Author name code: lemen
ADS astronomy entries on 2022-09-14
author:"Lemen, James R."
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Title: Coronal observations with the Multi-Slit Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Lemen, James; Cheung, Mark; Boerner, Paul
Bibcode: 2021cosp...43E1803D
Altcode:
Observations of the corona are key to constrain magnetic field
models of the solar atmosphere. In this abstract we describe novel
observations that will be enabled by the Multi-Slit Solar Explorer
(MUSE), a proposed MIDEX mission for studying the dynamics of the
corona and transition region. MUSE will use both conventional and novel
spectral imaging techniques, coupled to state-of-the-art numerical
modeling. MUSE will obtain EUV spectra and images with the highest
resolution in space (1/3 arcsec) and time (1-4 s) ever achieved for
the transition region and corona, along 37 slits and a large context
FOV simultaneously. The science goals of MUSE are to understand the
physical mechanisms responsible for energy release in the corona
and for driving flares and coronal mass ejections. MUSE contains two
instruments: an EUV spectrograph and an EUV context imager. The MUSE
spectrograph employs a novel multi-slit design that enables a 100x
improvement in spectral scanning rates, which will reveal crucial
information about the dynamics of the physical processes that are not
observable with current instruments. MUSE will provide key constraints
on the morphology and dynamics of the magnetic field. We will discuss
the MUSE design and how it has been optimized to minimize effects
from overlapping spectra dispersed from different slits. We will also
illustrate how MUSE observations will lead to a better understanding
of how the dynamic magnetic field drives flares and eruptions.
Title: Global helium abundance measurements in the solar corona
Authors: Moses, John D.; Antonucci, Ester; Newmark, Jeffrey; Auchère,
Frédéric; Fineschi, Silvano; Romoli, Marco; Telloni, Daniele;
Massone, Giuseppe; Zangrilli, Luca; Focardi, Mauro; Landini, Federico;
Pancrazzi, Maurizio; Rossi, Guglielmo; Malvezzi, Andrea M.; Wang,
Dennis; Leclec'h, Jean-Christophe; Moalic, Jean-Pierre; Rouesnel,
Frédéric; Abbo, Lucia; Canou, Aurélien; Barbey, Nicolas; Guennou,
Chloé; Laming, John M.; Lemen, James; Wuelser, Jean-Pierre; Kohl,
John L.; Gardner, Lawrence D.
Bibcode: 2020NatAs...4.1134M
Altcode: 2020NatAs.tmp..152M
Solar abundances have been historically assumed to be representative
of cosmic abundances. However, our knowledge of the solar abundance
of helium, the second most abundant element, relies mainly on
models1 and indirect measurements through helioseismic
observations2, because actual measurements of helium in the
solar atmosphere are very scarce. Helium cannot be directly measured
in the photosphere because of its high first ionization potential,
and measurements of its abundance in the inner corona have been
sporadic3,4. In this Letter, we present simultaneous global
images of the helium (out to a heliocentric distance of 3R⊙
(solar radii)) and hydrogen emission in the solar corona during
the minimum of solar activity of cycle 23 and directly derive the
helium abundance in the streamer region and surrounding corona
(out to 2.2R⊙). The morphology of the He+
corona is markedly different from that of the H corona, owing to
significant spatial variations in helium abundance. The observations
show that the helium abundance is shaped according to and modulated
by the structure of the large-scale coronal magnetic field and that
helium is almost completely depleted in the equatorial regions during
the quiet Sun. This measurement provides a trace back to the coronal
source of the anomalously slow solar wind observed in the heliosphere
at the Sun-Earth Lagrangian point L1 in 2009, during the exceptionally
long-lasting minimum of solar activity cycle 23.
Title: MUSE: the Multi-Slit Solar Explorer
Authors: De Pontieu, B.; Lemen, J. R.; Cheung, C. M. M.
Bibcode: 2019AGUFMSH33A..07D
Altcode:
The Multi-Slit Solar Explorer (MUSE) is a proposed MIDEX mission
for studying the dynamics of the corona and transition region using
both conventional and novel spectral imaging techniques, coupled to
state-of-the-art numerical modeling. MUSE will obtain EUV spectra
and images with the highest resolution in space (1/3 arcsec) and
time (1-4 s) ever achieved for the transition region and corona,
along 37 slits and a large context FOV simultaneously. The science
goals of MUSE are to understand the physical mechanisms responsible
for energy release in the corona and for driving flares and coronal
mass ejections. MUSE contains two instruments: an EUV spectrograph and
an EUV context imager. Both leverage extensive heritage from previous
high-resolution instruments such as IRIS and the HiC rocket payload. The
MUSE spectrograph employs a novel multi-slit design that enables a
100x improvement in spectral scanning rates, which will reveal crucial
information about the dynamics of the physical processes that are not
observable with current instruments. MUSE will address its science
goals by observing at the spatial and temporal scales on which advanced
numerical models make distinguishing and testable predictions. We will
discuss the MUSE design and how it has been optimized to minimize
effects from overlapping spectra dispersed from different slits. We
will also describe the robust compressed sensing techniques (or spectral
disambiguation code) developed to allow accurate spectral analysis from
the multi-slit observations of MUSE, as illustrated with 3D radiative
MHD models. The MUSE consortium includes LMSAL, SAO, UCB, MSU, GSFC,
MSFC, HAO, ITA Oslo, and other institutions.
Title: MUSE, the Multi-Slit Solar Explorer
Authors: Lemen, J. R.; Tarbell, T. D.; De Pontieu, B.; Wuelser, J. P.
Bibcode: 2017AGUFMSH51B2494L
Altcode:
The Multi-Slit Solar Explorer (MUSE) has been selected for a Phase A
study for the NASA Heliophysics Small Explorer program. The science
objective of MUSE is to make high spatial and temporal resolution
imaging and spectral observations of the solar corona and transition
region in order to probe the mechanisms responsible for energy release
in the corona and understand the dynamics of the solar atmosphere. The
physical processes are responsible for heating the corona, accelerating
the solar wind, and the rapid release of energy in CMEs and flares. The
observations will be tightly coupled to state-of-the-art numerical
modeling to provide significantly improved estimates for understanding
and anticipating space weather. MUSE contains two instruments:
an EUV spectrograph and an EUV context imager. Both have similar
spatial resolutions and leverage extensive heritage from previous
high-resolution instruments such as IRIS and the HiC rocket payload. The
MUSE spectrograph employs a novel multi-slit design that enables a
100x improvement in spectral scanning rates, which will reveal crucial
information about the dynamics (e.g., temperature, velocities) of the
physical processes that are not observable with current instruments. The
MUSE investigation builds on the success of IRIS by combining numerical
modeling with a uniquely capable observatory: MUSE will obtain EUV
spectra and images with the highest resolution in space (1/3 arcsec) and
time (1-4 s) ever achieved for the transition region and corona, along
35 slits and a large context FOV simultaneously. The MUSE consortium
includes LMSAL, SAO, Stanford, ARC, HAO, GSFC, MSFC, MSU, and ITA Oslo.
Title: GOES-R SUVI On-Orbit Calibration and Performance
Authors: Edwards, C. G.; Mathur, D.; Lemen, J. R.; Vasudevan, G.;
Shing, L.; Shaw, M.; Sabolish, D. S.; Seguin, R.; Tung, P.; Seaton,
D. B.; Darnel, J.; Nwachuku, C.; Tadikonda, S.; Comeyne, G.
Bibcode: 2017AGUFMSH21A2641E
Altcode:
The Solar Ultraviolet Imager (SUVI) is one of several instruments on
board the Geostationary Operational Environmental Satellite, GOES-R,
as part of NOAA's space weather monitoring fleet. SUVI is a Generalized
Cassegrain telescope with a large field of view that employs multilayer
coatings optimized to operate in six extreme ultraviolet (EUV) narrow
bandpasses centered at 9.4, 13.1, 17.1, 19.5, 28.4 and 30.4 nm. This
paper presents the results of the Post-Launch Test (PLT) campaign and
on-orbit calibration. It discusses topics such as focus, alignment,
mechanisms, CCD characterization, and flat-fielding.
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
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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: Synoptic Solar Cycle 24 in Corona, Chromosphere, and
Photosphere Seen by the Solar Dynamics Observatory
Authors: Benevolenskaya, E.; Slater, G.; Lemen, J.
Bibcode: 2014SoPh..289.3371B
Altcode: 2014SoPh..tmp...71B
The Solar Dynamics Observatory provides multiwavelength imagery from
extreme ultraviolet (EUV) to visible light as well as magnetic-field
measurements. These data enable us to study the nature of solar activity
in different regions of the Sun, from the interior to the corona. For
solar-cycle studies, synoptic maps provide a useful way to represent
global activity and evolution by extracting a central meridian band from
sequences of full-disk images over a full solar Carrington rotation (≈
27.3 days). We present the global evolution during Solar Cycle 24 from
20 May 2010 to 31 August 2013 (CR 2097 - CR 2140), using synoptic maps
constructed from full-disk, line-of-sight magnetic-field imagery and
EUV imagery (171 Å, 193 Å, 211 Å, 304 Å, and 335 Å). The synoptic
maps have a resolution of 0.1 degree in longitude and steps of 0.001
in sine of latitude. We studied the axisymmetric and non-axisymmetric
structures of solar activity using these synoptic maps. To visualize the
axisymmetric development of Cycle 24, we generated time-latitude (also
called butterfly) images of the solar cycle in all of the wavelengths,
by averaging each synoptic map over all longitudes, thus compressing
it to a single vertical strip, and then assembling these strips in
time order. From these time-latitude images we observe that during the
ascending phase of Cycle 24 there is a very good relationship between
the integrated magnetic flux and the EUV intensity inside the zone
of sunspot activities. We observe a North-South asymmetry of the EUV
intensity in high-latitudes. The North-South asymmetry of the emerging
magnetic flux developed and resulted in a consequential asymmetry in
the timing of the polar magnetic-field reversals.
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.
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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: The Association of Solar Flares with Coronal Mass Ejections
During the Extended Solar Minimum
Authors: Nitta, N. V.; Aschwanden, M. J.; Freeland, S. L.; Lemen,
J. R.; Wülser, J. -P.; Zarro, D. M.
Bibcode: 2014SoPh..289.1257N
Altcode: 2013arXiv1308.1465N
We study the association of solar flares with coronal mass ejections
(CMEs) during the deep, extended solar minimum of 2007 - 2009, using
extreme-ultraviolet (EUV) and white-light (coronagraph) images from the
Solar Terrestrial Relations Observatory (STEREO). Although all of the
fast (v>900 km s−1), wide (θ>100∘) CMEs
are associated with a flare that is at least identified in GOES soft
X-ray light curves, a majority of flares with relatively high X-ray
intensity for the deep solar minimum (e.g. ≳1×10−6
W m−2 or C1) are not associated with CMEs. Intense
flares tend to occur in active regions with a strong and complex
photospheric magnetic field, but the active regions that produce
CME-associated flares tend to be small, including those that have no
sunspots and therefore no NOAA active-region numbers. Other factors
on scales similar to and larger than active regions seem to exist that
contribute to the association of flares with CMEs. We find the possible
low coronal signatures of CMEs, namely eruptions, dimmings, EUV waves,
and Type III bursts, in 91 %, 74 %, 57 %, and 74 %, respectively, of
the 35 flares that we associate with CMEs. None of these observables
can fully replace direct observations of CMEs by coronagraphs.
Title: STEREO/ Extreme Ultraviolet Imager (EUVI) Event Catalog 2006
- 2012
Authors: Aschwanden, Markus J.; Wülser, Jean-Pierre; Nitta, Nariaki
V.; Lemen, James R.; Freeland, Sam; Thompson, William T.
Bibcode: 2014SoPh..289..919A
Altcode: 2013arXiv1306.3180A
We generated an event catalog with an automated detection algorithm
based on the entire EUVI image database observed with the two Solar
Terrestrial Relations Observatory (STEREO)-A and -B spacecraft over
the first six years of the mission (2006 - 2012). The event catalog
includes the heliographic positions of some 20 000 EUV events,
transformed from spacecraft coordinates to Earth-based coordinates,
and information on associated GOES flare events (down to the level
of GOES A5-class flares). The 304 Å wavelength turns out to be the
most efficient channel for flare detection (79 % of all EUVI event
detections), while the 171 Å (4 %), 195 Å (10 %), and the 284 Å
channel (7 %) retrieve substantially fewer flare events, partially
due to the suppressing effect of EUV dimming, and partially due
to the lower cadence in the later years of the mission. Due to the
Sun-circling orbits of STEREO-A and -B, a large number of flares have
been detected on the farside of the Sun, invisible from Earth, or seen
as partially occulted events. The statistical size distributions of
EUV peak fluxes (with a power-law slope of αP=2.5±0.2)
and event durations (with a power-law slope of αT=2.4±0.3)
are found to be consistent with the fractal-diffusive self-organized
criticality model. The EUVI event catalog is available on-line at
secchi.lmsal.com/EUVI/euvi_autodetection/euvi_events.txt and may serve
as a comprehensive tool to identify stereoscopically observed flare
events for 3D reconstruction and to study occulted flare events.
Title: Using the SDO Atmospheric Imaging Assembly to Study Solar
Activity
Authors: Lemen, James
Bibcode: 2014AAS...22346001L
Altcode:
The Atmospheric Imaging Assembly (AIA) is one of the instruments
on board NASA’s flagship Solar Dynamics Observatory (SDO) mission
that was launched in February 2010. AIA achieves 1.5 arcsec spatial
resolution of the entire solar corona with 12-second temporal resolution
in seven extreme ultraviolet (EUV) band passes centered on specific
lines: Fe XVIII (94 Å), Fe VIII, XXI (131 Å), Fe IX (171 Å),
Fe XII, XXIV (193 Å), Fe XIV (211 Å), He II (304 Å) and Fe XVI
(335 Å) one band pass observes C IV (near 1600 Å). In the past 3
years AIA has produced over 77M images and 1,200 Tbytes of data that
have challenged and clarified our understanding of the solar corona,
specifically how the solar magnetic field drives coronal evolution on
various scales. Multi-temperature, low-noise, full-Sun observations
have captured solar eruptions and flares, coronal field oscillations
(in loops and filaments), fast-mode waves (up to 2,000 km/s),
plasma instabilities, and a rare view of comet interactions with the
corona. Comparison with data from other instruments, such as SDO EUV
Variability Experiment (EVE), and with numerical models, provides the
ability to develop a comprehensive understanding of solar activity and
evolution. And the comparison of the information-rich spatial content
of the AIA observations with EVE spectra is instructive for similar
studies of stellar targets. The NASA heliophysics open-data policy
enables wide-scale participation by the international community. As
the time base of AIA observations and magnetic data obtained from the
companion SDO Helioseismic and Magnetic Imager (HMI) increases to a
good fraction of the solar dynamo cycle time scale, we anticipate that
the value of the SDO data will be similarly magnified. We present
highlights that have been gleaned from this already exceptional
mission. http://sdowww.lmsal.com
Title: Soft X-ray Fluxes of Major Flares Far Behind the Limb as
Estimated Using STEREO EUV Images
Authors: Nitta, N. V.; Aschwanden, M. J.; Boerner, P. F.; Freeland,
S. L.; Lemen, J. R.; Wuelser, J. -P.
Bibcode: 2013SoPh..288..241N
Altcode: 2013arXiv1304.4163N
With increasing solar activity since 2010, many flares from the backside
of the Sun have been observed by the Extreme Ultraviolet Imager (EUVI)
on either of the twin STEREO spacecraft. Our objective is to estimate
their X-ray peak fluxes from EUVI data by finding a relation of the EUVI
with GOES X-ray fluxes. Because of the presence of the Fe XXIV line at
192 Å, the response of the EUVI 195 Å channel has a secondary broad
peak around 15 MK, and its fluxes closely trace X-ray fluxes during
the rise phase of flares. If the flare plasma is isothermal, the EUVI
flux should be directly proportional to the GOES flux. In reality,
the multithermal nature of the flare and other factors complicate
the estimation of the X-ray fluxes from EUVI observations. We discuss
the uncertainties, by comparing GOES fluxes with the high cadence EUV
data from the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO). We conclude that the EUVI 195 Å data can
provide estimates of the X-ray peak fluxes of intense flares (e.g.,
above M4 in the GOES scale) to small uncertainties. Lastly we show
examples of intense flares from regions far behind the limb, some of
which show eruptive signatures in AIA images.
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Title, A. M.; Lemen, J.; Wuelser, J.;
Tarbell, T. D.; Schrijver, C. J.; Golub, L.; Kankelborg, C.; Carlsson,
M.; Hansteen, V. H.; Worden, S.; IRIS Team
Bibcode: 2013SPD....44...03D
Altcode:
The solar chromosphere and transition region (TR) form a highly
structured and dynamic interface region between the photosphere and
the corona. This 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. Nevertheless,
the chromosphere remains poorly understood, because of the complexity
of the required observational and analytical tools: the interface
region is highly complex with transitions from optically thick to
optically thin radiation, from pressure to magnetic field domination,
and large density and temperature contrasts on small spatial scales. The
Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
SMEX mission in 2009 and is scheduled to launch on 26-June-2013 (with
first light scheduled for mid July). IRIS addresses critical questions:
(1) Which types of non-thermal energy dominate in the chromosphere and
beyond? (2) How does the chromosphere regulate mass and energy supply
to the corona and heliosphere? (3) How do magnetic flux and matter
rise through the lower atmosphere, and what role does flux emergence
play in flares and mass ejections? These questions are addressed with
a high-resolution near and far UV imaging spectrometer sensitive to
emission from plasma at temperatures between 5,000 K and 10 MK. IRIS
has a field-of-view of 120 arcsec, a spatial resolution of 0.4 arcsec,
and velocity resolution of 0.5 km/s. The IRIS investigation includes
a strong numerical modeling component based on advanced radiative MHD
codes to facilitate interpretation of observations. We describe the
IRIS instrumentation and numerical modeling, and present the plans for
observations, calibration and data distribution. We will highlight some
of the issues that IRIS observations can help resolve. More information
can be found at http://iris.lmsal.com
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Wuelser, J.;
Tarbell, T. D.; Schrijver, C.; Golub, L.; Kankelborg, C. C.; Hansteen,
V. H.; Carlsson, M.
Bibcode: 2012AGUFMSH33D2256D
Altcode:
The solar chromosphere and transition region (TR) form a highly
structured and dynamic interface region between the photosphere and
the corona. This 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. Nevertheless,
the chromosphere remains poorly understood, because of the complexity
of the required observational and analytical tools: the interface
region is highly complex with transitions from optically thick to
optically thin radiation, from pressure to magnetic field domination,
and large density and temperature contrasts on small spatial scales. The
Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
SMEX mission in 2009 and is scheduled to launch in early 2013. IRIS
addresses critical questions: (1) Which types of non-thermal energy
dominate in the chromosphere and beyond? (2) How does the chromosphere
regulate mass and energy supply to the corona and heliosphere? (3)
How do magnetic flux and matter rise through the lower atmosphere, and
what role does flux emergence play in flares and mass ejections? These
questions are addressed with a high-resolution near and far UV imaging
spectrometer sensitive to emission from plasma at temperatures between
5,000 K and 10 MK. IRIS has a field-of-view of 120 arcsec, a spatial
resolution of 0.4 arcsec, and velocity resolution of 0.5 km/s. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative MHD codes to facilitate interpretation of
observations. We will describe the IRIS instrumentation and numerical
modeling, and present the status of the IRIS observatory development. We
will highlight some of the issues that IRIS observations can help
resolve.
Title: Quantifying Coronal Dimming as Observed in EUV and X-ray
Images in Eruptive Events
Authors: Nitta, N. V.; Aschwanden, M. J.; Boerner, P.; Hill, S. M.;
Lemen, J. R.; Liu, W.; Schrijver, C.; Wuelser, J.
Bibcode: 2012AGUFMSH41A2097N
Altcode:
Data from SOHO have shown that coronal dimming is closely related
with coronal mass ejections (CMEs). In particular, dimming areas in
EIT 195 A images often match the lateral extension of the associated
CMEs. In this presentation, we summarize how CMEs compare with dimming
as identified at different wavelengths and by other instruments, such as
Yohkoh SXT, TRACE, GOES (12-15) SXI, STEREO EUVI and SDO AIA. Emphasis
is placed on recent data, since the combination of AIA and STEREO
data can lead us to better characterize CMEs and to more accurately
estimate how much mass is ejected. We discuss technical issues that
arise when quantifying dimming as a proxy for a CME. The issues include
instrument calibration, effects of heating and cooling and integration
along the line of sight. We also touch on the relation of dimming with
globally propagating coronal fronts, which are routinely isolated in
running difference images, and its implications on the magnitudes of
the associated CMEs.
Title: Solar Stereoscopy with STEREO/EUVI A and B Spacecraft from
Small (6∘) to Large (170∘) Spacecraft
Separation Angles
Authors: Aschwanden, Markus J.; Wülser, Jean-Pierre; Nitta, Nariaki;
Lemen, James
Bibcode: 2012SoPh..281..101A
Altcode: 2012SoPh..tmp..197A; 2012arXiv1207.2787A
We performed for the first time stereoscopic
triangulation of coronal loops in active regions
over the entire range of spacecraft separation angles
(αsep≈6∘,43∘,89∘,127∘,and
170∘). The accuracy of stereoscopic correlation depends
mostly on the viewing angle with respect to the solar surface
for each spacecraft, which affects the stereoscopic correspondence
identification of loops in image pairs. From a simple theoretical model
we predict an optimum range of αsep≈22∘ -
125∘, which is also experimentally confirmed. The best
accuracy is generally obtained when an active region passes the central
meridian (viewed from Earth), which yields a symmetric view for both
STEREO spacecraft and causes minimum horizontal foreshortening. For
the extended angular range of αsep≈6∘
- 127∘ we find a mean 3D misalignment angle
of μPF≈21∘ - 39∘ of
stereoscopically triangulated loops with magnetic potential-field
models, and μFFF≈15∘ - 21∘
for a force-free field model, which is partly caused by stereoscopic
uncertainties μSE≈9∘. We predict optimum
conditions for solar stereoscopy during the time intervals of 2012 -
2014, 2016 - 2017, and 2021 - 2023.
Title: First Three-dimensional Reconstructions of Coronal Loops
with the STEREO A+B Spacecraft. IV. Magnetic Modeling with Twisted
Force-free Fields
Authors: Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki
V.; Lemen, James R.; DeRosa, Marc L.; Malanushenko, Anna
Bibcode: 2012ApJ...756..124A
Altcode: 2012arXiv1207.2790A
The three-dimensional coordinates of stereoscopically triangulated
loops provide strong constraints for magnetic field models of active
regions in the solar corona. Here, we use STEREO/A and B data from some
500 stereoscopically triangulated loops observed in four active regions
(2007 April 30, May 9, May 19, and December 11), together with SOHO/MDI
line-of-sight magnetograms. We measure the average misalignment angle
between the stereoscopic loops and theoretical magnetic field models,
finding a mismatch of μ = 19°-46° for a potential field model,
which is reduced to μ = 14°-19° for a non-potential field model
parameterized by twist parameters. The residual error is commensurable
with stereoscopic measurement errors (μSE ≈ 8°-12°). We
developed a potential field code that deconvolves a line-of-sight
magnetogram into three magnetic field components (Bx ,
By , Bz ), as well as a non-potential field
forward-fitting code that determines the full length of twisted loops
(L ≈ 50-300 Mm), the number of twist turns (median N twist
= 0.06), the nonlinear force-free α-parameter (median α ≈ 4 ×
10-11 cm-1), and the current density (median
jz ≈ 1500 Mx cm-2 s-1). All twisted
loops are found to be far below the critical value for kink instability,
and Joule dissipation of their currents is found to be far below the
coronal heating requirement. The algorithm developed here, based on an
analytical solution of nonlinear force-free fields that is accurate to
second order (in the force-free parameter α), represents the first
code that enables fast forward fitting to photospheric magnetograms
and stereoscopically triangulated loops in the solar corona.
Title: Design, performance prediction, and measurements of the
interface region imaging spectrograph (IRIS) telescope
Authors: Podgorski, William A.; Cheimets, Peter N.; Golub, Leon;
Lemen, James R.; Title, Alan M.
Bibcode: 2012SPIE.8443E..3DP
Altcode:
This paper discusses the design of the IRIS Small Explorer
(SMEX) Cassegrain telescope, as well as its intended and measured
performance. Lockheed Martin, along with SAO, Montana State University,
and Stanford University are developing the IRIS instrument for a mission
to examine the solar spectra in two bands, one centered on 1369 Å,
and the other centered on 2810 Å. SAO led the design and construction
of the telescope feed, with assistance from Lockheed and Montana State
University. The telescope posed a number of implementation challenges,
which are discussed here, including the fact that no effective filters
exist to isolate the science spectra to the exclusion of the rest
of the solar flux, making it necessary to allow full sunlight into
the telescope.
Title: The interface region imaging spectrograph for the IRIS Small
Explorer mission
Authors: Wülser, Jean-Pierre; Title, Alan M.; Lemen, James R.; De
Pontieu, Bart; Kankelborg, Charles C.; Tarbell, Theodore D.; Berger,
Thomas E.; Golub, Leon; Kushner, Gary D.; Chou, Catherine Y.; Weingrod,
Isaac; Holmes, Buck; Mudge, Jason; Podgorski, William A.
Bibcode: 2012SPIE.8443E..08W
Altcode:
The Interface Region Imaging Spectrograph (IRIS) is a NASA SMall
EXplorer mission scheduled for launch in January 2013. The primary goal
of IRIS is to understand how the solar atmosphere is energized. The
IRIS investigation combines advanced numerical modeling with a high
resolution UV imaging spectrograph. IRIS will obtain UV spectra
and images with high resolution in space (0.4 arcsec) and time (1s)
focused on the chromosphere and transition region of the Sun, a complex
interface region between the photosphere and corona. The IRIS instrument
uses a Cassegrain telescope to feed a dual spectrograph and slit-jaw
imager that operate in the 133-141 nm and 278-283 nm ranges. This paper
describes the instrument with emphasis on the imaging spectrograph,
and presents an initial performance assessment from ground test results.
Title: Large-Scale Coronal Disturbances as Observed by SDO AIA
Authors: Nitta, Nariaki; Schrijver, Carolus; Title, Alan; Lemen,
James; Liu, Wei
Bibcode: 2012cosp...39.1378N
Altcode: 2012cosp.meet.1378N
With increasing solar activity, the Atmospheric Imaging Assembly
(AIA) on the Solar Dynamics Observatory (SDO) has observed a number
of large-scale coronal disturbances, which may correspond to what we
have generally known as "EIT waves." Although their nature is still
actively debated, these disturbances usually accompany CMEs. In certain
cases, the fronts of the disturbances may signify CME-related shock
waves important for particle acceleration. Using the unprecedented
temporal resolution and broad temperature coverage of the AIA, we have
studied more than 100 such events. Here we discuss their kinematics
characterized by faster fronts than EIT waves in Solar Cycle 23, and
spatial relations with CMEs using STEREO data that provide triangulation
of the fronts. We also try plasma diagnostic using images in different
filters. Association of these disturbances with CMEs, flares and type
II bursts is discussed on a statistical basis. Lastly, we explore the
possible relation of the larger-scale coronal disturbances with SEP
events observed at widely separate longitudes and their onset times.
Title: Next-generation Technologies for EUV Solar Imagers
Authors: Martinez-Galarce, Dennis S.; Boerner, P.; Stern, R.; Soufli,
R.; Fernández-Perea, M.; Shing, L.; Lemen, J.; Gullikson, E.
Bibcode: 2012AAS...22052205M
Altcode:
The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory has convincingly demonstrated the importance of obtaining
high spatial ( 1 arc sec) and temporal ( 10 sec) resolution images
of solar extreme ultraviolet (EUV) radiation from the transition
region and corona. AIA full-disk observations indicate that such
radiation is being generated by events or features at spatial scales
ranging from large-sized events of several arc min (e.g., CMEs and
related flares), to much smaller scales observed at the limits of the
performance of AIA (e.g., moss and jet-like features). Although our
understanding of the solar atmosphere has advanced as a consequence of
these observations, furthering our knowledge of the detailed physics
will require improved instrumentation, i.e., fabrication of higher
performance EUV imaging telescopes with higher spatial resolution
(Δθ ≤ 0.1 arc sec) and higher temporal resolution (Δt ≤ few
sec), extending over previously un-observed wavelength ranges. Such
improved technologies, which are currently under development, can be
implemented in the next-generation EUV solar telescopes (for example, on
the Solar-C or RAM missions). Herein, we report on the status of three
technologies that have been investigated: development of super-polished
SiC substrates useful for large-diameter EUV telescopes; development
of a novel multilayer coating that produces high reflectivities above
300 Å and evaluation of new back-illuminated CMOS detector arrays
capable of rapid EUV imaging.
Title: Force-Free Magneto-Stereoscopy of Coronal Loops
Authors: Aschwanden, Markus J.; Malanushenko, A.; Wuelser, J.; Nitta,
N.; Lemen, J. R.; DeRosa, M.
Bibcode: 2012AAS...22041103A
Altcode:
We derive an analytical approximation of nonlinear force-free
magnetic field solutions (NLFFF) that can efficiently be used for
fast forward-fitting to solar magnetic data, constrained either by
observed line-of-sight magnetograms and stereoscopically triangulated
coronal loops, or by 3D vector-magnetograph data. We test the code by
forward-fitting to simulated data, to force-free solutions derived by
Low and Lou (1990), and to active regions observed with STEREO/EUVI and
SOHO/MDI. The forward-fitting tests demonstrate: (i) a satisfactory
convergence behavior (with typical misalignment angles of 1-10 deg),
(ii) a high fidelity of retrieved force-free alpha-parameters, and
(iii) relatively fast computation times (from seconds to minutes). The
novel feature of this NLFFF code is the derivation of a quasi-forcefree
field based on coronal constraints, which bypasses the non-forcefree
photosphere of standard magnetograms. Applications range from magnetic
modeling of loops to the determnination of electric currents, twist,
helicity, and free (non-potential) energy in active regions.
Title: Large-scale Coronal Disturbances As Observed By SDO AIA
Authors: Nitta, Nariaki; Schrijver, C.; title, A.; Liu, W.; Lemen, J.
Bibcode: 2012AAS...22051502N
Altcode:
With increasing solar activity, the Atmospheric Imaging Assembly
(AIA) on the Solar Dynamics Observatory (SDO) has observed a number
of large-scale coronal disturbances, which may correspond to what
we have generally known as "EIT waves." Their nature is still
actively debated. In certain cases, the fronts of the disturbances
may signify CME-related shock waves that are important for particle
acceleration. Using the unprecedented temporal resolution and broad
temperature coverage of the AIA, we have studied more than 100 such
events. Here we discuss their kinematics characterized by faster fronts
than EIT waves in Solar Cycle 23, and spatial relations with CMEs
using STEREO data that provide triangulation of the fronts. We also
try plasma diagnostic using images in different filters. Association
of these disturbances with other phenomena such as CMEs, flares and
type II bursts, is discussed on a statistical basis.
Title: The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics
Observatory (SDO)
Authors: Lemen, James R.; Title, Alan M.; Akin, David J.; Boerner,
Paul F.; Chou, Catherine; Drake, Jerry F.; Duncan, Dexter W.; Edwards,
Christopher G.; Friedlaender, Frank M.; Heyman, Gary F.; Hurlburt, Neal
E.; Katz, Noah L.; Kushner, Gary D.; Levay, Michael; Lindgren, Russell
W.; Mathur, Dnyanesh P.; McFeaters, Edward L.; Mitchell, Sarah; Rehse,
Roger A.; Schrijver, Carolus J.; Springer, Larry A.; Stern, Robert A.;
Tarbell, Theodore D.; Wuelser, Jean-Pierre; Wolfson, C. Jacob; Yanari,
Carl; Bookbinder, Jay A.; Cheimets, Peter N.; Caldwell, David; Deluca,
Edward E.; Gates, Richard; Golub, Leon; Park, Sang; Podgorski, William
A.; Bush, Rock I.; Scherrer, Philip H.; Gummin, Mark A.; Smith, Peter;
Auker, Gary; Jerram, Paul; Pool, Peter; Soufli, Regina; Windt, David
L.; Beardsley, Sarah; Clapp, Matthew; Lang, James; Waltham, Nicholas
Bibcode: 2012SoPh..275...17L
Altcode: 2011SoPh..tmp..106L; 2011SoPh..tmp..172L; 2011SoPh..tmp..241L;
2011SoPh..tmp..115L
The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous
high-resolution full-disk images of the corona and transition region
up to 0.5 R⊙ above the solar limb with 1.5-arcsec spatial
resolution and 12-second temporal resolution. The AIA consists of four
telescopes that employ normal-incidence, multilayer-coated optics to
provide narrow-band imaging of seven extreme ultraviolet (EUV) band
passes centered on specific lines: Fe XVIII (94 Å), Fe XVII, XXI
(131 Å), Fe IX (171 Å), Fe XII, XXIV (193 Å), Fe XIV (211 Å),
He II (304 Å), and Fe XVI (335 Å). One telescope observes C IV
(near 1600 Å) and the nearby continuum (1700 Å) and has a filter
that observes in the visible to enable coalignment with images from
other telescopes. The temperature diagnostics of the EUV emissions
cover the range from 6×104 K to 2×107 K. The
AIA was launched as a part of NASA's Solar Dynamics Observatory (SDO)
mission on 11 February 2010. AIA will advance our understanding of the
mechanisms of solar variability and of how the Sun's energy is stored
and released into the heliosphere and geospace.
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
Bibcode: 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: Large-scale Coronal Propagating Fronts During the Rising
Phase of Solar Cycle 24
Authors: Nitta, N. V.; Liu, W.; Schrijver, C. J.; Title, A. M.; Lemen,
J. R.
Bibcode: 2011AGUFMSH23A1941N
Altcode:
With increasing solar activity, the AIA on SDO has observed a number
of large-scale coronal propagating fronts, which are often called
"EIT waves." Although their nature is still actively debated,
these propagating fronts usually accompany CMEs, and, in certain
cases, may signify CME-related shock waves important for particle
acceleration. Using the unprecedented temporal resolution and broad
temperature coverage of the AIA, it is possible to characterize
the propagating fronts in the corona far better than before, as
demonstrated in the literature for a yet small number of cases. We
study the properties of more than 40 propagating fronts as observed
by AIA, and discuss the key properties for them to be associated with
other phenomena such as type II radio bursts, flares, CMEs, ICMEs,
and SEP events. We make use of data, both remote-sensing and in-situ,
from STEREO which provides two additional vantage points, to make the
associations more solid. For the associated phenomena, their basic
properties are correlated with those of the propagating fronts. We
also revisit the association of EIT waves with other phenomena during
the similar phase of Solar Cycle 23 and discuss possible differences
in terms of global magnetic field. Understanding their relation with
other phenomena, we can have a more complete picture of the coronal
propagating fronts in the context of CME acceleration and deceleration.
Title: The Interface Region Imaging Spectrograph (IRIS) NASA SMEX
Authors: Lemen, James; Title, A.; De Pontieu, B.; Schrijver, C.;
Tarbell, T.; Wuelser, J.; Golub, L.; Kankelborg, C.
Bibcode: 2011SPD....42.1512L
Altcode: 2011BAAS..43S.1512L
The solar chromosphere and transition region (TR) is highly structured,
dynamic, and intimately connected to the corona. It requires more
than ten times the energy required to heat the corona, and yet it
has received far less interest because of the complexity of the
required observational and analytical tools. In the TR the density
drops by six orders of magnitude and the temperature increases by
three orders of magnitude. Hinode observations reveal the importance
the magnetic field has on this region of the solar atmosphere that
acts as the interface between the photosphere and the corona. The
Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
SMEX mission in 2009 and is scheduled to launch in December 2012. IRIS
addresses critical questions in order to understand the flow of energy
and mass through the chromosphere and TR, namely: (1) Which types of
non-thermal energy dominate in the chromosphere and beyond? (2) How
does the chromosphere regulate mass and energy supply to the corona
and heliosphere? (3) How do magnetic flux and matter rise through the
lower atmosphere, and what roles dos flux emergence play in flares and
mass ejections? These questions are addressed with a high-resolution
imaging spectrometer that observes Near- and Far-VU emissions that
are formed at temperatures between 5,000K and 1.5 x 106
K. IRIS has a field-of-view of 120 arcsec, a spatial resolution
of 0.4 arcsec, and velocity resolution of 0.5 km/s. Members of the
IRIS investigation team are developing advanced radiative MHD codes
to facilitate comparison with and interpretation of observations. We
present the status of the IRIS observatory development, which completed
its Critical Design Review in December 2010.
Title: A novel forward-model technique for estimating EUV imaging
performance: design and analysis of the SUVI telescope
Authors: Martínez-Galarce, Dennis; Harvey, James; Bruner, Marilyn;
Lemen, James; Gullikson, Eric; Soufli, Regina; Prast, Evan; Khatri,
Shayna
Bibcode: 2010SPIE.7732E..37M
Altcode: 2010SPIE.7732E.100M
The Solar Ultraviolet Imager (SUVI) is one of several instruments being
fabricated for use on board the upcoming Geostationary Operational
Environmental Satellites, GOES-R and -S platforms, as part of NOAA's
space weather monitoring fleet. SUVI is a Generalized Cassegrain
telescope that employs multilayer coatings optimized to operate in six
extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2,
171.1, 195.1, 284.2 and 303.8 Å. Over the course of its operational
lifetime SUVI will image and record full disk, EUV spectroheliograms
approximately every few minutes, and telemeter the data to the ground
for digital processing. This data will be useful to scientists and
engineers wanting to better understand the effects of solar produced
EUV radiation with the near-Earth environment. At the focus of the SUVI
telescope is a thin, back-illuminated CCD sensor with 21 μm (2.5 arc
sec) pixels. At the shortest EUV wavelengths, image degradation from
mirror surface scatter effects due to residual optical fabrication
errors dominate the effects of both diffraction and geometrical
aberrations. Discussed herein, we present a novel forward model
that incorporates: (i) application of a new unified surface scatter
theory valid for moderately rough surfaces to predict the bidirectional
reflectance distribution function (BRDF) produced by each mirror (which
uses optical surface metrology to determine the power spectral density,
PSD, that characterizes the "smoothness" of an optical surface);
(ii) use of the BRDF for each mirror at each EUV wavelength, in tandem
with the optical design, to calculate the in-band point spread function
(PSF); (iii) use of the PSF to calculate the fractional ensquared energy
in the focal plane of SUVI; (iv) comparison of BRDF measurements taken
at 93.9 Å with the forward model predictions and (v) final prediction
of the in-band, total system responsivity.
Title: Coronal Dimming And Waves Observed In Flare-Associated CMEs
Authors: Nitta, Nariaki; Aschwanden, M.; Freeland, S.; Lemen, J.;
Wuelser, J.; Zarro, D.
Bibcode: 2010AAS...21640614N
Altcode: 2010BAAS...41..882N
The relationship between solar flares and coronal mass ejections
(CMEs) is still an active area of research. It is studied from
various aspects. Our goal is to understand the importance of magnetic
reconnection in launching CMEs and that of magnetic field environment
of the flaring regions to determine how eruptive flares are. We have
studied the association of solar flares during 2007-2009 with CMEs,
using primarily extreme-ultraviolet (EUV) and inner coronagraphic
images from the Solar Terrestrial Relations Observatory (STEREO). While
energetic CMEs tend to accompany a flare, flares with relatively high
soft X-ray intensity for the extended solar minimum conditions are often
found without an associated CME, even though the underlying photospheric
magnetic field is strong and complex. In contrast, some of the regions
hosting flare-associated CMEs have weak photospheric field, sometimes
not even classified as active regions because of no sunspots. Out of
several signatures in low coronal images previously raised as proxies
for CMEs, large-scale dimming that persists for at least an hour is
found to be a sufficient condition. Waves in EUV images, on the other
hand, may not necessarily signal an appreciable CME that is still
clearly observed beyond, for example, 5 Rsun, unless the concurrent
dimming is substantial. This suggests that waves detected in EUV images
may have more than one origins. We present the result of the survey
and discuss a number of well-observed cases focusing on the properties
of the flares and CMEs with respect to the extents of dimming and wave.
Title: CME-related Phenomena and Solar Flares
Authors: Nitta, Nariaki; Aschwanden, Markus; Freeland, Samuel; Lemen,
James; Wuelser, Jean-Pierre; Zarro, Dominic
Bibcode: 2010cosp...38.1792N
Altcode: 2010cosp.meet.1792N
The relationship between solar flares and coronal mass ejections
(CMEs) is still an active area of research. It is studied from
various aspects. Our goal is to understand the importance of magnetic
reconnection in launching CMEs and that of magnetic field environment
of the flaring regions to determine how eruptive flares are. We have
studied the association of solar flares dur-ing 2007-2009 with CMEs,
using primarily extreme-ultraviolet (EUV) and inner coronagraphic
images from the Solar Terrestrial Relations Observatory (STEREO). While
energetic CMEs tend to accompany a flare, flares with relatively high
soft X-ray intensity for the extended solar minimum conditions are often
found without an associated CME, even though the underlying photospheric
magnetic field is strong and complex. In contrast, some of the regions
hosting flare-associated CMEs have weak photospheric field, sometimes
not even classified as active regions because of no sunspots. Out of
several signatures in low coronal images previously raised as proxies
for CMEs, large-scale dimming that persists for at least an hour is
found to be a sufficient condition. Waves in EUV images, on the other
hand, may not necessarily signal an appreciable CME that is still
clearly observed beyond, for example, 5 Rsun, unless the concur-rent
dimming is substantial. This suggests that waves detected in EUV images
may have more than one origins. We present the result of the survey
and discuss a number of well-observed cases focusing on the properties
of the flares and CMEs with respect to the extents of dimming and wave.
Title: The Interface Region Imaging Spectrograph (IRIS) Small Explorer
Authors: de Pontieu, B.; Title, A. M.; Schryver, C. J.; Lemen, J. R.;
Golub, L.; Kankelborg, C. C.; Carlsson, M.
Bibcode: 2009AGUFMSH33B1499D
Altcode:
The Interface Region Imaging Spectrograph (IRIS) was recently selected
as a small explorer mission by NASA. The primary goal of IRIS is to
understand how the solar atmosphere is energized. The IRIS investigation
combines advanced numerical modeling with a high resolution 20 cm UV
imaging spectrograph that will obtain spectra covering temperatures
from 4,500 to 10 MK in three wavelength ranges (1332-1358 Angstrom,
1390-1406 Angstrom and 2785-2835 Angstrom) and simultaneous images
covering temperatures from 4,500 K to 65,000 K. IRIS will obtain UV
spectra and images with high resolution in space (1/3 arcsec) and time
(1s) focused on the chromosphere and transition region of the Sun, a
complex dynamic interface region between the photosphere and corona. In
this region, all but a few percent of the non-radiative energy leaving
the Sun is converted into heat and radiation. IRIS fills a crucial gap
in our ability to advance Sun-Earth connection studies by tracing the
flow of energy and plasma through this foundation of the corona and
heliosphere. The IRIS investigation is led by PI Alan Title (LMSAL)
with major participation by the Harvard Smithsonian Astrophysical
Observatory, Montana State University, NASA Ames Research Center,
Stanford University and the University of Oslo (Norway). IRIS is
scheduled for launch in late 2012, and will have a nominal two year
mission lifetime.
Title: First Measurements of the Mass of Coronal Mass Ejections from
the EUV Dimming Observed with STEREO EUVI A+B Spacecraft
Authors: Aschwanden, Markus J.; Nitta, Nariaki V.; Wuelser,
Jean-Pierre; Lemen, James R.; Sandman, Anne; Vourlidas, Angelos;
Colaninno, Robin C.
Bibcode: 2009ApJ...706..376A
Altcode:
The masses of coronal mass ejections (CMEs) have traditionally been
determined from white-light coronagraphs (based on Thomson scattering
of electrons), as well as from extreme ultraviolet (EUV) dimming
observed with one spacecraft. Here we develop an improved method
of measuring CME masses based on EUV dimming observed with the dual
STEREO/EUVI spacecraft in multiple temperature filters that includes
three-dimensional volume and density modeling in the dimming region
and background corona. As a test, we investigate eight CME events with
previous mass determinations from STEREO/COR2, of which six cases are
reliably detected with the Extreme Ultraviolet Imager (EUVI) using our
automated multi-wavelength detection code. We find CME masses in the
range of m CME = (2-7) × 1015 g. The agreement
between the two EUVI/A and B spacecraft is mA /mB
= 1.3 ± 0.6 and the consistency with white-light measurements by COR2
is m EUVI/m COR2 = 1.1 ± 0.3. The consistency
between EUVI and COR2 implies no significant mass backflows (or inflows)
at r < 4 R sun and adequate temperature coverage for the
bulk of the CME mass in the range of T ≈ 0.5-3.0 MK. The temporal
evolution of the EUV dimming allows us to also model the evolution
of the CME density ne (t), volume V(t), height-time h(t),
and propagation speed v(t) in terms of an adiabatically expanding
self-similar geometry. We determine e-folding EUV dimming times of
tD = 1.3 ± 1.4 hr. We test the adiabatic expansion model
in terms of the predicted detection delay (Δt ≈ 0.7 hr) between
EUVI and COR2 for the fastest CME event (2008 March 25) and find good
agreement with the observed delay (Δt ≈ 0.8 hr).
Title: SDO-AIA telescope design
Authors: Cheimets, Peter; Caldwell, David C.; Chou, Cathy; Gates,
Richard; Lemen, James; Podgorski, William A.; Wolfson, C. Jacob;
Wuelser, Jean-Pierre
Bibcode: 2009SPIE.7438E..0GC
Altcode: 2009SPIE.7438E..14C
The design of the 4 telescopes that make up the Solar Dynamics
Observatory Atmospheric Imaging Assembly (SDOAIA) is described. This
includes the optical design, optical mounting system, front aperture
filters, and launch protection system. SDO-AIA is a study of taking a
difficult telescope design and making four of them. We describe the
technical challenges associated with the telescope mounting, mirror
mounting, and the front aperture filter design and launch protection.
Title: Tracking The 3-d Structure Of Erupting Filaments With The
Stereo/secchi Euvi
Authors: Wuelser, Jean-Pierre; Aschwanden, M.; Lemen, J.; Nitta, N.;
Sandman, A.
Bibcode: 2009SPD....40.2605W
Altcode:
In May 2007, the STEREO/SECCHI EUVI observed several erupting filaments
that were associated with a CME. The stereoscopic observations in both
He II and Fe IX allow a detailed study of the 3-D geometry and dynamics
of the filaments as they erupt. Deconvolution of the EUVI imagery with
the instrument point spread function enhances image contrast and detail,
and improves the accuracy of the 3-D analysis. The quantitative results
of this analysis may potentially lead to a better understanding of
the early CME process.
Title: The AIA for SDO: Plans for Flight Operations
Authors: Lemen, James; Title, A. M.; Schrijver, K.; Boerner, P.;
Wolfson, C. J.; Nightingale, R.
Bibcode: 2009SPD....40.1703L
Altcode:
The Atmospheric Imaging Array (AIA) has been integrated to the NASA
Solar Dynamics Observatory for over a year and is being prepared for
launch in the fourth quarter of 2009. AIA will provide unprecedented
full-disk images of the solar corona simultaneously covering a
wide range of temperatures. Four normal incidence telescopes with
multilayer-coated optics obtain images with 0.6 arcsec pixels of
EUV-emitting iron lines (covering temperatures between 0.6 and 15 x
106 K), He II 304Å, and C IV in broadband UV. In normal
operations, AIA acquires eight 4k x 4k pixel images every 10s that are
compressed for transmission to the ground, and require approximately
1 TByte of ground storage per day if compressed by a factor of 2. The
instrument calibration has been completed and comprehensive performance
predictions are available (see Wolfson et al). The observing program is
configurable by tables that can be uploaded from the ground. AIA data
is processed to Level 1 in the JSOC pipeline and made available for
export to scientific users. Additional data products, such as movies
of active regions, light curves, and DEM maps, have been developed
for distribution. We present an update of the predicted instrument
performance, discuss the concept of operations, and describe the data
processing for Level 1 data products. Exported FITs data files conform
to SolarSoft standards and the data flow design enables a seamless
connection to the Heliosphysics Event Knowledgebase (see Hurlburt
et al).
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.
Bibcode: 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: Solar Flare and CME Observations with STEREO/EUVI
Authors: Aschwanden, M. J.; Wuelser, J. P.; Nitta, N. V.; Lemen, J. R.
Bibcode: 2009SoPh..256....3A
Altcode:
STEREO/EUVI observed 185 flare events (detected above the GOES class C1
level or at > 25 keV with RHESSI) during the first two years of the
mission (December 2006 - November 2008), while coronal mass ejections
(CMEs) were reported in about a third of these events. We compile a
comprehensive catalog of these EUVI-observed events, containing the peak
fluxes in soft X rays, hard X rays, and EUV, as well as a classification
and statistics of prominent EUV features: 79% show impulsive EUV
emission (coincident with hard X rays), 73% show delayed EUV emission
from postflare loops and arcades, 24% represent occulted flares, 17%
exhibit EUV dimming, 5% show loop oscillations or propagating waves,
and at least 3% show erupting filaments. We analyze an example of each
EUV feature by stereoscopic modeling of its 3D geometry. We find that
EUV emission can be dominated by impulsive emission from a heated,
highly sheared, noneruptive filament, in addition to the more common
impulsive EUV emission from flare ribbons or the delayed postflare
EUV emission that results from cooling of the soft-X-ray-emitting
flare loops. Occulted flares allow us to determine CME-related coronal
dimming uncontaminated from flare-related EUV emission. From modeling
the time evolution of EUV dimming we can accurately quantify the
initial expansion of CMEs and determine their masses. Further, we
find evidence that coronal loop oscillations are excited by the rapid
initial expansion of CMEs. These examples demonstrate that stereoscopic
EUV data provide powerful new methods to model the 3D aspects in the
hydrodynamics of flares and kinematics of CMEs.
Title: First Measurements of the Mass of Coronal Mass Ejections from
the EUV Dimming Observed with Stereo EUVI A and B Spacecraft
Authors: Aschwanden, Markus J.; Nitta, N. V.; Wuelser, J.; Lemen,
J. R.; Sandman, A.; Vourlidas, A.; Colaninno, R. C.
Bibcode: 2009SPD....40.2116A
Altcode:
The masses of Coronal Mass Ejections (CMEs) have traditionally
been determined from white-light coronagraphs, based on the Thomson
scattering of electrons. Here we develop a new method of measuring CME
masses from the EUV dimming seen with EUV imaging telescopes in multiple
temperature filters. As a test we compare the CME masses measured by
STEREO/EUVI A and B with those previously determined by STEREO/COR2, for
a set of 8 CME events of which we detected 7 with EUVI and determined
the masses in 6 cases. We find CME masses in the range of m = (2-7)
x 10(15) g. The agreement between the two EUVI/A and B spacecraft is
mA/mB =1.3 +/- 0.6 and the consistency with white-light measurements
by COR2 is mEUVI/mCOR2 = 1.1 +/- 0.3. The consistency between EUVI
and COR2 implies no significant mass backflows (or inflows) at r <
4 R and adequate temperature coverage for the bulk of the CME mass
in the range of T = 0.5-3.0 MK. The temporal evolution of the EUV
dimming allows us also to model the evolution of the CME density,
volume, height-time, and propagation speed in terms of an adiabatically
expanding self-similar geometry. We test this model with the predicted
detection delay between EUVI and COR2 for the 2008-Mar-25 event.
Title: The CME-Flare Relation Revisited With STEREO Observations
Authors: Nitta, Nariaki; Aschwanden, M.; Freeland, S.; Lemen, J.;
Wuelser, J.; Zarro, D.
Bibcode: 2009SPD....40.2105N
Altcode:
We study the association of solar flares since March 2007 with coronal
mass ejections (CMEs), using images taken by the EUV Imager (EUVI),
COR1 and COR2 coronagraphs on board STEREO. This is done by searching
EUVI data for low coronal signatures attributable to CMEs, such as
dimming, EUV waves and eruptions, following them to COR1 and COR2
fields of view. Base and running difference images (after correcting
for differential rotation) as well as raw images in all the four
filters of EUVI on STEREO A and STEREO B are viewed as movies to find
the CME-related signatures. The COR1 data are particularly helpful for
connecting the EUVI signatures with CMEs observed by COR2. Only 2 (out
of 11) M-class flares and 7 (out of 64) C-class flares are convincingly
associated with CMEs traceable beyond 5 Rs. There are also a handful
of less intense (B-class and A-class) flares associated with CMEs. We
discuss the "calibration" of the low coronal signatures with actual
CMEs, quantitatively re-defining them to be used as reliable proxies
for CMEs. Radio observations are also found to be of use to distinguish
flares associated and not associated with CMEs. Lastly we consider the
CME association of flares in terms of the the following items about the
flaring active regions: their basic properties, their relations with
more global field, and local (spatial or temporal) changes therein. This
study may help us understand the effect of (reconnection-driven)
flare processes on the initiation and subsequent dynamics of CMEs.
Title: Solar XUV Imaging and Non-dispersive Spectroscopy for Solar-C
Enabled by Scientific CMOS APS Arrays
Authors: Stern, Robert A.; Lemen, J. R.; Shing, L.; Janesick, J.;
Tower, J.
Bibcode: 2009SPD....40.3302S
Altcode:
Monolithic CMOS Advanced Pixel Sensor (APS) arrays are showing
great promise as eventual replacements for the current workhorse
of solar physics focal planes, the scientific CCD. CMOS APS devices
have individually addressable pixels, increased radiation tolerance
compared to CCDs, and require lower clock voltages, and thus lower
power. However, commercially available CMOS chips, while suitable
for use with intensifiers or fluorescent coatings, are generally
not optimized for direct detection of EUV and X-ray photons. A high
performance scientific CMOS array designed for these wavelengths will
have significant new capabilities compared to CCDs, including the
ability to read out small regions of the solar disk at high (sub sec)
cadence, count single X-ray photons with Fano-limited energy resolution,
and even operate at room temperature with good noise performance. Such
capabilities will be crucial for future solar X-ray and EUV missions
such as Solar-C. Sarnoff Corporation has developed scientific grade,
monolithic CMOS arrays for X-ray imaging and photon counting. One
prototype device, the "minimal" array, has 8 um pixels, is 15 to 25 um
thick, is fabricated on high-resistivity ( 10 to 20 kohm-cm) Si wafers,
and can be back-illuminated. These characteristics yield high quantum
efficiency and high spatial resolution with minimal charge sharing among
pixels, making it ideal for the detection of keV X-rays. When used with
digital correlated double sampling, the array has demonstrated noise
performance as low as 2 e, allowing single photon counting of X-rays
over a range of temperatures. We report test results for this device
in X-rays, and discuss the implications for future solar space missions.
Title: First Three-Dimensional Reconstructions of Coronal Loops with
the STEREO A+B Spacecraft. III. Instant Stereoscopic Tomography of
Active Regions
Authors: Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki
V.; Lemen, James R.; Sandman, Anne
Bibcode: 2009ApJ...695...12A
Altcode:
Here we develop a novel three-dimensional (3D) reconstruction method
of the coronal plasma of an active region by combining stereoscopic
triangulation of loops with density and temperature modeling of
coronal loops with a filling factor equivalent to tomographic volume
rendering. Because this method requires only a stereoscopic image
pair in multiple temperature filters, which are sampled within ≈1
minute with the recent STEREO/EUVI instrument, this method is about
four orders of magnitude faster than conventional solar rotation-based
tomography. We reconstruct the 3D density and temperature distribution
of active region NOAA 10955 by stereoscopic triangulation of 70 loops,
which are used as a skeleton for a 3D field interpolation of some
7000 loop components, leading to a 3D model that reproduces the
observed fluxes in each stereoscopic image pair with an accuracy
of a few percents (of the average flux) in each pixel. With the
stereoscopic tomography we infer also a differential emission
measure distribution over the entire temperature range of T ≈
104-107, with predictions for the transition
region and hotter corona in soft X-rays. The tomographic 3D model
provides also large statistics of physical parameters. We find that
the extreme-ultraviolet loops with apex temperatures of Tm
lsim 3.0 MK tend to be super-hydrostatic, while hotter loops with
Tm ≈ 4-7 MK are near-hydrostatic. The new 3D reconstruction
model is fully independent of any magnetic field data and is promising
for future tests of theoretical magnetic field models and coronal
heating models.
Title: Coronal Mass Ejections Associated With Impulsive Solar Flares -
Observations With SECCHI EUVI On STEREO
Authors: Nitta, N. V.; Lemen, J. R.; Wuelser, J.; Aschwanden, M. J.;
Freeland, S. L.; Zarro, D. M.
Bibcode: 2008AGUFMSH13B1538N
Altcode:
Long-duration flares, sometimes referred to as Long Decay Events (LDEs),
are known to be unmistakable signatures of coronal mass ejections
(CMEs), and often of fast and large ones. Short-duration or impulsive
flares, on the other hand, do not as frequently accompany CMEs,
even though X-ray plasmoid ejections seen in some of these flares may
suggest that all flares are eruptive irrespective of durations. Some
of these ejections in X-ray or EUV images could be failed ejections,
however, meaning that they do not move into interplanetary medium. A
complementary, and perhaps more reliable signature of a CME in the
low corona may be large-scale dimming typically observed at 1-2
MK. We report on high cadence observations of SECCHI EUVI on STEREO
that show this phenomenon in weak impulsive flares more frequently
than expected. We systematically study flare periods with good data
coverage. In order to avoid false dimming, we use both base and running
difference images after carefully co-aligning the image pairs. Some
of the dimming events were observed in more than one channel and
at two widely separated view angles, letting us better understand
the nature of dimming especially in terms of the associated CME. We
discuss how the properties of dimming are reflected in CME parameters,
how to distinguish the impulsive flares with large- scale effects from
those that are confined, and whether similar events could account for
orphan ICMEs without a clearly associated CME near the Sun.
Title: Tracking the 3-D Structure of an Erupting Filament With the
STEREO/SECCHI EUVI
Authors: Wuelser, J.; Aschwanden, M. J.; Lemen, J. R.; Nitta, N.;
Sandman, A.
Bibcode: 2008AGUFMSH12A..01W
Altcode:
On 2007 May 19, the STEREO/SECCHI EUVI observed an erupting filament
that was associated with a CME. The stereoscopic observations in both He
II and Fe IX allow a detailed study of the 3-D geometry and dynamics of
the filament as it erupts. Deconvolution of the EUVI imagery with the
instrument point spread function enhances image contrast and detail,
and improves the accuracy of the 3-D analysis. The quantitative results
of such an analysis may lead to a better understanding of the early
CME process.
Title: Instant Stereoscopic Tomography of Active Regions with
STEREO/EUVI
Authors: Aschwanden, M. J.; Wuelser, J.; Nitta, N.; Lemen, J.;
Sandman, A.
Bibcode: 2008AGUFMSH13B1555A
Altcode:
We develop a novel 3D reconstruction method of the coronal plasma of
an active region by combining stereoscopic triangulation of loops with
density and temperature modeling of coronal loops with a filling factor
equivalent to tomographic volume rendering. Because this method requires
only a stereoscopic image pair in multiple temperature filters, which
are sampled within ~1 minute with the recent STEREO/EUVI instrument,
this method is about 4 orders of magnitude faster than conventional
solar rotation-based tomography. We reconstruct the 3D density and
temperature distribution of active region NOAA 10955 by stereoscopic
triangulation of 70 loops, which are used as a skeleton for a 3D field
interpolation of some 7000 loop components, leading to a 3D model that
reproduces the observed fluxes in each stereosocpic image pair with an
accuracy of a few percent (of the average flux) in each pixel. With the
stereoscopic tomography we infer also a differential emission measure
(DEM) distribution over the entire temperature range of T~0.01-10 MK,
with predictions for the transition region and hotter corona in soft
X-rays. The tomographic 3D model provides also large statistics of
physical parameters. We find that the EUV loops with apex temperatures
of T = 1- 3 MK tend to be super-hydrostatic, while hotter loops with T =
4-7 MK are near-hydrostatic. The new 3D reconstruction model is fully
independent of any magnetic field data and is promising for future
tests of theoretical magnetic field models and coronal heating models.
Title: A study of GOES SXI entrance filter designs and the potential
for on-orbit degradation
Authors: LaVoy, Rachel McKay; Lemen, James; Benner, Steve; Morrison,
Mons; Datlowe, Dayton; Powell, Forbes; Lopez, Heidi; Smith, Ryan;
Anne, Joshi
Bibcode: 2008SPIE.7011E..2FL
Altcode: 2008SPIE.7011E..69L
The Solar X-ray Imager (SXI) was launched 24 May 2006 on Geostationary
Operational Environmental Satellite (GOES-13). SXI is a grazing
incidence X-ray telescope that focuses an image of the Sun onto a CCD
detector through a set of selectable filters. The X-ray image data are
transmitted at the rate of at least one image per minute, which permits
the reconstruction of near-real-time solar images in the 6-60Å range
(photon energy 2000-200 eV). Thin film filters consisting of aluminum,
titanium, and polyimide are used in the entrance of the telescope
to eliminate visible light. During the first six months of on-orbit
operations the amount of stray light transmitted increased approximately
linearly with time, consistent with the formation of small (less than 50
micron) pinholes. A laboratory investigation was initiated and witness
sample filters were subjected to energetic particles simulating the
on-orbit radiation environment and their quality was assessed using
visible light-leak testing and scanning electron microscope imaging. It
was concluded that galvanic corrosion of aluminum and titanium initiates
pinholes that subsequently grow in dendritic fashion by spalling off
of aluminum to relieve the internal film stress. The test program
also revealed that the geostationary radiation dose level can damage
polyimide and lead to filter failure. Radiation damage may have been
responsible in part for the increased light levels observed in the
GOES-12 SXI and with increased exposure a similar observation could
manifest on GOES-13 SXI. This paper presents the methodology and results
for the entrance filter test program for the GOES SXI telescopes and
presents recommended improvements for future instruments.
Title: First 3D Reconstructions of Coronal Loops with the STEREO
A+B Spacecraft. II. Electron Density and Temperature Measurements
Authors: Aschwanden, Markus J.; Nitta, Nariaki V.; Wuelser,
Jean-Pierre; Lemen, James R.
Bibcode: 2008ApJ...680.1477A
Altcode:
Using the stereoscopically derived three-dimensional (3D) geometry
of 30 loops observed with STEREO EUVI (described in Paper I) we
determine here the electron density profiles ne(s) and
electron temperature profiles Te(s) from a triple-filter
analysis of the stereoscopic images taken in the wavelengths of λ =
171, 195, and 284 Å. The statistical results of our analysis of
seven complete loops are: observed loop widths wobs =
2.6 +/- 0.1 Mm, corresponding to effective loop widths of w = 1.1
+/- 0.3 Mm if corrected for the instrumental point-spread function;
loop flux ratios floop/ftotal = 0.11 +/- 0.04;
mean loop (DEM peak) temperatures Tp = 1.1 +/- 0.2 MK;
DEM temperature Gaussian widths σDEM = 0.35 +/- 0.04 MK;
temperature variations along loops σT/Tp = 0.24
+/- 0.05; (resolution-corrected) loop base densities ne =
(2.2 +/- 0.5) × 109 cm-3 loop lengths of L = 130
+/- 67 Mm; and all quantities are found to agree between STEREO A and
B within a few percent. The temperature profiles T(s) along loops are
found to be nearly constant, within the uncertainties of the background
subtraction. The density profiles ne(s) are consistent with
the gravitational stratification of hydrostatic loops, ne(h)
= nbaseexp (- h/λT) , defined by the temperature
scale heights λT and stereoscopically measured from the
height profiles h(s) . The stereoscopic 3D reconstruction allows us for
the first time to accurately measure the loop length L and to test loop
scaling laws. We find that the observations are not consistent with
equilibrium solutions, but rather display the typical overpressures
of loops that have been previously heated to higher temperatures and
cool down in a nonequilibrium state, similar to earlier EIT and TRACE
measurements.
Title: First Three-Dimensional Reconstructions of Coronal Loops with
the STEREO A and B Spacecraft. I. Geometry
Authors: Aschwanden, Markus J.; Wülser, Jean-Pierre; Nitta, Nariaki
V.; Lemen, James R.
Bibcode: 2008ApJ...679..827A
Altcode:
We present one of the first triangulations and 3D reconstructions
of coronal loops, using the EUVI telescopes of the two STEREO A and
B spacecraft. The first triangulation of coronal loops was performed
in an active region, observed with STEREO A and B on 2007 May 9 with a
spacecraft separation angle of αsep = 7.3°, at a wavelength
of 171 Å. We identify 30 loop structures (7 complete loops and 23
partial segments) and compute their 3D coordinates (x,y,z) (the full
3D coordinates are available as an electronic file). We quantify the
height range, the stereoscopic height measurement errors, the loop
plane inclination angles, and the coplanarity and circularity of the
analyzed loops. The knowledge of the exact 3D geometry of a loop with
respect to the observer's line of sight has important consequences
for determining the correct vertical density scale height (used in
hydrostatic models), the aspect angle of loop cross sections (used in
inferring electron densities from optically thin emission measures),
the absolute flow speeds (used in siphon flow models), the correct
loop length (used in loop scaling laws), and the 3D vectors of the
coronal magnetic field (used in testing theoretical magnetic field
extrapolation models). The hydrodynamic and magnetic modeling of the
analyzed loops will be described in subsequent papers.
Title: Exploring large-scale coronal magnetic field over extended
longitudes by STEREO/EUVI and its effect on solar wind prediction
Authors: Nitta, N. V.; De Rosa, M. L.; Zarro, D. M.; Wuelser, J.;
Aschwanden, M. J.; Lemen, J. R.
Bibcode: 2008AGUSMSH23A..06N
Altcode:
The potential field source surface (PFSS) model forms the basis of
a wide range of heliospheric science and applications, including
prediction of the solar wind speed near Earth. Experience shows that
the model sometimes works quite well, but not always. Possible reasons
for failure include deviation of the interplanetary magnetic field from
the nominal Parker spiral, violation of the assumptions used in the
model such as the discontinuity at the source surface, and the lack of
simultaneous full-surface magnetograms. Here we study the impact of the
lack of simultaneous full-surface magnetograms, using observations of
the corona over an extended longitude range made possible by the EUVI
on board the STEREO mission. In spite of the lack of magnetographs on
STEREO, EUVI data with a growing separation angle between spacecraft
A and B at least allow us to locate major active regions and coronal
holes in the area not seen from Earth. The PFSS extrapolations and their
input synoptic maps are compared with EUVI data to measure how well the
model fits the observations. These comparisons are discussed in terms of
the solar wind speed predicted by the model and observed at L1 by ACE.
Title: Preliminary Pre-flight Calibration of the AIA instrument on SDO
Authors: Boerner, P.; Soufli, R.; Podgorski, W.; Rausch, A.; Shing,
L.; Stern, R.; Lemen, J.; Title, A.; Wolfson, C. J.
Bibcode: 2008AGUSMSP51B..10B
Altcode:
In this poster we present the preliminary pre-flight photometric
calibration of the Atmospheric Imaging Assembly (AIA) aboard the
Solar Dynamics Observatory (SDO). The AIA instrument is 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 in order to study energy input, storage
and release in the dynamic, three- dimensional solar corona. 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
functions. The effective areas are then used to produce temperature
response functions and expected count rates for observations of various
solar features.
Title: Tracing the 3-D coronal structure during CMEs with
STEREO/SECCHI EUVI observations
Authors: Wuelser, J.; Aschwanden, M.; De Rosa, M.; Lee, C.; Lemen,
J.; Nitta, N.; Sandman, A.
Bibcode: 2008AGUSMSH31A..05W
Altcode:
STEREO/SECCHI EUVI observations of solar coronal loops, filaments,
and dimming regions provide unique information on the 3-D topology
of the coronal magnetic field above active regions and its evolution
during coronal mass ejections (CMEs). Active Region #10956 produced
several CMEs during its passage across the solar disk in May 2007,
some of them showing filament eruptions and dimming. The SECCHI/EUVI
instrument on STEREO obtained high cadence observations in multiple
lines simultaneously from both STEREO spacecraft. 3-D reconstructions
of coronal features over the course of a CME show significant changes
of the field topology. Comparisons with the potential field topology
from magnetic field extrapolations show the degree of non-potentiality
of the real field and changes in the vicinity of the CME onset. We
present initial results of this study.
Title: Solar Flares and CMEs observed with STEREO/EUVI
Authors: Aschwanden, M. J.; Wuelser, J.; Nitta, N. V.; Lemen, J. R.
Bibcode: 2008AGUSMSP44A..01A
Altcode:
STEREO/EUVI observed a respectable number of small flares and CMEs
during the first year of its mission. A comprehensive survey between
Dec 2006 and Jan 2008 yields: 10 GOES >M1-class flares, 20 GOES
>C5-class flares, 80 >C1-class flares, 180 flares with >25 keV
hard X-ray emission observed by RHESSI, at least 35 flare events with
associated CME reports by LASCO or STEREO COR-1, and 25 flare events
are occulted by either STEREO A or B. Some flares associated with CMEs
clearly show an EUV dimming in the active region below the launched
CME, for which we determine for the first time the 3D geometry with
the two STEREO A and B spacecraft, allowing us to model the volume,
density, and ejected mass from the corona. Some flares show impulsive
signatures in EUV, simultaneously occurring with hard X-rays pulses,
indicative of the primary heating of the chromospheric plasma. In
larger flares, the bulk of the EUV emission is always substantially
delayed to the soft X-ray emission, as a result of the plasma cooling
from soft X-ray to EUV temperatures, from which we can estimate the
total thermal flare energy using hydrodynamic models.
Title: Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI)
Authors: Howard, R. A.; Moses, J. D.; Vourlidas, A.; Newmark, J. S.;
Socker, D. G.; Plunkett, S. P.; Korendyke, C. M.; Cook, J. W.; Hurley,
A.; Davila, J. M.; Thompson, W. T.; St Cyr, O. C.; Mentzell, E.;
Mehalick, K.; Lemen, J. R.; Wuelser, J. P.; Duncan, D. W.; Tarbell,
T. D.; Wolfson, C. J.; Moore, A.; Harrison, R. A.; Waltham, N. R.;
Lang, J.; Davis, C. J.; Eyles, C. J.; Mapson-Menard, H.; Simnett,
G. M.; Halain, J. P.; Defise, J. M.; Mazy, E.; Rochus, P.; Mercier,
R.; Ravet, M. F.; Delmotte, F.; Auchere, F.; Delaboudiniere, J. P.;
Bothmer, V.; Deutsch, W.; Wang, D.; Rich, N.; Cooper, S.; Stephens,
V.; Maahs, G.; Baugh, R.; McMullin, D.; Carter, T.
Bibcode: 2008SSRv..136...67H
Altcode: 2008SSRv..tmp...64H
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) is a five telescope package, which has been developed for
the Solar Terrestrial Relation Observatory (STEREO) mission by the
Naval Research Laboratory (USA), the Lockheed Solar and Astrophysics
Laboratory (USA), the Goddard Space Flight Center (USA), the University
of Birmingham (UK), the Rutherford Appleton Laboratory (UK), the
Max Planck Institute for Solar System Research (Germany), the Centre
Spatiale de Leige (Belgium), the Institut d’Optique (France) and the
Institut d’Astrophysique Spatiale (France). SECCHI comprises five
telescopes, which together image the solar corona from the solar disk to
beyond 1 AU. These telescopes are: an extreme ultraviolet imager (EUVI:
1 1.7 R⊙), two traditional Lyot coronagraphs (COR1: 1.5 4
R⊙ and COR2: 2.5 15 R⊙) and two new designs
of heliospheric imagers (HI-1: 15 84 R⊙ and HI-2: 66 318
R⊙). All the instruments use 2048×2048 pixel CCD arrays
in a backside-in mode. The EUVI backside surface has been specially
processed for EUV sensitivity, while the others have an anti-reflection
coating applied. A multi-tasking operating system, running on a PowerPC
CPU, receives commands from the spacecraft, controls the instrument
operations, acquires the images and compresses them for downlink
through the main science channel (at compression factors typically
up to 20×) and also through a low bandwidth channel to be used for
space weather forecasting (at compression factors up to 200×). An
image compression factor of about 10× enable the collection of images
at the rate of about one every 2 3 minutes. Identical instruments,
except for different sizes of occulters, are included on the STEREO-A
and STEREO-B spacecraft.
Title: Cross calibration of soft X-ray telescopes between Hinode/XRT
and GOES13/SXI
Authors: Narukage, N.; Sakao, T.; Kano, R.; Shimojo, M.; Cirtain,
J.; Deluca, E.; Nitta, N.; Lemen, J.
Bibcode: 2007AGUFMSH53A1050N
Altcode:
The X-Ray Telescope (XRT) aboard Hinode satellite is a grazing
incidence telescope to observe all the coronal features with a wide
temperature range from less than 1MK to more than 10MK. And the XRT
has 9 X-ray analysis filters which are optimized to observed the
almost whole coronal plasma and to derived the coronal temperature
distribution. Meanwhile, the GOES13 satellite carries a Solar X-ray
Imager (SXI) to monitor the solar X-rays. The SXI is also a grazing
incidence telescope and has 7 X-ray filters. The XRT and SXI are
similar telescopes to observe the dynamic solar corona. On 24 Nov 2006,
the XRT and SXI-team performed the simultaneous observation for the
cross calibration between XRT and SXI. In this study, we analyzed
this data set and checked the actual characteristics of each X-ray
analysis filter.
Title: 3D Geometry of Coronal Loops Measured with STEREO / EUVI
Authors: Aschwanden, M. J.; Wuelser, J.; Nitta, N.; Lemen, J.
Bibcode: 2007AGUFMSH41B..04A
Altcode:
Using images from the STEREO/EUVI A and B spacecraft we developed
an accurate method that performs stereoscopic triangulation and
reconstruction of the 3D geometry of curvi-linear structures in
the solar corona, such as loops, filaments, prominence threads, or
wave features. We test the coalignment of stereoscopic images and
establish an accuracy of better than <0.1 pixels in east-west
direction, <0.3 pixels in north-south direction, and <0.05
degrees in roll angle. We reconstruct the 3D geometry of some 100
coronal loops loops in active regions in May 2007, when the spacecraft
had a separation angle of ~10 degrees. We find that complete loops or
incomplete segments of loops can only be reconstructed up to altitudes
of about one hydrostatic scale height, which is h<50 Mm at a coronal
temperature of T=1 MK. The determination of the 3D geometry of coronal
loops is an important and necessary step to model their hydrodynamic
structure. We show also that this method can be used to determine
quantitatively the eigen-motion, oscillation, twisting, expansion,
acceleration, or other dynamics of coronal loops, erupting filaments,
and MHD wave fronts, in particular in association with flares and CMEs.
Title: Stereoscopic Observations of Low Coronal Ejections With and
Without CMEs
Authors: Nitta, N. V.; Wülser, J.; Aschwanden, M. J.; Lemen, J. R.
Bibcode: 2007AGUFMSH32A0775N
Altcode:
Yohkoh soft X-ray images of solar flares have frequently shown
characteristic ejections during the impulsive phase. They are
thought to be plasmoids that hold important information on magnetic
reconnection. These ejections are intimately associated with coronal
mass ejections (e.g., Nitta & Akiyama 1999; Kim et al. 2005). They
probably represent internal structures of CMEs, i.e., high-temperature
counterparts of filament eruptions. However, their relation with
ejections seen at low temperatures has not been studied systematically,
although TRACE has revealed many beautiful examples. In this work we
study ejections observed by the SECCHI EUVI on STEREO. Some of them are
associated with CMEs, and others are not. Using pairs of EUVI images
from spacecraft A and B, the trajectories of ejecta in individual
channels (with representative temperatures 0.1-2 MK) are reconstructed
in 3D. We discuss these ejections at different temperatures in the
context of CMEs. Specifically, we ask what kinetic properties are
correlated with CMEs and how they are related with CME manifestations
in the low corona such as dimming and waves.
Title: 3-D reconstruction of CME related transient coronal phenomena
observed with the STEREO/SECCHI Extreme Ultraviolet Imager
Authors: Wuelser, J.; Aschwanden, M. J.; Lemen, J. R.; Nitta, N.
Bibcode: 2007AGUFMSH32A0772W
Altcode:
One of the primary objectives of the SECCHI investigation on STEREO
is to study the initiation of CMEs in the low corona, and to better
understand CME related changes of the three-dimensional coronal
structure. The SECCHI Extreme Ultraviolet Imagers (EUVI) have been
observing the solar corona from two significantly different vantage
points since about March 2007. They have since captured several
CMEs, including a few during the SECCHI campaign in May 2007, at an
observatory separation angle of about 7-8 degrees. Observations at
relatively small separation angles allow for easier identification of
features in two views, which is critical for visually aided tie- point
tools, as well as for more automated 3-D reconstruction methods. EUVI
movies taken during the early onset of a CME show a range of transient
phenomena, including coronal ejecta that can be tracked into the
coronagraph fields of view, erupting filaments that trail the coronal
ejecta, displacement of active region loops, coronal dimming, and "EIT"
waves. We present preliminary results of our first 3-D reconstruction
attempts on a selection of such CME related phenomena, with emphasis
on coronal ejecta and active region loop displacements.
Title: Early Evolution of CMEs as Observed by SECCHI EUVI on STEREO
Authors: Lemen, J. R.; Nitta, N. V.; Wülser, J.; Aschwanden, M. J.
Bibcode: 2007AGUFMSH32A0768L
Altcode:
We report on two eruptions associated with small (C1 and B8) flares that
occurred in AR 956 on 2007 May 19 and 20, as observed stereoscopically
by EUVI. The separation of the two spacecraft was approximately 9
degrees. Pairs of images in 171~Å\ and 304~Å\ from two view angles
are used to constrain the trajectories of the ejecta or filaments
that appear to be responsible for the associated CMEs; they were not
homologous. We study how the 3D motions of the ejecta in the low corona
correspond to the CMEs at higher altitudes. We also discuss the possible
relation between the early CME propagation and the coronal magnetic
field topology inferred from EUV loops in EUVI and TRACE 171~Å\ images.
Title: The STEREO SECCHI/EUVI EUV coronal imager
Authors: Wülser, Jean-Pierre; Lemen, James R.; Nitta, Nariaki
Bibcode: 2007SPIE.6689E..05W
Altcode: 2007SPIE.6689E...3W
The SECCHI Extreme Ultraviolet Imager (EUVI) is a pair of EUV telescopes
on the NASA STEREO mission that was successfully launched in October
2006. The two telescopes, one on each STEREO spacecraft observe the
solar corona in three dimensions out to 1.7 solar radii, and with a
pixel resolution of 1.59 arcsec. The focus of the EUVI observations
is the initiation and early evolution of coronal mass ejections
(CMEs). This paper presents a preliminary assessment of the on-orbit
performance of the EUVI.
Title: The Sun To The Earth, A Panoramic View From SECCHI: Overview
Authors: Moses, John Daniel; Newmark, J.; Howard, R. A.; Plunkett,
S.; Socker, D.; Wang, D.; Vourlidas, A.; Halain, J.; Harrison, R. A.;
Eyles, C. J.; Davila, J.; Lemen, J.; Wuelser, J.
Bibcode: 2007AAS...21011904M
Altcode: 2007BAAS...39..244M
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) is the remote sensing component of the STEREO mission
to explore the source, initiation, and propagation through the
heliosphere of Coronal Mass Ejections (CMEs). To achieve this goal,
SECCHI must continuously observe CMEs from two different perspectives
beginning with the pre-event coronal configuration and ending with the
propagation of the event out of the inner heliosphere. Thus, each of
the two STEREO observatories carries a suite of SECCHI telescopes with
5 different fields of view providing an uninterrupted view of coronal
and Heliospheric phenomena from the solar chromosphere to 1 AU. This
is the first panoramic view of the inner heliosphere dedicated to
observing the spatial and temporal scales characteristic of CMEs at
elongation angles from 0 to almost 90 degrees. We present first
results from the SECCHI imaging suite with emphasis on the unprecedented
panoramic views of the heliosphere. We show direct observations of
CMEs and the solar wind from initiation on the Sun throughout the inner
heliosphere to 1 AU. The SECCHI suite performance exceeds that necessary
to achieve the Level 1 STEREO science objectives. Thus, as the STEREO
spacecraft separate to provide views from different directions we can
anticipate breakthrough observations for issues currently unresolved
by plane-of-sky projections through optically thin structures. The most current information on SECCHI can be obtained from the
STEREO mission website at http://stereo.gsfc.nasa.gov and the SECCHI
website at http://secchi.nrl.navy.mil. The NRL participation in the
STEREO mission is supported by NASA under S-13631-Y, and by the Office
of Naval Research.
Title: The SECCHI Experiment on the STEREO Mission
Authors: Howard, R. A.; Moses, J. D.; Vourlidas, A.; Newmark, J. S.;
Socker, D. G.; Wang, D.; Plunkett, S. P.; Baugh, R.; McMullin, D. R.;
Davila, J. M.; Thompson, W. T.; Lemen, J. R.; Wuelser, J.; Harrison,
R. A.; Waltham, N. R.; Davis, C. J.; Eyles, C. J.; Defise, J.; Halain,
J.; Bothmer, V.; Delaboudiniere, J.; Auchere, F.; Mercier, R.; Ravet,
M. F.
Bibcode: 2007AGUSMSH33A..01H
Altcode:
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of an
extreme ultraviolet (EUV) imager, two white light coronagraphs, and
two telescopes that comprise the heliospheric imager. SECCHI will
observe coronal mass ejections (CMEs) from their birth at the sun,
through the corona and into the heliosphere. A complete instrument
suite is being carried on each of the two STEREO spacecraft, which
will provide the first sampling of a CME from two vantage points. The
spacecraft, launched 25 October 2006, are orbiting the Sun, one Ahead
of the Earth and the other Behind, each separating from Earth at about
22 degrees per year. The varying separation means that we will have
different observational capabilities as the spacecraft separate and
therefore differing science goals. The primary science objectives
all are focused on understanding the physics of the CME process
their initiation, 3D morphology, propagation, interaction with the
interplanetary medium and space weather effects. By observing the CME
from multiple viewpoints with UV and coronagraphic telescopes and by
combining these observations with radio and in-situ observations from
the other instruments on STEREO as well as from other satellites and
ground based observatories operating at the same time, answers to some
of the outstanding questions will be obtained. We will show some of
the initial results.
Title: First 3d Triangulation Of Coronal Loops With Stereo/euvi
Authors: Aschwanden, Markus J.; Wuelser, J.; Lemen, J.; Nitta, N.
Bibcode: 2007AAS...210.2810A
Altcode: 2007BAAS...39..137A
The orbits of the two STEREO spacecraft A(head) and B(ehind) move to
progressively larger stereoscopic separation angles a, with a=1.2 deg
on March 1, a=3.0 deg on April 1, a=6.0 deg on May 1, and a=10.5 deg
on June 1. This range of small-angle separation enables the first 3D
triangulation of coronal features. Active region loops at 1 MK have
a scale height of 50 Mm, for which the parallax effect amounts up
to 7 EUVI pixels at a 10 deg separation angle. We present the first
triangulations of active region loops, with the goal to reconstruct
the 3D geometry along entire loop lengths. Such 3D reconstructions
yield the inclination angles of loop planes, which allow us to test
the relation between projected and vertical hydrostatic density scale
heights. Another important application is how the 3D geometry of the
stereoscopically reconstructed loops relates to theoretical (potential,
linear and nonlinear force-free) magnetic field extrapolations. We
attempt also to reconstruct the 3D geometry of filaments and to
track their motion in 3D before eruption and onset of flares and
CMEs. - This work is supported by the NASA STEREO under NRL contract
N00173-02-C-2035.
Title: The Early Development Phase Of An EIT Wave Observed With
GOES-13 SXI
Authors: Biesecker, Douglas A.; Reinard, A.; Hill, S.; Pizzo, V.;
Aulanier, C.; Lemen, J.; Nitta, N.
Bibcode: 2007AAS...210.9119B
Altcode: 2007BAAS...39..207B
On December 5th, the GOES-13 SXI imager observed an EIT wave
initiated at the solar limb. The cadence of full Sun EUV images was
approximately 30 seconds, providing unprecedented detail of an EIT wave
on both small and large scales, simultaneously. The wave was observed to
propagate across almost the full solar disk and to interact with coronal
holes and active regions. The 3-dimensional nature of the EIT wave is
clearly evident in the SXI images. We focus on the earliest phase of
the EIT wave, examining several outstanding questions, including how
and where an EIT wave is initiated and whether the wave begins from a
local or extended source. In particular, we will focus on discerning
the driver of the EIT wave.
Title: First Assessments Of EUVI Performance On STEREO SECCHI
Authors: Lemen, James; Wuelser, J. P.; Nitta, N.; Aschwanden, M.
Bibcode: 2007AAS...210.2801L
Altcode: 2007BAAS...39..135L
The SECCHI investigation on the STEREO mission contains two Extreme
Ultraviolet Imagers (EUVI), one on the ahead spacecraft and one on the
behind spacecraft. EUVI views the solar disk using multilayer-coated
normal-incidence optics that image onto 1.6 arcsec-per-pixel
back-thinned CCD detectors. Four wavelength bandpasses are observed
in series, 17.1 nm (Fe IX), 19.5 nm (Fe XII), 28.4 nm (Fe XV),
and 30.4 nm (He II), covering the chromospheric and coronal plasma
temperatures.Science operations began in January 2007 and both EUVIs
are working very well. The fine pointing system effectively removes
low frequency spacecraft pointing jitter, so the image resolution
quality is very good, approaching 3.5 arcsec. We present early on-orbit
assessments of the performance of both EUVIs and updated predictions
for the temperature dependent instrument response functions, which
are compared to early observations. The lunar transit observed by
the EUVI on the behind spacecraft is used to assess the point spread
function. This work is supported by the NASA STEREO mission under
NRL contract N00173-02-C-2035.
Title: Stereo Observations Of The Solar Corona Using The Secchi
Experiment
Authors: Plunkett, Simon P.; Howard, R. A.; Moses, J. D.; Vourlidas,
A.; Socker, D.; Newmark, J.; Wang, D.; Baugh, R.; Davila, J.;
Thompson, W.; St. Cyr, O. C.; Lemen, J.; Wuelser, J. P.; Harrison,
R. A.; Waltham, N.; Davis, C. J.; Eyles, C. J.; Defise, J. M.; Halain,
J. P.; Bothmer, V.; Delaboudiniere, J. P.; Auchere, F.; Mercier, R.;
Ravet, M. F.
Bibcode: 2007AAS...21011901P
Altcode: 2007BAAS...39..243P
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of an
extreme ultraviolet (EUV) imager, two white light coronagraphs,
and two telescopes that comprise the heliospheric imager. The main
objective of SECCHI is to observe coronal mass ejections (CMEs) from
their birth at the sun, through the corona and into the heliosphere. A
complete instrument suite is being carried on each of the two STEREO
spacecraft, which will provide the first sampling of a CME from two
vantage points as the spacecraft separate from each other at the rate
of about 45 degrees per year. We will show examples of some of the
data and some of the initial stereo results.
Title: The Sun To The Earth, A Panoramic View From SECCHI: CME
Observations Through The Inner Heliosphere
Authors: Newmark, Jeffrey; Moses, J. D.; Howard, R. A.; Plunkett, S.;
Socker, D.; Wang, D.; Vourlidas, A.; Halain, J. P.; Harrison, R. A.;
Eyles, C. J.; Davila, J.; Lemen, J.; Wuelser, J. P.
Bibcode: 2007AAS...21011905N
Altcode: 2007BAAS...39..244N
The STEREO SECCHI telescope suite is returning unprecedented viewsvof
the Sun and inner heliosphere. The SECCHI instruments on each of the two
STEREO spacecraft are observing Coronal Mass Ejections (CMEs) from their
initiation, through the corona, and into interplanetary space beyond the
Earth's orbit. We present a first analysis of a CME throughout the inner
heliosphere. We focus on the propagation characteristics of the CME
and the morphological properties of the CME as viewed from STEREO. This first glimpse of a CME in the heliosphere clearly demonstrates
the anticipated scientific returns that future STEREO observations
(at larger angular separations) of CMEs in interplanetary space will
provide. The most current information can be obtained on the STEREO
mission website at http://stereo.gsfc.nasa.gov and the SECCHI website
at http://secchi.nrl.navy.mil. The NRL participation on SECCHI is
supported by NASA under S-13631-Y, and by the Office of Naval Research.
Title: Low Coronal Manifestations Of Coronal Mass Ejections As
Observed By STEREO EUVI
Authors: Nitta, Nariaki; Wuelser, J.; Lemen, J.; Aschwanden, M.;
Attrill, G.
Bibcode: 2007AAS...210.2805N
Altcode: 2007BAAS...39..136N
Data from SOHO/EIT have tremendously advanced our knowledge about
the initiation of coronal mass ejections (CMEs) as observed by
SOHO/LASCO. The unequivocal EUV manifestations of CMEs include
dimming and waves, typically observed at EIT's 195 A channel. In
this presentation, we report mainly on these two observables in two
similar events as observed on 2007 January 24 and 25 by the Extreme
Ultraviolet Imagers (EUVI), which are part of SECCHI on STEREO. The
source region of the two events was most likely AR 0940, which was
located 20 degrees and 10 degrees behind the east limb at the times of
the events. Images in 171 A and 195 A were taken at a basic cadence of
10 minutes, slightly better than that of the EIT movie sequence. But
what is remarkable is the availability of nearly simultaneous (dt =
11 sec) full-disk images in the two wavelengths. We give detailed
comparisons of the wave propagations and dimming regions as observed
at 171 A and 195 A, and discuss their relations with the white-light
CMEs and their associated flares. This work has been supported by NASA
STEREO mission contract N00173-02-C-2035 through NRL.
Title: Coronal Temperature Properties Measured With the GOES-13 SXI
Authors: Lemen, J. R.; Nitta, N.; Boerner, P. F.; Morrison, M. D.
Bibcode: 2006AGUFMSH23B0357L
Altcode:
The Solar X-ray Imager (SXI) instrument, designed and built by the
Lockheed Martin Solar and Astrophysics Laboratory, was launched on May
24, 2006 on the National Oceanic and Atmospheric Administration (NOAA)
GOES-13 spacecraft. The SXI is operated by NOAA's Space Environment
Center (SEC) in Boulder, CO and its X-ray images of the Sun are used
by space weather forecasters to monitor solar activity. The GOES-13
SXI has better resolution than either the Yohkoh SXT or the GOES-12
SXI and its active internal jitter compensation system is performing
as expected to provide stable viewing even when the GOES-13 spacecraft
is moving. The SXI observes between 6 and 60A with broad-band filter
photometry. Full-disk images covering a 42 arcmin x 42 arcmin field
of view with 5-arcsec pixels are normally returned each minute. The
instrument is capable of viewing solar flares, active regions, and
coronal hole boundaries. We present updated computations of the response
of the SXI to thermal plasmas assuming Chianti V5.2 and present early
results from temperature and differential emission measure analyses
of solar active regions.
Title: The SECCHI Experiment on the STEREO Mission
Authors: Howard, R. A.; Moses, D.; Vourlidas, A.; Newmark, J.; Socker,
D. G.; Plunkett, S.; Wang, D.; Baugh, R.; McMullin, D.; Davila, J.;
St. Cyr, C.; Thompson, W. T.; Lemen, J.; Wuelser, J.; Harrison, R. A.;
Waltham, N. R.; Davis, C.; Eyles, C. J.; Defise, J.; Halain, J.;
Bothmer, V.; Delaboudiniere, J.; Auchere, F.; Mercier, R.; Ravet, M.
Bibcode: 2006AGUFMSM12A..02H
Altcode:
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of an
extreme ultraviolet (EUV) imager, two white light coronagraphs, and
two telescopes that comprise the heliospheric imager. SECCHI will
observe coronal mass ejections (CMEs) from their birth at the sun,
through the corona and into the heliosphere. A complete instrument
suite is being carried on each of the two STEREO spacecraft, which
will provide the first sampling of a CME from two vantage points. The
spacecraft will orbit the Sun, one Ahead of the Earth and the other
Behind, each separating from Earth at about 22 degrees per year. The
varying separation means that we will have different observational
capabilities as the spacecraft separate and therefore differing science
goals. The primary science objectives all are focused on understanding
the physics of the CME process their initiation, 3D morphology,
propagation, interaction with the interplanetary medium and space
weather effects. By observing the CME from multiple viewpoints with UV
and coronagraphic telescopes and by combining these observations with
radio and in-situ observations from the other instruments on STEREO as
well as from other satellites and ground based observatories operating
at the same time, answers to some of the outstanding questions will
be obtained. STEREO follows the very successful SOHO mission. SOHO's
success was primarily due to the highly complementary nature of the
instruments, but it was partly due to the very stable platform. The
L1 orbit enables an extremely stable thermal environment and thus
very stable pointing, as well as uninterrupted solar viewing. The
STEREO will have both of these characteristics, but in addition will
have multi-viewpoint viewing of CMEs, which will greatly enhance the
many discoveries that SOHO data have produced. We have been developing
techniques to interpret the observations from multiple viewpoints and
to perform 3-dimensional deconvolution of the CME observations using
forward modeling and inversion techniques. A continuous downlink of
STEREO data will provide a low-resolution, real- time view from all
of the instruments. The full data are downlinked once a day and will
be available about 24 hours later. We will present some preliminary
results from the instrument, which is expected to be launched in
October/November, 2006
Title: The Atmospheric Imaging Assembly (AIA) for the Solar Dynamics
Observatory
Authors: Smith, Peter L.; Golub, L.; Bookbinder, J. A.; Reid, P. B.;
Deluca, E. E.; Cheimets, P. N.; Podgorski, W. A.; Title, A. M.; Lemen,
J. R.; Boerner, P. F.; SAO, Science, and LMSAL Engineering Teams
Bibcode: 2006SPD....37.0119S
Altcode: 2006BAAS...38Q.218S
The Atmospheric Imaging Assembly (AIA) is being developed for the
Solar Dynamics Observatory (SDO), which is designed to study the
Sun as part of NASA's Living With a Star program. AIA comprises
four normal-incidence telescopes with multilayer-coated optics;
entrance-aperture and focal-plane filters limit the bandpasses. Solar
radiation from the upper solar atmosphere at six wavelengths
corresponding to temperatures between 6.3×105 and
1.5×107 K [Fe IX (171 Å) Fe XII, XXIV (193 Å) Fe XIV
(211 Å) Fe XVI (335 Å) Fe XVIII (94 Å) and Fe XX, XXIII (131 Å)]
will be recorded with high spatial resolution (0.6 arcsec pixels). Other
channels enable observations of the chromosphere (He II 304 Å C IV
1550 Å) and the photosphere. Each telescope contains a 4096 x 4096
CCD camera system and has a 41 arcmin field of view. AIA will return 8
full-solar-disk images every 10 s. The 5-year SDO mission is scheduled
to launch in late 2008. The imaging performance of the telescopes,
which are being provided by the Smithsonian Astrophysical Observatory,
and performance of the multilayer coatings, which are responsible for
the large effective area of AIA, will be discussed in the context of
AIA science goals.
Title: The SECCHI Experiment on the STEREO Mission
Authors: Howard, R.; Moses, D.; Vourlidas, A.; Davila, J.; Lemen, J.;
Harrison, R.; Eyles, C.; Defise, J. -M.; Bothmer, V.; Ravet, M. -F.;
Secchi Team
Bibcode: 2006cosp...36..870H
Altcode: 2006cosp.meet..870H
The Sun Earth Connection Coronal and Heliospheric Investigation SECCHI
on the NASA Solar Terrestrial Relations Observatory STEREO mission
is a suite of remote sensing instruments consisting of an extreme
ultraviolet EUV imager two white light coronagraphs and two telescopes
that comprise the heliospheric imager SECCHI will observe coronal mass
ejections CMEs from their birth at the sun through the corona and into
the heliosphere A complete instrument suite is being carried on each
of the two STEREO spacecraft which will provide the first sampling of
a CME from two vantage points The spacecraft will orbit the Sun one
Ahead of the Earth and the other Behind each separating from Earth at
about 22 degrees per year The varying separation means that we will
have different observational capabilities as the spacecraft separate
and therefore differing science goals The primary science objectives
all are focused on understanding the physics of the CME process -
their initiation 3D morphology propagation interaction with the
interplanetary medium and space weather effects By observing the CME
from multiple viewpoints with UV and coronagraphic telescopes and by
combining these observations with radio and in-situ observations from
the other instruments on STEREO as well as from other satellites and
ground based observatories operating at the same time answers to some
of the outstanding questions will be obtained STEREO follows the very
successful SOHO mission SOHO s success was primarily due to the highly
complementary nature of the instruments but it was
Title: The Atmospheric Imaging Assembly (AIA) investigation for the
NASA SDO mission
Authors: Lemen, J. R.; Title, A. M.; Golub, L.
Bibcode: 2005AGUSMSH43A..17L
Altcode:
The Atmospheric Imaging Assembly (AIA) is one of three science
investigations selected for the NASA Solar Dynamics Observatory, the
first mission in NASA's Living With a Star program that is designed to
study the Sun's influence on the Earth and the nearby environment. AIA
consists of four normal incidence telescopes with multilayer coated
optics. It records solar EUV emission with high spatial resolution
(0.6 arcsec pixels) at six wavelengths from iron ions in the solar
atmosphere at temperatures between 6.3 × 105 K and 15 × 106 K:
Fe IX (171Å); Fe XII,XXIV (193Å); Fe XIV (211 Å); Fe XVI (335Å);
Fe XVIII (94Å); and Fe XX,XXIII (131Å). Other wavelength channels
enable observations of the chromosphere (He II, 304Å; C IV) and the
photosphere. Each telescope contains a 16-Mpixel CCD/camera system and
has a 41 arcmin field of view. AIA will return 8 full solar-disk images
every 10 s, producing 2.2 Tbytes/day of data. The AIA investigation is
led by PI Alan Title (LMSAL) with major participation by the Harvard
Smithsonian Astrophysical Observatory, Montana State University, and
Stanford University. The SDO mission is scheduled for launch in 2008
and will have a nominal five year mission lifetime, but will carry
resources for at least ten years of mission operations.
Title: The Ability of Extreme Ultraviolet and Soft X-ray Imaging
Telescopes to Constrain Coronal Differential Emission Measure
Authors: Boerner, P.; Lemen, J.; Nitta, N.; Martinez-Galarce, D.
Bibcode: 2005AGUSMSP13B..05B
Altcode:
Using the Chianti database, we construct temperature response functions
for the extreme ultraviolet and soft x-ray imaging channels on a variety
of current and future solar observatories. Simulated observations in
these channels are then inverted to recover the coronal differential
emission measure. We investigate the effect of statistical error,
and systematic uncertainties in the atomic physics and instrument
calibration used to calculate the instrument temperature response
functions, on the accuracy of the DEM recovery. By selecting different
combinations of channels, we can characterize the ability of different
instrument architectures to constrain the DEM, and identify an optimal
combination of bandpasses for accurate DEM recovery.
Title: STEREO/SECCHI Simulations of CMEs and Flares using TRACE Images
Authors: Aschwanden, M. J.; Lemen, J.; Nitta, N.; Metcalf, T.; Wuelser,
J.; Alexander, D.
Bibcode: 2004AGUFMSH22A..02A
Altcode:
We simulate 3D models of EUV images of flare and CME events, using
TRACE EUV movies. TRACE movies show 2D images in projection along a
particular line-of-sight. We simulate 3D models of erupting filaments,
flare loops, and postflare loops using: (1) a ``finger printing''
technique to trace linear structures in 2D images; (2) geometric 3D
models based on force-free fields and curvature radius maximization
of flare loop and flux rope structures; (3) conservation of velocity
and acceleration parameters; (4) multi-temperature plasma filling
according to hydrodyamic scaling laws; and (5) 2D projections from
secondary line-of-sights that correspond to viewpoints of the secondary
STEREO spacecraft. From such simulations we envision to illustrat
3D time-dependent models, what would be observed at the two STEREO
spacecraft positions as well as from a near-Earth spacecraft such as
SoHO. These simulations are used to test STEREO analysis software and
to investigate what physical parameters and geometric 3D reconstructions
can be retrieved from STEREO/SECCHI data.
Title: Comparison of X-ray Images from Yohkoh/SXT and GOES-M/SXI
Authors: Nitta, N. V.; Lemen, J. R.; Hill, S. M.
Bibcode: 2004AAS...204.5601N
Altcode: 2004BAAS...36..761N
The Yohkoh satellite completed its mission on 14 December 2001. The Soft
X-ray Telescope (SXT) on board Yohkoh observed the dynamic solar corona
nearly continuously for more than 10 years, leading to many important
discoveries in solar physics. Now similar soft X-ray images of the Sun
are taken by the Soft X-ray Imager (SXI) on the GOES-M satellite. The
primary purpose of SXI is to improve space weather forecasting, but its
data are useful for science as well. In order to understand solar cycle
effect on the solar output, stationary or transient, it is important
to understand how SXI and SXT images compare with each other. We
study the images taken during the last few months of Yohkoh's life,
when SXI took more than 100000 images as a test run. We report on how
these images are photometrically compared and how different instrument
characteristics affect the capability to observe transient phenomena.
Title: The solar x-ray imager for GOES
Authors: Lemen, James R.; Duncan, Dexter W.; Edwards, Christopher
G.; Friedlaender, Frank M.; Jurcevich, Bruce K.; Morrison, Mons D.;
Springer, Larry A.; Stern, Robert A.; Wuelser, Jean-Pierre; Bruner,
Marilyn E.; Catura, Richard C.
Bibcode: 2004SPIE.5171...65L
Altcode:
The next generation of the National Oceanic and Atmospheric
Administration's (NOAA) Geo-Stationary Operational Environmental
Satellite (GOES) spacecraft will include an X-ray telescope that
will monitor the Sun for predicting solar energetic events and for
providing information about the large-scale solar magnetic field. The
Solar X-ray Imager that will be flown on the GOES N spacecraft in late
2004 makes use of a super-polished grazing incidence mirror, a highly
efficient back-thinned CCD, and thin metalized filters to observe
the million-degree corona with 10-arcsec resolution (5 arcsec pixel
size). Full-sun images will be acquired with SXI on a one-minute cadence
at wavelengths between approximately 10 and 60 Å. SXI data will be used
to forecast 'space weather', i.e., the effects of charged particles
that are produced at the Sun as they interact at the earth. Major
contributors to space weather include: variations in the Sun's solar
wind, solar flares, and solar mass ejections. Effects of space weather
include: radiation damage and particle events in high-inclination orbit
spacecraft, disruption of various kinds of communications equipment,
degradation of navigational tools such as GPS, potential health hazards
during space walks, and power blackouts. Data acquired by the SXI
will additionally provide invaluable context information for upcoming
solar missions such as STEREO and SDO. The Lockheed Martin Solar and
Astrophysics Laboratory has prepared two flight model SXIs that are
being readied for flight on the GOES N and GOES O or P spacecraft.
Title: X-ray calibration of the GOES-N/O solar X-ray imagers
Authors: Catura, Paul R.; Gantner, Brennan L.; Jurcevich, Bruce K.;
Kam, Claude K.; Lemen, James R.; Morrison, Mons D.; Shing, Lawrence;
Catura, Richard C.
Bibcode: 2004SPIE.5171...89C
Altcode:
The X-ray calibration of the GOES Solar X-ray Imagers (SXI) was
accomplished at the component level and at the instrument level. The
CCD and thin film filters were characterized in the facilities at the
Lockheed Martin Solar and Astrophysics Laboratory. The grazing incidence
telescope mirrors and the completed instruments were calibrated at
the X-ray Calibration Facility (XRCF) at NASA"s Marshall Space Flight
Center. The XRCF consists of an X-ray source at one end of a 518 m long
evacuated tube and a large vacuum chamber at the opposite end. The
X-ray source has a variety of interchangeable anodes and filters to
provide filtered characteristic K- and L-shell line emission in the
range from 0.109 to 8.6 keV. The absolute Photometric calibration of
the SXI telescopes is very important for analysis and interpretation
of their data, and to monitor the long-term solar variations at X-ray
wavelengths. This paper describes the results of these calibrations.
Title: A system to reduce jitter for the GOES-N/O/P solar X-ray imager
Authors: Gantner, Brennan L.; Lemen, James R.; Edwards, Christopher
G.; Catura, Paul R.; Hancock, Henry P.; Morrison, Mons D.
Bibcode: 2004SPIE.5171..101G
Altcode:
A jitter compensation system is incorporated in the Solar X-ray Imager
(SXI) that will be mounted to the solar array wing of the GOES N
spacecraft, the next in the series of NOAA weather satellites. The
SXI obtains images in a back-thinned CCD with 5 arcsec pixels. The
SXI incorporates a pointing aspect sensor manufactured by the Adcole
Corporation that is used in a semi-closed loop system with the SXI
flight computer to shift the detected image during an exposure along
the readout columns of the CCD in order to compensate for jitter in
one dimension. Simulations of the predicted motions caused by the GOES
spacecraft and self-induced by the SXI filter wheels indicate that the
jitter as experienced by the SXI instrument will be primarily along one
axis, parallel to the east-west direction, with amplitudes in the tens
of arcseconds and with dominant frequencies less than approximately 10
Hz. The SXI CCD columns are aligned along this direction in order to
make possible on-chip compensation. The SXI motion compensation system
has been evaluated with realistic models for the expected spacecraft
jitter and assuming a performance algorithm for the SXI instrument. Our
analysis indicates that the X-ray spatial imaging performance will be
improved when the jitter compensation system is used. We discuss the
design and analysis predictions.
Title: Characterization of the flight CCD detectors for the GOES N
and O solar x-ray imagers
Authors: Stern, Robert A.; Shing, Lawrence; Catura, Paul R.; Morrison,
Mons D.; Duncan, Dexter W.; Lemen, James R.; Eaton, Tim; Pool, Peter
J.; Steward, Roy; Walton, Dave M.; Smith, Alan
Bibcode: 2004SPIE.5171...77S
Altcode:
A new Solar X-ray Imager (SXI) using back-illuminated, anti-blooming CCD
technology will become part of the instrument complement on NOAA's GOES
(Geosynchronous Orbiting Environmental Satellite) N and O spacecraft,
with probable launch dates beginning in the 2004-2005 time frame. SXI N
and O were developed under a NASA contract by the Solar and Astrophysics
Laboratory at the Lockheed Martin Advanced Technology Center, and
are currently being integrated into their respective spacecrafts by
Boeing Space Systems. SXI N and O will each provide full disk images
of the Sun from 0.2 to 1.2 keV (10-60 Å) through the combination of
a grazing incidence telescope, bandpass filters, and an X-ray imaging
CCD. The custom designed, back-illuminated CCDs were fabricated and
initially tested by Marconi Technologies (formerly EEV Ltd, now e2v
technologies), screened in visible light by the Mullard Space Science
Laboratory, and fully characterized in both visible light and X-rays at
LMSAL. By minimizing the field-free region within the CCD, the spatial
resolution at low X-ray energies was significantly improved. The
SXI CCDs also exhibit only very modest response changes as a result
of solar X-ray exposure, based upon extended life tests. The flight
CCDs meet or surpass all specifications for quantum efficiency (QE),
spatial uniformity, defects, charge transfer efficiency, QE stability
in vacuum, read noise, linearity, full well and dark current. A QE
model based on earlier work with ion-implanted, laser-annealed CCDs
provides a consistent picture of the CCD response from soft X-rays
through far UV wavelengths.
Title: EUVI: the STEREO-SECCHI extreme ultraviolet imager
Authors: Wuelser, Jean-Pierre; Lemen, James R.; Tarbell, Theodore
D.; Wolfson, C. J.; Cannon, Joseph C.; Carpenter, Brock A.; Duncan,
Dexter W.; Gradwohl, Glenn S.; Meyer, Syndie B.; Moore, Augustus S.;
Navarro, Rosemarie L.; Pearson, J. D.; Rossi, George R.; Springer,
Larry A.; Howard, Russell A.; Moses, John D.; Newmark, Jeffrey S.;
Delaboudiniere, Jean-Pierre; Artzner, Guy E.; Auchere, Frederic;
Bougnet, Marie; Bouyries, Philippe; Bridou, Francoise; Clotaire,
Jean-Yves; Colas, Gerard; Delmotte, Franck; Jerome, Arnaud; Lamare,
Michel; Mercier, Raymond; Mullot, Michel; Ravet, Marie-Francoise;
Song, Xueyan; Bothmer, Volker; Deutsch, Werner
Bibcode: 2004SPIE.5171..111W
Altcode:
The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI instrument
suite currently being developed for the NASA STEREO mission. Identical
EUVI telescopes on the two STEREO spacecraft will study the structure
and evolution of the solar corona in three dimensions, and specifically
focus on the initiation and early evolution of coronal mass ejections
(CMEs). The EUVI telescope is being developed at the Lockheed Martin
Solar and Astrophysics Lab. The SECCHI investigation is led by the
Naval Research Lab. The EUVI"s 2048 x 2048 pixel detectors have a
field of view out to 1.7 solar radii, and observe in four spectral
channels that span the 0.1 to 20 MK temperature range. In addition to
its view from two vantage points, the EUVI will provide a substantial
improvement in image resolution and image cadence over its predecessor
SOHO-EIT, while complying with the more restricted mass, power, and
volume allocations on the STEREO mission.
Title: The Secchi Experiment on the Stereo Mission
Authors: Howard, R.; Moses, D.; Socker, D.; Cook, J.; Davila, J.;
Lemen, J.; Harrison, R.; Eyles, C.; Waltham, N.; Defise, J. -M.
Bibcode: 2004cosp...35.3893H
Altcode: 2004cosp.meet.3893H
The Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO)
mission is a suite of remote sensing instruments consisting of two
white light coronagraphs, an extreme ultraviolet (EUV) imager, and
a heliospheric imager. SECCHI will observe coronal mass ejections
(CMEs) from their birth at the sun, through the corona and into the
heliosphere. A complete instrument suite is being carried on each
of the two STEREO spacecraft, which will provide the first sampling
of a CME from two vantage points. The spacecraft will orbit the Sun,
one ahead of the Earth and the other behind, separating from Earth at
about 22 degrees per year. The varying separation means that we will
have different observational capabilities as the spacecraft separate
and therefore differing science goals. The primary science objectives
all are focused on understanding the physics of the CME process -
their initiation, 3D morphology, propagation, interaction with the
interplanetary medium and space weather effects. By observing the CME
from multiple viewpoints with UV and coronagraphic telescopes and by
combining these observations with radio and in-situ observations from
the other instruments on STEREO as well as from other satellites and
ground based observatories operating at the same time, answers to some
of the outstanding questions will be obtained.
Title: Cryogenic 3-D Detectors for Solar Physics Using Position
Sensitive Transition-Edge Sensors
Authors: Stern, R. A.; Martinez-Galarce, D.; Metcalf, T.; Lemen, J.;
Cabrera, B.; Brink, P.; Leman, S.; Deiker, S.; Irwin, K.; Alexander, D.
Bibcode: 2003AAS...203.1805S
Altcode: 2003BAAS...35Q1237S
Space and ground-based astronomy is currently undergoing a revolution
in detector technology with the advent of cryogenic sensors operating in
the sub-Kelvin temperature range. These detectors provide non-dispersive
energy resolution at optical through gamma ray energies (e.g, E/Δ E ∼
1500 at 6 keV), high time resolution (msec or better), and can be made
into imaging arrays through SQUID multiplexing of individual pixels or
employing macropixels with position sensing capability. The application
of such ``3-D'' detector technology to solar physics will lead to
significant advances in our understanding of magnetic reconnection
phenomena in the Sun, including flares and microflares, X-ray jets,
and active region dynamics. An Explorer-class solar mission based upon
these detectors is a distinct possibility within the next 5-10 years. In
this poster, we will describe some of the recent advances in cryogenic
detector technology with particular applicability to solar physics,
and future technical developments required to make such a mission a
reality. This work was supported in part by the Lockheed Martin
Independent Research Program.
Title: Soft X-ray observation of a large-scale coronal wave and
its exciter
Authors: Hudson, Hugh S.; Khan, Josef I.; Lemen, James R.; Nitta,
Nariaki V.; Uchida, Yutaka
Bibcode: 2003SoPh..212..121H
Altcode:
Recent extreme ultraviolet (EUV) observations from SOHO have shown
the common occurrence of flare-associated global coronal waves
strongly correlated with metric type II bursts, and in some cases
with chromospheric Moreton waves. Until now, however, few direct soft
X-ray detections of related global coronal waves have been reported. We
have studied Yohkoh Soft X-ray Telescope (SXT) imaging observations to
understand this apparent discrepancy, and describe the problems in this
paper. We have found good X-ray evidence for a large-scale coronal wave
associated with a major flare on 6 May 1998. The earliest direct trace
of the wave motion on 6 May consisted of an expanding volume within
20 Mm (projected) of the flare-core loops, as established by loop
motions and a dimming signature. Wavefront analyses of the soft X-ray
observations point to this region as the source of the wave, which began
at the time of an early hard X-ray spike in the impulsive phase of the
flare. The emission can be seen out to a large radial distance (some
220 Mm from the flare core) by SXT, and a similar structure at a still
greater distance by EIT (the Extreme Ultraviolet Imaging Telescope) on
SOHO. The radio dynamic spectra confirm that an associated disturbance
started at a relatively high density, consistent with the X-ray
observations, prior to the metric type II burst emission onset. The
wavefront tilted away from the vertical as expected from refraction if
the Alfvén speed increases with height in the corona. From the X-ray
observations we estimate that the electron temperature in the wave,
at a distance of 120 Mm from the flare core, was on the order of 2-4
MK, consistent with a Mach number in the range 1.1-1.3.
Title: Large-Scale Solar Coronal Structures in Soft X-Rays and Their
Relationship to the Magnetic Flux
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.;
Scherrer, P. H.; Slater, G. L.
Bibcode: 2002ApJ...571L.181B
Altcode:
We have investigated the relationship between magnetic activity
and coronal structures using soft X-ray data from the Yohkoh soft
X-ray telescope and magnetic field data from the Kitt Peak Solar
Observatory for the period of 1991-2001 and EUV data from the Solar
and Heliospheric Observatory EUV Imaging Telescope for 1996-2001. The
data are reduced to Carrington synoptic maps, which reveal two types of
migrating structures of coronal activity at low and high latitudes in
the time-latitudinal distribution. The low-latitude coronal structures,
migrating equatorward, correspond to photospheric sunspot activity,
and the high-latitude structures migrating toward the poles reflect
polar activity of the Sun. We present the following new results:1. The
migrating high-latitude coronal magnetic structures are revealed in the
soft X-ray data as complete bright giant loops connecting the magnetic
field of the following part of active regions with the polar field. They
appear during the rising phase and maximum of the solar cycle and show
quasi-periodic impulsive variations with a 1-1.5 yr period.2. The soft
X-ray intensity of these loops has a strong power-law correlation with
the photospheric magnetic flux. The power-law index, which on average
is close to 2, shows variations with the solar cycle: it is higher
for the period of the declining phase and minimum of solar activity
than for the rising phase and maximum.
Title: Large-scale coronal structures in EUV and soft X-rays in
solar cycle 23
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.;
Lemen, J. R.; Slater, G. L.
Bibcode: 2002ESASP.508..367B
Altcode: 2002soho...11..367B
We have analyzed the EIT/SOHO data in four EUV lines (171 Å, 195 Å,
284 Å and 304 Å) and soft X-ray YOHKOH data in two filters (AlMg and
Al) in the form of coronal synoptic maps for the period 1996 - 2001
yrs. Two types of the bright structures have been detected in EUV in
the axisymmetrically averaged synoptic maps. The structures of the first
type migrate equatorward as the solar cycle progresses. They are related
to complexes of sunspot activity and display the "butterfly"-type
distribution. The structures of the second type migrate polarward
and are associated with footpoints of giant coronal loops, which
connect the polar regions and the following parts of the active
complexes. These structures of coronal activity are also pronounced in
the soft X-ray maps. However, the whole structure of the giant polar
loops is visible in X-rays, and reveals connections to the low-latitude
coronal structures. The relationship between the soft X-rays emission
and the photospheric magnetic flux obtained from SOHO/MDI and Kitt
Peak Solar Observatory has been investigated. It has been found that
the relationship depends on the phase of the solar cycle. We discuss
the role of the magnetic flux in the formation and evolution of the
stable coronal structures during the rising phase of cycle 23.
Title: Coronal Patterns of Activity from Yohkoh and SOHO/EIT Data
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.;
Lemen, J. R.; Slater, G. L.
Bibcode: 2002mwoc.conf..329B
Altcode:
We have studied the evolution of large-scale coronal structures using
soft X-ray data from YOHKOH and EUV data from SOHO/EIT during the
rising phase of the current solar cycle 23, and compared with the
evolution of the photospheric magnetic field. During this period the
distribution of the coronal structures generally reflects the evolution
of the magnetic fields. However, the data from EIT and YOHKOH reveal
large-scale magnetic connections in the corona which probably play
significant role in the solar cycle. In particular, we have found that
coronal structures such as high-latitude giant loops may be important
for the topological evolution of magnetic structures during the solar
cycle and for polar magnetic field reversals. We discuss possible
mechanisms of the polar magnetic field reversals and their relations
to the observed coronal structures.
Title: The Yohkoh Public Outreach Project
Authors: Larson, M. B.; Slater, T.; McKenzie, D.; Acton, L.; Alexander,
D.; Lemen, J.; Freeland, S.; Metcalf, T.
Bibcode: 2002mwoc.conf..117L
Altcode:
The NASA funded Yohkoh Public Outreach Project (YPOP) began in 1995
with the goal of providing public access to high quality Yohkoh
SXT data via the World Wide Web. The project utilizes the intrinsic
excitement of the SXT data, and in particular the SXT movies, to develop
science learning tools and classroom activities. The WWW site at URL:
http://www.lmsal.com/YPOP/ uses a movie theater theme to highlight
available Yohkoh movies in a format that is entertaining and inviting
to non-scientists and well received by scientists. We will discuss
the wide range of people YPOP has reached over the past six years,
as well as lessons learned during the development of the project.
Title: The Yohkoh Public Outreach Project: A Space Science Resource
for Formal and Informal Education
Authors: Lemen, J. R.; Alexander, D.; Metcalf, T. R.; Freeland, S. L.;
Acton, L. W.; Larson, M.; McKenzie, D.; Slater, T.
Bibcode: 2001AGUFMED12A0160L
Altcode:
The Yohkoh Public Outreach Project (YPOP) is a NASA-funded web site
maintained by scientists and educators at Lockheed Martin Solar and
Astrophysics Lab. and Montana State University. YPOP includes a range
of activities for youngsters, parents, teachers and anyone interested
in learning more about the Sun. YPOP utilizes a number of approaches
to the dissemination of solar data which incorporates elements of both
formaleducation, via a number of lesson plans and classroom activities,
and informal education, via access to the latest solar images, a
solar tour, and updated movies. This combination has proved extremely
effective in providing quality access to scientific data for a broad
audience with a wide range of interests. The Yohkoh Public Outreach
Project can be found at http://www.LMSAL.com/YPOP.
Title: Solar Coronal Structures in Extreme Ultraviolet and Soft
X-rays and Their Relation to Magnetic Flux
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.;
Scherrer, P. H.; Slater, G. L.
Bibcode: 2001AGUFMSH11C0720B
Altcode:
The large-scale coronal structures are ultimately related to internal
magnetic fields and thus provide important information about the solar
dynamo. We have investigated the relationship between magnetic activity
and coronal structures using EUV data from SOHO/EIT and X-ray data
from Yohkoh/SXT, and magnetic field data from Kitt Peak and Wilcox
Solar Observatories for the period 1996-2000 years. We discuss the
non-uniform distribution of coronal heating and its connection with
long-lived complexes of solar activity during the current cycle. EUV
images reveal two sets of migrating structures of coronal activity
in the time-latitudinal distribution of the EUV intensity in 171A,
195A, 284A and 304A EIT wavelength channels. The low-latitude coronal
structures, migrating equatorward, correspond to photospheric sunspot
activity, and the high-latitude structures migrating towards the poles
reflect polar activity of the sun. The polar branches are cooler then
the equatorial branches. This is reflected in the time-latitudinal
distribution of the soft X-rays in two filters (Al and AlMg). We
discuss the physical properties and nature of these structures of
coronal activity and their role in the solar cycle.
Title: Onset of the Magnetic Explosion in Solar Flares and Coronal
Mass Ejections
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Hudson, Hugh S.;
Lemen, James R.
Bibcode: 2001ApJ...552..833M
Altcode:
We present observations of the magnetic field configuration and its
transformation in six solar eruptive events that show good agreement
with the standard bipolar model for eruptive flares. The observations
are X-ray images from the Yohkoh soft X-ray telescope (SXT) and
magnetograms from Kitt Peak National Solar Observatory, interpreted
together with the 1-8 Å X-ray flux observed by GOES. The observations
yield the following interpretation. (1) Each event is a magnetic
explosion that occurs in an initially closed single bipole in which the
core field is sheared and twisted in the shape of a sigmoid, having an
oppositely curved elbow on each end. The arms of the opposite elbows are
sheared past each other so that they overlap and are crossed low above
the neutral line in the middle of the bipole. The elbows and arms seen
in the SXT images are illuminated strands of the sigmoidal core field,
which is a continuum of sheared/twisted field that fills these strands
as well as the space between and around them. (2) Although four of
the explosions are ejective (appearing to blow open the bipole) and
two are confined (appearing to be arrested within the closed bipole),
all six begin the same way. In the SXT images, the explosion begins
with brightening and expansion of the two elbows together with the
appearance of short bright sheared loops low over the neutral line
under the crossed arms and, rising up from the crossed arms, long
strands connecting the far ends of the elbows. (3) All six events are
single-bipole events in that during the onset and early development
of the explosion they show no evidence for reconnection between the
exploding bipole and any surrounding magnetic fields. We conclude that
in each of our events the magnetic explosion was unleashed by runaway
tether-cutting via implosive/explosive reconnection in the middle of the
sigmoid, as in the standard model. The similarity of the onsets of the
two confined explosions to the onsets of the four ejective explosions
and their agreement with the model indicate that runaway reconnection
inside a sheared core field can begin whether or not a separate system
of overlying fields, or the structure of the bipole itself, allows the
explosion to be ejective. Because this internal reconnection apparently
begins at the very start of the sigmoid eruption and grows in step
with the explosion, we infer that this reconnection is essential for
the onset and growth of the magnetic explosion in eruptive flares and
coronal mass ejections.
Title: A Comparison of the Image Properties of Soft X-ray Imagers
Authors: Pizzo, V. J.; Hill, S.; Lemen, J.; Davis, J. M.
Bibcode: 2001AGUSM..SP61A07P
Altcode:
The imminent launch of the prototype NOAA Solar X-ray Imager (SXI)
aboard GOES-12 ushers in a new era in which nearly continuous,
high-cadence soft X-ray solar imagery will become available to the
space weather and basic science communities. Because of substantial
technical differences in the process by which images are formed (e.g.,
photographic film, CCDs, MCPs, mirror coatings) among past, present,
and future X-ray telescopes, this is a good juncture to place the
forthcoming GOES-12 SXI imagery in context with existing Skylab and
Yohkoh/SXT observations, along with the anticipated image properties
of the subsequent LMSAL-built SXIs. The comparison includes spatial
resolution/PSF, relative wavelength response, absolute sensitivity,
dynamic range, image cadence, filters, and temperature estimates
based upon filter ratios. All these factors influence the physical
interpretation of what is seen in any set of images. In particular, we
consider how the cadence, continuity, and softer X-ray response of the
MSFC-built prototype on GOES-12 and its LMSAL follow-ons should enhance
observations of coronal activity related to geospace disturbances.
Title: Performance of the engineering model x-ray mirror of the
Solar X-ray Imager (SXI) for future GOES missions
Authors: Catura, Richard C.; Bruner, Marilyn E.; Catura, Paul R.;
Jurcevich, Bruce K.; Kam, C.; Lemen, James R.; Meyer, Syndie B.;
Morrison, Mons D.; Magida, Matthew B.; Reid, Paul B.; Harvey, James
E.; Thompson, Patrick L.
Bibcode: 2000SPIE.4138...33C
Altcode:
We have measured the x-ray imaging performance of a grazing incidence
telescope mirror, the HT #17, employing a hyperboloid-hyperboloid
design. This design provides improved wide-field imaging compared to
an optimally defocused Wolter Type I mirror. This improvement will
be advantageous for future Geostationary Operational Environmental
Satellite (GOES) missions that will provide full disk images of the sun
with the Solar X-ray Imager (SXI). The x-ray measurements were made in
the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center
and the results are presented here.
Title: The STEREO-SECCHI Extreme Ultraviolet Imager
Authors: Wülser, J. -P.; Lemen, J. R.; Tarbell, T. D.; Wolfson,
C. J.; Howard, R. A.; Moses, J. D.; Delaboudinière, J. -P.
Bibcode: 2000SPD....31.0294W
Altcode:
The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI
investigation selected for flight on the STEREO mission. The twin EUVI
telescopes on the two STEREO spacecraft will study the structure and
evolution of the solar corona in three dimensions, and specifically
focus on the initiation and early evolution of coronal mass ejections
(CMEs). The EUVI's 2048 x 2048 pixel detectors will have a full sun
field of view, and will observe in four spectral channels that cover
the 0.1 to 2 MK temperature range. The EUVI's major advance is its
view from two vantage points in space. It will allow it to investigate
the structure of CMEs in three dimensions, while the EUVI's high image
cadence capability will allow it to resolve the CME's initiation and
early evolution.
Title: The STEREO-SECCHI extreme ultraviolet imager.
Authors: Wülser, J. -P.; Lemen, J. R.; Tarbell, T. D.; Wolfson,
C. J.; Howard, R. A.; Moses, J. D.; Delaboudinière, J. -P.
Bibcode: 2000BAAS...32..827W
Altcode:
No abstract at ADS
Title: Temperature Structure of the Quiet Corona: An SXT-SUMER
Discrepancy
Authors: Wolfson, Richard; Roald, Colin B.; Sturrock, P. A.; Lemen,
J.; Shirts, P.
Bibcode: 2000ApJ...529..570W
Altcode:
The Soft X-ray Telescope (SXT) on Yohkoh and the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) are both capable of providing
measures of temperature in the solar corona. A recent SUMER-based
study of a quiet coronal region suggests an isothermal plasma in the
range from 1.03 to 1.5 solar radii. In this work, we have analyzed
part of the same region using SXT data and find a temperature that
increases with height. This is consistent with earlier SXT-based
coronal temperature studies but obviously disagrees with SUMER results
for the same region. The SUMER study reveals a lower scale height for
emission in the Fe X, Fe XI, and Fe XII lines than for the lines of
lighter elements, an effect that may be attributable to gravitational
stratification. Because iron lines contribute heavily to the X-ray
emission detected with SXT, it is reasonable to suspect that the
more rapid decrease in iron abundance at higher altitudes might be
responsible for the SXT-SUMER discrepancy. We have therefore explored
the effect on SXT temperatures of altering individually the abundances
of all 14 elements used in standard SXT temperature calculations. We
find that only iron and carbon have any significant effect but that
this effect is not nearly sufficient to account for the SXT-SUMER
discrepancy.
Title: The transition region and coronal explorer
Authors: Handy, B. N.; Acton, L. W.; Kankelborg, C. C.; Wolfson, C. J.;
Akin, D. J.; Bruner, M. E.; Caravalho, R.; Catura, R. C.; Chevalier,
R.; Duncan, D. W.; Edwards, C. G.; Feinstein, C. N.; Freeland, S. L.;
Friedlaender, F. M.; Hoffmann, C. H.; Hurlburt, N. E.; Jurcevich,
B. K.; Katz, N. L.; Kelly, G. A.; Lemen, J. R.; Levay, M.; Lindgren,
R. W.; Mathur, D. P.; Meyer, S. B.; Morrison, S. J.; Morrison, M. D.;
Nightingale, R. W.; Pope, T. P.; Rehse, R. A.; Schrijver, C. J.;
Shine, R. A.; Shing, L.; Strong, K. T.; Tarbell, T. D.; Title, A. M.;
Torgerson, D. D.; Golub, L.; Bookbinder, J. A.; Caldwell, D.; Cheimets,
P. N.; Davis, W. N.; Deluca, E. E.; McMullen, R. A.; Warren, H. P.;
Amato, D.; Fisher, R.; Maldonado, H.; Parkinson, C.
Bibcode: 1999SoPh..187..229H
Altcode:
The Transition Region and Coronal Explorer (TRACE) satellite, launched
2 April 1998, is a NASA Small Explorer (SMEX) that images the solar
photosphere, transition region and corona with unprecedented spatial
resolution and temporal continuity. To provide continuous coverage
of solar phenomena, TRACE is located in a sun-synchronous polar
orbit. The ∼700 Mbytes of data which are collected daily are made
available for unrestricted use within a few days of observation. The
instrument features a 30-cm Cassegrain telescope with a field of view
of 8.5×.5 arc min and a spatial resolution of 1 arc sec (0.5 arc sec
pixels). TRACE contains multilayer optics and a lumogen-coated CCD
detector to record three EUV wavelengths and several UV wavelengths. It
observes plasmas at selected temperatures from 6000 K to 10 MK with
a typical temporal resolution of less than 1 min.
Title: Making YOHKOH SXT Images Available to the Public: The YOHKOH
Public Outreach Project
Authors: Larson, M. B.; McKenzie, D.; Slater, T.; Acton, L.; Alexander,
D.; Freeland, S.; Lemen, J.; Metcalf, T.
Bibcode: 1999AAS...194.7024L
Altcode: 1999BAAS...31..941L
The NASA funded Yohkoh Public Outreach Project (YPOP) provides public
access to high quality Yohkoh SXT data via the World Wide Web. The
products of this effort are available to the scientific research
community, K-12 schools, and informal education centers including
planetaria, museums, and libraries. The project utilizes the intrinsic
excitement of the SXT data, and in particular the SXT movies, to develop
science learning tools and classroom activities. The WWW site at URL:
http://solar.physics.montana.edu/YPOP/ uses a movie theater theme to
highlight available Yohkoh movies in a format that is entertaining and
inviting to non-scientists. The site features informational tours of
the Sun as a star, the solar magnetic field, the internal structure
and the Sun's general features. The on-line Solar Classroom has proven
very popular, showcasing hand-on activities about image filtering,
the solar cycle, satellite orbits, image processing, construction of a
model Yohkoh satellite, solar rotation, measuring sunspots and building
a portable sundial. The YPOP Guestbook has been helpful in evaluating
the usefulness of the site with over 300 detailed comments to date.
Title: Soft X-ray Observation of a Flare-Associated Coronal Wave
Authors: Hudson, H. S.; Lemen, J. R.; Thompson, B.; Uchida, Y.
Bibcode: 1999AAS...194.2205H
Altcode: 1999BAAS...31..860H
Recent EUV observations from the EIT instrument of SOHO have shown
the common occurrence of flare-associated global coronal waves, allies
of Type II burst exciters and chromospheric Moreton waves. Until now,
however, no direct soft X-ray detections have been reported. We have
studied Yohkoh SXT observations to understand this apparent discrepancy
between EUV and soft X-ray observations,and have now found good X-ray
evidence for a large-scale coronal wave launched during an X-class
flare of May 6, 1998. During the impulsive phase of this flare, a rapid
( ~ 10(3) km s(-1) ) bright front appeared to the north of the flare
core; later a more normal loop-like ejection emerged to the west at a
lower projected speed. We identify the rapid front with enhanced X-ray
emission from a global coronal wave. Wave signatures also appear in
SOHO EIT images and in the meter-wave dynamic spectrum from Hiraiso,
and SOHO LASCO detected a coronal mass ejection. NASA supported this
work under contract NAS 8-37334.
Title: Utilizing solar sails for solar physics
Authors: Strong, K. T.; Alexander, D.; McInnes, C. R.; Lemen, J. R.
Bibcode: 1999AAS...194.6508S
Altcode: 1999BAAS...31..928S
Recently, there has been much interest in the use of solar sail
technology for advanced space mission concepts. We present here some
trajectories and orbits for a number of potential solar missions. These
missions utilize the power of solar sails in a number of different ways,
providing unique capabilities in the study of the Sun. The first mission
concept is a solar polar mission using a "parking orbit" above one of
the solar poles, the second is a multi-spacecraft mission designed
to map out the three-dimensional solar atmosphere using identical
spacecraft at different heliographic latitudes, and the third is a
STEREO slowdown mission designed to extend the lifetime of the STEREO
mission using small sails attached to the STEREO payloads to slow
down the rate of drift ahead and behind the Earth. Here, the first two
payloads are assumed to be inert masses with possible instrument and
spacecraft packages to be defined by the specific goals of any mission.
Title: Coronal Abundances
Authors: Fludra, A.; Saba, J. L. R.; Henoux, J. -C.; Murphy, R. J.;
Reames, D. V.; Lemen, J. R.; Strong, K. T.; Sylwester, J.; Widing,
K. G.
Bibcode: 1999mfs..conf...89F
Altcode:
Flare X-Ray Measurements from BCS Calcium Abundance Fe/H and Fe/Ca
Abundance Relative Abundances of Ar. Ca. and Fe in Flares Factors
Affecting Abundance Determinations from X-Ray Spectra FCS Abundances
FCS Active-Region Abundances Abundance Variability in Active Regions
Impact of Resonance Scattering Assessment of FCS Active-Region Abundance
Results FCS Flare Abundance Studies Coronal CI/S and Ar/S Measurements
Dem Studies of Flare Abuncances Determination of Solar Abundances
by Solar Flare γ-Ray Spectrometry γ-Ray Spectral Analysis γ-Ray
Results Solar Energetic Particles Major Proton Events CIR Events from
Coronal Holes Impulsive Flare Events Theory of Abundance Fractionation
Gravitational Settling Pressure Gradient and Stationary Diffusion
Ion-Neutral Separation Due to Currents Ion-Neutral Separation Due to
Electromagnetic Forces Discussion Summary
Title: Observations of Coronal Structures Above an Active Region by
EIT and Implications for Coronal Energy Deposition
Authors: Neupert, W. M.; Newmark, J.; Delaboudinière, J. -P.;
Thompson, B. J.; Catura, R. C.; Moses, J. D.; Gurman, J. B.;
Portier-Fozzani, F.; Gabriel, A. H.; Artzner, G.; Clette, F.; Cugnon,
P.; Maucherat, A. J.; Defise, J. M.; Jamar, C.; Rochus, P.; Dere,
K. P.; Howard, R. A.; Michels, D. J.; Freeland, S.; Lemen, J. R.;
Stern, R. A.
Bibcode: 1998SoPh..183..305N
Altcode:
Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO
have been used to evaluate temperature and density as a function of
position in two largescale features in the corona observed in the
temperature range of 1.0-2.0 MK. Such observations permit estimates
of longitudinal temperature gradients (if present) in the corona and,
consequently, estimates of thermal conduction and radiative losses
as a function of position in the features. We examine two relatively
cool features as recorded in EIT's Fe ix/x (171 Å) and Fe xii (195 Å)
bands in a decaying active region. The first is a long-lived loop-like
feature with one leg, ending in the active region, much more prominent
than one or more distant footpoints assumed to be rooted in regions of
weakly enhanced field. The other is a near-radial feature, observed
at the West limb, which may be either the base of a very high loop
or the base of a helmet streamer. We evaluate energy requirements to
support a steady-state energy balance in these features and find in
both instances that downward thermal conductive losses (at heights
above the transition region) are inadequate to support local radiative
losses, which are the predominant loss mechanism. The requirement that a
coronal energy deposition rate proportional to the square of the ambient
electron density (or pressure) is present in these cool coronal features
provides an additional constraint on coronal heating mechanisms.
Title: Super-X: a soft x-ray telescope for Solar-B
Authors: Acton, Loren W.; Bookbinder, Jay A.; Bruner, Marilyn E.;
Golub, Leon; Lemen, James R.
Bibcode: 1998SPIE.3442..140A
Altcode:
This paper describes the conceptual design of a soft x-ray
telescope, super-x, which we will propose for the Japan/US/UK Solar-B
mission. Super-X will break new ground in both angular resolution
and solar coronal temperature discrimination. The telescope design
is based upon the successful transition region and coronal explorer
instrument. It features four XUV spectral channels spanning the 0.3 to
20 MK temperature range with an angular resolution of approximately 0.27
seconds of arc. We will describe considerations affecting spectral line
selection and some details of the characteristics of the instrument.
Title: X-ray coronal changes during Halo CMEs
Authors: Hudson, H. S.; Lemen, J. R.; St. Cyr, O. C.; Sterling, A. C.;
Webb, D. F.
Bibcode: 1998GeoRL..25.2481H
Altcode:
Using the Yohkoh soft X-ray images, we examine the coronal structures
associated with “halo” coronal mass ejections (CMEs). These may
correspond to events near solar disk center. Starting with a list
of eleven confirmed halo CMEs over the time range from December 1996
through May 1997, we find seven with surface features identifiable in
soft X-rays, with GOES classifications ranging from A1 to M1.3. These
have a characteristic pattern of sigmoid → arcade development. In each
of these events, the pre-flare structure disrupted during the flare,
leaving the appearance of compact transient coronal holes. The four
remaining events had weak or indistinguishable signatures in the X-ray
images. For the events for which we could see well-defined coronal
changes, we confirm our previous result that the estimated mass loss
inferred from the soft X-ray dimming is a small fraction of typical
CME masses [Sterling & Hudson 1997].
Title: Detailed Evidence for Flare-to-Flare Variations of the Coronal
Calcium Abundance
Authors: Sylwester, J.; Lemen, J. R.; Bentley, R. D.; Fludra, A.;
Zolcinski, M. -C.
Bibcode: 1998ApJ...501..397S
Altcode:
The analysis of X-ray solar flare spectra obtained by the Bent
Crystal Spectrometer on board the Solar Maximum Mission satellite is
presented. The ratio of the Ca XIX resonance line intensity to the
nearby continuum is used to measure the calcium abundance relative to
hydrogen (ACa). A description of the spectroscopic method
of determining the absolute calcium abundance is given. Possible
instrumental and solar effects that might influence the abundance
estimates are evaluated. Over 5000 spectra from more than 100 flares are
analyzed. We find a flare-to-flare variation for ACa that is
not correlated with flare size, Hα importance, or with several other
flare characteristics. For flares observed from two active regions, the
observed value of ACa increases as a function of time. The
average for all flares is <ACa> = (5.77 +/- 1.41) ×
10-6. A discussion of investigated correlations of derived
ACa values with several flare characteristics is presented.
Title: Spatial Structure of Solar Coronal Magnetic Loops Revealed
by Transient Microwave Brightenings
Authors: Zhang, J.; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
Bibcode: 1998SoPh..180..285Z
Altcode:
We present the measurement of magnetic field gradient in magnetic
loops in the solar corona, based on the multi-wavelength Very Large
Array observations of two transient microwave brightenings (TMBs)
in the solar active region 7135. The events were observed at 2 cm
(spatial resolution ∼ 2=) and 3.6 cm (spatial resolution ∼ 3=)
with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray
data (spatial resolution ∼ 2.5=) were available from the Soft X-ray
Telescope on board the Yohkoh satellite. The three-dimensional structure
of simple magnetic loops, where the transient brightenings occurred,
were traced out by these observations. The 2-cm and 3.6-cm sources
were very compact, located near the footpoint of the magnetic loops
seen in the X-ray images. For the two events reported in this paper,
the projected angular separation between the centroids of 2 and 3.6-cm
sources is about 2.3= and 3.1=, respectively. We interpret that the 2
and 3.6-cm sources come from thermal gyro-resonance emission. The 2-cm
emission is at the 3rd harmonic originating from the gyro-resonance
layer where the magnetic field is 1800 G. The 3.6-cm emission is at
the 2nd harmonic, originating from the gyro-resonance layer with a
magnetic field of 1500 G. The estimated magnetic field gradient near
the footpoint of the magnetic loop is about 0.09 G km=1 and
0.12 G km=1 for the two events. These values are smaller
than those observed in the photosphere and chromosphere by at least
a factor of 2.
Title: Radio and X-ray Investigations of Erupting Prominences (Review)
Authors: Gopalswamy, N.; Hanoka, Y.; Lemen, J. R.
Bibcode: 1998ASPC..150..358G
Altcode: 1998IAUCo.167..358G; 1998npsp.conf..358G
No abstract at ADS
Title: Multiwavelength EUVE/ASCA/RXTE Observations of Algol and the
[Fe/H] Abundance
Authors: Stern, Robert A.; Lemen, James R.; Antunes, Sandy; Drake,
Stephen A.; Nagase, Fumiaki; Schmitt, Jurgen H. M. M.; Singh,
Kulinderpal; White, Nicholas E.
Bibcode: 1998ASPC..154.1166S
Altcode: 1998csss...10.1166S
EUVE, ASCA, and XTE observed the eclipsing binary Algol (beta Per)
from 1-7 Feb 96. The coordinated observation covered ~2 binary orbits
of the system, with a net exposure of ~160 ksec for EUVE, 40 ksec
for ASCA (in 4 pointings), and 90 ksec for XTE (in 45 pointings). We
discuss results of modeling the combined EUVE, ASCA, and XTE data
using continuous differential emission measure distributions, and
provide constraints on the Fe abundance in the Algol system.
Title: Studies of Coronal Temperature
Authors: Acton, L. W.; Lemen, J. R.
Bibcode: 1998ASSL..229...15A
Altcode: 1998opaf.conf...15A
No abstract at ADS
Title: Iron and calcium abundances in solar flares from the
multitemperature analysis of X-ray spectra (abstract)
Authors: Fludra, A.; Bentley, R. D.; Culhane, J. L.; Lemen, J. R.;
Sylwester, J.
Bibcode: 1998PAICz..88...91F
Altcode:
No abstract at ADS
Title: Fast Time Structure during Transient Microwave Brightenings:
Evidence for Nonthermal Processes
Authors: Gopalswamy, N.; Zhang, J.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
Bibcode: 1997ApJ...491L.115G
Altcode: 1997astro.ph.10200G
Transient microwave brightenings (TMBs) are small-scale energy releases
from the periphery of sunspot umbrae with a flux density 2 orders
of magnitude smaller than that from a typical flare. Gopalswamy et
al. first reported the detection of the TMBs, and it was pointed out
that the radio emission implied a region of very high magnetic field
so that the emission mechanism has to be gyroresonance or nonthermal
gyrosynchrotron, but not free-free emission. It was not possible to
decide between gyroresonance and gyrosynchrotron processes because
of the low time resolution (30 s) used in the data analysis. We have
since performed a detailed analysis of the Very Large Array data with
full time resolution (3.3 s) at two wavelengths (2 and 3.6 cm), and we
can now adequately address the question of the emission mechanism of
the TMBs. We find that nonthermal processes indeed take place during
the TMBs. We present evidence for nonthermal emission in the form of
temporal and spatial structure of the TMBs. The fast time structure
cannot be explained by a thermodynamic cooling time and therefore
requires a nonthermal process. Using the physical parameters obtained
from X-ray and radio observations, we determine the magnetic field
parameters of the loop and estimate the energy released during the
TMBs. The impulsive components of TMBs imply an energy release rate
of ~1.3×1022 ergs s-1, so the thermal energy
content of the TMBs could be less than ~1024 ergs.
Title: EIT Observations of the Extreme Ultraviolet Sun
Authors: Moses, D.; Clette, F.; Delaboudinière, J. -P.; Artzner,
G. E.; Bougnet, M.; Brunaud, J.; Carabetian, C.; Gabriel, A. H.;
Hochedez, J. F.; Millier, F.; Song, X. Y.; Au, B.; Dere, K. P.; Howard,
R. A.; Kreplin, R.; Michels, D. J.; Defise, J. M.; Jamar, C.; Rochus,
P.; Chauvineau, J. P.; Marioge, J. P.; Catura, R. C.; Lemen, J. R.;
Shing, L.; Stern, R. A.; Gurman, J. B.; Neupert, W. M.; Newmark,
J.; Thompson, B.; Maucherat, A.; Portier-Fozzani, F.; Berghmans, D.;
Cugnon, P.; Van Dessel, E. L.; Gabryl, J. R.
Bibcode: 1997SoPh..175..571M
Altcode:
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO
spacecraft has been operational since 2 January 1996. EIT observes
the Sun over a 45 x 45 arc min field of view in four emission line
groups: Feix, x, Fexii, Fexv, and Heii. A post-launch determination
of the instrument flatfield, the instrument scattering function, and
the instrument aging were necessary for the reduction and analysis
of the data. The observed structures and their evolution in each
of the four EUV bandpasses are characteristic of the peak emission
temperature of the line(s) chosen for that bandpass. Reports on the
initial results of a variety of analysis projects demonstrate the range
of investigations now underway: EIT provides new observations of the
corona in the temperature range of 1 to 2 MK. Temperature studies of
the large-scale coronal features extend previous coronagraph work
with low-noise temperature maps. Temperatures of radial, extended,
plume-like structures in both the polar coronal hole and in a low
latitude decaying active region were found to be cooler than the
surrounding material. Active region loops were investigated in detail
and found to be isothermal for the low loops but hottest at the loop
tops for the large loops.
Title: EIT and LASCO Observations of the Initiation of a Coronal
Mass Ejection
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Kreplin, R. W.; Michels, D. J.; Moses, J. D.;
Moulton, N. E.; Socker, D. G.; St. Cyr, O. C.; Delaboudinière, J. P.;
Artzner, G. E.; Brunaud, J.; Gabriel, A. H.; Hochedez, J. F.; Millier,
F.; Song, X. Y.; Chauvineau, J. P.; Marioge, J. P.; Defise, J. M.;
Jamar, C.; Rochus, P.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.;
Neupert, W.; Clette, F.; Cugnon, P.; Van Dessel, E. L.; Lamy, P. L.;
Llebaria, A.; Schwenn, R.; Simnett, G. M.
Bibcode: 1997SoPh..175..601D
Altcode:
We present the first observations of the initiation of a coronal mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
experiment on SOHO show that the CME began in a small volume and was
initially associated with slow motions of prominence material and a
small brightening at one end of the prominence. Shortly afterward,
the prominence was accelerated to about 100 km s-1 and
was preceded by a bright loop-like structure, which surrounded an
emission void, that traveled out into the corona at a velocity of
200-400 km s-1. These three components, the prominence,
the dark void, and the bright loops are typical of CMEs when seen at
distance in the corona and here are shown to be present at the earliest
stages of the CME. The event was later observed to traverse the LASCO
coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest
is the fact that this large-scale event, spanning as much as 70 deg in
latitude, originated in a volume with dimensions of roughly 35" (2.5
x 104 km). Further, a disturbance that propagated across
the disk and a chain of activity near the limb may also be associated
with this event as well as a considerable degree of activity near the
west limb.
Title: Association of Extreme-Ultraviolet Imaging Telescope (EIT)
Polar Plumes with Mixed-Polarity Magnetic Network
Authors: Wang, Y. -M.; Sheeley, N. R.; Dere, K. P.; Duffin, R. T.;
Howard, R. A.; Michels, D. J.; Moses, J. D.; Harvey, J. W.; Branston,
D. D.; Delaboudinière, J. -P.; Artzner, G. E.; Hochedez, J. F.;
Defise, J. M.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.; Neupert,
W. M.; Newmark, J.; Thompson, B.; Maucherat, A.; Clette, F.
Bibcode: 1997ApJ...484L..75W
Altcode:
SOHO EIT spectroheliograms showing the polar coronal holes during the
present sunspot minimum are compared with National Solar Observatory
(Kitt Peak) magnetograms taken in Fe I λ8688 and Ca II λ8542. The
chromospheric λ8542 magnetograms, obtained on a routine, near-daily
basis since 1996 June, reveal the Sun's strong polar fields with
remarkable clarity. We find that the Fe IX λ171 polar plumes occur
where minority-polarity flux is in contact with flux of the dominant
polarity inside each polar hole. Moreover, the locations of ``plume
haze'' coincide approximately with the patterns of brightened He
II λ304 network within the coronal hole. The observations appear
to be consistent with mechanisms of plume formation involving
magnetic reconnection between unipolar flux concentrations and nearby
bipoles. The fact that minority-polarity fields constitute only a small
fraction of the total magnetic flux within the polar holes suggests
that plumes are not the main source of the high-speed polar wind.
Title: Multi-wavelength Observations of Transient Microwave
Brightenings in a Solar Active Region
Authors: Zhang, Jie; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
Bibcode: 1997SPD....28.0163Z
Altcode: 1997BAAS...29..891Z
We present multi-wavelength Very Large Array observations of two
transient microwave brightenings (TMBs) in the solar active region
7135. The events were observed at 2 cm (spatial resolution ~ 2'') and
3.6 cm (spatial resolution ~ 3'') with a temporal resolution of 3.3 s
in a time-sharing mode. Soft X-ray data (about 5'' spatial resolution)
were available from the Soft X-ray Telescope on board the YOHKOH
satellite. The 2 cm and 3.6 cm emission sources were very compact,
located near the footpoint of the magnetic loops seen in the X-ray
images. The TMBs traced out the three dimensional structure of the
magnetic loops where the transient brightenings occurred. For the
two events reported in this paper, the projected angular separation
between the centroids of 2 and 3.6 cm source is about 2.3'' and 3.1'',
respectively. We interpret the spatial and temporal distributions
as implying that the 2 and 3.6 cm flux is mainly due to thermal
gyro-resonance emmision. The 2 cm emission seems to be at the 3rd
gyro-harmonic coming from the 1800 G gyro-resonance layer. The 3.6 cm
emission seems to be at both the 2nd and 3rd harmonics, originating
from gyro-resonance layers with a magnetic field of 1500 G and 1000
G, respectively. However, the two gyro-resonance layers for 3.6 cm
emission are not resolved with the current spatial resolution. The
estimated magnetic field gradient near the footpoint of the magnetic
loop is about 0.17 G km(-1) and 0.22 G km(-1) for the two events.
Title: A Reconnection Model for Observed Transient Loop Brightenings
Authors: Longcope, D. W.; Fisher, G. H.; Metcalf, T. R.; Lemen, J.;
Zarro, D. M.; Kucera, T.; Griffiths, N.; Siegmund, O. H. W.
Bibcode: 1997SPD....28.0128L
Altcode: 1997BAAS...29..884L
Several recent theoretical models explain coronal activity in terms of
magnetic reconnection at ``separator'' field lines. These are field
lines lying at the boundary between domains of coronal flux with
distinct photospheric origin. Transient brightenings of X-ray loops
(Shimizu et al. 1992) may be the manifestations of such localized events
(Longcope 1996). Their relative simplicity, compared to large events
such as flares, makes them ideal objects for exploring reconnection
models. Toward this end, a campaign of coordinated observations of
loop brightenings in a small active region was undertaken on June 6,
1996. High time cadence observations were made of the transition region
and low corona in EUV (SUMER and CDS) and of the high corona in soft
X-rays (Yohkoh), while high cadence, high resolution vector magnetograms
were obtained with the Imaging Vector Magnetograph at the University of
Hawaii. This series of magnetograms is used to calculate the magnetic
topology of the coronal field, and to locate the separator field
lines. The high time cadence of the magnetograms allows the estimation
of reconnection rates: the rate at which flux must be exchanged between
domains. The "minimum current corona" model (Longcope 1996) is then
used to provide quantitative predictions of energy released on each
separator due to this reconnection. The observational results of the
campaign are described in a companion paper by Zarro et al at this
meeting; we discuss our predictions in the context of their results.
Title: Movies of flares observed by YOHKOH/HXT
Authors: Lemen, J. R.; Alexander, D.; Metcalf, T. R.; Freeland, S. L.;
Nitta, N.
Bibcode: 1997SPD....28.0169L
Altcode: 1997BAAS...29..892L
The Yohkoh Hard X-ray Telescope (HXT) has revealed new information
about solar flares by providing high spatial resolution (5 arcsec)
images in four energy bands covering 14 to 99 keV. The comparison of
images obtained in hard X-rays with those obtained with the Yohkoh Soft
X-ray Telescope (SXT) has led to important interpretations of flare
heating mechanisms (e.g., Masuda et al, 1994, Nature, 374, 495). The
HXT images are formed by reconstructing data obtained from 64 detectors
located behind a bi-grid modulation pattern. Reconstruction algorithms
using Maximum Entropy and PIXON methods have been successfully applied
to the HXT data (Alexander and Metcalf, 1997, ApJ, submitted). At the
recent HXT Coordinated Data Analysis Workshop held in January 1997, new
calibration data for the response of the grids were incorporated and an
error in the application of the reconstruction algorithms was identified
and corrected (see Kosugi et al 1997 in these proceedings). As a result,
it is now possible to reconstruct the HXT images semi-automatically to
produce quick-look movies. We are in the process of generating movies
for all flares obtained with the HXT using an MEM reconstruction. The
automated procedure selects time intervals on the basis of the count
rate statistics. We present a selection of reconstructed images and
movies from this on-going project. We expect that the ability to view
easily time sequences from many flares observed with the HXT will
provide new insights for flare studies.
Title: Boundary Conditions of a Meridional Coronal Hole
Authors: Handy, B. N.; Lemen, J. R.; Moses, D.
Bibcode: 1997SPD....28.0131H
Altcode: 1997BAAS...29..885H
Observational evidence from Skylab suggests that some coronal holes
rotate almost rigidly, in contrast to the underlying photospheric
plasma which rotates differentially. Wang & Sheeley (1996 Science
271, 417 and references therein) suggest these rotational properties
are consistent with a nearly current-free coronal field undergoing
continual field-line reconnection at the coronal hole boundaries. If
true, this effect may be observable in currently available solar
observations. A rigidly rotating coronal hole anchored in an equatorial
bipolar magnetic region would in effect "sweep out" a region at the
mid-lattitudes, reconnecting with the magnetic terrain on the leading
edge boundary and then succumbing back into the background field on
the trailing edge. It is not clear how this phenomena takes place,
although Kahler and Moses (1990 ApJ 362,728), based on evidence from
Skylab, argue that the evolution of the large scale boundary is largely
controlled by the evolution of small-scale bright points. We present a
simple model of the evolution of the coronal hole boundary. Assuming
a meridional coronal hole extending from the polar hole to an active
region near the equatorial plane, we evaluate the rate of magnetic
reconnection at the leading and trailing edges based on a nominal
level of magnetic field, plasma density, temperature and chromospheric
differential rotation rate. We compare this study to observations from
EIT and MDI on \it{SoHO} and SXT on \it{Yohkoh}.
Title: Using the WWW to Make YOHKOH SXT Images Available to the
Public: The YOHKOH Public Outreach Project
Authors: Larson, M.; McKenzie, D.; Slater, T.; Acton, L.; Alexander,
D.; Freeland, S.; Lemen, J.; Metcalf, T.
Bibcode: 1997SPD....28.0231L
Altcode: 1997BAAS...29..898L
The Yohkoh Public Outreach Project (YPOP) is funded by NASA as one of
the Information Infrastructure Technology and Applications Cooperative
Agreement Teams to create public access to high quality Yohkoh SXT data
via the World Wide Web. These products are being made available to the
scientific research community, K-12 schools, and informal education
centers including planetaria, museums, and libraries. The project aims
to utilize the intrinsic excitement of the SXT data, and in particular
the SXT movies, to develop science learning tools and classroom
activities. The WWW site at URL: http://www.space.lockheed.com/YPOP/
uses a movie theater theme to highlight available Yohkoh movies in a
non-intimidating and entertaining format for non-scientists. The site
features lesson plans, 'solar' activities, slide shows and, of course,
a variety of movies about the Sun. Classroom activities are currently
undergoing development with a team of scientists and K-12 teachers
for distribution in late 1997. We will display the products currently
online, which include a solar classroom with activities for teachers,
background resources, and a virtual tour of our Sun.
Title: Automated He II 304A Limb Feature Detection
Authors: Freeland, S. L.; Slater, G. L.; Lemen, J. R.
Bibcode: 1997SPD....28.0220F
Altcode: 1997BAAS...29..896F
We describe algorithms and software designed to automatically identify,
catalog, and extract the prominence features from cleaned, full disk
He II 304A images of the solar atmosphere recorded by the The Extreme
Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric
Observatory (SoHO). Sequences of partial frame images extracted in
this manner will be presented, together with parameters automatically
derived from the data, such as limb location, 'center of mass' location,
and apparent radial velocity of the features. It has been observed that
limb prominences show up exceptionally well in the 304A images, which
therefore provide excellent candidates for automated feature recognition
software. Specifically, these 'above the limb' prominence features
are highly contrasted with the surrounding pixels in individual 304A
images. When assembled into three dimensional data cubes, the growth,
shrinkage, and possible eruption of prominences are identifiable with
software. Moreover, for events identified as eruptive, the 304A signal
might provide a valuable proxy to identify and extract corresponding
events in less "well behaved" data sets, including those of EIT at
other wavelengths, Yohkoh/SXT, and SOHO/LASCO. The software design
permits near real time execution in anticipation that identification
of eruptive prominence events will provide some future predictive or
automated notification value. To optimize use of existing software
capabilities and to facilitate cross reference with other data
sets, we use the SolarSoft system as our development environment [
http://www.space.lockheed.com/solarsoft/ ].
Title: The TRACE Mission
Authors: Wolfson, J.; Bruner, M.; Jurcevich, B.; Lemen, J.; Schrijver,
K.; Shine, R.; Strong, K.; Tarbell, T.; Title, A.; Golub, L.;
Bookbinder, J.; Deluca, E.; Acton, L.; Handy, B.; Kankelborg, C.;
Fisher, R.
Bibcode: 1997SPD....28.0143W
Altcode: 1997BAAS...29..887W
The TRACE (Transition Region and Coronal Explorer) mission will explore
the connections between fine-scale magnetic fields and plasma structures
in the coronal, transition zone and temperature minimum regions of the
sun. TRACE will collect images of solar plasmas at temperatures from
10(4) to 10(7) K, with one arc second spatial resolution and excellent
temporal resolution and continuity. With a scheduled launch date of 15
December 1997, the mission will emphasize collaborative observations
with SoHO, enabling simultaneous observations of high-resolution images,
spectra, and magnetograms. The 30 cm aperture TRACE telescope uses four
normal-incidence coatings for the EUV and UV on quadrants of the primary
and secondary mirrors. Interference filters further isolate 5 different
UV bands. The images are co-aligned and internally stabilized against
spacecraft jitter. A 1024 x 1024 lumigen-coated CCD detector collects
images over an 8.5 x 8.5 arc minute field-of-view. LMATC, SAO, and GSFC
built the TRACE instrument, which was integrated with the GSFC-produced
SMEX spacecraft on 28 February (just over two years from the start
of its development). It will be put into a Sun-synchronous orbit and
operated in coordination with the SoHO Experiment Operations Facility at
GSFC. We are committed to maintaining a publicly accessible data base
for TRACE data. Browsing and data set requesting capabilities will be
provided at Web site www.space.lockheed.com/TRACE/TRACElinks.html. This
site already contains a large volume of information on the mission
including preliminary scientific observing programs and directions
as to how to participate in the mission now and in the future. This
project is supported by NASA contract NAS5-38099.
Title: Temporal Variations of Solar Flare Spectral Properties: Hard
X-Ray Fluxes and Fe XXV, Ca XIX, and Wide-Band Soft X-Ray Fluxes,
Temperatures, and Emission Measures
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R.;
Zarro, Dominic A.
Bibcode: 1997ApJS..110..115S
Altcode:
We present fluxes, temperatures, and emission measures for nine
solar flares, using data from both the Fe XXV and Ca XIX channels
of the Bragg Crystal Spectrometer (BCS) experiment on the Yohkoh
satellite and from the wide-band soft X-ray spectrometers on the GOES
spacecraft. We also present hard X-ray fluxes from the Hard X-ray
Telescope (HXT) on Yohkoh and the BATSE spectrometer on the Compton
Gamma-Ray Observatory (CGRO). All events occurred during 1992 and
ranged in size from GOES class C5 to M2. Three of the events occurred
near the solar limb. For each flare we give two sets of plots. The
first set shows flux, electron temperature, and emission measures
for Fe XXV, Ca XIX, and GOES as functions of time. The second set of
plots gives log electron temperature as functions of log (emission
measure)1/2 for these three wavelength ranges; we refer to
these plots as E1/2-T diagrams. Hard X-ray flux information
is included in both sets of plots. Our observations indicate that (1)
cooler plasmas are located along the legs of, or are evenly distributed
along, the flaring loops, while hotter plasmas are concentrated near
the loop tops, (2) peaks in temperature in each of the wavelength
bands are closely associated with hard X-ray enhancements, and (3)
the emission from both relatively hot and relatively cool flaring
plasmas emanates from the same loop or from closely related loops.
Title: Observations of Coronal Features by EIT above an Active Region
by EIT and Implications for Coronal Heating
Authors: Neupert, W. M.; Newmark, J.; Thompson, B. J.; Catura, R.;
Moses, J. D.; Portier-Fozzani, F.; Delaboudiniere, J. P.; Gabriel, A.;
Artzner, G.; Clette, F.; Cugnon, P.; Maucherat, A.; Defise, J. M.;
Jamar, C.; Rochus, P.; Howard, R.; Michels, D.; Dere, K.; Freeland,
S.; Lemen, J.; Stern, R.; Gurman, J.
Bibcode: 1997SPD....28.0115N
Altcode: 1997BAAS...29..881N
The EUV Imaging Telescope (EIT) on the SOHO provides the capability
for multi-wavelength imaging of the corona in four spectral bands,
centered at 171, 195, 284, and 304 Angstroms, using multilayer telescope
technology. These bands encompass coronal temperatures from 1 MK
to 2.5 MK as well as the upper chromosphere, at about 60,000 K. In
particular, nearly simultaneous imaging in the 171 and 195 Angstrom
bands, the former including major Fe IX and Fe X emission lines, the
latter including a strong Fe XII line, provides a capability to infer
the morphology and characteristics of the corona at temperatures of
1.0 - 1.7 MK. We have examined the corona in this temperature range
over an active region observed from SOHO from May - September, 1996 and
find that low-lying loops (below a density scale height of 75,000 km,
characteristic of Fe X) vary little in brightness and temperature along
their length. For features extending to greater heights, however, both
brightness gradients and temperature gradients are observed. Preliminary
analysis of the observations when the region was on the West limb
on September 30 indicates a small positive temperature gradient of
approximately 0.5 K/km in one loop system that extended above 100,000
km. On the other hand, a nearly radial feature extending to the edge of
the EIT FOV was isothermal or had at most a slight negative temperature
gradient. Such measurements may have application to the modeling of
coronal loops and streamers and the processes of coronal heating and
solar wind acceleration.
Title: Using the World Wide Web to Make YOHKOH SXT Images Available
to the Public: The YOHKOH Public Outreach Project
Authors: McKenzie, D.; Larson, M. B.; Slater, T.; Acton, L.; Alexander,
D.; Freeland, S.; Lemen, J.; Metcalf, T.
Bibcode: 1997ESASP.404..561M
Altcode: 1997cswn.conf..561M
No abstract at ADS
Title: The Dynamic Quiet Solar Corona: 4 Days of Joint Observing
with MDI and EIT
Authors: Schrijver, C. J.; Shine, R. A.; Hurlburt, N. E.; Tarbell,
T. D.; Lemen, J. R.
Bibcode: 1997ESASP.404..669S
Altcode: 1997cswn.conf..669S
No abstract at ADS
Title: Imaging the solar corona in the EUV
Authors: Delaboudiniere, J. -P.; Stern, R. A.; Maucherat, A.;
Portier-Fozzani, F.; Neupert, W. M.; Gurman, J. B.; Catura, R. C.;
Lemen, J. R.; Shing, L.; Artzner, G. E.; Brunaud, J.; Gabriel, A. H.;
Michels, D. J.; Moses, J. D.; Au, B.; Dere, K. P.; Howard, R. A.;
Kreplin, R.; Defise, J. M.; Jamar, C.; Rochus, P.; Chauvineau, J. P.;
Marioge, J. P.; Clette, F.; Cugnon, P.; van Dessel, E. L.
Bibcode: 1997AdSpR..20.2231D
Altcode:
The SOHO (SOlar and Heliospheric Observatory) satellite was launched on
December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point
on February 14th 1996, it began to continuously observe the Sun. As
one of the instruments onboard SOHO, the EIT (Extreme ultraviolet
Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The
He II filter at 304 A˚ images the chromosphere and the base of the
transition region at a temperature of 5 - 8 x 10^4 K; the Fe IX-X
filter at 171 A˚ images the corona at a temperature of ~ 1.3 x 10^6 K;
the Fe XII filter at 195 A˚ images the quiet corona outside coronal
holes at a temperature of ~ 1.6 x 10^6 K; and the Fe XV filter at 284
A˚ images active regions with a temperature of ~ 2.0 x 10^6 K. About
5000 images have been obtained up to the present. In this paper,
we describe also some aspects of the telescope and the detector
performance for application in the observations. Images and movies
of all the wavelengths allow a look at different phenomena present in
the Sun's corona, and in particular, magnetic field reconnection.
Title: Radio and X-Ray Studies of a Coronal Mass Ejection Associated
with a Very Slow Prominence Eruption
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Enome, S.; Lemen,
J. R.; Akioka, M.; Lara, A.
Bibcode: 1997ApJ...475..348G
Altcode:
We report on the observations of an X-ray coronal mass ejection
(CME) with its three part structure: frontal loop, coronal cavity,
and the eruptive prominence core. The prominence core was observed in
microwaves, and the frontal loop was observed in X-rays. A coronal
volume much larger than that occupied by the prominence seems to be
affected by the eruption. Formation of an arcade structure was also
observed beneath the erupting prominence. X-ray enhancement at the
arcade persisted for several hours similar to long decay events. At
the apex of the arcade there was a bright knot, which we interpret
as the reconnection region from which the filament gets detached. We
determined the trajectories of the frontal loop and the prominence core
and found them to have very different characteristics. The CME showed an
extremely small acceleration, while the prominence had a linear motion
in the beginning followed by an exponential rise. However, during the
several hours of simultaneous observation, the prominence did not catch
up with the frontal loop. We determined the evolution of the CME mass,
which increased by a factor of 4 during our observations. We discuss
the implications of the observations in the general context of coronal
mass ejections.
Title: Calcium abundance measurements using the Yohkoh BCS
Authors: Bentley, R. D.; Sylwester, J.; Lemen, J. R.
Bibcode: 1997AdSpR..20.2275B
Altcode:
Soft X-ray observations by SMM and other spacecraft have shown
that the abundance of certain elements in solar corona varies from
flare to flare. In this study, observations made by the Yohkoh Bragg
Crystal Spectrometer (BCS) in helium-like Ca XIX have been analysed,
and Ca abundance determined for 177 flares observed during the first
four years of the mission (1991-1995). The average abundance of Ca
relative to H for all flares is < A_Ca > = (3.64 +/- 0.39) x
10^-6. As with an earlier study of SMM data, the abundance is found to
be enhanced compared to the photosphere ((2.24 +/- 0.10) x 10^-6), and
with only minor variation from flare to flare. However, the absolute
value and range of values determined by this study is smaller than in
the previous study; these differences are discussed.
Title: A Giant Prominence Eruption Observed by Nobeyama
Radioheliograph and YOHKOH Spacecraft
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Shibasaki, K.;
Koshiishi, H.; Enome, S.; Lemen, J. R.
Bibcode: 1997IAUJD..19E...4G
Altcode:
The results of an investigation of a giant prominence which erupted from
the northwest limb of the Sun on 1994 April 05, will be reported. The
event could be traced back to a large prominence of March 19, 1994
above the east limb. The filament was located in the north-south
direction when it appeared on the disk. At about 23:00 UT on April 05,
the filament started slowly rising and then accelerated. The speed of
the prominence was was only 75 km s^{-1} when it reached a height of
about 0.5 R_ odot above the surface. Preliminary examination shows that
the eruption caused a geomagnetic storm on April 07 at 20:00 UT. We
study the dynamical and physical properties of the erupting prominence
and obtain physical parameters of the prominence plasma. In X-rays, the
region of eruption was relatively faint. After the eruption, however,
there was a large void at the previous location of the prominence and
an arcade formed progressively spreading from south to north along
the limb. Based on the X-ray and radio observations, we determine the
characteristics of the pre- and post-eruption structures.
Title: First Results from EIT
Authors: Clette, F.; Delaboudiniere, J. -P.; Artzner, G. E.; Brunaud,
J.; Gabriel, A. H.; Hochedez, J. -F.; Millier, F.; Song, X. Y.; Au, B.;
Dere, K. P.; Howard, R. A.; Kreplin, R.; Michels, D. J.; Moses, J. D.;
Defise, J. -M.; Jamar, C.; Rochus, P.; Chauvineau, J. -P.; Marioge,
J. -P.; Catura, R. C.; Lemen, J. R.; Shing, L.; Stern, R. A.; Gurman,
J. B.; Neupert, W. M.; Maucherat, A.; Cugnon, P.; van Dessel, E. L.
Bibcode: 1997ASPC..118..268C
Altcode: 1997fasp.conf..268C
The Extreme-UV Imaging telescope has already produced more than 15000
wide-field images of the corona and transition region, on the disk
and up to 1.5R_⊙ above the limb, with a pixel size of 2.6\arcsec. By
using four different emission lines, it provides the global temperature
distribution in the quiet corona, in the range 0.5 to 3*E(6) K. Its
excellent sensitivity and wide dynamic range allow unprecedented views
of low emission features, even inside coronal holes. Those so-called
``quiet'' regions actually display a wide range of dynamical phenomena,
in particular at small spatial scales and at time scales going down
to only a few seconds, as revealed by all EIT time sequences of
full- or partial-field images. The initial results presented here
demonstrate the importance of this wide-field imaging experiment for
a good coordination between SOHO and ground-based solar telescopes,
as well as for science planning.
Title: Yohkoh/SXT observations of a coronal mass ejection near the
solar surface
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.; Akioka, M.
Bibcode: 1996NewA....1..207G
Altcode:
We report the observations of a coronal mass ejection (CME) using
the Soft X-ray Telescope on board the Yohkoh Mission. The CME had
the familiar three part structure (frontal loop, prominence core
and a cavity). The erupting prominence was observed by the Nobeyama
radioheliograph. We were able to determine the mass of the CME (2.6
× 1014 g) from X-ray observations which seems to be at
the lower end of the range of CME masses reported before from white
light observations. This is the first time the mass of a CME has been
determined from X-ray observations. The height of onset of the CME
was 0.3R⊙. The CME moved much faster than the erupting
prominence while its acceleration was smaller than that of the erupting
prominence. J. Leonard Culhane
Title: Next-generation EUV imaging spectrometer for solar flare
observations
Authors: Moses, J. Daniel; Brueckner, Guenter E.; Dere, Kenneth P.;
Korendyke, Clarence M.; Moulton, Norman E.; Prinz, Dianne K.; Seely,
John F.; Socker, Dennis G.; Bruner, Marilyn E.; Lemen, James R.
Bibcode: 1996SPIE.2804..260M
Altcode:
The Naval Research Laboratory Skylab SO82A slitless spectrograph
provided solar flare observations that have never been equaled
in diagnostic capabilities for interpreting thermal flare
physics. Improvements in detector technology, optics and optical
coating technology, and almost two decades of analysis of SO82A data
can be combined with the basic concept of an EUV objective grating
spectrograph to build an instrument to address many of the remaining
mysteries of solar flares. This next generation instrument incorporates
two sets of two identical, orthogonally mounted slitless spectrographic
Cassegrain telescopes. Each telescope consists of a multilayer coated,
Wadsworth mount objective grating and multilayer coated spherical
secondary mirror; a backside illuminated CCD detector is installed
at the focal plane. The orthogonal mounting changes the dispersion
direction by 90 degrees on the disk image; processing on the two
resulting images allows recovery of the undispersed disk image and
spectral line profiles. The resulting instrument will obtain high time
cadence, spectrally-dispersed images with improved spatial resolution,
dynamic range, signal-to-noise ratio, and velocity discrimination.
Title: Solar identification of solar-wind disturbances observed
at Ulysses
Authors: Lemen, J. R.; Acton, L. W.; Alexander, D.; Galvin, A. B.;
Harvey, K. L.; Hoeksema, J. T.; Zhao, X.; Hudson, H. S.
Bibcode: 1996AIPC..382...92L
Altcode:
The Ulysses polar passages are producing a unique set of observations of
solar-wind disturbances at high heliographic latitudes. In this paper
we use the Yohkoh soft X-ray telescope (SXT) to locate some of these
events, as defined by the Ulysses/SWICS data, in the solar corona. Of 8
events, we identify two with flares, three with front-side large arcade
events, two with far-side events, and one was not seen in the Ulysses
data. The arcade events generally resemble long-duration flares seen
in active regions, but are larger, slower, and cooler. We present
Yohkoh images of each of these events. In the large arcade events
(see Alexander et al., 1996, for a detailed look at one of them) the
magnetic morphology at the location of the Yohkoh arcade is generally
consistent with the development of a large system of loops. Some of
the identifications are ambiguous, and we summarize the reasons for
this. From the SWICS data we have obtained ionization temperatures for
several events, and find that they have no obvious pattern in relation
to the X-ray temperatures; this may be expected on the basis that the
interplanetary plasma cloud is physically distinct from the plasma
trapped in the corona. Soft X-ray observations of the solar corona
show occasional occurrences of large-scale brightenings in the form
of arcades of loops. Such structures have been known since Skylab
(e.g., Sturrock, 1980), and have a clear relationship with coronal
mass ejections (e.g., Kahler, 1977). We now may study this phenomenon
statistically with the much more comprehensive Yohkoh observations;
with Yohkoh movies we can also begin to extend our knowledge to the
three-dimensional development of the structures. At the same time
Ulysses has sampled the latitude dependence of the interplanetary
effects. With this paper we introduce this subject and provide a
preliminary listing of events from the passage of Ulysses through
high heliographic latitudes. The starting point of the present
survey is a list of interplanetary plasma clouds (IPC's) derived
from Ulysses/SWICS data. These are essentially the same as the events
termed CMEs by Gosling et al. (1994a, 1994b). For this identification
the presence of bidirectional streaming in the suprathermal electron
distribution is one of the main criteria. We note that there are no
direct coronagraph observations, however. The Yohkoh observations
were examined at the apparent time of origin of each Ulysses event,
resulting in some clear and some less-certain identifications. We
also studied the ionization temperatures of the IPC material as a
beginning step to give the identifications a physical basis. There
has been little study thus far of the Yohkoh soft X-ray observations
in relationship to CMEs, which we believe to be closely related to
the interplanetary disturbances. Hiei et al. (1993) reported the only
Yohkoh event yet studied in conjunction with white-light coronagraph
observations. However Klimchuk et al. (1994) showed that X-ray eruptive
phenomena with parameters similar to those of CMEs occur frequently at
the limb, and there have been several studies of individual eruptive
events (e.g., Watanabe et al., 1992). Presently there is no systematic
knowledge of the X-ray coronal counterparts of CMEs, and the survey
represented here is part of the effort to rectify this situation.
Title: Yohkoh/SXT soft x-ray observations of sudden mass loss from
the solar corona
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Freeland, S. L.;
Lemen, J. R.; Harvey, K. L.
Bibcode: 1996AIPC..382...88H
Altcode:
With soft X-ray imaging we can study the entire coronal volume, except
for cold inclusions such as prominences, as a function of time. This
should allow us to observe the origins of coronal mass ejections. We
report here an initial survey of the Yohkoh/SXT observations at the
times of reported or apparent mass ejections: three LDE flare events
and two large-scale arcade formations. For each of the events we
can easily detect sudden coronal dimming, which we interpret as the
launch interval of a CME. In one of the flare events we have found
a well-defined plasma cloud, apparently formed from a set of loop
structures, which rises and disappears during the growth phase of the
flare emission. Its mass amounted to some 4×1014 g with
a density of 3×108 cm-3 and a temperature of
2.8 MK before its disappearance.
Title: The solar origins of two high-latitude interplanetary
disturbances
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Harvey, K. L.;
Kahler, S. W.; Kurokawa, H.; Lemen, J. R.
Bibcode: 1996AIPC..382...84H
Altcode:
Two extremely similar interplanetary forward/reverse shock events,
with bidirectional electron streaming, were detected by Ulysses in
1994 [Gosling et al., 1994]. Both events resulted in geomagnetic
storms and presumably were associated with coronal mass ejections. In
this paper we use the Yohkoh soft X-ray observations to characterize
the conditions in the lower corona at the times appropriate for the
launching of these two events. We find two strikingly different solar
events to be the likeliest candidates: an LDE flare on 20 Feb. 1994,
and a extremely large-scale arcade event on 14 April 1994.
Title: YOHKOH Observations of an Over-the-Limb Solar Flare with
Large Spectral Line Shifts
Authors: Sterling, Alphonse C.; Harra-Murnion, Louise K.; Hudson,
Hugh S.; Lemen, James R.
Bibcode: 1996ApJ...464..498S
Altcode:
We present observations of a solar flare of 1993 April 15 near 9 UT,
using data from the Yohkoh Bragg crystal spectrometer (BC S) and soft
X-ray telescope (SXT). Observations from SXT indicate that the flare
occurred well beyond the solar limb, meaning that our observations
are restricted to the uppermost portions of the flaring structure. BCS
spectra show strong bulk blueshifts of the spectral line profiles for a
short period near the start of the event, followed by an extended period
of strong bulk redshifts of the line profiles. Concurrent with these
bulk line shifts, the spectra show "blue wing" asymmetries. Both bulk
line shifts and blue wings are infrequent characteristics of flares
observed near the solar limb. Our observations are consistent with
strong upward mass motions occurring on a high-altitude flaring loop
oriented edge-on with the Earth. We find nonthermal line broadenings
in the spectra which are qualitatively and quantitatively similar to
line broadenings in spectra of disk flares. Near peak intensity of the
flare, ≤10% of the residual nonthermal broadening can be explained
by the spatial distribution of the soft X-ray flaring structure.
Title: Radio and X-ray manifestations of a bright point flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
Bibcode: 1996AIPC..374..408G
Altcode: 1996hesp.conf..408G
We have found remarkably different manifestations of a bright point
flare in X-ray and radio (microwave) wavelengths, unlike previous
observations. In X-rays, the BP flare was relatively simple while
in radio, the bright point flare had a large scale component and
a transient moving component. The large scale structure may be the
radio counterpart of large scale structures sometimes seen during
X-ray BP flares. The transient component was also compact and moved
away from the location of the X-ray BP flare with a speed of ∼60
km s-1. The compact source also showed fast time structure
which suggests nonthermal emission mechanism for the transient sources.
Title: Temporal Variations of Solar Flare Spectral Properties in CA
XIX and GOES
Authors: Sterling, A. C.; Hudson, H. S.; Lemen, J. R.; Zarro, D. A.
Bibcode: 1996AAS...188.1905S
Altcode: 1996BAAS...28..850S
Since the advent of space borne X-ray observations, there has been
a strong interest in the nature of the X-ray solar flare. Examining
the relationships between radiations produced in different portions
of the X-ray spectrum gives us information on the properties of the
constituent flaring plasmas. We have studied the joint variation of
electron temperatures and emission measures for a number of flares in
two different wavelength ranges, using data from the narrow band Ca xix
channel (near 3.18 Angstroms) of the Bragg crystal spectrometer (BCS)
experiment on board the Yohkoh spacecraft, and data from the wide band
X-ray monitors on the Geostationary Operational Environmental Satellites
(GOES, covering 0.5---8 Angstroms). A power law relationship often
describes the relationship between temperature and emission measure
during the decay phase in both wavelength ranges. According to work of
Sylwester et al. (1993, A&A 267, 586), energy input parameters and
physical properties of the flaring loop(s) determine the slope of this
power law. We find that ratios of Ca xix to GOES slopes generally fall
between .6 and 1.0, when slopes in both channels are measured during the
flare decay in each respective wavelength range. This relatively good
agreement between slopes in the two channels suggests that emissions
in both wavelength ranges originate from either the same flaring loop,
or differing loops with similar global properties.
Title: Post-Flare Loops of 26 June 1992, II
Authors: Schmieder, B.; Heinzel, P.; Van Driel-Gesztelyi, L.; Lemen,
J. R.
Bibcode: 1996SoPh..165..303S
Altcode:
We observed the large post-flare loop system, which developed after the
X 3.9 flare of 25 June 1992 at 20∶11 UT, in Hα with the Multichannel
Subtractive Double Pass Spectrograph at Pic-du-Midi and in X-rays with
the it Yohkoh/SXT instrument. Following the long-term development of
cool and hot plasmas, we have determined the emission measure of the
cool plasma and, for the first time, the temporal evolution of the
hot-loop emission measure and temperature during the entire gradual
phase. Thus, it was possible to infer the temporal variation of electron
densities, leading to estimates of cooling times. A gradual decrease of
the hot-loop emission measure was observed, from 4 × 1030
cm−5 at 23∶00 UT on 25 June 1992 to 3 × 1028
cm−5 at 13∶10 UT on 26 June 1992. During the same period,
the temperature decreased only slowly from 7.2 to 6.0 × 106
K. Using recent results of NLTE modeling of prominence-like plasmas,
we also derive the emission measure of cool Hα loops and discuss
their temperature and ionisation degree. During two hours of Hα
observations (11-13 hours after the flare) the averaged emission
measure does not show any significant change, though the amount
of visible cool material decreases and the volume of the loops
increases. The emission measure in Hα, after correction for the
Doppler-brightening effect, is slightly lower than in soft X-rays. Since
the hot plasma seems to be more spatially extended, we arrive at
electron densities in the range ninfesupho≤
ninfesupcool∼ 2 × 1010
cm−3 at the time of the Hα observations.
Title: Coordinated EUVE/ASCA/XTE/VLA Observations of Algol
Authors: Stern, R. A.; Lemen, J. R.; Antunes, S.; Drake, S. A.;
Nagase, F.; Schmitt, J. H. M. M.; Singh, K. P.; White, N. E.
Bibcode: 1996AAS...188.6012S
Altcode: 1996BAAS...28S.921S
EUVE, ASCA, and XTE observed the eclipsing binary Algol (beta Per)
from 1--7 Feb 96. EUVE was continuously pointing at Algol (with the
exception of earth block, SAA passages, etc.) for ~ 2 binary orbits,
with a net exposure time of 160 ksec, ASCA for ~ 40 ksec net exposure
in 4 separate pointings, and XTE for ~ 90 ksec in 45 pointings. The
objective of the combined EUV/X-ray observations is to definitively
determine the temperature distribution and Fe abundance in the quiescent
spectrum, and, with luck, catch a flare or two. In addition, ~ 24
hours of coordinated VLA time were scheduled, with the primary goal
of comparing the microwave data with the XTE spectrum to search for
evidence of hard X-ray emission characteristic of microflares. The
EUVE quicklook lightcurve data in the 70-170 Angstroms \ band show
evidence of continual variability, most likely from a combination
of geometric effects (i.e. eclipses and rotational modulation) and
flaring. One moderate (~ x2) flare is evident in the EUVE data: the
flare decay should be visible in the (as yet unreduced) XTE data. The
ASCA data were taken largely during quiescent periods, which will be
helpful in a combined emission measure and Fe abundance analysis. We
will discuss preliminary results from this coordinated campaign,
including first attempts at modeling the combined spectra.
Title: TRACE: the Transition Region and Coronal Explorer
Authors: Schrijver, C.; Title, A.; Acton, L.; Bruner, M.; Fischer,
R.; Golub, L.; Harrison, R.; Lemen, J.; Rosner, R.; Scharmer, G.;
Scherrer, P.; Strong, K.; Tarbell, T.; Wolfson, J.
Bibcode: 1996AAS...188.6704S
Altcode: 1996BAAS...28..934S
The TRACE mission is designed to obtain images of the solar
transition region and corona of unprecedented quality. With these
images we will be able to explore quantitatively the connections
between the photospheric magnetic field and the associated hot and
tenuous structures in the outer atmosphere. The TRACE telescope has
an aperture of 30 cm, and will observe an 8.5 x 8.5 arcminute field of
view with a resolution of one arcsecond. Finely tuned coatings on four
quadrants on the primary and secondary normal--incidence mirrors will
allow observations in narrow EUV and UV spectral bands. The passbands
are set to Fe IX, XII, and XV lines in the EUV band, while filters
allow observations in C IV, Ly alpha , and the UV continuum using
the UV mirror quadrant. The data thus cover temperatures from 10(4)
K up to 10(7) K. The Sun--synchronous orbit allows long intervals of
uninterrupted viewing. Observations at different wavelengths can be
made in rapid succession with an alignment of 0.1 arcsec. Coordinated
observing with TRACE, SoHO and YOHKOH will give us the first opportunity
to observe all temperature regimes in the solar atmosphere, including
magnetograms, simultaneously from space. TRACE is currently scheduled
to be launched in October 1997. More information can be found on the
web at ``http://pore1.space.lockheed.com/TRACE/welcome.html''.
Title: A Signature of CME Onsets in Soft X-rays
Authors: Webb, D.; Hudson, H.; Lemen, J.
Bibcode: 1996AAS...188.7008W
Altcode: 1996BAAS...28..939W
Some CME models involve the opening of previously closed magnetic
field lines as the plasma erupts through the lower corona. However, the
identification of observational signatures of this process has proven
illusive. We report on Yohkoh/SXT observations of large-scale arcade
events which reveal the dimming, or depletion, of coronal material
above the bright long-duration arcade region. Viewed in video form, the
impression is of an opening up and evacuation of a local portion of the
lower corona. We interpret this as the process of field line opening
in the initial phase of a CME and, therefore, as the first direct
signature of the mass ejection in soft X-rays. The dimming appears as a
reduction of the soft X-ray intensity by about a factor of 2-3. We are
studying several events of this type which reveal different aspects of
the geometry and kinematics of this process. Highly structured loops
can be seen expanding in the dimming regions of some events and can
be used to characterize the velocity field of the initial CME expansion.
Title: Observations of Coronal Depletion and Ejection
Authors: Lemen, J. R.; Hudson, H.; Webb, D.; Tsuneta, S.
Bibcode: 1996AAS...188.7007L
Altcode: 1996BAAS...28..939L
We present the analysis of the Yohkoh/SXT observations of a long-decay
event that was observed on 1992 February 21. This event, previously
reported by Tsuneta et al. \ 1992, had a clearly observed compact
ejection at its onset. There is also evidence for a depletion
of material in the corona above the flare site (coronal dimming)
accompanying the onset of flare brightening. We find a lower limit of
3 x 10(14) g for this mass depletion. This event was observed near the
limb as an arcade viewed almost end-on. Its morphology resembles the
classical reconnection model for a solar flare. Here we describe the
early phase of this event when the outward motions as observed in the
SXT images are interpreted as the X-ray signature of a coronal mass
ejection (no white-light images are available). The coronal depletion
marks the beginning of the outward motion and occurs simultaneously
with hard X-ray emission. If this marks the beginning of a CME, then
this event provides support for a close connection between of X-ray
flares and coronal mass ejections.
Title: Observations of the South coronal hole from EIT and YOHKOH
Authors: Handy, B. N.; Catura, R.; Freeland, S.; Lemen, J.; Stern,
R.; Gurman, J. B.; Delaboudiniere, J. P.; Artzner, G.; Gabriel, A.;
Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; Cyr,
O. C. St.; Catura, R.; Freeland, S.; Lemen, J.; Stern, R.; Neupert,
W.; Einfalt, E.; Newmark, J.
Bibcode: 1996AAS...188.0206H
Altcode: 1996BAAS...28..821H
The Extreme ultraviolet Imaging Telescope (EIT) on board the
SOHO spacecraft is capable of studying solar transition region,
chomospheric and coronal plasmas over bandpasses optimized for He II
304 Angstroms (0.08 MK), Fe IX/X 171, 173 Angstroms (0.8 - 1.0 MK),
Fe XII 195 Angstroms (1.5 MK), and Fe XV 284 Angstroms (2.0 - 2.5
MK) with 2.5 arcsecond spatial resolution. This telescope in concert
with the Yohkoh/SXT instrument allows us to simultaneously observe
solar structures at temperatures ranging from less than 0.1MK in the
transition region to over 3MK in the solar corona. EIT has had several
opportunities to observe the South coronal hole with high spatial and
temporal resolution. We compare observations from EIT and SXT with
an eye towards correlating temporal variations over the range of
wavelengths, activity of polar crown filament systems and relating
large-scale morphology of the X-ray corona to the transition region
in He II.
Title: There's No Such Thing as the Quiet Sun: EUV Movies from SOHO
Authors: Gurman, J. B.; Delaboudiniere, J. P.; Artzner, G.; Gabriel,
A.; Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; Cyr,
O. C. St.; Catura, R.; Freeland, S.; Lemen, J.; Stern, R.; Neupert,
W.; Einfalt, E.; Newmark, J.
Bibcode: 1996AAS...188.3718G
Altcode: 1996BAAS...28..880G
We present unique time series of high-resolution solar images from the
normal-incidence Extreme ultraviolet Imaging Telescope (EIT) on board
the SOHO spacecraft. With a pixel scale of 2.6 arc sec and a detector
dynamic range of > 10(4) , the EIT can be used to study the dynamics
of chromospheric and coronal features in multilayer bandpasses optimized
for He II 304 Angstroms (0.08 MK), Fe IX/X 171, 173 Angstroms (0.8 -
1.0 MK), Fe XII 195 Angstroms (1.5 MK), and Fe XV 284 Angstroms (2.0 -
2.5 MK). Among the most striking features of the digital movies we will
display are: the dynamic nature of small-scale loop features in the
polar coronal holes, the constant activity of the polar crown filament
systems, the locations of the bases of polar plumes, the presence
of dark (scattering) filament material in the coronal emission line
images, and the evolution of a unique, linear, dark feature in a young
active region. The latter feature is suggestive of the ``coronal void''
observed in the electron scattering corona by Macqueen et al./ (1983).
Title: Helium like sulphur X-ray emission in solar flares and
laboratory plasmas.
Authors: Harra-Murnion, L. K.; Phillips, K. J. H.; Lemen, J. R.;
Zarro, D. M.; Greer, C. J.; Foster, V. J.; Barnsley, R.; Coffey,
I. H.; Dubau, J.; Keenan, F. P.; Fludra, A.; Rachlew-Kaellne, E.;
Watanabe, T.; Wilson, M.
Bibcode: 1996A&A...308..670H
Altcode:
Theoretical X-ray spectra of He-like sulphur (S xv) derived from the
General Relativistic Atomic Structure Package, the Dirac R-matrix code
and other calculations are compared to laboratory spectra obtained
from the Alcator C tokamak and JET, and solar flare spectra obtained
from the Yohkoh Bragg Crystal Spectrometer (BCS) and with the SMM Flat
Crystal Spectrometer. The spectra depend on electron temperature and
electron density for plasma densities greater than 10^14^ cm^-3^. The
fits of the derived synthetic spectra to the laboratory spectra at
measured density and temperature are in fair agreement. Very good
agreement can be achieved with the solar flare spectra, which are
in general consistent with the S xv low-density limit, by adjusting
temperature. Thus, S xv line spectra can be used to determine the
temperatures of relatively weak flares for which diagnostics from
higher-temperature ions are unavailable. Using the synthetic spectra,
a search for density effects in Yohkoh BCS data at the time of compact
flares was made. None was found, so that it can be deduced that for
such flares the electron density is less than 10^14^cm^-3^. Density
estimates are made from emission measures and image sizes using
Yohkoh Soft X-ray Telescope data. Research has been carried out with
the results of laboratory spectra which indicate a variation of the
I_x_/I_y_ line intensity ratio across the tokamak minor radius. We
have studied various flares which occur at different locations across
the solar disk to determine if the same effect exists on the Sun.
Title: A high-temperature component in coronal holes observed with
YOHKOH SXT
Authors: Hara, H.; Tsuneta, S.; Acton, L. W.; Bruner, M. E.; Lemen,
J. R.; Ogawara, Y.
Bibcode: 1996AdSpR..17d.231H
Altcode: 1996AdSpR..17..231H
Temperatures of coronal holes are estimated from several sets of soft
X-ray images taken through various broad-band filters with the Soft
X-ray Telescope (SXT) aboard Yohkoh. The effect of scattered X-rays from
bright regions surrounding a temperature determination area, especially
those from nearby active regions, is carefully removed with the point
spread function derived from the post-launch data. An isothermal
approximation is applied to thus corrected data. The temperatures of
coronal holes near the disk center are found to be 1.8 - 2.4 x 10^6
K, which is almost the same as those derived for quiet regions. The
emission measures in coronal holes are estimated to be 10^25.5-26.2
cm^-5, about ten times smaller than in quiet regions. We conclude that
temperatures in coronal holes do not differ from those in quiet regions,
and that the depression in soft X-ray intensity of coronal hole regions
results from a lower density by a factor of 3 than quiet regions. We
propose that the coronal hole component observed with the SXT is not
the same one which is observed with the Skylab EUV instrument. An
X-ray intensity from a coronal hole is independently confirmed by the
eclipse observation on 1993 November 13, and consistent with intensities
derived from the scattering correction.
Title: Structure and evolution of post-flare loops: analysis of
YOHKOH and MSDP observations
Authors: Schmieder, B.; Heinzel, P.; Wiik, J. E.; Lemen, J.; Hiei, E.
Bibcode: 1996AdSpR..17d.111S
Altcode: 1996AdSpR..17..111S
Using coordinated observations of the June 26 1992 post-flare loops
(Yohkoh-SXT and MSDP at Pic-du-Midi), we have analyzed the physical
conditions in both hot and cool loops and studied their spatial
structure and temporal evolution. Coalignment of high-resolution images
from SXT and MSDP indicates that the cool Hα loops are located just
below the hot ones and that the whole loop system grows in time with
a velocity 1.4 km s^-1. The temperature of hot loops as derived from
SXT data amounts to 5 x 10^6 K, while the cool loops have temperatures
around 10^4 K. The electron density of hot loops was estimated from
SXT emission-measure analysis to 7 x 10^9 cm^-3, while Hα integrated
intensity gives an electron density in cool loops of 2.2 x 10^10
cm^-3. With these plasma parameters we have solved the energy equation
in order to estimate the cooling time. The basic result of this work
is that the cooling time is comparable to the characteristic growing
time of the loop system (~ 1500 - 2000 sec), which is in agreement
with the scenario of the post-flare loop system development.
Title: Detection of Large-Scale Radio Structure and Plasma Flow
during a Solar Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
Bibcode: 1996ApJ...457L.117G
Altcode:
We report on the detection of a large-scale radio structure and
plasma flow associated with a bright point flare observed on 1993
July 11. The bright point (BP) flare was simultaneously imaged by the
Nobeyama radioheliograph at 17 GHz and the Soft X-Ray Telescope on board
the Yohkoh mission. The microwave emission consists of a large-scale
structure and a compact moving source. The large-scale component seems
to be the radio counterpart of large-scale loop structures sometimes
observed in association with BP flares in X-rays. The compact source
moved from the location of the X-ray BP flare with a speed of about 60
km s-1, which suggests a plasma flow. Spatial comparison between X-ray
and radio data shows that the BP flare had different manifestations in
the two wavelength domains. The emission peaks in the two wavelength
domains did not coincide, which suggests cool plasma flow along the
large-scale radio structure. We were able to determine the temperature
and emission measure of the BP flare plasma from the X-ray data,
and thus we computed the expected radio flux from the X-ray--emitting
plasma. We found that the computed radio flux was much smaller than
the total observed radio flux.
Title: Comparison and Relation of HeI 1083 NM Two-Ribbon Flares and
Large-Scale Coronal Arcades Observed by YOHKOH
Authors: Harvey, Karen L.; McAllister, Alan; Hudson, Hugh; Alexander,
David; Lemen, James R.; Jones, Harrison P.
Bibcode: 1996ASPC...95..100H
Altcode: 1996sdit.conf..100H
No abstract at ADS
Title: Observations of the south coronal hole from EIT and Yohkoh.
Authors: Handy, B. N.; Catura, R.; Freeland, S.; Lemen, J.; Stern,
R.; Gurman, J. B.; Delaboudinière, J. P.; Artzner, G.; Gabriel,
A.; Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; St. Cyr,
O. C.; Neupert, W.; Einfalt, E.; Newmark, J.
Bibcode: 1996BAAS...28Q.821H
Altcode:
No abstract at ADS
Title: YOHKOH SXT and BCS Observations of the "Reconnection Region"
of a Solar Flare
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R.
Bibcode: 1996ASPC..111..177S
Altcode: 1997ASPC..111..177S
The authors find strong line shifts in Bragg crystal spectrometer
(BCS) spectra of a flare which occurred well beyond the solar limb on
1993 April 15. Since the flare is beyond the limb, only the uppermost
regions of the flare are visible. If reconnection is acting in flares,
than one may expect that the line shifts from this event are due to
reconnection jets emanating from above the region of the main flaring
loops. The authors show, however, that details of the line shifts
are not consistent with this picture. Rather than being a result of
reconnection jets, it is more likely that the line shifts are due
to plasma motions on a flaring loop oriented edge on with respect to
the Earth.
Title: Coordinated EUVE/ASCA/XTE/VLA observations of Algol.
Authors: Stern, R. A.; Lemen, J. R.; Antunes, S.; Drake, S. A.;
Nagase, F.; Schmitt, J. H. M. M.; Singh, K. P.; White, N. E.
Bibcode: 1996BAAS...28..921S
Altcode:
No abstract at ADS
Title: Large-Scale Active Coronal Phenomena in YOHKOH SXT Images
Authors: Svestka, Z.; Farnik, F.; Hudson, H. S.; Uchida, Y.; Hick,
P.; Lemen, J. R.
Bibcode: 1996mpsa.conf..609S
Altcode: 1996IAUCo.153..609S
No abstract at ADS
Title: Three Part Structure of a CME Revealed by X-Ray and Microwave
Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Lara, A.; Hanaoka, Y.; Enome,
S.; Lemen, J. R.; Akioka, M.
Bibcode: 1996ASPC..111..393G
Altcode: 1997ASPC..111..393G
The authors present X-ray (Yohkoh/SXT) and microwave (17 GHz Nobeyama)
observations of the 1993 July 10 - 11 CME. During this event, all the
substructures of a classical CME are revealed: frontal loop in X-rays,
prominence core in microwaves, dark cavity between prominence and
frontal loop in X-rays, and arcade structure beneath the prominence
in X-rays.
Title: Hot and Cool Post-Flare Loops: Formation and Dynamics
Authors: Schmieder, B.; Heinzel, P.; van Driel-Gesztelyi, L.; Wiik,
J. E.; Lemen, J.
Bibcode: 1996mpsa.conf..211S
Altcode: 1996IAUCo.153..211S
No abstract at ADS
Title: Helium-like sulfur emission in solar flares and laboratory
plasmas.
Authors: Harra-Murnion, L. K.; Phillips, K. J. H.; Lemen, J. R.;
Zarro, D. M.; Greer, C. J.; Foster, V. J.; Barnsley, R.; Coffey,
I. H.; Dubau, J. D.; Keenan, F. P.; Fludra, A.; Rachlew-Källne, E.;
Watanabe, T.; Wilson, M.
Bibcode: 1996uxsa.conf..417H
Altcode: 1996uxsa.coll..417H
Theoretical X-ray spectra of S XV derived from the General Relativistic
Structure Package, the Dirac R-matrix code and other calculations are
compared to laboratory spectra obtained from the Alcator C tokamak and
JET, and solar flare spectra obtained from the Yohkoh Bragg Crystal
Spectrometer (BCS) and with the SMM Flat Crystal Spectrometer. The
spectra depend on electron temperature and, electron density for
plasma densities greater than 1014cm-3. The
fits of the derived synthetic spectra to the laboratory spectra at
measured density and temperature are in fair agreement. Very good
agreement can be achieved with the solar flare spectra, which are
in general consistent with the S XV low-density limit, by adjusting
temperature. Thus, S XV line spectra can be used to determine the
temperatures of relatively weak flares for which diagnostics from
higher-temperature ions are unavailable.
Title: Coronal X-Ray Dimming in Two Limb Flares
Authors: Hudson, Hugh S.; Lemen, James R.; Webb, David F.
Bibcode: 1996ASPC..111..379H
Altcode: 1997ASPC..111..379H
Yohkoh SXT observations of flares and large-scale arcade events
frequently show coronal dimming accompanying X-ray brightening in
long-duration events. The authors tentatively identify this with the
process of field-line opening in the initial phase of a coronal mass
ejection (CME), although few simultaneous coronagraph and soft X-ray
observations have yet been described. The dimming signature may reduce
the coronal soft X-ray intensity by as much as a factor of 2 - 3, and
thus has a higher contrast than the cavity often seen in white-light
CME observations. In the cases examined thus far, the authors find
a close match between the onsets of X-ray brightening and coronal
dimming, suggesting a close physical relationship. The dimming appears
(in movie representations) to result from outward expansion; highly
structured features (multiple loops) are recognizable in the dimming
regions of some events, suggesting that the soft X-ray data may be
used to characterize the velocity field of the expansion.
Title: X-ray Observations of an Over-the-Limb Solar Flare with Large
Spectral Line Shifts
Authors: Sterling, A. C.; Harra-Murnion, L. K.; Hudson, H. S.; Lemen,
J. R.; Strong, K. T.
Bibcode: 1996mpsa.conf..557S
Altcode: 1996IAUCo.153..557S
No abstract at ADS
Title: EUVE spectroscopy of Algol.
Authors: Stern, R. A.; Schmitt, J. H. M. M.; Lemen, J. R.; Pye, J. P.
Bibcode: 1996uxsa.conf...97S
Altcode: 1996uxsa.coll...97S
The authors discuss results from the first extreme ultraviolet spectrum
of the prototypical eclipsing binary Algol (β Per), obtained with the
spectrometers on the Extreme Ultraviolet Explorer (EUVE). EUVE observed
Algol over nearly 1.5 orbital periods (≡4 d). The Algol spectrum in
the 80 - 350 Å range is dominated by emission lines of Fe XV-XXIV,
and the He II 304 Å line.
Title: Temperature Structure of the Diffuse Corona
Authors: Foley, C. R.; Culhane, J. L.; Acton, L. W.; Lemen, J. R.
Bibcode: 1996mpsa.conf..419F
Altcode: 1996IAUCo.153..419F
No abstract at ADS
Title: A Loop Flare Observed by YOHKOH on 1992 July 11
Authors: Khan, Josef I.; Hudson, Hugh S.; Sterling, Alphonse C.;
Lemen, James R.
Bibcode: 1996ASPC..111..162K
Altcode: 1997ASPC..111..162K
The authors present Yohkoh soft and hard X-ray observations of a
flare. Soft X-ray morphology shows the structure of this flare to
be a relatively simple loop. Nonetheless several interesting points
were found including: (i) bright soft X-ray footpoints persist long
after completion of the impulsive hard X-ray bursts; (ii) both legs
and footpoints of the flare loop appear to move together rather than
apart during the course of the flare; (iii) initially the flare loop
appears to have a fairly uniform thickness but as the flare progresses
the loop-top region becomes broader; (iv) 'low energy' hard X-rays
appear to originate from high in the loop near the loop apex; and (v)
soft X-ray spectra show strong line asymmetries suggesting the presence
of upflowing plasma oriented nearly directly towards the Earth.
Title: A U.S.--Russian Industrial Partnership to Develop a Low-Cost
IUE-2
Authors: Haisch, B.; Robb, P.; Strong, K.; Stern, R.; Schrijver,
C. J.; Lemen, J.
Bibcode: 1995AAS...187.7204H
Altcode: 1995BAAS...27.1388H
In 18 years as a NASA observatory IUE has generated more than 10(5)
spectra and 3000 articles, hosted over 2000 guest observers and launched
more than 200 doctoral dissertations. On 1 October 1995 science
operations were transferred entirely to ESA. IUE has been a central
facility in many multiwavelength programs. It has also supported
HST by carrying out projects that require more dedicated time than
HST can accomodate, including the ability to carry out uninterrupted
observations. Ready access to the UV spectrum has become a routine part
of modern astronomical capability, especially with respect to surveying
classes of objects and monitoring for variability and cycles. A
feasibility study has been initiated in the Solar and Astrophysics
Laboratory and the Optical Sciences Laboratory to examine an upgraded
IUE-2 to be developed in partnership with the Vavilov State Optical
Institute of St. Petersburg, Russia. The Vavilov Institute is the
premier space optics facility in the former Soviet Union. The recent
``swords into plowshares'' industrial partnership with Vavilov and
cost-effective capabilities involving commercial boosters such as LLV-2
and a version of the Commercial Remote Sensing Satellite (CRSS) bus
open innovative new opportunities for developing scientific facilities
in space. We are also investigating the economics of a shared launch on
the large capacity Proton rocket now operated jointly at the Baikonur
complex in Kazakhstan by Lockheed Martin, Khrunichev Enterprises and
NPO Energia. The centerpiece of IUE-2 would be a lightweight, advanced
techology silicon carbide mirror up to 1.2 m in diameter coupled to
modern imaging detectors. The Vavilov Institute has developed a robust
ceramic material of remarkable specific rigidity and thermal stability
that shows no distortion or hysteresis when thermally cycled between
cryogenic and room temperatures. Mirrors are routinely polished
to 0.03 waves in the visible. Spectroscopic capabilities would be
similar to the current IUE. The CRSS spacecraft provides 10 GBytes
of onboard data storage. In the interest of cost-savings, a highly
eccentric Exosat-like elliptical orbit is under consideration to
provide uninterrupted viewing times of at least 12 hours. This study,
now underway, will examine innovative ways in which a science-driven
program can be successfully developed and provided to NASA as a
purchased commercial product. Inputs are solicited, especially from
IUE guest observers and potentially interested IUE-2 users.
Title: The TRACE Mission
Authors: Title, A.; Bruner, M.; Jurcevich, B.; Lemen, J.; Strong,
K.; Tarbell, T.; Wolfson, J.; Golub, L.; Fisher, R.
Bibcode: 1995AAS...18710107T
Altcode: 1995BAAS...27.1427T
We have seen significant progress in the flight preparation of the
TRACE (Transition Region and Coronal Explorer) instrument during
the last few months. TRACE, approved for 1997 launch, will collect
images of solar plasmas at temperatures from 10(4) to 10(7) K, with
one arc second spatial resolution and excellent temporal resolution
and continuity. TRACE will explore the connections between fine-scale
magnetic fields and plasma structures in the coronal, transition
zone and temperature minimum regions of the sun. The 1997 launch
opportunity allows for collaborative observations from Earth orbit
with the SoHO instruments stationed at L1. Simultaneous observations
including high-resolution images, spectra, and magnetograms are
possible. The 30 cm aperture TRACE telescope uses four normal-incidence
coatings for the EUV and UV on quadrants of the primary and secondary
mirrors. Interference filters further isolate 5 different UV bands. The
images are coaligned and internally stabilized against spacecraft
jitter. A 1024 x 1024 CCD detector collects images over an 8.5 x 8.5
arc minute field-of-view. TRACE is launched on a GSFC SMEX spacecraft
into a Sun-synchronous orbit. It will operate in coordination with
the SoHO Experiment Operations Facility at GSFC. We are committed to
maintaining an publicly accessible data base for TRACE data. Browsing
and data set requesting capabilities will be included at our World
Wide Web site (see http://www.space.lockheed.com/TRACE/welcome.html).
Title: VLA and YOHKOH Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Raulin, J. -P.; Kundu, M. R.; Nitta, N.;
Lemen, J. R.; Herrmann, R.; Zarro, D.; Kosugi, T.
Bibcode: 1995ApJ...455..715G
Altcode:
A major solar flare (X-ray importance M1.5 and optical importance SB)
was fully observed by the Very Large Array and the Yohkoh mission on
1993 April 22. Both thermal and nonthermal emissions were observed
in radio. In soft X-rays, the flare was confined to a compact region
in an arcade. In hard X-rays, there were two prominent footpoints,
coincident in projection with the soft X-ray footpoints and located
on either side of the magnetic neutral line inferred from photospheric
magnetograms The Yohkoh Bent Crystal Spectrometer (B CS) data provided
important context information which was helpful in cross-checking the
quantitative agreement between the radio and X-ray data. The microwave
spectrum peaked around 10 GHz and showed Razin suppression in the
beginning. Later on, the low-frequency spectral index dropped to a
value of 2, suggesting thermal emission. The VLA images of the flare at
1.5 GHz show that the flare emission started as a single source above
one footpoint; later on, the emission centroid moved toward the soft
X-ray structure to finally become cospatial with the latter. The two
locations of the 20 cm source corresponded to nonthermal (footpoint
source) and thermal (source cospatial with the soft X-ray structure)
emissions. We performed temperature and emission measure analysis of
the X-ray data (SXT, BCS, and HXT) and used them as input to determine
the expected radio emission. While there is morphological agreement
between the radio and soft X-ray structures in the thermal phase,
the 20 cm brightness temperature shows quantitative agreement with
temperature derived from the BCS data. We were able to identify
three emission mechanisms contributing to the 20 cm radio emission
at different times without any ad hoc assumption regarding emission
mechanisms. Razin-suppressed nonthermal gyroresonance emission,
plasma emission, and thermal free-free emission seem to be operating
and are found to be consistent with the plasma parameters derived
from the X-ray data. The magnetic field structure in the flaring
region showed differences before and after the flare as traced b soft
X-ray structures in the flaring region and confirmed by 20 cm radio
images. The superhot component with a temperature of 32 MK was observed
in hard X-ray images and in light curves during the impulsive phase of
the flare with possible radio signatures at 20 cm wavelength. We derived
the physical parameters of the flaring plasma, the magnetic field,
and the characteristics of nonthermal particles in the flaring region.
Title: EIT: Extreme-Ultraviolet Imaging Telescope for the SOHO Mission
Authors: Delaboudinière, J. -P.; Artzner, G. E.; Brunaud, J.; Gabriel,
A. H.; Hochedez, J. F.; Millier, F.; Song, X. Y.; Au, B.; Dere, K. P.;
Howard, R. A.; Kreplin, R.; Michels, D. J.; Moses, J. D.; Defise,
J. M.; Jamar, C.; Rochus, P.; Chauvineau, J. P.; Marioge, J. P.;
Catura, R. C.; Lemen, J. R.; Shing, L.; Stern, R. A.; Gurman, J. B.;
Neupert, W. M.; Maucherat, A.; Clette, F.; Cugnon, P.; Van Dessel,
E. L.
Bibcode: 1995SoPh..162..291D
Altcode:
The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field
images of the corona and transition region on the solar disc and up to
1.5 R⊙ above the solar limb. Its normal incidence multilayer-coated
optics will select spectral emission lines from Fe IX (171 å), Fe
XII (195 å), Fe XV (284 å), and He II (304 å) to provide sensitive
temperature diagnostics in the range from 6 × 104 K to 3
× 106 K. The telescope has a 45 x 45 arcmin field of view
and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial
resolution. The EIT will probe the coronal plasma on a global scale,
as well as the underlying cooler and turbulent atmosphere, providing
the basis for comparative analyses with observations from both the
ground and other SOHO instruments. This paper presents details of the
EIT instrumentation, its performance and operating modes.
Title: Evolution of two small solar flares.
Authors: Fludra, A.; Doyle, J. G.; Metcalf, T.; Lemen, J. R.; Phillips,
K. J. H.; Culhane, J. L.; Kosugi, T.
Bibcode: 1995A&A...303..914F
Altcode:
Data from the YOHKOH satellite have been analysed for two small flares
(GOES class C) of total duration of 10 and 60 minutes. Upflows in S
XV, Ca XIX and Fe XXV lines were compared and the presence of a range
of upflow velocities was found. Emission from flare loop footpoints
corresponding to plasma moving with a typical velocity of 200-400km/s
is seen in soft X-ray images. In one of these events (23 June 1992),
which occurred in sheared loops being part of a sparse magnetic arcade,
with initial energy release taking place near one of the footpoints, a
large proportion of upflowing plasma was seen at least 1 minute before
the first peak in hard X-rays. In the second event (13 July 1992), the
increase of soft X-ray emission began more than 3 minutes before, and
weak mass upflows one minute before the rapid increase of temperature
and the onset of the detectable hard X-ray emission. This event was
probably triggered by emerging magnetic flux and accompanied by heating
and restructuring of two nearby magnetic loops. In both events the
emission measure of upflowing plasma is present simultaneously to,
and is very well correlated in time with the hard X-ray flux in the
14-23keV band. Differential emission measure in the temperature range
5-60x10^6^K was derived from S XV, Ca XIX and Fe XXV line and continuum
fluxes, and from images in two broad band soft X-ray filters, and
used to analyse the thermal contribution to the hard X-ray emission. A
non-thermal component of the hard X-ray emission is found at the peak
of the 23 June 1992 flare. The hard X-ray emission in the 13 July 1992
flare is primarily thermal, however, a possibility of an enhanced tail
of the electron energy distribution above 14keV is also indicated. The
chromospheric evaporation in these flares was driven both by electron
beams and thermal conduction, with conduction predominating during most
of the rise phase of the 13 July 1992 flare. In both events, the soft
X-ray emission measure at flare maximum was a few times 10^48^cm^-3^
with an electron temperature 19 and 24x10^6^K; the estimated lower
limit of the electron density is ~10^11^cm^-3^. The broadening of
Ca XIX spectral lines in the decay phase of these flares indicates
persisting random motions with a velocity of 60km/s, which is very
similar to the non-thermal broadening observed previously by SMM in
M and X class flares.
Title: Large-Scale Active Coronal Phenomena in YOHKOH SXT Images, I
Authors: Švestka, Zdeněk; Fárník, František; Hudson, Hugh S.;
Uchida, Yutaka; Hick, Paul; Lemen, James R.
Bibcode: 1995SoPh..161..331S
Altcode:
We have found several occurrences of slowly rising giant arches inYohkoh
images. These are similar to the giant post-flare arches previously
discovered by SMM instruments in the 80s. However, we see them now
with 3-5 times better spatial resolution and can recognize well their
loop-like structure. As a rule, these arches followeruptive flares
with gradual soft X-ray bursts, and rise with speeds of 1.1-2.4 km
s−1 which keep constant for >5 to 24 hours, reaching
altitudes up to 250 000 km above the solar limb. These arches differ
from post-flare loop systems by their (much higher) altitudes, (much
longer) lifetimes, and (constant) speed of growth. One event appears
to be a rise of a transequatorial interconnecting loop.
Title: Yohkho Soft X-Ray Spectroscopic Observations of the Bright
Loop-Top Kernels of Solar Flares
Authors: Khan, Josef I.; Harra-Murnion, Louise K.; Hudson, Hugh S.;
Lemen, James R.; Sterling, Alphonse C.
Bibcode: 1995ApJ...452L.153K
Altcode:
Observations of solar flares by the Soft X-ray Telescope (SXT) on
board Yohkoh frequently show strongly enhanced brightenings near the
tops of the magnetic loops containing hot plasma. The Yohkoh Bragg
Crystal Spectrometer (BCS) cannot normally make observations of these
loop-top sources in the absence of contamination by the legs and the
feet of the loops since it has no spatial resolution. We have overcome
this limitation by using the solar limb as an occulting edge in a
sequence of similar flares that occurred over an interval of ~10 hr
near the west limb on 1992 November 24. The progressive occultation by
the limb restricts the line of sight to higher and higher altitudes
during this sequence, with the final event showing only a compact
source of the type often found at loop tops. BCS observations in Fe
XXV, Ca XIX, and S XV show that electron temperatures and nonthermal
velocities in these compact sources are similar to those quantities
determined for disk flares in previous studies. As with disk flares,
the nonthermal line broadening persists late into the decay phase
of the flaring isolated loop tops. Our results favor mechanisms for
nonthermal-velocity generation that are either independent of height
or place the source near the apex of the flaring loop. In addition,
there may be a temporal relationship between the hard X-ray emission
and the nonthermal velocity, which suggests a possible association
between the primary energy release of the flare, the nonthermal-velocity
generation mechanism, and the loop top.
Title: The Transition Region and Coronal Explorer (trace)
Authors: Title, A.; Bruner, M.; Jurcevich, B.; Lemen, J.; Strong,
K.; Tarbell, T.; Wolfson, J.; Golub, L.; Bookbinder, J.; Fisher, R.
Bibcode: 1995ESASP.376b.505T
Altcode: 1995help.confP.505T; 1995soho....2..505T
No abstract at ADS
Title: Comparison of YOHKOH x-ray coronal events with ULYSSES
interplanetary events
Authors: Lemen, J. R.; Acton, L. W.; Alexander, D.; Galvin, A. B.;
Harvey, K. L.; Hoecksema, J. T.; Zhao, X.; Hudson, H.
Bibcode: 1995sowi.conf...58L
Altcode:
The Yohkoh soft X-ray telescope (SXT) has observed several
largescale eruptive events per year for the first three years
of observations (Aug. 1991 - Nov. 1994) Such events are most
prominent at high latitudes, but resemble long-duration flare
events seen in active regions. Some of the high-latitude events
have now been identified in the Ulysses/SWICS data base during the
Ulysses south polar passage. There are puzzling examples of solar
events with no interplanetary counterparts. A comparison of coronal
and interplanetary events can lead to better models for mapping
interplanetary disturbances back to their source location, especially
by combining Yohkoh morphology with three-dimensional representations
of the coronal magnetic field. In this paper we describe the parameters
of the hot plasma seen by SXT. There is clear evidence for non radial
motion in specific events. We present comparisons between the ionization
temperature of the interplanetary plasma with that observed at the
Sun in cases where this is possible.
Title: Yohkoh/SXT soft x-ray observations of sudden mass loss from
the solar corona
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Freeland, S. L.;
Lemen, J. R.; Harvey, K. L.
Bibcode: 1995sowi.confR..58H
Altcode:
Direct X-ray observations allow us to estimate the hot coronal mass
before and after a flare or other disturbance of the type leading to
a coronal mass ejection. The sudden disappearance of a large coronal
structure (scale greater than 105 km) gives evidence that an ejection
has occurred, if the time scales are much shorter than the conductive
or radiative cooling times for such structures. A flare also typically
adds large amounts of new material to the corona via evaporation
resulting from the coronal energy release. This provides a competing
mechanism that makes the estimation of the total mass loss somewhat
difficult. We note that the X-ray observations have the advantage of
covering the entire corona rather than the limb regions unlike the
coronagraph observations. We have identified two examples of coronal
mass disappearances. before and during long duration flare events on
21 Feb. 1992 (on the E limb) and 13 Nov. 1994 (near disk center). In
latter case the total mass amounted to some 4 x 1014 g with a
density of 3 x 108cm-3 and a temperature of 2.8 MK
before its disappearance. This corresponds to a radiative cooling time
of some 104 S. much longer than the observed time of disappearance. We
therefore suggest that these sudden mass disappearances correspond with
coronal mass ejections (CMEs), and suggest that further data analysis
will be able to confirm this by comparison with optical observations
of specific CMEs.
Title: The solar origins of two high-latitude interplanetary
disturbances
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Harvey, K. L.;
Kurokawa, H.; Kahler, S.; Lemen, J. R.
Bibcode: 1995sowi.confS..58H
Altcode:
Two extremely similar interplanetary forward/reverse shock events,
with bidirectional electron streaming were detected by Ulysses in
1994. Ground-based and Yohkoh/SXT observations show two strikingly
different solar events that could be associated with them: an LDE flare
on 20 Feb. 1994, and a extremely large-scale eruptive event on 14 April
1994. Both events resulted in geomagnetic storms and presumably were
associated with coronal mass ejections. The sharply contrasting nature
of these solar events argues against an energetic causal relationship
between them and the bidirectional streaming events observed by Ulysses
during its S polar passage. We suggest instead that for each pair of
events. a common solar trigger may have caused independent instabilities
leading to the solar and interplanetary phenomena.
Title: Yohkoh/SXT x-ray synoptic maps of coronal brightness and
temperature
Authors: Slater, G. L.; Lemen, J. R.; Hick, P.; Jackson, B. V.
Bibcode: 1995sowi.conf...68S
Altcode:
The Yohkoh soft X-ray telescope (SXT) records on the order of 50
solar images per day in two different color filters. These provide
material for the generation of synoptic maps, which compress the
3-dimensional data cube into two dimensions. We are creating synoptic
maps from strips of data both at disk center and at different heights,
including limb maps that are analogous to those produced by ground-based
coronagraphs. The ratios of intensities in images taken in two filters
provide estimates of the electron temperature in the range 1 - 3 x
106 K. These are broad-band temperature maps; rather than
maps created with discrete sampling as in the case of the coronal
green and red lines. We discuss the properties of these maps and their
application to the study of energy release in the corona.
Title: EUVE Observations of Algol: Detection of a Continuum and
Implications for the Coronal [Fe/H] Abundance
Authors: Stern, Robert A.; Lemen, James R.; Schmitt, Jurgen H. M. M.;
Pye, John P.
Bibcode: 1995ApJ...444L..45S
Altcode:
We report results from the first extreme ultraviolet spectrum of the
prototypical eclipsing binary Algol (beta Per), obtained with the
spectrometers on the Extreme Ultraviolet Explorer (EUVE). The Algol
spectrum in the 80-350 A range is dominated by emission lines of Fe
XVI-XXIV, and the He II 304 A line. The Fe emission is characteristic
of high-temperature plasma at temperatures up to at least log
T approximately 7.3 K. We have successfully modeled the observed
quiescent spectrum using a continuous emission measure distribution
with the bulk of the emitting material at log T greater than 6.5. We
are able to adequately fit both the coronal lines and continuum
data with a cosmic abundance plasma, but only if Algol's quiescent
corona is dominated by material at log T greater than 7.5, which is
physically ruled out by prior X-ray observations of the quiescent
Algol spectrum. Since the coronal (Fe/H) abundance is the principal
determinant of the line-to-continuum ratio in the EUV, allowing the
abundance to be a free parameter results in models with a range of
best-fit abundances approximately = 15%-40% of solar photospheric
(Fe/H). Since Algol's photospheric (Fe/H) appears to be near-solar,
the anomalous EUV line-to-continuum ratio could either be the result
of element segregation in the coronal formation process, or other,
less likely mechanisms that may enhance the continuum with respect to
the lines.
Title: Ulysses observations of a coronal origin particle event at
32° south heliographic latitutde
Authors: Pick, M.; Buttighoffer, A.; Kerdraon, A.; Armstrong, T. P.;
Roelof, E. C.; Hoang, S.; Lanzerotti, L. J.; Simnett, G. M.; Lemen, J.
Bibcode: 1995SSRv...72..315P
Altcode:
A remarkable streaming beam-like particle event of 60 keV-5 MeV ions
and of 38 315 keV electrons has been reported previously. This event
has been associated with the passage of a Coronal Mass Ejection (CME)
over the Ulysses spacecraft on June 9 13, 1993. At this time, the
spacecraft was located at 4.6 AU from the sun and at an heliolatitude
of 32° south. It was proposed (Armstrong et al., 1994) that the
particle injection source could have been of coronal origin. In this
study, we analyse the solar activity during this period. We identify
a region of solar radio noise storms in the corona and in particular,
a flare on June 7 that presents all the required characteristics to
produce the hot plasma beam observed in the interplanetary medium.
Title: Observations of Coronal Temperature Structure by Yohkoh
Authors: Acton, L. W.; Culhane, J. L.; Lemen, J. R.; Sturrock, P. A.
Bibcode: 1995SPD....26..615A
Altcode: 1995BAAS...27..964A
No abstract at ADS
Title: Radio Counterpart of an X-ray Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
Bibcode: 1995SPD....26.1317G
Altcode: 1995BAAS...27Q.991G
No abstract at ADS
Title: Yohkoh Multi-Wavelength Observations of the Bright Loop-Top
Kernels in Solar Flares
Authors: Sterling, A.; Khan, J.; Harra-Murnion, L.; Hudson, H.;
Lemen, J.
Bibcode: 1995SPD....26.1211S
Altcode: 1995BAAS...27..985S
No abstract at ADS
Title: Temperature Structure of the Diffuse Corona
Authors: Foley, C. A.; Acton, L. W.; Culhane, J. L.; Lemen, J. R.
Bibcode: 1995SPD....26..716F
Altcode: 1995BAAS...27R.969F
No abstract at ADS
Title: The point spread function of the soft X-ray telescope aboard
Yohkoh
Authors: Martens, Petrus C.; Acton, Loren W.; Lemen, James R.
Bibcode: 1995SoPh..157..141M
Altcode:
The point spread function of the SXT telescope aboardYohkoh has been
measured in flight configuration in three different X-ray lines
at White Sands Missile Range. We have fitted these data with an
elliptical generalization of the Moffat function. Our fitting method
consists of χ2 minimizationin Fourier space, especially
designed for matching of sharply peaked functions. We find excellent
fits with a reduced χ2 of order unity or less for single
exposure point spread functions over most of the CCD. Near the edges
of the CCD the fits are less accurate due to vignetting. From fitting
results with summation of multiple exposures we find a systematic
error in the fitting function of the order of 3% near the peak of the
point spread function, which is close to the photon noise for typical
SXT images in orbit. We find that the full width to half maximum and
fitting parameters vary significantly with CCD location. However, we
also find that point spread functions measured at the same location
are consistent to one another within the limit determined by photon
noise. A `best' analytical fit to the PSF as function of position
on the CCD is derived for use in SXT image enhancement routines. As
an aside result we have found that SXT can determine the location of
point sources to about a quarter of a 2.54 arc sec pixel.
Title: Relation between Cool and Hot Post-Flare Loops of 26 June
1992 Derived from Optical and X-Ray (SXT-YOHKOH) Observations
Authors: Schmieder, B.; Heinzel, P.; Wiik, J. E.; Lemen, J.; Anwar,
B.; Kotrc, P.; Hiei, E.
Bibcode: 1995SoPh..156..337S
Altcode:
We have analyzed the physical conditions of the plasma in post-flare
loops with special emphasis on dynamics and energy transport using
SXT-data (hot plasma) and optical ground-based data from Pic du Midi,
Wrocław, and Ondřejov (cool plasma). By combining the Hα observations
with the SXT images we can understand the relationship between cool and
hot plasmas, the process of cooling post-flare loops and the mechanism
which maintains the long duration of these loops. Using recent results
of NLTE modeling of prominence-like plasmas, we derive the emission
measure of cool Hα loops and this gives us a realistic estimate of
the electron density (2.2 × 1010 cm−3). Then,
by comparing this emission measure with that of hot loops derived from
SXT data, we are able to estimate the ratio between electron densities
in hot and cool loops taking into account the effect of geometrical
filling factors. This leads to the electron density in hot loops 7 ×
109 cm−3. We also derive the temperature of
hot X-ray loops (≃ 5.5 × 106 K), which, together with
the electron density, provides the initial values for solving the
time-dependent energy balance equation. We obtain the cooling times
which are compared to a typical growth-time of the whole loop system
(∼ 2000 s). In the legs of cool Hα loops, we observe an excess
of the emission measure which we attribute to the effect of Doppler
brightening (due to large downflow velocities).
Title: ULYSSES Observations of a Coronal Origin Particle Event at
32 deg South Heliographic Latitude
Authors: Pick, M.; Buttighoffer, A.; Kerdraon, A.; Armstrong, T. P.;
Roelof, E. C.; Hoang, S.; Lanzerotti, L. J.; Simnett, G. M.; Lemen, J.
Bibcode: 1995hlh..conf..315P
Altcode:
No abstract at ADS
Title: The transition region and coronal explorer (TRACE)
Authors: Tarbell, T. D.; Bruner, M.; Jurcevich, B.; Lemen, J.; Strong,
K.; Title, A.; Wolfson, J.
Bibcode: 1994ESASP.373..375T
Altcode: 1994soho....3..375T
No abstract at ADS
Title: EUVE Observations of Algol
Authors: Stern, R. A.; Lemen, J. R.; Schmitt, J. H. M. M.; Pye, J. P.
Bibcode: 1994AAS...185.8516S
Altcode: 1994BAAS...26.1462S
The EUVE satellite spectrometers observed the prototype eclipsing
binary Algol over nearly 1.5 orbital periods. Effective exposure
times were 100 ksec and 89 ksec in the short wave (70-180 Angstroms)
and medium wave (140-370 Angstroms) channels. High temperature (up to
20 MK) Fe XVI-XXIV emission lines are clearly detected in the overall
spectrum. In addition, a quiescent continuum is present which increases
towards shorter wavelengths. Using synthesized spectra of optically
thin line and continuum emission folded through the instrumental
response, we have examined constraints on the [Fe/H] coronal abundance
in Algol. We find that the coronal Fe is underabundant by factors of
~2--4 relative to solar photospheric values, unless an unreasonably
large quantity of coronal plasma at T > 30 MK is present in the
quiescent spectrum. The latter possibility is, however, inconsistent
with available X-ray data. Lightcurves of the high temperature EUV
lines compared to line emission at He II 304 A show considerable
differences, with much deeper minima present in the He II line during
both primary and secondary eclipses. Toward the end of the observation
a moderate flare lasting ~ 6 hours was detected in the high temperature
Fe emission lines. This work was supported in part by NASA Contract
NAS5-32492 and by the Lockheed Independent Research Program.
Title: Transient Microwave Brightenings in Solar Active Regions:
Comparison between VLA and YOHKOH Observations
Authors: Gopalswamy, N.; Payne, T. E. W.; Schmahl, E. J.; Kundu, M. R.;
Lemen, J. R.; Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
Bibcode: 1994ApJ...437..522G
Altcode:
We report observations of transient microwave (2 cm) brightenings
and their relationship with brightenings in soft X-rays. The peak
flux of the microwave brightenings observed by the Very Large Array
(VLA) is smaller than the previously reported fluxes by two orders
of magnitude. The microwave sources were highly polarized (up to
100%) and were situated on the periphery of a sunspot umbra. Among
the many transients observed in X-rays by Yohkoh, two were observed
simultaneously in microwaves. The microwave sources were found to
be closer to the umbra of the sunspot than were the X-ray loops. It
seems that the microwave sources are located at the footpoints of
the looplike X-ray transients. Using the combined VLA, Yohkoh, and
Mees data set, we determine the physical parameters of the loop in
which the brightenings occur. We find that an increase in emission
measure accompanied by small-scale heating can account for the X-ray
brightening. The microwave emission can be interpreted as thermal
gyroresonance or nonthermal gyrosynchrotron processes during the X-ray
brightening. The magnetic field in the microwave-source region is
found to be 1200-1800 G. The observations also provide evidence for
temperature gradient in the coronal loops.
Title: Temperatures of Coronal Holes Observed with the YOHKOH SXT
Authors: Hara, Hirohisa; Tsuneta, Saku; Acton, Loren W.; Bruner,
Marilyn E.; Lemen, James R.; Ogawara, Yoshiaki
Bibcode: 1994PASJ...46..493H
Altcode:
Temperatures of coronal holes have been estimated from several sets
of soft X-ray images taken through various broad-band filters with the
Soft X-ray Telescope (SXT) aboard Yohkoh. Since coronal holes are dark
areas, a detailed examination of the telescope point spread function,
which is slightly dependent on the X-ray wavelength, is of crucial
importance. The calibration is made using post-launch data, and the
effect of scattered X-rays from bright regions surrounding coronal
holes, especially those from nearby active regions, is carefully
removed. An isothermal approximation is applied to the thus-corrected
data. The temperatures of coronal holes near the disk center are found
to be 1.8--2.4 times 10(6) K, which is almost the same as those derived
for quiet regions not including active regions. The emission measures
in coronal holes are estimated to be 10(25.5--26.2) cm(-5) , about ten
times smaller than those of quiet regions. We conclude that temperatures
in coronal holes do not differ from those in quiet regions, and that
the depression in the soft X-ray intensity of coronal hole regions
results from a lower density by a factor of 3 than quiet regions.
Title: Combined HRTS-8 Sounding Rocket Observations and YOHKOH Soft
X-ray Observations of NOAA Active Region 7260 at the Solar Limb
Authors: Korendyke, C. M.; Dere, K. P.; Brueckner, G. E.; Waljeski,
K.; Lemen, J. R.
Bibcode: 1994kofu.symp..293K
Altcode:
On 24 August 1992, the Naval Research Laboratory (NRL) High Resolution
Telescope and Spectrograph (HRTS) was launched aboard a Black Brant
sounding rocket from White Sands, New Mexico. During the flight, the
instrument recorded a unique set of near ultraviolet slit spectra and
1550 A spectroheliograms of an active region at the solar limb. An
extensive set of observations of this region were obtained with the
Yohkoh Soft X-ray Telescope (SXT) near the time of the flight. The C IV
spectroheliograms obtained during this flight are some of the highest
resolution images of the solar transition region ever obtained. The
spectra and spectroheliograms dramatically demonstrate the fundamental
difference between coronal and chromospheric/transition-region plasmas
at 700 km spatial scales. The cooler plasmas exhibit a great deal of
dynamic, fine scale structure with significant flows or proper motion
particularly in the transition zone loops. The coronal emission lines
in the spectra! are relatively uniform and quiescent. The Yohkoh data
during the period before and after the flight show a set of diffuse
high temperature coronal loops with only minimal correspondence to
the structures visible in the C IV spectroheliograms.
Title: Temperature Analysis of the Post-Flare Loops of June 25-26,
1992
Authors: Anwer, B.; Hiei, E.; Hudson, H. S.; Acton, L. W.; Lemen,
J.; Metcalf, T. R.
Bibcode: 1994kofu.symp..137A
Altcode:
We have performed an analysis of temperatures and emission measures
of thermal plasma on a post--flare loop system following an X3.9
flare of June 25, 1992, at 20:14 UT in NOAA active region 7205 near
the west limb (N09, W67). The filter ratio method was applied to the
data sets taken using the Al 0.1 micron (thin Al) and Al 12 micron
(thick Al) filters of the Yohkoh Soft X-ray Telescope (SXT). We found
that the plasma temperature of the top of loops was in the range 5 -
8 x 10^6 K and log emission measure between 44.6 and 46.7 cm^(-3)
for data sets taken from 22:56:57 UT of June 25 to 09:00 UT of June
26. Furthermore, the occurrence of a C1-class flare at the top of the
flare loops increased the plasma temperature from 5.5 x 10^6 K to 6.6
x 10^6 K at 06:57:11 UT. The loops top was much brighter than the legs
and footpoints, with delta_T was about 0.1 x 10^6 K.
Title: Study of Active Region Magnetic Field Structures Using VLA
Radio, YOHKOH X-ray and MEES Optical Observations
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
Bibcode: 1994kofu.symp..347G
Altcode:
We report on the observation of compact magnetic flux tubes from the
boundary between the umbra and penumbra of a large sunspot in AR 7135
on April 24, 1992. The structure and geometry of one such flux tube
was determined using the coordinated observations obtained by the
Very Large Array, the Yohkoh Soft X-ray Telescope and the Mees Solar
Observatory. From radio observations we infer that the magnetic field
of the flux tube at the spot-side footpoint is ~ 1300-1800 G.
Title: Imaging Spectroscopy of Solar Microwave Radiation. I. Flaring
Emission
Authors: Lim, Jeremy; Gary, Dale E.; Hurford, Gordon J.; Lemen,
James R.
Bibcode: 1994ApJ...430..425L
Altcode:
We present observations of an impulsive microwave burst on the
Sun with both high spatial and spectral resolution, made with the
Solar Array at the Owens Valley Radio Observatory (OVRO). We used
the measured brightness temperature spectrum to infer the emission
process responsible for each microwave source, and to derive physical
conditions in the source region. We confimed our predictions using
soft X-ray measurements from Geostationary Operational Environmental
Satellite (GOES), soft X-ray images from Yohkoh, and H-alpha flare
images together with sunspots and magnetogram images from the Big Bear
Solar Observatory.
Title: Morphology of Active Region Transient Brightenings with the
YOHKOH Soft X-Ray Telescope
Authors: Shimizu, Toshifumi; Tsuneta, Saku; Acton, Loren W.; Lemen,
James R.; Ogawara, Yoshiaki; Uchida, Yutaka
Bibcode: 1994ApJ...422..906S
Altcode:
Frequent transient X-ray brightenings occur in solar active regions. The
Yohkoh Soft X-ray Telescope observed 142 transient brightenings
during an interval of time in late 1991 October. We classify them
in terms of morphology and time evolution: (1) simultaneous multiple
loop brightenings are more often seen than brightenings of single and
pointlike structures; (2) for multiple-loop brightenings, the loops
tend to brighten from their footpoints and/or the apparent contact
point in the initial phase of transient brightenings, followed by
the brightening of the entire loops; (3) more than one-half of the
multiple-loop brightenings have Y-type configurations in which the
apparent contact points are located close to their footpoints. Though
transient brightenings show great variety in morphology, these
results suggest that most of them are due to the magnetic interaction
of multiple loops. X-ray emission from the footpoints in the early
phase suggests that the hot plasma in the brightening loops comes from
chromospheric matter or low-temperature coronal matter present around
the bases of the coronal loops prior to the brightening. Enhanced X-ray
emission at the contact points implies local plasma heating by magnetic
interaction. The predominance of the Y-type configuration suggests that
the interaction of coronal loops tends to occur near the footpoints.
Title: Soft X-Ray Line Profiles Predicted by the Jet Model of
Chromospheric Evaporation
Authors: Bornmann, P. L.; Lemen, J. R.
Bibcode: 1994xspy.conf..265B
Altcode:
No abstract at ADS
Title: Eclipses of the solar X-ray corona by Mercury and the Moon.
Authors: Hudson, H.; Freeland, S.; Lemen, J.; Kosugi, T.; Soma, M.;
Watanabe, T.; Hara, H.; Shimizu, T.
Bibcode: 1994BAAS...26..795H
Altcode:
No abstract at ADS
Title: Interplanetary Consequences of Transient Coronal Events
Authors: Watanabe, Ta.; Kojima, M.; Kozuka, Y.; Tsuneta, S.; Lemen,
J. R.; Hudson, H.; Joselyn, J. A.; Klimchuk, J. A.
Bibcode: 1994xspy.conf..207W
Altcode:
No abstract at ADS
Title: Dynamics of a Low Energetic Solar Flare
Authors: Doyle, J. G.; Fludra, A.; Bentley, R. D.; Culhane, J. L.;
Metcalf, T.; Lemen, J. R.; Kosugi, T.
Bibcode: 1994ASPC...64..402D
Altcode: 1994csss....8..402D
No abstract at ADS
Title: Temperature of Coronal Holes Measured by YOHKOH SXT
Authors: Hara, H.; Tsuneta, S.; Acton, L. W.; Lemen, J. R.; Ogawara, Y.
Bibcode: 1994xspy.conf..217H
Altcode:
No abstract at ADS
Title: Temperature and Density Structure of a Solar Flare Observed
by the YOHKOH SXT and HXT
Authors: McTiernan, J.; Kane, S.; Loran, J.; Lemen, J.; Acton, L.;
Hara, H.; Tsuneta, S.; Kosugi, T.
Bibcode: 1994xspy.conf..255M
Altcode:
No abstract at ADS
Title: Morphological Evolution of the Post-Flare Loops of June
25-26, 1992
Authors: Anwar, B.; Hiei, E.; Hudson, H. S.; Acton, L. W.; Metacalf,
T.; Lemen, J.; Martens, P.
Bibcode: 1994xspy.conf..121A
Altcode:
No abstract at ADS
Title: Magnetospheres of Solar Active Regions Inferred from
Spectral-Polarization Observations with High Spatial Resolution
Authors: Lang, K. R.; Willson, R. F.; Kile, J. N.; Lemen, J.; Strong,
K. T.; Bogod, V. L.; Gelfreikh, G. B.; Ryabov, B. I.; Hafizov, S. R.;
Abramov, V. E.; Svetkov, S. V.
Bibcode: 1993ApJ...419..398L
Altcode:
The strong magnetic fields of active regions organize both the plasma
structures and energy processes in the chromosphere and corona. Recent
radio observations with high spatial resolution permit measurements
of the magnetic fields in these regions and also localize regions of
thermal and nonthermal energy release. They can additionally be used
to determine temperatures and electron densities in these regions. The
results of such diagnostics suggest the term magnetosphere for the
space surrounding an active region in the solar atmosphere where
the basic structures and physical processes are controlled by the
magnetic fields/electric currents of the particular region. The
physical parameters of quiescent, or nonflaring, structures in the
low solar corona and upper chromosphere have been inferred from
nearly simultaneous spectral polarization observations (RATAN 600)
and high-spatial-resolution radio observations (VLA). They have been
compared with images from the Soft X-ray Telescope (SXT) aboard the
Yohkoh satellite, indicating that bright radio (20 cm) and X-ray
structures coincide, but that there is radio emission that is not
detectable at X-ray wavelengths. Variable soft X-ray emission on
time scales of hours suggests continued, varying, low-level heating
or particle acceleration in localized areas of active regions. The
RATAN-600 observations have been combined with the theory of thermal
cyclotron emission to infer magnetic field strengths in the low corona
above practically all large sunspots with an accuracy of 2 or 3 %. They
indicate that the magnetic field strength of the thermal plasma
at the million-degree level above large sunspots is 75%-80% of the
magnetic field strength in the underlying photospheric sunspots. The
evolution of the magnetic structures is specified. Coronal potential
field extrapolations are also provided, suggesting that the magnetic
fields in the corona diverge more slowly than expected from a simple
dipole located below the surface. Theoretical models are compared with
multiple-wavelength VLA observations and potential field extrapolations,
indicating that the radio emission from one active region can be
explained by thermal gyroresonance radiation in a conductive flux
model. However, the high brightness temperature and steep spectrum
of the radio emission of another active region cannot be explained
by conventional thermal models, and instead suggest long-lasting
nonthermal heating in localized coronal sources above the magnetic
neutral line in the underlying photosphere Gyrosynchrotron radiation of
nonthermal electrons cannot explain the observations of one such source,
but heating within a localized neutral current sheet might account for
them. Long-lasting radio sources with high brightness temperatures ≥
107 K and steep radiation spectra are often associated with
active regions with a multipolar δ configuration of the photospheric
sunspots. These "peculiar" coronal radio sources appear above the
magnetic neutral line in the photosphere, and appear to require nearly
continuous acceleration of energetic nonthermal electrons by a yet
unknown process.
Title: Performance of back-illuminated Tektronix CCDs in the extreme
ultraviolet
Authors: Moses, John D.; Howard, Russell A.; Wang, Dennis; Catura,
Richard C.; Lemen, J. R.; Shing, Lawrence; Stern, Robert A.; Hochedez,
Jean-Francois E.; Delaboudiniere, Jean-Pierre
Bibcode: 1993SPIE.2006..252M
Altcode:
The quantum efficiency (QE) and flat field characteristics of
back-illuminated 1024 X 1024 Tektronix CCDs have been measured in the
extreme ultraviolet (EUV) between 44 and 1216 angstroms. These CCDs have
been fabricated for the focal plane detector of the Extreme-ultraviolet
Imaging Telescope (EIT) on the Solar and Heliospheric Observing
spacecraft. The back-side surface of the EIT CCDs have been specially
processed to enhance and stabilize the EUV QE. All requirements for
QE are met by these devices, although a poorly understood variation
of QE with temperature will complicate data analysis.
Title: Temperature and Density Structure of the 1991 November 2 Flare
Observed by the YOHKOH Soft X-Ray Telescope and Hard X-Ray Telescope
Authors: McTiernan, James M.; Kane, Sharad R.; Loran, Jon M.; Lemen,
James R.; Acton, Loren W.; Hara, Hirohisa; Tsuneta, Saku; Kosugi, Takeo
Bibcode: 1993ApJ...416L..91M
Altcode:
No abstract at ADS
Title: Spatial and spectral characteristics of the X-ray sources in
the 15 November 1991 solar flare
Authors: Kane, S. R.; McTiernan, J. M.; Loran, J.; Lemen, J.;
Yoshimori, M.; Ohki, K.; Kosugi, T.
Bibcode: 1993AdSpR..13i.237K
Altcode: 1993AdSpR..13..237K
Since the experiment turn-on in October 1991, many flares have been
observed with instruments aboard the Yohkoh satellite. The flare on 15
November 1991 (2238 UT) is of particular interest because, in addition
to Yohkoh, it was observed also by hard X-ray/gamma-ray spectrometers
aboard Ulysses, Pioneer Venus Orbiter, and Compton Observatory/GRO
spacecraft. We present preliminary results obtained from an analysis
of the spatial and spectral parameters for the soft X-ray source and
the spectrum and directivity of the hard X-ray source.
Title: Imaging Spectroscopy of a Solar Microwave Flare
Authors: Lim, J.; Gary, D. E.; Hurford, G. J.; Lemen, J. R.
Bibcode: 1993BAAS...25.1198L
Altcode:
No abstract at ADS
Title: CoMStOC'92: Coronal-Plasma Conditions Derived from Yohkoh-SXT
Observations on 1-2 May 92
Authors: Lemen, J. R.; Strong, K. T.; Willson, R.; Lang, K.
Bibcode: 1993BAAS...25.1214L
Altcode:
No abstract at ADS
Title: A Study of the Solar Active Regions Using Simultaneous VLA
and Yohkoh Soft X-ray Imaging: CoMStOC `92
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Schmelz, J. T.
Bibcode: 1993BAAS...25R1213G
Altcode:
No abstract at ADS
Title: VLA and Yohkoh Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Lemen, J. R.; Nitta, N.;
Strong, K. T.
Bibcode: 1993BAAS...25.1186G
Altcode:
No abstract at ADS
Title: Is Hydrogen Acting Like a High FIP or a Low FIP Element in
the Solar Corona?
Authors: Schmelz, J. T.; Strong, K. T.; Lemen, J. R.
Bibcode: 1993BAAS...25R1201S
Altcode:
No abstract at ADS
Title: Yohkoh-SXT Observations of AR Brightenings
Authors: Linford, G. A.; Lemen, J. R.; Hudson, H. S.
Bibcode: 1993BAAS...25Q1187L
Altcode:
No abstract at ADS
Title: Temperatures in Flares Determined from Fe XXV Spectra,
Resonance Line Ratios, and GOES X-ray Flux
Authors: Sterling, A. C.; Doschek, G. A.; Pike, C. D.; Hudson, H. S.;
Lemen, J. R.; Zarro, D. M.
Bibcode: 1993BAAS...25.1178S
Altcode:
No abstract at ADS
Title: VLA, OVRO, Yohkoh and Optical Observations During CoMStOC
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.; Lemen, J.;
Strong, K. T.; de La Beaujardiere, J.
Bibcode: 1993BAAS...25.1213S
Altcode:
No abstract at ADS
Title: Multitemperature Observations of an Emerging Flux Region
Authors: Bruner, M. E.; Acton, L. W.; Brown, W. A.; Lemen, J. R.;
Shine, R.; Strong, K. T.; Tarbell, T.; Dulk, G.; Tsuneta, S.; Bastian,
T.; Dame, L.
Bibcode: 1993BAAS...25.1179B
Altcode:
No abstract at ADS
Title: The Yohkoh Software and Database System
Authors: Morrison, M. D.; Freeland, S. L.; Lemen, J. R.; Acton, L. W.;
Bentley, R. D.
Bibcode: 1993BAAS...25R1188M
Altcode:
No abstract at ADS
Title: Observations of an Emerging Flux Region
Authors: Brown, W. A.; Acton, L. W.; Bruner, M. E.; Lemen, J. R.;
Shine, R.; Strong, K. T.; Tarbell, T.; Dulk, G.; Tsuneta, S.; Bastian,
T.; Dame, L.
Bibcode: 1993BAAS...25Q1214B
Altcode:
No abstract at ADS
Title: The Extended and Diffuse X-Ray Corona Observed by Yohkoh-SXT
Authors: Lemen, J. R.; Slater, G. L.; Hudson, H. S.; Acton, L. W.
Bibcode: 1993BAAS...25.1179L
Altcode:
No abstract at ADS
Title: Yohkoh-SXT Observations from the Spartan and Nixt Max91
Campaign
Authors: Morrison, M.; Bruner, M.; Freeland, S.; Lemen, J.; Linford,
G.; Nitta, N.; Slater, G.; Strong, K.; Hara, H.; Kano, R.; Shimizu,
T.; Tsuneta, S.; Hudson, H.; Ogawara, Y.; Kosugi, T.; Sakao, T.;
Watanabe, T.; Takeda, A.; Acton, L.
Bibcode: 1993BAAS...25.1213M
Altcode:
No abstract at ADS
Title: Dynamics of the Solar Corona Observed with the YOHKOH Soft
X-ray Telescope
Authors: Tsuneta, S.; Lemen, J. R.
Bibcode: 1993ASSL..183..113T
Altcode: 1993pssc.symp..113T
No abstract at ADS
Title: Solar corona synoptic observations from SOHO with an Extreme
Ultraviolet Imaging Telescope.
Authors: Delaboudinière, J. P.; Gabriel, A. H.; Artzner, G. E.;
Dere, K.; Howard, R.; Michels, D.; Catura, R.; Lemen, J.; Stern, R.;
Gurman, J.; Neupert, W.; Cugnon, P.; Koeckelenbergh, A.; van Dessel,
E. L.; Jamar, C.; Maucherat, A.
Bibcode: 1992ESASP.348...21D
Altcode: 1992cscl.work...21D
The major scientific objective of the EUV Imaging Telescope (EIT)
is to study the evolution of coronal structure over a wide range
of spatial and temporal scales and temperatures. A second strategic
objective is to provide full disk synoptic maps of the global corona
to aid in unifying SOHO (Solar and Heliospheric Observatory)/Cluster
investigations. EIT will also provide images to support the planning
of detailed spectroscopic investigations by the CDS (Coronal Diagnostic
Spectrometer) and SUMER spectrometers in SOHO. EIT observations will be
made in four narrow spectral bands, centered at 171 A (Fe 9), 195 A(Fe
12), 284 A (Fe 15), and 304 A (He 2) representing restricted temperature
domains within a wide temperature range from 40,000 to 3,000,000
K. The results will be images of the solar atmosphere from the upper
chromosphere and transition region to the active region corona. These
maps, made at appropriate time intervals, will be used to study the fine
structures in the solar corona and to relate their dynamic properties
to the underlying chromosphere and photosphere. Dynamic events in the
inner corona will be related to white light transients in the outer
corona, and observations of the internal structure of coronal holes
will be used to investigate origins of the solar wind.
Title: The Morphology of 20times 10(6) K Plasma in Large Non-Impulsive
Solar Flares
Authors: Acton, Loren W.; Feldman, Uri; Bruner, Marilyn E.; Doschek,
George A.; Hirayama, Tadashi; Hudson, Hugh S.; Lemen, James R.;
Ogawara, Yoshiaki; Strong, Keith T.; Tsuneta, Saku
Bibcode: 1992PASJ...44L..71A
Altcode:
We have examined images of 10 flares observed by the Soft X-ray
Telescope on-board the Yohkoh spacecraft. These images show that the
hottest portion of the soft X-ray flare is located in compact regions
that appear to be situated at the tops of loops. These compact regions
form at, or shortly after, flare onset, and persist well into the decay
phase of the flares. In some cases, the compact regions are only a
few thousand kilometers in size and are small compared to the lengths
of flaring loops. This is inconsistent with the smoother intensity
distribution along the loops expected from models of chromospheric
evaporation.
Title: Thickness Variations along Coronal Loops Observed by the Soft
X-Ray Telescope on YOHKOH
Authors: Klimchuk, James A.; Lemen, James R.; Feldman, Uri; Tsuneta,
Saku; Uchida, Yutaka
Bibcode: 1992PASJ...44L.181K
Altcode:
It has been suggested that observed coronal loops have constant
thicknesses. However, if plasma loops coincide with magnetic loops,
then we might expect many loops to be significantly broader at their
tops than at their footpoints (since, on average, magnetic fields
must diverge with height in the solar corona). It is important to
understand how the thicknesses of loops vary along their lengths, since
such a variation is related to the distribution of electric currents
in the corona and is therefore relevant to solar flares and coronal
heating. We here present preliminary results of our investigation of
thickness variations along coronal loops observed with the Soft X-ray
Telescope (SXT) on board the Yohkoh satellite.
Title: The Status of YOHKOH in Orbit: an Introduction to the Initial
Scientific Results
Authors: Ogawara, Yoshiaki; Acton, Loren W.; Bentley, Robert D.;
Bruner, Marilyn E.; Culhane, J. Leonard; Hiei, Eijiro; Hirayama,
Tadashi; Hudson, Hugh S.; Kosugi, Takeo; Lemen, James R.; Strong, Keith
T.; Tsuneta, Saku; Uchida, Yutaka; Watanabe, Tetsuya; Yoshimori, Masato
Bibcode: 1992PASJ...44L..41O
Altcode:
In this introductory article accompanying the initial scientific
papers from the Yohkoh mission, we briefly summarize the design
and in-orbit function of the spacecraft and its four scientific
instruments. Although these initial results include mainly studies
based upon individual Yohkoh experiments at this early stage, there
are also analyses of combined data sets provided by several on-board
and ground-based instruments in progress. The results presented here,
and anticipated future results, suggest that the Yohkoh observations
with their comprehensive coverage of solar high-energy phenomena will
come to represent a significant milestone in the progress of solar
physics. This will be true not only regarding flares, but also for
fainter coronal structures and even coronal holes.
Title: The YOHKOH mission for high-energy solar physics
Authors: Acton, L.; Tsuneta, S.; Ogawara, Y.; Bentley, R.; Bruner, M.;
Canfield, R.; Culhane, L.; Doschek, G.; Hiei, E.; Hirayama, T. Hudson,
H.; Kosugi, T.; Lang, J.; Lemen, J.; Nishimura, J.; Makishima, K.;
Uchida, Y.; Watanabe, T.
Bibcode: 1992Sci...258..618A
Altcode: 1992Sci...258..591A
Data on solar flare mechanisms and the sun's corona will be generated
by Japan's Yohkoh satellite's X-ray imaging sensors and X-ray and
gamma-ray spectrometers. It is noted that the X-ray corona above active
regions expands, in some cases almost continually, in contradiction of
the widely accepted model of magnetohydrostatic equilibrium in such
regions. Flaring X-ray bright points have been discovered to often
involve ejecta into an adjacent, much larger and fainter magnetic loop,
which brightens along its length at speeds up to 1000 km/sec.
Title: High-Temperature Plasmas in Active Regions Observed with the
Soft X-Ray Telescope aboard YOHKOH
Authors: Hara, Hirohisa; Tsuneta, Saku; Lemen, James R.; Acton,
Loren W.; McTiernan, James M.
Bibcode: 1992PASJ...44L.135H
Altcode:
High-temperature plasmas reaching 5--6times 10(6) K in solar
active regions have been found with the soft X-ray telescope aboard
Yohkoh. NOAA region 6919 was investigated in detail using five different
X-ray filters: The temperature of a bright loop in the active region
is 5.7times 10(6) K, with an emission measure of 5.0times 10(28)
cm(-5) ; in a fainter part of the region plasma, we find 5.0times
10(6) \ K and 4.0times 10(27) cm(-5) . This indicates that such
high-temperature plasmas exist in the active region, irrespective of
the brightness. Another observation of the quiet corona was conducted in
order to investigate the reliability of a temperature analysis with the
same filter pairs which show such high temperatures in active regions:
The inferred temperature was 2.7times 10(6) K, and the emission measure
1.3times 10(26) cm(-5) , which is consistent with the typical results
of Skylab. Therefore, the high-temperature plasmas in solar active
regions are considered to be real.
Title: Transient Brightenings in Active Regions Observed by the Soft
X-Ray Telescope on YOHKOH
Authors: Shimizu, Toshifumi; Tsuneta, Saku; Acton, Loren W.; Lemen,
James R.; Uchida, Yutaka
Bibcode: 1992PASJ...44L.147S
Altcode:
The Soft X-ray Telescope (SXT) aboard the Yohkoh satellite has revealed
that active regions show many compact loop brightenings which we call
``active-region transient brightenings.'' The released energy by an
``active-region transient brightening'' is considerably less than
10(29) erg, which is the low end of the subflare energy range. Small
soft X-ray enhancements observed by the GOES satellites are identified
to relatively intense ``active-region transient brightenings.'' The
transient brightening occurs on the average of one every ~ 3 min in
``active'' active regions and down to one every ~ 1 hr in ``quieter''
active regions. This suggests that the transient brightening is a
very common phenomenon in active regions and that the magnetic loops
in active regions are far from static.
Title: Early Results from the YOHKOH Soft X-ray Telescope
Authors: Bruner, M. E.; Acton, L. W.; Lemen, J.; Hirayama, T.;
Tsuneta, S.
Bibcode: 1992AAS...180.2301B
Altcode: 1992BAAS...24..759B
The The Soft X-ray Telescope on the Yohkoh satellite, launched by
Japan on August 30, 1992, has proved to be a resounding success. It
is providing a wealth of new information and many surprises, both on
flares and on the behavior of the solar corona. Performance of the
telescope has met or exceed our most optimistic expectations and
it appears to be in perfect focus. Unlike the Skylab instruments,
the Yohkoh telescope is not limited by a finite supply of film,
permitting long sequences of images to be made with relatively high
time resolution. Repetition rates for a given exposure / filter
combination are typically a few seconds per frame to a few minutes
per frame, depending on the selected field size. Movies assembled from
long exposure sequences have shown the corona to be even more dynamic
than expected. Major re-structuring, involving large fractions of the
visible corona, can take place in an hour or two. Smaller regions are
even more dynamic, changing almost continuously. Movies, created from
long exposure sequences, have demonstrated the fundamental importance of
large-scale coronal loops in connecting widely separated regions such
that activity in one region quickly affects the physical conditions
at remote sites. The images also show that the majority of the loops
have nearly constant cross sections along their lengths, rather than
one that increases with height. Several X-class flares have been
observed; the surprising result is that they do not appear to be very
dynamic in soft X-rays. The flare kernels seem to consist of compact
loop structures that brighten and then fade without changing size or
shape. Bright points are not as prominent as in the Skylab images;
a result of using a CCD (a linear detector) rather than film which has
a logarithmic response. The other instruments on Yohkoh are producing
equally exciting results; it seems clear that the Yohkoh mission will
produce many major advances in our knowledge of the flare mechanism.
Title: Thickness Variations Along Coronal Loops Observed by Yohkoh
Authors: Klimchuk, J. A.; Kluge, K.; Lemen, J. R.; Feldman, U.;
Uchida, Y.
Bibcode: 1992AAS...180.2304K
Altcode: 1992BAAS...24Q.760K
No abstract at ADS
Title: Temperature Structure of Solar Flares Observed by the
YOHKOH SXT
Authors: McTiernan, J. M.; Kane, S. R.; Loran, J. M.; Lemen, J. R.;
Acton, L. W.; Hara, H.; Tsuneta, S.
Bibcode: 1992AAS...180.3002M
Altcode: 1992BAAS...24Q.775M
Hot plasmas from several solar flares have been observed by the Soft
X-ray Telescope (SXT) on board the Yohkoh satellite. For a sample of
flares observed by the SXT with a variety of X-ray filters, we have
calculated temperature and emission measures as functions of space and
time. Initial results from this analysis show the following: (1) The
flare plasmas range in temperarure from several million degrees K up to
greater than 20 million degrees K, depending on the individual event;
(2) The region with the higest temperature does not coincide with
the brightest region. For example, for the flare of 15 November 1991
(2238 UT) the temperature was typically 8-9 million degrees K on the
bright kernels, with temperatures of 15-25 million degrees K on the
edges of the bright regions. The average temperature for the flare was
approximately 10 million degrees K. A preliminary interpretation of
these observational results in terms of the temperature and density
structure inside a magnetic loop will be presented.
Title: Fluid Flow in a Jet and the Caxix Line Profiles Observed
during Solar Flares
Authors: Bornmann, P. L.; Lemen, J. R.
Bibcode: 1992LNP...399..105B
Altcode: 1992esf..coll..105B; 1992IAUCo.133..105B
No abstract at ADS
Title: Fluid Flow in a Jet and the CA XIX Line Profiles Observed
during Solar Flares
Authors: Bornmann, P. L.; Lemen, J. R.
Bibcode: 1992ApJ...385..363B
Altcode:
The present study considers two types of fluid models as methods for
reproducing the blueshifts and line broadening observed in soft X-ray
lines during the rise of solar flares. The fluid models representing
the laminar flow of material in a jet and through a pipe were used
to derive the velocity at each location in the flow. The optimal
values for the free parameters in the jet model were within the
ranges expected for solar flare conditions. The jet was much smaller
than typical flare volumes estimated from spatial images, but the
resulting densities were consistent with the upper limit of densities
derived using density-sensitive line ratios. This supports previous
reports of small filling factors and is interpreted as evidence for a
chromospheric origin for the flow. Stability analysis indicates that,
although the laminar jet can reproduce the observations, instabilities
may cause the flow to become turbulent, and that this laminar treatment
is not strictly valid.
Title: The Soft X-ray Telescope for the SOLAR-A mission
Authors: Tsuneta, S.; Acton, L.; Bruner, M.; Lemen, J.; Brown, W.;
Caravalho, R.; Catura, R.; Freeland, S.; Jurcevich, B.; Morrison,
M.; Ogawara, Y.; Hirayama, T.; Owens, J.
Bibcode: 1991SoPh..136...37T
Altcode:
The Soft X-ray Telescope (SXT) of the SOLAR-A mission is designed
to produce X-ray movies of flares with excellent angular and time
resolution as well as full-disk X-ray images for general studies. A
selection of thin metal filters provide a measure of temperature
discrimination and aid in obtaining the wide dynamic range required for
solar observing. The co-aligned SXT aspect telescope will yield optical
images for aspect reference, white-light flare and sunspot studies,
and, possibly, helioseismology. This paper describes the capabilities
and characteristics of the SXT for scientific observing.
Title: SOLAR-A Reformatted Data Files and Observing Log
Authors: Morrison, M. D.; Lemen, J. R.; Acton, L. W.; Bentley, R. D.;
Kosugi, T.; Tsuneta, S.; Ogawara, Y.; Watanabe, T.
Bibcode: 1991SoPh..136..105M
Altcode:
All of the SOLAR-A telemetry data will be reformatted before
distribution to the analysis computers and the various users. This
paper gives an overview of the files which will be created and the
format and organization which the files will use. The organization
has been chosen to be efficient in space, to ease access to the data,
and to allow for the data to be transportable to different machines. An
observing log file will be created automatically using the reformatted
data files as the input. It will be possible to perform searches with
the observing log to list cases where instruments are in certain modes
and/or seeing certain signal levels.
Title: The AXAF Low-Energy Transmission Grating Spectrometer /
LETGS / Diagnostic Capabilities for the Study of Stellar Coronae
Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J.
Bibcode: 1991Ap&SS.182...35M
Altcode:
We study the diagnostic capabilities of the high-resolution,
Low-Energy Transmission Grating Spectrometer, LETGS, of NASA's planned
Advanced X-ray Astrophysics Facility, AXAF, for optically thin stellar
coronae. Spectra are simulated on the basis of isothermal and source
loop models and are analyzed with particular emphasis on the extraction
of the differential emission measure distribution. The AXAF-LETGS is
shown to be particularly sensitive for plasma at temperatures between
0.5 and 15 MK. Emission from temperatures in excess of 20 MK can
be observed, but the lack of strong spectral lines hampers accurate
temperature determinations. We simulate spectra of close binaries to
demonstrate the observability of the Doppler effects associated with
orbital motions. We present lists of spectral lines that can be used
for density diagnostics, and we simulate and compare various spectra
at different electron densities.
Title: Interrelation of Soft and Hard X-Ray Emissions during Solar
Flares. I. Observations
Authors: Winglee, R. M.; Kiplinger, A. L.; Zarro, D. M.; Dulk, G. A.;
Lemen, J. R.
Bibcode: 1991ApJ...375..366W
Altcode:
The interrelation between the acceleration and heating of electrons
and ions during impulsive solar flares is determined on the basis of
simulataneous observations of hard and soft X-ray emission from the
Solar Maximum Mission at high time resolution (6 s). For all the flares,
the hard X-rays are found to have a power-law spectrum which breaks
down during the rise phase and beginning of the decay phase. After
that, the spectrum changes to either a single power law or a power
law that breaks up at high energies. The characteristics of the soft
X-ray are found to depend on the flare position. It is suggested that
small-scale quasi-static electric fields are important for determining
the acceleration of the X-ray-producing electrons and the outflowing
chromospheric ions.
Title: Iron and calcium abundances in solar flares from the
multi-temperature analysis of X-ray spectra
Authors: Fludra, A.; Bentley, R. D.; Culhane, J. L.; Lemen, J. R.;
Sylwester, J.
Bibcode: 1991AdSpR..11a.155F
Altcode: 1991AdSpR..11Q.155F
A generalized method of calculating the distribution of the emission
measure with temperature (DEM) for optically thin plasma has been
developed. The method simultaneously uses line flux ratios in addition
to line fluxes. When a ratio of lines from the same element is used,
the resulting DEM is independent of this element's abundance. The method
has been applied to derive the absolute abundances of iron in solar
flares from X-ray spectra recorded by the Bent Crystal Spectrometer on
SMM. The iron abundances have been found to vary between flares. The
calcium abundances have also been calculated using the same method and
are found to be in close agreement with the values derived from the
line-to-continuum technique (Lemen et al., 1990 and Sylwester et al.,
1990). The variation of iron and calcium abundances is compared. A
correction to the ionization balance for iron is proposed.
Title: A statistical study of high coronal densities from X-ray
line-ratios of Mg XI
Authors: Linford, G. A.; Lemen, J. R.; Strong, K. T.
Bibcode: 1991AdSpR..11a.147L
Altcode: 1991AdSpR..11..147L
We applied an X-ray line-ratio density diagnostic to 50 Mg XI spectra
of flaring active regions on the Sun recorded by the Flat Crystal
Spectrometer on the Solar Maximum Mission. The plasma density is derived
from R, the flux ratio of the forbidden to intercombination lines of the
He-like ion, Mg XI. The R ratio for Mg XI is only density sensitive when
the electron density exceeds a critical value (about 1012
cm-3), the low-density limit (LDL). This theoretical value
of the low-density limit is uncertain as it depends on complex atomic
theory. Reported coronal densities above 1012 cm-3
are uncommon. In this study, we estimate the distribution of R ratio
values about the LDL and derive the empirical values for the 1st and
2nd moments of this distribution from 50 Mg XI spectra. From these
derived parameters we establish the percentage of our observations
which indicated densities above this limit and discuss other aspects
of these observations such as the types of events and the time during
which spectra were obtained (e.g. rise phase or decay).
Title: Simulated SXT Observations of Coronal Loops
Authors: Dixon, W. W.; Klimchuk, J. A.; Sturrock, P. A.; Lemen, J. R.
Bibcode: 1991LNP...387..297D
Altcode: 1991fpsa.conf..297D
We have simulated the appearance of two static coronal loops as they
might be observed by the Soft X-ray Telescope onboard the Solar-A
spacecraft. One loop corresponds to a non-flaring active region loop,
and the other corresponds to a post-flare loop. We find that the
loops have fundamentally different appearances: the quiescent loop is
brightest at its apex, while the hotter post-flare loop is brightest
at, or near, its base (depending on the particular X-ray filter assumed
for the observations).
Title: Abundance variations in solar active regions
Authors: Strong, K. T.; Lemen, J. R.; Linford, G. A.
Bibcode: 1991AdSpR..11a.151S
Altcode: 1991AdSpR..11Q.151S
The diversity in the published values of coronal abundances is
unsettling, especially as the range of results seems to be beyond the
quoted uncertainties. We present measurements of the relative abundance
of iron and neon derived from soft X-ray spectra of active regions. From
a data base of over 200 spectra taken by the Solar Maximum Mission Flat
Crystal Spectrometer, we find that the relative abundance can vary by
as much as a factor of about 7 and can change on timescales of <1 h.
Title: Imaging capabilities of SXT for Solar-A
Authors: Lemen, J. R.; Acton, L. W.; Brown, W. A.; Bruner, M. E.;
Catura, R. C.; Strong, K. T.; Watanabe, T.
Bibcode: 1991AdSpR..11e..69L
Altcode: 1991AdSpR..11...69L
The Soft X-ray Telescope (SXT) is a grazing-incidence solar X-ray
telescope which will be flown on the Japanese Solar-A satellite. The
Solar-A satellite, which is scheduled for launch in 1991, will carry
an ensemble of instruments designed to study the Sun during the next
solar sunspot maximum. The SXT will be the first high-resolution
X-ray telescope since Skylab to be flown on an extended-duration
mission. Measurements have been conducted to determine the focal length,
point spread function, and effective area of the SXT mirror. The results
indicate a half-power diameter of 4.9 arcsec and an effective area
of 1.33 cm2 at 13.3 Å. The mirror achieves high-contrast
imaging with very little X-ray scattering. The telescope fwhm is 3.2
arcsec at 8.32 Å. A coaligned aspect telescope operating at visible
wavelengths will permit imaging of magnetic plage or solar continuum
radiation with the same plate scale as the X-ray images.
Title: Plasma diagnostic capabilities of the Soft X-Ray Telescope
on Solar-A
Authors: Strong, K. T.; Acton, L. W.; Brown, W. A.; Claflin, E. S.;
Lemen, J. R.; Tsuneta, S.
Bibcode: 1991AdSpR..11e..73S
Altcode: 1991AdSpR..11...73S
We present the predicted response of the Solar-A Soft X-Ray Telescope
(SXT) to various solar targets. From prelaunch calibrations of the
SXT flight mirror, X-ray filters, and CCD detector, we are able to
predict exposure times and image cadence for a representative range of
temperatures and emission measures of the coronal plasma. We find that
the SXT is very sensitive; it should be able to observe active regions
and flares at its nominal cadence (2 s) with exposure times ranging
from 0.0001 to 1 s. The SXT temperature diagnostic capabilities are
presented for various combinations of the X-ray filters. SXT data can
be used to reproduce accurately the temperature and emission measure
of an isothermal plasma. However, if there is a wide distribution
of temperatures in a pixel, reconstructing the original differential
emission measure distribution becomes more uncertain.
Title: The Decay Phase of Three Large Solar Flares
Authors: Fludra, A.; Bentley, R. D.; Culhane, J. L.; Jakimiec, J.;
Lemen, J. R.; Sylwester, J.; Moorthy, S. T.
Bibcode: 1990PDHO....7..266F
Altcode: 1990ESPM....6..266F; 1990dysu.conf..266F
No abstract at ADS
Title: Momentum Balance in Four Solar Flares
Authors: Canfield, Richard C.; Zarro, Dominic M.; Metcalf, Thomas R.;
Lemen, James R.
Bibcode: 1990ApJ...348..333C
Altcode:
Solar Maximum Mission soft X-ray spectra and National Solar Observatory
(Sacramento Peak) H-alpha spectra were combined in a study of high-speed
flows during the impulsive phase of four solar flares. In all events,
a blue asymmetry (indicative of upflows) was observed in the coronal Ca
XIX line during the soft X-ray rise phase. In all events a red asymmetry
(indicative of downflows) was observed simultaneously in chromospheric
H-alpha. These oppositely directed flows were concurrent with impulsive
hard X-ray emission. Combining the velocity data with estimates of the
density based on emission measurements and volume estimates, it is shown
that for the impulsive phase as a whole the total momentum of upflowing
soft X-ray plasma equaled that of the downflowing H-alpha plasma, to
within an order of magnitude, in all four events. Only the chromospheric
evaporation model predicts equal total momentum in the upflowing soft
X-ray-emitting and downflowing H-alphba-emitting materials.
Title: Temperatures of coronae of cool stars, derived from EXOSAT
observations
Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J.
Bibcode: 1990AdSpR..10b.129M
Altcode: 1990AdSpR..10..129M
We observed the late-type stars Capella, σ2 CrB, λ And,
AD Leo, GL494, GL569 and Procyon with different combinations of three
instruments aboard EXOSAT : the low-energy channel multiplier array
(LE), the medium-energy proportional counters (ME), and the transmission
grating spectrometer (TGS). We derive crude temperature information on
the coronae of these stars from the photometric data, using one- and
two-temperature models of optically thin, thermal plasmas. We compare
the results with 2-T fits and differential emission measure analyses
of three grating observations and with simulations for mixtures of two
plasma components with varying emission measure ratios. But for Procyon,
all sources have a strong, hot component between 10 and 25 MK. The TGS
spectra of Capella and σ2 CrB reveal a cooler component
with comparable emission measure around 5 MK. The emission from the
corona of Procyon is dominated by a very cool (0.6 MK) component,
with an additional contribution from a 2-3 MK component.
Title: X-Ray calibration of a virtual-phase 1024 X 1024 CCD
Authors: Catura, Richard C.; Lemen, James R.; Morrison, Mons D.;
Windt, David L.; Jordan, W. C.; Acton, Loren W.
Bibcode: 1989SPIE.1159..578C
Altcode:
Results are presented on a calibration with X-rays of a
front-illuminated virtual phase CCD with a 1024 x 1024 pixel array,
performed as a part of the Solar-A preparation, which is a joint
Japanese-U.S.-UK space project scheduled for a launch in August
1991. In the experiment, absolute quantum efficiency (QE) of a virtual
CCD was measured at 14 wavelengths between 5.4 and 67.7 A, and its
flat field responses to the illumination by C-K and Al-K X-rays
were investigated together with its imaging properties in visible
light. Higher than expected QE measurements were obtained at soft X-ray
and EUV wavelengths; these are considered to be caused by fluorescence
occurring in the absorbing layers on the CCD-entrance aperture.
Title: Turbulent and Directed Plasma Motions in Solar Flares
Authors: Fludra, A.; Lemen, J. R.; Jakimiec, J.; Bentley, R. D.;
Sylwester, J.
Bibcode: 1989ApJ...344..991F
Altcode:
An improved method for fitting asymmetric soft X-ray line profiles
from solar flares is presented. A two-component model is used where one
component represents the total emission from directed upflow plasma and
the other the emission from the plasma at rest. Unlike previous methods,
the width of the moving component is independent from that of the
stationary component. Time variations of flare plasma characteristics
(i.e., temperature, emission measure of moving and stationary plasma,
upflow and turbulent velocities) are derived from the Ca XIX and Fe XXV
spectra recorded by the Bent Crystal Spectrometer on the Solar Maximum
Mission. The fitting technique provides a statistical estimation
for the uncertainties in the fitting parameters. The relationship
between the directed and turbulent motions has been studied, and
a correlation of the random and directed motions has been found in
some flares with intensive plasma upflows. Mean temperatures of the
upflowing and stationary plasmas are compared for the first time from
ratios of calcium to iron X-ray line intensities. Finally, evidence
for turbulent motions and the possibility of plasma upflow late into
the decay phase is presented and discussed.
Title: A comparison of theoretical and solar-flare intensity ratios
for the Fe XIX X-ray lines
Authors: Bhatia, A. K.; Fawcett, B. C.; Phillips, K. J. H.; Lemen,
J. R.; Mason, H. E.
Bibcode: 1989MNRAS.240..421B
Altcode:
Atomic data including energy levels, gf-values, and wavelengths are
given for the Fe XIX transitions that give rise to lines in solar-flare
and active-region X-ray spectra. Collision strengths and theoretical
intensity ratios are presented for lines which occur in the 13.2-14.3-A
range. Observed spectra are found to be consistent with those derived
from the present Fe XIX atomic data. For the case of spectra in which
the Fe XIX lines are very strong, such as those at the maxima of hot
flares, two observed line features due to Fe XIX are shown to have
larger intensities than calculated. The calculated Fe XIX and Ne IX line
spectra are used to determine electron densities from Ne IX line ratios.
Title: Extreme ultraviolet imaging telescope on board the Solar
Heliospheric Observatory
Authors: Delaboudiniere, Jean-Pierre; Gabriel, Alan H.; Artzner,
Guy E.; Millier, F.; Michels, Donald J.; Dere, Kenneth P.; Howard,
Russell A.; Kreplin, Robert W.; Catura, Richard C.; Stern, Robert A.;
Lemen, James R.; Neupert, Werner M.; Gurman, Joseph B.; Cugnon, P.;
Koeckelenbergh, A.; van Dessel, E. L.; Jamar, Claude A.; Maucherat,
Andre J.; Chauvineau, Jean-Pierre; Marioge, Jean-Paul
Bibcode: 1989SPIE.1160..518D
Altcode: 1989xeoa.conf..518D
The design of the multibandpass Extreme-Ultraviolet Imaging Telescope
designed for 1996 launch on board the Solar Heliospheric Observatory
is described. The telescope will observe simultaneously distinct
temperature ranges in the solar corona, defined by well chosen emission
lines. Images in four narrow bandpasses at wavelengths ranging from 17
to 31 nm will be obtained using normal-incidence multilayered optics
deposited on quadrants of a Ritchey-Chretien telescope. Results are
presented on the performances measured on a 2/3 scale mock-up. The
bandpasses could be adjusted to better than 1 percent in wavelength.
Title: Measurement of the point spread function and effective area
of the Solar-A soft x-ray telescope mirror
Authors: Lemen, James R.; Claflin, E. S.; Brown, William A.; Bruner,
Marilyn E.; Catura, Richard C.; Morrison, Mons D.
Bibcode: 1989SPIE.1160..316L
Altcode: 1989xeoa.conf..316L
A grazing incidence solar X-ray telescope, Soft X-ray Telescope (SXT),
will be flown on the Solar-A satellite in 1991. Measurements have been
conducted to determine the focal length, Point Spread Function (PSF),
and effective area of the SXT mirror. The measurements were made
with pinholes, knife edges, a CCD, and a proportional counter. The
results show the 1/r character of the PSF, and indicate a half power
diameter of 4.9 arcsec and an effective area of 1.33 sq cm at 13.3 A
(0.93 keV). The mirror was found to provide a high contrast image with
very little X-ray scattering.
Title: Optical performance versus prediction analysis for the soft
x-ray telescope mirror assembly at x-ray wavelengths
Authors: Hull-Allen, C. G.; Jordan, David C.; Kumler, James J.;
Slomba, Albert F.; Kusha, Ray G.; Glenn, Paul E.; Lemen, James R.;
Catura, Richard C.
Bibcode: 1989SPIE.1160..409H
Altcode: 1989xeoa.conf..409H
Accurate prediction of focal plane performance is difficult at X-ray
wavelengths for grazing incidence optical systems with very highly
obscured apertures like the SXT mirror assembly. This paper describes a
modeling approach that was used to set telescope surface specifications
in order to achieve a desired encircled energy and spot size at an
operating wavelength of 13.3 A. Assumptions that were made before
fabrication will be presented first. Next, performance predicted by
replacing many of these assumptions with actual parameters obtained
from measurement of the as-built surfaces was compared to test data
taken in the NASA/Marshall X-ray testing facility. Finally, an estimate
was made of the rms spot size, from knife edge data. This is discussed
in terms of its usefulness as a descriptor of telescope performance.
Title: Coronal Activity in F-, G-, and K-Type Stars. III. The
Coronal Differential Emission Measure Distribution of Capella,
sigma 2 Coronae Borealis, and Procyon
Authors: Lemen, J. R.; Mewe, R.; Schrijver, C. J.; Fludra, A.
Bibcode: 1989ApJ...341..474L
Altcode:
EXOSAT soft X-ray spectra of three binary systems of cool stars
are analyzed: Capella (G6 III + F9 III), Sigma-squared CrB (F8 V +
G1 V), and Procyon (F5 IV-V + DF). The EXOSAT transmission grating
spectrometer permits the study of individual spectral lines and line
complexes between 10 and 200 A with approximately 3 A resolution. First
it is demonstrated that the spectra can be described reasonably well
by a two-temperature model corona. Then the assumption that only two
temperatures exist in the stellar coronas is relaxed and differential
emission measure distributions are derived from the three spectra. The
results from the multithermal modeling are consistent with those of
the two-temperature models: emission from the coronas of each of the
three stars is dominated by plasma in two relative narrow temperature
intervals. These intervals are centered on 5 MK and 25 MK in the cases
of Capella and Sigma-squared CrB, and 0.6 MK and 3 MK in the case of
Procyon. The implications of the results for the structure of stellar
coronas are briefly discussed.
Title: Coronal Activity in F-, G-, and K-Type Stars. IV. Evidence
for Expanding Loop Geometries in Stellar Coronae
Authors: Schrijver, C. J.; Lemen, J. R.; Mewe, R.
Bibcode: 1989ApJ...341..484S
Altcode:
A detailed analysis is presented of X-ray spectra of Capella and of
Sigma2 CrB. The spectra of both stars are compatible with coronae
consisting of two different ensembles of static loops with different
maximum temperatures and ratios of the cross sectional areas at the
loop top and at the footpoint. The cool (5 MK) loop components in both
stars show evidence of relatively strong expansion with height. The hot
(30 MK) components appear to expand much less.
Title: The Soft X-ray Telescope for SOLAR-A
Authors: Brown, W. A.; Acton, L. W.; Bruner, M. E.; Lemen, J. R.;
Strong, K. T.
Bibcode: 1989BAAS...21..862B
Altcode:
No abstract at ADS
Title: A Solar Flare Observed with the SMM and Einstein Satellites
Authors: Schmitt, J. H. M. M.; Lemen, J. R.; Zarro, D.
Bibcode: 1989SoPh..121..361S
Altcode: 1989IAUCo.104..361S
We present X-ray observations of the 21 July, 1980 flare which was
observed both with the Einstein Observatory Imaging Proportional Counter
(IPC) and the X-Ray Polychromator (XRP) and Gamma-Ray Spectrometer
onboard the SMM satellite. The Einstein observations were obtained
in scattered X-ray light, i.e., in X-rays scattered off the Earth's
atmosphere. In this way it is possible to obtain spatially unresolved
X-ray data of a solar flare with the same instrument that observed
many X-ray flares on other stars. This paper juxtaposes the results and
implications of the `stellar interpretation' to those obtained from the
far more detailed SMM observations. The result of this `calibration'
observation is that the basic properties of the flaring plasma can
be reliably determined from the `stellar' data, however, the basic
physics issues can only be studied through models.
Title: Coronal Abundances and Their Variations
Authors: Strong, K. T.; Lemen, J. R.; Linford, G. A.; Waljeski, K.
Bibcode: 1989BAAS...21..833S
Altcode:
No abstract at ADS
Title: The soft X ray telescope for Solar-A
Authors: Brown, W. A.; Acton, L. W.; Bruner, M. E.; Lemen, J. R.;
Strong, K. T.
Bibcode: 1989dots.work..158B
Altcode:
The Solar-A satellite being prepared by the Institute for Sapce and
Astronautical Sciences (ISAS) in Japan is dedicated to high energy
observations of solar flares. The Soft X Ray Telescope (SXT) is being
prepared to provide filtered images in the 2 to 60 A interval. The
flight model is now undergoing tests in the 1000 foot tunnel at
MSFC. Launch will be in September 1991. Earlier resolution and
efficiency tests on the grazing incidence mirror have established its
performance in soft x rays. The one-piece, two mirror grazing incidence
telescope is supported in a strain free mount separated from the focal
plane assembly by a carbon-epoxy metering tube whose windings and
filler are chosen to minimize thermal and hygroscopic effects. The
CCD detector images both the x ray and the concentric visible light
aspect telescope. Optical filters provide images at 4308 and 4700
A. The SXT will be capable of producing over 8000 of the smallest
partial frame images per day, or fewer but larger images, up to 1024 x
1024 pixel images. Image sequence with two or more of the five x ray
analysis filters, with automatic exposure compensation to optimize
the charge collection by the CCD detector, will be used to provide
plasma diagnostics. Calculations using a differential emission measure
code were used to optimize filter selection over the range of emission
measure variations and to avoid redundancy, but the filters were chosen
primarily to give ratios that are monotonic in plasma temperature.
Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veck, N. J.
Bibcode: 1989epos.conf..377W
Altcode:
The authors have sought to establish a comprehensive and self-consistent
picture of the sources and transport of energy within a flare. To
achieve this goal, they chose five flares in 1980 that were well
observed with instruments on the Solar Maximum Mission, and with other
space-borne and ground-based instruments. The events were chosen to
represent various types of flares. Details of the observations available
for them and the corresponding physical parameters derived from these
data are presented. The flares were studied from two perspectives,
the impulsive and gradual phases, and then the results were compared
to obtain the overall picture of the energetics of these flares. The
authors also discuss the role that modeling can play in estimating the
total energy of a flare when the observationally determined parameters
are used as the input to a numerical model. Finally, a critique of
our current understanding of flare energetics and the methods used to
determine various energetics terms is outlined, and possible future
directions of research in this area are suggested.
Title: EIT: Solar corona synoptic observations from SOHO with an
Extreme-ultraviolet Imaging Telescope
Authors: Delaboudiniere, J. P.; Gabriel, A. H.; Artzner, G. E.;
Michels, D. J.; Dere, K. P.; Howard, R. A.; Catura, R.; Stern, R.;
Lemen, J.; Neupert, W.
Bibcode: 1988sohi.rept...43D
Altcode:
The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and
heliospheric observatory) will provide full disk images in emission
lines formed at temperatures that map solar structures ranging from
the chromospheric network to the hot magnetically confined plasma in
the corona. Images in four narrow bandpasses will be obtained using
normal incidence multilayered optics deposited on quadrants of a
Ritchey-Chretien telescope. The EIT is capable of providing a uniform
one arc second resolution over its entire 50 by 50 arc min field of
view. Data from the EIT will be extremely valuable for identifying
and interpreting the spatial and temperature fine structures of the
solar atmosphere. Temporal analysis will provide information on the
stability of these structures and identify dynamical processes. EIT
images, issued daily, will provide the global corona context for aid
in unifying the investigations and in forming the observing plans for
SOHO coronal instruments.
Title: Conduction-driven Chromospheric Evaporation in a Solar Flare
Authors: Zarro, Dominic M.; Lemen, James R.
Bibcode: 1988ApJ...329..456Z
Altcode:
Observations of gentle chromospheric evaporation during the
cooling phase of a solar flare are presented. Line profiles of the
low-temperature (T of about 6 x 10 to the 6th K) coronal Mg XI line,
observed with the X-Ray Polychromator on the Solar Maximum Mission,
show a blueshift that persisted for several minutes after the
impulsive heating phase. This result represents the first detection
of an evaporation signature in a soft X-ray line formed at this low
temperature. By combining the Mg XI blueshift velocity data with
simultaneous measurements of the flare temperature derived from Ca
XIX observations, it is demonstrated that the upward flux of enthalpy
transported by this gently evaporating plasma varies linearly with
the downward flux of thermal energy conducted from the corona. This
relationship is consistent with models of solar flares in which thermal
conduction drives chromospheric evaporation during the early part of
the cooling phase.
Title: SMM X-ray polychromator
Authors: Strong, Keith T.; Haisch, Bernhard M.; Lemen, James R.;
Acton, L. W.; Bawa, H. S.; Claflin, E. S.; Freeland, S. L.; Slater,
G. L.; Kemp, D. L.; Linford, G. A.
Bibcode: 1988lock.reptR....S
Altcode:
The range of observing and analysis programs accomplished with the
X-Ray Polychromator (XRP) instruments during the decline of solar
cycle 21 and the rise of the solar cycle 22 is summarized. Section
2 describes XRP operations and current status. This is meant as
a guide on how the instrument is used to obtain data and what its
capabilities are for potential users. The science section contains
a series of representative abstracts from recently published papers
on major XRP science topics. It is not meant to be a complete list
but illustrates the type of science that can come from the analysis
of the XRP data. There then follows a series of appendixes that
summarize the major data bases that are available. Appendix A is a
complete bibliography of papers and presentations produced using XRP
data. Appendix B lists all the spectroscopic data accumulated by the
Flat Crystal Spectrometer (FCS). Appendix C is a compilation of the
XRP flare catalogue for events equivalent to a GOES C-level flare or
greater. It lists the start, peak and end times as well as the peak
Ca XIX flux.
Title: Momentum Balance in Four Solar Flares
Authors: Canfield, R. C.; Zarro, D. M.; Metcalf, T. R.; Lemen, J. R.
Bibcode: 1988BAAS...20..688C
Altcode:
No abstract at ADS
Title: Time variations of the calcium elemental abundance in flares
from NOAA active regions 2562 and 2779.
Authors: Sylwester, J.; Zolcinski-Couet, M. -C.; Bentley, R. D.;
Lemen, J. R.
Bibcode: 1988JPhys..49..189S
Altcode: 1988IAUCo.102..189S
Analysis of flare spectra obtained with the Bent Crystal Spectrometer
aboard the Solar Maximum Mission (SMM) satellite enables the
determination of the fluxes in the resonance (w) line of Ca XIX and
the near-by continuum. The line-to-continuum intensity ratio is a
sensitive measure of the calcium elemental abundance (ACa)
relative to hydrogen in the emitting plasma. The authors analyse
the variations of ACa for flares which occurred in two
active regions well observed by SMM. They conclude that it is not
possible to correlate the abundance variations with the time of the
flare occurrence as suggested in an earlier paper for flares produced
from a single active region. Further, the authors find no convincing
correlation of abundance variation with any other flare characteristics.
Title: Analytic Capabilities of the Soft X-Ray Telescope for Solar-A
Authors: Brown, W. A.; Bruner, M. E.; Acton, L. W.; Lemen, J. R.
Bibcode: 1988BAAS...20..710B
Altcode:
No abstract at ADS
Title: Coronal temperature diagnostics from high-resolution soft
X-ray spectra
Authors: Strong, K. T.; Claflin, E. S.; Lemen, J. R.; Linford, G. A.
Bibcode: 1988AdSpR...8k.167S
Altcode: 1988AdSpR...8..167S
The Flat Crystal Spectrometer (FCS) on the Solar Maximum Mission has
accumulated over 300 spectral atlas scans of the soft X-ray spectrum
(1.4 to 23Å). We present here the results of a study which compares
these data with theoretical predictions of the relative intensities of
some of the brighter lines to determine which line intensity ratios give
the most reliable temperature diagnostics for the coronal plasma. The soft X-ray spectrum contains a vast selection of bright lines
formed by a variety of elements and their various ionisation stages. The
atomic physics is comparatively well understood, since these transitions
originate from ions stripped of most of their electrons (e.g, H-like
and He-like ions, which dominate this part of the spectrum). For this
reason, soft X-ray lines are often used to characterise the temperature
and emission measure of the coronal plasma. The purpose of this study is
to investigate how accurately and consistently the temperature of the
coronal plasma can be derived from soft X-ray spectra. For derivation
of coronal temperatures, the plasma is often assumed to be isothermal,
sometimes even for flares! While this is a convenient assumption, a full
differential emission measure model is the best way of representing the
distribution of temperatures in the plasma. Unfortunately, it is not
always possible to get enough data to calculate a differential emission
model. Using these data, we investigate under what circumstances the
isothermal assumption becomes invalid. However, we find that the
accuracy of the atomic data and the measured elemental abundances
limit the interpretation of the observations.
Title: Investigations of turbulent and directed motions in solar
flares
Authors: Lemen, J. R.; Fludra, A.; Jakimiec, J.
Bibcode: 1988AdSpR...8k.161L
Altcode: 1988AdSpR...8..161L
During the past solar maximum, spectrally resolved observations
obtained with the P78-1, Hinotori, and Solar Maximum Mission (SMM)
satellites have revealed strongly asymmetric line profiles as well as
symmetrically broadened (in excess of thermal broadening) line profiles
during the impulsive phase of most solar flares. These line profiles
are the result of emissions from plasmas which have high upflow bulk
velocities in the flaring loop added to the emission from the plasma
which has a relatively low bulk velocity. The large observed symmetric
broadening is the result of random ionic or turbulent motions within
the flaring loop. Most observations have been made in soft X-rays
of the 107 K and hotter plasma, although, similar effects
have been noted in UV emissions. The importance of these observations
is clear: the soft X-ray emission represents the thermal response
of the rapidly heated flare plasma, and a proper understanding of
these emissions necessarily constraints the interpretation for the
heating source. For example, plasma heated by fast electrons or thermal
conduction fronts may produce different directed and turbulent motions
which could be detected in the observed X-ray spectra. We present a
new method for fitting these asymmetric spectra which we have applied
to over 40 flares observed with the Bent Crystal Spectrometer (BCS)
on board the SMM. Correlations between turbulent and directed motions
are discussed and we infer the temperature of the upflowing component
separately from the stationary component from ratios of Ca xix and Fe
xxv line intensities.
Title: Intercomparison of flare observations with two SMM
spectrometers: BCS and HXIS
Authors: Jakimiec, J.; Prés, P.; Fludra, A.; Bentley, R. D.; Lemen,
J. R.; Mewe, R.; Schrijver, J.; Sylwester, J.
Bibcode: 1988AdSpR...8k.231J
Altcode: 1988AdSpR...8..231J
The temperature diagnostics of hot flare plasma, obtained from two
Solar Maximum Mission instruments (HXIS and BCS), is compared. A good
general agreement between the HXIS and BCS-Fe temperature scales has
been found. However, for the growth phase of some flares a systematic
difference, THXIS>TFe, has been found,
which is not likely to be due to the typical non-thermal electron
beams. Possible explanation of this effect is briefly discussed.
Title: The SOLAR-A soft X-ray telescope experiment
Authors: Acton, L.; Bruner, M.; Brown, W.; Lemen, J.; Hirayama, T.;
Tsuneta, S.; Watanabe, T.; Ogawara, Y.
Bibcode: 1988AdSpR...8k..93A
Altcode: 1988AdSpR...8...93A
The Japanese SOLAR-A mission for the study of high energy solar physics
is timed to observe the sun during the next activity maximum. This small
spacecraft includes a carefully coordinated complement of instruments
for flare studies. In particular, the soft X-ray telescope (SXT)
will provide X-ray images of flares with higher sensitivity and time
resolution than have been available before. This paper describes the
scientific capabilities of the SXT and illustrates it application to
the study of an impulsive compact flare.
Title: Coordinated soft X-ray and Hα observations of solar flares
Authors: Zarro, D. M.; Canfield, R. C.; Metcalf, T. R.; Lemen, J. R.
Bibcode: 1988AdSpR...8k.149Z
Altcode: 1988AdSpR...8..149Z
We have analyzed a unique set of four solar flares for which coordinated
soft X-ray Ca XIX and Hα spectral observations were obtained during
the impulsive phase. In all events, a blue asymmetry (indicative of
upflows) was observed in the coronal Ca XIX line during the soft X-ray
rise phase. In all events, a red asymmetry (indicative of downflows)
was observed simultaneously in chromospheric Hα at spatial locations
associated with enhanced flare heating. Combining the velocity data with
estimates of the evaporated mass based on soft X-ray emission measure,
we demonstrate that the impulsive phase momentum of upflowing soft
X-ray plasma equalled that of the downflowing Hα plasma, to within an
order of magnitude. This equality supports the explosive chromospheric
evaporation model of solar flares - the only model that predicts equal
momentum content in upflowing coronal and downflowing chromospheric
plasmas. under contract with Lockheed Palo Alto Research Laboratory
Title: A statistical study of coronal densities from X-ray line
ratios of helium-like ions: Ne IX and Mg XI
Authors: Linford, G. A.; Lemen, J. R.; Strong, K. T.
Bibcode: 1988AdSpR...8k.173L
Altcode: 1988AdSpR...8..173L
Since the repair of the Solar Maximum Mission (SMM) spacecraft, the
Flat Crystal Spectrometer (FCS) has recorded many high temperature
spectra of helium-like ions under a wide variety of coronal conditions:
active regions, long duration events, compact events, and double
flares. The potential usefulness of the helium-like lines for studying
coronal plasma was first demonstrated by Gabriel and Jordan /1/. The
plasma density and temperature are derived from the ratios R and G,
where R = f/i, G = (f + i)/r, and r, f, and i denote the resonance,
forbidden, and intercombination line fluxes. The density of the
plasma must exceed a critical value, the low-density limit (LDL,
e.g. ne >= 1012 cm-3 for Mg xi),
in order for the R ratio to be density sensitive. This low-density
limit increases with the atomic number of the ion. Traditionally,
densities have been obtained from individual line profile fits to
the triplet lines which are then corrected for blends with satellite
lines at specific temperatures. Unfortunately, any correction for the
blends will change the temperature. In addition, satellites near the
resonance line make it difficult to obtain reliable fluxes and, hence,
the G ratio measurement. It is important to obtain reliable density
measurements in order to determine the thermodynamic properties of
the loop, the cooling timescale of the plasma, and the flare loop
morphology. We present a new method for obtaining the density and
temperature for events observed with the FCS aboard SMM. The results
for these events are presented and compared to earlier results, and
the method is evaluated based on these comparisons.
Title: New spectral line identifications in high-temperature flares
Authors: Fawcett, B. C.; Phillips, K. J. H.; Jordan, C.; Lemen, J. R.
Bibcode: 1987MNRAS.225.1013F
Altcode:
A solar flare spectrum in the wavelength region between 7.8 and 10.0
Å, recorded by the Flat Crystal Spectrometer on Solar Maximum Mission
during a flare on 1985 July 2, is presented. It includes several
spectral emission lines not hitherto reported. Most are identified
through comparison with wavelengths either measured in laser-produced
spectra or calculated ab initio. It is found that they are mainly
due to n = 2-4, 5 transitions in Fe XIX to Fe XXIII. In a few cases,
previous identifications are corrected. The more intense lines appear
in second order in another channel of the spectrometer. The potential
of line-intensity ratios for temperature and density diagnostics
is discussed.
Title: Investigations of Turbulent and Direct Motions in Solar Flares
Authors: Bentley, R. D.; Fludra, A.; Lemen, J. R.; Jakimiec, J.;
Sylwester, J.
Bibcode: 1987BAAS...19R.750B
Altcode:
No abstract at ADS
Title: Evidence for Expanding Loop Geometries in Stellar Coronae
Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J.; Fludra, A.
Bibcode: 1987LNP...291...60M
Altcode: 1987csss....5...60M; 1987LNP87.291...60M
No abstract at ADS
Title: Variation in Calcium Abundance during Flares
Authors: Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley, R. D.;
Sylwester, B.
Bibcode: 1987sman.work..123S
Altcode:
The authors discuss the variation of the line-to-continuum ratio
throughout the entire flare including the temperature rise phase.
Title: High-Temperature Plasma Diagnostics of Solar Flares and
Comparison with Model Calculations
Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.; Lemen, J. R.;
Mewe, R.; Bentley, R. D.; Peres, G.; Serio, S.; Schrijver, J.
Bibcode: 1987sman.work...91J
Altcode:
The present state of flare diagnostics from X-ray spectra is briefly
outlined. The authors discuss how improved diagnostic results can be
used in flare heating process investigations.
Title: Characterization of the Total Flare Energy
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.41W
Altcode: 1986epos.confE..41W
No abstract at ADS
Title: Energetics of the Impulsive Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf..5.5W
Altcode: 1986epos.confE...5W
No abstract at ADS
Title: Energetics of the Gradual Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.20W
Altcode: 1986epos.confE..20W
No abstract at ADS
Title: Review of Impulsive Phase Phenomena
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.60W
Altcode: 1986epos.confE..60W
No abstract at ADS
Title: Flares Chosen for Energetics Study
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.47W
Altcode: 1986epos.confE..47W
No abstract at ADS
Title: Relationships among the Phases
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.39W
Altcode: 1986epos.confE..39W
No abstract at ADS
Title: Calculated X-radiation from optically thin plasmas. VI -
Improved calculations for continuum emission and approximation
formulae for nonrelativistic average Gaunt actors.
Authors: Mewe, R.; Lemen, J. R.; van den Oord, G. H. J.
Bibcode: 1986A&AS...65..511M
Altcode:
The continuum spectrum of an optically thin plasma whose electrons
have a Maxwellian energy distribution is calculated for the wavelength
range 1 - 1000 Å and temperature range 0.01 - 100 MK. The effect of
recombination to excited states on the free-bound emission is taken
into account. Simple analytic approximations to the total free-free,
free-bound and two-photon Gaunt factors are presented for various
wavelength and temperature intervals covering the whole considered
range. A simple computer routine for calculating the continuum emission
with the aid of this approximation is given.
Title: Differential emission measure distributions of Capella and
σ2 CrB
Authors: Mewe, R.; Schrijver, C. J.; Lemen, J. R.; Bentley, R. D.
Bibcode: 1986AdSpR...6h.133M
Altcode: 1986AdSpR...6..133M
The active late-type stars Capella (α Aur G6III+F9III) and
σ2 CrB (F6V+GV) (X-ray candidate emitters underlined)
were observed with the EXOSAT Transmission Grating Spectrometer
(TGS) in the region 10-200 Å. We have made an analysis of the
differential emission measure (DEM) distribution. The derived DEM
peaks between 3 and 7 MK and above 10 MK. The results disagree with
models for static loops as developed by Rosner, Tucker and Vaiana [1,
hereafter referred to as RTV]: the contrast in emission between the
maximal and lower temperatures in the loop is larger than predicted by
the RTV model. Other models which predict DEM distributions falling
off more steeply towards lower temperatures are briefly discussed:
e.g. quasi-static loops with varying cross-sectional area or dynamic
loops with strong downward flows.
Title: Soft X-ray observations of high-velocity features in the 29
June 1980 flares
Authors: Bentley, R. D.; Lemen, J. R.; Culhane, J. L.; Phillips,
K. J. H.
Bibcode: 1986A&A...154..255B
Altcode:
During the impulsive phase of two flares on 29 June 1980, short
lived emission line features have been observed in soft X-rays,
near the resonance lines of Fe XXV and Ca XIX, by the Bent Crystal
Spectrometer on the Solar Maximum Mission. They are coincident with hard
X-ray bursts and with the onset of Hα sprays. They appear to result
from a different type of phenomenon from the unresolved blue-shifted
component from the resonance lines reported by Feldman et al. (1980)
and Antonucci et al. (1982). The authors believe that these discrete
line features are due to Doppler-shifted resonance line emission from
well collimated, moving plasma with large line-of-sight velocities.
Title: Investigations of turbulent motions and particle acceleration
in solar flares
Authors: Jakimiec, J.; Fludra, A.; Lemen, J. R.; Dennis, B. R.;
Sylwester, J.
Bibcode: 1986AdSpR...6f.191J
Altcode: 1986AdSpR...6..191J
Investigations of X-ray spectra of solar flares show that intense
random (turbulent) motions are present in hot flare plasma. Here we
argue that the turbulent motions are of great importance for flare
development. They can efficiently enhance flare energy release and
accelerate particles to high energies.
Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veck, N. J.
Bibcode: 1986NASCP2439....5W
Altcode:
In this investigation of flare energetics, the authors establish a
comprehensive and self-consistent picture of the sources and transport
of energy within a flare. They chose five flares in 1980 that were
well observed with instruments on the SMM, and with other space-borne
and ground-based instruments. Details of the observations available
for them and the corresponding physical parameters derived from these
data are presented. The flares were studied from two perspectives,
the impulsive and gradual phases, and then the results were compared
to obtain the overall picture of the energetics of these flares. The
authors also discuss the role that modeling can play in estimating the
total energy of a flare when the observationally determined parameters
are used as the input to a numerical model.
Title: Determination of the calcium elemental abundance for 43 flares
from SMM-XRP solar X-ray spectra
Authors: Lemen, J. R.; Sylwester, J.; Bentley, R. D.
Bibcode: 1986AdSpR...6f.245L
Altcode: 1986AdSpR...6..245L
The helium and lithium-like X-ray transitions of Ca XVIII-XIX have been
used to make an absolute measurement of the coronal calcium elemental
abundance relative to hydrogen (ACa) in solar flares. Cooling
phase spectra of 43 flares obtained in channel 1 of the Bent Crystal
Spectrometer (BCS) on the Solar Maximum Mission have been analyzed. The
abundance is determined from the intensity ratio of the Ca XIX resonance
line (1S0 - 1P1) and
nearby continuum. A large variation is observed in the values of the
derived abundances, ranging up to a factor of 2.5 between the extreme
cases. This confirms the earlier results of Sylwester, Lemen, and Mewe
[1], who investigated a smaller sample of flares. In addition to the
variability of ACa observed between different flares, it
was suggested [1] that ACa varies during the heating phase
of some flares. We neglect this phenomenon in the present work, and
concentrate on the cooling phase during which ACa appears
to remain constant for any individual flare. Attempts to correlate
the ACa measurements with other observable features are
discussed.
Title: Solar X-ray spectrum simulations for flaring loop models with
emphasis on transient ionization effects during the impulsive phase
Authors: Mewe, R.; Lemen, J. R.; Peres, G.; Schrijver, J.; Serio, S.
Bibcode: 1985A&A...152..229M
Altcode:
X-ray spectra are simulated for observations with the Bent Crystal
Spectrometer (BCS) on the Solar Maximum Mission (SMM) spacecraft
(around 1.9 A and 3 A) using results of a time-dependent numerical
code for a dynamic flaring loop model. The spectra are integrated
over the whole loop and fully take into account the effects of
deviations from ionization equilibrium and Doppler shifts resulting
from plasma movements. The effect of transient ionization on the
spectra emitted during the initial impulsive phase is emphasized. In
all the cases considered a strong depletion (relative to the continuum)
of high-ionization spectral lines takes place during about the first
minute of the flare for electron densities below about 10 to the 11th/cu
cm. A preliminary comparison to observations made with the BCS show
some indications for such effects in a few strong flares, but more
sensitive instruments will be needed in the future to exploit such
transient ionization effects as a possible valid density diagnostic
for hot solar flares.
Title: Soft X-ray observations of high-velocity features in the 29
June 1980flares.
Authors: Bentley, R. D.; Lemen, J. R.; Phillips, K. J. H.; Culhane,
J. L.
Bibcode: 1985RALR...85.....B
Altcode:
During the impulsive phase of two flares on 29 June 1980, short
lived emission line features have been observed in soft X-rays,
near the resonance lines of Fe XXV and Ca XIX, by the Bent Crystal
Spectrometer on the Solar Maximum Mission. They are coincident with hard
X-ray bursts and with the onset of Hα sprays. They appear to result
from a different type of phenomenon from the unresolved blue-shifted
component from the resonance lines reported by Feldman et al. (1980)
and Antonucci et al. (1982). The authors believe that these discrete
line features are due to Doppler-shifted resonance line emission from
well collimated, moving plasma with large line-of-sight velocities.
Title: Variation in observed coronal calcium abundance of X-ray
flare plasmas
Authors: Sylwester, J.; Lemen, J. R.; Mewe, R.
Bibcode: 1984Natur.310..665S
Altcode:
Variations in chemical composition during solar flares have been
inferred from elemental abundance changes in cosmic ray fluxes, but
have so far not been detected spectroscopically. We present here the
first spectroscopic evidence for the variation of the coronal calcium
abundance in high-temperature solar flare plasmas. The analysed data
consist of the high-resolution X-ray flare spectra (λ /Δλ ~ 4,000)
observed with the Bent Crystal Spectrometer (BCS) on board the Solar
Maximum Mission (SMM) satellite and described in detail by Acton
et al.1. The observed abundance variation has important
consequences for the analysis and interpretation of XUV and X-ray
spectra.
Title: Recent Soft X-ray Spectra During a Flare Decay
Authors: Phillips, K. J. H.; Lemen, J. R.; Strong, K. T.
Bibcode: 1984BAAS...16..730P
Altcode:
No abstract at ADS
Title: Inner-shell transitions of Fe XXIII and Fe XXIV in the X-ray
spectra of solar flares
Authors: Lemen, J. R.; Phillips, K. J. H.; Cowan, R. D.; Hata, J.;
Grant, I. P.
Bibcode: 1984A&A...135..313L
Altcode:
An analysis of the satellite lines of Fe XX III of the 1s - 2p
transition near 1.9 A in solar flare spectra is presented. Wavelengths
and intensities are obtained from a set of Dirac-Fock and Hartree-Fock
equations. The collisional excitation contribution was characterized
by a distorted wave formalism and the corresponding spectrum obtained
with Voight line profiles describing instrumental and Doppler
broadening. Three calculations for the q/w line intensity ratio are
compared in terms of contributions from Fe XX III satellites. The
application of the j/w and q/w ratios as diagnostics for solar plasmas
is discussed. Finally, the calculated Fe X II-XXV spectra are compared
with crystal spectrometer data.
Title: Recent Solar Observations from the X-Ray Polychromator on
the Repaired SMM Satellite
Authors: Saba, J. L. R.; Slater, G. L.; Levay, M. X.; Smith, K. L.;
Strong, K. T.; Bentley, R. D.; Lemen, J. R.; Caffey, R. R.; Freeland,
S. L., Jr.; Mathur, D. P.; Phillips, K. J. H.; Waters, T. A.
Bibcode: 1984BAAS...16..726S
Altcode:
No abstract at ADS
Title: Variation in the Observed Coronal Calcium Abundance for
Various X-Ray Flare Plasmas
Authors: Lemen, J. R.; Sylwester, J.; Mewe, R.
Bibcode: 1984BAAS...16..545L
Altcode:
No abstract at ADS
Title: X-80, a European X-ray astrophysics mission.
Authors: Brinkman, A. C.; Lemen, J.; Lund, N.; Olthof, H.; Pacault,
R.; Peacock, A.; Reppin, C.; Rocchia, R.; Scheepmaker, A.; Schnopper,
H. W.; Silver, E. H.; Spada, G.; Staubert, R.; Taylor, B. G.; Turner,
M.; Westergaard, N. J.
Bibcode: 1984PhST....7..200B
Altcode: 1984PhyS....7..200B
X-80 is one of the five missions being studied by ESA and a candidate
for selection. The scientific aims and the main characteristics of
the model payload are discussed.
Title: Differential emission measure analysis of hot-flare plasma
from solar-maximum mission X-ray data
Authors: Jakimiec, J.; Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley,
R. D.; Fludra, A.; Schrijver, J.; Sylwester, B.
Bibcode: 1984AdSpR...4g.203J
Altcode: 1984AdSpR...4..203J
We have investigated differential emission measure (DEM) distribution
of hot flare plasma (T>10 MK) using SMM X-ray data from Bent Crystal
Spectrometer (BCS) and Hard X-ray Imaging Spectrometer (HXIS). We have
found that the analysis provide a very sensitive test of consistency
of observational data coming from different instruments or different
channels of the same instrument. This has allowed to eliminate some
systematic differences contained in the analysed data. Typical
examples of the DEM distribution are discussed. It is stressed that
these improvements in the multitemperature flare diagnostics are very
important for the discussion of flare energetics.
Title: Soft X-Ray Spectroscopy from the X-Ray Polychromator on the
Newly Repaired Solar Maximum Mission -
Authors: Strong, K. T.; Stern, R. A.; Lemen, J. R.; Phillips, K. J. H.
Bibcode: 1984uxsa.coll....9S
Altcode: 1984IAUCo..86....9S; 1984uxsa.conf....9S
No abstract at ADS
Title: New Calculations of Inner-Shell X-Ray Lines in ti, cr, and
NI as Density Diagnostics (short Abstract)
Authors: Lemen, J. R.; Phillips, K. J. H.; Doschek, G. A.; Cowan, R. D.
Bibcode: 1984uxsa.coll...50L
Altcode: 1984IAUCo..86...50L; 1984uxsa.conf...50L
No abstract at ADS
Title: Variation of the Observed Coronal Calcium Abundance for
Various X-Ray Flare Plasmas (short Abstract)
Authors: Sylwester, J.; Lemen, J. R.; Mewe, R.
Bibcode: 1984uxsa.coll...21S
Altcode: 1984uxsa.conf...21S; 1984IAUCo..86...21S
No abstract at ADS
Title: Inner-shell transitions in Fe XIX-XXII in the X-ray spectra
of solar flares and Tokamaks
Authors: Phillips, K. J. H.; Lemen, J. R.; Cowan, R. D.; Doschek,
G. A.; Leibacher, J. W.
Bibcode: 1983ApJ...265.1120P
Altcode:
Calculated spectra of the ions Fe XIX-XXII for various densities
and temperatures are presented, thereby extending the work begun by
Doschek, Feldman, and Cowan (1981). The calculations are based on a code
(the Cowan code) that computes both the level structure of an ion and
intensity factors for the 1s-2p satellite lines. A comparison is made
between the calculated spectra and those observed in solar flares by
the P78-1 and SMM instruments. The observed intensities of Fe XX lines,
which are the most sensitive to density, are found to agree well with
those calculated in the low-density limit. The agreement for lines
arising from other ions is also very good. It is also seen that the
predicted density variations in Fe XX are confirmed by the higher
density Princeton Large Torus plasmas. Thus a possible useful density
diagnostic is indicated for tokamak and high-density astrophysical
plasmas, perhaps including some solar flares.
Title: Application of the wedge and strip anode to position sensing
with microchannel plates and proportional counters.
Authors: Siegmund, O. H. W.; Clothier, S.; Thornton, J.; Lemen, J.;
Harper, R.; Mason, I. M.; Culhane, J. L.
Bibcode: 1983ITNS...30..503S
Altcode:
No abstract at ADS
Title: A Solar Flare X-Ray Polarimeter for the Space Shuttle
Authors: Lemen, J. R.; Chanan, G. A.; Hughes, J. P.; Laser, M. R.;
Novick, R.; Rochwarger, I. T.; Sackson, M.; Tramiel, L. J.
Bibcode: 1982SoPh...80..333L
Altcode:
We have recently built and tested an instrument designed to measure
the polarization of the hard (5-30 keV) X-ray emission from solar
flares, and thereby to investigate the energy release mechanism and
constrain flare models. In particular, these measurements will help
to determine whether hard X-ray bursts are produced by nonthermal
or by thermal electrons. The polarimeter makes use of the angular
dependence of Thomson scattering from targets of metallic lithium. It
has an energy resolution of a few keV, a time resolution of 5 s,
and sufficient sensitivity to measure polarization levels (3σ) of
a few percent in about 10 s for a moderate strength solar flare. The
instrumental polarization has been directly measured and found to be
within the design goal of ∼1%. This polarimeter is scheduled to be
flown as part of the OSS-1 pallet on an early Space Shuttle mission.
Title: The Effect of Fe XXIII on Fe XXIV Satellite Line Ratios
Authors: Lemen, J. R.; Phillips, K. J. H.; Doschek, G. A.; Cowan, R. D.
Bibcode: 1982BAAS...14..608L
Altcode:
No abstract at ADS
Title: X-80, a European X-ray astrophysics mission
Authors: Taylor, B. G.; Berthelsdorf, R.; Lemen, J.; Brinkman, A. C.;
Lund, N.; Schnopper, H.; Olthof, H.; Pacault, R.; Reppin, C.; Rocchia,
R.; Scheepmaker, A.; Spada, G.; Staubert, R.; Turner, M.
Bibcode: 1982AdSpR...2d.301T
Altcode: 1982AdSpR...2..301T
The salient features of X-80, a European X-ray Astrophysics Mission,
and a candidate for selection as the next satellite in the European
Space Agency's scientific programme, is described.
Title: Inner-Shell Transitions in fe Xix-Xxiii in the X-Ray Spectra
of Solar Flares and Tokamaks.
Authors: Lemen, J. R.; Phillips, K. J. H.; Cowan, R. P.; Doschek, G. A.
Bibcode: 1982uxsa.coll....3L
Altcode: 1982IAUCo..73....3L
No abstract at ADS
Title: X-80 - the Spectroscopy, Timing and Variability Mission.
Authors: Lemen, J. R.; Brinkman, A. C.; Lund, N.; Olthof, H.; Pacault,
R.; Reppin, C.; Rocchia, R.; Scheepmaker, A.; Schnopper, H.; Spada,
G.; Staubert, R.; Taylor, B.; Turner, M.
Bibcode: 1982uxsa.coll...13L
Altcode: 1982IAUCo..73...13L
No abstract at ADS
Title: Flare Densities from Iron Kα Lines
Authors: Lemen, J. R.; Phillips, K. J. H.
Bibcode: 1981BAAS...13Q.543L
Altcode:
No abstract at ADS
Title: Solar X-Ray Flares: Spectroscopic Results from the Eighth
Orbiting Solar Observatory and the Development of a Space Shuttle
Borne Polarimeter.
Authors: Lemen, J. R.
Bibcode: 1981PhDT.........4L
Altcode:
Solar flares are dramatic eruptions of the slar atmosphere which,
although they have been extensively studied for the past decade, still
remain for the most part enigmatic. Since the flare plasma temperature
typically reaches ten million degrees Kelvin or more, a large amount
of the radiation is emitted at X-ray wavelengths. Therefore, X-ray
observations provide the best overall means to view solar flares. We
discuss spectroscopic observations made with spectrometers on board the
eighth Orbiting Solar Observatory satellite which observed flares during
the previous slar minimum period. The spectrometers had a bandwidth
of 1.5-6.7 Angstrom and 10 second time resolution. The spectrometers
resolved 29 lines including transitions in calcium, argon, sulfur,
silicon and iron. Several satellite lines to silicon XIII and silicon
XIV have been resolved and identified, six of these for the first
time. We show that dielectronic recombination accounts for the observed
intensities of these satellites. The high reflectivity of the crystal
spectrometers enabled the observation of the X-ray continuum through
all phases of flare development. A survey of 30 flares was made to
investigate various coronal cooling theories. Details of this study are
given. We conclude that neighter radiative nor conductive cooling models
alone are capable of explaining the majority of events observed. A
viable cooling model probably must also include convection. Current
models which include convection, conduction, and radiation predict
that in the decaying phase of the flare the emission measure should
increase. We find, however, that in 17 cases the emission measure
remains constant throughout a substantial part of the cooling phase,
in contrast to theoretical prediction. In only five cases did the
emission measure actually increase, and in eight cases the emission
measure was seen to decrease, suggesting that the coronal cooling
models will have to be revised. Finally, a new polarimeter, which
has been built and is scheduled to fly on the fourth test flight of
the Space Shuttle is described. The polarimeter has a bandwidth of
5 to 30 kiloelectron volts and is sufficiently sensitive to measure
polarization with an accuracy of 1 to 2 percent over times as short
as 10 seconds. The design of the polarimeter reduces the possible
instrumental effects so that they add an uncertainty of only about one
percent to the observed polarization. In addition, redundant background
rejection techniques minimize the possibility of a false indication of
plarization due to anisotropic background signals. With these features,
we should be able to avoid the systematic effects which have plagued
earlier experiments. Measurements of the linear polarization of hard
X-rays from the early phase of slar flares will provide information
concerning the angular distribution of accelerated electrons, a key
problem for understanding solar flares. Current models of the solar
mechanisms responsible for this polarized emission and the techniques
employed to measure it are discussed.
Title: Solar x-ray flares: spectroscopic results from the eighth
Orbiting Solar Observatory and the development of a space shuttle
borne polarimeter
Authors: Lemen, James Randall
Bibcode: 1981PhDT.......149L
Altcode:
No abstract at ADS
Title: A Solar Flare X-Ray Polarimeter for OSS-1
Authors: Chanan, G. A.; Hughes, J. P.; Lemen, J. R.; Novick, R.;
Rochwarger, I.; Sackson, M.; Tramiel, L. J.
Bibcode: 1980BAAS...12..475C
Altcode:
No abstract at ADS
Title: An investigation of the 1.9 Å feature in solar-flare X-ray
spectra.
Authors: Parkinson, J. H.; Veck, N. J.; Ashfield, M. E. C.; Culhane,
J. L.; Ku, W. H. -M.; Lemen, J. R.; Novic, R.; Acton, L. W.; Wolfson,
C. J.
Bibcode: 1979ApJ...231..551P
Altcode:
The 1.9 A feature, observed in the X-ray spectra of three solar flares
with the Columbia University and Lockheed Palo Alto Research Laboratory
spectrometers on the OSO 8 satellite, is shown to be due to a blend of
1s-2p transitions in a range of Fe ions. In the temperature range 9-16
x -10 to the 6th K, the feature has a mean wavelength of 1.900 + or -
0.009 A and is 0.04 A wider than a single line, indicating that the
main contributors are Fe XIX-Fe XXII. Most of the emission originates
from the dielectronic recombination process, and when inner-shell
excitation is included together with normal collisional excitation, the
observed intensity of the feature can be accounted for adequately. For
these events, if the electron density is below approximately 10 to the
12th/cu cm, deviations from ionization equilibrium will be significant
for ions more highly ionized than Fe XXI.
Title: Columbia/OSO-8 Spectrometer Observations of Iron Line Emission
from Solar Flares
Authors: Lemen, J. R.; Ku, W. H. -M.; Parkinson, J. H.; Veck, N. J.
Bibcode: 1979BAAS...11..411L
Altcode:
No abstract at ADS
Title: Evidence from X-Ray and Radio Observations for Electron
Acceleration in the Source Region of a Moving Type-Iv Solar Radio
Burst
Authors: Stewart, R. T.; Wolfson, C. J.; Lemen, J. R.
Bibcode: 1979NZJS...22..567S
Altcode: 1981NZJS...22..567S
No abstract at ADS
Title: Silicon X-ray line emission from solar flares and active
regions.
Authors: Parkinson, J. H.; Wolff, R. S.; Kestenbaum, H. L.; Ku,
W. H. -M.; Lemen, J. R.; Long, K. S.; Novick, R.; Suozzo, R. J.;
Weisskopf, M. C.
Bibcode: 1978SoPh...60..123P
Altcode:
New observations of solar flare and active region X-ray spectra obtained
with the Columbia University instrument on OSO-8 are presented and
discussed. The high sensitivity of the graphite crystal panel has
allowed both line and continuum spectra to be observed with moderate
spectral resolution. Observations with higher spectral resolution have
been made with a panel of pentaerythritol crystals. Twenty-nine lines
between 1.5 and 7.0 Å have been resolved and identified, including
several dielectronic recombination satellite lines to Si XIV and
Si XIII lines which have been observed for the first time. It has
been found that thermal continuum models specified by single values
of temperature and emission measure have fitted the data adequately,
there being good agreement with the values of these parameters derived
from line intensity ratios.
Title: Solar Flare X-Ray Line Studies.
Authors: Veck, N. J.; Ku, W. H. -M.; Lemen, J. R.; Novick, R.;
Parkinson, J. H.
Bibcode: 1978BAAS...10..441V
Altcode:
No abstract at ADS
Title: Observations of Solar Flare X-Ray Continua
Authors: Lemen, J. R.; Ku, W. H. -M.; Novick, R.; Parkinson, J. H.;
Veck, N. J.
Bibcode: 1978BAAS...10R.440L
Altcode:
No abstract at ADS