40 MK, of which the
latter dominates the flux by a ratio 6:1 on average. The total emission
measures range between 3-8 × 1054 cm-3 and are
comparable to active coronal sources. The fits to the Ne ix He-Like
K-shell lines indicate forbidden to inter-combination line ratios
consistent with the low-density limit. Observed abundances compare
well with active coronal sources underlying the coronal nature of
these sources. The surface flux in this sample of 0.6-2.3 {M}⊙
 classical T Tauri stars shows that coronal activity increases
significantly between ages 0.1 and 10 Myr. The results demonstrate
the power of X-ray line diagnostics to study coronal properties of T
Tauri stars in young stellar clusters.

---------------------------------------------------------
Title: Thermal Diagnostics with the Atmospheric Imaging Assembly
on board the Solar Dynamics Observatory: A Validated Method for
Differential Emission Measure Inversions
Authors: Cheung, Mark C. M.; Boerner, P.; Schrijver, C. J.; Testa,
P.; Chen, F.; Peter, H.; Malanushenko, A.
2015ApJ...807..143C Altcode: 2015arXiv150403258C
We present a new method for performing differential emission measure
(DEM) inversions on narrow-band EUV images from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory. The
method yields positive definite DEM solutions by solving a linear
program. This method has been validated against a diverse set of
thermal models of varying complexity and realism. These include
(1) idealized Gaussian DEM distributions, (2) 3D models of NOAA
Active Region 11158 comprising quasi-steady loop atmospheres in a
nonlinear force-free field, and (3) thermodynamic models from a fully
compressible, 3D MHD simulation of active region (AR) corona formation
following magnetic flux emergence. We then present results from the
application of the method to AIA observations of Active Region 11158,
comparing the region's thermal structure on two successive solar
rotations. Additionally, we show how the DEM inversion method can be
adapted to simultaneously invert AIA and Hinode X-ray Telescope data,
and how supplementing AIA data with the latter improves the inversion
result. The speed of the method allows for routine production of DEM
maps, thus facilitating science studies that require tracking of the
thermal structure of the solar corona in time and space.

---------------------------------------------------------
Title: Pinning Down Coronal Heating Properties in the Presence of
Non-Equilibrium Ionization
Authors: Bradshaw, Stephen; Testa, Paola
2015TESS....120405B Altcode:
We examine the effects that non-equilibrium ionization can have
on the evolution of light curves emitted by transition region and
coronal ions during impulsive heating, and how this can lead to the
plasma and heating properties being misdiagnosed. Furthermore, through
detailed numerical and forward modeling we demonstrate how the effects
of non-equilibrium ionization can be mitigated and accounted for so
that robust diagnostics can be developed.

---------------------------------------------------------
Title: Internetwork Chromospheric Bright Grains Observed With IRIS
and SST
Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson,
Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt,
Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan;
Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean;
Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli,
Sarah; Kankelborg, Charles
2015ApJ...803...44M Altcode: 2015arXiv150203490M
The Interface Region Imaging Spectrograph (IRIS) reveals small-scale
rapid brightenings in the form of bright grains all over coronal holes
and the quiet Sun. These bright grains are seen with the IRIS 1330,
1400, and 2796 Å slit-jaw filters. We combine coordinated observations
with IRIS and from the ground with the Swedish 1 m Solar Telescope
(SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H
3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å,
Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps
in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.}
33), temporal, and spectral resolution. We conclude that the IRIS
slit-jaw grains are the counterpart of so-called acoustic grains,
i.e., resulting from chromospheric acoustic waves in a non-magnetic
environment. We compare slit-jaw images (SJIs) with spectra from the
IRIS spectrograph. We conclude that the grain intensity in the 2796
Å slit-jaw filter comes from both the Mg ii k core and wings. The
signal in the C ii and Si iv lines is too weak to explain the presence
of grains in the 1300 and 1400 Å SJIs and we conclude that the grain
signal in these passbands comes mostly from the continuum. Although
weak, the characteristic shock signatures of acoustic grains can often
be detected in IRIS C ii spectra. For some grains, a spectral signature
can be found in IRIS Si iv. This suggests that upward propagating
acoustic waves sometimes reach all the way up to the transition region.

---------------------------------------------------------
Title: Stellar activity and coronal heating: an overview of recent
results
Authors: Testa, Paola; Saar, Steven H.; Drake, Jeremy J.
2015RSPTA.37340259T Altcode: 2015arXiv150207401T
Observations of the coronae of the Sun and of solar-like stars provide
complementary information to advance our understanding of stellar
magnetic activity, and of the processes leading to the heating of
their outer atmospheres. While solar observations allow us to study
the corona at high spatial and temporal resolution, the study of
stellar coronae allows us to probe stellar activity over a wide range
of ages and stellar parameters. Stellar studies therefore provide us
with additional tools for understanding coronal heating processes,
as well as the long-term evolution of solar X-ray activity. We discuss
how recent studies of stellar magnetic fields and coronae contribute
to our understanding of the phenomenon of activity and coronal heating
in late-type stars.

---------------------------------------------------------
Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode
and Magnetic Modeling With Data-Driven Simulations
Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.;
Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner,
P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint,
L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.;
Carlsson, M.; Hansteen, V.
2015ApJ...801...83C Altcode: 2015arXiv150101593C
We report on observations of recurrent jets by instruments on board
the Interface Region Imaging Spectrograph, Solar Dynamics Observatory
(SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21,
recurrent coronal jets were observed to emanate from NOAA Active Region
11793. Far-ultraviolet spectra probing plasma at transition region
temperatures show evidence of oppositely directed flows with components
reaching Doppler velocities of ±100 km s-1. Raster Doppler
maps using a Si iv transition region line show all four jets to have
helical motion of the same sense. Simultaneous observations of the
region by SDO and Hinode show that the jets emanate from a source
region comprising a pore embedded in the interior of a supergranule. The
parasitic pore has opposite polarity flux compared to the surrounding
network field. This leads to a spine-fan magnetic topology in the
coronal field that is amenable to jet formation. Time-dependent
data-driven simulations are used to investigate the underlying drivers
for the jets. These numerical experiments show that the emergence of
current-carrying magnetic field in the vicinity of the pore supplies
the magnetic twist needed for recurrent helical jet formation.

---------------------------------------------------------
Title: Neon and Oxygen Abundances and Abundance Ratio in the Solar
Corona
Authors: Landi, E.; Testa, P.
2015ApJ...800..110L Altcode:
In this work we determine the Ne/O abundance ratio from Solar and
Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) off-disk observations of quiescent streamers over
the 1996-2008 period. We find that the Ne/O ratio is approximately
constant over solar cycle 23 from 1996 to 2005, at a value of 0.099
± 0.017 this value is lower than the transition region determinations
from the quiet Sun used to infer the neon photospheric abundance from
the oxygen photospheric abundance. Also, the Ne/O ratio we determined
from SUMER is in excellent agreement with in situ determinations
from ACE/SWICS. In 2005-2008, the Ne/O abundance ratio increased with
time and reached 0.25 ± 0.05, following the same trend found in the
slowest wind analyzed by ACE/SWICS. Further, we measure the absolute
abundance in the corona for both oxygen and neon from the data set
of 1996 November 22, obtaining A o = 8.99 ± 0.04 and
A Ne = 7.92 ± 0.03, and we find that both elements are
affected by the first ionization potential (FIP) effect, with oxygen
being enhanced by a factor of 1.4-2.1 over its photospheric abundance,
and neon being changed by a factor of 0.75-1.20. We conclude that the
Ne/O ratio is not constant in the solar atmosphere, both in time and
at different heights, and that it cannot be reliably used to infer
the neon abundance in the photosphere. Also, we argue that the FIP
effect was less effective during the minimum of solar cycle 24, and
that the Ne/O = 0.25 ± 0.05 value measured at that time is closer to
the true photospheric value, leading to a neon photospheric abundance
larger than assumed by ≈40%. We discuss the implications of these
results for the solar abundance problem, for the FIP effect, and for
the identification of the source regions of the solar wind.

---------------------------------------------------------
Title: Upgrading the Solar-Stellar Connection: News about activity
in Cool Stars
Authors: Gunther, H. M.; Poppenhaeger, K.; Testa, P.; Borgniet, S.;
Brun, A. S.; Cegla, H. M.; Garraffo, C.; Kowalski, A.; Shapiro, A.;
Shkolnik, E.; Spada, F.; Vidotto, A. A.
2015csss...18...25G Altcode: 2014arXiv1408.3068G
In this splinter session, ten speakers presented results on solar
and stellar activity and how the two fields are connected. This was
followed by a lively discussion and supplemented by short, one-minute
highlight talks. The talks presented new theoretical and observational
results on mass accretion on the Sun, the activity rate of flare stars,
the evolution of the stellar magnetic field on time scales of a single
cycle and over the lifetime of a star, and two different approaches
to model the radial-velocity jitter in cool stars that is due to the
granulation on the surface. Talks and discussion showed how much the
interpretation of stellar activity data relies on the sun and how the
large number of objects available in stellar studies can extend the
parameter range of activity models.

---------------------------------------------------------
Title: IRIS diagnostics of non-thermal particles in coronal loops
heated by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J. C.; Carlsson, M.;
Reale, F.; Daw, A. N.
2014AGUFMSH53D..08T Altcode:
The variability of emission of the "moss", i.e., the upper transition
region (TR) layer of high pressure loops in active regions, provides
stringent constraints on the characteristics of heating events. We
will discuss the new coronal heating diagnostics provided by the
Interface Region Imaging Spectrograph (IRIS) together with SDO/AIA. IRIS
provides imaging and spectral observations of the solar chromosphere
and transition region, at high spatial (0.166 arcsec/pix) and temporal
(down to ~1s) resolution at FUV and NUV wavelengths. We discuss how
simultaneous IRIS and AIA observations, together with loop modeling
(with the RADYN code) including chromosphere, transition region and
corona, allow us to study impulsive heating events (nanoflares) and the
energy transport mechanism between the corona and the lower atmospheric
layers (thermal conduction vs. beams of non-thermal particles). We will
show how the modeling of rapid moss brightenings provides diagnostics
for the presence and properties of non-thermal particles in nanoflares,
which are below the detectability threshold of hard X-ray observations.

---------------------------------------------------------
Title: Bright Hot Impacts by Erupted Fragments Falling Back on the
Sun: UV Redshifts in Stellar Accretion
Authors: Reale, F.; Orlando, S.; Testa, P.; Landi, E.; Schrijver, C. J.
2014ApJ...797L...5R Altcode: 2014arXiv1410.7193R
A solar eruption after a flare on 2011 June 7 produced EUV-bright
impacts of fallbacks far from the eruption site, observed with the
Solar Dynamics Observatory. These impacts can be taken as a template
for the impact of stellar accretion flows. Broad redshifted UV lines
have been commonly observed in young accreting stars. Here we study
the emission from the impacts in the Atmospheric Imaging Assembly's
UV channels and compare the inferred velocity distribution to stellar
observations. We model the impacts with two-dimensional hydrodynamic
simulations. We find that the localized UV 1600 Å emission and its
timing with respect to the EUV emission can be explained by the
impact of a cloud of fragments. The first impacts produce strong
initial upflows. The following fragments are hit and shocked by these
upflows. The UV emission comes mostly from the shocked front shell of
the fragments while they are still falling, and is therefore redshifted
when observed from above. The EUV emission instead continues from the
hot surface layer that is fed by the impacts. Fragmented accretion
can therefore explain broad redshifted UV lines (e.g., C IV 1550 Å)
to speeds around 400 km s-1 observed in accreting young
stellar objects.

---------------------------------------------------------
Title: Hot explosions in the cool atmosphere of the Sun
Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.;
De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint,
L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.;
Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.
2014Sci...346C.315P Altcode: 2014arXiv1410.5842P
The solar atmosphere was traditionally represented with a simple
one-dimensional model. Over the past few decades, this paradigm shifted
for the chromosphere and corona that constitute the outer atmosphere,
which is now considered a dynamic structured envelope. Recent
observations by the Interface Region Imaging Spectrograph (IRIS) reveal
that it is difficult to determine what is up and down, even in the cool
6000-kelvin photosphere just above the solar surface: This region hosts
pockets of hot plasma transiently heated to almost 100,000 kelvin. The
energy to heat and accelerate the plasma requires a considerable
fraction of the energy from flares, the largest solar disruptions. These
IRIS observations not only confirm that the photosphere is more complex
than conventionally thought, but also provide insight into the energy
conversion in the process of magnetic reconnection.

---------------------------------------------------------
Title: The unresolved fine structure resolved: IRIS observations of
the solar transition region
Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title,
A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira,
T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
Martínez-Sykora, J.
2014Sci...346E.315H Altcode: 2014arXiv1412.3611H
The heating of the outer solar atmospheric layers, i.e., the transition
region and corona, to high temperatures is a long-standing problem
in solar (and stellar) physics. Solutions have been hampered by an
incomplete understanding of the magnetically controlled structure of
these regions. The high spatial and temporal resolution observations
with the Interface Region Imaging Spectrograph (IRIS) at the solar
limb reveal a plethora of short, low-lying loops or loop segments
at transition-region temperatures that vary rapidly, on the time
scales of minutes. We argue that the existence of these loops solves
a long-standing observational mystery. At the same time, based on
comparison with numerical models, this detection sheds light on a
critical piece of the coronal heating puzzle.

---------------------------------------------------------
Title: Evidence of nonthermal particles in coronal loops heated
impulsively by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale,
F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.;
Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kleint, L.; Kankelborg, C.; Jaeggli, S.
2014Sci...346B.315T Altcode: 2014arXiv1410.6130T
The physical processes causing energy exchange between the Sun’s
hot corona and its cool lower atmosphere remain poorly understood. The
chromosphere and transition region (TR) form an interface region between
the surface and the corona that is highly sensitive to the coronal
heating mechanism. High-resolution observations with the Interface
Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to
60 seconds) of intensity and velocity on small spatial scales (≲500
kilometers) at the footpoints of hot and dynamic coronal loops. The
observations are consistent with numerical simulations of heating by
beams of nonthermal electrons, which are generated in small impulsive
(≲30 seconds) heating events called “coronal nanoflares.” The
accelerated electrons deposit a sizable fraction of their energy
(≲1025 erg) in the chromosphere and TR. Our analysis
provides tight constraints on the properties of such electron beams
and new diagnostics for their presence in the nonflaring corona.

---------------------------------------------------------
Title: Prevalence of small-scale jets from the networks of the solar
transition region and chromosphere
Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.;
Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves,
K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber,
M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli,
S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
2014Sci...346A.315T Altcode: 2014arXiv1410.6143T
As the interface between the Sun’s photosphere and corona, the
chromosphere and transition region play a key role in the formation and
acceleration of the solar wind. Observations from the Interface Region
Imaging Spectrograph reveal the prevalence of intermittent small-scale
jets with speeds of 80 to 250 kilometers per second from the narrow
bright network lanes of this interface region. These jets have lifetimes
of 20 to 80 seconds and widths of ≤300 kilometers. They originate from
small-scale bright regions, often preceded by footpoint brightenings
and accompanied by transverse waves with amplitudes of ~20 kilometers
per second. Many jets reach temperatures of at least ~105
kelvin and constitute an important element of the transition region
structures. They are likely an intermittent but persistent source of
mass and energy for the solar wind.

---------------------------------------------------------
Title: On the prevalence of small-scale twist in the solar
chromosphere and transition region
Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.;
Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen,
J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser,
J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
Martinez-Sykora, J.
2014Sci...346D.315D Altcode: 2014arXiv1410.6862D
The solar chromosphere and transition region (TR) form an interface
between the Sun’s surface and its hot outer atmosphere. There,
most of the nonthermal energy that powers the solar atmosphere
is transformed into heat, although the detailed mechanism remains
elusive. High-resolution (0.33-arc second) observations with NASA’s
Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere
and TR that are replete with twist or torsional motions on sub-arc
second scales, occurring in active regions, quiet Sun regions, and
coronal holes alike. We coordinated observations with the Swedish
1-meter Solar Telescope (SST) to quantify these twisting motions and
their association with rapid heating to at least TR temperatures. This
view of the interface region provides insight into what heats the low
solar atmosphere.

---------------------------------------------------------
Title: An Interface Region Imaging Spectrograph First View on Solar
Spicules
Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen,
V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt,
N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.;
McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli,
S.; Kankelborg, C.
2014ApJ...792L..15P Altcode: 2014arXiv1407.6360P
Solar spicules have eluded modelers and observers for decades. Since
the discovery of the more energetic type II, spicules have become
a heated topic but their contribution to the energy balance of the
low solar atmosphere remains unknown. Here we give a first glimpse of
what quiet-Sun spicules look like when observed with NASA's recently
launched Interface Region Imaging Spectrograph (IRIS). Using IRIS
spectra and filtergrams that sample the chromosphere and transition
region, we compare the properties and evolution of spicules as
observed in a coordinated campaign with Hinode and the Atmospheric
Imaging Assembly. Our IRIS observations allow us to follow the thermal
evolution of type II spicules and finally confirm that the fading
of Ca II H spicules appears to be caused by rapid heating to higher
temperatures. The IRIS spicules do not fade but continue evolving,
reaching higher and falling back down after 500-800 s. Ca II H type
II spicules are thus the initial stages of violent and hotter events
that mostly remain invisible in Ca II H filtergrams. These events
have very different properties from type I spicules, which show lower
velocities and no fading from chromospheric passbands. The IRIS spectra
of spicules show the same signature as their proposed disk counterparts,
reinforcing earlier work. Spectroheliograms from spectral rasters also
confirm that quiet-Sun spicules originate in bushes from the magnetic
network. Our results suggest that type II spicules are indeed the
site of vigorous heating (to at least transition region temperatures)
along extensive parts of the upward moving spicular plasma.

---------------------------------------------------------
Title: Observations of Subarcsecond Bright Dots in the Transition
Region above Sunspots with the Interface Region Imaging Spectrograph
Authors: Tian, H.; Kleint, L.; Peter, H.; Weber, M.; Testa, P.;
DeLuca, E.; Golub, L.; Schanche, N.
2014ApJ...790L..29T Altcode: 2014arXiv1407.1060T
Observations with the Interface Region Imaging Spectrograph (IRIS)
have revealed numerous sub-arcsecond bright dots in the transition
region above sunspots. These bright dots are seen in the 1400 Å and
1330 Å slit-jaw images. They are clearly present in all sunspots we
investigated, mostly in the penumbrae, but also occasionally in some
umbrae and light bridges. The bright dots in the penumbrae typically
appear slightly elongated, with the two dimensions being 300-600 km and
250-450 km, respectively. The long sides of these dots are often nearly
parallel to the bright filamentary structures in the penumbrae but
sometimes clearly deviate from the radial direction. Their lifetimes
are mostly less than one minute, although some dots last for a few
minutes or even longer. Their intensities are often a few times stronger
than the intensities of the surrounding environment in the slit-jaw
images. About half of the bright dots show apparent movement with
speeds of ~10-40 km s-1 in the radial direction. Spectra of
a few bright dots were obtained and the Si IV 1402.77 Å line profiles
in these dots are significantly broadened. The line intensity can be
enhanced by one to two orders of magnitude. Some relatively bright
and long-lasting dots are also observed in several passbands of the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory,
and they appear to be located at the bases of loop-like structures. Many
of these bright dots are likely associated with small-scale energy
release events at the transition region footpoints of magnetic loops.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s−1 velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.

---------------------------------------------------------
Title: Accretion impacts studied on the Sun
Authors: Reale, F.; Orlando, S.; Testa, P.; Peres, G.; Landi, E.;
Schrijver, C.
2014xru..confE.169R Altcode:
Accretion in star-forming regions is a hot topic. The Sun has recently
offered an interesting opportunity to study accretion impacts observed
in great detail at high energies (Reale et al. 2013, Science, 341,
6143, 251). After the eruption of a dense filament triggered by an
energetic flare on June 7, 2011 part of the ejected material falls
back onto the solar surface. The impact of the downfalling plasma is
similar to that of accretion flows on young stellar objects, and was
imaged in the EUV by the Atmospheric Imaging Assembly (AIA) on-board
the Solar Dynamics Observatory (SDO). Hydrodynamic simulations confirm
that the high energy emission is produced by the impact of high-density
plasma at the highest free-fall speeds and show the importance of
the absorption in reducing the X-ray emission and of fragmentation
in explaining the line broadenings. Impacts such as these present
a laboratory for stellar astronomers to study the impact of dense
(accreting) circumstellar material in unique detail.

---------------------------------------------------------
Title: Detection of Supersonic Downflows and Associated Heating
Events in the Transition Region above Sunspots
Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.;
De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.;
McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen,
J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.;
Kankelborg, C.
2014ApJ...789L..42K Altcode: 2014arXiv1406.6816K
Interface Region Imaging Spectrograph data allow us to study the solar
transition region (TR) with an unprecedented spatial resolution of
0.”33. On 2013 August 30, we observed bursts of high Doppler shifts
suggesting strong supersonic downflows of up to 200 km s-1
and weaker, slightly slower upflows in the spectral lines Mg II h
and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated
with brightenings in the slitjaw images (SJIs). The bursty behavior
lasts throughout the 2 hr observation, with average burst durations
of about 20 s. The locations of these short-lived events appear to
be the umbral and penumbral footpoints of EUV loops. Fast apparent
downflows are observed along these loops in the SJIs and in the
Atmospheric Imaging Assembly, suggesting that the loops are thermally
unstable. We interpret the observations as cool material falling
from coronal heights, and especially coronal rain produced along the
thermally unstable loops, which leads to an increase of intensity
at the loop footpoints, probably indicating an increase of density
and temperature in the TR. The rain speeds are on the higher end of
previously reported speeds for this phenomenon, and possibly higher
than the free-fall velocity along the loops. On other observing days,
similar bright dots are sometimes aligned into ribbons, resembling
small flare ribbons. These observations provide a first insight into
small-scale heating events in sunspots in the TR.

---------------------------------------------------------
Title: Diagnostics of coronal heating and mechanisms of energy
transport from IRIS and AIA observations of active region moss
Authors: Testa, Paola; De Pontieu, Bart; Allred, Joel C.; Carlsson,
Mats; Reale, Fabio; Daw, Adrian N.; Hansteen, Viggo
2014AAS...22431305T Altcode:
The variability of emission of the "moss", i.e., the upper transition
region (TR) layer of high pressure loops in active regions provides
stringent constraints on the characteristics of heating events. The
Interface Region Imaging Spectrograph (IRIS), launched in June
2013, provides imaging and spectral observations at high spatial
(0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV
and NUV wavelengths, and together with the high spatial and temporal
resolution observations of SDO/AIA, can provide important insights
into the coronal heating mechanisms. We present here an analysis of
the temporal variability properties of moss regions at the footpoints
of hot active region core loops undergoing heating, as observed by IRIS
and AIA, covering emission from the corona to the transition region and
the chromosphere. We model the observations using dynamic loop models
(the Palermo-Harvard code, and RADYN, which also includes the effects of
non-thermal particles) and discuss the implications on energy transport
mechanisms (thermal conduction vs beams of non-thermal particles).

---------------------------------------------------------
Title: Photometric and Thermal Cross-calibration of Solar EUV
Instruments
Authors: Boerner, P. F.; Testa, P.; Warren, H.; Weber, M. A.;
Schrijver, C. J.
2014SoPh..289.2377B Altcode: 2013arXiv1307.8045B
We present an assessment of the accuracy of the calibration measurements
and atomic physics models that go into calculating the SDO/AIA response
as a function of wavelength and temperature. The wavelength response
is tested by convolving SDO/EVE and Hinode/EIS spectral data with the
AIA effective area functions and by comparing the predictions with
AIA observations. For most channels, the AIA intensities summed over
the disk agree with the corresponding measurements derived from the
current version (V2) of the EVE data to within the estimated 25 %
calibration error. This agreement indicates that the AIA effective
areas are generally stable in time. The AIA 304 Å channel, however,
does show degradation by a factor of almost 3 from May 2010 through
September 2011, when the throughput apparently reached a minimum. We
also found some inconsistencies in the 335 Å passband, possibly due to
higher-order contamination of the EVE data. The intensities in the AIA
193 Å channel agree to within the uncertainties with the corresponding
measurements from EIS full CCD observations. Analysis of high-resolution
X-ray spectra of the solar-like corona of Procyon and of EVE spectra
allowed us to investigate the accuracy and completeness of the CHIANTI
database in the AIA shorter wavelength passbands. We found that in
the 94 Å channel, the spectral model significantly underestimates the
plasma emission owing to a multitude of missing lines. We derived an
empirical correction for the AIA temperature responses by performing
differential emission measure (DEM) inversion on a broad set of EVE
spectra and adjusting the AIA response functions so that the count
rates predicted by the full-disk DEMs match the observations.

---------------------------------------------------------
Title: Thermal Diagnostics with SDO/AIA: A new method and application
to Eruptive Active Regions
Authors: Cheung, Mark; Boerner, Paul; Testa, Paola
2014AAS...22432322C Altcode:
We present a new method for the retrieval of the emission measure (EM)
distribution of coronal plasma using SDO/AIA EUV images. Unlike some
existing EM inversion algorithms, this inversion scheme does not make
assumptions about the functional form (e.g. Gaussian, power law etc.) of
the solution. The method returns positive definite solutions and runs
at a speed ~O(10^4) pixels per second in a Solarsoft implementation. We
apply the method to a selection of eruptive active regions (ARs) to
study the thermal evolution of AR loops. In terms of both morphology
and temporal evolution, synthetic Hinode/XRT images calculated from
EM solutions retrieved using only AIA data show good agreement with
actual XRT images.

---------------------------------------------------------
Title: The Temperature of Quiescent Streamers during Solar Cycles
23 and 24
Authors: Landi, E.; Testa, P.
2014ApJ...787...33L Altcode:
Recent in-situ determinations of the temporal evolution of the charge
state distribution in the fast and slow solar wind have shown a general
decrease in the degree of ionization of all the elements in the solar
wind along solar cycles 23 and 24. Such a decrease has been interpreted
as a cooling of the solar corona which occurred during the decline and
minimum phase of solar cycle 23 from 2000 to 2010. In the present work,
we investigate whether spectroscopic determinations of the temperature
of the quiescent streamers show signatures of coronal plasma cooling
during cycles 23 and 24. We measure the coronal electron density and
thermal structure at the base of 60 quiescent streamers observed from
1996 to 2013 by SOHO/SUMER and Hinode/EIS and find that both quantities
do now show any significant dependence on the solar cycle. We argue
that if the slow solar wind is accelerated from the solar photosphere
or chromosphere, the measured decrease in the in-situ wind charge
state distribution might be due to an increased efficiency in the wind
acceleration mechanism at low altitudes. If the slow wind originates
from the corona, a combination of density and wind acceleration changes
may be responsible for the in-situ results.

---------------------------------------------------------
Title: High-resolution Observations of the Shock Wave Behavior for
Sunspot Oscillations with the Interface Region Imaging Spectrograph
Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu,
B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.;
Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kankelborg, C.; Jaeggli, S.; McIntosh, S. W.
2014ApJ...786..137T Altcode: 2014arXiv1404.6291T
We present the first results of sunspot oscillations from observations
by the Interface Region Imaging Spectrograph. The strongly nonlinear
oscillation is identified in both the slit-jaw images and the
spectra of several emission lines formed in the transition region and
chromosphere. We first apply a single Gaussian fit to the profiles of
the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the
sunspot. The intensity change is ~30%. The Doppler shift oscillation
reveals a sawtooth pattern with an amplitude of ~10 km s-1
in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and
~12 s, respectively. The line width suddenly increases as the Doppler
shift changes from redshift to blueshift. However, we demonstrate
that this increase is caused by the superposition of two emission
components. We then perform detailed analysis of the line profiles at
a few selected locations on the slit. The temporal evolution of the
line core is dominated by the following behavior: a rapid excursion
to the blue side, accompanied by an intensity increase, followed by a
linear decrease of the velocity to the red side. The maximum intensity
slightly lags the maximum blueshift in Si IV, whereas the intensity
enhancement slightly precedes the maximum blueshift in Mg II. We find
a positive correlation between the maximum velocity and deceleration,
a result that is consistent with numerical simulations of upward
propagating magnetoacoustic shock waves.

---------------------------------------------------------
Title: Thermal structure of a hot non-flaring corona from Hinode/EIS
Authors: Petralia, A.; Reale, F.; Testa, P.; Del Zanna, G.
2014A&A...564A...3P Altcode: 2014arXiv1402.6554P
 Aims: In previous studies, a very hot plasma component has
been diagnosed in solar active regions through the images in three
different narrow-band channels of Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamics Observatory (SDO). This diagnostic from
extreme ultraviolet (EUV) imaging data has also been supported
by the matching morphology of emission in the hot Ca XVII line,
as observed with Extreme-Ultraviolet Imaging Spectrometer (EIS)
on board Hinode. This evidence is debated because of the unknown
distribution of the emission measure along the line of sight. Here
we investigate in detail the thermal distribution of one such region
using EUV spectroscopic data. Methods: In an active region
observed with SDO/AIA, Hinode/EIS, and X-ray telescope (XRT), we
select a sub-region with a very hot plasma component and another cooler
sub-region for comparison. The average spectrum is extracted for both,
and 14 intense lines are selected for analysis that probe the 5.5 &lt;
log T &lt; 7 temperature range uniformly. From these lines, the emission
measure distributions are reconstructed with the Markov-chain Monte
Carlo method. Results are cross-checked in comparison with the two
sub-regions, with a different inversion method, with the morphology
of the images, and with the addition of fluxes measured with narrow,
and broadband imagers. Results: We find that, whereas the
cool region has a flat and featureless distribution that drops at
temperature log T ≥ 6.3, the distribution of the hot region shows
a well-defined peak at log T = 6.6 and gradually decreasing trends on
both sides, thus supporting the very hot nature of the hot component
diagnosed with imagers. The other cross-checks are consistent with
this result. Conclusions: This study provides a completion of
the analysis of active region components, and the resulting scenario
supports the presence of a minor very hot plasma component in the core,
with temperatures log T &gt; 6.6.

---------------------------------------------------------
Title: Diagnostics of coronal heating and mechanisms of energy
transport from IRIS and AIA observations of active region moss
Authors: Testa, Paola; Reale, Fabio; De Pontieu, Bart; Hansteen,
Viggo; Carlsson, Mats; Allred, Joel; Daw, Adrian
2014cosp...40E3323T Altcode:
The variability of emission of the "moss", i.e., the upper transition
region (TR) layer of high pressure loops in active regions provides
stringent constraints on the characteristics of heating events. The
Interface Region Imaging Spectrograph (IRIS), launched in June
2013, provides imaging and spectral observations at high spatial
(0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV
and NUV wavelengths, and together with the high spatial and temporal
resolution observations of SDO/AIA, can provide important insights
into the coronal heating mechanisms. We present here an analysis of
the temporal variability properties of moss regions at the footpoints
of hot active region core loops undergoing heating, as observed by IRIS
and AIA, covering emission from the corona to the transition region and
the chromosphere. We model the observations using dynamic loop models
(the Palermo-Harvard code, and RADYN, which also includes the effects of
non-thermal particles) and discuss the implications on energy transport
mechanisms (thermal conduction vs beams of non-thermal particles).

---------------------------------------------------------
Title: Thermal Diagnostics with SDO/AIA: A new method and application
to Eruptive Active Regions
Authors: Cheung, Mark; Testa, Paola; Boerner, Paul
2014cosp...40E.535C Altcode:
We present a new method for the retrieval of the emission measure (EM)
distribution of coronal plasma using SDO/AIA EUV images. Unlike some
existing EM inversion algorithms, this inversion scheme does not make
assumptions about the functional form (e.g. Gaussian, power law etc.) of
the solution. The method returns positive definite solutions and runs
at a speed ~O(10^4) pixels per second in a Solarsoft implementation. We
apply the method to a selection of eruptive active regions (ARs) to
study the thermal evolution of AR loops. In terms of both morphology
and temporal evolution, synthetic Hinode/XRT images calculated from
EM solutions retrieved using only AIA data show good agreement with
actual XRT images.

---------------------------------------------------------
Title: The HETG Orion Legacy Project: X-Ray Properties of Trapezium
Stars
Authors: Schulz, Norbert S.; Huenemoerder, David P.; Testa, Paola;
Canizares, Claude R.
2013prpl.conf1K095S Altcode:
The ONC is an ideal astrophysical laboratory to study very young
stars. The HETG Orion Legacy Project is designed to obtain a large
number of high-resolution X-ray spectra of very young late type
pre-main sequence stars, and several young massive and intermediate
mass stars. Its extreme proximity and youth makes the core of the ONC a
Chandra legacy project involving the only high resolution spectroscopic
study of young embedded cluster stars for decades to come. For several
PMS stars we derive abundance fractions from temperature-insensitive
line ratios using an approximation with respect to the non-detection
of the O~VII line in most cases. From these fraction we consrtuct a
single abundance distribution involving O, Mg, Ne, Si, S, Ar, and Fe to
fit all X-ray spectra simultaneously. We compare this common abundance
distribution to abundances determined recently in more massive Orion
Trapezium stars and results from several other abundance studies of
Orion stars and clusters.

---------------------------------------------------------
Title: Bright Hot Impacts by Erupted Fragments Falling Back on the
Sun: A Template for Stellar Accretion
Authors: Reale, Fabio; Orlando, Salvatore; Testa, Paola; Peres,
Giovanni; Landi, Enrico; Schrijver, Carolus J.
2013Sci...341..251R Altcode:
Impacts of falling fragments observed after the eruption of a filament
in a solar flare on 7 June 2011 are similar to those inferred for
accretion flows on young stellar objects. As imaged in the ultraviolet
(UV)-extreme UV range by the Atmospheric Imaging Assembly onboard
the Solar Dynamics Observatory, many impacts of dark, dense matter
display uncommonly intense, compact brightenings. High-resolution
hydrodynamic simulations show that such bright spots, with plasma
temperatures increasing from ~104 to ~106
kelvin, occur when high-density plasma (&gt;&gt;1010
particles per cubic centimeter) hits the solar surface at several
hundred kilometers per second, producing high-energy emission as in
stellar accretion. The high-energy emission comes from the original
fragment material and is heavily absorbed by optically thick plasma,
possibly explaining the lower mass accretion rates inferred from x-rays
relative to UV-optical-near infrared observations of young stars.

---------------------------------------------------------
Title: Observing Coronal Nanoflares in Active Region Moss
Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan;
DeLuca, Ed; Hansteen, Viggo; Cirtain, Jonathan; Winebarger, Amy;
Golub, Leon; Kobayashi, Ken; Korreck, Kelly; Kuzin, Sergey; Walsh,
Robert; DeForest, Craig; Title, Alan; Weber, Mark
2013ApJ...770L...1T Altcode: 2013arXiv1305.1687T
The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193Å
images of the upper transition region moss at an unprecedented spatial
(~0.”3-0.”4) and temporal (5.5 s) resolution. The Hi-C observations
show in some moss regions variability on timescales down to ~15 s,
significantly shorter than the minute-scale variability typically found
in previous observations of moss, therefore challenging the conclusion
of moss being heated in a mostly steady manner. These rapid variability
moss regions are located at the footpoints of bright hot coronal
loops observed by the Solar Dynamics Observatory/Atmospheric Imaging
Assembly in the 94 Å channel, and by the Hinode/X-Ray Telescope. The
configuration of these loops is highly dynamic, and suggestive of
slipping reconnection. We interpret these events as signatures of
heating events associated with reconnection occurring in the overlying
hot coronal loops, i.e., coronal nanoflares. We estimate the order
of magnitude of the energy in these events to be of at least a few
1023 erg, also supporting the nanoflare scenario. These
Hi-C observations suggest that future observations at comparable
high spatial and temporal resolution, with more extensive temperature
coverage, are required to determine the exact characteristics of the
heating mechanism(s).

---------------------------------------------------------
Title: Multi-wavelength Observations of Solar Flares with a
Constrained Peak X-Ray Flux
Authors: Bowen, Trevor A.; Testa, Paola; Reeves, Katharine K.
2013ApJ...770..126B Altcode:
We present an analysis of soft X-ray (SXR) and extreme-ultraviolet
(EUV) observations of solar flares with an approximate C8 Geostationary
Operational Environmental Satellite (GOES) class. Our constraint
on peak GOES SXR flux allows for the investigation of correlations
between various flare parameters. We show that the duration of the
decay phase of a flare is proportional to the duration of its rise
phase. Additionally, we show significant correlations between the
radiation emitted in the flare rise and decay phases. These results
suggest that the total radiated energy of a given flare is proportional
to the energy radiated during the rise phase alone. This partitioning
of radiated energy between the rise and decay phases is observed
in both SXR and EUV wavelengths. Though observations from the EUV
Variability Experiment show significant variation in the behavior of
individual EUV spectral lines during different C8 events, this work
suggests that broadband EUV emission is well constrained. Furthermore,
GOES and Atmospheric Imaging Assembly data allow us to determine
several thermal parameters (e.g., temperature, volume, density,
and emission measure) for the flares within our sample. Analysis of
these parameters demonstrate that, within this constrained GOES class,
the longer duration solar flares are cooler events with larger volumes
capable of emitting vast amounts of radiation. The shortest C8 flares
are typically the hottest events, smaller in physical size, and have
lower associated total energies. These relationships are directly
comparable with several scaling laws and flare loop models.

---------------------------------------------------------
Title: X-ray and EUV Observations of GOES C8 Solar Flare Events
Authors: Bowen, Trevor A.; Testa, Paola; Reeves, Katharine K.
2013enss.confE..39B Altcode: 2013arXiv1305.1680B
We present an analysis of soft X-rays (SXR) and extreme-ultraviolet
(EUV) imaging and spectral observations of solar flares with an
approximate C8 GOES class. Our constraint on peak GOES SXR flux
allows for the investigation of correlations between various flare
parameters. We show that the the duration of the decay phase is
proportional to the duration of its rise phase. Additionally, we show
significant correlations between the radiation emitted in the rise
and decay phases of a flare: the total radiated energy of a given
flare is proportional to the energy radiated during the rise phase
alone. This partitioning of radiated energy between the rise and decay
phases is observed in both soft X-ray (SXR) extreme ultraviolet (EUV)
wavelengths. Though observations from the EUV Variability Experiment
(EVE) show significant variation in the behavior of individual EUV
spectral lines during different C8 events, we show that the broadband
EUV emission is well constrained. Furthermore, using GOES and AIA data,
we determine several thermal parameters of these events: temperature,
volume, density, and emission measure. Analysis of these parameters
demonstrate that the longer duration solar flares are cooler events
with larger volumes capable of emitting vast amounts of radiation. The
shortest C8 flares are typically the hottest events, smaller in physical
size, and have lower associated total energies. These relationships
are directly comparable with several sample scaling laws and flare
loop models.

---------------------------------------------------------
Title: Hot Thermal X-Ray Emission from the Be Star HD 119682
Authors: Torrejón, J. M.; Schulz, N. S.; Nowak, M. A.; Testa, P.;
Rodes, J. J.
2013ApJ...765...13T Altcode: 2013arXiv1301.2913T
We present an analysis of a series of four consecutive Chandra
high-resolution transmission gratings observations, amounting to a
total of 150 ks, of the Be X-ray source HD 119682 (=1WGA J1346.5-6255),
a member of the new class of γ Cas analogs. The Chandra light curve
shows significant brightness variations on timescales of hours. However,
the spectral distribution appears rather stable within each observation
and during the whole campaign. A detailed analysis is not able to
detect any coherent pulsation up to a frequency of 0.05 Hz. The Chandra
High Energy Transmission Gratings spectrum seems to be devoid of any
strong emission line, including Fe Kα fluorescence. The continuum
is well described with the addition of two collisionally ionized
plasmas of temperatures kT ≈ 15 keV and 0.2 keV, respectively, by
the apec model. Models using photoionized plasma components (mekal)
or non-thermal components (powerlaw) give poorer fits, providing
support for the pure thermal scenario. These two components are
absorbed by a single column with N H = (0.20+0.15
-0.03) × 1022 cm-2 compatible with
the interstellar value. We conclude that HD 119682 can be regarded as
a pole-on γ Cas analog.

---------------------------------------------------------
Title: The thermal and spatial structure of the solar corona over
the cycle and its implication for the coronae of inactive stars
Authors: Testa, P.; Landi, E.; Saar, S.
2012AGUFMSH42A..05T Altcode:
We use spectral (SOHO/SUMER and Hinode/EIS) and imaging (Hinode/XRT
and SDO/AIA) solar coronal data to systematically measure the thermal
structure of different types of solar features (coronal hole, quiet
Sun, X-ray bright points, active regions...), and how they vary over
the solar cycle. We use a combination of these structures to construct
a model for the quiet corona of the inactive G8V star tau Ceti, which
is a candidate stellar analog of a solar magnetic minimum. Since tau
Ceti is significantly metal-poor relative to the Sun, we reconstruct
the solar results with corresponding lower metallicities to generate
more appropriate coronal structures.

---------------------------------------------------------
Title: The Thermal Structure of the Corona as observed with SDO/AIA,
With and Without Image Deconvolution
Authors: Boerner, P.; Cheung, C.; Schrijver, C.; Testa, P.; Weber, M.
2012AGUFMSH33B2240B Altcode:
We describe a fast, robust method for deriving a differential emission
measure function DEM(T) that matches the observations in the six coronal
channels of SDO/AIA pixel-by-pixel over the full image, and present
some of the results obtained by applying this technique to AIA movies
of a variety of phenomena including "AIA waves," post-flare loops, and
coronal holes. In addition, we discuss the effect of deconvolving the
AIA point-spread function from the images on the inferred temperature
structures.;

---------------------------------------------------------
Title: Investigating the Reliability of Coronal Emission Measure
Distribution Diagnostics using Three-dimensional Radiative
Magnetohydrodynamic Simulations
Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan;
Hansteen, Viggo; Carlsson, Mats
2012ApJ...758...54T Altcode: 2012arXiv1208.4286T
Determining the temperature distribution of coronal plasmas can provide
stringent constraints on coronal heating. Current observations with
the Extreme ultraviolet Imaging Spectrograph (EIS) on board Hinode
and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory provide diagnostics of the emission measure distribution
(EMD) of the coronal plasma. Here we test the reliability of temperature
diagnostics using three-dimensional radiative MHD simulations. We
produce synthetic observables from the models and apply the Monte
Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
the "true" distributions from the model, we assess the limitations
of the diagnostics as a function of the plasma parameters and the
signal-to-noise ratio of the data. We find that EMDs derived from
EIS synthetic data reproduce some general characteristics of the true
distributions, but usually show differences from the true EMDs that
are much larger than the estimated uncertainties suggest, especially
when structures with significantly different density overlap along
the line of sight. When using AIA synthetic data the derived EMDs
reproduce the true EMDs much less accurately, especially for broad
EMDs. The differences between the two instruments are due to the:
(1) smaller number of constraints provided by AIA data and (2) broad
temperature response function of the AIA channels which provide looser
constraints to the temperature distribution. Our results suggest that
EMDs derived from current observatories may often show significant
discrepancies from the true EMDs, rendering their interpretation
fraught with uncertainty. These inherent limitations to the method
should be carefully considered when using these distributions to
constrain coronal heating.

---------------------------------------------------------
Title: Stars in magnetic grand minima: where are they and what are
they like?
Authors: Saar, Steven H.; Testa, Paola
2012IAUS..286..335S Altcode:
We explore various ideas of what a star in a Maunder-like magnetic
minimum would look like, and ways of finding stars in such a state,
and make some estimates of their physical and magnetic activity
properties. We discuss new X-ray observations of a small selection of
candidates for being in magnetic grand minima. These are then compared
with the Sun and other low activity stars.

---------------------------------------------------------
Title: Temperature Diagnostics of a Solar Active Region Using a
Single-Filter Observation of Hinode/XRT
Authors: Terzo, S.; Testa, P.; Reale, F.
2012ASPC..456..141T Altcode:
Broad-band X-ray observations can provide limited temperature
diagnostics through filter ratios. A high cadence observation of an
active region made with a single Hinode/XRT filter allows us to use
an alternative approach in which we measure the time fluctuations of
the pixel count rate and use the variance as temperature proxy. We
show the results and discuss limitations of method.

---------------------------------------------------------
Title: The HETG Orion Legacy Project: Abundances in Trapezium Stars
Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Shen, N.; Testa,
P.; Nichols, J.; Canizares, C. R.
2012AAS...22052306S Altcode:
The ONC is an ideal astrophysical laboratory to study very young
stars. The HETG Orion Legacy Project is designed to obtain a large
number of high-resolution X-ray spectra of very young late type
pre-main sequence stars, and several young massive and intermediate
mass stars. Its extreme proximity and youth makes the core of the ONC a
Chandra legacy project involving the only high resolution spectroscopic
study of young embedded cluster stars for decades to come. For several
PMS stars we derive abundance fractions from temperature-insensitive
line ratios. From these fractions we construct a single abundance
distribution involving O, Mg, Ne, Si, S, Ar, and Fe to fit all X-ray
spectra simultaneously. We compare this common abundance distribution
to abundances determined recently in more massive Orion Trapezium
stars and to results from several other abundance studies of Orion
stars and clusters.

---------------------------------------------------------
Title: Statistical Analysis of Eruptive Events Reported by the Flare
Detective Module
Authors: Winter, Henry D., III; Testa, P.
2012AAS...22020108W Altcode:
As part of the Feature Finding Team (FFT) software suite the Flare
Detective Module automatically detects and characterizes solar flares
observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar
Dynamics Observatory (SDO). Basic quantities such as time intervals,
positions, and peak fluxes have been calculated and provided to the
Heliophysics Event Knowledgebase (HEK) to allow the module to keep up
with the extremely large size of the incoming data stream and provide
near real-time information for space weather monitoring. Physically
important parameters such as temperatures and emission measures,
projected areas, light-curves, etc., are calculated in a second,
post-processing step. While flares have been traditionally studied in
isolation, the wealth of information provided by the Flare Detective
Module allows for the study of the distribution flare properties
across a large number of events. In this work we will investigate
the correlation between the clustering of eruptive events with flare
parameters such as peak temperature, duration, and projected extent
of flares, as well as present other examples of statistical analyses
that are possible with the Flare Detective Module.

---------------------------------------------------------
Title: Hinode/EIS Spectroscopic Validation of Very Hot Plasma Imaged
with the Solar Dynamics Observatory in Non-flaring Active Region Cores
Authors: Testa, Paola; Reale, Fabio
2012ApJ...750L..10T Altcode: 2012arXiv1204.0041T
We use coronal imaging observations with the Solar
Dynamics Observatory/Atmospheric Imaging Assembly (AIA), and
Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) spectral data to
explore the potential of narrowband EUV imaging data for diagnosing the
presence of hot (T &gt;~ 5 MK) coronal plasma in active regions. We
analyze observations of two active regions (AR 11281, AR 11289) with
simultaneous AIA imaging and EIS spectral data, including the Ca XVII
line (at 192.8 Å), which is one of the few lines in the EIS spectral
bands sensitive to hot coronal plasma even outside flares. After
careful co-alignment of the imaging and spectral data, we compare
the morphology in a three-color image combining the 171, 335, and 94
Å AIA spectral bands, with the image obtained for Ca XVII emission
from the analysis of EIS spectra. We find that in the selected active
regions the Ca XVII emission is strong only in very limited areas,
showing striking similarities with the features bright in the 94 Å
(and 335 Å) AIA channels and weak in the 171 Å band. We conclude that
AIA imaging observations of the solar corona can be used to track hot
plasma (6-8 MK), and so to study its spatial variability and temporal
evolution at high spatial and temporal resolution.

---------------------------------------------------------
Title: Hot Plasma Detected in Active Regions by HINODE/XRT and SDO/AIA
Authors: Reale, F.; Testa, P.; Guarrasi, M.; DeLuca, E.; Peres, G.;
Golub, L.
2012ASPC..456..129R Altcode:
Multiple ratios of Hinode/XRT filters showed evidence of a minor
very hot emission measure component in active regions. Recently also
SDO/AIA detected hot plasma in the core of an active region. Here
we provide estimates showing that the amount of emission measure of
the hot component detected with SDO is consistent with that detected
with Hinode/XRT.

---------------------------------------------------------
Title: Using 3D MHD realistic simulations of the solar corona to
test plasma diagnostics
Authors: Testa, P.; De Pontieu, B.; Martinez-Sykora, J.; Hansteen,
V.; Carlsson, M.
2012decs.confE..27T Altcode:
We synthesize coronal images and spectra from advanced 3D MHD
simulations obtained from the state-of-the art Bifrost code, and
explore how well they reproduce coronal observations with SDO/AIA and
Hinode/EIS. We apply standard diagnostic techniques (e.g., density, and
temperature diagnostics) to the synthetic observations and investigate
how accurately the derived physical information matches the plasma
parameters of the model. We discuss the limitations of the diagnostics
and their implications.

---------------------------------------------------------
Title: Monte Carlo Markov chain DEM reconstruction of isothermal
plasmas
Authors: Landi, E.; Reale, F.; Testa, P.
2012A&A...538A.111L Altcode: 2011arXiv1112.2857L
Context. Recent studies carried out with SOHO and Hinode high-resolution
spectrometers have shown that the plasma in the off-disk solar corona is
close to isothermal. If confirmed, these findings may have significant
consequences for theoretical models of coronal heating. However,
these studies have been carried out with diagnostic techniques whose
ability to reconstruct the plasma distribution with temperature has
not been thoroughly tested. Aims: In this paper, we carry out
tests on the Monte Carlo Markov chain (MCMC) technique with the aim
of determining: 1) its ability to retrieve isothermal plasmas from a
set of spectral line intensities, with and without random noise; 2)
to what extent can it discriminate between an isothermal solution and a
narrow multithermal distribution; and 3) how well it can detect multiple
isothermal components along the line of sight. We also test the effects
of 4) atomic data uncertainties on the results, and 5) the number of
ions whose lines are available for the DEM reconstruction. 
Methods: We first use the CHIANTI database to calculate synthetic
spectra from different thermal distributions: single isothermal
plasmas, multithermal plasmas made of multiple isothermal components,
and multithermal plasmas with a Gaussian DEM distribution with variable
width. We then apply the MCMC technique on each of these synthetic
spectra, so that the ability of the MCMC technique at reconstructing
the original thermal distribution can be evaluated. Next, we add a
random noise to the synthetic spectra, and repeat the exercise, in
order to determine the effects of random errors on the results. We
also we repeat the exercise using a different set of atomic data from
those used to calculate synthetic line intensities, to understand the
robustness of the results against atomic physics uncertainties. The
size of the temperature bin of the MCMC reconstruction is varied in
all cases, in order to determine the optimal width. Results: We
find that the MCMC technique is unable to retrieve isothermal plasmas to
better than Δlog T ≃ 0.05. Also, the DEM curves obtained using lines
calculated with an isothermal plasma and with a Gaussian distribution
with FWHM of log T ≃ 0.05 are very similar. Two near-isothermal
components can be resolved if their temperature separation is Δlog
T = 0.2 or larger. Thus, DEM diagnostics has an intrinsic resolving
power of log T = 0.05. Atomic data uncertainties may significantly
affect both temperature and peak DEM values, but do not alter our
conclusions. The availability of small sets of lines also does not
worsen the performance of the MCMC technique, provided these lines are
formed in a wide temperature range. Conclusions: Our analysis
shows the present limitations in our ability to identify the presence
of strictly isothermal plasmas in stellar and solar coronal spectra.

---------------------------------------------------------
Title: Testing EUV/X-Ray Atomic Data for the Solar Dynamics
Observatory
Authors: Testa, Paola; Drake, Jeremy J.; Landi, Enrico
2012ApJ...745..111T Altcode: 2011arXiv1110.4611T
The Atmospheric Imaging Assembly (AIA) and the Extreme-ultraviolet
Variability Experiment (EVE) on board the Solar Dynamics Observatory
(SDO) include spectral windows in the X-ray/EUV band. Accuracy and
completeness of the atomic data in this wavelength range is essential
for interpretation of the spectrum and irradiance of the solar corona,
and of SDO observations made with the AIA and EVE instruments. Here,
we test the X-ray/EUV data in the CHIANTI database to assess their
completeness and accuracy in the SDO bands, with particular focus on the
94 Å and 131 Å AIA passbands. Given the paucity of solar observations
adequate for this purpose, we use high-resolution X-ray spectra of the
low-activity solar-like corona of Procyon obtained with the Chandra Low
Energy Transmission Grating Spectrometer (LETGS). We find that while
spectral models overall can reproduce quite well the observed spectra
in the soft X-ray range λ &lt;~ 50 Å, and at the EUV wavelengths λ
&gt;~ 130 Å, they significantly underestimate the observed flux in the
50-130 Å wavelength range. The model underestimates the observed flux
by a variable factor ranging from ≈1.5, at short wavelengths below
~50 Å, up to ≈5-7 in the ~70-125 Å range. In the AIA bands covered
by LETGS, i.e., 94 Å and 131 Å, we find that the observed flux can be
underestimated by large factors (~3 and ~1.9, respectively, for the case
of Procyon presented here). We discuss the consequences for analysis
of AIA data and possible empirical corrections to the AIA responses
to model more realistically the coronal emission in these passbands.

---------------------------------------------------------
Title: Computer Vision for the Solar Dynamics Observatory (SDO)
Authors: Martens, P. C. H.; Attrill, G. D. R.; Davey, A. R.; Engell,
A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.;
Savcheva, A.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P. N.;
Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F.; Cirtain, J. W.;
DeForest, C. E.; Angryk, R. A.; De Moortel, I.; Wiegelmann, T.;
Georgoulis, M. K.; McAteer, R. T. J.; Timmons, R. P.
2012SoPh..275...79M Altcode: 2011SoPh..tmp..144M; 2011SoPh..tmp..213M; 2011SoPh..tmp....8M
In Fall 2008 NASA selected a large international consortium to produce
a comprehensive automated feature-recognition system for the Solar
Dynamics Observatory (SDO). The SDO data that we consider are all of the
Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field
images from the Helioseismic and Magnetic Imager (HMI). We produce
robust, very efficient, professionally coded software modules that
can keep up with the SDO data stream and detect, trace, and analyze
numerous phenomena, including flares, sigmoids, filaments, coronal
dimmings, polarity inversion lines, sunspots, X-ray bright points,
active regions, coronal holes, EIT waves, coronal mass ejections
(CMEs), coronal oscillations, and jets. We also track the emergence and
evolution of magnetic elements down to the smallest detectable features
and will provide at least four full-disk, nonlinear, force-free magnetic
field extrapolations per day. The detection of CMEs and filaments is
accomplished with Solar and Heliospheric Observatory (SOHO)/Large
Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα
data, respectively. A completely new software element is a trainable
feature-detection module based on a generalized image-classification
algorithm. Such a trainable module can be used to find features that
have not yet been discovered (as, for example, sigmoids were in the
pre-Yohkoh era). Our codes will produce entries in the Heliophysics
Events Knowledgebase (HEK) as well as produce complete catalogs for
results that are too numerous for inclusion in the HEK, such as the
X-ray bright-point metadata. This will permit users to locate data on
individual events as well as carry out statistical studies on large
numbers of events, using the interface provided by the Virtual Solar
Observatory. The operations concept for our computer vision system is
that the data will be analyzed in near real time as soon as they arrive
at the SDO Joint Science Operations Center and have undergone basic
processing. This will allow the system to produce timely space-weather
alerts and to guide the selection and production of quicklook images and
movies, in addition to its prime mission of enabling solar science. We
briefly describe the complex and unique data-processing pipeline,
consisting of the hardware and control software required to handle
the SDO data stream and accommodate the computer-vision modules, which
has been set up at the Lockheed-Martin Space Astrophysics Laboratory
(LMSAL), with an identical copy at the Smithsonian Astrophysical
Observatory (SAO).

---------------------------------------------------------
Title: Initial Calibration of the Atmospheric Imaging Assembly (AIA)
on the Solar Dynamics Observatory (SDO)
Authors: Boerner, Paul; Edwards, Christopher; Lemen, James; Rausch,
Adam; Schrijver, Carolus; Shine, Richard; Shing, Lawrence; Stern,
Robert; Tarbell, Theodore; Title, Alan; Wolfson, C. Jacob; Soufli,
Regina; Spiller, Eberhard; Gullikson, Eric; McKenzie, David; Windt,
David; Golub, Leon; Podgorski, William; Testa, Paola; Weber, Mark
2012SoPh..275...41B Altcode:
The Atmospheric Imaging Assembly (AIA) instrument onboard the Solar
Dynamics Observatory (SDO) is an array of four normal-incidence
reflecting telescopes that image the Sun in ten EUV and UV wavelength
channels. We present the initial photometric calibration of AIA,
based on preflight measurements of the response of the telescope
components. The estimated accuracy is of order 25%, which is consistent
with the results of comparisons with full-disk irradiance measurements
and spectral models. We also describe the characterization of the
instrument performance, including image resolution, alignment,
camera-system gain, flat-fielding, and data compression.

---------------------------------------------------------
Title: Models and Comparisons of Long Duration and Impulsive Solar
Flare Events from SDO
Authors: Bowen, Trevor; Testa, P.; Reeves, K.
2012AAS...21914407B Altcode:
We compare observational signatures of two GOES C8-class solar flares
through instrumentation on Solar Dynamics Observatory (SDO). Data from
the Atmospheric Imaging Assembly (AIA) and the Extreme Ultraviolet
Variability Experiment (EVE) provide a unique look at the sun through
global scale, fast cadence, high-resolution photometric and spectral
measurements; this data is ideal for analyzing the temporal evolution
of flare properties. The two flares studied differ in both time scale
and morphology, one may be classified as a long duration event (LDE),
while the other is highly impulsive. Differences are noted in behavior
in the AIA EUV bands as well as several spectral lines. Furthermore,
we apply both zero and one dimensional multi-threaded hydrodynamic loop
models to synthesize light curves and spectra for each flare. Funding
provided by NSF REU solar physics program at CfA, grant number
ATM-0851866 and Marlboro College.

---------------------------------------------------------
Title: Forward Modeling of Emission in Solar Dynamics
Observatory/Atmospheric Imaging Assembly Passbands from Dynamic
Three-dimensional Simulations
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Testa, Paola;
Hansteen, Viggo
2011ApJ...743...23M Altcode: 2011arXiv1109.0704M
It is typically assumed that emission in the passbands of the
Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory (SDO) is dominated by single or several strong lines
from ions that under equilibrium conditions are formed in a narrow
range of temperatures. However, most SDO/AIA channels also contain
contributions from lines of ions that have formation temperatures
that are significantly different from the "dominant" ion(s). We
investigate the importance of these lines by forward modeling the
emission in the SDO/AIA channels with three-dimensional radiative MHD
simulations of a model that spans the upper layer of the convection
zone to the low corona. The model is highly dynamic. In addition,
we pump a steadily increasing magnetic flux into the corona, in
order to increase the coronal temperature through the dissipation
of magnetic stresses. As a consequence, the model covers different
ranges of coronal temperatures as time progresses. The model covers
coronal temperatures that are representative of plasma conditions in
coronal holes and quiet Sun. The 131, 171, and 304 Å AIA passbands
are found to be the least influenced by the so-called non-dominant
ions, and the emission observed in these channels comes mostly from
plasma at temperatures near the formation temperature of the dominant
ion(s). On the other hand, the other channels are strongly influenced
by the non-dominant ions, and therefore significant emission in these
channels comes from plasma at temperatures that are different from the
"canonical" values. We have also studied the influence of non-dominant
ions on the AIA passbands when different element abundances are assumed
(photospheric and coronal), and when the effects of the electron
density on the contribution function are taken into account.

---------------------------------------------------------
Title: Testing coronal plasma diagnostics using 3D MHD models of
the solar atmosphere
Authors: Testa, P.; Martinez-Sykora, J.; Hansteen, V. H.; De Pontieu,
B.; Carlsson, M.
2011AGUFMSH53C..06T Altcode:
We synthesize coronal images and spectra from advanced 3D radiative
MHD simulations obtained from the state-of-the-art Bifrost code, and
explore how well they reproduce coronal observations with SDO/AIA
and Hinode/EIS and XRT. We apply standard diagnostic techniques
(e.g., density, temperature, abundance diagnostics) to the synthetic
observations and investigate how accurately the derived physical
information matches the plasma parameters of the model. We discuss
the limitations of the diagnostics and their implications.

---------------------------------------------------------
Title: Comparing Long Duration and Impulsive Solar Flares Using
SDO Data
Authors: Bowen, T.; Testa, P.; Reeves, K. K.
2011AGUFMSH13B1943B Altcode:
We present observations of two solar flares as recorded by instruments
on the Solar Dynamics Observatory (SDO). Combining observations from
the Atmospheric Imaging Assembly (AIA) and the Extreme Ultraviolet
Variability Experiment (EVE) Spectrometer provide a robust set of
data for solar flare analysis. The two instruments together provide
a unique look at the sun through global scale, fast cadence, high
resolution images and spectral measurements. Our study compares two
solar flares--occurring on 05/29/2011 and 06/21/2011--of similar
GOES X-ray flux classification, but which differ in both time
scale and morphology. We note striking differences between the two
flares; particularly in the behavior of the 131Å, 304Å, and 335Å
wavebands. The results of this study have implications for numeric
simulations of flaring loops, and may help constrain certain free
parameters in modeling flare dynamics. We show that for the long
duration flare, both EVE lightcurves and the peak flare spectrum are
successfully simulated by multi-threaded loop models. Furthermore,
we show that these same models accurately reproduce the lightcurves
of hotter AIA channels for both flare types.

---------------------------------------------------------
Title: Cross-Calibration and Thermal Analysis with SDO/AIA
Authors: Boerner, P.; Warren, H. P.; Testa, P.; Weber, M.; Schrijver,
C. J.
2011AGUFMSH13B1955B Altcode:
The measured intensity in each pixel of the images from SDO/AIA and
similar narrowband EUV imagers can be used to perform quantitative
analysis of the temperature and density of the plasma along the
line of sight. This type of analysis depends very sensitively on the
accuracy of the instrument calibration and the atomic physics models
used to estimate the plasma emissivity. Unfortunately, it is difficult
to assess the accuracy of these parameters, other than by verifying
the consistency of datasets from different instruments and analysis
techniques. Here we use differential emission measure models of the
plasma temperature structure constrained by spectroscopic observations
from SDO/EVE and Hinode/EIS to assess the AIA temperature response
functions. The response functions generated using the CHIANTI database
underestimate the emission from the non-flaring corona in the 94 and 131
Å channels. We find empirical corrections to the temperature response
functions for these channels that are internally consistent and provide
good agreement with DEMs obtained from other instruments. We present an
assessment of the reliability of thermal analysis using AIA data based
on the current state of the instrument calibration and spectral models.

---------------------------------------------------------
Title: Fe IX Calculations for the Solar Dynamics Observatory
Authors: Foster, Adam R.; Testa, Paola
2011ApJ...740L..52F Altcode: 2011arXiv1107.0470F
New calculations of the energy levels, radiative transition rates,
and collisional excitation rates of Fe IX have been carried out using
the Flexible Atomic Code, paying close attention to experimentally
identified levels and extending existing calculations to higher energy
levels. For lower levels, R-matrix collisional excitation rates from
earlier work have been used. Significant emission is predicted by these
calculations in the 5f-3d transitions, which will impact analysis of
Solar Dynamics Observatory Atmospheric Imaging Assembly observations
using the 94 Å filter.

---------------------------------------------------------
Title: Observations and Interpretation of a Low Coronal Shock Wave
Observed in the EUV by the SDO/AIA
Authors: Ma, Suli; Raymond, John C.; Golub, Leon; Lin, Jun; Chen,
Huadong; Grigis, Paolo; Testa, Paola; Long, David
2011ApJ...738..160M Altcode: 2011arXiv1106.6056M
Taking advantage of both the high temporal and spatial resolutions
of the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory, we studied a limb coronal shock wave and its associated
extreme ultraviolet (EUV) wave that occurred on 2010 June 13. Our main
findings are: (1) the shock wave appeared clearly only in the channels
centered at 193 Å and 211 Å as a dome-like enhancement propagating
ahead of its associated semi-spherical coronal mass ejection (CME)
bubble; (2) the density compression of the shock is 1.56 according
to radio data and the temperature of the shock is around 2.8 MK
(3) the shock wave first appeared at 05:38 UT, 2 minutes after the
associated flare has started and 1 minute after its associated CME
bubble appeared; (4) the top of the dome-like shock wave set out
from about 1.23 R sun and the thickness of the shocked
layer is ~2 × 104 km (5) the speed of the shock wave is
consistent with a slight decrease from about 600 km s-1
to 550 km s-1 and (6) the lateral expansion of the shock
wave suggests a constant speed around 400 km s-1, which
varies at different heights and directions. Our findings support the
view that the coronal shock wave is driven by the CME bubble, and the
on-limb EUV wave is consistent with a fast wave or at least includes
the fast wave component.

---------------------------------------------------------
Title: Solar Dynamics Observatory Discovers Thin High Temperature
Strands in Coronal Active Regions
Authors: Reale, Fabio; Guarrasi, Massimiliano; Testa, Paola; DeLuca,
Edward E.; Peres, Giovanni; Golub, Leon
2011ApJ...736L..16R Altcode: 2011arXiv1106.1591R
One scenario proposed to explain the million degree solar corona
is a finely stranded corona where each strand is heated by a rapid
pulse. However, such fine structure has neither been resolved through
direct imaging observations nor conclusively shown through indirect
observations of extended superhot plasma. Recently, it has been shown
that the observed difference in the appearance of cool and warm coronal
loops (~1 MK and ~2-3 MK, respectively)—warm loops appearing "fuzzier"
than cool loops—can be explained by models of loops composed of
subarcsecond strands, which are impulsively heated up to ~10 MK. That
work predicts that images of hot coronal loops (gsim 6 MK) should
again show fine structure. Here we show that the predicted effect is
indeed widely observed in an active region with the Solar Dynamics
Observatory, thus supporting a scenario where impulsive heating of
fine loop strands plays an important role in powering the active corona.

---------------------------------------------------------
Title: Detailed X-Ray Line Properties of θ2 Ori A in
Quiescence
Authors: Mitschang, Arik W.; Schulz, Norbert S.; Huenemoerder, David
P.; Nichols, Joy S.; Testa, Paola
2011ApJ...734...14M Altcode: 2010arXiv1009.1896M
We investigate X-ray emission properties of the peculiar X-ray source
θ2 Ori A in the Orion Trapezium region using more than 500
ks of HETGS spectral data in the quiescent state. The amount of exposure
provides tight constraints on several important diagnostics involving O,
Ne, Mg, and Si line flux ratios from He-like ion triplets, resonance
line ratios of the H- and He-like lines, and line widths. Accounting
for the influence of the strong UV radiation field of the O9.5V star, we
can now place the He-like line origin well within two stellar radii of
the O-star's surface. The lines are resolved with average line widths
of 341 ± 38 km s-1. In the framework of standard wind
models, this likely implies a rather weak wind with moderate post-shock
velocities. The emission measure distribution of the X-ray spectrum, as
reported previously, includes very high temperature components which are
not easily explained in this framework. The X-ray properties are also
not consistent with coronal emissions from an unseen low-mass companion
nor with typical signatures from colliding wind interactions. The
properties are more consistent with X-ray signatures observed in the
massive Trapezium star θ1 Ori C which has recently been
successfully modeled with a magnetically confined wind model.

---------------------------------------------------------
Title: The HETG Orion Legacy Project
Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Canizares, C. R.;
Testa, P.; Nichols, J.; Mitschang, A.
2011AAS...21822832S Altcode: 2011BAAS..43G22832S
The ONC is an ideal astrophysical laboratory to study very young
stars. The HETG Orion Legacy Project is designed to obtain a large
number of high-resolution X-ray spectra of very young late type
pre-main sequence stars, and several young massive and intermediate
mass stars. Its extreme proximity and youth makes the core of the ONC a
Chandra legacy project involving the only high resolution spectroscopic
study of young embedded cluster stars for decades to come. We present
new results for the second most massive star θ 2 Ori A, the intermdiate
mass binary θ 1 Ori E, and six late-type stars including MT Ori and
LQ Ori.

---------------------------------------------------------
Title: Magneto-thermal convection in solar prominences
Authors: Berger, Thomas; Testa, Paola; Hillier, Andrew; Boerner, Paul;
Low, Boon Chye; Shibata, Kazunari; Schrijver, Carolus; Tarbell, Ted;
Title, Alan
2011Natur.472..197B Altcode:
Coronal cavities are large low-density regions formed by
hemispheric-scale magnetic flux ropes suspended in the Sun's outer
atmosphere. They evolve over time, eventually erupting as the dark
cores of coronal mass ejections. Although coronal mass ejections are
common and can significantly affect planetary magnetospheres, the
mechanisms by which cavities evolve to an eruptive state remain poorly
understood. Recent optical observations of high-latitude `polar crown'
prominences within coronal cavities reveal dark, low-density `bubbles'
that undergo Rayleigh-Taylor instabilities to form dark plumes rising
into overlying coronal cavities. These observations offered a possible
mechanism for coronal cavity evolution, although the nature of the
bubbles, particularly their buoyancy, was hitherto unclear. Here we
report simultaneous optical and extreme-ultraviolet observations of
polar crown prominences that show that these bubbles contain plasma at
temperatures in the range (2.5-12)×105 kelvin, which is
25-120 times hotter than the overlying prominence. This identifies a
source of the buoyancy, and suggests that the coronal cavity-prominence
system supports a novel form of magneto-thermal convection in the solar
atmosphere, challenging current hydromagnetic concepts of prominences
and their relation to coronal cavities.

---------------------------------------------------------
Title: Temperature Distribution of a Non-flaring Active Region from
Simultaneous Hinode XRT and EIS Observations
Authors: Testa, Paola; Reale, Fabio; Landi, Enrico; DeLuca, Edward E.;
Kashyap, Vinay
2011ApJ...728...30T Altcode: 2010arXiv1012.0346T
We analyze coordinated Hinode X-ray Telescope (XRT) and Extreme
Ultraviolet Imaging Spectrometer (EIS) observations of a non-flaring
active region to investigate the thermal properties of coronal plasma
taking advantage of the complementary diagnostics provided by the
two instruments. In particular, we want to explore the presence of
hot plasma in non-flaring regions. Independent temperature analyses
from the XRT multi-filter data set, and the EIS spectra, including
the instrument entire wavelength range, provide a cross-check of the
different temperature diagnostics techniques applicable to broadband and
spectral data, respectively, and insights into cross-calibration of the
two instruments. The emission measure distributions, (EM(T)), we derive
from the two data sets have similar width and peak temperature, but
show a systematic shift of the absolute values, the EIS (EM(T)) being
smaller than the XRT (EM(T)) by approximately a factor two. We explore
possible causes of this discrepancy, and we discuss the influence of the
assumptions for the plasma element abundances. Specifically, we find
that the disagreement between the results from the two instruments
is significantly mitigated by assuming chemical composition closer
to the solar photospheric composition rather than the often adopted
"coronal" composition. We find that the data do not provide conclusive
evidence on the high temperature (log T(K) &gt;~ 6.5) tail of the
plasma temperature distribution, however, suggesting its presence to
a level in agreement with recent findings for other non-flaring regions.

---------------------------------------------------------
Title: Beyond the Limb: A Narrow Band EUV Search for Background
Objects with the AIA
Authors: Schonfeld, Sam; Testa, P.; Saar, S.
2011AAS...21715505S Altcode: 2011BAAS...4315505S
As the star closest to Earth, the Sun provides us with the opportunity
to study up close and test models for X-ray stellar activity. Its close
proximity (and consequent brightness), however, makes it challenging to
observe the Sun and other celestial objects with the same instrument;
thus instrumental cross-calibration difficulties have complicated
comparison of the Sun with other stars. The new Solar Dynamics
Observatory (SDO) launched in February 2010 may at last allow for
direct comparison of the Sun and other stars. The Atmospheric Imaging
Assembly (AIA) onboard the SDO, a series of telescopes taking images of
the full Sun at high spatial and temporal resolution in seven extreme
ultraviolet (EUV) pass bands, can potentially observe background objects
passing within the field of view of the telescopes off the limb of the
Sun. Young stars, active galactic nuclei and other strong X-ray and
EUV emitters may be bright enough to observe after careful background
subtraction. Using technical specifications of the telescopes and
measured X-ray fluxes of various background sources, we determined that
with exposure times of the order of minutes, significantly longer than
the standard 3s exposure, we should be able to observe the brightest
background sources when they pass in the AIA field of view. We also
determined what kinds of instrumental limitations we need to overcome
and how best to make observations of these dim background sources.

---------------------------------------------------------
Title: Element Abundances in X-ray Emitting Plasmas in Stars
Authors: Testa, Paola
2010SSRv..157...37T Altcode: 2010SSRv..tmp..138T; 2010arXiv1012.0343T
Studies of element abundances in stars are of fundamental interest for
their impact in a wide astrophysical context, from our understanding
of galactic chemistry and its evolution, to their effect on models of
stellar interiors, to the influence of the composition of material
in young stellar environments on the planet formation process. We
review recent results of studies of abundance properties of X-ray
emitting plasmas in stars, ranging from the corona of the Sun and
other solar-like stars, to pre-main sequence low-mass stars, and
to early-type stars. We discuss the status of our understanding of
abundance patterns in stellar X-ray plasmas, and recent advances made
possible by accurate diagnostics now accessible thanks to the high
resolution X-ray spectroscopy with Chandra and XMM-Newton.

---------------------------------------------------------
Title: Thermal study of active region plasma from Hinode and SDO
observations
Authors: Testa, P.
2010AGUFMSH41E..04T Altcode:
We investigate temporal variability and temperature structuring
of active region plasma by using Hinode and SDO observations, which
provide complementary diagnostics and excellent temporal resolution and
temperature coverage. We also discuss some limits of the diagnostics
in the light of the estimated completeness and accuracy of the atomic
data, in particular in the SDO/AIA passbands.

---------------------------------------------------------
Title: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)
Authors: Golub, L.; Cirtain, J. W.; Kobayashi, K.; Winebarger, A. R.;
Korreck, K. E.; Testa, P.
2010AGUFMSH11B1631G Altcode:
We present a novel design for a stigmatic grazing incidence X-ray
spectrograph for flight on a NASA sounding rocket. MaGIXS is comprised
of a Wolter I telescope, a slit, a pair of parabolic mirrors, a plano
variable line-spaced grating and a CCD detector. This design and layout
have been optimized to produce an optical system with peak effective
area of 5 mm^2, a wavelength range of 0.6-2.4 nm, spectral resolution of
2.0 pm, and spatial pixels of 2.5 arcsec along a 5 arcminute slit. The
resulting instrument will resolve the solar spectrum for features in
the solar corona with a two orders of magnitude increase over previous
soft x-ray spectrographs in spatial and spectral resolution.

---------------------------------------------------------
Title: X-ray Flares of EV Lac: Statistics, Spectra, and Diagnostics
Authors: Huenemoerder, David P.; Schulz, Norbert S.; Testa, Paola;
Drake, Jeremy J.; Osten, Rachel A.; Reale, Fabio
2010ApJ...723.1558H Altcode: 2010arXiv1006.2558H
We study the spectral and temporal behavior of X-ray flares from the
active M dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We
derive flare parameters by fitting an empirical function which
characterizes the amplitude, shape, and scale. The flares range from
very short (&lt;1 ks) to long (~104 s) duration events with
a range of shapes and amplitudes for all durations. We extract spectra
for composite flares to study their mean evolution and to compare
flares of different lengths. Evolution of spectral features in the
density-temperature plane shows probable sustained heating. The short
flares are significantly hotter than the longer flares. We determined
an upper limit to the Fe K fluorescent flux, the best-fit value being
close to what is expected for compact loops.

---------------------------------------------------------
Title: Testing Atomic Data for the SDO AIA and EVE Missions
Authors: Testa, Paola; Landi, E.; Drake, J.
2010AAS...21640203T Altcode: 2010BAAS...41..873T
The Solar Dynamic Observatory carries two instruments, AIA and EVE, that
include spectral windows in the X-ray/EUV band ( 15-170A). Accuracy
in the atomic data in this wavelength range is essential for the
interpretation of the solar EUV irradiance data from EVE and of
the variability of the high temperature corona. Here we carry out a
detailed benchmark of X-ray/EUV data in the CHIANTI 6.0.1 database
to assess their completeness and accuracy. Given the paucity of solar
observations, we use high-resolution X-ray spectra of the low-activity
corona of Procyon obtained with the Low Energy Transmission Grating
Spectrometer onboard Chandra.

---------------------------------------------------------
Title: Computer Vision for SDO: First Results from the SDO Feature
Finding Algorithms
Authors: Martens, Petrus C.; Attrill, G.; Davey, A.; Engell, A.;
Farid, S.; Grigis, P.; Kasper, J.; Korreck, K.; Saar, S.; Su, Y.;
Testa, P.; Wills-Davey, M.; Bernasconi, P.; Raouafi, N.; Georgoulis,
M.; Deforest, C.; Peterson, J.; Berghoff, T.; Delouille, V.; Hochedez,
J.; Mampaey, B.; Verbeek, C.; Cirtain, J.; Green, S.; Timmons, R.;
Savcheva, A.; Angryk, R.; Wiegelmann, T.; McAteer, R.
2010AAS...21630804M Altcode:
The SDO Feature Finding Team produces robust and very efficient
software modules that can keep up with the relentless SDO data stream,
and detect, trace, and analyze a large number of phenomena including:
flares, sigmoids, filaments, coronal dimmings, polarity inversion
lines, sunspots, X-ray bright points, active regions, coronal holes,
EIT waves, CME's, coronal oscillations, and jets. In addition we track
the emergence and evolution of magnetic elements down to the smallest
features that are detectable, and we will also provide at least four
full disk nonlinear force-free magnetic field extrapolations per day. During SDO commissioning we will install in the near-real time data
pipeline the modules that provide alerts for flares, coronal dimmings,
and emerging flux, as well as those that trace filaments, sigmoids,
polarity inversion lines, and active regions. We will demonstrate
the performance of these modules and illustrate their use for science
investigations.

---------------------------------------------------------
Title: The SDO flare detective
Authors: Grigis, Paolo; Davey, A.; Martens, P.; Testa, P.; Timmons,
R.; Su, Y.; SDO Feature Finding Team
2010AAS...21640208G Altcode: 2010BAAS...41..874G
We present the flare detective, a software module to automatically
detect and characterize solar flares observed with the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The
flare detective works in two steps. First, flares are detected in
EUV images by analyzing lightcurves in macropixels. At this time,
only basic quantities such as time intervals, positions, and peak
fluxes will be determined. This will allow the module to keep up
with the extremely large size of the incoming data stream and provide
near real-time information for space weather monitoring. Second, the
flare detective will be run again on the subset of images around the
time intervals where a flare has been already detected, where more
sophisticated (and slower) processing will be performed to better
characterize the flare and provide physically important parameters such
as temperatures and emission measures, projected areas and lightcurves
in different channels. The events detected will be made available to
the Heliophysics Events Knowledgebase (HEK) and also as a flare list
in text format accessible on the web. This module is part of a larger
effort to detect and track solar features and events that is optimized
to run on the very large datasets provided by SDO.

---------------------------------------------------------
Title: X-ray emission processes in stars and their immediate
environment
Authors: Testa, Paola
2010PNAS..107.7158T Altcode: 2010arXiv1008.4343T
A decade of X-ray stellar observations with Chandra and XMM-Newton
has led to significant advances in our understanding of the physical
processes at work in hot (magnetized) plasmas in stars and their
immediate environment, providing new perspectives and challenges,
and in turn the need for improved models. The wealth of high-quality
stellar spectra has allowed us to investigate, in detail, the
characteristics of the X-ray emission across the Hertzsprung-Russell
(HR) diagram. Progress has been made in addressing issues ranging from
classical stellar activity in stars with solar-like dynamos (such as
flares, activity cycles, spatial and thermal structuring of the X-ray
emitting plasma, and evolution of X-ray activity with age), to X-ray
generating processes (e.g., accretion, jets, magnetically confined
winds) that were poorly understood in the preChandra/XMM-Newton era. I
will discuss the progress made in the study of high energy stellar
physics and its impact in a wider astrophysical context, focusing on
the role of spectral diagnostics now accessible.

---------------------------------------------------------
Title: Automated Feature and Event Detection with SDO AIA and HMI Data
Authors: Davey, Alisdair; Martens, P. C. H.; Attrill, G. D. R.;
Engell, A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar,
S. H.; Su, Y.; Testa, P.; Wills-Davey, M.; Savcheva, A.; Bernasconi,
P. N.; Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F. .; Cirtain,
J. W.; Deforest, C. E.; Angryk, R. A.; de Moortel, I.; Wiegelmann,
T.; Georgouli, M. K.; McAteer, R. T. J.; Hurlburt, N.; Timmons, R.
2010cosp...38.2878D Altcode: 2010cosp.meet.2878D
The Solar Dynamics Observatory (SDO) represents a new frontier in
quantity and quality of solar data. At about 1.5 TB/day, the data will
not be easily digestible by solar physicists using the same methods
that have been employed for images from previous missions. In order for
solar scientists to use the SDO data effectively they need meta-data
that will allow them to identify and retrieve data sets that address
their particular science questions. We are building a comprehensive
computer vision pipeline for SDO, abstracting complete metadata
on many of the features and events detectable on the Sun without
human intervention. Our project unites more than a dozen individual,
existing codes into a systematic tool that can be used by the entire
solar community. The feature finding codes will run as part of the SDO
Event Detection System (EDS) at the Joint Science Operations Center
(JSOC; joint between Stanford and LMSAL). The metadata produced will
be stored in the Heliophysics Event Knowledgebase (HEK), which will be
accessible on-line for the rest of the world directly or via the Virtual
Solar Observatory (VSO) . Solar scientists will be able to use the
HEK to select event and feature data to download for science studies.

---------------------------------------------------------
Title: Towards accurate cross-calibration of Hinode XRT with other
X-ray observatories: tentative detection of the F star HD199143
with XRT
Authors: Testa, Paola; Saar, Steven
2010cosp...38.2910T Altcode: 2010cosp.meet.2910T
Despite decades of X-ray observations of both solar and stellar
coronae with various instruments, placing solar X-ray emission
levels in a broader astrophysical context is on surprisingly shaky
ground. This is largely due to cross-calibration problems and the
difficulty of observing the same targets with both solar and stellar
instruments. Here we report on a new attempt at direct cross-calibration
between solar and stellar missions: observations by the Hinode X-ray
Telescope (XRT) of a young X-ray active F star, HD199143. This star
has been previously studied by ROSAT and Chandra, and is eclipsed
by the Sun every January. We observed the star for a total of 12.6
hours on ingress and egress, and tentatively detect the source at an
emission level broadly consistent with expectations based on the most
up-to-date calibrations of Hinode, Chandra, and ROSAT count rates for
this star. We discuss further observational and analysis plans.

---------------------------------------------------------
Title: XRT Detection of Hot Plasma in Active Regions and Nanoflare
Heating
Authors: Reale, F.; Klimchuk, J. A.; Parenti, S.; Testa, P.
2009ASPC..415..256R Altcode:
Nanoflares occurring in sub-resolution strands have been long invoked
as strong candidates for the heating of active region (AR) coronal
loops. However, the frequent occurrence of nanoflares requires the
steady presence of flare-hot plasma in the active region, which
has been difficult to detect so far. We report on the analysis of
multi-filter Hinode/XRT observations of an active region, which may
show the widespread presence of 10 MK plasma.

---------------------------------------------------------
Title: Using Solar Regions as Seen by Hinode XRT to Model the Coronae
of Inactive Stars and Magnetic Minima
Authors: Saar, S.; Testa, P.; Weber, M.; Marsh, J.
2009ASPC..416..543S Altcode:
We use carefully calibrated, multi-filter X-ray data from Hinode XRT to
compute differential emission measures (DEM) for spatially averaged,
less active solar features (coronal holes, quiet Sun, X-ray bright
points). We use linear combinations of these regions to construct model
quiet coronae for comparison with inactive stars, specifically, stars
which may be in Maunder-like magnetic minima. In this way, test how
well a mix of existing solar features can be used to model conditions
in magnetic minima.

---------------------------------------------------------
Title: The Chandra HETG Orion Legacy Project
Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Testa, P.; Canizares,
C. R.
2009AAS...21460408S Altcode:
The HETG Orion Legacy Project is designed to accumulate a large number
of high resolution X-ray spectra from young massive, intermediate mass,
and low mass stars. The status as the nearest site of massive star
formation and rich low-mass, pre-main sequence stellar population
makes the core of the ONC an ideal Chandra Legacy high resolution
spectroscopic study of young embedded cluster stars. This Chandra
project is a unique enterprise to uncover properties and origins of the
X-ray emission in young stellar objects with unprecedented spectral
resolution. The project so far has acquired about half a dozen
HETG spectra of young stars in the ONC with up to 600 ks of exposure
since the launch of the Chandra X-ray Observatory. These observations
have allowed tremendous advances in our understanding of young stars,
the origin of their X-ray emission, and the structure of their winds and
coronae. We present most recent results and outline future perspectives.

---------------------------------------------------------
Title: The SDO Flare Detective
Authors: Grigis, P. C.; Davey, A. R.; Martens, P. C.; Su, Y.; Testa,
P.; Timmons, R. P.
2009AGUFMSH51B1277G Altcode:
We present the flare detective, a software module to automatically
detect and characterize solar flares observed with the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The
flare detective works in two steps. First, flares will be detected
in EUV images by analysing lightcurves in macropixels. At this time,
only basic quantities such as time intervals, positions, and peak
fluxes will be determined. This will allow the module to keep up
with the extremely large size of the incoming data stream and provide
near real-time information for space weather monitoring. Second, the
flare detective will be run again on the subset of images around the
time intervals where a flare has been already detected, where more
sophisticated (and slower) processing will be performed to better
characterize the flare and provide physically important parameters such
as temperatures and emission measures, projected areas and lightcurves
in different channels. The events detected will be made available to
the Heliophysics Knowledgebase (HEK) and also as a flare list in text
format accessible on the web. This module is part of a larger effort
to detect and track solar features and events that is optimized to
run on very large datasets such as the ones provided by SDO.

---------------------------------------------------------
Title: X-Ray Emission and Corona of the Young Intermediate-Mass
Binary θ1 Ori E
Authors: Huenemoerder, David P.; Schulz, Norbert S.; Testa, Paola;
Kesich, Anthony; Canizares, Claude R.
2009ApJ...707..942H Altcode: 2009arXiv0911.0189H
θ1 Ori E is a young, moderate mass binary system, a rarely
observed case of spectral-type G-giants of about 3 solar masses, which
are still collapsing toward the main sequence, where they presumably
become X-ray faint. We have obtained high-resolution X-ray spectra with
Chandra and find that the system is very active and similar to coronal
sources, having emission typical of magnetically confined plasma. It has
a broad temperature distribution with a hot component and significant
high energy continuum; narrow emission lines from H- and He-like ions,
as well as a range of Fe ions, and relative luminosity, Lx
/L bol = 10-3, at the saturation limit. Density,
while poorly constrained, is consistent with the low density limits, our
upper limits being ne &lt; 1013 cm-3
for Mg XI and ne &lt; 1012 cm-3 for
Ne IX. Coronal elemental abundances are sub-solar, with Ne being the
highest at about 0.4 times solar. We find a possible trend in Trapezium
hot plasmas toward low relative abundances of Fe, O, and Ne, which is
hard to explain in terms of the dust depletion scenarios of low-mass
young stars. Variability was unusually low during our observations
relative to other coronally active stars. Qualitatively, the emission
is similar to post-main-sequence G-stars. Coronal structures could be
compact or comparable to the dimensions of the stellar radii. From
comparison to X-ray emission from similar mass stars at various
evolutionary epochs, we conclude that the X-rays in θ1 Ori
E are generated by a convective dynamo, present during contraction,
but which will vanish during the main-sequence epoch possibly to be
resurrected during post-main-sequence evolution.

---------------------------------------------------------
Title: Hinode/XRT and STEREO Observations of a Diffuse Coronal
"Wave"-Coronal Mass Ejection-Dimming Event
Authors: Attrill, Gemma D. R.; Engell, Alexander J.; Wills-Davey,
Meredith J.; Grigis, Paolo; Testa, Paola
2009ApJ...704.1296A Altcode:
We report on observations of the first diffuse coronal wave detected
by Hinode/XRT. The event occurred near the west solar limb on 2007
May 23, originating from active region (AR) 10956 and was associated
with a coronal mass ejection (CME) and coronal dimmings. The bright
emission forming the coronal wave expanded predominantly to the east
and south of the AR. We use X-Ray Telescope (XRT) and STEREO Behind
(B) data combined with a potential magnetic field extrapolation to
derive an understanding of the global magnetic field connectivity. We
attribute the brightening to the east of the AR to compression and
channeling of the plasma along large-scale loops. The brightening to
the south of the AR expands across the quiet Sun, making the southern
component a likely candidate for identification as a diffuse coronal
wave. We analyze the bright front in STEREO/EUVI (B) 171, 195, and 284
Å images, as well as in XRT data, finding the strongest components to
be largely cospatial in all bandpasses. We also exploit the near-limb
location of this event by combining STEREO/COR1 and Extreme Ultra-Violet
Imaging Telescope (EUVI) data. Using all the data, we derive a full
picture of the low-coronal development of the eruption. The COR1 data
show that the southernmost outer edge of the CME is progressively
displaced southward during the expansion. EUVI data below the COR1
occulting disk show that the CME is significantly distorted in the
low corona as a result of the associated filament eruption. The core
coronal dimmings map to the core of the CME; the secondary coronal
dimmings map to the CME cavity; and the diffuse coronal wave maps to
the outermost edge of the expanding CME shell. The analysis of this
near-limb event has important implications for understanding earlier
eruptions originating from the same AR on 2007 May 16, 19, and 20.

---------------------------------------------------------
Title: Comparison of Hinode/XRT and RHESSI Detection of Hot Plasma
in the Non-Flaring Solar Corona
Authors: Reale, Fabio; McTiernan, James M.; Testa, Paola
2009ApJ...704L..58R Altcode: 2009arXiv0909.2529R
We compare observations of the non-flaring solar corona made
simultaneously with Hinode/XRT and RHESSI. The analyzed corona is
dominated by a single active region on 2006 November 12. The comparison
is made on emission measures. We derive emission measure distributions
versus temperature of the entire active region from multifilter XRT
data. We check the compatibility with the total emission measure
values estimated from the flux measured with RHESSI if the emission
comes from isothermal plasma. We find that RHESSI and XRT data analyses
consistently point to the presence of a minor emission measure component
peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI
results is within a factor of a few and indicates an acceptable level
of cross-consistency.

---------------------------------------------------------
Title: X-ray emission processes in stars and their immediate
environment
Authors: Testa, Paola
2009cfdd.confE...5T Altcode:
A decade of X-ray stellar observations with Chandra and XMM-Newton
has led to significant advances in our understanding of the physical
processes at work in hot (magnetized) plasmas in stars and their
immediate environment, providing new perspectives and challenges, and in
turn the need for improved models. The wealth of high-quality stellar
spectra has allowed us to investigate, in detail, the characteristics
of the X-ray emission across the HR diagram. Progress has been made
in addressing issues ranging from classical stellar activity in stars
with solar-like dynamos (such as, flares, activity cycles, spatial and
thermal structuring of the X-ray emitting plasma, evolution of X-ray
activity with age,...), to X-ray generating processes (e.g. accretion,
jets, magnetically confined winds,..) that were poorly understood in
the pre-Chandra/XMM-Newton era. I will discuss the progress made in
the study of high energy stellar physics and its impact in a wider
astrophysics context, focusing on the role of spectral diagnostics
now accessible.

---------------------------------------------------------
Title: Summing Flares From EV Lac
Authors: Huenemoerder, David; Testa, Paola; Schulz, Norbert; Drake,
Jeremy; Reale, Fabio; Canizares, Claude; Osten, Rachel
2009cfdd.confE.118H Altcode:
We present preliminary results of a study of the spectral and
temporal behavior of flares from the active M-dwarf EV Lac. We
will apply three powerful techniques: high-resolution spectroscopic
diagnostics to infer flaring loop conditions (temperature, density,
dynamics); measurement of flare scale heights from Fe K fluorescence;
and state-of-the-art hydrodynamic flare models. The high rate of
short flares, the X-ray signature of high density, and the evidence
for opacity in X-ray resonance lines make EV Lac an ideal target. A
deep flare exposure obtained by summing short events will provide
some of the best high-resolution time-resolved spectra possible for
constraining physical models of M-dwarf coronae and flares with detail
which can only be achieved through high resolution X-ray spectroscopy.

---------------------------------------------------------
Title: X-ray emission mechanism in the Be star HD 42054
Authors: Testa, Paola
2009cxo..prop.2782T Altcode:
We propose to obtain a HETGS spectrum of the Be star HD 42054 to
investigate the X-ray emission mechanisms in this mid B-type emission
line star characterized by hot and variable X-ray thermal emission. This
study, through detailed line-based diagnostics accessible only with
high resolution spectroscopy, will allow us to shed light into the
issue of X-ray emission from Be stars. Remarkably, beta Cephei is the
only Be star to date for which high-resolution X-ray spectra have been
obtained, excluding the very peculiar class of gamma Cas analogs.

---------------------------------------------------------
Title: Evidence of Widespread Hot Plasma in a Nonflaring Coronal
Active Region from Hinode/X-Ray Telescope
Authors: Reale, Fabio; Testa, Paola; Klimchuk, James A.; Parenti,
Susanna
2009ApJ...698..756R Altcode: 2009arXiv0904.0878R
Nanoflares, short and intense heat pulses within spatially unresolved
magnetic strands, are now considered a leading candidate to solve
the coronal heating problem. However, the frequent occurrence of
nanoflares requires that flare-hot plasma be present in the corona at
all times. Its detection has proved elusive until now, in part because
the intensities are predicted to be very faint. Here, we report on the
analysis of an active region observed with five filters by Hinode/X-Ray
Telescope (XRT) in 2006 November. We have used the filter ratio method
to derive maps of temperature and emission measure (EM) both in soft and
hard ratios. These maps are approximate in that the plasma is assumed
to be isothermal along each line of sight. Nonetheless, the hardest
available ratio reveals the clear presence of plasma around 10 MK. To
obtain more detailed information about the plasma properties, we have
performed Monte Carlo simulations assuming a variety of nonisothermal
EM distributions along the lines of sight. We find that the observed
filter ratios imply bi-modal distributions consisting of a strong cool
(log T ~ 6.3 - 6.5) component and a weaker (few percent) and hotter (6.6
&lt; log T &lt; 7.2) component. The data are consistent with bi-modal
distributions along all lines of sight, i.e., throughout the active
region. We also find that the isothermal temperature inferred from a
filter ratio depends sensitively on the precise temperature of the cool
component. A slight shift of this component can cause the hot component
to be obscured in a hard ratio measurement. Consequently, temperature
maps made in hard and soft ratios tend to be anti-correlated. We
conclude that this observation supports the presence of widespread
nanoflaring activity in the active region.

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Title: Computer Vision for The Solar Dynamics Observatory
Authors: Martens, Petrus C.; Angryk, R. A.; Bernasconi, P. N.; Cirtain,
J. W.; Davey, A. R.; DeForest, C. E.; Delouille, V. A.; De Moortel,
I.; Georgoulis, M. K.; Grigis, P. C.; Hochedez, J. E.; Kasper, J.;
Korreck, K. E.; Reeves, K. K.; Saar, S. H.; Savcheva, A.; Su, Y.;
Testa, P.; Wiegelmann, T.; Wills-Davey, M.
2009SPD....40.1711M Altcode:
NASA funded a large international consortium last year to produce
a comprehensive system for automated feature recognition in SDO
images. The data we consider are all AIA and EVE data plus surface
magnetic field images from HMI. Helioseismology is addressed by another
group. We will produce robust and very efficient software modules
that can keep up with the relentless SDO data stream and detect, trace,
and analyze a large number of phenomena, including: flares, sigmoids,
filaments, coronal dimmings, polarity inversion lines, sunspots,
X-ray bright points, active regions, coronal holes, EIT waves, CME's,
coronal oscillations, and jets. In addition we will track the emergence
and evolution of magnetic elements down to the smallest features
that are detectable, and we will also provide at least four full
disk nonlinear force-free magnetic field extrapolations per day. A completely new software element that rounds out this suite is a
trainable feature detection module, which employs a generalized image
classification algorithm to produce the texture features of the images
analyzed. A user can introduce a number of examples of the phenomenon
looked and the software will return images with similar features. We
have tested a proto-type on TRACE data, and were able to "train" the
algorithm to detect sunspots, active regions, and loops. Such a module
can be used to find features that have not even been discovered yet,
as, for example, sigmoids were in the pre-Yohkoh era. Our codes
will produce entries in the Helio Events Knowledge base, and that will
permit users to locate data on individual events as well as carry out
statistical studies on large numbers of events, using the interface
provided by the Virtual Solar Observatory.

---------------------------------------------------------
Title: Observations of Nanoflare Produced Hot ( 10 Mk) Plasma
Authors: Klimchuk, James A.; Reale, F.; Testa, P.; Parenti, S.
2009SPD....40.1214K Altcode:
Indirect observational evidence suggests that some or most of
the corona is heated impulsively on sub-resolution scales by
nanoflares. Theoretical studies of possible heating mechanisms
also support this picture. However, the most direct evidence of
nanoflares---plasma hotter than 5 MK---has been difficult to obtain
because the emission is expected to be very faint. The reason is
two-fold: first, hot plasma cools very rapidly by thermal conduction;
and second, densities are small because chromospheric evaporation
has not had time to fill the corona. Recent observations from several
instruments have now provided strong evidence of hot plasma. We report
here on the detection of 10 MK plasma by the X-Ray Telescope (XRT)
on Hinode. We show that the intensity of the emission is consistent
with nanoflare models, but is extremely difficult to explain with
steady heating.

---------------------------------------------------------
Title: Hinode/XRT and Stereo Observations of the May 2007 Coronal
Wave-cme-dimming Events
Authors: Attrill, Gemma; Engell, A. J.; Wills-Davey, M. J.; Grigis,
P.; Testa, P.
2009SPD....40.2108A Altcode:
We report observations of the first diffuse coronal wave detected by
Hinode/XRT. The event occurred near the West solar limb on 23 May 2007,
originating from active region (AR) 10956. The bright emission expanded
both to the East and South of the AR. We combine the XRT results with
data from STEREO (B) and a potential magnetic field extrapolation
to understand the global magnetic field connectivity. We consider
that the brightenings seen to the East and South of the source AR
are generated by different physical processes, due to the distinct
magnetic environments in these regions. We attribute the brightening to
the East of the AR to compression and channelling of the plasma along
large-scale loops. The brightening to the South of the AR expands across
the quiet Sun, making the southern component a likely candidate for
a classical diffuse coronal wave. We analyse the bright front in
STEREO/EUVI 171, 195 and 284 A images, as well as in XRT data, finding
it to be largely co-spatial in all bandpasses. The expansion velocity
of the diffuse bright front is 250 (± 85) km/s. We also exploit the
near-limb properties of this event by combining STEREO/COR1 and EUVI
data to derive a full picture of the low-coronal development of the
eruption. The COR1 data show that the southern-most outer edge of the
CME is progressively displaced southward. The core coronal dimmings map
to the bright core of the CME; the secondary coronal dimmings map to
the CME cavity; and the diffuse coronal "wave” maps to the outermost
edge of the expanding CME shell. The analysis of this near-limb event
has implications for understanding earlier eruptions originating from
the same AR. In particular, we present a new analysis of the 19 May 2007
event. NASA grants NNX09AB11G and NNH07AB97C supported this work.

---------------------------------------------------------
Title: Pre-flight Calibration Of The AIA Instrument On SDO
Authors: Wolfson, C. Jacob; Boerner, P.; Soufli, R.; Podgorski, W.;
Title, A.; Lemen, J.; Rausch, A.; Shing, L.; Stern, R.; McKenzie,
D.; Testa, P.; Weber, M.
2009SPD....40.1704W Altcode:
The Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics
Observatory (SDO) is a set of four reflecting telescopes designed to
acquire high-resolution images of the solar atmosphere in a variety of
extreme ultraviolet, ultraviolet and visible-light wavelength bands
(see Lemen et al.). AIA takes images in ten wavelength channels,
whose bandpasses are determined by the collecting area dedicated to
each channel and the efficiency of the mirror coatings, filters, and
detector. We describe the measurements of each of these components,
and present the resulting effective area as functions of wavelength. The
measured effective area functions will be cross-calibrated on orbit by
comparing full-disk integrated fluxes from each of the AIA channels
with the calibrated irradiance measurements from the EUV Variability
Experiment (EVE) on SDO. The AIA effective areas are used to calculate
temperature response functions and expected count rates in each channel
for observations of various solar features.

---------------------------------------------------------
Title: Testing magnetically confined wind shock models for β Cephei
using XMM-Newton and Chandra phase-resolved X-ray observations
Authors: Favata, F.; Neiner, C.; Testa, P.; Hussain, G.; Sanz-Forcada,
J.
2009A&A...495..217F Altcode: 2008arXiv0806.2275F
Aims: We have performed a set of high- and low-spectral resolution
phase-resolved X-ray observations of the magnetic B star β Cep,
for which theoretical models predict the presence of a confined wind
emitting X-rays from stationary shocks. Given the peculiar geometry
of β Cep, some of the models predict strong rotational modulation of
the X-ray emission, while other models predict a much lower amplitude
modulation at 90 deg phase shift from the modulation predicted from
the first group of models. Our observations were designed to provide
a stringent test of such models. Methods: We obtained four
observations spaced in rotational phase with XMM-Newton (using both
the EPIC cameras and the RGS spectrograph) and with Chandra (using the
LETG spectrograph). A detailed analysis of the data was performed to
derive both photometric and spectral parameters from the EPIC data,
searching for rotational modulation, and to derive the location of the
X-ray plasma from the line ratios in the He-like triplets of N, O, and
Ne from the RGS data. The LETG data were used to constrain the presence
of bulk motions in the plasma. Results: The strong rotational
modulation predicted by the early, static magnetically-confined
wind model for the X-ray emission is not observed in β Cep. The
small modulation present goes in the opposite direction, pointing
to the absence of any optically thick disk of neutral material,
and showing a modulation consistent with the later, dynamic models of
magnetically-confined wind models in B stars. The lack of observed bulk
motion points to the plasma being confined by a magnetic field, but the
low plasma temperature and lack of any flaring show that the plasma is
not heated by magnetic reconnection. Therefore, the observations point
to X-ray emission from shocks in a magnetically confined wind, with
no evidence of an optically thick, dense disk at the magnetic equator.

---------------------------------------------------------
Title: Characterization of X-ray emission from T Tauri Stars
Authors: Shukla, Sonali J.; Weintraub, David; Kastner, Joel;
Huenemoerder, David; Schulz, Norbert; Testa, Paola
2009AIPC.1094..333S Altcode: 2009csss...15..333S
We are analyzing high-resolution Chandra ACIS-S/HETGS long integration
spectra for a sample of young stars, including classical, weak-lined,
and post-T Tauri stars as well as a young main sequence star. We have
identified flaring and quiescent periods, based on overall X-ray
luminosity, for several of the stars. We have measured line fluxes
in the He-like ions separately in the flaring and quiescent epochs to
determine forbidden-to-intercombination line ratios. Results from out
analysis of four wTTS and one post-T Tauri star with Chandra/HETGS are
included in this presentation. The temperature and density diagnostics
for V987 Tau indicate that X-rays are emitted by a cool, high density
plasma in the quiescent phase.

---------------------------------------------------------
Title: Neon and Chemical Fractionation Trends in Late-type Stellar
Atmospheres
Authors: García-Alvarez, David; Drake, Jeremy J.; Testa, Paola
2009AIPC.1094..796G Altcode: 2008arXiv0808.1794G; 2009csss...15..796G
A survey of Ne, O and Fe coronal abundances culled from the recent
literature for about 60 late-type stars confirms that the Ne/O ratio
of stellar outer atmospheres is about two times the value recently
recommended by Asplund et al. The mean Ne/O remains flat from the
most active stars down to at least intermediate activity levels
(-5&lt;LX/Lbol&lt;-2), with some evidence for
a decline toward the lowest activity levels sampled. The abundances
surveyed are all based on emission measure distribution analyses
and the mean Ne/O is about 0.1 dex lower than that found from line
ratios in the seminal study of mostly active stars by Drake &amp;
Testa (2005), but is within the systematic uncertainties of that
study. We also confirm a pattern of strongly decreasing Fe/O with
increasing stellar activity. The observed abundance patterns are
reminiscent of the recent finding of a dependence of the solar Ne/O
and Fe/O ratios on active region plasma temperature and indicate a
universal fractionation process is at work. The firm saturation in
stellar Ne/O at higher activity levels combined with variability in the
solar coronal Ne/O leads us to suggest that Ne is generally depleted
in the solar outer atmosphere and photospheric values are reflected in
active stellar coronae. The solution to the recent solar model problem
would then appear to lie in a combination of the Asplund et al. (2005)
O abundance downward revision being too large, and the Ne abundance
being underestimated for the Sun by about a factor of 2.

---------------------------------------------------------
Title: Polar Exploration and Coronal Structure in the Active Binary
HR 5110
Authors: Huenemoerder, David P.; Osten, Rachel A.; Kesich, Anthony;
Testa, Paola; Schulz, Norbert
2009AIPC.1094..656H Altcode: 2009csss...15..656H
Overwhelming evidence exists for the importance of polar regions in
controlling stellar atmospheric structure and dynamics in active binary
systems. Uncertainties about the geometry of coronal emission have
made conclusions about coronal structures on such stars ambiguous. We
have obtained Chandra, VLA and VLBA observations of the nearly pole-on
active binary system HR 5110 in order to investigate coronal structures
without such ambiguity. The X-ray spectra will constrain thermal
coronal volumes through determinaion of electron densities; radio
observations will constrain non-thermal coronal volumes directly, and
allow an estimation of the relative importance of thermal and nonthermal
plasma in controlling and structuring active stellar coronae. Here we
present preliminary results from the Chandra observations.

---------------------------------------------------------
Title: Structure and Evolution of Pre-Main Sequence Stars
Authors: Schulz, Norbert S.; Allen, Glenn; Bautz, Mark W.; Canizares,
Claude C.; Davis, John; Dewey, Dan; Huenemoerder, David P.; Heilmann,
Ralf; Houck, John; Marshall, Herman L.; Nowak, Mike; Schattenburg,
Mark; Audard, Marc; Drake, Jeremy; Gagne, Marc; Kastner, Joel; Kallman,
Tim; Lautenegger, Maurice; Lee, Julia; Miller, Jon; Montmerle, Thierry;
Mukai, Koji; Osten, Rachel; Parerels, Frits; Pollock, Andy; Preibisch,
Thomas; Raymond, John; Reale, Fabio; Smith, Randall; Testa, Paola;
Weintraub, David
2009astro2010S.263S Altcode: 2009arXiv0904.3385S; 2009astro2010S.263A
Low-mass pre-main sequence (PMS) stars are strong and variable
X-ray emitters, as has been well established by EINSTEIN and ROSAT
observatories. It was originally believed that this emission was
of thermal nature and primarily originated from coronal activity
(magnetically confined loops, in analogy with Solar activity) on
contracting young stars. Broadband spectral analysis showed that
the emission was not isothermal and that elemental abundances were
non-Solar. The resolving power of the Chandra and XMM X-ray gratings
spectrometers have provided the first, tantalizing details concerning
the physical conditions such as temperatures, densities, and abundances
that characterize the X-ray emitting regions of young star. These
existing high resolution spectrometers, however, simply do not have
the effective area to measure diagnostic lines for a large number
of PMS stars over required to answer global questions such as: how
does magnetic activity in PMS stars differ from that of main sequence
stars, how do they evolve, what determines the population structure
and activity in stellar clusters, and how does the activity influence
the evolution of protostellar disks. Highly resolved (R&gt;3000)
X-ray spectroscopy at orders of magnitude greater efficiency than
currently available will provide major advances in answering these
questions. This requires the ability to resolve the key diagnostic
emission lines with a precision of better than 100 km/s.

---------------------------------------------------------
Title: Understanding X-ray emission from Young Stars
Authors: Shukla, Sonali J.; Weintraub, D.; Huenemoerder, D.; Schulz,
N.; Testa, P.; Kastner, J.
2009AAS...21341404S Altcode: 2009BAAS...41..224S
High-resolution X-ray observations over long integration times have
advanced our understanding of the X-ray emitting plasmas of young
stars. We have identified and are analyzing a sample of ten stars
from the Chandra archives observed with the High Energy Transmission
Grating Spectrometer (HETGS) spanning the various evolutionary phases
(classical, weak-lined, post-T Tauri and main sequence) of young
stars. We have identified flaring and quiescent periods, based on
overall X-ray luminosity, for several of the stars. By measuring the
X-ray line fluxes from these stars, we are able to discern temperatures,
densities, and abundances that indicate the physical characteristics of
the X-ray emitting plasmas. Of the analysis thus far, the temperature
and density diagnostics for V987 Tau in quiescence indicate a cool,
high density plasma.

---------------------------------------------------------
Title: Fe Kα and Hydrodynamic Loop Model Diagnostics for a Large
Flare on II Pegasi
Authors: Ercolano, Barbara; Drake, Jeremy J.; Reale, Fabio; Testa,
Paola; Miller, Jon M.
2008ApJ...688.1315E Altcode: 2008arXiv0807.2093E
The observation by the Swift X-ray Telescope of the Fe Kα1,
α2 doublet during a large flare on the RS CVn binary
system II Peg represents one of only two firm detections to date
of photospheric Fe Kα from a star other than our Sun. We present
models of the Fe Kα equivalent widths reported in the literature for
the II Peg observations and show that they are most probably due to
fluorescence following inner shell photoionization of quasi-neutral
Fe by the flare X-rays. Our models constrain the maximum height of
flare the to 0.15R* assuming solar abundances for the
photospheric material, and 0.1R* and 0.06R*
assuming depleted photospheric abundances ([M/H] = -0.2 and -0.4,
respectively). Accounting for an extended loop geometry has the effect
of increasing the estimated flare heights by a factor of ~3. These
predictions are consistent with those derived using results of
flaring-loop models, which are also used to estimate the flaring loop
properties and energetics. From loop models we estimate a flare loop
height of 0.13R*, plasma density of ~4 × 1012
cm-3, and emitting volume of ~6 × 1030
cm3. Our estimates for the flare dimensions and density
allow us to estimate the conductive energy losses to Econd
&lt;= 2 × 1036 erg, consistent with upper limits previously
obtained in the literature. Finally, we estimate the average energy
output of this large flare to be ~1033 erg s-1,
or 1/10th of the stellar bolometric luminosity.

---------------------------------------------------------
Title: X-Ray Emission from Young Stellar Objects in the epsilon
Chamaeleontis Group: The Herbig Ae Star HD 104237 and Associated
Low-Mass Stars
Authors: Testa, Paola; Huenemoerder, David P.; Schulz, Norbert S.;
Ishibashi, Kazunori
2008ApJ...687..579T Altcode: 2008arXiv0807.0059T
We present Chandra HETGS observations of the Herbig Ae star HD 104237
and the associated young stars comprising lower mass stars, in the
0.15-1.75 M⊙ mass range, in their pre-main-sequence
phase. The brightest X-ray source in the association is the central
system harboring the Herbig Ae primary and a K3 companion. Its X-ray
variability indicates modulation possibly on timescales of the rotation
period of the Herbig Ae star, and this would imply that the primary
significantly contributes to the overall emission. The spectrum of the
Herbig Ae+K3 system shows a soft component significantly more pronounced
than in other K-type young stars. This soft emission is reminiscent
of the unusually soft spectra observed for the single Herbig Ae stars
HD 163296 and AB Aur, and therefore we tentatively attribute it to
the Herbig Ae of the binary system. The HETGS spectrum shows strong
emission lines corresponding to a wide range of plasma temperatures. The
He-like triplet of Mg XI and Ne IX suggests the presence of plasma at
densities of about 1012 cm-3, possibly indicating
an accretion-related X-ray production mechanism. The analysis of the
zeroth-order spectra of the other sources indicates X-ray emission
characteristics typical of pre-main-sequence stars of similar spectral
type, with the exception of the T Tauri HD 104237-D, whose extremely
soft emission is very similar to the emission of the classical T Tauri
star TW Hya and suggests X-ray production by shocked accreting plasma.

---------------------------------------------------------
Title: The Analysis of Hinode/XRT Observations
Authors: Deluca, E. E.; Weber, M.; Savcheva, A.; Saar, S.; Testa,
P.; Cirtain, J. W.; Sakao, T.; Noriyuki, N.; Kano, R.; Shimizu, T.
2008AGUSMSP51B..02D Altcode:
This poster will present the current state of Hinode/XRT analysis
software. We will give an overview of the XRT Analysis Guide. We will
include a detailed discussion of the following topics: Co-alignment
with SOT and EIS Spot removal for dynamics studies Filter calibration
for thermal studies Dark calibrations Sample data sets will be
discussed and links to the data products will be provided.

---------------------------------------------------------
Title: Diagnostics of the Thermal Structure of Off-Disk Quiet
Sun Plasmas
Authors: Testa, P.; Landi, E.
2008AGUSMSP51A..02T Altcode:
It has been suggested recently that the quiet solar corona, when
observed outside the solar disk, is isothermal or near isothermal. If
true, this result has profound consequences for any theoretical model
trying to explain the thermal structure and the temperature of the
quiet solar corona. In this work we study the thermal structure of
the solar corona by combining simultaneous, long-exposure SOHO/SUMER
and Hinode/EIS observations of the quiet solar corona that include
the entire wavelength range of both instruments. We also analyze
simultaneous Hinode/XRT observations of the study region. This
comprehensive dataset includes lines emitted by many different types
of transitions and by a very large number of ions, that enable us to
obtain a very accurate determination of the thermal structure of the
quiet solar corona.

---------------------------------------------------------
Title: X-Ray Properties of Very Young Massive Stars in the Orion
Trapezium Cluster
Authors: Schulz, N. S.; Huenemoerder, D. P.; Testa, P.; Canizares,
C. R.
2008ASPC..387..355S Altcode:
The HETG Orion Legacy Project aims to study plasma properties of a large
number of highly resolved X-ray spectra from young stars over a large
range of masses and evolutionary stages. The spectra are collected
throughout the lifetime of Chandra and thus not only provide highly
significant X-ray line strengths for detailed plasma diagnostics but
also longterm X-ray monitoring. The heart of the Orion Nebula Cluster
(ONC) with a dynamic age of ∼ 3× 10^5 yr is one of the youngest
and closest star forming regions to our Sun and contains an ensemble
of the youngest massive and intermediate mass stars we know in the
Galaxy. Three out of at least four of the most massive ZAMS stars,
θ^1 Ori A, C and θ^2 Ori A show coronal properties indicative
of magnetic activity that is very likely not due to known or unseen
low-mass PMS companions. θ^1 Ori E, now identified as an intermediate
mass PMS binary, is the second most luminous X-ray source in the ONC,
and shows very high persistent X-ray temperatures and high plasma
densities which are quite unusual properties in comparison with the
coronal activities observed in low-mass PMS stars in the neighborhood.

---------------------------------------------------------
Title: Geometry Diagnostics of a Stellar Flare from Fluorescent X-Rays
Authors: Testa, Paola; Drake, Jeremy J.; Ercolano, Barbara; Reale,
Fabio; Huenemoerder, David P.; Affer, Laura; Micela, Giuseppina;
Garcia-Alvarez, David
2008ApJ...675L..97T Altcode: 2008arXiv0801.3857T
We present evidence of Fe fluorescent emission in the Chandra HETGS
spectrum of the single G-type giant HR 9024 during a large flare. In
analogy to solar X-ray observations, we interpret the observed Fe Kα
line as being produced by illumination of the photosphere by ionizing
coronal X-rays, in which case, for a given Fe photospheric abundance,
its intensity depends on the height of the X-ray source. The HETGS
observations, together with three-dimensional Monte Carlo calculations
to model the fluorescence emission, are used to obtain a direct
geometric constraint on the scale height of the flaring coronal
plasma. We compute the Fe fluorescent emission induced by the emission
of a single flaring coronal loop that well reproduces the observed X-ray
temporal and spectral properties according to a detailed hydrodynamic
modeling. The predicted Fe fluorescent emission is in good agreement
with the observed value within observational uncertainties, pointing
to a scale height lesssim 0.3R*. Comparison of the HR 9024
flare with that recently observed on II Peg by Swift indicates the
latter is consistent with excitation by X-ray photoionization.

---------------------------------------------------------
Title: The HETG Orion Legacy Project
Authors: Schulz, Norbert S.; Testa, P.; Huenemoerder, D. P.; Canizares,
C. R.
2008HEAD...10.1312S Altcode:
The HETG Orion Legacy Project aims to study high energy plasma
properties of a large number of highly resolved X-ray spectra from
young stars over a large range of masses and evolutionary stages. The
spectra are collected throughout the lifetime of Chandra and thus
not only provide highly significant X-ray line strengths for detailed
plasma diagnostics but also long-term X-ray monitoring. The heart
of the Orion Nebula Cluster with a dynamic age of 300000 yr is one of
the youngest and closest star forming regions to our Sun and contains an
ensemble of the youngest stars the Galaxy. The survey produces emission
measure distributions and allows us to perform plasma diagnostics
using H-, He-, Li-like lines in over a dozen stars. We investigate
the hypothesis further that X-ray production in very young massive
stars is consistent with the standard model but very weak and low in
energy unless there is enhancement by additional processes. The
survey produces HETG spectra for about a dozen of mostly K-type T Tauri
stars various quality levels. By spreading the observing time over
many Chandra observation cycles the recording of HETG spectra of a few
serendipitous flares is anticipated. This work was supported by
NASA through the Smithsonian Astrophysical Observatory (SAO) contract
SV3-73016 for the Chandra X-Ray Center and Science Instruments.

---------------------------------------------------------
Title: HETG Observations of Hot Stars: From Predicted to Bizarre
Authors: Schulz, Norbert S.; Testa, Paola; Huenemoerder, David P.;
Canizares, Claude R.
2008ChNew..15....1S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evidence for Accretion in the High-Resolution X-Ray Spectrum
of the T Tauri Star System Hen 3-600
Authors: Huenemoerder, David P.; Kastner, Joel H.; Testa, Paola;
Schulz, Norbert S.; Weintraub, David A.
2007ApJ...671..592H Altcode: 2007arXiv0708.4393H
We present high-resolution X-ray spectra of the nearby multiple T
Tauri star (TTS) system Hen 3-600, obtained with the High Energy
Transmission Grating Spectrograph (HETGS) aboard the Chandra X-Ray
Observatory. Both principal binary components of Hen 3-600 (A and B,
separation 1.4") were detected in the zeroth-order Chandra HETGS
X-ray image. Hen 3-600-A, the component with a large mid-infrared
excess, is a factor of ~2-3 fainter in X-rays than Hen 3-600-B, due
to a large flare at Hen 3-600-B during our observation. The dispersed
X-ray spectra of the two primary components overlap significantly, so
spectral analysis was performed primarily on the first-order spectrum of
the combined A + B system, with analysis of the individual dispersed
spectra limited to regions where the contributions of A and B can
be disentangled via cross-dispersion profile fitting. This analysis
results in two lines of evidence indicating that the X-ray emission
from Hen 3-600 A + B is derived, in part, from accretion processes. (1)
The line ratios of He-like O VII in the spectrum of Hen 3-600 A + B
indicate that the characteristic density of its X-ray-emitting plasma
is significantly larger than those of coronally active main-sequence and
pre-main-sequence stars. (2) A significant component of low-temperature
(2-3 MK) plasma is present in the Hen 3-600 A + B spectrum; this “soft
excess” appears somewhat stronger in component A. These results for
Hen 3-600 A + B are consistent with, although less pronounced than,
results obtained from X-ray grating spectroscopy of more rapidly
accreting TTS systems. Indeed, all of the emission signatures of Hen
3-600 A + B that are potential diagnostics of accretion activity-from
its high-resolution X-ray spectrum, through its UV excess and Hα
emission-line strengths, to its weak near-infrared excess-suggest
that its components (and component A in particular) represent a
transition phase between rapidly accreting, classical T Tauri stars
and nonaccreting, weak-lined T Tauri stars.

---------------------------------------------------------
Title: Magnetic Activity in Orion's Massive Young Stars
Authors: Huenemoerder, David; Schulz, N.; Testa, P.; Kastner, J.;
Canizares, C.
2007AAS...21114506H Altcode: 2007BAAS...39..998H
In the heart if the Orion Nebula Cluster, one of the youngest and
nearest star forming regions, is an ensemble of the youngest massive
stars we know in the Galaxy. Having a dynamic age of about 300,000
years, it harbors a number of very young and hot ZAMS stars. Recent
X-ray studies implied that some of these stars showed coronal type
X-ray spectra, but some seemingly not. So far the most compelling cases
for magnetic activity in these cases have been made for Theta-1 Ori
C and Theta-2 Ori A. As part of our HETG Orion Legacy Project we are
in the process of obtaining high quality and highly resolved X-ray
spectra from all massive Trapezium stars. We will present spectra
and analysis of some of these stars, including line-based spectral characterization of spectra and dynamics. This work was supported by
NASA through the Smithsonian Astrophysical Observatory (SAO) contract
SV3-73016 for the Chandra X-Ray Center and Science Instruments.

---------------------------------------------------------
Title: On X-Ray Optical Depth in the Coronae of Active Stars
Authors: Testa, Paola; Drake, Jeremy J.; Peres, Giovanni; Huenemoerder,
David P.
2007ApJ...665.1349T Altcode: 2007arXiv0706.4080T
We have investigated the optical thickness of the coronal plasma
through the analysis of high-resolution X-ray spectra of a large sample
of active stars observed with the High Energy Transmission Grating
Spectrometer on Chandra. In particular, we probed for the presence of
significant resonant scattering in the strong Lyman series lines arising
from hydrogen-like oxygen and neon ions. The active RS CVn-type binaries
II Peg and IM Peg and the single M dwarf EV Lac show significant
optical depth. For these active coronae, the Lyα/Lyβ ratios are
significantly depleted as compared with theoretical predictions and
with the same ratios observed in similar active stars. Interpreting
these decrements in terms of resonance scattering of line photons out
of the line of sight, we are able to derive an estimate for the typical
size of coronal structures, and from these we also derive estimates of
coronal filling factors. For all three sources we find that both the
photon path length as a fraction of the stellar radius and the implied
surface filling factors are very small and amount to a few percent at
most. The measured Lyα/Lyβ ratios are in good agreement with APED
theoretical predictions, thus indicating negligible optical depth,
for the other sources in our sample. We discuss the implications for
coronal structuring and heating flux requirements. For the stellar
sample as a whole, the data suggest increasing quenching of Lyα
relative to Lyβ as a function of both LX/Lbol
and the density-sensitive Mg XI forbidden-to-intercombination line
ratio, as might generally be expected.

---------------------------------------------------------
Title: Detailed Diagnostics of an X-Ray Flare in the Single Giant
HR 9024
Authors: Testa, Paola; Reale, Fabio; Garcia-Alvarez, David;
Huenemoerder, David P.
2007ApJ...663.1232T Altcode: 2007astro.ph..3422T
We analyze a 96 ks Chandra HETGS observation of the single G-type
giant HR 9024. The high flux allows us to examine spectral line and
continuum diagnostics at high temporal resolution, to derive plasma
parameters. A time-dependent one-dimensional hydrodynamic model of a
loop with half-length L=5×1011 cm (~R*/2) and
cross-sectional radius r=4.3×1010 cm, with a heat pulse
of 15 ks and 2×1011 ergs cm-2 s-1
deposited at the loop footpoints, satisfactorily reproduces the observed
evolution of temperature and emission measure, derived from the analysis
of the strong continuum emission. For the first time we can compare
predictions from the hydrodynamic model with single spectral features,
other than with global spectral properties. We find that the model
closely matches the observed line emission, especially for the hot
(~108 K) plasma emission of the Fe XXV complex at ~1.85
Å. The model loop has L/R*~1/2 and aspect ratio r/L~0.1,
as typically derived for flares observed in active stellar coronae,
suggesting that the underlying physics is the same for these very
dynamic and extreme phenomena in stellar coronae independently of
stellar parameters and evolutionary stage.

---------------------------------------------------------
Title: Magnetic Activity in Orion's Very Young Massive Stars
Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Testa, P.; Kastner,
J. H.; Canizares, C. R.
2007AAS...210.4007S Altcode: 2007BAAS...39R.154S
The heart of the Orion Nebula Cluster contains an ensemble of the
youngest massive stars we know in the Galaxy. The Orion Trapezium is
Cluster is one of the youngest and closest star forming regions to our
Sun. With a dynamic age of about 300000 yr it harbors a number of very
young and hot ZAMS stars. Recent X-ray studies implied that some of
these stars show coronal type X-ray spectra, but some seemingly not. So
far the most compelling cases for magnetic activity have been made for
θ 1 Ori C and θ 2 Ori A. As part of our HETG Orion Legacy Project we
are in the process of obtaining high quality and highly resolved X-ray
spectra from a large number of Trapezium cluster stars. With now 380
ks of exposure we have high spectral quality for all massive
Trapezum stars but θ 1 Ori D, which is surprisingly faint. With
few exceptions the spectra appear of coronal nature. We present
results on emissivity, temperatures, emission radius, density as well
as longterm variability. We compare the new results with properties
previously found specifically for θ 1 Ori C and θ 2 Ori A as well
as other hot and cool stars.

---------------------------------------------------------
Title: X-Ray Variability in the Young Massive Triple θ2
Orionis A
Authors: Schulz, Norbert S.; Testa, Paola; Huenemoerder, David P.;
Ishibashi, Kazunori; Canizares, Claude R.
2006ApJ...653..636S Altcode: 2006astro.ph..8420S
Massive stars rarely show intrinsic X-ray variability. One exception
is θ2 Ori A, which has shown strong variability over the
last 5 years. We observed a large outburst of the X-ray source with
the High Energy Transmission Grating Spectrometer on board Chandra and
compare the emissivity and line properties in states of low and high
flux. The low state indicates temperatures well above 25 MK. In the
high state we find high emissivities in the range from 3 to over 100
MK. The outburst event in stellar terms is one of the most powerful
ever observed and the most energetic one in the ONC, with a lower
total energy limit of 1.5×1037 ergs. The line diagnostics
indicate that the line-emitting regions in the low states are as close
as within 1-2 stellar radii from the O star's photosphere, whereas
the hard states suggest a distance of 3-5 stellar radii. We discuss
the results in the context of stellar flares, magnetic confinement,
and binary interactions. By matching the dates of all observations
with the orbital phases of the spectroscopy binary orbit, we find that
outbursts occur very close to the periastron passage of the stars. We
argue that the high X-ray states are possibly the result of reconnection
events from magnetic interactions of the primary and secondary stars of
the spectroscopic binary. Effects from wind collisions seem unlikely
for this system. The line properties in the low state seem consistent
with some form of magnetic confinement. We also detect Fe fluorescence
indicative of the existence of substantial amounts of neutral Fe in
the vicinity of the X-ray emission.

---------------------------------------------------------
Title: X-ray Variability in the Young Massive Triple θ2
Ori A
Authors: Schulz, Norbert S.; Testa, P.; Huenemoerder, D. P.; Ishibashi,
K.; Canizares, C. R.
2006AAS...20913305S Altcode: 2006BAAS...38.1080S
Massive stars rarely show intrinsic X-ray variability. The only O-stars
credited to be intrinsically variable are theta1 Ori C due
to effects from magnetic confinement of its wind, and theta2
Ori A suspected of similar activity. In the latter case early Chandra
observations have shown rapid variability on time scales of hours. We
determined X-ray fluxes from all observations with Chandra and find that
the star shows very strong variability over the last 5 years in addition
to short term varibility. There indications that this variability is
connnected to the 21 day orbital period of the massive spectrocopic
binary causing eruptive outbursts near periastron. A second large
outburst of the X-ray source in November 2004 was observed with the
high resolution transmission grating spectrometer onboard Chandra and
we compare the emissivity and line properties in states of low and
high flux. The outburst event in stellar terms is one of the most
powerful ever observed and the most energetic one in the ONC with
a lower total energy limit of 1.5 ×1037 ergs. Both flux
states reveal high X-ray emissivities with temperatures well above 25
MK, during outbursts over 100 MK. The line diagnostics show that under
the assumption that the He-like ions are photoexcited the line emitting
regions in the low states are very close to the O-star's photosphere,
whereas the high states indicate somewhat larger separation. We discuss
the results in the context of stellar flares, magnetic reconnection, and
binary interactions. We argue that the high X-ray states are possibly
the result of reconnection events from magnetic interactions of the
primary and secondary star of the spectroscopic binary. Effects from
wind collisions seem unlikely for this system. The low state emissivity
and R-ratios strengthen the predicament that X-ray emission is enhanced
by magnetic confinement of the primary wind.

---------------------------------------------------------
Title: Extraordinarily Hot X-Ray Emission from the O9 Emission-Line
Star HD 119682
Authors: Rakowski, Cara E.; Schulz, N. S.; Wolk, S. J.; Testa, Paola
2006ApJ...649L.111R Altcode: 2006astro.ph..8321R
We present new optical and X-ray observations to show that the X-ray
source 1WGA J1346.5-6255 previously associated with the SNR G309.2-0.6
can be unequivocally identified with the emission-line star HD 119682
located in the foreground open cluster NGC 5281. Images from Chandra
in the X-ray band as well as from Magellan in the narrow optical Hα
band show a coincidence of the source positions within 0.5". The
X-ray source appears extremely hot for an OB star identified as
of O9.7e type. XMM-Newton spectra show plasma temperatures of 1 and
&gt;8 keV with an X-ray luminosity of (6.2+/-0.1)×1032 ergs
s-1. The optical and X-ray properties are very reminiscent of
the prototype emission-line star γ Cas. We discuss the ramifications
of this similarity with respect to very early type emission-line stars
as a new class of hard X-ray sources.

---------------------------------------------------------
Title: X-Ray Spectroscopy of the Contact Binary VW Cephei
Authors: Huenemoerder, David P.; Testa, Paola; Buzasi, Derek L.
2006ApJ...650.1119H Altcode: 2006astro.ph..6690H
Short-period binaries represent extreme cases in the generation of
stellar coronae via a rotational dynamo. Such stars are important
for probing the origin and nature of coronae in the regimes of rapid
rotation and activity saturation. VW Cep (P=0.28 days) is a relatively
bright, partially eclipsing, very active object. Light curves made
from Chandra HETGS data show flaring and rotational modulation but
no eclipses. Velocity modulation of emission lines indicates that one
component dominates the X-ray emission. The emission measure is highly
structured, having three peaks. Helium-like triplet lines give electron
densities of about (3-18)×1010 cm-3. We conclude
that the corona is predominantly on the polar regions of the primary
star and is compact.

---------------------------------------------------------
Title: X-ray spectral diagnostics of accretion processes in pre-main
sequence stars: TWA14
Authors: Testa, Paola
2006cxo..prop.2107T Altcode:
We propose to obtain a 160 ks Chandra LETG+ACIS-S spectrum of TWA14, one
of the very few accreting pre-main sequence stars easily accessible to
high-resolution spectroscopy, being in the nearby TW Hydrae Association
and X-ray bright. This observation will provide unique X-ray diagnostics
of accretion and grain depletion of accreting gas, and will determine
the role of accretion and star-disk interaction in the high energy
emission of classical T Tauri stars.

---------------------------------------------------------
Title: Chandra/HETGS Observation of Young Stellar Objects in the
epsilon Chamaeleontis Group: Probing Proto-planetary Disk Systems
in the HD 102437 Field
Authors: Testa, Paola; Huenemoerder, D. P.; Schulz, N. S.; Ishibashi,
K.; Canizares, C. R.
2006HEAD....9.0307T Altcode: 2006BAAS...38..346T
We present 150 ks Chandra/HETGS observations of a group of young
stars comprising a Herbig Ae star (HD 102437), three T Tauri stars
(one classical T Tauri star, and two weak-lined T Tauri stars),
and a supposed brown dwarf. The HETG spectrum of the Herbig Ae
star shows strong emission lines corresponding to a wide range of
plasma temperatures; spectral diagnostics provide clues to the yet
unestablished X-ray production mechanisms in young intermediate mass
stars. We also present 0th order spectra, obtained for all group
members.

---------------------------------------------------------
Title: X-ray Flare on the Single Giant HR9024
Authors: Testa, P.
2006hrxs.confE..39T Altcode:
We analyze a Chandra-HETGS observation of the single G-type giant HR
9024. The high flux allows us to examine spectral line and continuum
diagnostics at high temporal resolution, to derive plasma parameters
(thermal distribution, abundances, temperature, ...). A time-dependent
1D hydrodynamic loop model with semi-length 1012 cm
(~Rstar), and impulsive footpoint heating triggering the
flare, satisfactorily reproduces the observed evolution of temperature
and emission measure, derived from the analysis of the strong continuum
emission.

---------------------------------------------------------
Title: Chandra/HETGS Observations of the Capella System: The Primary
as a Dominating X-Ray Source
Authors: Ishibashi, Kazunori; Dewey, Daniel; Huenemoerder, David P.;
Testa, Paola
2006ApJ...644L.117I Altcode: 2006astro.ph..5383I
Using the Chandra/High Energy Transmission Grating Spectrometer (HETGS),
we have detected the Doppler motion of Capella's X-ray emission lines in
the 6-25 Å wave band. The observed motion follows the expected orbital
motion of Capella's primary. This finding implies that the primary
G8 III star, not the secondary G1 III star in the Hertzsprung gap,
has been the dominant source of hot 106.8-107
K plasma at least in the last 6 years. In addition, the results
demonstrate the long-term stability of the HETGS, and they demonstrate
small uncertainties of 25 and 33 km s-1 in the velocity
determination with the High and Medium Energy Gratings (HEG and MEG),
respectively.

---------------------------------------------------------
Title: X-ray Flare Modeling in the Single Giant HR 9024
Authors: Testa, P.; Garcia-Alvarez, D.; Reale, F.; Huenemoerder, D.
2006ESASP.604..117T Altcode: 2006xru..conf..117T; 2005astro.ph.12624T
We analyze a Chandra-HETGS observation of the single G-type giant HR
9024. The high flux allows us to examine spectral line and continuum
diagnostics at high temporal resolution, to derive plasma parameters
(thermal distribution, abundances, temperature, ...). A time-dependent
1D hydrodynamic loop model with semi-length 10$^{12}$cm ($\sim
R_{\star}$), and impulsive footpoint heating triggering the flare,
satisfactorily reproduces the observed evolution of temperature and
emission measure, derived from the analysis of the strong continuum
emission. The observed characteristics of the flare appear to be common
features in very large flares in active stars (also pre-main sequence
stars), possibly indicating some fundamental physics for these very
dynamic and extreme phenomena in stellar coronae.

---------------------------------------------------------
Title: The `solar model problem' solved by the abundance of neon in
nearby stars
Authors: Drake, Jeremy J.; Testa, Paola
2005Natur.436..525D Altcode: 2005astro.ph..6182T
The interior structure of the Sun can be studied with great accuracy
using observations of its oscillations, similar to seismology of the
Earth. Precise agreement between helioseismological measurements and
predictions of theoretical solar models has been a triumph of modern
astrophysics. A recent downward revision by 25-35 per cent of the solar
abundances of light elements such as C, N, O and Ne (ref. 2) has,
however, broken this accordance: models adopting the new abundances
incorrectly predict the depth of the convection zone, the depth
profiles of sound speed and density, and the helium abundance. The
discrepancies are far beyond the uncertainties in either the data or
the model predictions. Here we report neon-to-oxygen ratios measured
in a sample of nearby solar-like stars, using their X-ray spectra. The
abundance ratios are all very similar and substantially larger than
the recently revised solar value. The neon abundance in the Sun is
quite poorly determined. If the Ne/O abundance in these stars is
adopted for the Sun, the models are brought back into agreement with
helioseismology measurements.

---------------------------------------------------------
Title: X-Ray Diagnostics of Grain Depletion in Matter Accreting onto
T Tauri Stars
Authors: Drake, Jeremy J.; Testa, Paola; Hartmann, Lee
2005ApJ...627L.149D Altcode: 2005astro.ph..6185H
Recent analysis of high-resolution Chandra X-ray spectra has shown
that the Ne/O abundance ratio is remarkably constant in stellar
coronae. Based on this result, we point out the utility of the Ne/O
ratio as a discriminant for accretion-related X-rays from T Tauri stars
and for probing the measure of grain depletion of the accreting material
in the inner disk. We apply the Ne/O diagnostic to the classical T Tauri
stars BP Tau and TW Hya-the two stars found to date whose X-ray emission
appears to originate, at least in part, from accretion activity. We
show that TW Hya appears to be accreting material that is significantly
depleted in O relative to Ne. In contrast, BP Tau has an Ne/O abundance
ratio consistent with that observed for post-T Tauri stars. We interpret
this result in terms of the different ages and evolutionary states
of the circumstellar disks of these stars. In the young BP Tau disk
(age ~0.6 Myr), dust is still present near the disk corotation radius
and can be ionized and accreted, rereleasing elements depleted onto
grains. In the more evolved TW Hya disk (age ~10 Myr), evidence points
to ongoing coagulation of grains into much larger bodies, and possibly
planets, that can resist the drag of inward-migrating gas, and the
accreting gas is consequently depleted of grain-forming elements.

---------------------------------------------------------
Title: X-ray diagnostics of grain depletion in matter accreting onto
T Tauri stars
Authors: Testa, Paola; Drake, Jeremy; Hartmann, Lee
2005sfet.confE..21T Altcode:
Recent analysis of high resolution Chandra X-ray spectra has shown
that the Ne/O abundance ratio is remarkably constant in stellar
coronae. Based on this result, we point out the utility of the Ne/O
ratio as a discriminant for accretion-related X-rays from T Tauri stars,
and for probing the measure of grain-depletion of the accreting material
in the inner disk. We apply the Ne/O diagnostic to the classical T
Tauri stars BP Tau and TW Hya---the two stars found to date whose
X-ray emission appears to originate, at least in part, from accretion
activity. We show that TW Hya appears to be accreting material which
is significantly depleted in O relative to Ne. In constrast, BP Tau
has an Ne/O abundance ratio consistent with that observed for post-T
Tauri stars. We interpret this result in terms of the different ages
and evolutionary states of the circumstellar disks of these stars. In
the young BP Tau disk (age ∼ 0.6 Myr) dust is still present near the
disk corotation radius and can be ionized and accreted, re-releasing
elements depleted onto grains. In the more evolved TW Hya disk (age
∼ 10 Myr), evidence points to ongoing coagulation of grains into
much larger bodies that can resist the drag of inward-migrating gas,
and accreting gas is consequently depleted of grain-forming elements.

---------------------------------------------------------
Title: The structure of coronal plasma in active stellar coronae
from density measurements
Authors: Testa, P.; Drake, J. J.; Peres, G.
2005ESASP.560..997T Altcode: 2005csss...13..997T
No abstract at ADS

---------------------------------------------------------
Title: Emission Measure Distribution in Loops Impulsively Heated at
the Footpoints
Authors: Testa, Paola; Peres, Giovanni; Reale, Fabio
2005ApJ...622..695T Altcode: 2004astro.ph.12482T
This work is prompted by evidence of sharply peaked emission measure
distributions in active stars and by the claims of isothermal loops
in solar coronal observations, at variance with the predictions
of hydrostatic loop models with constant cross section and
uniform heating. We address the problem with loops heated at the
footpoints. Since steady heating does not allow static loop model
solutions, we explore whether pulse-heated loops can exist and appear
as steady loops on a time average. We simulate pulse-heated loops,
using the Palermo-Harvard 1-D hydrodynamic code, for different initial
conditions corresponding to typical coronal temperatures of stars
ranging from intermediate to active [T~(3-10)×106 K]. We
find long-lived quasi-steady solutions even for heating concentrated at
the footpoints over a spatial region of the order of ~1/5 of the loop
half-length and broader. These solutions yield an emission measure
distribution with a peak at high temperature, and the cool side
of the peak is as steep as ~T5, in contrast to the usual
~T3/2 of hydrostatic models with constant cross section and
uniform heating. Such peaks are similar to those found in the emission
measure distribution of active stars around 107 K.

---------------------------------------------------------
Title: Size of coronal structures in active stellar coronae from
the detection of X-ray resonant scattering
Authors: Testa, P.; Drake, J. J.; Peres, G.; Deluca, E. E.
2005ESASP.560...43T Altcode: 2005csss...13...43T
No abstract at ADS

---------------------------------------------------------
Title: X-Ray Diagnostics of Grain Depletion in Matter Accreting onto
T Tauri Stars
Authors: Drake, J. J.; Testa, P.; Hartmann, L.
2005prpl.conf.8167D Altcode: 2005LPICo1286.8167D
No abstract at ADS

---------------------------------------------------------
Title: The Density of Coronal Plasma in Active Stellar Coronae
Authors: Testa, Paola; Drake, Jeremy J.; Peres, Giovanni
2004ApJ...617..508T Altcode: 2004astro.ph..5019T
We have analyzed high-resolution X-ray spectra of a sample of 22 active
stars observed with the High Energy Transmission Grating Spectrometer on
Chandra in order to investigate their coronal plasma density. Densities
were investigated using the lines of the He-like ions O VII, Mg XI,
and Si XIII. Si XIII lines in all stars of the sample are compatible
with the low-density limit (i.e., ne&lt;~1013
cm-3), casting some doubt on results based on lower
resolution Extreme Ultraviolet Explorer (EUVE) spectra finding densities
ne&gt;1013 cm-3. Mg XI lines betray
the presence of high plasma densities up to a few times 1012
cm-3 for most of the sources with higher X-ray luminosity
(&gt;~1030 ergs s-1) stars with higher
LX and LX/Lbol tend to have higher
densities at high temperatures. Ratios of O VII lines yield much lower
densities of a few times 1010 cm-3, indicating
that the “hot” and “cool” plasma resides in physically different
structures. In the cases of EV Lac, HD 223460, Canopus, μ Vel, TY Pyx,
and IM Peg, our results represent the first spectroscopic estimates
of coronal density. No trends in density-sensitive line ratios with
stellar parameters effective temperature and surface gravity were found,
indicating that plasma densities are remarkably similar for stars with
pressure scale heights differing by up to 3 orders of magnitude. Our
findings imply remarkably compact coronal structures, especially for
the hotter (~7 MK) plasma emitting the Mg XI lines characterized by
the coronal surface filling factor, fMgXI, ranging from
10-4 to 10-1, while we find fOVII
values from a few times 10-3 up to ~1 for the cooler (~2
MK) plasma emitting the O VII lines. We find that fOVII
approaches unity at the same stellar surface X-ray flux level as
characterizes solar active regions, suggesting that these stars become
completely covered by active regions. At the same surface flux level,
fMgXI is seen to increase more sharply with increasing
surface flux. These results appear to support earlier suggestions that
hot 107 K plasma in active coronae arises from flaring
activity and that this flaring activity increases markedly once the
stellar surface becomes covered with active regions. Comparison of our
measured line fluxes with theoretical models suggests that significant
residual model inaccuracies might be present and, in particular,
that cascade contributions to forbidden and intercombination lines
resulting from dielectronic recombination might be to blame.

---------------------------------------------------------
Title: Detection of X-Ray Resonance Scattering in Active Stellar
Coronae
Authors: Testa, Paola; Drake, Jeremy J.; Peres, Giovanni; DeLuca,
Edward E.
2004ApJ...609L..79T Altcode: 2004astro.ph..5520T
An analysis of Lyman series lines arising from hydrogen-like oxygen
and neon ions in the coronae of the active RS CVn-type binaries II Peg
and IM Peg, observed using the Chandra High Resolution Transmission
Grating Spectrograph, shows significant decrements in the Lyα/Lyβ
ratios as compared with theoretical predictions and with the same ratios
observed in similar active binaries. We interpret these decrements in
terms of resonance scattering of line photons out of the line of sight;
these observations present the first strong evidence of this effect in
active stellar coronae. The net line photon loss implies a nonuniform
and asymmetric surface distribution of emitting structures on these
stars. Escape probability arguments, together with the observed line
ratios and estimates of the emitting plasma density, imply typical
line-of-sight sizes of the coronal structures that dominate the X-ray
emission of 1010 cm at temperatures of 3×106 K
and of 108 cm at 107 K. These sizes are an order
of magnitude larger than predicted by simple quasi-static coronal loops
models but are still very small compared to the several 1011
cm radii of the underlying stars.

---------------------------------------------------------
Title: Hydrodynamic Model of Loops Heated by Microflares at the
Footpoints
Authors: Testa, P.; Peres, G.
2003SPD....34.1702T Altcode: 2003BAAS...35..837T
We simulate loops maintained in coronal conditions by random heat pulses
concentrated close to the footpoints, by using the Palermo-Harvard
1-D hydrodynamic code. We have explored the existence of dynamic
but quasi-static solutions when the heating is very concentrated at
footpoints whereas the heating concentrated at footpoints does not allow
static loop models solutions. We studied the characteristics of the
solutions (in terms of stability, density and temperature structure,
emission measure distribution) as a function of the parameters that
define the heating function, for three different loop lengths. We
found stable solutions even for heating concentrated over spatial
regions of the order of L/5 and higher values. For these stable
solutions, the average temperature profiles as a function of the loop
coordinate show a flatter or even inverted profile (for the case with
more concentrated heating) with respect to the standard static models;
the emission measure distribution as a function of temperature is
much steeper (up to ∼ T5) than the usual behavior as
T3/2 of the hydrostatic standard models.

---------------------------------------------------------
Title: Temperature and Density Structure of Hot and Cool Loops
Derived from the Analysis of TRACE Data
Authors: Testa, P.; Peres, G.; Reale, F.; Orlando, S.
2002ApJ...580.1159T Altcode:
We study the transversal structure (in particular the filamentation)
and the longitudinal plasma stratification in two sets of solar
coronal loops observed with TRACE in the 171 and 195 Å passbands. The
density stratification and the thermal structuring of the plasma along
the fibrils that form the loops are derived using two techniques
simultaneously: (1) a filter ratio diagnostic (195/171 Å) and
(2) modeling intensity profiles along the fibrils with hydrostatic
models; in both techniques we remove the background flux. We find
consistent values of temperature and density with both methods in the
coronal structures selected. We find evidence of a very warm fibril
(T~5×106 K) and of rather cold ones (T~2×105
K). The hot fibril appears to have a thermal structure with a maximum
at the apex compatible with temperature and density stratification,
dictated by energy balance, typical of a nonisothermal hydrostatic
loop. The cold fibrils appear to be isothermal and are probably in
dynamical conditions.

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Title: Temperature and density structure of hot and cool loops
derived from the analysis of TRACE data
Authors: Testa, P.; Peres, G.; Reale, F.; Orlando, S.
2002ESASP.505..203T Altcode: 2002solm.conf..203T; 2002IAUCo.188..203T
We address the plasma structuring both across and along the magnetic
field in two sets of solar coronal loops, observed with TRACE in the 171
Å and 195 Å passbands. We derive, after proper background removal,
the density stratification and the thermal structure of the plasma in
the fibrils forming the loops with two techniques: a) filter ratio
diagnostic (195 Å/171 Å) and b) modeling intensity profiles along
the fibrils with hydrostatic models. We find evidence of a hot fibril
(T ~ 5×106K), with temperature and density stratification
well-described with a typical non-isothermal hydrostatic loop model,
and evidence of rather cold fibrils (T ~ 2×105K), isothermal
and probably in dynamic conditions.