Author name code: doschek
ADS astronomy entries on 2022-09-14
author:"Doschek, George A."
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Title: Adventures in Space Science
Authors: Doschek, George
Bibcode: 2021SoPh..296..123D
Altcode:
This memoir is a summary of my early childhood, education, and
research career at the Naval Research Laboratory (NRL) in Washington,
DC. I describe my early interest in astronomy and how I wound up
working in the fields of solar physics and X-ray-UV spectroscopy of
high temperature plasmas. I describe some of my home life and other
interests, my education at the University of Pittsburgh, and the
various projects and management activities that I have been fortunate
to work on at NRL. I have been blessed with being able to work at a
first-class research laboratory populated by outstanding scientists. I
am particularly blessed to have worked with my many friends and
colleagues in the NRL Space Science Division. Perhaps I am most blessed
by having had wonderful parents that gave me the interests I have in
life and the passion to pursue them, and an outstanding wife that has
been my partner through good and bad times for over 50 years. I am now
retired but for three years I was a participant in the NRL Voluntary
Emeritus Program (VEP). However, this memoir is a personal account,
and not work done as a VEP.
Title: The Variability of Solar Coronal Abundances in Active Regions
and the Quiet Sun
Authors: Doschek, G. A.; Warren, H. P.
Bibcode: 2019ApJ...884..158D
Altcode:
Measurements of elemental abundances hold important clues to how mass
and energy flow through the solar atmosphere. Variations in abundances
are organized by an element’s first ionization potential (FIP),
and many previous studies have assumed that low FIP (less than 10 eV)
elements are enriched by a factor of 3-4 in the corona. In this paper,
we use spatially resolved observations from the Extreme-ultraviolet
Imaging Telescope on board the Hinode spacecraft to examine the spatial
variability of elemental abundance in and around active regions. We find
substantial variations within some active regions. In general, however,
we find that the enrichment of low FIP elements is limited to bright,
active region structures. In faint active region structures and in the
dark, quiet regions around active regions, the measured abundances are
close to photospheric. These measurements use the ratio of low FIP
Si to high FIP S. Similar conclusions concerning quiet Sun regions
have been reached recently by Del Zanna using full-Sun spectra. He
has found that the coronal quiet Sun (at temperatures greater than
1 MK) has photospheric abundances. Transition region abundances (at
temperatures less than 1 MK in the solar atmosphere) have been found
to be photospheric. These results and results from this paper suggest
that a coronal composition is not a general property of million-degree
plasma, but is limited to bright active region loops, and is variable.
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
Bibcode: 2019PASJ...71R...1H
Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.
Title: Probing the evolution of a coronal cavity within a solar
coronal mass ejection.
Authors: Harra, Louise K.; Doschek, G. A.; Hara, Hirohisa; Long,
David; Warren, Harry; Matthews, Sarah; Lee, Kyoung-Sun; Jenkins, Jack
Bibcode: 2018cosp...42E1381H
Altcode:
On the 10 September 2017, an X-class solar flare erupted at the solar
limb. The associated coronal mass ejection (CME) had the classic three
part structure with a bright core surrounded by a dark cavity. This
event was captured perfectly by the Hinode EUV imaging spectrometer
(EIS). The EIS instrument captured spectroscopically the flaring
loops, the current sheet and the cavity for the first time. In the
'standard flare model', magnetic reconnection of coronal loops occurs
following the eruption of a magnetic flux rope. The flux rope is a key
element of the flare process and eruption but is inherently difficult
to observe. Dark cavities observed within a CME are assumed to be
flux ropes. The observations we describe here, provide an insight
into the characteristics of a cavity, and how the rapid injection of
energy from the flare underneath forces the rapid expansion of the
flux rope resulting in the eruption. Doppler shifts of over 200 km/s
are measured at either end of the cavity. There is mixed temperature
plasma - cool material in the centre that also has strong flows, and
hot FeXXIV emission being observed. SDO Atmospheric Imaging Assembly
(AIA) data shows that the cavity erupts rapidly, and is being driven
by the non-thermal energy input from the flare below as measured from
Fermi data.
Title: Spectroscopic Observations of Current Sheet Formation and
Evolution
Authors: Warren, Harry; Brooks, David; Ugarte-Urra, Ignacio; Crump,
Nicholas A.; Doschek, George A.; Stenborg, Guillermo; Reep, Jeffrey W.
Bibcode: 2018tess.conf31904W
Altcode:
<span class="s1" We report on the structure and evolution of
a current sheet that formed in the wake of an eruptive X8.3 flare
observed at the west limb of the Sun on September 10, 2017. Using
observations from the Hinode/EIS and SDO/AIA, we find that plasma
in the current sheet reaches temperatures of about 20MK and that the
range of temperatures is relatively narrow. The highest temperatures
occur at the base of the current sheet, in the region near the top
of the post-flare loop arcade. The broadest high temperature line
profiles, in contrast, occur at the largest observed heights. Further,
line broadening is strong very early in the flare and diminishes over
time. The current sheet can be observed in the AIA 211 and 171 channels,
which have a considerable contribution from thermal bremsstrahlung
at flare temperatures. Comparisons of the emission measure in these
channels with other EIS wavelengths and AIA channels dominated by
Fe line emission indicate a coronal composition and suggest that
the current sheet is formed by the heating of plasma already in the
corona. Finally, we also investigate the structure in the current sheet
as imaged by AIA and find clear evidence for collapsing loops. Taken
together, these observations suggest that some flare heating occurs
in the current sheet while additional energy is released as newly
reconnected field lines relax and become more dipolar.
Title: Plasma Evolution within an Erupting Coronal Cavity
Authors: Long, David M.; Harra, Louise K.; Matthews, Sarah A.; Warren,
Harry P.; Lee, Kyoung-Sun; Doschek, George A.; Hara, Hirohisa; Jenkins,
Jack M.
Bibcode: 2018ApJ...855...74L
Altcode: 2018arXiv180201391L
Coronal cavities have previously been observed to be associated
with long-lived quiescent filaments and are thought to correspond
to the associated magnetic flux rope. Although the standard flare
model predicts a coronal cavity corresponding to the erupting flux
rope, these have only been observed using broadband imaging data,
restricting an analysis to the plane-of-sky. We present a unique set of
spectroscopic observations of an active region filament seen erupting
at the solar limb in the extreme ultraviolet. The cavity erupted and
expanded rapidly, with the change in rise phase contemporaneous with an
increase in nonthermal electron energy flux of the associated flare. Hot
and cool filamentary material was observed to rise with the erupting
flux rope, disappearing suddenly as the cavity appeared. Although
strongly blueshifted plasma continued to be observed flowing from
the apex of the erupting flux rope, this outflow soon ceased. These
results indicate that the sudden injection of energy from the flare
beneath forced the rapid eruption and expansion of the flux rope,
driving strong plasma flows, which resulted in the eruption of an
under-dense filamentary flux rope.
Title: Photospheric and Coronal Abundances in an X8.3 Class Limb Flare
Authors: Doschek, G. A.; Warren, H. P.; Harra, L. K.; Culhane, J. L.;
Watanabe, T.; Hara, H.
Bibcode: 2018ApJ...853..178D
Altcode:
We analyze solar elemental abundances in coronal post-flare
loops of an X8.3 flare (SOL2017-09-10T16:06) observed on the west
limb on 2017 September 10 near 18 UT using spectra recorded by
the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft. The abundances in the corona can differ from photospheric
abundances due to the first ionization potential (FIP) effect. In
some loops of this flare, we find that the abundances appear to be
coronal at the loop apices or cusps, but steadily transform from
coronal to photospheric as the loop footpoint is approached. This
result is found from the intensity ratio of a low-FIP ion spectral
line (Ca XIV) to a high-FIP ion spectral line (Ar XIV) formed at
about the same temperature (4-5 MK). Both lines are observed close in
wavelength. Temperature, which could alter the interpretation, does
not appear to be a factor based on intensity ratios of Ca XV lines
to a Ca XIV line. We discuss the abundance result in terms of the
Laming model of the FIP effect, which is explained by the action of
the ponderomotive force in magnetohydrodynamic (MHD) waves in coronal
loops and in the underlying chromosphere.
Title: Spectroscopic Observations of Current Sheet Formation and
Evolution
Authors: Warren, Harry P.; Brooks, David H.; Ugarte-Urra, Ignacio;
Reep, Jeffrey W.; Crump, Nicholas A.; Doschek, George A.
Bibcode: 2018ApJ...854..122W
Altcode: 2017arXiv171110826W
We report on the structure and evolution of a current sheet that formed
in the wake of an eruptive X8.3 flare observed at the west limb of
the Sun on 2017 September 10. Using observations from the EUV Imaging
Spectrometer (EIS) on Hinode and the Atmospheric Imaging Assembly
(AIA) on the Solar Dynamics Observatory, we find that plasma in the
current sheet reaches temperatures of about 20 MK and that the range
of temperatures is relatively narrow. The highest temperatures occur
at the base of the current sheet, in the region near the top of the
post-flare loop arcade. The broadest high temperature line profiles,
in contrast, occur at the largest observed heights. Furthermore,
line broadening is strong very early in the flare and diminishes over
time. The current sheet can be observed in the AIA 211 and 171 channels,
which have a considerable contribution from thermal bremsstrahlung
at flare temperatures. Comparisons of the emission measure in these
channels with other EIS wavelengths and AIA channels dominated by
Fe line emission indicate a coronal composition and suggest that
the current sheet is formed by the heating of plasma already in the
corona. Taken together, these observations suggest that some flare
heating occurs in the current sheet, while additional energy is released
as newly reconnected field lines relax and become more dipolar.
Title: METIS, the Multi Element Telescope for Imaging and
Spectroscopy: an instrument proposed for the solar orbiter mission
Authors: Antonucci, E.; Andretta, V.; Cesare, S.; Ciaravella, A.;
Doschek, G.; Fineschi, S.; Giordano, S.; Lamy, P.; Moses, D.; Naletto,
G.; Newmark, J.; Poletto, L.; Romoli, M.; Solanki, S.; Spadaro, D.;
Teriaca, L.; Zangrilli, L.
Bibcode: 2017SPIE10566E..0LA
Altcode:
METIS, the Multi Element Telescope for Imaging and Spectroscopy,
is an instrument proposed to the European Space Agency to be part of
the payload of the Solar Orbiter mission. The instrument design has
been conceived for performing extreme ultraviolet (EUV) spectroscopy
both on the solar disk and off-limb, and near-Sun coronagraphy
and spectroscopy. The proposed instrument suite consists of three
different interconnected elements, COR, EUS and SOCS, sharing the
same optical bench, electronics, and S/C heat shield aperture. COR is
a visible-EUV multiband coronagraph based on a classical externally
occulted design. EUS is the component of the METIS EUV disk spectrometer
which includes the telescope and all the related mechanisms. Finally,
SOCS is the METIS spectroscopic component including the dispersive
system and the detectors. The capability of inserting a small telescope
collecting coronal light has been added to perform also EUV coronal
spectroscopy. METIS can simultaneously image the visible and ultraviolet
emission of the solar corona and diagnose, with unprecedented temporal
coverage and space resolution the structure and dynamics of the full
corona in the range from 1.2 to 3.0 (1.6 to 4.1) solar radii (R⊙,
measured from Sun centre) at minimum (maximum) perihelion during the
nominal mission. It can also perform spectroscopic observations of the
solar disk and out to 1.4 R⊙ within the 50-150 nm spectral region,
and of the geo-effective coronal region 1.7-2.7 R⊙ within the 30-125
nm spectral band.
Title: Sunspots, Starspots, and Elemental Abundances
Authors: Doschek, George A.; Warren, Harry P.
Bibcode: 2017SPD....4810601D
Altcode:
The composition of plasma in solar and stellar atmospheres is not fixed,
but varies from feature to feature. These variations are organized by
the First Ionization Potential (FIP) of the element. Solar measurements
often indicate that low FIP elements (< 10eV, such as Fe, Si, Mg)
are enriched by factors of 3-4 in the corona relative to high FIP
elements (>10 eV, such as C, N, O, Ar, He) compared to abundances
in the photosphere. Stellar observations have also shown similar
enrichments. An inverse FIP effect, where the low FIP elements are
depleted, has been observed in stellar coronae of stars believed
to have large starspots in their photospheres. The abundances are
important for determining radiative loss rates in models, tracing the
origin of the slow solar wind, and for understanding wave propagation
in the chromosphere and corona. Recently, inverse FIP effects have
been discovered in the Sun (Doschek, Warren, & Feldman 2015, ApJ,
808, L7) from spectra obtained by the Extreme-ultraviolet Imaging
Spectrometer (EIS) on the Hinode spacecraft. The inverse FIP regions
seem always to be near sunspots and cover only a very small area
(characteristic length = a few arcseconds). However, in pursuing the
search for inverse FIP regions, we have found that in some sunspot
groups the coronal abundance at a temperature of 3-4 MK can be near
photospheric over much larger areas of the sun near the sunspots (e.g.,
6,000 arcsec2). Also, sometimes the abundances at 3-4 MK
are in between coronal and photospheric values. This can occur in small
areas of an active region. It is predicted (Laming 2015, Sol. Phys., 12,
2) that the FIP effect should be highly variable in the corona. Several
examples of coronal abundance variations are presented. Our work
indicates that a comprehensive re-investigation of solar abundances
is highly desirable. This work is supported by a NASA Hinode grant.
Title: Sunspots, Starspots, and Elemental Abundances
Authors: Doschek, G. A.; Warren, H. P.
Bibcode: 2017ApJ...844...52D
Altcode:
Element abundances in the solar photosphere, chromosphere, transition
region, and corona are key parameters for investigating sources of
the solar wind and for estimating radiative losses in the quiet corona
and in dynamical events such as solar flares. Abundances in the solar
corona and photosphere differ from each other depending on the first
ionization potential (FIP) of the element. Normally, abundances with
FIP values less than about 10 eV are about 3-4 times more abundant in
the corona than in the photosphere. However, recently, an inverse FIP
effect was found in small regions near sunspots where elements with
FIP less than 10 eV are less abundant relative to high FIP elements
(≥slant 10 eV) than they are in the photosphere. This is similar to
fully convective stars with large starspots. The inverse FIP effect
is predicted to occur in the vicinity of sunspots/starspots. Up to
now, the solar anomalous abundances have only been found in very
spatially small areas. In this paper, we show that in the vicinity of
sunspots there can be substantially larger areas with abundances that
are between coronal and photospheric abundances and sometimes just
photospheric abundances. In some cases, the FIP effect tends to shut
down near sunspots. We examine several active regions with relatively
large sunspots that were observed with the Extreme-ultraviolet Imaging
Spectrometer on the Hinode spacecraft in cycle 24.
Title: Measuring Velocities in the Early Stage of an Eruption:
Using “Overlappogram” Data from Hinode EIS
Authors: Harra, Louise K.; Hara, Hirohisa; Doschek, George A.;
Matthews, Sarah; Warren, Harry; Culhane, J. Leonard; Woods, Magnus M.
Bibcode: 2017ApJ...842...58H
Altcode:
In order to understand the onset phase of a solar eruption, plasma
parameter measurements in the early phases are key to constraining
models. There are two current instrument types that allow us to make
such measurements: narrow-band imagers and spectrometers. In the
former case, even narrow-band filters contain multiple emission lines,
creating some temperature confusion. With imagers, however, rapid
cadences are achievable and the field of view can be large. Velocities
of the erupting structures can be measured by feature tracking. In the
spectrometer case, slit spectrometers can provide spectrally pure images
by “rastering” the slit to build up an image. This method provides
limited temporal resolution, but the plasma parameters can be accurately
measured, including velocities along the line of sight. Both methods
have benefits and are often used in tandem. In this paper we demonstrate
for the first time that data from the wide slot on the Hinode EUV
Imaging Spectrometer, along with imaging data from AIA, can be used to
deconvolve velocity information at the start of an eruption, providing
line-of-sight velocities across an extended field of view. Using He
II 256 Å slot data at flare onset, we observe broadening or shift(s)
of the emission line of up to ±280 km s-1. These are seen at
different locations—the redshifted plasma is seen where the hard X-ray
source is later seen (energy deposition site). In addition, blueshifted
plasma shows the very early onset of the fast rise of the filament.
Title: The Electron Density in Explosive Transition Region Events
Observed by IRIS
Authors: Doschek, G. A.; Warren, H. P.; Young, P. R.
Bibcode: 2016ApJ...832...77D
Altcode:
We discuss the intensity ratio of the O IV line at 1401.16 Å to the
Si IV line at 1402.77 Å in Interface Region Imaging Spectrograph
(IRIS) spectra. This intensity ratio is important if it can be used
to measure high electron densities that cannot be measured using line
intensity ratios of two different O IV lines from the multiplet within
the IRIS wavelength range. Our discussion is in terms of considerably
earlier observations made from the Skylab manned space station and
other spectrometers on orbiting spacecraft. The earlier data on the O
IV and Si IV ratio and other intersystem line ratios not available to
IRIS are complementary to IRIS data. In this paper, we adopt a simple
interpretation based on electron density. We adopt a set of assumptions
and calculate the electron density as a function of velocity in the Si
IV line profiles of two explosive events. At zero velocity the densities
are about 2-3 × 1011 cm-3, and near 200 km
s-1 outflow speed the densities are about 1012
cm-3. The densities increase with outflow speed up to
about 150 km s-1 after which they level off. Because of the
difference in the temperature of formation of the two lines and other
possible effects such as non-ionization equilibrium, these density
measurements do not have the precision that would be available if
there were some additional lines near the formation temperature of O IV.
Title: A Parabolic Equation Approach to Modeling Acousto-Gravity
Waves for Local Helioseismology
Authors: Del Bene, Kevin; Lingevitch, Joseph; Doschek, George
Bibcode: 2016SoPh..291.1581D
Altcode: 2016SoPh..tmp..101D
A wide-angle parabolic-wave-equation algorithm is developed and
validated for local-helioseismic wave propagation. The parabolic
equation is derived from a factorization of the linearized
acousto-gravity wave equation. We apply the parabolic-wave equation
to modeling acoustic propagation in a plane-parallel waveguide with
physical properties derived from helioseismic data. The wavenumber
power spectrum and wave-packet arrival-time structure for receivers
in the photosphere with separation up to 30∘ is computed,
and good agreement is demonstrated with measured values and a reference
spectral model.
Title: The Mysterious Case of the Solar Argon Abundance near Sunspots
in Flares
Authors: Doschek, G. A.; Warren, H. P.
Bibcode: 2016ApJ...825...36D
Altcode:
Recently we discussed an enhancement of the abundance of Ar xiv relative
to Ca xiv near a sunspot during a flare, observed in spectra recorded
by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft. The observed Ar xiv/Ca xiv ratio yields an argon/calcium
abundance ratio seven times greater than expected from the photospheric
abundance. Such a large abundance anomaly is unprecedented in the solar
atmosphere. We interpreted this result as being due to an inverse first
ionization potential (FIP) effect. In the published work, two lines of
Ar xiv were observed, and one line was tentatively identified as an Ar
xi line. In this paper, we report observing a similar enhancement in a
full-CCD EIS flare spectrum in 13 argon lines that lie within the EIS
wavelength ranges. The observed lines include two Ar xi lines, four
Ar xiii lines, six Ar xiv lines, and one Ar xv line. The enhancement
is far less than reported in Doschek et al. but exhibits similar
morphology. The argon abundance is close to a photospheric abundance
in the enhanced area, and the abundance could be photospheric. This
enhancement occurs in association with a sunspot in a small area only
a few arcseconds (1″ = about 700 km) in size. There is no enhancement
effect observed in the normally high-FIP sulfur and oxygen line ratios
relative to lines of low-FIP elements available to EIS. Calculations of
path lengths in the strongest enhanced area in Doschek et al. indicate
a depletion of low-FIP elements.
Title: Transition Region Abundance Measurements During Impulsive
Heating Events
Authors: Warren, Harry P.; Brooks, David H.; Doschek, George A.;
Feldman, Uri
Bibcode: 2016ApJ...824...56W
Altcode: 2015arXiv151204447W
It is well established that elemental abundances vary in the solar
atmosphere and that this variation is organized by first ionization
potential (FIP). Previous studies have shown that in the solar corona,
low-FIP elements such as Fe, Si, Mg, and Ca, are generally enriched
relative to high-FIP elements such as C, N, O, Ar, and Ne. In this paper
we report on measurements of plasma composition made during impulsive
heating events observed at transition region temperatures with the
Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these
events the intensities of O IV, v, and VI emission lines are enhanced
relative to emission lines from Mg v, VI, and vii and Si VI and vii,
and indicate a composition close to that of the photosphere. Long-lived
coronal fan structures, in contrast, show an enrichment of low-FIP
elements. We conjecture that the plasma composition is an important
signature of the coronal heating process, with impulsive heating leading
to the evaporation of unfractionated material from the lower layers of
the solar atmosphere and higher-frequency heating leading to long-lived
structures and the accumulation of low-FIP elements in the corona.
Title: The Mysterious Case of the Solar Argon Abundance Near Sunspots
in Flares
Authors: Doschek, George A.; Warren, Harry
Bibcode: 2016SPD....4730207D
Altcode:
Recently Doschek et al. (2015, ApJL, 808, L7) reported on an observation
of an enhancement of the abundance of Ar XIV relative to Ca XIV
of about a factor of 30 near a sunspot during a flare, observed in
spectra recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS)
on the Hinode spacecraft. This enhancement yields an argon/calcium
abundance ratio 7 times greater than expected from the photospheric
abundances. Such a large abundance anomaly is unprecedented in the
solar atmosphere. We interpreted this result as due to an inverse
First Ionization Potential (FIP) effect. Argon is a high-FIP element
and calcium is a low-FIP element. In the published work two lines of
Ar XIV were observed and one line was tentatively identified as an Ar
XI line. The number of argon lines was limited by the limitations of
the flare study that was executed. In this paper we report observing
a similar enhancement in a full-CCD EIS flare spectrum in argon lines
with reasonable statistics and lack of blending that lie within the
EIS wavelength ranges. The observed lines include two Ar XI lines,
four Ar XIII lines, six Ar XIV lines, and one Ar XV line. The
enhancement is far less than reported in Doschek et al. (2015)
but exhibits similar morphology. The argon abundance is close to a
photospheric abundance in the enhanced area, and is only marginally
an inverse FIP effect. However, as for the published cases, this newly
discovered enhancement occurs in association with a sunspot in a small
area only a few arcsec in size and therefore we feel it is produced
by the same physics that produced the strong inverse FIP case. There
is no enhancement effect observed in the normally high-FIP sulfur and
oxygen line ratios relative to lines of low-FIP elements available
to EIS. Calculations of path lengths in the strongest enhanced area
in Doschek et al. (2015) indicate that the argon/calcium enhancement
is due to a depletion of low-FIP elements. This work is supported by
a NASA Hinode grant.
Title: Flare Footpoint Regions and a Surge Observed by Hinode/EIS,
RHESSI, and SDO/AIA
Authors: Doschek, G. A.; Warren, H. P.; Dennis, B. R.; Reep, J. W.;
Caspi, A.
Bibcode: 2015ApJ...813...32D
Altcode: 2015arXiv151007088D
The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft observed flare footpoint regions coincident with a surge
for an M3.7 flare observed on 2011 September 25 at N12 E33 in active
region 11302. The flare was observed in spectral lines of O vi, Fe x,
Fe xii, Fe xiv, Fe xv, Fe xvi, Fe xvii, Fe xxiii, and Fe xxiv. The
EIS observations were made coincident with hard X-ray bursts observed
by RHESSI. Overlays of the RHESSI images on the EIS raster images
at different wavelengths show a spatial coincidence of features in
the RHESSI images with the EIS upflow and downflow regions, as well
as loop-top or near-loop-top regions. A complex array of phenomena
were observed, including multiple evaporation regions and the surge,
which was also observed by the Solar Dynamics Observatory/Atmospheric
Imaging Assembly telescopes. The slit of the EIS spectrometer covered
several flare footpoint regions from which evaporative upflows in Fe
xxiii and Fe xxiv lines were observed with Doppler speeds greater than
500 km s-1. For ions such as Fe xv both evaporative outflows
(∼200 km s-1) and downflows (∼30-50 km s-1)
were observed. Nonthermal motions from 120 to 300 km s-1
were measured in flare lines. In the surge, Doppler speeds are
found from about 0 to over 250 km s-1 in lines from ions
such as Fe xiv. The nonthermal motions could be due to multiple
sources slightly Doppler-shifted from each other or turbulence in
the evaporating plasma. We estimate the energetics of the hard X-ray
burst and obtain a total flare energy in accelerated electrons of ≥7
× 1028 erg. This is a lower limit because only an upper
limit can be determined for the low-energy cutoff to the electron
spectrum. We find that detailed modeling of this event would require
a multithreaded model owing to its complexity.
Title: Anomalous Relative Ar/Ca Coronal Abundances Observed by the
Hinode/EUV Imaging Spectrometer Near Sunspots
Authors: Doschek, G. A.; Warren, H. P.; Feldman, U.
Bibcode: 2015ApJ...808L...7D
Altcode:
In determining the element abundance of argon (a high first ionization
potential; FIP element) relative to calcium (a low FIP element) in
flares, unexpectedly high intensities of two Ar xiv lines (194.40,
187.96 Å) relative to a Ca xiv line (193.87 Å) intensity were
found in small (a few arcseconds) regions near sunspots in flare
spectra recorded by the Extreme-ultraviolet Imaging Spectrometer
on the Hinode spacecraft. In the most extreme case the Ar xiv line
intensity relative to the Ca xiv intensity was 7 times the value
expected from the photospheric abundance ratio, which is about 30
times the abundance of argon relative to calcium in active regions,
i.e., the measured Ar/Ca abundance ratio is about 10 instead of 0.37
as in active regions. The Ar xiv and Ca xiv lines are formed near 3.4
MK and have very similar contribution functions. This is the first
observation of the inverse FIP effect in the Sun. Other regions show
increases of 2-3 over photospheric abundances, or just photospheric
abundances. This phenomenon appears to occur rarely and only over
small areas of flares away from the regions containing multi-million
degree plasma, but more work is needed to quantify the occurrences
and their locations. In the bright hot regions of flares the Ar/Ca
abundance ratio is coronal, i.e., the same as in active regions. In
this Letter we show three examples of the inverse FIP effect.
Title: Measuring Elemental Abundances in Impulsive Heating Events
with EIS
Authors: Warren, Harry; Doschek, George A.; Young, Peter
Bibcode: 2015TESS....121306W
Altcode:
It is well established that elemental abundances vary in the solar
atmosphere and that this variation is organized by first ionization
potential (FIP). Previous studies have indicated that in the solar
corona low FIP elements, such as Fe, Si, and Mg, are enriched relative
to high FIP elements, such as H, He, C, N, and O. In this paper we
report on measurements of plasma composition made during transient
heating events observed at transition region temperatures with the
Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these
events the intensities of O IV, V, and VI emission lines are enhanced
relative to emission lines from Mg V, VI, and VII and indicate a
composition close to that of the photosphere. Differential emission
measure calculations show a broad distribution of temperatures in
these events. Long-lived coronal structures, in contrast, show an
enrichment of low FIP elements and relatively narrow temperature
distributions. We conjecture that plasma composition is an important
signature of the coronal heating process, with impulsive heating
leading to the evaporation of unfractionated material from the lower
layers of the solar atmosphere and higher frequency heating leading
to the accumulation of low-FIP elements in the corona.
Title: An X-ray-EUV Spectroscopic View of the Solar Atmosphere
Authors: Doschek, George A.
Bibcode: 2015TESS....120801D
Altcode:
Much of our knowledge of physical conditions in the solar chromosphere,
transition region, and corona, such as temperature, electron density,
element abundances, mass motions and turbulent motions, depends on
analysis of high resolution X-ray-EUV spectroscopic data. The analysis
of spectroscopic data depends in turn on spectral line identifications,
and the atomic processes governing the production of the spectral
lines in the solar atmosphere. In terms of astronomy, X-ray and
EUV spectroscopy is relatively new and is a product of the space age
combined with laboratory programs such as the inertial confinement laser
fusion program and spectra obtained from tokamak plasmas. In addition
there are parallel developments in the theory of atomic structure and
the calculation of essential atomic parameters. This all began in the
1960s and continues even today. The 1960s and 1970s saw the discovery of
the cosmic background radiation, the discovery of quasars and pulsars,
and the launch of multitudinous spacecraft in almost every area of
astronomy. I have been privileged to be a participant in this solar and
cosmic adventure to understand plasmas far from home. I will review how
we got from very little knowledge of the X-ray and EUV solar spectrum
to the excellent data that we have today as well as theoretical tools
such as CHIANTI. I will also highlight some of the achievements in the
development of high-resolution spectrometers. I will review the major
results learned about the solar atmosphere from spectroscopy and how
they bear on understanding the fundamental physical processes that heat
the corona, drive solar flares, and generate coronal mass ejections.
Title: The Impact of a Filament Eruption on Nearby High-lying
Cool Loops
Authors: Harra, L. K.; Matthews, S. A.; Long, D. M.; Doschek, G. A.;
De Pontieu, B.
Bibcode: 2014ApJ...792...93H
Altcode: 2014arXiv1409.0377H
The first spectroscopic observations of cool Mg II loops above the
solar limb observed by NASA's Interface Region Imaging Spectrograph
(IRIS) are presented. During the observation period, IRIS is pointed
off-limb, allowing the observation of high-lying loops, which reach
over 70 Mm in height. Low-lying cool loops were observed by the IRIS
slit-jaw camera for the entire four-hour observing window. There is no
evidence of a central reversal in the line profiles, and the Mg II h/k
ratio is approximately two. The Mg II spectral lines show evidence of
complex dynamics in the loops with Doppler velocities reaching ±40
km s-1. The complex motions seen indicate the presence
of multiple threads in the loops and separate blobs. Toward the end
of the observing period, a filament eruption occurs that forms the
core of a coronal mass ejection. As the filament erupts, it impacts
these high-lying loops, temporarily impeding these complex flows,
most likely due to compression. This causes the plasma motions in the
loops to become blueshifted and then redshifted. The plasma motions
are seen before the loops themselves start to oscillate as they reach
equilibrium following the impact. The ratio of the Mg h/k lines also
increases following the impact of the filament.
Title: Plasma Dynamics Above Solar Flare Soft X-Ray Loop Tops
Authors: Doschek, G. A.; McKenzie, D. E.; Warren, H. P.
Bibcode: 2014ApJ...788...26D
Altcode:
We measure non-thermal motions in flare loop tops and above the loop
tops using profiles of highly ionized spectral lines of Fe XXIV and Fe
XXIII formed at multimillion-degree temperatures. Non-thermal motions
that may be due to turbulence or multiple flow regions along the line of
sight are extracted from the line profiles. The non-thermal motions are
measured for four flares seen at or close to the solar limb. The profile
data are obtained using the Extreme-ultraviolet Imaging Spectrometer on
the Hinode spacecraft. The multimillion-degree non-thermal motions are
between 20 and 60 km s-1 and appear to increase with height
above the loop tops. Motions determined from coronal lines (i.e., lines
formed at about 1.5 MK) tend to be smaller. The multimillion-degree
temperatures in the loop tops and above range from about 11 MK to 15 MK
and also tend to increase with height above the bright X-ray-emitting
loop tops. The non-thermal motions measured along the line of sight,
as well as their apparent increase with height, are supported by
Solar Dynamics Observatory Atmospheric Imaging Assembly measurements
of turbulent velocities in the plane of the sky.
Title: Non-thermal Motions in and Above Flare Loop Tops Measured by
the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode
Authors: Doschek, George A.; McKenzie, David Eugene; Warren, Harry P
Bibcode: 2014AAS...22411105D
Altcode:
The plasma volume above the soft X-ray emitting loop tops is of
particular interest for studying the formation of flare loops. We
present EIS observations of non-thermal motions (turbulence) determined
from spectral line profiles of Fe XXIII and Fe XXIV ions for three
well-observed flares near the solar limb. We compare the non-thermal
motions at temperatures near 10 MK with the motions along the same
lines-of-sight determined from lines of coronal ions such as Fe XII, Fe
XIV, and Fe XV formed at 1-2 MK. The take-away is that the non-thermal
motions obtained from Fe XXIII and Fe XXIV lines increase with height
towards the reconnection region, up to speeds of about 50-60 km/s
for the largest heights that we can observe. The implication is that
considerable plasma heating occurs outside the reconnection region. In
addition, we discuss the implications of results obtained for flares
from earlier X-ray Yohkoh observations of line profiles of Fe XXV and
Ca XIX on the current results from EIS and AIA. Fe XXV is formed at
significantly higher temperatures than any strong flare EUV spectral
line observed by EIS or by imaging telescopes such as AIA or TRACE. This
work is supported by NASA grants.
Title: Analysing spectroscopically the propagation of a CME from
its source on the disk to its impact as it propagates outwards
Authors: Harra, Louise K.; Doschek, G. A.; Matthews, Sarah A.; De
Pontieu, Bart; Long, David
Bibcode: 2014cosp...40E1159H
Altcode:
We analyse a complex coronal mass ejection observed by Hinode, SDO and
IRIS. SDO AIA shows that the eruption occurs between several active
regions with flaring occurring in all of them. Hinode EIS observed one
of the flaring active regions that shows a fast outwards propagation
which is related to the CME lifting off. The eruption is then observed
as it propagates away from the Sun, pushing the existing post-flare
loops downwards as it goes. Spectroscopic observations are made during
this time with IRIS measuring the impact that this CME front has as
it pushes the loops downwards. Strong enhancements in the cool Mg II
emission at these locations that show complex dynamics. We discuss
these new observations in context of CME models.
Title: Solar Eruptive Events (SEE) 2020 Mission Concept
Authors: Lin, R. P.; Caspi, A.; Krucker, S.; Hudson, H.; Hurford,
G.; Bandler, S.; Christe, S.; Davila, J.; Dennis, B.; Holman, G.;
Milligan, R.; Shih, A. Y.; Kahler, S.; Kontar, E.; Wiedenbeck, M.;
Cirtain, J.; Doschek, G.; Share, G. H.; Vourlidas, A.; Raymond, J.;
Smith, D. M.; McConnell, M.; Emslie, G.
Bibcode: 2013arXiv1311.5243L
Altcode:
Major solar eruptive events (SEEs), consisting of both a large flare and
a near simultaneous large fast coronal mass ejection (CME), are the most
powerful explosions and also the most powerful and energetic particle
accelerators in the solar system, producing solar energetic particles
(SEPs) up to tens of GeV for ions and hundreds of MeV for electrons. The
intense fluxes of escaping SEPs are a major hazard for humans in space
and for spacecraft. Furthermore, the solar plasma ejected at high speed
in the fast CME completely restructures the interplanetary medium
(IPM) - major SEEs therefore produce the most extreme space weather
in geospace, the interplanetary medium, and at other planets. Thus,
understanding the flare/CME energy release process(es) and the related
particle acceleration processes are major goals in Heliophysics. To
make the next major breakthroughs, we propose a new mission concept,
SEE 2020, a single spacecraft with a complement of advanced new
instruments that focus directly on the coronal energy release and
particle acceleration sites, and provide the detailed diagnostics of
the magnetic fields, plasmas, mass motions, and energetic particles
required to understand the fundamental physical processes involved.
Title: Turbulence in the Flare Reconnection Region
Authors: Doschek, George A.; McKenzie, D. E.; Warren, H.
Bibcode: 2013SPD....4430401D
Altcode:
The physical conditions such as temperature, density, and dynamical
properties in the flare reconnection region, located above the bright
soft X-ray loops, are basically not known although there have been
measurements of non-thermal hard X-ray emission properties by RHESSI
and earlier by HXT on Yohkoh. The advent of Hinode and the Solar
Dynamics Observatory (SDO) spatially resolved observations, however,
has changed this and it is now possible to measure in more detail some
of the properties of the reconnection region. AIA imagery on SDO and
the Extreme-ultraviolet Imaging Spectrometer (EIS) and X-ray Telescope
(XRT) on Hinode allow values of non-thermal motions or turbulence in
the reconnection region to be determined. Turbulence is predicted by
theoretical models of magnetic reconnection in flares (e.g., see Liu et
al. 2008, ApJ, 676, 704) and has long been inferred spectroscopically
from non-thermal broadening of flare emission lines. Studies with
Hinode/XRT and SDO/AIA demonstrate that two-dimensional investigations
of flare velocity fields can be made, by imaging the plasma sheets
above post-CME flare arcades. These measurements are made possible
through the use of local correlation tracking (LCT), as shown by
McKenzie (2013), ApJ, 766, 39, and reveal signatures of turbulence,
including temporally and spatially varying vorticity. For some flares
the AIA and XRT results can be combined with Doppler measurements of
turbulence obtained with EIS. EIS data consist of raster scans that
include the reconnection region for flares on the limb or near the
limb. A set of spectral lines are observed that cover temperatures
from 0.25 MK up to ~20 MK. A temperature in the reconnection region
is calculated from the Fe XXIII/Fe XXIV line ratio and the thermal
Doppler and instrumental widths are subtracted from the total line
widths. The remainder is non-thermal motions or turbulence. We will
present coordinated analyses of EIS and AIA observations of plasma
sheets in post-CME flares, and demonstrate that the turbulent speeds
found by LCT are about the same magnitude as those derived from EIS
spectral line profiles obtained in the same or nearby locations.
Title: Progress toward high resolution EUV spectroscopy
Authors: Korendyke, C.; Doschek, G. A.; Warren, H.; Young, P. R.;
Chua, D.; Hassler, D. M.; Landi, E.; Davila, J. M.; Klimchuck, J.;
Tun, S.; DeForest, C.; Mariska, J. T.; Solar C Spectroscopy Working
Group; LEMUR; EUVST Development Team
Bibcode: 2013SPD....44..143K
Altcode:
HIgh resolution EUV spectroscopy is a critical instrumental technique
to understand fundamental physical processes in the high temperature
solar atmosphere. Spectroscopic observations are used to measure
differential emission measure, line of sight and turbulent flows,
plasma densities and emission measures. Spatially resolved, spectra of
these emission lines with adequate cadence will provide the necessary
clues linking small scale structures with large scale, energetic
solar phenomena. The necessary observations to determine underlying
physical processes and to provide comprehensive temperature coverage
of the solar atmosphere above the chromosphere will be obtained by the
proposed EUVST instrument for Solar C. This instrument and its design
will be discussed in this paper. Progress on the VEry high Resolution
Imaging Spectrograph (VERIS) sounding rocket instrument presently under
development at the Naval Research Laboratory will also be discussed.
Title: Observations of Thermal Flare Plasma with the EUV Variability
Experiment
Authors: Warren, Harry P.; Mariska, John T.; Doschek, George A.
Bibcode: 2013ApJ...770..116W
Altcode: 2012arXiv1211.1875W
One of the defining characteristics of a solar flare is the impulsive
formation of very high temperature plasma. The properties of the
thermal emission are not well understood, however, and the analysis of
solar flare observations is often predicated on the assumption that the
flare plasma is isothermal. The EUV Variability Experiment (EVE) on the
Solar Dynamics Observatory provides spectrally resolved observations of
emission lines that span a wide range of temperatures (e.g., Fe XV-Fe
XXIV) and allow for thermal flare plasma to be studied in detail. In
this paper we describe a method for computing the differential emission
measure distribution in a flare using EVE observations and apply it to
several representative events. We find that in all phases of the flare
the differential emission measure distribution is broad. Comparisons
of EVE spectra with calculations based on parameters derived from
the Geostationary Operational Environmental Satellites soft X-ray
fluxes indicate that the isothermal approximation is generally a poor
representation of the thermal structure of a flare.
Title: Properties of a Solar Flare Kernel Observed by Hinode and SDO
Authors: Young, P. R.; Doschek, G. A.; Warren, H. P.; Hara, H.
Bibcode: 2013ApJ...766..127Y
Altcode: 2012arXiv1212.4388Y
Flare kernels are compact features located in the solar chromosphere
that are the sites of rapid heating and plasma upflow during the rise
phase of flares. An example is presented from a M1.1 class flare in
active region AR 11158 observed on 2011 February 16 07:44 UT for which
the location of the upflow region seen by EUV Imaging Spectrometer (EIS)
can be precisely aligned to high spatial resolution images obtained by
the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic
Imager (HMI) on board the Solar Dynamics Observatory (SDO). A string
of bright flare kernels is found to be aligned with a ridge of strong
magnetic field, and one kernel site is highlighted for which an upflow
speed of ≈400 km s-1 is measured in lines formed at 10-30
MK. The line-of-sight magnetic field strength at this location is
≈1000 G. Emission over a continuous range of temperatures down to
the chromosphere is found, and the kernels have a similar morphology
at all temperatures and are spatially coincident with sizes at the
resolution limit of the AIA instrument (lsim400 km). For temperatures
of 0.3-3.0 MK the EIS emission lines show multiple velocity components,
with the dominant component becoming more blueshifted with temperature
from a redshift of 35 km s-1 at 0.3 MK to a blueshift of
60 km s-1 at 3.0 MK. Emission lines from 1.5-3.0 MK show a
weak redshifted component at around 60-70 km s-1 implying
multi-directional flows at the kernel site. Significant non-thermal
broadening corresponding to velocities of ≈120 km s-1 is
found at 10-30 MK, and the electron density in the kernel, measured
at 2 MK, is 3.4 × 1010 cm-3. Finally, the Fe
XXIV λ192.03/λ255.11 ratio suggests that the EIS calibration has
changed since launch, with the long wavelength channel less sensitive
than the short wavelength channel by around a factor two.
Title: Chromospheric Evaporation in an M1.8 Flare Observed by the
Extreme-ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Young, P. R.
Bibcode: 2013ApJ...767...55D
Altcode: 2012arXiv1212.4027D
We discuss observations of chromospheric evaporation for a complex
flare that occurred on 2012 March 9 near 03:30 UT obtained from the
Extreme-ultraviolet Imaging Spectrometer (EIS) on board the Hinode
spacecraft. This was a multiple event with a strong energy input
that reached the M1.8 class when observed by EIS. EIS was in raster
mode and fortunately the slit was almost at the exact location of
a significant energy input. Also, EIS obtained a full-CCD spectrum
of the flare, i.e., the entire CCD was readout so that data were
obtained for about the 500 lines identified in the EIS wavelength
ranges. Chromospheric evaporation characterized by 150-200 km
s-1 upflows was observed in multiple locations in
multi-million degree spectral lines of flare ions such as Fe XXII,
Fe XXIII, and Fe XXIV, with simultaneous 20-60 km s-1
upflows in million degree coronal lines from ions such as Fe XII-Fe
XVI. The behavior of cooler, transition region ions such as O VI, Fe
VIII, He II, and Fe X is more complex, but upflows were also observed
in Fe VIII and Fe X lines. At a point close to strong energy input in
space and time, the flare ions Fe XXII, Fe XXIII, and Fe XXIV reveal
an isothermal source with a temperature close to 14 MK and no strong
blueshifted components. At this location there is a strong downflow
in cooler active region lines from ions such as Fe XIII and Fe XIV,
on the order of 200 km s-1. We speculate that this downflow
may be evidence of the downward shock produced by reconnection in the
current sheet seen in MHD simulations. A sunquake also occurred near
this location. Electron densities were obtained from density sensitive
lines ratios from Fe XIII and Fe XIV. Atmospheric Imaging Assembly
(AIA) observations from the Solar Dynamics Observatory are used with
JHelioviewer to obtain a qualitative overview of the flare. However,
AIA data are not presented in this paper. In summary, spectroscopic data
from EIS are presented that can be used for predictive tests of models
of chromospheric evaporation as envisaged in the Standard Flare Model.
Title: Flare Footpoint Regions Observed by the Extreme-ultraviolet
Imaging Spectrometer (EIS) on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Young, P. R.; Caspi, A.
Bibcode: 2013enss.confE..74D
Altcode:
The Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode has
observed flare footpoints using a variety of studies designed to
observe various aspects of the solar flare Standard Model. Some of
these observations are accompanied by imaging data from RHESSI. We
present observations of upflows in flare footpoint regions obtained
from picket-fence raster observations of two flares that occurred
on 24 and 25 September 2011. The observations consist of upflow and
non-thermal speeds at various temperatures (from about 1 MK to 15
MK) at footpoint regions as well as a limited differential emission
measure. RHESSI observations provide constraints on the energetic
electron precipitation into the footpoints. Electron densities are
available from an Fe XIV ratio, and SDO AIA data are also investigated
for context. The RHESSI energy input will be assessed in terms of 1D
models of the footpoint regions.
Title: SDO and Hinode observations of coronal heating at a flare
kernel site
Authors: Young, P. R.; Doschek, G. A.; Warren, H. P.; Hara, H.
Bibcode: 2013enss.confE..36Y
Altcode:
Flare kernels are compact features located in the chromosphere that
are the sites of rapid heating and plasma upflow during the rise phase
of flares. They provide an excellent opportunity for testing models of
energy transport and dissipation in the solar atmosphere as they are
very bright and emit over a wide temperature range. A M1.1 class flare
that peaked at 07:44 UT on 2011 February 16 was observed simultaneously
by SDO and Hinode, and one flare kernel observed prior to the flare
peak is highlighted. It is found to emit at all temperatures from
the chromosphere through to 30 MK, with all AIA channels brightening
simultaneously and rise times of only 1 minute. The kernel is located on
a ridge of strong magnetic field close to a neutral line in the active
region. The kernel is at the resolution limit of AIA, suggesting a size
of < 0.6 arcsec. Hinode/EIS allows velocity patterns in the kernel
to be tracked over a wide temperature range and reveals a dominant high
speed upflow of 400 km/s at temperatures of 10-30 MK, with both down
and upflows measured at cooler temperatures of 1.5-3.0 MK, suggesting
unresolved structures. All emission lines show evidence of significant
non-thermal broadening, and the electron density of the plasma is 3.4
x 10^10 cm-3. The observations are compared to models of chromospheric
evaporation and similarities and differences are highlighted.
Title: Chromospheric Evaporation in an M1.8 Flare Observed by the
Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode
Authors: Doschek, G. A.; Warren, H. P.
Bibcode: 2012AGUFMSH52B..04D
Altcode:
We discuss observations of chromospheric evaporation for a flare
that occurred on 9 March 2012 near 03:30 UT obtained from the
Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft. This was a multiple event with a strong energy input
that reached the M1.8 class when observed by EIS. EIS was in raster
mode and fortunately the slit reached almost the exact location of a
significant energy input. Also, fortunately EIS obtained a full-CCD
spectrum of the flare, i.e., the entire CCD was readout so that data
were obtained for about the 500 lines identified in the EIS wavelength
ranges. Chromospheric evaporation characterized by 150-200 km/s upflows
was observed in several locations in multi-million degree spectral lines
of flare ions such as Fe XXII, Fe XXIII, Fe XXIV, with simultaneous 20 -
60 km/s upflows in a host of million degree coronal lines from ions such
as Fe XI - Fe XVI. The behavior of cooler, transition region ions such
as O VI, Fe VIII, He II, and Fe X is more complex. At a point close
to strong energy input, the flare ions reveal an isothermal source
with a temperature close to 14 MK. At this point there is a strong
downflow in cooler active region lines from ions such as Fe XIII
and Fe XIV. Electron densities were obtained from density sensitive
lines ratios from Fe XIII and Fe XIV. The results to be presented
are refined from the preliminary data given above and combined with
context AIA observations for a comparison with predictions of models
of chromospheric evaporation as envisaged in the Standard Flare Model.
Title: A Space Weather Mission to the Earth's 5th Lagrangian Point
(L5)
Authors: Howard, R. A.; Vourlidas, A.; Ko, Y.; Biesecker, D. A.;
Krucker, S.; Murphy, N.; Bogdan, T. J.; St Cyr, O. C.; Davila, J. M.;
Doschek, G. A.; Gopalswamy, N.; Korendyke, C. M.; Laming, J. M.;
Liewer, P. C.; Lin, R. P.; Plunkett, S. P.; Socker, D. G.; Tomczyk,
S.; Webb, D. F.
Bibcode: 2012AGUFMSA13D..07H
Altcode:
The highly successful STEREO mission, launched by NASA in 2006,
consisted of two spacecraft in heliocentric orbit, one leading and
one trailing the Earth and each separating from Earth at the rate
of about 22.5 degrees per year. Thus the two spacecraft have been
probing different probe/Sun/Earth angles. The utility of having remote
sensing and in-situ instrumentation away from the Sun-Earth line was
well demonstrated by STEREO. Here we propose the concept of a mission
at the 5th Lagrangian "point" in the Earth/Sun system, located behind
Earth about 60 degrees to the East of the Sun-Earth line. Such a mission
would enable many aspects affecting space weather to be well determined
and thus improving the prediction of the conditions of the solar wind
as it impinges on geospace. For example, Coronal Mass Ejections can
tracked for a significant distance toward Earth, new active regions
can be observed before they become visible to the Earth observer, the
solar wind can be measured before it rotates to Earth. The advantages
of such a mission will be discussed in this presentation.
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
Bibcode: 2012ExA....34..273T
Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1'' and 0.3''), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with
0.14'' per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
Title: The Dynamics and Heating of Active Region Loops
Authors: Doschek, G. A.
Bibcode: 2012ApJ...754..153D
Altcode:
I examine the dynamics of active regions using spectra obtained by
the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft. I show the relationship between non-thermal velocities,
Doppler outflows and downflows, intensities, and electron density for
two representative active regions out of a group of 18 active regions
examined. Results from the other active regions are summarized. Imaging
spectra of these active regions were obtained from a number of
different EIS raster observations. In the case of the outflows for
the two representative regions, two-Gaussian fits were made to line
profiles of Fe XII and Fe XIII to obtain quantitative information on
high-speed components of the outflows. A three-Gaussian fit was made
for the Fe XII line at λ195.119. The highest speed outflows occur in
weak regions adjacent to the bright loops in active regions. They are
weak (less than 5% of the intensity of the main spectral component
in the brightest parts of active regions) and even in the extensive
flow regions they are generally less than 25% of the intensity of the
main component. The outflow regions are characterized by long or open
magnetic field lines and I suggest that the apparent absence of these
higher speed outflows in bright regions is due to abundant stationary
plasma in the closed bright loop regions that mask or overwhelm the
outflow signal.
Title: Hinode/EIS Flare Spectra During RHESSI Hard X-ray Bursts
Authors: Young, Peter R.; Warren, H.; Doschek, G.
Bibcode: 2012AAS...22020442Y
Altcode:
The standard flare model requires a beam of non-thermal electrons
- generated at the coronal flare site - to hit the chromosphere
and trigger heating and chromospheric evaporation. Ultraviolet
spectrometers allow the heated, evaporating plasma to be observed
and its properties measured. Observations of a M3 flare observed in
2011 September with Hinode/EIS, RHESSI and SDO/AIA will be presented,
revealing the physical conditions in the flare ribbons at the time of
the hard X-ray bursts. At the hottest temperatures (20 MK) upflowing
plasma with speeds up to 500 km/s are found co-spatial with stationary
plasma, while at cooler temperatures (0.5-2 MK) small downflows and
large non-thermal broadening are found. These observations will be
compared with predictions from multi-strand hydrodynamic simulations
that take the RHESSI-derived electron beam spectrum as input.
Title: Measurements of the Super-Hot Flare Component Using the Fe
XXV and Fe XXVI Lines Near 1.8 Å
Authors: Doschek, George A.
Bibcode: 2012AAS...22041004D
Altcode:
The so-called magnetic reconnection region in the Standard Flare Model
has not been adequately explored observationally, and theoretical
predictions are difficult to make due to the complexity of the magnetic
reconnection process. Observations from RHESSI and other spacecraft
have indicated that many flares exhibit hot plasma that may extend up
to 50 MK, producing copious hard and soft X-rays (e.g., Caspi &
Lin 2010, ApJ, 725, L161). Some of this plasma must be contained in the
reconnection region as well as in closed flare loops via chromospheric
evaporation. In this contribution I discuss the spectroscopy of the Fe
XXV and Fe XXVI multiplets near 1.8 Angstroms and how these multiplets
may be used to infer physical conditions in the reconnection region that
include electron temperature, departure from ionization equilibrium,
non-thermal motions, bulk Doppler motions, electron density, and
polarization. I also consider briefly the types of instrumentation
necessary to obtain the spectral observations. I also briefly discuss
the diagnostic potential of the entire X-ray spectrum from about 2
to 25 Angstroms for diagnosing physical conditions is multi-million
degree flare plasmas.
Title: Redshifts, Widths, and Radiances of Spectral Lines Emitted
by the Solar Transition Region
Authors: Feldman, U.; Dammasch, I. E.; Doschek, G. A.
Bibcode: 2011ApJ...743..165F
Altcode:
A long-standing problem in understanding the physics of the transition
region has been the ubiquitous redshifts of transition region
ultraviolet spectral lines relative to chromospheric emission lines,
a result known since the Skylab era. Extended spectral scans performed
for various regions of the solar disk by the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer on the Solar and
Heliospheric Observatory contain thousands of line profiles per study
and allow a thorough investigation of the redshift phenomenon. In using
these data from seven distinct disk areas made in lines spanning the
chromosphere to coronal temperature range, we derive a relationship
between Doppler wavelength shifts and radiances and a relationship
between line widths and radiances. While chromospheric and coronal
lines emitted by very bright plasmas may in some cases show pronounced
redshifts, transition-region lines predominantly show redshifts
everywhere in the quiet Sun and in active regions. In coronal holes,
however, they display a reduced shift, which at times altogether
disappears. The observations and the findings will be described,
and possible explanations will be considered.
Title: LEMUR (Large European Module for solar Ultraviolet Research):
a VUV imaging spectrograph for the JAXA Solar-C Mission
Authors: Korendyke, Clarence M.; Teriaca, Luca; Doschek, George A.;
Harra, Louise K.; Schühle, Udo H.; Shimizu, Toshifumi
Bibcode: 2011SPIE.8148E..0IK
Altcode: 2011SPIE.8148E..17K
LEMUR is a VUV imaging spectrograph with 0.28" resolution. Incident
solar radiation is imaged onto the spectrograph slit by a single
mirror telescope consisting of a 30-cm steerable f/12 off-axis
paraboloid mirror. The spectrograph slit is imaged and dispersed by
a highly corrected grating that focuses the solar spectrum over the
detectors. The mirror is coated with a suitable multilayer with B4C
top-coating providing a reflectance peak around 18.5 nm besides the
usual B4C range above 500Å. The grating is formed by two halves, one
optimized for performances around 185Å and the other above 500Å. Three
intensified CCD cameras will record spectra above 50 nm while a large
format CCD array with an aluminum filter will be used around 185Å.
Title: The coronal suprathermal particle explorer (C-SPEX)
Authors: Moses, J. Daniel; Brown, Charles; Doschek, George; Ko,
Yuan-Kuen; Korendyke, Clarence; Laming, J. Martin; Socker, Dennis;
Tylka, Allen; McMullin, Donald; Ng, Chee; Wassom, Steven; Lee, Martin;
Auchère, Frédéric; Fineschi, Silvano; Carter, Tim
Bibcode: 2011SPIE.8148E..0JM
Altcode: 2011SPIE.8148E..18M
The primary science objective of the Coronal Suprathermal Particle
Explorer (C-SPEX) is to investigate the spatial and temporal
variations of coronal suprathermal particle populations that are
seeds for acceleration to solar energetic particles (SEPs). It is
understood that such seed particle populations vary with coronal
structures and can change responding to solar flare and coronal mass
ejection (CME) events. Models have shown that higher densities of
suprathermal protons can result in higher rates of acceleration to
high energies. Understanding the variations in the suprathermal seed
particle population is thus crucial for understanding the variations
in SEPs. However, direct measurements are still lacking. C-SPEX
will measure the variation in the suprathermal protons across
various coronal magnetic structures, before/after the passage of CME
shocks, in the post-CME current sheets, and before/after major solar
flares. Understanding the causes for variation in the suprathermal
seed particle population and its effect on the variation in SEPs
will also help build the predictive capability of SEPs that reach
Earth. The CSPEX measurements will be obtained from instrumentation
on the International Space Station (ISS) employing well-established
UV coronal spectroscopy techniques.
Title: Solar Eruptive Events (SEE) Mission for the Next Solar Maximum
Authors: Lin, Robert P.; Krucker, S.; Caspi, A.; Hurford, G.; Dennis,
B.; Holman, G.; Christe, S.; Shih, A. Y.; Bandler, S.; Davila, J.;
Milligan, R.; Kahler, S.; Weidenbeck, M.; Doschek, G.; Vourlidas,
A.; Share, G.; Raymond, J.; McConnell, M.; Emslie, G.
Bibcode: 2011SPD....42.2204L
Altcode: 2011BAAS..43S.2204L
Major solar eruptive events consisting of both a large flare and a
near simultaneous large fast coronal mass ejection (CME), are the most
powerful explosions and also the most powerful and energetic particle
accelerators in the solar system, producing solar energetic particles
(SEPs) up to tens of GeV for ions and 10s-100s of MeV for electrons. The
intense fluxes of escaping SEPs are a major hazard for humans in space
and for spacecraft. Furthermore, the solar plasma ejected at high speed
in the fast CME completely restructures the interplanetary medium,
producing the most extreme space weather in geospace, at other planets,
and in the heliosphere. Thus, the understanding of the flare/CME
energy release process and of the related particle acceleration
processes in SEEs is a major goal in Heliophysics. Here we present
a concept for a Solar Eruptive Events (SEE) mission, consisting of a
comprehensive set of advanced new instruments on the single spacecraft
in low Earth orbit, that focus directly on the coronal energy release
and particle acceleration in flares and CMEs. SEE will provide new
focussing hard X-ray imaging spectroscopy of energetic electrons in the
flare acceleration region, new energetic neutral atom (ENA) imaging
spectroscopy of SEPs being accelerated by the CME at altitudes above
2 solar radii, gamma-ray imaging spectroscopy of flare-accelerated
energetic ions, plus detailed EUV/UV/Soft X-ray diagnostics of the
plasmas density, temperature, and mass motions in the energy release and
particle acceleration regions. Together with ground-based measurements
of coronal magnetic fields from ATST, FASR, and COSMO, SEE will enable
major breakthroughs in our understanding of the fundamental physical
processes involved in major solar eruptive events.
Title: Flares Observed By Hinode During 14-18 February 2011
Authors: Young, Peter R.; Doschek, G. A.; Warren, H. P.
Bibcode: 2011SPD....42.2213Y
Altcode: 2011BAAS..43S.2213Y
Active region AR 11158 produced an X1 flare and several M flares during
2011 February 14-18, and yielded the best set of flare observations
captured by the Hinode satellite in four years. Finding the mechanisms
responsible for flares was one of the major science goals of the Hinode
mission, and data from AR 11158 will be presented to demonstrate how
this goal is being achieved with Hinode data. A particular focus will
be on relating plasma flows and temperature and density changes measured
with the EIS instrument to the magnetic field evolution observed by SOT,
and the coronal evolution observed with SDO/AIA.
Title: The Coronal Suprathermal Particle Explorer (C-SPEX)
Authors: Moses, John Daniel; Brown, C. M.; Doschek, G. A.; -. Ko,
Y.; Korendyke, C. M.; Laming, J. M.; Rakowski, C. E.; Socker, D. G.;
Tylka, A.; Ng, C. K.; Wassom, S. R.; McMullin, D. R.; Lee, M. A.;
Auchere, F.; Fineschi, S.
Bibcode: 2011SPD....42.1519M
Altcode: 2011BAAS..43S.1519M
The primary science objective of the Coronal Suprathermal Particle
Explorer (C-SPEX) is to investigate the spatial and temporal
variations of coronal suprathermal particle populations that are
seeds for acceleration to solar energetic particles (SEPs). It is
understood that such seed particle populations vary with coronal
structures and can change responding to solar flare and coronal mass
ejection (CME) events. Models have shown that higher densities of
suprathermal protons can result in higher rates of acceleration to
high energies. Understanding the variations in the suprathermal seed
particle population is thus crucial for understanding the variations
in SEPs. However, direct measurements are still lacking. C-SPEX
will measure the variation in the suprathermal protons across various
coronal magnetic structures, before/after the passage of CME shocks, in
the post-CME current sheets, and before/after major solar flares. The
measurements will not only constrain models of SEP acceleration but
also constrain models of the production of suprathermal particles from
processes such as magnetic reconnection at the Sun. Understanding the
causes for variation in the suprathermal seed particle population and
its effect on the variation in SEPs will also help build the predictive
capability of SEPs that reach Earth. The C-SPEX measurements will
be obtained from instrumentation on the International Space Station
(ISS) employing well-established UV coronal spectroscopy techniques. The
unique aspect of C-SPEX is a >100-fold increase of light gathering
power over any previous UV coronal spectrometer. It is demonstrated
C-SPEX will thus overcome the limitations in signal to noise that have
thwarted prior attempts to observe suprathermals in the corona. The
present lack of a means to predict the variability of SEP intensities
and the likelihood C-SPEX will help develop such predictions makes the
proposed investigation directly relevant to each of the three strategic
objectives of the NASA Heliophysics Research Strategic Objectives.
Title: TOPICAL REVIEW The solar UV-x-ray spectrum from 1.5 to 2000 Å
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 2010JPhB...43w2001D
Altcode:
This review illustrates the potential of UV-x-ray spectroscopy
for determining the physical conditions in the solar chromosphere,
transition region and corona, and how spectroscopy can be used as a
tool to understand the physical mechanisms governing the atmosphere. It
also illustrates the potential for understanding transient events
such as solar flares. This is a vast topic, and therefore the review
is necessarily not complete, but we have tried to be as general as
possible in showing in particular how solar spectra are currently being
used to understand the solar upper atmosphere. The review is intended
for non-solar physicists with an interest in spectroscopy as well as
for solar physicists who are not specialists in spectroscopy.
Title: The Case for Ultra-High Spatial Resolution (~0.2'' or better)
EUV Solar Spectroscopy: Spatial Scales in the Transition Region and
Corona Derived from SOHO/SUMER and Hinode/EIS Spectra
Authors: Doschek, G. A.
Bibcode: 2010AGUFMSH11B1653D
Altcode:
EUV spectrometers on SOHO (SUMER) and Hinode (EIS) have 1” pixels
which translate to a spatial resolution at the Sun of about 1400 km. We
discuss spectroscopic results from SUMER demonstrating that current
orbital solar instrumentation greatly under-resolves the transition
region at temperatures ranging from about 20,000 K to 1 million degrees
K. From EIS spectra, we show with specific examples using active region
and coronal hole bright point data that coronal structures may be close
to being resolved at 0.2-0.3” and that heating to active region
temperatures can occur over regions with spatial scales well-below
1-2”. These results are obtained from electron density measurements
that allow filling factors and path lengths to be determined, from
spatial images constructed from the spectra, and also from line widths
in some transition region cases that allow path lengths to be estimated
from opacity. The EIS results could be considerably improved by new
and detailed calculations of the atomic structure and electron impact
excitation data for EUV emission lines of Fe XII and Fe XIII. Putting
together the SUMER and EIS data implies that in order to trace the flow
of energy into the corona from lower temperature regions significantly
higher spatial resolution instrumentation is required. It is difficult
to imagine how problems such as the coronal heating problem can be
solved without such instrumentation.
Title: Physical Properties of Solar Flares: New Results from EVE/SDO
Authors: Warren, H. P.; Mariska, J. T.; Doschek, G. A.; Eve Team
Bibcode: 2010AGUFMSH13A..06W
Altcode:
Much of our current understanding of the temperature and density
structure of solar flares has been derived from broad band X-ray
instruments, such as RHESSI, GOES, and SXT/Yohkoh, or the observation
of isolated emission lines, such as from BCS/Yohkoh. This has lead
to uncertainties in determining the distribution of temperatures and
densities in a flare. The EUV Variability Experiment (EVE) on the Solar
Dynamics Observatory (SDO) provides an unprecedented opportunity to
observe a very wide range of high-temperature emission lines at high
cadence (10 s) and relatively high spectral resolution (1 A). The
spectral range between 90 and 200 Angstroms is particularly rich in
emission lines from Fe that are formed at temperatures above 7 MK
(Fe XVIII - Fe XXIV). This range also includes one of the few density
diagnostics (Fe XXI 145.66/128.75) that is useful in solar flare
observations. Our initial calculations suggest very broad differential
emission measure distributions and indicate high densities (Log Ne as
high as 11.7), which implies a very rapid cooling of flare plasma. These
observations are broadly consistent with flare models that allow for
the release of energy on many independent threads and we will discuss
these results in the context of current theories of solar flares.
Title: Science Objectives for an X-Ray Microcalorimeter Observing
the Sun
Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M;
Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse,
N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.;
DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra,
A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg,
C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.;
Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska,
J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres,
G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.;
Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz,
J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.;
Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B.
Bibcode: 2010arXiv1011.4052L
Altcode:
We present the science case for a broadband X-ray imager with
high-resolution spectroscopy, including simulations of X-ray spectral
diagnostics of both active regions and solar flares. This is part of
a trilogy of white papers discussing science, instrument (Bandler et
al. 2010), and missions (Bookbinder et al. 2010) to exploit major
advances recently made in transition-edge sensor (TES) detector
technology that enable resolution better than 2 eV in an array that
can handle high count rates. Combined with a modest X-ray mirror, this
instrument would combine arcsecondscale imaging with high-resolution
spectra over a field of view sufficiently large for the study of
active regions and flares, enabling a wide range of studies such as
the detection of microheating in active regions, ion-resolved velocity
flows, and the presence of non-thermal electrons in hot plasmas. It
would also enable more direct comparisons between solar and stellar
soft X-ray spectra, a waveband in which (unusually) we currently have
much better stellar data than we do of the Sun.
Title: Multiple Component Outflows in an Active Region Observed with
the EUV Imaging Spectrometer on Hinode
Authors: Bryans, P.; Young, P. R.; Doschek, G. A.
Bibcode: 2010ApJ...715.1012B
Altcode: 2010arXiv1004.5085B
We have used the Extreme Ultraviolet Imaging Spectrometer on the
Hinode spacecraft to observe large areas of outflow near an active
region. These outflows are seen to persist for at least 6 days. The
emission line profiles suggest that the outflow region is composed of
multiple outflowing components, Doppler-shifted with respect to each
other. We have modeled this scenario by imposing a double-Gaussian fit
to the line profiles. These fits represent the profile markedly better
than a single-Gaussian fit for Fe XII and XIII emission lines. For
the fastest outflowing components, we find velocities as high as 200
km s-1. However, there remains a correlation between the
fitted line velocities and widths, suggesting that the outflows are
not fully resolved by the double-Gaussian fit and that the outflow
may be comprised of further components.
Title: A new approach for deriving the solar irradiance from
nonflaring solar upper atmosphere plasmas at 2 × 104
≤ T ≤ 2 × 107 K
Authors: Feldman, U.; Brown, C. M.; Seely, J. F.; Dammasch, I. E.;
Landi, E.; Doschek, G. A.; Colgan, J.; Abdallah, J.; Fontes, C. J.;
Sherrill, M. E.
Bibcode: 2010JGRA..115.3101F
Altcode: 2010JGRA..11503101F
We propose a new approach for deriving the solar irradiance due to the
emission by solar upper atmosphere plasmas at 2 × 104 ≤
T ≤ 2 × 107 K for wavelengths shorter than 800 Å. Our
approach is based on a new understanding of the properties of the solar
upper atmosphere; specifically, the discovery that the majority of
emission from the nonflaring solar upper transition region and corona in
the temperature range 3 × 105 ≤ T ≤ 3 × 106
K arises from isothermal plasmas that have four distinct temperatures:
0.35, 0.9, 1.4, and 3 × 106 K. Although the lower transition
region (2 × 104 ≤ T ≤ 2 × 105 K) of coronal
holes, quiet regions or active regions, is multithermal and variable
in brightness, the shape of emission measure versus temperature curves
in this region is almost constant. At any given time, flaring plasmas
are for the most part isothermal, although their emission measure and
temperature continuously change. In this paper we review these recent
results and propose a set of simple spectrometers for recording the
solar spectrum in several narrow bands. The solar emission measure,
average plasma temperature, and composition can be derived using the
measured line fluxes. By combining the emission measure and other
plasma properties with the output of a suite of atomic physics codes,
which are also described here, the solar irradiance at wavelengths
shorter than 800 Å can be calculated.
Title: Bright Points and Jets in Polar Coronal Holes Observed by
the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Landi, E.; Warren, H. P.; Harra, L. K.
Bibcode: 2010ApJ...710.1806D
Altcode:
We present observations of polar coronal hole bright points (BPs)
made with the Extreme-ultraviolet Imaging Spectrometer (EIS) on the
Hinode spacecraft. The data consist of raster images of BPs in multiple
spectral lines from mostly coronal ions, e.g., Fe X-Fe XV. The BPs
are observed for short intervals and thus the data are snapshots of
the BPs obtained during their evolution. The images reveal a complex
unresolved temperature structure (EIS resolution is about 2''), with the
highest temperature being about 2 × 106 K. Some BPs appear
as small loops with temperatures that are highest near the top. But
others are more point-like with surrounding structures. However, the
thermal time evolution of the BPs is an important factor in their
appearance. A BP may appear quite different at different times. We
discuss one BP with an associated jet that is bright enough to allow
statistically meaningful measurements. The jet Doppler speed along the
line of sight is about 15-20 km s-1. Electron densities of
the BPs and the jet are typically near 109 cm-3,
which implies path lengths along the line of sight on the order of a
few arcsec. We also construct differential emission measure curves for
two of the best observed BPs. High spatial resolution (significantly
better than 1'') is required to fully resolve the BP structures.
Title: The Effect of Hot Coronal Electrons on Extreme-Ultraviolet
Spectral Lines of He II Emitted by Solar Transition Region Plasmas
Authors: Feldman, U.; Ralchenko, Yu.; Doschek, G. A.
Bibcode: 2010ApJ...708..244F
Altcode:
The cause of the lower intensities of extreme-ultraviolet (EUV) He II
lines emitted by coronal hole (CH) plasmas compared with quiet Sun
(QS) plasmas has been the subject of many studies dating back over
half a century. In this paper, we study the effect of small amounts
of "hot" electrons at coronal temperatures (Te = 1.4 ×
106 K) on the intensities of EUV He II lines, as well
as on the intensities of EUV lines of C III, C IV, O III, and O IV
emitted by 1.5 × 104 K-1.5 × 105 K (4.2 <=
log Te <= 5.2) plasmas in the QS. We show that although
the influence of a fraction as small as 10-4-10-3
of hot electrons on the intensities of the C and O lines is noticeable,
the effect on the intensities of the He lines is much larger, to the
extent that it could explain the excess brightness of He II lines
emitted by QS regions relative to CH plasmas.
Title: The Electron Temperature of the Solar Transition Region as
Derived from EIS and SUMER
Authors: Muglach, K.; Landi, E.; Doschek, G. A.
Bibcode: 2010ApJ...708..550M
Altcode:
We use UV and extreme-UV emission lines observed in quiet regions on the
solar disk with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) instrument and the Extreme Ultraviolet Imaging Spectrometer
(EIS) to determine the electron temperature in solar transition region
plasmas. Prominent emission lines of O IV and O VI are present in
the solar spectrum, and the measured intensity line ratios provide
electron temperatures in the range of log T = 5.6-6.1. We find that the
theoretical O IV and O VI ion formation temperatures are considerably
lower than our derived temperatures. The line ratios expected from
a plasma in ionization equilibrium are larger by a factor of about
2-5 than the measured line ratios. A careful cross-calibration of
SUMER and EIS has been carried out, which excludes errors in the
relative calibration of the two instruments. We checked for other
instrumental and observational effects, as well as line blending,
and can exclude them as a possible source of the discrepancy between
theoretical and observed line ratios. Using a multi-thermal quiet-Sun
differential emission measure changes the theoretical line ratio by
up to 28% which is not sufficient as an explanation. We also explored
additional excitation mechanisms. Photoexcitation from photospheric
blackbody radiation, self-absorption, and recombination into excited
levels cannot be a possible solution. Adding a second Maxwellian to
simulate the presence of non-thermal, high-energy electrons in the
plasma distribution of velocities also did not solve the discrepancy.
Title: Ultra-Hot Plasma in Active Regions Observed by the
Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Ko, Y. -K.; Doschek, G. A.; Warren, H. P.; Yount, P. R.
Bibcode: 2009ASPC..415..275K
Altcode:
We present a specific algorithm to extract the Ca XVII λ192.858
line from the blending with two Fe XI and six O V lines in the
Hinode/EIS data. This is a review of the work to be published by Ko et
al. (2009). We demonstrate that the Ca XVII line can be satisfactorily
extracted from the blend if the Ca XVII emission contributes to at
least 10% of the blend. This Ca XVII line, with formation temperature
at 6 million degrees, is thus a viable line in the EIS data to probe the
thermal structure in non-flaring active regions at its high temperature
end and provides valuable constraints for coronal heating models.
Title: Hot Plasma in Nonflaring Active Regions Observed by the
Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Ko, Yuan-Kuen; Doschek, George A.; Warren, Harry P.; Young,
Peter R.
Bibcode: 2009ApJ...697.1956K
Altcode: 2009arXiv0903.3029K
The Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft obtains high-resolution spectra of the solar atmosphere
in two wavelength ranges: 170-210 and 250-290 Å. These wavelength
regions contain a wealth of emission lines covering temperature regions
from the chromosphere/transition region (e.g., He II, Si VII) up to
flare temperatures (Fe XXIII, Fe XXIV). Of particular interest for
understanding coronal heating is a line of Ca XVII at 192.858 Å,
formed near a temperature of 6 × 106 K. However, this
line is blended with two Fe XI and six O V lines. In this paper we
discuss a specific procedure to extract the Ca XVII line from the
blend. We have performed this procedure on the raster data of five
active regions (ARs) and a limb flare, and demonstrated that the Ca
XVII line can be satisfactorily extracted from the blend if the Ca XVII
flux contributes to at least ~10% of the blend. We show examples of the
high-temperature corona depicted by the Ca XVII emission and find that
the Ca XVII emission has three morphological features in these ARs: (1)
"fat" medium-sized loops confined in a smaller space than the 1 million
degree corona, (2) weaker, diffuse emission surrounding these loops that
spread over the core of the AR, and (3) the locations of the strong Ca
XVII loops are often weak in line emission formed from the 1 million
degree plasma. We find that the emission measure ratio of the 6 million
degree plasma relative to the cooler 1 million degree plasma in the
core of the ARs, using the Ca XVII to Fe XI line intensity ratio as a
proxy, can be as high as 10. Outside of the AR core where the 1 million
degree loops are abundant, the ratio has an upper limit of about 0.5.
Title: Diagnostics of High Temperature Active Region Plasma with
EIS/Hinode
Authors: Warren, Harry; Ko, Y.; Doschek, G.
Bibcode: 2009SPD....40.1212W
Altcode:
Solar active region loops at different temperatures appear to have very
different properties. Coronal loops with apex temperatures near 1 MK
have high densities and lifetimes long relative to a characteristic
cooling time. The properties of these loops are generally consistent
with impulsive heating models. Higher temperature coronal emission,
in contrast, is generally consistent with steady heating models. This
conclusion is largely based on the analysis of broad-band observations
from the SXT on Yohkoh, which had modest spatial resolution and
temperature discrimination. Because of these diagnostic limitations the
time scale for the heating in the core of an active region is still
an open question. The high resolution EIS spectrometer on Hinode
provides new spectroscopic diagnostics of high temperature plasma
in active region cores through the observation of Ca XIV, XV, XVI,
and XVII emission lines. An initial survey of active regions cores
indicates that the emission measure at high temperatures ( 3 MK) is
uncorrelated with the emission measure at lower temperatures ( 1 MK),
suggesting that these loops are not fully cooling. These results will
be discussed in the context of hydrodynamic models.
Title: Multiple Component Outflows in Active Regions observed by EIS
Authors: Bryans, Paul; Doschek, G. A.; Young, P. R.
Bibcode: 2009SPD....40.1221B
Altcode:
We have used the Extreme Ultraviolet Imaging Spectrometer (EIS) on
the Hinode spacecraft to observe large areas of outflow near an active
region. These outflows are seen to persist for a number of days. The
emission line profiles suggest that the outflow region is composed of
multiple outflowing components, Doppler-shifted with respect to each
other. We have modelled this scenario by imposing a double-Gaussian fit
to the line profiles; these fits represent the profile markedly better
than a single Gaussian fit. For the fastest outflowing components,
we find velocities as high as 200 km/s. However, there remains a
correlation between the fitted line velocities and widths, suggesting
that the outflows are not fully resolved by the double-Gaussian fit
and that the outflow may be comprised of further components.
Title: Can the Composition of the Solar Corona Be Derived from
Hinode/Extreme-Ultraviolet Imaging Spectrometer Spectra?
Authors: Feldman, U.; Warren, H. P.; Brown, C. M.; Doschek, G. A.
Bibcode: 2009ApJ...695...36F
Altcode:
Elemental abundances appear to be the same everywhere in the
photosphere, but in the solar corona they vary in different
regions. Abundances in quiet Sun (closed) flux tubes are different from
those in coronal hole (CH, open) magnetic field regions, and therefore
abundance variations might possibly be used to determine locations of
slow and fast solar wind in the corona. In active regions, abundances
can change from region to region and can vary with the age of the
region. In the present paper, we evaluate the feasibility of determining
relative elemental abundances in the corona using spectra acquired by
the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. As test
cases, we attempt to evaluate the coronal composition above the limb
in an equatorial quiet region and in a polar CH. We also determine
the elemental composition of coronal regions with moderate activity on
the disk and at the limb. To estimate the accuracy of the instrumental
calibration and the atomic physics used in the calculations, we compare
the derived composition with earlier derivations from spectra recorded
by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
in similar regions. We find that EIS can be used to determine relative
abundance variations in the inner solar corona. The determination of
absolute abundances can also be attempted after additional calibrations
in space are accomplished.
Title: Coronal Nonthermal Velocity Following Helicity Injection
Before an X-Class Flare
Authors: Harra, L. K.; Williams, D. R.; Wallace, A. J.; Magara, T.;
Hara, H.; Tsuneta, S.; Sterling, A. C.; Doschek, G. A.
Bibcode: 2009ApJ...691L..99H
Altcode:
We explore the "pre-flare" behavior of the corona in a three-day
period building up to an X-class flare on 2006 December 13 by analyzing
EUV spectral profiles from the Hinode EUV Imaging Spectrometer (EIS)
instrument. We found an increase in the coronal spectral line widths,
beginning after the time of saturation of the injected helicity as
measured by Magara & Tsuneta. In addition, this increase in line
widths (indicating nonthermal motions) starts before any eruptive
activity occurs. The Hinode EIS has the sensitivity to measure changes
in the buildup to a flare many hours before the flare begins.
Title: Observations of Active Region Loops with the EUV Imaging
Spectrometer on Hinode
Authors: Warren, Harry P.; Ugarte-Urra, Ignacio; Doschek, George A.;
Brooks, David H.; Williams, David R.
Bibcode: 2008ApJ...686L.131W
Altcode: 2008arXiv0808.3227W
Previous solar observations have shown that coronal loops near 1 MK
are difficult to reconcile with simple heating models. These loops have
lifetimes that are long relative to a radiative cooling time, suggesting
quasi-steady heating. The electron densities in these loops, however,
are too high to be consistent with thermodynamic equilibrium. Models
proposed to explain these properties generally rely on the existence
of smaller scale filaments within the loop that are in various stages
of heating and cooling. Such a framework implies that there should be
a distribution of temperatures within a coronal loop. In this paper
we analyze new observations from the EUV Imaging Spectrometer (EIS)
on Hinode. EIS is capable of observing active regions over a wide range
of temperatures (Fe VIII-Fe XVII) at relatively high spatial resolution
(1''). We find that most isolated coronal loops that are bright in Fe
XII generally have very narrow temperature distributions (σT
lesssim 3 × 105 K), but are not isothermal. We also derive
volumetric filling factors in these loops of approximately 10%. Both
results lend support to the filament models.
Title: Flows and Nonthermal Velocities in Solar Active Regions
Observed with the EUV Imaging Spectrometer on Hinode: A Tracer of
Active Region Sources of Heliospheric Magnetic Fields?
Authors: Doschek, G. A.; Warren, H. P.; Mariska, J. T.; Muglach, K.;
Culhane, J. L.; Hara, H.; Watanabe, T.
Bibcode: 2008ApJ...686.1362D
Altcode: 2008arXiv0807.2860D
From Doppler velocity maps of active regions constructed from spectra
obtained by the EUV Imaging Spectrometer (EIS) on the Hinode spacecraft
we observe large areas of outflow (20-50 km s-1) that can
persist for at least a day. These outflows occur in areas of active
regions that are faint in coronal spectral lines formed at typical
quiet-Sun and active region temperatures. The outflows are positively
correlated with nonthermal velocities in coronal plasmas. The bulk
mass motions and nonthermal velocities are derived from spectral line
centroids and line widths, mostly from a strong line of Fe XII at
195.12 Å. The electron temperature of the outflow regions estimated
from an Fe XIII to Fe XII line intensity ratio is about (1.2-1.4) ×
106 K. The electron density of the outflow regions derived
from a density-sensitive intensity ratio of Fe XII lines is rather low
for an active region. Most regions average around 7 × 108
cm-3, but there are variations on pixel spatial scales
of about a factor of 4. We discuss results in detail for two active
regions observed by EIS. Images of active regions in line intensity,
line width, and line centroid are obtained by rastering the regions. We
also discuss data from the active regions obtained from other orbiting
spacecraft that support the conclusions obtained from analysis of the
EIS spectra. The locations of the flows in the active regions with
respect to the longitudinal photospheric magnetic fields suggest that
these regions might be tracers of long loops and/or open magnetic
fields that extend into the heliosphere, and thus the flows could
possibly contribute significantly to the solar wind.
Title: Strongly Blueshifted Phenomena Observed with Hinode EIS in
the 2006 December 13 Solar Flare
Authors: Asai, Ayumi; Hara, Hirohisa; Watanabe, Tetsuya; Imada,
Shinsuke; Sakao, Taro; Narukage, Noriyuki; Culhane, J. L.; Doschek,
G. A.
Bibcode: 2008ApJ...685..622A
Altcode: 2008arXiv0805.4468A
We present a detailed examination of strongly blueshifted emission
lines observed with the EUV Imaging Spectrometer on board the Hinode
satellite. We found two kinds of blueshifted phenomenon associated
with the X3.4 flare that occurred on 2006 December 13. One was related
to a plasmoid ejection seen in soft X-rays. It was very bright in all
the lines used for the observations. The other was associated with the
faint arc-shaped ejection seen in soft X-rays. The soft X-ray ejection
is thought to be a magnetohydrodynamic (MHD) fast-mode shock wave. This
is therefore the first spectroscopic observation of an MHD fast-mode
shock wave associated with a flare.
Title: Long Duration Flare Observed with Hinode EIS
Authors: Culhane, J. L.; Hara, H.; Watanabe, T.; Matsuzaki, K.; Harra,
L. K.; Cargill, P.; Mariska, J. T.; Doschek, G. A.
Bibcode: 2008ASPC..397..121C
Altcode:
The first Long Duration Event (LDE) observed with Hinode EIS using
a high spectral resolution raster scan is described. The hot plasma
features include a cusp-shaped arcade associated with a thermal RHESSI
source, cooling post-flare loops, complex plasma flows and an EIT
observation that shows expanding loops and inflows characteristic of
the standard magnetic reconnection model for solar flares. A Coronal
Mass Ejection (CME) is also seen by LASCO. The cusp is well observed
in the Ca XVII line and we find enhanced line broadening above this
region. Doppler velocity observations for the post-flare loops show both
up-flows and down-flows that are interpreted as due to siphon flows.
Title: Line Intensity Ratios in the EIS Range Sensitive to Electron
Densities in 107 K Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
Bibcode: 2008ApJ...679..843F
Altcode:
Electron density variations during the rise, maximum, and decay phases
of flaring plasmas at T simeq 10 MK are important quantities to be
used to test flare models. To date, electron density values measured
in solar flares are, with few exceptions, only lower limits. With the
launch of the EUV Imaging Spectrometer (EIS) on Hinode, it has become
possible for the first time to measure electron densities and their
time evolution during flares. In this paper we discuss electron density
diagnostics in the 1010-1013 cm-3
range by means of intensity ratios of lines emitted by Ti, Cr, and Mn
ions within the Hinode/EIS wavelength range.
Title: The Electron Temperature of the Solar Transition Region
Authors: Muglach, K.; Landi, E.; Doschek, G. A.
Bibcode: 2008AGUSMSP43C..05M
Altcode:
There are few spectroscopic measurements of electron temperature
in the solar transition region (the temperature region from about
2×104 K to 8×105 K). This is because UV and EUV spectral lines
from which temperature sensitive intensity ratios can be formed
are usually far separated in wavelength and cannot be observed
by a single instrument. Therefore, temperatures inferred for the
transition region are usually obtained from experimentally untested
theory that furthermore depends on the assumption of ionization
equilibrium. However, between 30 March 2007 and 14 April 2007 there
was a joint campaign between the SUMER spectrometer on SOHO and the
EIS spectrometer on Hinode. The EIS spectrometer operates in two
narrow wavelength bands: 170 — 210 and 250 — 290 Å. The SUMER
spectrometer operates roughly between about 500 and 1610 Å. Both SUMER
and EIS jointly observed portions of quiet Sun and active regions and
obtained spectra that include lines from a number of the same transition
region ions. The ratios of some of these lines from the same ion are
temperature sensitive and provide an unprecedented opportunity to
measure the temperatures of ion formation in the transition region and
to compare these temperatures with the values obtained from theoretical
ionization equilibrium calculations. A good example is the lines of
O VI at 183.94, 184.12 Å (EIS) and 1031.92, 1037.61 Å (SUMER). We
discuss temperatures derived for quiet Sun and active region transition
regions from joint spectra obtained during the SUMER/EIS campaign.
Title: Coronal Plasma Motions near Footpoints of Active Region Loops
Revealed from Spectroscopic Observations with Hinode EIS
Authors: Hara, Hirohisa; Watanabe, Tetsuya; Harra, Louise K.; Culhane,
J. Leonard; Young, Peter R.; Mariska, John T.; Doschek, George A.
Bibcode: 2008ApJ...678L..67H
Altcode:
The solar active region 10938 has been observed from the disk center
to the west limb with the Hinode EUV Imaging Spectrometer. In the
disk-center observation, subsonic upflow motions of tens of km
s-1 and enhanced nonthermal velocities have been found
near the footpoints of the active region loops assuming a single
Gaussian approximation for the emission-line profiles. When the same
part of the active region is observed near the limb, both upflows
and enhanced nonthermal velocities essentially decrease. There
is a strong correlation between Doppler velocity and nonthermal
velocity. Significant deviations from a single Gaussian profile are
found in the blue wing of the line profiles for the upflows. These
suggest that there are unresolved high-speed upflows. We discuss the
implications for coronal heating mechanisms.
Title: Ultra-Hot Plasma in Active Regions Observed by the
Extreme-ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Feldman, U.
Bibcode: 2008AGUSMSP43C..01D
Altcode:
The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft obtains high resolution spectra of the solar atmosphere in
two wavelength ranges: 170 - 210 and 250 — 290 Angstroms. These
wavelength regions contain a wealth of emission lines covering
temperature regions from the chromosphere/transition region (e.g.,
He II, Si VII) up to soft X-ray flare temperatures (Fe XXIII,
Fe XXIV). EIS can obtain line profiles and intensities for the
spectral lines in these wavelength regions. Of particular interest
for understanding coronal heating is a line of Ca XVII, formed near
a temperature of 6 MK. This line is blended with lines of Fe XI and O
V. However, by using unblended lines of these ions, the Ca XVII line
can be deconvolved from the blended emission. EIS has obtained many
raster observations of active regions by stepping the slit in small
increments across the active region, producing monochromatic images
of the active region. The Ca XVII blend has been included in many of
these rasters. In this paper we discuss the appearance and frequency
of 6 MK plasma in active regions in the absence of strong flaring
activity. This temperature region is not well-observed by normal
incidence imaging spectrometers and therefore the EIS data shed light
on higher temperature areas of active regions than normally available
from imaging instruments alone. We discuss how to deconvolve the blend
and show examples of 6 MK plasma emission in several active regions.
Title: Observation and Modeling of Coronal "Moss" With the EUV
Imaging Spectrometer on Hinode
Authors: Warren, Harry P.; Winebarger, Amy R.; Mariska, John T.;
Doschek, George A.; Hara, Hirohisa
Bibcode: 2008ApJ...677.1395W
Altcode: 2007arXiv0709.0396W
Observations of transition region emission in solar active regions
represent a powerful tool for determining the properties of hot coronal
loops. We present the analysis of new observations of active region
moss taken with the Extreme Ultraviolet Imaging Spectrometer (EIS)
on the Hinode satellite. EIS observations of a density sensitive Fe
XII line ratio suggest moss densities of approximately 1010
cm-3 and pressures of 3 × 1016 cm-3
K. We find that the moss intensities predicted by steady, uniformly
heated loop models are too intense relative to the observations,
consistent with previous work. To bring the steady heating model into
agreement with the observations a filling factor is required. Our
analysis indicates that the filling factor in the moss is nonuniform
and varies inversely with the loop pressure. The intensities predicted
by steady uniform heating are generally consistent with the EIS moss
observations. There are, however, significant discrepancies for the
coolest emission line available in the data we analyze.
Title: 2006 December 17 Long Duration Flare Observed with the Hinode
EUV Imaging Spectrometer
Authors: Hara, Hirohisa; Watanabe, Tetsuya; Matsuzaki, Keiichi; Harra,
Louise K.; Culhane, J. Leonard; Cargill, Peter; Mariska, John T.;
Doschek, George A.
Bibcode: 2008PASJ...60..275H
Altcode:
A GOES C-class long-duration flare that occurred near the west limb on
2006 December 17 was observed with the Hinode EUV Imaging Spectrometer
(EIS) in raster-scan observations. Cusp-shaped arcades are prominent in
the spectroheliogram of the CaXVII emission line at 192.86Å. Spatial
relationships between hot flare loops with a cusp apex and cool post
flare loops with various temperatures are clearly shown in the EIS
observations. We find an enhanced line broadening above the bright
loop-top region in the CaXVII observation. The Doppler observations of
cooling post flare loops with coronal temperatures show both downflows
and upflows along the loops, and these are interpreted as a part of
siphon flows. Enhanced nonthermal line broadenings are identified at
the top of the post flare loops.
Title: A proposed new method for the determination of the solar
irradiance at EUV wavelength range
Authors: Feldman, Uri; Doschek, G. A.; Seely, J. F.; Landi, E.;
Dammasch, I.
Bibcode: 2008cosp...37..866F
Altcode: 2008cosp.meet..866F
The solar irradiance in the far ultraviolet (FUV) and extreme
ultraviolet (EUV) and its time variability are important inputs to
geospace models. It provides the primary mechanism for heating the
earth's upper atmosphere and creating the ionosphere. Understanding
various space weather phenomena requires reliable detailed knowledge
of the solar EUV irradiance. Ideally one would like to have a single
well-calibrated, high-resolution spectrometer that can continuously
monitor the solar irradiance over the relevant wavelengths range. Since
this is much too difficult to accomplish, a number of monitoring
instruments were constructed in the past, each covering a fraction
of the required wavelength range. Assembling solar irradiance from
measurements by a number of instruments is extremely difficult and
is usually plagued by large uncertainties. To overcome some of the
difficulties resulting from such procedures, empirical models have
been developed that rely in large part on solar activity levels as
proxies. In recent years a different approach has been established for
the determination of the solar irradiance, an approach independent
of irradiance observations. The new approach is based on the line
intensities calculated from emission measure (EM) distributions across
the solar surface. The EM distributions are derived from spatially and
spectrally resolved measurements of line intensities and describe the
temperature and density structure of the basic large scale features of
the solar atmosphere, specifically coronal holes, quiet Sun, and active
regions. Recently, as a result of detailed analysis of solar upper
atmosphere (SUA) spectra recorded by SUMER/SoHO it was discovered that,
in contrast to earlier beliefs, the solar EM in 3x105 -4x106 K plasmas
does not appear to vary continuously with temperature as previously
assumed. Instead it appears to be composed of isothermal structures
where each can attain but one of the following four main temperatures:
5x105 , 9x105 , 1.4x106 and 3x106 K. At the transition region (2x104
-2x105 K) where the structures are not isothermal the slopes of the
emission measure vs. temperature stay the same independent of the solar
activity. In our talk we will propose a variation to the EM method for
the determination of the solar irradiance described above. The modified
method will be based on line intensity calculations from the actual
solar EM values at the above specified discrete temperatures. The
EM in those temperatures could in principle be derived from solar
observations spanning a fairly limited wavelengths range.
Title: Coronal Plasma Motions near Footpoints of Active Region Loops
Revealed from Spectroscopic Observations with {it Hinode} EIS
Authors: Hara, Hirohisa; Watanabe, Tetsuya; Harra, Louise K.; Culhane,
J. Leonard; Young, Peter R.; Doschek, G. A.; Mariska, John
Bibcode: 2008cosp...37.1175H
Altcode: 2008cosp.meet.1175H
We have observed the solar active region 10938 from the disk center
to the west limb with the Hinode EUV Imaging Spectrometer. In the
disk center observation subsonic upflow motions of tens of km s-1 and
enhanced nonthermal velocities have been found near the footpoints of
the active-region loops assuming a single Gaussian approximation for
the emission-line profiles. When the same part of the active region
is observed near the limb, both upflows and enhanced nonthermal
velocities essentially decrease, clearly showing that the enhanced
nonthermal velocities in the disk center observation are mainly due to
line-of-sight motions, which are likely parallel to magnetic field lines
of the coronal loops. There is a strong correlation between Doppler
velocity and nonthermal velocity in the upflow regions. The enhancement
in the blue wing of the line profiles is found for the upflows as a
significant deviation from a single Gaussian profile. These suggest
that there are unresolved high-speed upflows near the footpoints of
active region loops. We discuss the implications for coronal heating
mechanisms.
Title: Structures in flaring loops seen in FeXXIII 263.76A line
Authors: Watanabe, T.; Doschek, G. A.; Harra, L. K.; Hara, H.
Bibcode: 2007AGUFMSH52C..03W
Altcode:
EIS observed the highest temperature lines of FeXXIII263.76A,
FeXXIV192.10A, 255.10A in the EIS observing wavelengths during a C4.2
flare occurred on 16-Jan-07, as well as an FeXVII line at 254.83A. The
raster scan of the flaring area took place during 2:36 - 2:41 UT nearly
at the maximum phase of the flare. Comparing a monochromatic FeXXIII
raster image with the other high spatial resolution images taken by the
instruments on board the Hinode and those by Nobeyama Radio Heliograph,
electron precipitation cites are indentified. Foot points with fast
chromospheric evaporation are compact at the size of a few arcseconds,
and the turbulence still remain around the top of flaring loops. Down
flows are also seen in the lower temperature lines just outside the
flaring loops.
Title: Non-thermal Motions in Solar Active Regions
Authors: Doschek, G. A.
Bibcode: 2007AGUFMSH53A1059D
Altcode:
Optically thin ultraviolet, extreme-ultraviolet (EUV), and X-ray
spectral lines emitted by ions in the solar transition region and
corona usually have Gaussian widths in excess of the ion temperature
thermal Doppler width expected assuming the ions are formed in
ionization equilibrium. Also, because of the densities in the lower
solar corona and transition region, the electron temperature is
assumed to be equal to the ion temperature. The excess line widths
do not produce asymmetries in the line profiles and are interpreted
as a non-thermal random Doppler motion in the plasma producing the
lines. First discovered in 1975, these mysterious motions are still
unexplained. They may be a signature of wave propagation, magnetic
reconnection, random unresolved bulk flows, or some other as yet
unspecified physical mechanism. Up to the present, it has not been
possible to relate these motions spatially to coronal structures in
active regions in considerable detail. However, the recent launch of the
Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft
has made it now possible to establish detailed relationships. We
analyze EUV coronal (i.e., lines from ions such as Fe XII) spectral
lines obtained from EIS spectra of two active regions and discuss
the relationship of the non-thermal line widths to the temperatures,
densities, and positions in the active region loops and inter-loop
regions. We also discuss the relationship of the line widths to
line-of-sight flows in the active regions as determined from the
centroid wavelengths of the spectral lines.
Title: The Structure and Dynamics of the Quiet Corona from
Observations with the Extreme ultraviolet Imaging Spectrometer
Authors: Dere, K. P.; Doschek, G. A.; Mariska, J. T.; Harra, L. K.;
Matsuzaki, K.; Hansteen, V.; Thomas, R. J.
Bibcode: 2007AGUFMSH53A1046D
Altcode:
The goal of the Extreme-ultraviolet Imaging Spectrometer (EIS) on the
Hinode satellite is to measure such physical parameters as the velocity
and density of the solar corona in order to provide an observational
basis to understand how coronal plasmas are heated and accelerated. On
2007 January 20, EIS performed a raster of a 128 x 512 arc-sec. area
of a quiet region near Sun center. The observing program recorded
spectra of He II λ256, formed at 9 × 104 K, and lines of Fe VIII-XV,
formed at temperatures spanning the range from 5 × 105 through 2 × 106
K. Maps of intensities, velocities and electron densities derived from
these observations are presented and discussed. Intensity maps in He II
λ256 show the chromospheric network. Line intensities of Fe X-XIV show
small-scale bright points and more extended structures. The intensity
map of Fe VIII shows a transition between the two temperatures. The
coronal lines reveal regions of high outflow velocities on the
order of 100 km s-1 in a compact region and 12 km s-1 in an extended
region. The presence of these high velocities in the quiet corona
is an entirely new and unexpected result. Electron densities derived
from density sensitive line ratios of Fe XII and XIII are typically
about 3 - 20×108 cm-3. The highest densities are found in bright,
compact areas. For the first time, explosive events in the quiet sun
have been observed in the extreme-ultraviolet in He II λ256 profiles
and have properties similar to those previously reported.
Title: Obituary: Herbert Gursky, 1930-2006
Authors: Doschek, George; Dahlburg, Jill
Bibcode: 2007BAAS...39.1060D
Altcode:
Dr. Herbert Gursky, Acting Associate Director of Research for the
Naval Research Laboratory's (NRL's) Systems Directorate, and formerly
Superintendent of the Space Science Division and Chief Scientist of
the E. O. Hulburt Center for Space Research. Dr. Gursky died following
a long illness on late Friday afternoon, December 1, 2006. Dr. Gursky
was a great friend, valued colleague, and distinguished researcher
who will be missed greatly. Dr. Gursky was born in Bronx, New
York, on May 27, 1930. He was educated in secondary schools in Miami,
Florida, and received a Bachelor's Degree from the University of Florida
in 1951. He did graduate work in physics at Vanderbilt University
(Master's degree in 1953) and Princeton University (Doctorate degree in
1959). His first professional position was at Columbia University as an
instructor in the Physics Department from 1958 to 1961. In 1961, he
joined American Science and Engineering, Inc. (AS&E) in Cambridge,
Massachusetts, as a senior scientist and rose to the position of Vice
President, Space Research in 1967. In 1973 he joined the Smithsonian
Astrophysical Observatory (SAO) as a supervisory astrophysicist. In
1974, Dr. Gursky was appointed Professor in the Practice of Astronomy
at Harvard University and in 1976 was named Associate Director of
the Center for Astrophysics for the Division of Optical and Infrared
Astronomy. In 1981, Dr. Gursky joined NRL as Superintendent of its Space
Science Division and Chief Scientist of the E. O. Hulburt Center for
Space Research. He moved to the position of Acting Associate Director
of Research for NRL's Systems Directorate in 2006. Dr. Gursky's
primary research interests were in the area of X-ray astronomy. He
published more than 100 articles in this area and edited two books on
the subject. Before arriving at NRL, he was the principal investigator
for NASA-sponsored space programs on the Astronomical Netherlands
Satellite (ANS) and the High Energy Astrophysics Observatory (HEAO)-1
satellite, and a co-investigator on numerous other rocket and satellite
experiments. At AS&E, Dr. Gursky managed research activities
encompassing solar physics and magnetospheric research, and at SAO, he
managed programs of ground-based astronomy and infrared astronomy. At
SAO, he oversaw the completion of the Multiple Mirror Telescope, a joint
program of SAO and the University of Arizona, comprising a 4.5-meter
(equivalent) telescope of novel design that is situated at Mount
Hopkins in Arizona. Dr. Gursky's work at NRL involved direction of
a broad-ranging research effort involving about fifty Ph.D. scientists
conducting investigations in the areas of high-energy astronomy, solar
physics, solar terrestrial effects and atmospheric science. NRL is the
corporate research laboratory for the Navy and has the responsibility
for assuring that future Navy systems take full advantage of all
available technology and scientific understandings. Dr. Gursky
had the ability to distill and seize the most important nuggets from
any research program and envision its application to a variety of new
problems and directions. In numerous areas of atmospheric, solar and
space science technology, Dr. Gursky recognized key scientific issues
and their potential DoD applications. In solar physics, he spurred
the development of semi-empirical modeling to predict solar storms
that has been successfully transitioned to operational systems. He
also supported participation in all NASA and other agency Sun-Earth
connection orbiting space programs which resulted in a succession
of spectacularly successful experiments in solar physics such as
the high resolution rocket spectrograph and its flight on the NASA
Spacelab 2, the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM)
on the NASA Upper Atmosphere Research Satellite, the Bragg crystal
spectrometer solar flare experiment on the Japanese Yohkoh spacecraft,
and the Large Angle and Spectrometric Coronagraph Experiment (LASCO)
and extreme ultraviolet imaging telescope (EIT) on the ESA/NASA Solar
and Heliospheric Observatory. These experiments have shed considerable
light on how solar activity affects the near-Earth environment with many
potential space weather applications. In high-energy astronomy,
Dr. Gursky made many contributions. He provided scientific oversight
for the Advanced Research and Global Observation Satellite (ARGOS)
Space Test Program spacecraft that contained five NRL instruments:
the Unconventional Stellar Aspect (USA) experiment, the Global Imaging
Monitor of the Ionosphere (GIMI), the High Resolution Airglow/Aurora
Spectroscopy (HIRAAS) experiment, the Extreme Ultraviolet Imaging
Photometer (EUVIP), and the Coherent Electromagnetic Radio Tomography
(CERTO) instrument. He continued his interest in X-ray astronomy
with the USA experiment, which obtained observations of many celestial
sources such as galactic binary X-ray sources and pulsars. Always with
an eye toward applications, Dr. Gursky was interested in using X-ray
sources, specifically X-ray pulsars, as precise clocks to provide
spacecraft with autonomous timing and navigation. Dr. Gursky also
supported research in gamma ray astrophysics, such as the development of
NRL's Oriented Scintillation Spectrometer Experiment (OSSE) for the NASA
Compton Gamma Ray Observatory (CGRO) satellite, and analysis of solar
flare gamma ray spectra obtained from the NASA Solar Maximum Mission. In atmospheric science, Dr. Gursky particularly encouraged practical
applications of basic research. He recognized the importance of remote
sensing for space weather, which resulted in the development at NRL of
operational ultraviolet sensors on Defense Meteorological Satellite
Program (DMSP) spacecraft that are now providing environmental data
products to the Air Force Space Weather Agency. He initiated a program
in middle atmosphere research that has been enormously successful
and has spawned numerous experimental and theoretical advances, such
as the Middle Atmosphere High Resolution Spectrograph Investigation
(MAHRSI) to measure trace constituents in the middle atmosphere such
as the hydroxyl radical (OH). Dr. Gursky supported the development
of theoretical middle atmosphere models such as the Mountain Wave
Forecast Model that was used to predict flight conditions for allied
aircraft during operations Southern Watch, Enduring Freedom, and Iraqi
Freedom, which has been a boon to stratospheric flight operations
over mountainous terrain. He also supported the HIRAAS experiment on
ARGOS. Dr. Gursky provided outstanding leadership in the continued
development of the United States space program. Under his stewardship,
the NRL Space Science Division substantially expanded its leadership
role in understanding the space environment and its effects on military
and civilian systems. The Laboratory and the world are now witnessing
the newest results of his scientific acumen and sound decision-making
as exemplified in the very recent successful completions and launches
of these major Space Science Division instruments: Delivery of
GLAST LAT (September 2006): Delivery of the collaborative NRL Large
Area Telescope (LAT) for the NASA Gamma Ray Large Area Space Telescope
(GLAST) satellite integration; when deployed, GLAST will measure the
most energetic processes in the universe — from X-ray bursts, black
holes, neutron stars, and solar flares — and has the potential to
discover previously unknown relics of the Big Bang; Launch of
SOLAR-B (September 2006): The Japan Aerospace Exploration Agency's
Hinode (Japanese for Sunrise, formerly known as SOLAR-B) launched
September 23 carrying NRL's collaborative Extreme-ultraviolet Imaging
Spectrometer (EIS), which achieved first light on October 28. EIS is
now observing emission lines produced by highly ionized elements in the
solar coronal and upper transition region of the Sun's atmosphere. Space
Science Division scientists expect much exciting science concerning
the coupling of solar activity to the near-Earth space environment to
be produced by the EIS instrument; and, Launch of STEREO (October
2006): NASA's Solar Terrestrial Relations Observatory (STEREO) launched
25 October, carrying the collaborative NRL Sun-Earth Connection Coronal
and Heliospheric Investigation (SECCHI) instruments suite, which is
currently successfully functioning in the pre-commissioning phase. The
instruments onboard STEREO's twin spacecraft will make observations
to help NRL researchers construct the first-ever three-dimensional
views of coronal mass ejections, vital data — in complement with
the long-operational NRL-built NASA LASCO — for understanding how
the Sun creates space weather Perhaps Dr. Gursky's most personal
research successes were as a member of the group that made the discovery
of cosmic X-ray sources in 1961, his work with sounding rockets that
culminated in the optical identification of the bright X-ray source
Scorpius X1 in 1966, his work on clusters of galaxies and the diffuse
X-ray background from the Uhuru Satellite and the discovery of X-ray
bursters on the ANS satellite.
Title: Solar Transition Region Features Observed with Hinode/EIS
Authors: Young, Peter R.; Del Zanna, Giulio; Mason, Helen E.; Doschek,
George A.; Culhane, Len; Hara, Hirohisa
Bibcode: 2007PASJ...59S.727Y
Altcode: 2007arXiv0706.1856Y
Two types of solar active region feature prominent at transition region
temperatures are identified in Hinode/EIS data of AR 10938 taken on
2007 January 20. The footpoints of 1 MK TRACE loops are shown to emit
strongly in emission lines formed at log T = 5.4-5.8, allowing the
temperature increase along the footpoints to be clearly seen. A density
diagnostic of Mg VII yields the density in the footpoints, with one
loop showing a decrease from 3 × 109 cm-3 at the
base to 1.5 × 109 cm-3 at a projected height
of 20 Mm. The second feature is a compact active region transition
region brightening which is particularly intense in O V emission
(log T = 5.4) but also has a signature at temperatures up to log T =
6.3. The Mg VII diagnostic gives a density of 4 × 1010
cm-3, and emission lines of Mg VI and Mg VII show line
profiles broadened by 50kms-1 and wings extending beyond
± 200kms-1. Continuum emission in the short wavelength
band is also found to be enhanced, and is suggested to be free-bound
emission from recombination onto He+.
Title: The Structure and Dynamics of the Quiet Corona from
Observations with the Extreme Ultraviolet Imaging Spectrometer
on Hinode
Authors: Dere, Kenneth P.; Doschek, George A.; Mariska, John T.;
Hansteen, Viggo H.; Harra, Louise K.; Matsuzaki, Keiichi; Thomas,
Roger J.
Bibcode: 2007PASJ...59S.721D
Altcode:
The goal of the Hinode mission is to provide an observational basis for
understanding the heating and acceleration of coronal plasmas. On 2007
January 20, the Extreme ultraviolet Imaging Spectrometer performed
a raster of a quiet region near Sun center. Maps of intensities,
velocities, and electron densities derived from these observations are
presented and discussed. Intensity maps in HeII λ 256, formed at 9
× 104 K, show the chromospheric network. Line intensities
of FeX-XIV, formed at temperatures from 1-2 × 106 K, show
small-scale bright points and more extended structures. The intensity
map of FeVIII shows a transition between the two temperatures. The
coronal lines reveal regions of high outflow velocities on the order
of 100kms-1 in a compact region and 12kms-1 in
an extended region. The presence of such high velocities in the quiet
corona is an entirely new and unexpected result. Electron densities
derived from density sensitive line ratios of FeXII and XIII are
typically 3-20 × 108cm-3. The highest densities
are found in bright, compact areas. For the first time, explosive
events in the quiet sun have been observed in the extreme-ultraviolet
in HeII λ 256 profiles.
Title: Hinode EUV Study of Jets in the Sun's South Polar Corona
Authors: Culhane, Len; Harra, Louise K.; Baker, Deborah; van
Driel-Gesztelyi, Lidia; Sun, Jian; Doschek, George A.; Brooks, David
H.; Lundquist, Loraine L.; Kamio, Suguru; Young, Peter R.; Hansteen,
Viggo H.
Bibcode: 2007PASJ...59S.751C
Altcode:
A number of coronal bright points and associated plasma jet features
were seen in an observation of the South polar coronal hole during
2007 January. The 40" wide slot was used at the focus of the Hinode
EUV Imaging Spectrometer to provide spectral images for two of these
events. Light curves are plotted for a number of emission lines that
include He II 256Å (0.079MK) and cover the temperature interval from
0.4MK to 5.0MK. Jet speed measurements indicate values less than the
escape velocity. The light curves show a post-jet enhancement in a
number of the cooler coronal lines indicating that after a few minutes
cooling, the plasma fell back to its original acceleration site. This
behavior has not been previously observed by e.g., the Yohkoh Soft
X-ray Telescope due to the comparatively high temperature cut-off
in its response. The observations are consistent with the existing
models that involve magnetic reconnection between emerging flux and the
ambient open field lines in the polar coronal hole. However we do not
have sufficient coverage of lines from lower temperature ion species
to register the Hα-emitting surge material that is associated with
some of these models.
Title: Temperature and Density Structures of Solar Corona, A Test
of Iron Line Diagnostic Capability of EIS Instrument on Board Hinode
Authors: Watanabe, Tetsuya; Hara, Hirohisa; Culhane, Len; Harra,
Louise K.; Doschek, George A.; Mariska, John T.; Young, Peter R.
Bibcode: 2007PASJ...59S.669W
Altcode:
Increased diagnostic capability of the EUV Imaging Spectrometer
(EIS) aboard Hinode (former Solar-B) has been demonstrated with
a set of iron emission lines emerging in the two EIS observing
wavelength bands (170-210Å and 250-290Å) and their line-intensity
ratios. ``Abundance-uncertainty'' free relative emission measure
distributions as a function of temperature were deduced using only iron
emission lines of various ionization stages. First-light spectra of a
small active region show iron lines ranging from FeVIII (185.2Å and
186.6Å) through FeXVII (204.7Å, 254.9Å, and 269.4Å). Spectra of a
C-class flare confirms the presence of one of these higher temperature
lines (FeXVII at 254.9Å) more clearly, as well showing FeXXIV (192.0Å
and 255.1Å) and FeXXIII (263.8Å), which are normally only seen at
flare temperatures.
Title: The Temperature and Density Structure of an Active Region
Observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, George A.; Mariska, John T.; Warren, Harry P.;
Culhane, Len; Watanabe, Tetsuya; Young, Peter R.; Mason, Helen E.;
Dere, Kenneth P.
Bibcode: 2007PASJ...59S.707D
Altcode:
The Extreme-Ultraviolet Imaging Spectrometer (EIS) on Hinode
produces high resolution spectra that can be combined via rasters
into monochromatic images of solar structures, such as active
regions. Electron temperature and density maps of the structures can
be obtained by imaging the structures in different spectral lines with
ratios sensitive to either temperature or density. Doppler maps and
ion temperature maps can be made from spectral line wavelengths and
profiles, respectively. In this paper we discuss coronal temperature
and density distributions within an active region, illustrating the
power of EIS for solar plasma diagnostics.
Title: EUV Emission Lines and Diagnostics Observed with Hinode/EIS
Authors: Young, Peter R.; Del Zanna, Giulio; Mason, Helen E.; Dere,
Ken P.; Landi, Enrico; Landini, Massimo; Doschek, George A.; Brown,
Charles M.; Culhane, Len; Harra, Louise K.; Watanabe, Tetsuya; Hara,
Hirohisa
Bibcode: 2007PASJ...59S.857Y
Altcode: 2007arXiv0706.1857Y
Quiet Sun and active region spectra from the Hinode/EIS instrument are
presented, and the strongest lines from different temperature regions
discussed. A list of emission lines recommended to be included in EIS
observation studies is presented based on analysis of blending and
diagnostic potential using the CHIANTI atomic database. In addition
we identify the most useful density diagnostics from the ions covered
by EIS.
Title: Wavelength Determination for Solar Features Observed by the
EUV Imaging Spectrometer on Hinode
Authors: Brown, Charles M.; Hara, Hirohisa; Kamio, Suguru; Feldman,
Uri; Seely, John F.; Doschek, George A.; Mariska, John T.; Korendyke,
Clarence M.; Lang, James; Dere, Kenneth P.; Culhane, Len; Thomas,
Roger J.; Davila, Joseph M.
Bibcode: 2007PASJ...59S.865B
Altcode:
A wavelength calibration of solar lines observed by the high
resolution EUV Imaging Spectrometer (EIS) on the Hinode satellite
is reported. Spectral features of the quiet sun and of two mildly
active areas were measured and calibrated. A listing of the stronger
observed lines with identification of the leading contributor ions
is presented. 41 lines are reported, with 90% identified. Wavelength
precisions (2σ) of ±0.0031Å for the EIS short band and ±0.0029Å
for the EIS long band are obtained. These lines, typical of 1-2
×106 K plasmas, are recommended as standards for the
establishment of EIS wavelength scales. The temperature of EIS varies
by about 1D.5 C around the orbit and also with spacecraft pointing. The
correlation of these temperature changes with wavelength versus pixel
number scale changes is reported.
Title: Towards Understanding the Solar Atmosphere
Authors: Doschek, G. A.
Bibcode: 2007ASPC..369..263D
Altcode:
This paper is partly a review of recent work by the author and
colleagues and partly the presentation of new work in progress. Detailed
presentations of the work can be found in Doschek, Mariska, &
Akiyama (2004), Doschek & Feldman (2004), Akiyama, Doschek, &
Mariska (2005), Warren & Doschek (2005), Doschek & Warren
(2005), and Doschek (2006). Below I discuss some of the new work to
be published by Doschek (2006).
Title: Nonthermal Velocities in Solar Active Regions Observed with
the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Brown, C. M.;
Culhane, J. L.; Hara, H.; Watanabe, T.; Young, P. R.; Mason, H. E.
Bibcode: 2007ApJ...667L.109D
Altcode:
We discuss nonthermal velocities in an active region as revealed
by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft. The velocities are derived from spectral line profiles in
the extreme-ultraviolet (EUV) from a strong line of Fe XII at 195.12 Å
by fitting each line profile to a Gaussian function. We compare maps
of the full width at half-maximum values, the Fe XII spectral line
intensity, the Fe XII Doppler shift, the electron temperature, and
electron density. We find that the largest widths in the active region
do not occur in the most intense regions, but seem to concentrate in
less intense regions, some of which are directly adjacent to coronal
loops, and some of which concentrate in regions which also exhibit
relative Doppler outflows. The increased widths can also occur over
extended parts of the active region.
Title: Comparison of solar spectra from the Hinode extreme-ultraviolet
imaging spectrometer (EIS) to preflight calibrations
Authors: Seely, John; Feldman, Uri; Brown, Charles; Doschek, George;
Hara, H.
Bibcode: 2007SPIE.6688E..0WS
Altcode: 2007SPIE.6688E..29S
The Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
satellite records high-resolution solar spectra in the 170-210 Å
and 246-290 Å wavelength ranges. The EIS optics operate at near
normal incidence and consist of an off-axis parabolic mirror, a
toroidal diffraction grating, two CCD detectors, and two thin aluminum
filters. To increase the normal incidence efficiency, high-reflectance
multilayer interference coatings were deposited on the mirror and the
grating. Prior to launch, each of the optical components was calibrated
using synchrotron radiation, and the spectral and spatial resolution
of the complete instrument were measured. In this paper, we compare the
preflight calibrations with the first-light spectra recorded in space.
Title: Improved low-lying energy levels determined from solar coronal
forbidden and spin-forbidden lines in the 500 1500 Å range
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 2007ADNDT..93..779F
Altcode:
We list observed parity-forbidden and spin-forbidden lines in
the 500 1600 Å range emitted by solar coronal plasmas and derive
improved energy levels from their wavelengths. The lines, emitted
by astrophysical abundant elements, belong to transitions within the
ground configurations of the type ns2npk, for n
= 2, 3 and k = 0 5, and between the lowest term of the first excited
configuration 2s2pk+1 and the 2s22pk
ground configurations for k = 0, 1, 2. For each line we give the newly
measured wavelength, and the measured or predicted wavelength from
the NIST Atomic Spectra Database (ASD) (which except for a few cases
includes the previously reported compilation of Kaufman and Sugar
[J. Phys. Chem. Ref. Data 15 (1986) 321]), and the values of the
transition probability taken from the ASD and CHIANTI database. The
list contains measured wavelengths of 136 lines of which over 100 were
not available for the Kaufman and Sugar compilation. In addition we
provide energy levels that were derived from the reported lines.
Title: The EUV Imaging Spectrometer for Hinode
Authors: Culhane, J. L.; Harra, L. K.; James, A. M.; Al-Janabi, K.;
Bradley, L. J.; Chaudry, R. A.; Rees, K.; Tandy, J. A.; Thomas, P.;
Whillock, M. C. R.; Winter, B.; Doschek, G. A.; Korendyke, C. M.;
Brown, C. M.; Myers, S.; Mariska, J.; Seely, J.; Lang, J.; Kent,
B. J.; Shaughnessy, B. M.; Young, P. R.; Simnett, G. M.; Castelli,
C. M.; Mahmoud, S.; Mapson-Menard, H.; Probyn, B. J.; Thomas, R. J.;
Davila, J.; Dere, K.; Windt, D.; Shea, J.; Hagood, R.; Moye, R.; Hara,
H.; Watanabe, T.; Matsuzaki, K.; Kosugi, T.; Hansteen, V.; Wikstol, Ø.
Bibcode: 2007SoPh..243...19C
Altcode:
The EUV Imaging Spectrometer (EIS) on Hinode will observe solar corona
and upper transition region emission lines in the wavelength ranges
170 - 210 Å and 250 - 290 Å. The line centroid positions and profile
widths will allow plasma velocities and turbulent or non-thermal line
broadenings to be measured. We will derive local plasma temperatures and
densities from the line intensities. The spectra will allow accurate
determination of differential emission measure and element abundances
within a variety of corona and transition region structures. These
powerful spectroscopic diagnostics will allow identification
and characterization of magnetic reconnection and wave propagation
processes in the upper solar atmosphere. We will also directly study
the detailed evolution and heating of coronal loops. The EIS instrument
incorporates a unique two element, normal incidence design. The optics
are coated with optimized multilayer coatings. We have selected highly
efficient, backside-illuminated, thinned CCDs. These design features
result in an instrument that has significantly greater effective area
than previous orbiting EUV spectrographs with typical active region
2 - 5 s exposure times in the brightest lines. EIS can scan a field
of 6×8.5 arc min with spatial and velocity scales of 1 arc sec and
25 km s−1 per pixel. The instrument design, its absolute
calibration, and performance are described in detail in this paper. EIS
will be used along with the Solar Optical Telescope (SOT) and the X-ray
Telescope (XRT) for a wide range of studies of the solar atmosphere.
Title: The Hinode (Solar-B) Mission: An Overview
Authors: Kosugi, T.; Matsuzaki, K.; Sakao, T.; Shimizu, T.; Sone,
Y.; Tachikawa, S.; Hashimoto, T.; Minesugi, K.; Ohnishi, A.; Yamada,
T.; Tsuneta, S.; Hara, H.; Ichimoto, K.; Suematsu, Y.; Shimojo, M.;
Watanabe, T.; Shimada, S.; Davis, J. M.; Hill, L. D.; Owens, J. K.;
Title, A. M.; Culhane, J. L.; Harra, L. K.; Doschek, G. A.; Golub, L.
Bibcode: 2007SoPh..243....3K
Altcode:
The Hinode satellite (formerly Solar-B) of the Japan Aerospace
Exploration Agency's Institute of Space and Astronautical Science
(ISAS/JAXA) was successfully launched in September 2006. As the
successor to the Yohkoh mission, it aims to understand how magnetic
energy gets transferred from the photosphere to the upper atmosphere
and results in explosive energy releases. Hinode is an observatory
style mission, with all the instruments being designed and built to
work together to address the science aims. There are three instruments
onboard: the Solar Optical Telescope (SOT), the EUV Imaging Spectrometer
(EIS), and the X-Ray Telescope (XRT). This paper provides an overview
of the mission, detailing the satellite, the scientific payload, and
operations. It will conclude with discussions on how the international
science community can participate in the analysis of the mission data.
Title: Hinode Euv Study Of Jets In The Sun’s South Polar Corona
Authors: Culhane, J. L.; Brooks, D. H.; Doschek, G. A.; Harra, L. K.;
van Driel-Gesztelyi, L.; Baker, D.; Lundquist, L. L.; Hansteen, V. H.;
Kamio, S.
Bibcode: 2007AAS...210.7201C
Altcode: 2007BAAS...39..178C
Using the Hinode EUV Imaging Spectrometer coronal jets were observed
on 20-JAN-2007 over a range of emission lines and corresponding plasma
temperatures using the 40 arc sec wide slot images. In this preliminary
analysis, jet plasma temperature and emissivity have been estimated
while, based on assumptions about the jet morphology, electron density
estimates are given and jet velocity measured. The evolution of the
jets will be followed in a number of different EUV emission lines and
jet energy input as a function of time will be assessed with reference
to the magnetic field topologies involved.
Title: A Long-duration Flare Observed With Hinode EIS
Authors: Hara, Hirohisa; Watanabe, T.; Harra, L.; Culhane, L.; Cargill,
P.; Doschek, G.; Mariska, J.
Bibcode: 2007AAS...210.6802H
Altcode: 2007BAAS...39..175H
Long-duration solar flares generally have a cusp apex at the loop
top. The cusp shape reflects the topology of magnetic fields near
the flare-loop top and it is one of the indirect pieces of evidence
supporting the occurrence of the magnetic reconnection process above
flare loops. The Hinode EUV Imaging Spectrometer (EIS) observed a
long-duration flare that occurred on 2006 Dec 17. We present the first
EIS spectroscopic observation of cusp-shaped flare loops. We also
report velocity fields around the cusp structures and post-flare loops.
Title: Hinode EIS Observations of Solar Active Regions
Authors: Mariska, John T.; Doschek, G. A.; Warren, H. P.; Brooks,
D. H.; Young, P. R.; Watanabe, T.; Culhane, J. L.
Bibcode: 2007AAS...210.7202M
Altcode: 2007BAAS...39R.178M
The EUV Imaging Spectrometer (EIS) on the Hinode satellite provides
high spatial and spectral resolution data along a 512 arcsec slit in
two wavelength ranges, 170--210 Angstroms and 250--290 Angstroms. These
wavelengths mostly contain emission lines from upper transition region
and coronal plasmas. Emission from these wavelengths is routinely
imaged using instruments such as the EIT on SOHO and TRACE, but there
are few high-resolution spectra to aid in more deeply understanding
the physical conditions and dynamics associated with the intensity
variations seen in the images. In this presentation, we show some
initial results from EIS active region studies aimed at mapping the
density, temperature, nonthermal broadening, and Doppler shifts in
active regions. This presentation focusses on spectroheliograms of
active regions in diagnostically interesting spectral lines. These
show the overall active region morphology and the behavior of Doppler
shifts, nonthermal velocities, and densities as a function of position,
but at the expense of high time resolution. Other presentations will
focus on how the observed physical parameters vary with time.
Title: Iron Line Ratio Analysis in an Active Region
Authors: Watanabe, Tetsuya; Hara, H.; Culhane, J. L.; Harra, L. K.;
Doschek, G. A.; Mariska, J. T.; Young, P. R.; Hinode EIS Team
Bibcode: 2007AAS...210.7204W
Altcode: 2007BAAS...39..179W
Increased diagnostic capability of the EIS instrument on board Hinode
(Solar-B) is demonstrated with a set of iron emission lines appearing
in the two EIS observing wavelengths (170 - 210 A & 250 - 290
A) and their line intensity ratios. First-light spectra of a small
active region show iron lines at the ionization stages of FeVIII
(185.2 A & 186.6 A) through FeXVII (204.7 A, 254.9 A, & 269.4
A). Decay phase spectra of a C-class flare confirms the presence of
this higher temperature line; FeXVII at 254.9 A more clearly, as well
as those lines of flare temperatures; FeXXIV (192.0 A & 255.1 A)
and FeXXIII (263.8 A).
Title: New Vistas of the Sun from Hinode
Authors: Doschek, George A.
Bibcode: 2007AAS...210.5901D
Altcode: 2007BAAS...39..169D
In this talk I will show spectacular new observations of the
Sun's atmosphere obtained from the solar physics Hinode mission
launched 23 September 2006. Hinode is a Japanese mission with US
and UK participation designed to understand the structure, origin,
and energetics of the solar atmosphere. Hinode contains three
instruments that observe the solar atmosphere from the photosphere
into the corona. Two of the instruments are also capable of observing
multi-million degree solar flare plasma. I will briefly review the
science instruments on Hinode, but the bulk of the talk will focus
on the observations themselves, and their implications for solving
fundamental physics problems of the solar atmosphere. These include
problems such as the emergence, dynamics and evolution of coronal
magnetic flux tubes, the connectivity of coronal structures to surface
magnetic fields including their response to photospheric surface
motions, and the role of magnetic reconnection in the heating and
eruption of the atmosphere. Hinode is inaugurating an exciting new
era for solar physics with the promise of significant breakthroughs in
our understanding of the basic physics of hot solar and stellar plasmas.
Title: Diagnostics of Suprathermal Electrons in Active-Region Plasmas
Using He-like UV Lines
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
Bibcode: 2007ApJ...660.1674F
Altcode:
In the present paper we use UV lines emitted by He-like ions as a
tool to test the presence of nonthermal high-energy electrons and
to quantify their number and energy. The He-like lines we consider
are the He-like 1s2s3S-1s2p3P lines observed
in the UV, and their use capitalizes on the high excitation energies
for the 1s2p3P levels and on the near-unity ion abundances
of the He-like ions for large temperature ranges. We investigate the
presence of nonthermal high-energy electrons in solar active regions,
placing upper limits on the presence of electrons capable of exciting
the upper levels of Ne IX, Mg XI, and Si XIII.
Title: Neon and Oxygen Absolute Abundances in the Solar Corona
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2007ApJ...659..743L
Altcode:
In the present work we use the UV spectrum of a solar
flare observed with SOHO SUMER to measure the absolute
abundance of Ne in the solar atmosphere. The measurement
is carried out using the intensity ratio between the allowed
1s2s3S1-1s2p3P2 Ne IX
line at 1248.28 Å and the free-free continuum radiation observed
close to the Ne IX line. We find a value of the absolute Ne abundance
ANe=8.11+/-0.12, in agreement with previous estimates
but substantially higher than the very recent estimate by Asplund et
al. based on the oxygen photospheric abundance and the Ne/O relative
abundance. Considering our measured ANe value, we argue
that the absolute oxygen abundance of Asplund et al. is too low by a
factor 1.9. This result has important consequences for models of the
solar interior based on helioseismology measurements, as well as on
the FIP bias determination of the solar upper atmosphere, solar wind,
and solar energetic particles.
Title: Is There a High-Energy Particle Population in the Quiet
Solar Corona?
Authors: Ralchenko, Yu.; Feldman, U.; Doschek, G. A.
Bibcode: 2007ApJ...659.1682R
Altcode:
A study of spectra emitted by the quiet solar corona indicates that
the majority of line intensities originating in low-lying levels
are consistent with isothermal plasma of ~1.3×106
K. Nevertheless, a number of line intensities and, in particular,
those belonging to ions that are typical of higher temperatures
are brighter than expected. We show in this paper that the excess
brightness of the hotter lines may be satisfactorily accounted for by
a two-Maxwellian electron distribution function. We have calculated
the effects on the line intensities and ionization balance under the
assumption of both single- and two-Maxwellian electron distribution
functions. One Maxwellian is characterized by a temperature of about 110
eV (1.35×106 K). The second Maxwellian is assumed to be a
high-energy component ranging in temperatures between 150 and 1000 eV,
with electron fractions relative to the total electron density that
vary from 0.5% to 10%. We found that a good match to the quiet-Sun
intensities could be achieved by adding ~5% electrons with a 300-400
eV Maxwellian temperature to the cooler component at 110 eV. We also
found that the calculated line intensities become inconsistent with the
quiet solar corona measurements if more than 3% of a Te=500
eV plasma or more than 1% of a Te=1000 eV plasma is added
to the cooler Maxwellian.
Title: NRL EUV Imager: The Solar EUV Atmospheric Research Of The
Corona And Heliosphere (SEARCH) Experiment
Authors: Newmark, J. S.; Doschek, G. A.; Brown, C. M.; Cook, J. W.;
Kilmchuk, J. A.; Korendyke, C. M.; Moses, J. D.; Myers, S. H.; Seely,
J. F.
Bibcode: 2007ESASP.641E..74N
Altcode:
Achieving the Solar Orbiter primary science goals requires knowledge
of the fine structure of the solar atmosphere from chromospheric
to coronal temperatures, and the structural links between these
different temperature regions. An EUV imager is an ideal instrument
for providing this crucial information, and the Solar Orbiter mission
gives a unique opportunity to investigate the fine structure of the
chromosphere, transition region, and corona at unprecedented high
spatial resolution. We present a concept from the US Naval Research
Laboratory (NRL) for providing an Extreme Ultraviolet (EUV) Imager for
the Solar Orbiter mission, the "Solar EUV Atmospheric Research of the
Corona and Heliosphere" (SEARCH) experiment.
Title: 2006 LWS TR & T Solar Wind Focused Science Topic Team:
The Beginnings
Authors: Miralles, M. P.; Bhattacharjee, A.; Landi, E.; Markovskii,
S.; Cranmer, S. R.; Doschek, G. A.; Forbes, T. G.; Isenberg, P. A.;
Kohl, J. L.; Ng, C.; Raymond, J. C.; Vasquez, B. J.
Bibcode: 2006AGUFMSH11A0371M
Altcode:
The Solar Wind Focused Science Topic (FST) team was created to
apply a combination of theoretical studies, numerical simulations,
and observations to the understanding of how the fast and slow solar
wind are heated and accelerated. Four proposals were selected for this
FST team. They will investigate the role of energy sources and kinetic
mechanisms responsible for the heating and acceleration of the solar
wind. In particular, the FST team will examine magnetic reconnection
and turbulence as possible heating mechanisms. Plasma properties and
their evolution over the solar cycle, determined from the analysis of
remote and in situ measurements, will be used to put firm constraints
on the models. The work of the Solar Wind FST team is in its initial
stages. The organization, planning, and findings resulting from the
first FST team meeting will be reported.
Title: Doppler Shift Correlations in the Solar Transition Region
Authors: Doschek, G. A.
Bibcode: 2006ApJ...649..515D
Altcode:
I investigate dynamical correlations between the lower transition
region and the upper transition region using spectra from the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
on the Solar and Heliospheric Observatory (SOHO) spacecraft. The
measured quantity is the Doppler shift (mostly solar radial) along
the line of sight. The purpose is to shed light on the fraction of the
lower transition region that resides in cool structures not physically
associated with higher temperature regions and the fraction that can be
described by a classical transition region with a physical connection
from the chromosphere into the corona. ``Transition region'' in this
context means the transition region sufficiently bright in ultraviolet
spectral lines to be observed. I find strong Doppler shift correlations
between two different lower region lines from C IV and S V, but much
weaker correlations between these lines and a line of Ne VIII formed
well into the upper transition region. I conclude that most of the
lower transition region that is observable because of its brightness
arises in cool loop structures. The results also favor a scenario in
which the lower transition region is heated and cooled transiently
on timescales less than or perhaps comparable to the SUMER exposure
times of 21 s for the data analyzed in this work.
Title: Plasma Diagnostics of the Large-Scale Corona with SUMER
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2006ESASP.617E..12L
Altcode: 2006soho...17E..12L
No abstract at ADS
Title: The extreme UV imaging spectrometer for the JAXA Solar-B
mission
Authors: Culhane, J. L.; Doschek, G. A.; Watanabe, T.; Smith, A.;
Brown, C.; Hara, H.; Harra, L. K.; James, A. M.; al Janabi, K.;
Kent, B.; Korendyke, C.; Lang, J.; Mariska, J.; Myers, S.; Seely,
J.; Simnett, G.; Tandy, J.; Thomas, R.; Windt, D. L.
Bibcode: 2006SPIE.6266E..0TC
Altcode: 2006SPIE.6266E..22C
The ISAS/JAXA Solar-B mission includes an Extreme-UV Imaging
Spectrometer (EIS). It detects photons in the wavelength ranges 17 -
21 nm and 25 - 29 nm which include emission lines from several highly
ionised species that exist at temperatures log T = 4.7, 5.6, 5.8,
5.9 and 6.0 - 7.3 K. Instrument throughput is increased substantially
by the use of multilayer coatings optimized for maximum reflectance
in the two selected wavelength bands. The use of back-illuminated
CCDs provides significantly enhanced quantum efficiency over that
previously available from microchannel plate systems. In this paper we
will describe the design and operation of the instrument and present
its performance parameters e.g. spectral and spatial resolution and
sensitivity. Preliminary results of recent calibration measurements
will be described. The role of EIS in the Solar-B mission will be
illustrated with reference to the anticipated observing strategy for
the first three months of the mission which will be outlined.
Title: Plasma Diagnostics of the Large-Scale Corona with
SUMER. I. Measurements at the West Limb
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2006ApJ...643.1258L
Altcode:
In the present work we analyze the physical properties of the quiet-Sun
plasma measured in a 0.5×1.8 Rsolar region above the west
solar limb (Rsolar=solar radius). We make use of large
scans obtained with the SUMER spectrometer on board SOHO to construct
two-dimensional spatial maps of line intensities, electron temperature,
emission measure, element abundances, line widths and nonthermal
velocities, and photoexcitation effects covering the entire field
of view. Electron densities were measured in a more limited portion
of the field of view. The aim of the paper is to identify tracers of
coronal hole and quiet-Sun plasma at high altitudes that allow us to
measure the position of the coronal hole/quiet-Sun boundaries, and
to provide a comprehensive, empirical picture of the off-limb solar
corona that can provide theoreticians with experimental constraints
to their models of the large-scale coronal structure, coronal heating,
and solar wind acceleration.
Title: Modeling High Resolution Flare Spectra Using Hydrodynamic
Simulations
Authors: Warren, Harry; Doschek, G.
Bibcode: 2006SPD....37.2702W
Altcode: 2006BAAS...38..253W
Understanding the hydrodynamic response of the solar atmosphere to
the release of energy during a flare has been a long standing problem
in solar physics. Early time-dependent hydrodynamic simulations were
able to reproduce the high temperatures and densities observed in solar
flares, but were not able to model the observations in any detail. For
example, these simulations could not account for the relatively slow
decay of the observed emission or the absence of blueshifts in high
spectral resolution line profiles at flare onset. We have found that by
representing the flare as a succession of independently heated filaments
it is possible to reproduce both the evolution of line intensity and
the shape of the line profile using hydrodynamic simulations. Here
we present detailed comparisons between our simulation results and
several flares observed with the Yohkoh Bragg Crystal Spectrometer
(BCS). Comparisons with 3D MHD simulations will also be discussed.
Title: The Extreme Ultraviolet Imaging Spectrometer (EIS) on Solar-B
Authors: Doschek, George A.; Brown, C. M.; Korendyke, C. M.; Mariska,
J. T.; Myers, S. H.; Seely, J. F.; Dere, K. P.; Lang, J.; Culhane,
J. L.; Watanabe, T.
Bibcode: 2006SPD....37.3604D
Altcode: 2006BAAS...38S.260D
The Extreme Ultraviolet Imaging Spectrometer (EIS) for Solar-B is a
high throughput state-of-the-art instrument designed to obtain solar
spectra and images in two wavelength bands centered near 195 and 270
Angstroms. Traditional spectra can be obtained using narrow slits or
images of solar structures can be obtained in individual spectral
lines using wide slots. Essentially, the instrument obtains images
in wavebands similar to TRACE but in each spectral line within the
waveband. This removes electron temperature ambiguities inherent in
broadband imagers and allows dynamic effects to be detected via Doppler
shifts and densities and other plasma parameters to be measured via
spectroscopic plasma diagnostics. After a brief description of how
the instrument works and a comparison with previous instrumentation
(sensitivity, etc.), the presentation will focus on the science that
can be accomplished with EIS, presented in the form of sample observing
sequences. The focus will be on active regions and solar flares with a
consideration of topics such as temperature and density distributions
in active region loops and their evolution, dynamical motions in active
region loops, the reconnection site in solar flares, and temperature
evolution of multimillion degree flare loops.
Title: High-resolution X-ray spectra of solar flares
Authors: Doschek, G. A.
Bibcode: 2006AdSpR..38.1482D
Altcode:
I discuss high-resolution solar flare soft X-ray spectra and also
comment on some recent results from extreme ultraviolet (EUV)
spectroscopy. Spectra of solar flares at these wavelengths have
been recorded since the late 1960s, beginning primarily with the NASA
Orbiting Solar Observatory (OSO) series of spacecraft. Knowledge of EUV
flare spectra took a quantum leap with the NASA Skylab Apollo Telescope
Mount spectrographs in the early 1970s. Knowledge of the X-ray spectrum
took a similar leap in the 1980s with the US Department of Defense
P78-1 spacecraft, the NASA Solar Maximum Mission spacecraft (SMM), and
the Japanese ISAS Hinotori spacecraft. Investigations of flare X-ray
spectra continued with the Bragg Crystal Spectrometer (BCS) experiment
on the Japanese Yohkoh mission. EUV solar flare spectroscopy has been
extended with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer and the Coronal Diagnostics Spectrometer (CDS) on
the ESA Solar and Heliospheric Observatory (SOHO) spacecraft. Recently,
more Bragg crystal spectra have become available from experiments such
as the RESIK spectrometers on the Russian Coronas-F spacecraft. In
addition to the above missions, significant earlier contributions
were made with instrumentation on a number of other spacecraft,
e.g., the Soviet Intercosmos X-ray spectrometers. Our knowledge of
the physical conditions in solar flares has been greatly expanded
from analyses of X-ray and EUV flare spectra. I discuss the general
characteristics of the flare emission line and continuum spectra,
and the physical processes that produce them. I summarize what we
have learned about solar flares from the spectra, and highlight a few
problems and prospects for future solar flare research.
Title: Temperature-sensitive line ratio diagnostics based on Si
satellite-to-resonance line ratios for 1s2 1snp transitions
Authors: Phillips, K. J. H.; Dubau, J.; Sylwester, J.; Sylwester,
B.; Culhane, J. L.; Doschek, G. A.; Lang, J.
Bibcode: 2006AdSpR..38.1543P
Altcode:
Dielectronic satellite lines due to 1s2n‧l‧ 1snpn‧l‧
(n = 3, 4) transitions in Li-like Si (Si XII) occur at 5.818 and
5.565 Å, on the long wavelength side of the He-like Si (Si XIII)
1s2 1s3p and 1s2 1s4p lines at 5.681 and 5.384 Å,
respectively. They have been extensively observed with the RESIK crystal
spectrometer on the Russian spacecraft CORONAS-F. As with corresponding
satellites 1s2nl 1s2pnl on the long-wavelength side of
the Si XIII 1s2 1s2p resonance line, there is an inverse
temperature dependence of the intensity ratio of the satellites to the
He-like ion lines (Isat/IHe). New atomic data
are used to calculate the Si XII satellite line intensities and thus
the Isat/IHe ratio. RESIK observations of the
ratio in solar flares, together with temperatures from the ratio of
the two GOES X-ray channels, are compared with theoretical variation
of the ratio with temperature. The good agreement indicates this to
be a valuable temperature diagnostic for solar flares and laboratory
plasmas such as tokamaks. There are implications for similar satellites
in Fe line spectra which are observed with broad-band resolution by
the RHESSI solar flare mission.
Title: Observing the Solar atmosphere with the Extreme Ultraviolet
Imaging Spectrometer on Solar B
Authors: Korendyke, C. M.; Brown, C.; Dere, K.; Doschek, G.; Klimchuk,
J.; Landi, E.; Mariska, J.; Warren, H.; Lang, J.
Bibcode: 2005AGUFMSH41B1124K
Altcode:
The Extreme Ultraviolet Imaging Spectrometer (EIS) is part of the
instrument complement on the Solar B satellite, scheduled for launch
in the summer of 2006. The instrument has been calibrated and is
presently mounted on the spacecraft. EIS is the most sensitive EUV
solar spectrometer to be flown. The instrument is the first of a new
generation of two optical element, solar spectrographs. Preliminary
results from the laboratory focussing and calibration of the
instrument will be shown. The instrument wavelength coverage includes
reasonably bright spectral lines emitted by plasmas from 0.1 to 20 MK
in temperature. The wavelength range also provides coronal density
diagnostics. Temperature, density and velocity diagnostics will be
discussed. An example observing program for exploring active region
evolution and dynamics will be discussed.
Title: Doing Solar Science With Extreme-ultraviolet and X-ray High
Resolution Imaging Spectroscopy
Authors: Doschek, G. A.
Bibcode: 2005AGUFMSH41B1126D
Altcode:
In this talk I will demonstrate how high resolution extreme-ultraviolet
(EUV) and/or X-ray imaging spectroscopy can be used to provide unique
information for solving several current key problems of the solar
atmosphere, e.g., the morphology and reconnection site of solar flares,
the structure of the transition region, and coronal heating. I will
describe the spectra that already exist relevant to these problems
and what the shortcomings of the data are, and how an instrument such
as the Extreme-ultraviolet Imaging Spectrometer (EIS) on Solar-B
as well as other proposed spectroscopy missions such as NEXUS and
RAM will improve on the existing observations. I will discuss a few
particularly interesting properties of the spectra and atomic data
for highly ionized atoms that are important for the science problems.
Title: A new method for in-flight intensity calibration of
high-resolution EUV and FUV spectrometers
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2005A&A...441.1211F
Altcode:
We introduce a new technique for the measurement of the in-flight
relative intensity calibration of high resolution spectrometers. This
technique makes use of the free-free radiation in hot, dense active
regions and flares, and combines it with spectral line intensities
in an iterative procedure. After a few iterations, the relative
intensity calibration and the temperature of the emitting plasma are
determined. The application of this technique to the EIS instrument
on board the Solar-B satellite (launch in 2006) is discussed.
Title: Chromospheric Evaporation in Solar Flares Revisited
Authors: Doschek, G. A.; Warren, H. P.
Bibcode: 2005ApJ...629.1150D
Altcode:
We investigate the initial stage of chromospheric evaporation in flares
using soft X-ray spectra obtained by the Bragg Crystal Spectrometer
(BCS) experiment on Yohkoh. We find that the centroid wavelength
of the Ca XIX line in spectra with the first detectable emission is
within about 8.5×10-4 Å of the rest wavelength, which
corresponds to a Doppler shift of no more than 80 km s-1. We
also determine the minimum detectable soft X-ray flare volume emission
measure from BCS Ca XIX flare spectra. We find that the minimum
detectable emission measured by BCS is produced by an X-ray flux
that is about equal to the peak intensity of a class A6 flare. These
results are difficult to reconcile with one-dimensional hydrodynamic
simulations of an impulsively heated flare loop, which predict large
Doppler shifts during the initial stage of the heating. Furthermore,
inspection of high spatial resolution TRACE images of flare plasma
indicate significant differences between the observed morphology and
the predictions of hydrodynamic models. The evolution of the intensity
and the Doppler shifts are more consistent with models that assume the
sequential heating of small-scale threads rather than the heating of an
individual loop. However, the bright knots of emission and asymmetrical
intensity distributions seen in flare images cannot be explained by
current numerical models of chromospheric evaporation.
Title: Properties of the Solar Corona Outside the West Solar Limb
Authors: Doschek, G. A.; Feldman, U.; Landi, E.
Bibcode: 2005AGUSMSP21B..08D
Altcode:
We discuss the analysis of 36 spectral observations recorded by the
SUMER spectrometer on SOHO on April 22-23, 1998, at the onset of the
new solar cycle. The observations were made with the 4" x 300" slit,
and are distributed over the west hemisphere between 1.02 and 1.5 solar
radii along the equatorial direction and between -0.9 solar radii south
of the equator and +0.9 solar radii north of it. At the far corners of
the studied region the solar distance was 1.74 solar radii. We have
found that the physical characteristics of the central part of the
region are typical of quiet Sun coronal plasmas. The regions furthest
from the equator resemble coronal hole plasmas and the intermediate
regions are consistent with a transition between the two. We believe
that this is the most comprehensive work of its kind undertaken thus
far using UV spectral lines. We use the recorded line intensities
and line shapes to describe, as a function of coronal position,
electron temperatures, electron densities, elemental abundances,
line-of-sight emission measures (EM), nonthermal mass motions, and
mass dependent elemental settling. By using intensity ratios between
the two component resonance lines of Li-like O VI, Ne VIII and Mg X,
we determine the fractional excitation in the Li-like lines produced
by electron collisions and the fractional excitation produced by
photo-excitation of transition region radiation emitted just above
the photosphere.
Title: Chromospheric Evaporation in Solar Flares Revisited
Authors: Doschek, G. A.; Warren, H. P.
Bibcode: 2005AGUSMSP52A..05D
Altcode:
We investigate the initial stage of chromospheric evaporation in
flares using soft X-ray flare spectra obtained by the Bragg Crystal
Spectrometer (BCS) experiment on Yohkoh. We determine the minimum
detectable soft X-ray flare volume emission measure from BCS Ca XIX
flare spectra. We find that the minimum detectable emission measure
by BCS is produced by an X-ray flux that is about equal to the peak
intensity of a class A5 flare. We also find that the centroid wavelength
of the Ca XIX line in spectra with the first detectable emission is
within about 8.5E-4 Angstroms of the rest wavelength, which is 80
km/s in terms of a Doppler shift. We interpret our results assuming
sequential chromospheric evaporation into a multi-threaded flare loop
envelop. Under this assumption, by comparing the BCS results with
images of flares from the Soft X-ray Telescope (SXT) on Yohkoh and
from TRACE, we have determined the minimum energy and electron density
of multi-million degree soft X-ray plasma that can be detected using
presently available spectroscopic X-ray data. In addition we consider
the implications of a multi-thread loop model on TRACE and Yohkoh flare
images, and the differences between the images and the multi-thread
predictions. We find that the multi-million degree flare plasma in TRACE
images frequently exhibits structures that do not resemble the images
of loops expected from the numerical simulations of evaporation. Thus,
while observational signatures of flare dynamics can be consistent
with chromospheric evaporation simulations, problems still remain in
understanding the loop morphology of the multi-million degree plasma.
Title: The Extreme Ultraviolet Imaging Spectrometer on Solar-B
Authors: Mariska, J. T.; Brown, C. M.; Doschek, G. A.; Korendyke,
C. M.; Myers, S. H.; Seely, J. F.; Dere, K. P.; Lang, J.; Culhane,
J. L.; Watanabe, T.
Bibcode: 2005AGUSMSP43A..02M
Altcode:
The Extreme Ultraviolet Imaging Spectrometer (EIS) is currently under
development for flight on the Japanese Solar-B satellite. EIS uses a
multilayer-coated off-axis telescope mirror and a multilayer-coated
toroidal grating spectrometer to produce stigmatic spectra of solar
regions isolated by a 1024 arcsec high slit. The instrument produces
monochromatic images either by rastering the solar image across a
narrow entrance slit or by using a very wide slit. Half of each optic
is coated to optimize reflectance at 19.5 nm, and the other half to
optimize reflectance at 27.0 nm, with each wavelength range imaged
onto a separate CCD detector. EIS can provide key dynamical and density
diagnostic information. Combining EIS data with observations from the
other instruments on Solar-B should provide a detailed picture of solar
atmospheric processes from the visible surface into the corona. In
this presentation, we provide details of the instrument's expected
performance based on calibration of the individual flight optics and
end-to-end testing at the Rutherford Appleton Laboratory in the UK.
Title: Nonthermal Velocities in Different Temperature Regions of
the Solar Lower Transition Region
Authors: Akiyama, S.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2005ApJ...623..540A
Altcode:
We analyze the relationship between nonthermal velocities derived from
spectral lines of ions formed at different temperatures in the solar
lower transition region, using spectra from the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on board the
Solar and Heliospheric Observatory (SOHO). We find a high degree of
correlation among nonthermal motions arising at temperatures ranging
from 3×104 to 2.5×105 K over 1" spatial scales
in quiet-Sun regions. We discuss the implications of these results in
terms of the physical nature of the transition region.
Title: Resik: A Bent Crystal X-ray Spectrometer for Studies of Solar
Coronal Plasma Composition
Authors: Sylwester, J.; Gaicki, I.; Kordylewski, Z.; Kowaliński,
M.; Nowak, S.; Płocieniak, S.; Siarkowski, M.; Sylwester, B.;
Trzebiński, W.; Bakała, J.; Culhane, J. L.; Whyndham, M.; Bentley,
R. D.; Guttridge, P. R.; Phillips, K. J. H.; Lang, J.; Brown, C. M.;
Doschek, G. A.; Kuznetsov, V. D.; Oraevsky, V. N.; Stepanov, A. I.;
Lisin, D. V.
Bibcode: 2005SoPh..226...45S
Altcode:
We describe the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami)
instrument, consisting of two double-channel X-ray spectrometers,
designed to observe solar active region and flare plasmas. RESIK is
one of the instruments making up the scientific payload of the Russian
CORONAS-F solar mission. The uncollimated spectrometer uses two silicon
and two quartz bent crystals observing flare, active region and coronal
spectra in four wavelength bands with a resolving power (λ/Δ λ)
of ∼1000. The wavelength coverage, 3.3-6.1 Å, includes emission
lines of Si, S, Cl, Ar, and K and in the third diffraction order,
the wavelength range includes He-like Fe lines (1.85 Å) and Ni lines
(1.55 Å) with dielectronic satellites, emitted during intense, hot
flares. The instrument is believed to be the best calibrated space-borne
crystal spectrometer flown to date. The spectrometer dynamically adjusts
the data gathering intervals from 1 s to 5 minutes, depending on the
level of solar X-ray emission at the time of observation. The principal
aims of RESIK are the measurements of relative and absolute element
abundances in the emitting plasma and the temperature distribution of
plasma (differential emission measure) over the temperature interval 3
and 50 MK. This paper summarizes the scientific objectives of RESIK
and describes the design, characteristics, and performance of the
instrument.
Title: Reconciling Hydrodynamic Simulations with Spectroscopic
Observations of Solar Flares
Authors: Warren, Harry P.; Doschek, George A.
Bibcode: 2005ApJ...618L.157W
Altcode:
Chromospheric evaporation is a central element of current models
of solar flares. The high-velocity upflows that should accompany
evaporation, however, are rarely observed in high-resolution solar flare
spectra. Thus the absence of blueshifted line profiles represents a
significant discrepancy between the theory and observations of this
phenomenon. In this Letter we present an algorithm for computing
multiple-loop time-dependent hydrodynamic simulations of solar flares
using a minimum of assumptions. We show that these simulations can
accurately reproduce the Ca XIX and S XV line profiles observed with
the Bragg Crystal Spectrometer on Yohkoh during the earliest stages
of a flare. Since our model represents the flare as a succession
of independently heated threads, the strongly blueshifted emission
evident during the initial heating of a thread is largely masked by
emission from threads that have been heated previously and do not show
bulk motions.
Title: The Solar-B EUV imaging spectrometer and its science goals
Authors: Culhane, J. L.; Harra, L. K.; Doschek, G. A.; Mariska, J. T.;
Watanabe, T.; Hara, H.
Bibcode: 2005AdSpR..36.1494C
Altcode:
The Solar-B mission includes an Extreme-UV Imaging Spectrometer
(EIS). It detects photons in the ranges 170-210 and 250-290 Å which
include emission lines from several highly ionised species that exist
at temperatures log T = 4.7, 5.6, 5.8, 5.9 and 6.0-7.3 K. In this
paper, we will describe the design and operation of the instrument
and present its performance parameters, e.g., spectral and spatial
resolution and sensitivity. Preliminary results of recent calibration
measurements will be described. Its role in the Solar-B mission will
be illustrated with reference to several key science topics that the
EIS is expected to address. The anticipated observing strategy for
the first three months of the mission will be outlined.
Title: Observations Indicating That ~1 × 107 K Solar
Flare Plasmas May Be Produced in Situ from ~1 × 106
K Coronal Plasma
Authors: Feldman, U.; Dammasch, I.; Landi, E.; Doschek, G. A.
Bibcode: 2004ApJ...609..439F
Altcode:
We discuss a set of flare observations obtained at a position of
0.10 Rsolar above the solar northwest limb. The data
were acquired by the Solar Ultraviolet Measurement of Emitted
Radiation (SUMER) spectrometer on the Solar and Heliospheric
Observatory (SOHO). We derive time-dependent comparisons of
physical properties, such as electron temperature and density,
between flare plasma and background coronal plasma observed along
the same lines of sight. In addition to temperature and density,
we discuss emission measures, elemental abundances, nonthermal mass
motions (from line widths), and bulk mass motions (from Doppler
shifts). The observations appear to indicate that the flaring plasmas
(4×106K<=Te<=1×107K)
along the lines of sight were formed by in situ heating
and possibly by compression of the ambient coronal material
(Te<=2×106 K).
Title: The Relationship of the Chromosphere to the Lower Solar
Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Akiyama, S.
Bibcode: 2004ApJ...609.1153D
Altcode:
We examine the intensity correlations among lower transition region
emission lines of N III, N IV, N V, O II, O III, O IV, O V, S IV, and S
V. We find strong intensity correlations, with 1 σ deviations in line
intensity ratios less than about 35% on spatial scales of 1". For strong
lines the percent deviations are significantly less than this. The line
intensities were obtained from the Solar Ultraviolet Measurement of
Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric
Observatory (SOHO). We find a dependence of the O II/O III and O V/N V
ratios with intensity. The degree of correlation we obtain on arcsecond
spatial scales is consistent with size scales for the basic transition
region structures that are significantly less than 1" (730 km).
Title: Performance of multilayer-coated gratings for the
extreme-ultraviolet imaging spectrometer (EIS) for the Solar-B mission
Authors: Seely, John F.; Windt, David L.; Donguy, Soizik; Brown,
Charles; Holland, Glenn; Hunter, William R.; Kowalski, Michael
P.; Kjornrattanawanich, Benjawan; Doschek, George; Mariska, John;
Korendyke, Clarence; Dere, Ken
Bibcode: 2004SPIE.5168...12S
Altcode:
The measured efficiencies of two flight gratings and the reflectances
of two flight mirrors developed for the Extreme-Ultraviolet Imaging
Spectrometer (EIS) for the Japanese Solar-B mission are presented. Each
optic has two sectors with Mo/Si multilayers that refelct the 17 -
21 nm and 25 - 29 nm wavebands at normal incidence. The efficiencies
that were measured using monochromatic synchrotron radiation are in
good agreement with the calculated efficiencies.
Title: Properties of the Lower Transition Region: The Widths of
Optically Allowed and Intersystem Spectral Lines
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 2004ApJ...600.1061D
Altcode:
The widths of spectral lines in the ultraviolet (UV) and extreme
ultraviolet (EUV) spectral regions that are formed in the solar
transition region and corona are usually greater than the optically
thin widths due to thermal Doppler broadening calculated under the
assumption of ionization equilibrium. Although opacity can explain the
widths of some lines, there are a host of optically thin lines for which
the excess widths are attributed to nonthermal motions. Interest in
these motions for coronal heating theories has led to the measurement
and comparison of spectral line profiles/widths throughout the solar
UV and EUV spectrum. We find that for the quiet Sun the widths of some
optically allowed lower transition region lines, deduced from spectra
obtained by the Solar Ultraviolet Measurements of Ultraviolet Radiation
(SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO)
spacecraft, are considerably larger than predicted from simply scaling
previously measured wavelengths of other lines from the same ion. For
example, the O III lines of the multiplet near 834 Å are considerably
wider than predicted from the previously measured (from Skylab) width of
the optically thin O III 1666.15 Å intersystem line. The excess widths
are not due to nonthermal motions, as these are already included in
the width of the 1666.15 Å line. In this paper, we analyze the widths
of some prominent optically allowed lines and discuss possible causes
for discrepancies with previous measurements of intersystem lines.
Title: High Resolution Spectra of Solar Flares
Authors: Doschek, G. A.
Bibcode: 2004cosp...35.1529D
Altcode: 2004cosp.meet.1529D
I discuss high-resolution solar flare spectra from the soft X-ray region
through the extreme ultraviolet (EUV) wavelength regions. Spectra of
solar flares at these wavelengths have been recorded since the late
1960s, beginning primarily with the NASA Orbiting Solar Observatory
(OSO) series of spacecraft. Knowledge of EUV flare spectra took a
quantum leap with the NASA Skylab Apollo Telescope Mount spectrographs
in the early 1970s. Knowledge of the X-ray spectrum took a similar
leap in the 1980s with the US Department of Defense P78-1 spacecraft,
the NASA Solar Maximum Mission spacecraft (SMM), and the Japanese
Hinotori spacecraft. Investigations of flare X-ray spectra continued
with the BCS X-ray spectrometer experiment on the Japanese Yohkoh
mission. Recently, EUV solar flare spectroscopy has been extended with
the SUMER spectrometer on the ESA SOHO spacecraft. In addition to the
above missions, significant contributions were made with instrumentation
on a number of other spacecraft, e.g., the Soviet Intercosmos X-ray
spectrometers. Our knowledge of the physical conditions in solar
flares has been greatly expanded from analyses of X-ray and EUV flare
spectra. I will discuss the general characteristics of the flare
emission line and continuum spectra, and the physical processes that
produce them. I will discuss what we have learned about solar flares
from the spectra, and discuss solar flare spectra in terms of spectra
expected from other astrophysical sources.
Title: Temperature-sensitive Line Ratios Diagnostics of the
non-flaring Corona based on Satellite-to-Resonance Line Ratios for
1s^2-1s(np) Transitions
Authors: Phillips, K. J. H.; Dubau, J.; Sylwester, J.; Sylwester,
B.; Kordylewski, Z.; Culhane, J. L.; Doschek, G. A.; Lang, J.
Bibcode: 2004cosp...35.2579P
Altcode: 2004cosp.meet.2579P
One of the most convenient electron temperature diagnostics of
hot astrophysical plasmas is the intensity ratio of dielectronic
satellite lines to resonance lines in the X-ray region. Until now,
this diagnostic has been applied to satellites near the 1s-2p lines of
H-like ions or the 1s^2 - 1s2p lines of He-like ions, these lines being
extensively observed with crystal spectrometers during flares. However,
satellites near the 1s^2 - 1snp (n>2) lines of He-like ions,
unlike those near the 1s^2 - 1s2p lines, have the important advantage
of being well separated from their parent lines and unblended with
other lines. Spectra from the RESIK spectrometer on Coronas-F,
covering the wavelength range 3.4 Å,- 6.1 Å, are highly suited
for observation of these satellites, due to transitions from the n =
3, 4 and 5 levels to the n = 1 level, near corresponding resonance
lines of H-like and He-like Si (Si XIII, Si XIV) and S (S XV, S XVI)
ions. New calculations of satellite intensity factors presented in
this paper enable temperatures to be calculated from observed ratios
of Li-like Si (Si XII) 1s^2 2p ^2P1/2,3/2 - 1s 2p (^3P) 3p
^2D3/2,5/2 satellite complex (5.816 Å) near He-like Si (Si
XIII) 1s^2 ^1S_0 - 1s 3p ^1P_1} resonance (5.681 Å) line. These lines
are well observed in recent quiet and non-flaring active region RESIK
X-ray spectra, and therefore provide the most sensitive temperature
diagnostic tool for physical conditions in weakly active corona.
Title: Patterns of X-ray line emission variability as observed by
the RESIK Bragg spectrometer
Authors: Sylwester, J.; Sylwester, B.; Culhane, J. L.; Doschek, G. A.;
Oraevsky, V. N.; Phillips, K. J. H.
Bibcode: 2003ESASP.535..733S
Altcode: 2003iscs.symp..733S
RESIK is a unique Bragg bent crystal spectrometer operating continuously
since August 2001. By now, it has collected ~10 GB of solar flare and
active region spectra in a very much unexplored spectral region between
3.2 Å and 6.1 Å. In this paper we present a number of representative
observations covering periods of various solar activity: from the most
active level (M+ flares) to exceptionally quiet corona. We present also
a tentative list of the spectral features observed. In the wavelength
range observed by RESIK there are a number of strong emission lines
corresponding to H- and He-like resonance transitions of Si, S, Ar and K
ions. These lines are formed by thermal plasma of temperature between
5 and 50 MK, and therefore their analysis reveal the distribution
of hot plasma over this interval. RESIK sees lines from a number of
different elements, so it is possible to do abundance analyses. The
elements concerned have a wide range of first ionisation potentials
(FIPs) so it has been possible to examine the dependence of coronal or
flare abundances on FIP. We have observed substantial variations of
the K/Ar line ratio, and respective line/continuum ratios, which can
be best explained by allowing for changes in the chemical composition
of the coronal plasma
Title: The spatial correlation of the non-thermal velocities for O
IV and Si IV in the lower transition region
Authors: Akiyama, S.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2003AdSpR..32.1137A
Altcode:
We analyze the spatial relationship between non-thermal velocities
derived from spectral lines of O IV. λ1401.16 (1.6×105 K) and Si
IV λ1402.77 (6.3x10 4 K) in the solar lower transition
region. The lines formed at different temperatures are observed
simultaneously and at the same locations on the solar disk by the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
on board the Solar and Heliospheric Observatory (S OHO). In order to
improve the accuracy of the non-thermal velocities determined from the
full width at half maximum (FVJHM) intensities of the lines, we select
data with sufficient counting statistics such that the uncertainty
of the non-thermal velocity is less than 10 % of its value derived
from the FWHMs. The spatial relationship between lines of O IV and
Si IV shows a strong correlation. The correlation coefficient of the
turbulent velocity is 0.856 for bright quiet Sun regions.
Title: Free-Free Emission in the Far-Ultraviolet Spectral Range:
A Resource for Diagnosing Solar and Stellar Flare Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Dammasch, I.;
Curdt, W.
Bibcode: 2003ApJ...593.1226F
Altcode:
We report the detection of free-free (bremsstrahlung) emission near 1200
Å from a flare at the solar limb observed with the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) spacecraft. The observations
consist of a time series of slit spectra at a fixed pointing that
lasted almost 2 hr, during which the observed solar region produced
a C8 flare. Using the free-free continuum intensities in conjunction
with intensities of high-temperature (106-107
K) emission lines that appear in the same wavelength range, we
derive the flare plasma electron density, electron temperature,
emission measure, and nonthermal mass motions before, during, and
after the flare. We describe a new diagnostic method for determining
the temperature of cooling plasmas. Because the free-free radiation
is emitted primarily by the interaction of electrons with nuclei of
H and He atoms, we are also able to derive the Fe/H, Al/H, and Ca/H
abundance ratios from the line intensities of highly ionized Fe, Al,
and Ca lines and the intensities of the free-free emission, assuming
a He abundance. The present work demonstrates the exceptional plasma
diagnostic potential of ultraviolet free-free continuum radiation when
coupled with emission-line intensities. We demonstrate that a similar
technique could be employed to diagnose plasma properties of stellar
flares using a high-resolution spectrometer with a sufficiently large
effective collecting area.
Title: Temperature Measurements in the Solar Transition Region Using
N III Line Intensity Ratios
Authors: Doron, R.; Doschek, G. A.; Laming, J. M.; Feldman, U.;
Bhatia, A. K.
Bibcode: 2003ApJ...590.1121D
Altcode:
UV emission from B-like N and O ions offers a rather rare opportunity
for recording spectral lines in a narrow wavelength range that can
potentially be used to derive temperatures relevant to the solar
transition region. In these ions, the line intensity ratios of the type
(2s2p2-2p3)/(2s22p-2s2p2)
are very sensitive to the electron temperature. In addition, the lines
involving the ratios fall within a range of only ~12 Å in N III
the lines fall in the 980-992 Å range, and in O IV in the 780-791
Å range. In this work, we explore the use of these atomic systems,
primarily in N III, for temperature diagnostics of the transition
region by analyzing UV spectra obtained by the Solar Ultraviolet
Measurement of Emitted Radiation spectrometer flown on the Solar and
Heliospheric Observatory. The N III temperature-sensitive line ratios
are measured in more than 60 observations. The mean measured ratios are
lower by ~30% than those predicted in the typical quiet Sun. Assuming
an isothermal plasma, most of the measured ratios correspond to
temperatures in the range 5.7×104-6.7×104
K. This range is considerably lower than the calculated temperature of
maximum abundance of N III, which is ~7.6×104 K. Detailed
analysis of the spectra further indicates that the measured ratios
are probably somewhat overestimated because of resonant scattering
effects in the 2s22p-2s2p2 lines and small
blends in the 2s2p2-2p3 lines. Actual lower
ratios would only increase the discrepancy between the ionization
balance calculations and present temperature measurements based on
a collisional excitation model. In the case of the O IV spectra,
we determine that because of the close proximity in wavelength of the
weak line (2s2p2-2p3 transitions) to a strong Ne
VIII line, sufficiently accurate ratio measurements cannot be obtained.
Title: Expected Performance of the Extreme Ultraviolet Imaging
Spectrometer on Solar-B
Authors: Mariska, J. T.; Brown, C. M.; Dere, K. P.; Doschek, G. A.;
Korendyke, C. M.; Myers, S. H.; Seely, J. F.; Culhane, J. L.;
Watanabe, T.
Bibcode: 2003SPD....34.2006M
Altcode: 2003BAAS...35..845M
The Extreme Ultraviolet Imaging Spectrometer (EIS) is currently under
development for flight on the Japanese Solar-B satellite. EIS uses a
multilayer-coated off-axis telescope mirror and a multilayer-coated
toroidal grating spectrometer to produce stigmatic spectra of solar
regions isolated by a 1024 arcsec high slit. The instrument produces
monochromatic images either by rastering the solar image across a
narrow entrance slit or by using a very wide slit. Half of each optic
is coated to optimize reflectance at 19.5 nm, and the other half to
optimize reflectance at 27.0 nm, with each wavelength range imaged
onto a separate CCD detector. In this presentation we provide an
update on the EIS hardware development and show details of the expected
performance of the instrument in solar quiet regions, active regions,
and flares.
Title: Properties of the Lower Transition Region Deduced from Widths
of Optically Allowed Lines in SUMER Spectra
Authors: Doschek, G. A.
Bibcode: 2003SPD....34.1706D
Altcode: 2003BAAS...35..838D
The widths of spectral lines in the ultraviolet (UV) and extreme
ultraviolet (EUV) spectral regions that are formed in the solar
transition region and corona are usually greater than the optically
thin widths due to thermal Doppler broadening calculated under the
assumption of ionization equilibrium. Although opacity can explain
the widths of some lines, there are a host of optically thin lines
for which the excess widths are attributed to nonthermal motions of
unknown origin. Interest in these motions has lead to the measurement
of spectral line profiles and widths throughout the solar UV and EUV
spectrum. I find that for the quiet Sun the widths of the optically
allowed lower transition region O III lines of the multiplet near 834 Å
deduced from SUMER/SOHO spectra are considerably wider than predicted
from simply scaling the previously measured (from Skylab) width of the
optically thin O III 1666.15 Å intersystem line. The excess widths
are not due to nonthermal motions as these are already included in the
width of the 1666.15 Å line, and opacity in the 834 Å lines does
not appear to be adequate in itself to explain the result. I find a
similar result for optically allowed lines of other ions observed in
SUMER spectra. I discuss possible causes for the excess widths and show
that they can be explained by several effects. In some cases opacity
is significant and excess broadening due to opacity provides a direct
measure of the path length through lower transition region structures
at Sun center. This work was supported by the Naval Research Laboratory
basic research program.
Title: The X-ray Spectra Predicted to Be Emitted From Hot
Astrophysical Plasmas Abnormally Enriched With High-Z Elements -
The Case of Mercury
Authors: Doron, R.; Feldman, U.; Doschek, G. A.; Bar-Shalom, A.
Bibcode: 2002ASPC..277..461D
Altcode: 2002sccx.conf..461D
No abstract at ADS
Title: X-ray and EUV Observations of Solar Flares
Authors: Doschek, G. A.
Bibcode: 2002ASPC..277...89D
Altcode: 2002sccx.conf...89D
No abstract at ADS
Title: RESIK observations of highly ionized argon and potassium
X-ray emission lines in solar flares
Authors: Sylwester, J.; Culhane, J. L.; Doschek, G. A.; Oraevsky,
V. N.; Phillips, K. J. H.; Sylwester, B.
Bibcode: 2002ESASP.506..765S
Altcode: 2002svco.conf..765S; 2002ESPM...10..765S
The first detailed solar X-ray spectra obtained by the RESIK bent
crystal spectrometer aboard the CORONAS-F obervatory are presented
and instrument performance discussed. RESIK is a bent crystal
spectrometer covering four soft X-ray spectral ranges (3.369-3.879 Å,
3.821-4.326 Å, 4.307-4.890 Å 4.960-6.086 Å), some of which have
not been well covered by previous instruments. RESIK forms spectra
in each of these ranges in 250 bins simultaneously in intervals
of 10 s or so. Many flares, including several of GOES X-class,
and bright active regions have now been observed in detail. (See
http://www.cbk.pan.wroc.pl/2002.htm for examples.) In this paper,
observations of spectral lines due to K XVIII, Ar XVIII, Ar XVII, S XV,
Si XIV and Si XIII ions will be shown and the time evolution of their
intensities will be discussed. These observations will eventually
allow for precise determination of differential emission measure
(DEM) and chemical composition of the hot flare plasma, and should,
alongside data from the RHESSI, TRACE, and SOHO spacecraft, enable
new and detailed insight into solar flare mechanisms.
Title: Atomic Data and Spectral Line Intensities for fe XI
Authors: Bhatia, A. K.; Doschek, G. A.; Eissner, W.
Bibcode: 2002ADNDT..82..211B
Altcode:
Electron impact collision strengths and spontaneous radiative
decay rates are calculated for Fe XI. The data pertain to the
96 levels of the configurations 3s23p4,
3s3p5, 3s23p33d,
3p6, 3s23p34s, and
3s23p34d. Collision strengths are calculated
at 10 incident electron energies: 1.0, 3.4, 6.0, 12.0, 15.0, 30.0,
45.0, 60.0, 75.0, and 90.0 Ry. These atomic data are generated to
support the interpretation of spectra of astrophysical objects, which
frequently contain emission lines from Fe XI and similar ions. This
work supplements previous work published on Fe XI by extending the
calculation of collision strengths and radiative decay rates to levels
within n=4 configurations. Relative spectral line intensities are
calculated for all astrophysically important transitions. These are
obtained by computing the excitation rate coefficients (cm3
s-1), i.e., the collision strengths integrated over a
Maxwellian electron distribution, and then solving the equations
of detailed balance for the populations of the 96 energy levels,
assuming a collisional excitation model and an electron temperature
of 1.3×106 K. This temperature is typical for Fe XI when
formed at equilibrium by collisional ionization and recombination. Using
the excitation rate coefficients and the radiative decay rates, level
populations are computed for several electron densities. The calculation
of line intensities and level populations includes proton excitation
because hydrogen is the most abundant element in astrophysical plasmas
relevant to Fe XI emission.
Title: The Effect of High-Lying Configurations and Ionization and
Recombination Processes on Analyses of Solar and Stellar Coronal
Spectra
Authors: Doron, Rami; Behar, Ehud; Doschek, George A.; Feldman, Uri
Bibcode: 2002AIPC..636..125D
Altcode:
This work addresses two topics important for the appropriate
interpretation of astrophysical spectra. The first is the effect
of high-lying levels on the atomic models and the second is the
importance of ionization and recombination processes in forming
line emission. In the first part of the work we study the influence
of high-lying configurations on the calculated intensities of UV
lines, particularly of O-like ions, observed by the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer aboard the SOHO
satellite. The high-lying configurations alter the line intensities
through radiative cascades and configuration interaction effects. We
find that cascades can significantly enhance the intensities of
some lines of the considered ions by up to 65% at temperatures
of the ion maximum fractional abundance. The enhancement due to
cascades increases with increasing temperature and charge state. The
configuration mixing effects can either enhance or reduce the line
intensities. In a second study, we calculate the theoretical intensities
of the soft X-ray Fe16+ lines arising from 2l-3l' transitions using a
three-ion collisional-radiative model that includes the contribution of
recombination and ionization processes to line formation. Dielectronic
recombination is found to be particularly important. The newly
calculated line intensities can explain the high values of the 2p-3s
/ 2p-3d intensity ratios, which are often obtained in astrophysical
observations. Observed intensity ratios among the 2p-3s lines are also
better reproduced.
Title: The Effect of High-lying Levels on Atomic Models Relevant to
Spectroscopic Analyses of Solar Extreme-Ultraviolet Spectra
Authors: Doron, R.; Doschek, G. A.; Feldman, U.; Bhatia, A. K.;
Bar-Shalom, A.
Bibcode: 2002ApJ...574..504D
Altcode:
In this work we investigate the effect of including high-lying
configurations in the collisional-radiative models used to calculate
spectral line intensities recorded by the Solar Ultraviolet
Measurement of Emitted Radiation (SUMER) spectrometer on board the
SOHO satellite. Many of the emission lines observed by SUMER are
attributed to transitions within the L and M electronic shells of
ions isoelectronic to sequences from Li I to Na I. By using atomic
data that are mostly generated by the Hebrew University Lawrence
Livermore Atomic Code (HULLAC), we incorporate in the atomic models
configurations from higher shells and systematically study their effect
on the calculated line intensities in selected ions. The high-lying
configurations alter the line intensities through radiative cascades
and configuration interaction effects. We find that cascades can
significantly enhance the line intensities of the considered ions by
up to 60% at temperatures of the ion maximum fractional abundance. The
enhancement due to cascades increases with increasing temperature and
charge state. The configuration mixing effects can either enhance or
reduce the line intensities. Generally, the mixing effect becomes less
important for higher charge states.
Title: What Solar Atmospheric Pnenomena Produce the Sun's X-ray-EUV-UV
Spectrum?
Authors: Doschek, G. A.
Bibcode: 2002AAS...200.5205D
Altcode: 2002BAAS...34Q.727D
Recently high-resolution X-ray-EUV-UV spectra of unprecedented
spectral resolution have been obtained from non-solar cosmic sources
from missions such as Chandra, EUVE, and HST. These spectra have
resolving power that rivals the best solar spectra, and detailed
plasma diagnostic techniques can be used to interpret them. Many of
the plasma diagnostic techniques were first developed and used for the
interpretation of high-resolution solar, tokamak, and laser-produced
plasma spectra. However, detailed spatial resolution of at least stellar
sources is still lacking. In this talk I will illustrate what regions
and processes in the solar atmosphere produce different sections of
the Sun's high-energy spectrum. I will link various spectral features
with the most recent high-resolution spatial observations of the Sun,
and discuss the physical mechanisms that are believed to define the
morphology and energetics of the structures that produce the spectra. I
will also discuss new spectral and atomic physics results that are
emerging from the analysis of spectra from the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) spacecraft. This work was funded
by NASA Solar Physics Guest Investigator Grant S137816.
Title: The Relationship between SiIV and OIV for Non-thermal
Turbulenc Velocity
Authors: Akiyama, S.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2002AAS...200.3810A
Altcode: 2002BAAS...34..700A
We report nonthermal turbulence velocities of spectral lines of O IV
λ 1401.16 and Si IV λ 1402.77 observed with SUMER spectrometer abord
SOHO spacecraft. In ionization equilibrium, the electron temperatures
of these ions are 1.6X105 and 6.3X104 K,
respectively. Although their spectral line intensities and ratio are
vely similar at the quiet area in the lower solar transition region
in spite of differential emission measures (Doschek & Mariska
2001). Since these observations help to understand the physical
property and the morphology of the transition region, we take note of
nonthermal turbulence velocities in this study and compare O IV with
Si IV lines using by the observational data of Doschek & Mariska
(2001). In order to improve in accuracy, we select the points which
error of turbulence velocity are less then 10 % of turbulence velocity
both O IV and Si IV line. In the result, the correlation of turbulence
velocity between O IV and Si IV is 0.846, we can see strong correlation
at the bright points in the quiet region. We discuss the implications
of these results for the physical conditions of the transition region.
Title: The Structure of the Lower Solar Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Akiyama, S.
Bibcode: 2002AAS...200.3811D
Altcode: 2002BAAS...34Q.700D
Recent high-spatial resolution monochromatic images obtained from
the SUMER spectrometer on SOHO have shown that the lower transition
region ( 2 x 104 - 2 x 105 K) is composed of
small loops and knots of emission (seen on the disk), and thread-like
structures (seen above the limb) (Feldman, Widing, & Warren, ApJ,
522, 1133 (1999)). The structures seen in images of different spectral
lines formed at significantly different electron temperatures look
quite similar. However, because the temperatures are different, the
emitting plasma cannot be the same for the different images. What is
the physical relationship between lower transition region structures
that appear in lines formed at different temperatures? The answer to
this question can begin to be addressed by examining SUMER spectra of
lower transition region lines formed at different temperatures that
appear on the same SUMER exposures. In this case the spatial region on
the Sun viewed in both spectral lines is precisely the same, and both
lines are recorded simultaneously. The intensity relationship between
lines of Si IV (6.3 x 104 K) and O IV (1.3 x 105
K) for such spectra has already been discussed by Doschek & Mariska
(ApJ, 560, 420 (2001)), and a strong correlation between Si IV and O IV
intensities was found. We will discuss an extension of this work to line
groups of, (1) O II, O III (3 x 104, 9.0 x 104
K), (2) C IV, S V, O IV (1 x 105, 1.6 x 105,
1.6 x 105 K), and (3) N IV, O V (1.4 x 105,
2.5 x 105 K). The O II, O III comparison does not show
the strong correlation found for higher temperature lines, indicating
that chromospheric structures are significantly different from lower
transition region structures. The S V and O IV temperature regions
strongly overlap but are not identical. Nevertheless, the intensity
correlation is quite high. This work was supported by NASA solar
physics Guest Investigator Grant S137816.
Title: The O+ and O++ emission lines near 834
Å in the quiet sun solar spectrum
Authors: Doschek, G. A.
Bibcode: 2002GeoRL..29.1159D
Altcode: 2002GeoRL..29g..63D
I present quiet Sun solar disk averaged emission line intensities (at
the Earth) and the full widths at half maximum intensity (FWHM) for
the O+ and O++ emission lines that fall near 834
Å. These lines are important as excitation sources for O+
and O++ emission in the Earth's upper ionosphere,
plasmasphere and magnetosphere. I also discuss the variation of
the ratio of O+ to O++ emission as a function
of solar spatial fine structure in the quiet Sun. The spectra were
obtained from the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer flown on the Solar and Heliospheric Observatory
spacecraft. There are five O+ and O++ features
in the solar spectrum involving nine spectral lines. The peak quiet
Sun intensities (in units of 109 photons cm-2
s-1 Å-1) of these features and their approximate
centroid wavelengths are: 0.717, 832.85 Å 0.717, 833.30 Å 1.76,
833.74 Å 1.16, 834.45 Å and 2.68, 835.29 Å. The average O+
and O++ FWHMs are 0.177 Å and 0.179 Å, respectively. The
difference in widths is not significant.
Title: An Inquiry into the Nature of Spectra from Hot Astrophysical
Plasma Abnormally Enriched with Mercury
Authors: Doron, R.; Feldman, U.; Doschek, G. A.; Bar-Shalom, A.
Bibcode: 2002ApJS..139..297D
Altcode:
Observatories such as Chandra, XMM-Newton, and more likely future
instruments with higher effective collecting area of radiation will
offer the opportunity to study the nature of chemically peculiar
sources using observations in the X-ray and EUV range. In the present
work we explore the possibility to observe the spectral signature
of highly stripped Hg ions that might be present in possible coronae
or winds of HgMn stars. A systematic theoretical survey of the most
intense X-ray spectral features predicted to be emitted by H-like to
Pd-like Hg ions (Hg+79-Hg+34) is performed. The
calculated intensities (photons s-1 ion-1)
of the various spectral features of the Hg ions are compared to the
intensities calculated for the lines of Fe ions that may be observed
in the same range of the X-ray spectrum, but not necessarily from the
same temperature domain. Fe lines corresponding to transitions from the
L electronic shell were already observed in the coronae of stars, e.g.,
by Chandra in Capella. Assuming a similar abundance for Hg and Fe ions,
many of the calculated Hg lines are found to be of comparable intensity
to the Fe lines and in some cases stronger by about a factor of 20. We
also discuss possible density and temperature diagnostic applications
for some of the Hg lines.
Title: The EUV Imaging Spectrometer and its Role in the Solar-B
Mission
Authors: Culhane, J. L.; Doschek, G. A.; Watanabe, T.; Lang, J.
Bibcode: 2002ISSIR...2..327C
Altcode: 2002rcs..conf..327C; 2002ESASR...2..327C
Given the importance of the SOHO EUV instrument calibration techniques
for the Japan/US/UK Solar-B mission, the nature of Solar-B is briefly
described and the three scientific instruments on board the spacecraft
are discussed. The EUV Imaging Spectrometer (EIS) instrument is
described in some detail since it is anticipated that the SOHO
calibration techniques will have direct application to the absolute
calibration of EIS. The key scientific aims of Solar-B are presented.
Title: The spatial correlation between the non-thermal velocities
of different lines in the solar lower transition region
Authors: Akiyama, S.; Doschek, G.; Mariska, J.
Bibcode: 2002cosp...34E2769A
Altcode: 2002cosp.meetE2769A
The physical relationship between different temperature regions of
the solar transition region is unclear. In an attempt to understand
this relationship, we analyze SUMER/SOHO spectra of lines formed at
different temperatures that are observed simultaneously at the same
locations on the solar disk. The present work concerns the relationship
in quiet Sun regions among non-thermal turbulent velocities measured in
several spectral lines. For each line, the velocity is determined from
the full width at half maximum intensity. To improve the accuracy of
the line width measurements, we select data with counting statistics
such that the uncertainty in the turbulent velocity is less than 10%
of the turbulent velocity. The spatial relationship between lines of
O IV1401.16 (1.6 ×105 K) and Si IV1402.77 (6.3 × 104 K) for such
spectra shows a strong correlation. The correlation coefficient of
the turbulent velocity between O IV and Si IV is 0.784 for bright
quiet Sun regions. In this poster we will discuss an extension of this
work to line groups of (1) O II, O III (3.2 × 104 , 1.0 × 105 K),
(2) N IV, S V, O IV (1.3 × 105 , 1.4 × 105 1.6 × 105 K). The N IV,
S V, O IV comparisons also show the correlation. We present these and
other results, and discuss the implications for the physical nature
of the transition region.
Title: The Physics of the Solar Lower Transition Region
Authors: Doschek, G. A.; Mariska, J. T.
Bibcode: 2001ApJ...560..420D
Altcode:
We discuss quiet-Sun intensities of spectral lines of O IV λ1401.16
and Si IV λ1402.77, their ratio, and their relation to expected
properties of the lower solar transition region. The data consist
of simultaneous measurements of the two line intensities for
16,988 pixels with spatial dimensions of 1" square obtained by the
Solar Ultraviolet Measurement of Emitted Radiation spectrometer on
the Solar and Heliospheric Observatory spacecraft. In ionization
equilibrium, the electron temperatures of maximum concentration
of the two ions are 1.6×105 and 6.3×104 K,
respectively. Assuming ionization equilibrium, the line intensity
ratio is directly proportional to the emission measure ratio between
plasma at these temperatures. Thus, the observations represent 16,988
snapshots of two temperature regions of the differential emission
measure at arcsecond spatial scales in the quiet Sun. We derive an
average quiet-Sun λ1401.16/λ1402.77 ratio, acquired from observations
over 3 hr and a 30''×290'' spatial region,
of 0.267+/-0.050. The 1 σ deviation of this ratio is only 20%,
but it is about 2.4 times greater than expected purely from counting
statistics. We also find that the ratio is about 20% smaller for the
most intense features in the spectra. From analysis of another ratio,
i.e., O IV λ1399.77/O IV λ1401.16, we argue that this decrease could
be due to a higher electron density in the intense features relative
to the lower intensity features. We discuss the implications of these
observations for understanding the morphology of the transition region.
Title: Intensity Ratios between the 2s2
1S0-2s2p 3P1
and 2s2p 1P1-2p2
1D2 Transitions in Be-like Ions as Electron
Temperature Indicators for Solar Upper Atmosphere Plasmas
Authors: Landi, E.; Doron, R.; Feldman, U.; Doschek, G. A.
Bibcode: 2001ApJ...556..912L
Altcode:
We investigate the relative intensities of
the two moderately bright Be-like 2s2
1S0-2s2p 3P1 and 2s2p
1P1-2p2 1D2
lines as a function of electron temperature. We show that the intensity
ratios of the lines in the beryllium isoelectronic sequence from C
III to Ni XXV ions can serve as sensitive temperature indicators for
a large variety of solar plasmas. While the C III-Ne VII lines can be
used to diagnose unresolved fine structures in relatively cold solar
atmosphere plasmas [(1-5)×105 K], the Na VIII-Ar XV ions
can be used to diagnose coronal plasmas [(0.8-3)×106
K], and Ca XVII-Ni XXV lines are useful to measure the temperature
in flaring plasmas [(5-16)×107 K]. We investigate the
effects on the temperature determination caused by varying the number of
energy levels that are included in the atomic model for the considered
ions. It is found that a model that includes the 2l2l'
and 2l3l' configurations is sufficient for adequately
describing the relevant level populations of the Be-like ions in
coronal conditions. We compare theoretical ratios obtained using
collisional cross section and transition probability values derived
by different theoretical methods. The atomic data are obtained from
the CHIANTI database, the Hebrew University Lawrence Livermore Atomic
Code (HULLAC) suite of programs, and other available sources in the
literature. Finally, we use spectra of an apparently isothermal
coronal plasma observed by the Solar Ultraviolet Measurement of
Emitted Radiation instrument on the Solar and Heliospheric Observatory
to determine the electron temperature of streamer plasma using the
HULLAC and CHIANTI atomic data sets. The result is compared with the
temperature derived in an earlier study using different methods.
Title: Solar Flare Doppler Blueshifted Soft X-Ray Emission and Hard
X-Ray Bursts
Authors: Rilee, M. L.; Doschek, G. A.
Bibcode: 2001ApJ...554..464R
Altcode:
Hard X-ray emission and the dynamics of soft X-ray emitting plasma
are among the most immediate manifestations of solar flare energy
release. To understand better the early impulsive phase of solar
flare energy release, we have examined Ca XIX and Fe XXV soft X-ray
resonance line spectra that exhibit strong blue-wing asymmetries
from 32 flares. These spectra were obtained with the Bragg Crystal
Spectrometer on the Japanese Yohkoh spacecraft, which is up to 10
times more sensitive than previously flown crystal spectrometers. The
increased sensitivity allowed the comparison of Doppler blueshifted
X-ray emission to hard X-ray emission observed with the Compton Gamma
Ray Observatory's Burst and Transient Source Experiment, the Yohkoh
Wide Band Spectrometer, and Yohkoh Hard X-Ray Telescope. We found that
(1) hard X-ray burst light curves and resonance line blue-wing light
curves are similar for most flares that exhibit strong blueshifts;
(2) the time evolution of the intensity ratio of the blue wing to
the peak unshifted spectral component resembles higher energy hard
X-ray emission more closely than the blue-wing light curve alone; (3)
though many flares had blue-wing/resonance peak ratios that resembled
or peaked at the same time as the hard X-ray burst, nearly one-third of
the flares exhibited ratio curves that either were nonzero before the
detection of burst hard X-rays or peaked before the hard X-ray burst
peaked-a few of these flares exhibited small blueshifted line profiles
before the detection of hard X-ray emission; (4) a few flares with
strong blueshifts had little or no detectable emission above 30 keV;
and (5) the time derivative of the resonance peak emission usually
resembles the blue-wing light curve. The implication of these results
for current flare models is discussed.
Title: The Extreme Ultraviolet Imaging Spectrometer on Solar-B
Authors: Mariska, J. T.; Brown, C. M.; Dere, K. P.; Doschek, G. A.;
Korendyke, C. M.; Culhane, J. L.; Watanabe, T.
Bibcode: 2001AGUSM..SH41A12M
Altcode:
Emission lines in the extreme ultraviolet spectral region provide a
sensitive probe of the high-temperature plasma in the solar transition
region and corona. Simultaneously achieving high spatial, spectral, and
temporal resolution in this wavelength region has been challenging. We
describe the design and capabilities of the Extreme Ultraviolet
Imaging Spectrometer (EIS) planned for flight on the Japanese Solar-B
satellite. EIS consists of a multilayer-coated off-axis telescope
mirror and a multilayer-coated toroidal grating spectrometer. The
telescope mirror forms a solar image on the spectrometer entrance slit
assembly and the spectrometer forms stigmatic spectra of the solar
region isolated by the 1024 arcsec high slit. The instrument includes
thin-film aluminum filters to reject longer wavelength radiation and
CCD detectors at the focal plane. Articulation of the primary mirror
provides roughly 1600 arcsec of east-west coarse pointing freedom
and 360 arcsec of fine east-west motion for rastering. Monochromatic
images are formed either by rastering the solar image across a narrow
entrance slit or by using a very wide slit. Half of each optic is
coated to optimize reflectance at 19.5 nm, and the other half to
optimize reflectance at 27.0 nm. Each wavelength range is imaged onto
a separate CCD detector. The EIS spectral range contains emission lines
formed over a temperature range from roughly 0.1 to 20 MK. Bright lines
in the selected wavelength bands will yield precision measurements of
line-of-sight velocities and nonthermal plasma motions. This spectral
range also includes several pairs of density-sensitive lines.
Title: High Resolution Imaging Spectroscopy as a Key for Understanding
Coronal Heating and Solar Activity
Authors: Doschek, G. A.
Bibcode: 2001AGUSM..SH31D07D
Altcode:
The development of high spectral resolution solar spectroscopy has
occurred in three main steps: (1) The Exploration of the Solar Spectrum
(spectral line identifications, determining atomic energy levels of
solar abundant ions), (2) The Spectrum as a Tool for Solar Physics
(understanding atomic processes in hot plasmas and developing plasma
diagnostics useful for solar physics), and, (3) Imaging Spectroscopy
(applying well-developed plasma diagnostic techniques to individual
structures in the solar atmosphere with simultaneous high spatial
and temporal resolution). Due to technological advances such as
multilayer optics and the development of CCDs for extreme-ultraviolet
wavelength regions, high resolution imaging spectroscopy is now on the
threshold of providing key information for testing theories of coronal
heating and the mechanisms of solar activity. Apart from providing
detailed information on solar element abundances, electron and ion
temperatures, electron densities and filling factors, high resolution
solar spectroscopy provides unambiguous information on the dynamics of
individual solar structures through measurements of Doppler effects in
the profiles of spectral emission lines. And it is the dynamics that
provide key tests for coronal heating and solar activity theories
involving physical processes such as magnetic reconnection and wave
heating. In this talk I will discuss how a new generation of imaging
spectrometers should provide breakthroughs in our understanding of
many of the major problems of the solar atmosphere. This work was
supported by NASA and NRL/ONR
Title: Properties of Solar Polar Coronal Hole Plasmas Observed above
the Limb
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Schühle, U.;
Wilhelm, K.
Bibcode: 2001ApJ...546..559D
Altcode:
We determine the line-of-sight emission measure distribution and
nonthermal motions as a function of height above the limb in the
north and south polar coronal holes. These quantities are derived from
extreme-ultraviolet (EUV) spectra obtained from the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
and Heliospheric Observatory (SOHO) spacecraft. The SUMER slit was
oriented along the north-south direction for all the observations,
and the spatial resolution is about 1". The spectra were obtained
from a number of different types of observations in 1996. We select
a group of emission lines for analysis for which, under the usual
assumption of ionization equilibrium, the maximum emissivities span
the temperature range from about 3×105 K up to about
1.1×106 K. We compare our results with recently published
similar observations of a west limb quiet-Sun streamer region, with
other coronal hole results based on SUMER spectra, and with earlier
observations of the quiet Sun and coronal holes obtained from Skylab
and rocket spectra. We find that the electron temperature in the polar
holes increases with height above the limb, that the emission measure
distribution of plasma located at line-of-sight heights less than
about 60" peaks at a temperature of about 9×105 K, and that
nonthermal motions sometimes, but not always, increase slightly with
height above the limb. When observed, these increases level off above
the limb at about 120". We speculate that the increases with height
above the limb may be a manifestation of the fast solar wind. They
may also be due to the reduction in transition region structures with
increasing limb height. We also discuss wave heating as a cause of
the line width increases.
Title: Extreme-ultraviolet imaging spectrometer designed for the
Japanese Solar-B satellite
Authors: Culhane, J. L.; Korendyke, Clarence M.; Watanabe, Tetsuya;
Doschek, George A.
Bibcode: 2000SPIE.4139..294C
Altcode:
The Extreme-ultraviolet Imaging Spectrometer combines, for the first
time, high spectral, spatial and temporal resolution in a satellite
based, solar extreme ultraviolet instrument. The instrument optical
design consists of a multilayer-coated off- axis paraboloid mirror
telescope followed by a toroidal grating spectrometer. The instrument
includes thin film aluminum filters to reject longer wavelength solar
radiation and employs CCD detectors at the focal plane. The telescope
mirror is articulated to allow sampling of a large fraction of the
solar surface from a single spacecraft pointing position. Monochromatic
images are obtained either by rastering the solar image across the
narrow entrance slit or by using a wide slit or slot in place of
the slit. Monochromatic images of the region centered on the slot are
obtained in a single exposure. Half of each optic is coated to maximize
reflectance at 195 angstrom; the other half is coated to maximize
reflectance at 270 angstrom. The two EUV wavelength bands were selected
to optimize spectroscopic plasma diagnostic capabilities. Particular
care was taken to choose wavelength ranges with relatively bright
emission lines to obtain precision line of sight and turbulent bulk
plasma velocity measurements from observed line profiles. The EIS
spectral range contains emission lines formed over a temperature
range from approximately 105 - 107 K. The
wavelength coverage also includes several density sensitive emission
line pairs. These line pairs provide spatial resolution independent
density diagnostics at nominal coronal temperatures and densities. Each
wavelength band is imaged onto a separate CCD detector. The main EIS
instrument characteristics are: wavelength bands -- 180 - 204 angstrom
and 250 - 290 angstrom; spectral resolution -- 0.0223 angstrom/pixel
(23 - 34 km/second-pixel); slit dimensions -- 4 slits: 1 X 1024 arc-
seconds and 50 X 1024 arc-seconds with two positions unspecified as
of this writing; fine raster range -- >6 arc-minutes on the sun;
coarse raster range -- > 1600 arc- seconds on the sun; largest
spatial field of view in a single exposure -- 50 X 1024 arc-seconds;
nominal time resolution for active region velocity studies -- 3.4s. The
Solar-B satellite is scheduled for launch in August 2005 into a nominal
600 km sun-synchronous orbit.
Title: Emission-Line Intensity Ratios in Fe XVII Observed with a
Microcalorimeter on an Electron Beam Ion Trap
Authors: Laming, J. M.; Kink, I.; Takacs, E.; Porto, J. V.; Gillaspy,
J. D.; Silver, E. H.; Schnopper, H. W.; Bandler, S. R.; Brickhouse,
N. S.; Murray, S. S.; Barbera, M.; Bhatia, A. K.; Doschek, G. A.;
Madden, N.; Landis, D.; Beeman, J.; Haller, E. E.
Bibcode: 2000ApJ...545L.161L
Altcode:
We report new observations of emission line intensity ratios
of Fe XVII under controlled experimental conditions, using the
National Institute of Standards and Technology electron beam
ion trap (EBIT) with a microcalorimeter detector. We compare our
observations with collisional-radiative models using atomic data
computed in distorted wave and R-matrix approximations, which
follow the transfer of the polarization of level populations
through radiative cascades. Our results for the intensity
ratio of the 2p61S0-
2p53d1P1 15.014
Å line to the 2p61S0-
2p53d3D1 15.265 Å line are 2.94+/-0.18
and 2.50+/-0.13 at beam energies of 900 and 1250 eV, respectively. These
results are not consistent with collisional-radiative models and
support conclusions from earlier EBIT work at the Lawrence Livermore
National Laboratory that the degree of resonance scattering in the solar
15.014 Å line has been overestimated in previous analyses. Further
observations assess the intensity ratio of the three lines between
the 2p6-2p53s configurations to the three lines
between the 2p6-2p53d configurations. Both
R-matrix and distorted wave approximations agree with each other and
our experimental results much better than most solar and stellar
observations, suggesting that other processes not present in our
experiment must play a role in forming the Fe XVII spectrum in solar
and astrophysical plasmas.
Title: The Relationship of Solar Abundance Measurements to the
Electron Temperature in a Polar Coronal Hole
Authors: Doschek, G. A.; Laming, J. M.
Bibcode: 2000ApJ...539L..71D
Altcode:
We discuss the behavior of the intensity of the Mg VI λ1191.64 spectral
line relative to the intensity of the Ne VI λ1005.78 spectral line as
a function of height above the limb in the solar north polar coronal
hole. The intensities of Mg VI lines relative to Ne VI lines have
been shown to be excellent indicators of element abundance variations
due to the first ionization potential (FIP) effect. We find that
the Mg VI/Ne VI intensity ratio increases with height above the limb
by factors ranging from 1.7 to 4 over a height range extending from
about 6" above the limb to 28" above the limb. We conclude that this
intensity ratio increase is primarily due to an increase of electron
temperature with height, rather than the result of an FIP effect,
and therefore caution must be exercised in using any Mg VI/Ne VI
line ratio as an abundance diagnostic above the limb in the polar
holes. At 6" above the limb, the Mg VI/Ne VI line ratio indicates that
the solar Mg/Ne abundance ratio is probably within a factor of 2 of
the photospheric abundance ratio. The spectra we use were recorded by
the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
on the Solar and Heliospheric Observatory spacecraft.
Title: Properties of Solar Polar Coronal Hole Plasmas Observed Above
the Limb
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.
Bibcode: 2000SPD....31.1307D
Altcode: 2000BAAS...32Q.846D
We discuss nonthermal motions, line-of-sight emission measures, and
relative element abundances as a function of height in the solar polar
coronal holes. The data pertain to the upper transition region and
coronal regions of the atmosphere at heights ranging from the solar limb
to about 150'' above the limb. The spatial resolution is 1\arcsec. The
physical quantities are derived from spectral line intensities and
profiles obtained by the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) spacecraft. The line width information is important for wave
theories of coronal heating. We find that the electron temperature
in the polar holes increases with height above the limb, that the
emission measure distribution of plasma at line-of-sight heights less
than 60'' peaks at a temperature of about 9 x 105 K, and
that nonthermal motions sometimes, but not always, increase slightly
with height above the limb. When observed, these increases level off
above the limb at about 120\arcsec. We speculate that the line width
increases with height above the limb may be a manifestation of the
fast solar wind. Finally, we find that increases of a Mg VI/Ne VI
line ratio with height above the north polar limb are probably due
to the increase of electron temperature with height, and not due to
a relative element abundance variation caused by the first ionization
potential (FIP) effect. This work was supported by NASA SR&T Grant
W-19,329 and by the ONR/NRL Research Option, Solar Magnetism and the
Earth's Environment.
Title: The Electron Temperature and Fine Structure of Soft X-ray
Solar Flares
Authors: Doschek, G. A.
Bibcode: 2000ASPC..206..204D
Altcode: 2000hesp.conf..204D
No abstract at ADS
Title: Extreme-Ultraviolet Spectral Line Widths in Quiet-Sun Coronal
Plasmas at Distances of 1.03<=Rsolar<=1.45 along
the Solar Equatorial Plane
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 2000ApJ...529..599D
Altcode:
We measure the full width at half-maximum intensity (FWHM)
of extreme-ultarviolet (EUV) spectral line profiles as a function
of height in the Sun's equatorial west limb streamer region using
EUV spectra recorded by the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) spacecraft. The spectra were recorded on 1996 November 21 and
22, during a special ``roll'' maneuver in which the SUMER slit was
oriented in the east-west direction. Because the SUMER spectrometer
is stigmatic along the slit length, the spectra are spatially resolved
in the east-west direction. The spectra we discuss cover an effective
distance range outside the west limb from 1.03 to 1.45 Rsolar
the maximum spatial resolution is 1''. We select a group of
emission lines for analysis that under the usual ionization equilibrium
assumption have maximum fractional abundances at temperatures ranging
from 3×105 up to 2×106 K. We determine
nonthermal motions as a function of position in the streamer region
from the FWHMs under the assumption that the ion temperature equals the
electron temperature of the streamer plasma. The electron temperature
was derived previously by Feldman and coworkers.
Title: The Electron Temperature and Fine Structure of Soft X-Ray
Solar Flares
Authors: Doschek, G. A.
Bibcode: 1999ApJ...527..426D
Altcode:
I discuss the determination of the electron temperature of soft X-ray
solar flares using data obtained from the iron-line Bragg Crystal
Spectrometer (BCS) and Soft X-ray Telescope (SXT) instruments on the
Yohkoh spacecraft. I find that there is a substantial difference in
the derived temperatures obtained from the two instruments, with the
highest temperatures obtained from the BCS. However, in some regions of
certain flares, the SXT temperatures equal the temperatures expected
from the iron-line spectra. These hot regions are almost always
considerably weaker in intensity than the brightest regions in the
SXT flare images. I discuss the relationship of the SXT hot regions
to the brightest regions in the flare and show that, at least in some
cases, the hot SXT regions appear to be related to the hard X-ray
flare component. I also show that the temperature data from the two
instruments can be reconciled by concluding that flare loops that appear
to be single loops are actually collections of loops with different
temperatures on arcsecond or less spatial scales. This result was
obtained indirectly by Doschek, Strong, & Tsuneta in 1995 from an
analysis of SXT flare images and is substantiated so far by flare images
from TRACE. The appearance of a soft X-ray flare depends critically
on the electron temperature response of the imaging instrumentation.
Title: Concept Study Report: Extreme-Ultraviolet Imaging Spectrometer
Solar-B
Authors: Doschek, George A.; Brown, Charles M.; Davila, Joseph M.;
Dere, Kenneth P.; Korendyke, Clarence M.; Mariska, John T.; Seely,
John F.
Bibcode: 1999STIN...0011153D
Altcode:
We propose a next generation Extreme-ultraviolet Imaging Spectrometer
(EIS) that for the first time combines high spectral, spatial, and
temporal resolution in a single solar spectroscopic instrument. The
instrument consists of a multilayer-coated off-axis telescope mirror
and a multilayer-coated grating spectrometer. The telescope mirror
forms solar images on the spectrometer entrance slit assembly. The
spectrometer forms stigmatic spectra of the solar region located
at the slit. This region is selected by the articulated telescope
mirror. Monochromatic images are obtained either by rastering the solar
region across a narrow entrance slit, or by using a very wide slit
(called a slot) in place of the slit. Monochromatic images of the
region centered on the slot are obtained in a single exposure. Half
of each optic is coated to maximize reflectance at 195 Angstroms; the
other half to maximize reflectance at 270 Angstroms. The two Extreme
Ultraviolet (EUV) wavelength bands have been selected to maximize
spectral and dynamical and plasma diagnostic capabilities. Spectral
lines are observed that are formed over a temperature range from about
0.1 MK to about 20 MK. The main EIS instrument characteristics are:
wavelength bands - 180 to 204 Angstroms; 250 to 290 Angstroms; spectral
resolution - 0.0223 Angstroms/pixel (34.3km/s at 195 Angstroms and
23.6 km/s at 284 Angstroms); slit dimensions - 4 slits, two currently
specified dimensions are 1" x 1024" and 50" x 1024" (the slot);
largest spatial field of view in a single exposure - 50" x 1024";
highest time resolution for active region velocity studies - 4.4 s.
Title: A Comparison of Measurements of Solar Extreme-Ultraviolet
Spectral Line Intensities Emitted by C, N, O, and S Ions with
Theoretical Calculations
Authors: Doschek, E. E.; Laming, J. M.; Doschek, G. A.; Feldman, U.;
Wilhelm, K.
Bibcode: 1999ApJ...518..909D
Altcode:
Atomic data for ionized atoms are important for many astrophysical
applications. The launch of the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER) extreme-ultraviolet (EUV) spectrometer aboard
the Solar and Heliospheric Observatory (SOHO) allows us to test the
accuracy of certain computed relative excitation rate coefficients
and transition probabilities for a number of important astrophysical
ions. We use spectral line intensity ratios derived from SUMER spectra
to compare these quantities with the best available theoretical
calculations for transitions within the ions C II, N III, N IV, O III,
O IV, O V, S III, S IV, and S V. The results of this work are important
for many current and upcoming NASA astrophysics missions. In addition
to the published atomic data, we calculate some new atomic data using
the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Our
comparison of measured intensity ratios with theoretical predictions
reveals significant discrepancies between the predicted and measured
intensity ratios for several ions, particularly for S III, S IV, and
S V. S III and S IV produce strong line emission in the Io torus. We
discuss the methods we used to ensure that our ratios are accurate,
the possible effects of Lyman continuum absorption on our data, and the
ramifications of ignoring dielectronic capture resonances in certain
transitions as a possible explanation for some of the discrepancies.
Title: Properties of Quiet-Sun Coronal Plasmas at Distances of
1.03<=Rsolar<=1.50 along the Solar Equatorial Plane
Authors: Feldman, U.; Doschek, G. A.; Schühle, U.; Wilhelm, K.
Bibcode: 1999ApJ...518..500F
Altcode:
We determine the physical properties, i.e., electron temperature,
density, line-of-sight emission measure, and element-abundance variation
with height, in the Sun's equatorial west limb streamer region from
extreme-ultraviolet (EUV) spectra recorded by the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and
Heliospheric Observatory (SOHO) spacecraft. The spectra were recorded
on 1996 November 21-22 during a special ``roll'' maneuver in which
the SUMER slit was oriented in the east-west direction. Because the
SUMER spectrometer is stigmatic along the slit length, the spectra are
spatially resolved in the east-west direction. The spectra we discuss
cover an effective distance range outside the west limb from 1.03 to
1.50 solar radii (Rsolar) the maximum spatial resolution is
1''. We select a group of emission lines for analysis that
under the usual ionization equilibrium assumption span the temperature
range from 3×105 up to 2×106 K. However,
we note that above the limb a major fraction of a line intensity may
arise at a temperature that is far from the temperature of maximum
emitting efficiency in ionization equilibrium. In this paper we assume
ionization equilibrium in deriving plasma parameters. Readers can redo
our analysis without this assumption if desired, because the line
intensities we present in this paper are simply the measured photon
production rates in the lines. Assuming ionization equilibrium, we
determine the electron temperature, electron density, line-of-sight
emission measure, and abundance variation with height above the limb
from the line intensities and line intensity ratios. The spatial
resolution has allowed us to detect an apparent element-abundance
variation as a function of height above the west limb that is strong
evidence for gravitational settling of ``heavy'' elements.
Title: Properties of the Quiet Sun Corona in the West Limb Equatorial
Streamer Region
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1999AAS...19410005D
Altcode: 1999BAAS...31..997D
We determine physical properties, such as electron temperature and
density, in the Sun's west limb equatorial streamer region from spectra
recorded by the SUMER spectrometer on SOHO. The spectra were recorded
on 1996 November 21-22 during a special roll maneuver in which the
stigmatic SUMER slit was oriented in the east-west direction. Results
are obtained as a function of height from close to the limb out to about
1.5 solar radii. We find that the streamer region is well-represented
by an isothermal plasma at 1.3 x 10(6) K between 1.03 and 1.5 solar
radii. The electron density falls from 1.8 x 10(8) cm(-3) near the limb
to about 1.6 x 10(7) cm(-3) at 1.3 solar radii. For ions with similar
atomic weights, we find that the typical quiet Sun FIP enhancement of
about a factor of 4 does not vary with height above the limb. Perhaps
of most interest, we find strong evidence for gravitational settling
of Fe relative to the lighter elements such as Ne, Mg, and Si. This
adds a complicating factor in determining physical parameters in
the corona. The above results are discussed in detail in Feldman et
al. 1999, ApJ, 518, June 10 issue. We also measure the full width at
half maximum intensity of spectral line profiles for lines of several
upper transition region and coronal ions formed in the streamer. If we
adopt our measured electron temperature and assume that the electron
and ion temperatures are equal, we obtain typical nonthermal speeds of
about 33 km s(-1) and in addition find that the speed does not increase
with height between about 1.03 and 1.3 solar radii. The line profile
results are discussed in detail in Doschek & Feldman 1999, ApJ,
submitted. This work was funded by the 6.1 NRL/ONR Solar Magnetism
and the Earth's Environment Research Option.
Title: Atomic Data and Spectral Line Intensities for Ni XVI
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1999ADNDT..71...69B
Altcode:
Electron impact collision strengths and spontaneous radiative
decay rates are calculated for Ni XVI. The data pertain to the 40
levels of the configurations 3s23p, 3s3p2,
3s23d, 3p3, and 3s3p3d. Collision strengths are
calculated at five incident electron energies: 10.0, 20.0, 30.0, 40.0,
and 50.0 Ry. Relative spectral line intensities are calculated for all
astrophysically important transitions. These are obtained by computing
the excitation rate coefficients (cm3s-1),
that is, the collision strengths integrated over a Maxwellian electron
distribution, and then solving the equations of detailed balance for the
populations of the 40 energy levels, assuming a collisional excitation
model and an electron temperature of 2.51 × 106K. This
temperature is typical for Ni XVI when formed in equilibrium by
collisional ionization and recombination. With the excitation rate
coefficients and the radiative decay rates, level populations are
computed for several electron densities and are given in this paper. We
also investigate the effects of proton excitation and solar radiative
excitation on the level populations and line intensities.
Title: On the Ability of an Extreme-Ultraviolet Multilayer
Normal-Incidence Telescope to Provide Temperature Information for
Solar Plasmas
Authors: Feldman, U.; Laming, J. M.; Doschek, G. A.; Warren, H. P.;
Golub, L.
Bibcode: 1999ApJ...511L..61F
Altcode:
In recent years, multilayer-coated optics have been used in solar-soft
X-ray and extreme-ultraviolet telescopes to record high-resolution,
full Sun images. The multilayer coatings reflect efficiently over rather
narrow wavelength bands that are selected to contain spectral emission
lines considered to have plasma diagnostic importance for determining
approximate electron temperatures. The purpose of this Letter is to
discuss the effect of continuum emission on the response of multilayer
passbands and the effect of this response on temperature determinations
in the 4×106-2×107 K range. Significant effects
are largely confined to continuum emission from flare plasma. The
flare free-free continuum in the EUV range is nearly temperature and
wavelength insensitive and dominates the emission in passbands that
are centered on quiet- to active-Sun coronal lines emitted by ions
such as Fe IX-Fe XV.
Title: The Electron Pressure in the Solar Lower Transition Region
Determined from O V and Si III Density-sensitive Line Ratios
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Warren, H. P.;
Schüle, U.; Wilhelm, K.
Bibcode: 1998ApJ...507..991D
Altcode:
We determine the electron density at the temperatures of formation
of O+4 and Si+2 ions, which are about 2.5 ×
105 and 3.2 × 104 K in ionization equilibrium,
respectively. These temperatures occur in the lower transition
region of the Sun's atmosphere and allow a test of the often invoked
assumption of constant pressure in quiet-Sun models. The O+4
density is determined from a density-sensitive spectroscopic O V
line ratio involving 2s2p3P-2p23P
transitions that fall near 760 Å. The Si+2 density is
determined from a density-sensitive Si III line ratio within the
3s3p3P-3p23P multiplet near 1300
Å. There are few available line ratio techniques for determining
the density and hence electron pressure in the quiet-Sun and coronal
hole transition regions using lines emitted by the same ion, and
determining these quantities is the principal motivation for this
work. The spectra used in our analysis were obtained from the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the
Solar and Heliospheric Observatory (SOHO). We determine the electron
density and pressure in typical quiet-Sun/coronal hole regions, and
densities in active region brightenings and in an explosive event. Our
O V and Si III results indicate that constant pressure is valid or
nearly valid in quiet-Sun lower transition regions, although there
are complications arising from the weakness of a key Si III line in
the quiet-Sun disk spectra. We also discuss our results in light of
other density measurements and theories regarding the structure and
heating of the transition region.
Title: The Si/Ne Abundance Ratio in Polar Coronal Hole and Quiet-Sun
Coronal Regions
Authors: Doschek, G. A.; Laming, J. M.; Feldman, U.; Wilhelm, K.;
Lemaire, P.; Schühle, U.; Hassler, D. M.
Bibcode: 1998ApJ...504..573D
Altcode:
Using spectra obtained from the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer flown on the Solar and
Heliospheric Observatory (SOHO) spacecraft, we determine the Si/Ne
abundance ratio in diffuse, interplume polar coronal hole regions,
as well as the ratio relative to quiet-Sun coronal regions. Ne has
the second highest first ionization potential (FIP) of solar abundant
elements, and Si is a low-FIP element. Thus the Si/Ne ratio is a
sensitive indicator of abundance variations due to the FIP effect. We
develop new spectroscopic diagnostics for the determination of the
Si/Ne abundance ratio. Assuming ionization equilibrium, we find that
the Si/Ne abundance ratio in interplume polar coronal hole regions is
about a factor of 2 greater than the photospheric value and is close
to or the same as in coronal quiet-Sun regions. This result pertains
to the electron temperature range 5-8 × 105 K. However,
the combined atomic physics, instrumental, and statistical uncertainty
in this result is about a factor of 2, and therefore this observed
enhancement is consistent with no enhancement in the polar hole
abundances. Nevertheless, our results follow the same trend, i.e., a
greater than photospheric abundance ratio of low-FIP elements in the
corona relative to high-FIP elements, as found from other abundance
measurements in the corona that involve different atomic physics and
different instruments. Therefore we feel that our results reflect
an actual abundance enhancement, despite being within an uncertainty
level bar that encompasses photospheric abundances. We also examine
the Ne/Mg abundance ratio over a 24.5 hr observation and find no
significant abundance variations. (Mg is a low-FIP element.) Thus,
no large transient abundance variations appear to occur on timescales
shorter than about a day, although this result is based on only
one observation. From lines of Mg VII, Mg VIII, Mg IX, and Mg X we
find that the electron temperature along the line of sight increases
with height above the limb over the polar coronal holes, as has been
previously reported. We determine the emission measure distribution as
a function of height from Mg VII, Mg VIII, and Mg X lines. We determine
average temperatures along the line of sight over the polar holes from
Ne VIII/Ne VII, Mg VIII/Mg VII, and Si VIII/Si VII line ratios. We also
discuss the temperature properties of the coronal hole and quiet-Sun
regions using forbidden lines of Fe X and Fe XI. We comment on the
possibility that ionization equilibrium is not valid in polar coronal
hole regions, a possible scenario in light of recent observations that
show outflows in coronal holes beginning at about the temperature of
formation of Ne VIII.
Title: High-Temperature Lines in SUMER Spectra Recorded Above a
Bright Solar Active Region
Authors: Feldman, U.; Curdt, W.; Doschek, G. A.; Schühle, U.; Wilhelm,
K.; Lemaire, P.
Bibcode: 1998ApJ...503..467F
Altcode:
We identify spectral lines emitted by solar abundant elements due
primarily to transitions within the 2s22pk and
3s23pk (where k = 1, 5) ground configurations
of ions that are formed in ionization equilibrium between 2 ×
106 and 8 × 106 K. The transitions were
identified in spectra of a bright active region recorded 1997
September 6, by the Solar Ultraviolet Measurements of Emitted Radiation
Spectrometer (SUMER) flown on the Solar and Heliospheric Observatory
(SOHO). Some of these lines provide useful plasma diagnostic tools
for measuring the physical conditions in the solar corona.
Title: A Compact Spectral Range and Matching Extreme-Ultraviolet
Spectrometer for the Simultaneous Study of 1 × 104-2 ×
107 K Solar Plasmas
Authors: Feldman, U.; Brown, C. M.; Laming, J. M.; Seely, J. F.;
Doschek, G. A.
Bibcode: 1998ApJ...502..997F
Altcode:
An EUV spectral range of less than 100 Å in first order has been found
that includes sufficient spectral lines and critical combinations
of lines in first and second order to permit dynamic and diagnostic
investigations of the solar atmosphere with a relatively simple
spectrometer. An optical design of such a spectrometer, based on the
performance of the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) spacecraft, and sample stigmatic solar spectra for the range
1334-1428 Å from SUMER are presented to illustrate the utility of
this range. Lines of almost all abundant solar elements except H and He
are present within this wavelength band in first or second order. The
lines cover the large temperature range from 1 × 104 K
(chromosphere) to 2 × 107 K (flares). The spectrometer's
resolution is sufficiently high to permit measuring line profiles and
wavelength shifts which allows plasma dynamical studies of individual
solar structures from the chromosphere up into the corona. In addition,
electron density diagnostics are available within the spectral range
that cover the temperature range from 8 × 104 to 1 ×
106 K and an electron density range from 108
to 1013 cm-3.
Title: The Magnetic Reconnection Explorer (MAGREX)
Authors: Schühle, U.; Antionchos, S. K.; Barbee, T. W., Jr.; Bixler,
J. V.; Brown, C. M.; Carter, P. H., II; Curdt, W.; Davila, J. M.;
Doschek, G.; Feldman, U.; Goldstein, W. H.; Kordas, J.; Lemaire, P.;
Mariska, J. T.; Marsch, E.; Moses, J. D.; Seely, J. F.; Wilhelm, K.;
Woods, T. N.
Bibcode: 1998ESASP.417..289S
Altcode: 1998cesh.conf..289S
No abstract at ADS
Title: RESIK: High Sensitivity Soft X-ray Spectrometer for the Study
of Solar Flare Plasma
Authors: Sylwester, J.; Gaicki, I.; Kordylewski, Z.; Nowak, M.;
Kowalinski, S.; Sjarkowski, M.; Bentley, W.; Trzebinski, R. D.;
Whyndham, M. W.; Guttridge, P. R.; Culhane, J. L.; Lang, J.; Phillips,
K. J. H.; Brown, C. M.; Doschek, G. A.; Oraevsky, V. N.; Boldyrev,
S. I.; Kopaev, I. M.; Stepanov, A. I.; Klepikov, V. Yu.
Bibcode: 1998ESASP.417..313S
Altcode: 1998cesh.conf..313S
No abstract at ADS
Title: Atomic Data and Spectral Line Intensities for Ni XIII
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1998ADNDT..68...49B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for Ni XIII. The data pertain to the 48 levels of
the configurations 3s23p4, 3s3p5,
3s23p33d, and 3p6. Collision
strengths are calculated at five incident electron energies: 10.0,
20.0, 30.0, 40.0, and 50.0 Ry. Relative spectral line intensities
are calculated for all astrophysically important transitions. These
are obtained by computing the excitation rate coefficients
(cm3s-1), i.e., the collision strengths
integrated over a Maxwellian electron distribution, and then solving
the equations of detailed balance for the populations of the 48 energy
levels, assuming a collisional excitation model and an electron
temperature of 2.0 × 106K. This temperature is typical
for Ni XIII when formed in equilibrium by collisional ionization
and recombination. Using the excitation rate coefficients and the
radiative decay rates, level populations are computed for several
electron densities and are given in this paper. We also investigate
the effects of proton excitation and solar radiative excitation on
the level populations and line intensities.
Title: New Results from Solar Coronal Spectroscopy (SOHO/SUMER)
Authors: Doschek, G. A.
Bibcode: 1998ASPC..154..413D
Altcode: 1998csss...10..413D
I review some of the recent high resolution solar spectroscopic results
obtained from the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) experiment flown on the Solar and Heliospheric Observatory
(SOHO). SOHO was launched in December, 1995 and has been returning a
wealth of high quality solar data that is providing new insights into
the physics of the solar atmosphere and the magnetic field in which it
is embedded. This review is not unbiased, but is mostly a description
of work carried out at the Naval Research Laboratory (NRL). First,
I briefly discuss the SUMER spectrometer. Second, I discuss plasma
dynamics results, i.e., results obtained from spectral line shapes,
widths, and wavelength shifts. Third, I discuss plasma diagnostics
results, i.e., temperatures, densities, etc. deduced from spectral
line intensities and intensity ratios.
Title: Coronal Abundances: What are They?
Authors: Jordan, C.; Doschek, G. A.; Drake, J. J.; Galvin, A. B.;
Raymond, J. C.
Bibcode: 1998ASPC..154...91J
Altcode: 1998csss...10...91J
Derivation of coronal abundances in the Sun and cool stars has led
to conflicting results. In some stars, the coronal abundances appear
metal deficient (MAD: a metal abundance deficiency), in others the
abundance seems dependent on the ionization potential of the first ion
(FIP-effect: First Ionization potential). Additionally, in the Sun
there may be evidence for abundance variations from one feature to
another. If abundance differences are real, they could give valuable
insight to the physical processes of heating and mass transport in
the chromospheres and coronas of cool stars.
Title: Observations of Thermal Plasma in a Solar Limb Flare
Authors: Mariska, John T.; Doschek, G. A.
Bibcode: 1997ApJ...485..904M
Altcode:
All but a small portion of the top of the 1991 October 21 flare was
occulted by the solar limb. Thus, both the Bragg crystal spectrometer
(BCS) and the soft X-ray telescope (SXT) on Yohkoh observed only a small
region of flaring plasma. Using observations from those instruments,
we have determined the temporal behavior of the emission measure,
temperature, and nonthermal broadening in the loop-top source. We find
that for a portion of the decay phase of this flare, the temperatures
determined using the Fe XXV, Ca XIX, and S XV BCS channels and SXT
filter ratios all agree. Assuming that the plasma is isothermal, we
determine the abundances of Fe XXII, Fe XXIII, and Fe XXIV relative
to Fe XXV. Comparing the results with recent ionization equilibrium
calculations, we find that there are discrepancies between the
Fe XXII-to-Fe XXV ratio, the Fe XXIII-to-Fe XXV ratio, and the Fe
XXIV-to-Fe XXV ratio and ionization equilibrium calculations, which
we attribute to uncertainties in the ionization balance calculations.
Title: The Solar-B Mission
Authors: Antiochos, Spiro; Acton, Loren; Canfield, Richard; Davila,
Joseph; Davis, John; Dere, Kenneth; Doschek, George; Golub, Leon;
Harvey, John; Hathaway, David; Hudson, Hugh; Moore, Ronald; Lites,
Bruce; Rust, David; Strong, Keith; Title, Alan
Bibcode: 1997STIN...9721329A
Altcode:
Solar-B, the next ISAS mission (with major NASA participation), is
designed to address the fundamental question of how magnetic fields
interact with plasma to produce solar variability. The mission has
a number of unique capabilities that will enable it to answer the
outstanding questions of solar magnetism. First, by escaping atmospheric
seeing, it will deliver continuous observations of the solar surface
with unprecedented spatial resolution. Second, Solar-B will deliver the
first accurate measurements of all three components of the photospheric
magnetic field. Solar-B will measure both the magnetic energy driving
the photosphere and simultaneously its effects in the corona. Solar-B
offers unique programmatic opportunities to NASA. It will continue an
effective collaboration with our most reliable international partner. It
will deliver images and data that will have strong public outreach
potential. Finally, the science of Solar-B is clearly related to the
themes of origins and plasma astrophysics, and contributes directly
to the national space weather and global change programs.
Title: Electron Densities in the Solar Polar Coronal Holes from
Density-Sensitive Line Ratios of Si VIII and S X
Authors: Doschek, G. A.; Warren, H. P.; Laming, J. M.; Mariska, J. T.;
Wilhelm, K.; Lemaire, P.; Schühle, U.; Moran, T. G.
Bibcode: 1997ApJ...482L.109D
Altcode:
We derive electron densities as a function of height in the north and
south polar coronal holes from a forbidden spectral line ratio of Si
VIII. Si VIII is produced at about 8 × 105 K in ionization
equilibrium. We also derive densities from a similar line ratio of S X
(1.3 × 106 K). The spectra were obtained with the Solar
Ultraviolet Measurements of Emitted Radiation spectrometer flown on
the Solar and Heliospheric Observatory spacecraft. In addition to the
primary mechanism of electron impact excitation, the derivation of
theoretical level populations for Si VIII and S X includes both proton
and resonance capture excitation. We compare the coronal hole results
to quiet-Sun coronal measurements obtained outside the east and west
limbs. We find for distances of a few arcseconds outside the solar
limb that the average line-of-sight electron densities in the coronal
holes are about a factor of 2 lower than in quiet-Sun regions. The
decrease of density with height is exponential in the polar holes. We
also confirm the result known from a variety of earlier observations
that the temperature of most of the plasma in coronal holes does not
exceed about 106 K.
Title: The Electron Density, Temperature, and Si/Ne Abundance Ratio
in Polar Coronal Holes from SUMER
Authors: Doschek, G. A.; Laming, J. M.; Warren, H. P.; Lemaire, P.;
Wilhelm, K.
Bibcode: 1997SPD....28.0404D
Altcode: 1997BAAS...29Q.908D
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer flown on the Solar and Heliospheric Observatory (SOHO)
covers a wavelength range with spectral and spatial resolution and
sensitivity not previously obtained by any other solar spectrometer
experiment. Consequently, new plasma diagnostic techniques have been
used and developed to measure plasma parameters such as electron
density. In this paper we discuss the electron density as a function
of height above the solar surface in the polar coronal holes as
determined from line ratios of Si VIII and S X. The densities vary
between about 3 x 10(6) cm(-3) and 10(8) cm(-3) . We determine the
emission measure at selected temperatures as a function of position
above the polar limbs from lines of Mg VII, Mg VIII, Mg IX, and Mg
X. The electron temperature is lower in the polar holes than in the
quiet Sun. This result is also based on intensities of lines of Fe X,
Fe XI, and Fe XII. We determine the Si/Ne abundance ratio (low/high
first ionization potential elements) using lines of Ne VII, Ne VIII,
Si VII, and Si VIII. The preliminary result is that the Si/Ne abundance
ratio in interplume regions is close to photospheric. We also compare
the coronal hole density and abundance results with similar results
obtained for the quiet Sun in the east and west coronal streamers. We
discuss our conclusions in light of results from previous missions.
Title: Determination of the Formation Temperature of Si IV in the
Solar Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Wilhelm, K.;
Lemaire, P.; Kucera, T.; Schühle, U.
Bibcode: 1997ApJ...477L.119D
Altcode:
Using spectra obtained with the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer flown on the Solar and
Heliospheric Observatory spacecraft, we deduce the temperature
of formation of the Si IV ion in the solar transition region
from the Si IV ultraviolet spectral line intensity ratio, 3p
2P3/2-3d 2D3/2,5/2/3s
2S1/2-3p 2P1/2,
and compare the result to the temperature predicted under the
assumption of ionization equilibrium. The wavelengths are as
follows: 2D3/2,5/2, 1128.325, 1128.340 Å
2P1/2, 1402.770 Å. Ratios are derived for
typical features of the quiet Sun, such as cell center and network,
and are systematically higher than those predicted at the 6.3 ×
104 K ionization equilibrium temperature of formation
of Si IV. For most solar features the ratios imply a temperature
of formation of about 8.5 × 104 K. The ratios for the
faintest features imply a temperature of formation of up to 1.6 ×
105 K. It is not clear, however, that all the discrepancies
between the measured and theoretical ratios are due to a temperature
effect. Accurate temperature measurements are important since a large
discrepancy from ionization equilibrium has significant implications
for the physics of the transition region, such as the possible presence
of nonthermal electrons.
Title: Emission Measures and Electron Densities for the Solar
Transition Region
Authors: Doschek, G. A.
Bibcode: 1997ApJ...476..903D
Altcode:
I analyze high spectral resolution ultraviolet spectra (1200-2000 Å)
recorded by the Naval Research Laboratory slit spectrograph (S082-B) on
the Skylab space station. The spectra were obtained from the quiet Sun,
a polar coronal hole, and two active regions. One goal of this work is
to determine electron densities and emission measures for transition
region lines formed between about 3 × 104 K and 2.5 ×
105 K, using the best available atomic data. The majority
of these data were not available during the Skylab era. Another goal
of this work is to compare results using two independent instrument
calibrations that differ at the extreme short- and long-wavelength ends
of the spectrograph's useful wavelength range. The overall shape
of the emission measure distribution with temperature derived in this
analysis is similar to that found from other data sets. However, as
found by other researchers recently, I find significant discrepancies
in emission measures obtained for ions that should be formed at the
same temperature. Most of these discrepancies are independent of
the calibration used and are also independent of the solar region
and element abundances adopted. Apart from inaccuracies in atomic
physics, some of the discrepancies may be real and may reflect the
unresolved fine structure of the transition region. No indication of
non-Maxwellian distributions was found from the lines analyzed. The
temperatures of formation for transition region ions seem to be close
to their predicted temperatures in ionization equilibrium, although
the sample of temperature-sensitive diagnostics is very limited over
the S082-B wavelength range. Derived electron pressures (product of
electron density and temperature) in the different solar regions range
from 9.0 × 1013 K cm-3 in a coronal hole up to
2.4 × 1016 K cm-3 in an active region.
Title: The Occurrence Rate of Soft X-Ray Flares as a Function of
Solar Activity
Authors: Feldman, U.; Doschek, G. A.; Klimchuk, J. A.
Bibcode: 1997ApJ...474..511F
Altcode:
In this paper we investigate the occurrence rate of soft X-ray
solar flares observed by the Geostationary Operational Environmental
Satellites (GOES). The analysis includes all flares classified as equal
to or brighter than A1 and covers the time period from 1993 November
to 1995 July. We find a power-law relationship between the number of
flares per hour and peak X-ray brightness in the 1-8 Å range. The
average power-law index for dN/dF, where N is the number of events
per hour and F, the GOES flux, is about -1.88 +/- 0.21. A similar
result was found from previous work based on uncollimated GOES-type
observations concerning flares brighter than about C2. This index is
independent of the background flux level (which is related to the solar
activity level) to within our statistical uncertainties. We obtain the
FWHM distribution of flare lifetimes from our sample and find that the
distribution is independent of X-ray brightness class. We extrapolate
the soft X-ray flare occurrence rate obtained for the Sun to other
very active solar-like stars.
Title: Solar flare dynamics as revealed by Yohkoh observations
Authors: Doschek, G. A.
Bibcode: 1996AIPC..374..353D
Altcode: 1996hesp.conf..353D
Solar flare dynamics are reviewed as revealed by the X-ray Bragg
Crystal Spectrometer (BCS) package and the Soft X-ray Telescope (SXT)
on the Yohkoh spacecraft. Doppler motions are detected by BCS as
spectral line intensity asymmetries. Motions can be detected by SXT
by studying time sequences of images. High speed upflows (400-800 km
s-1) are correlated to within a few seconds with the onset of
hard X-ray bursts. However, for most flares a strong non-Doppler shifted
(stationary) spectral line component exists even at flare onset, which
is not predicted by standard 1D numerical simulations of chromospheric
evaporation into a low density coronal loop. In about 10% of all flares,
an intense blueshifted component is present at flare onset. These
flares appear to be morphologically complex, but this conclusion is
based on poor statistics. The blueshifted plasma shows a longitude
dependence, consistent with radial flow. Low speed upflows (<100 km
s-1) appear to occur in some instances before the onset of
hard X-ray bursts. In some cases flare loops appear to either twist,
expand, or have footpoints that shift in position after the flare rise
phase. These motions are slow, e.g., <50 km s-1. As found
from previous missions, during the rise phase of flares, line profiles
also reveal nonthermal Doppler broadening that decreases during the rise
phase from about 200 km s-1 to 60 km s-1 or less.
Title: Emission Measures and Electron Densities for the Solar
Transition Region
Authors: Doschek, G. A.
Bibcode: 1996AAS...188.8009D
Altcode: 1996BAAS...28..957D
I analyze high spectral resolution ultraviolet spectra in the
wavelength region from 1200 to 2000 Angstroms, recorded by the Naval
Research Laboratory slit spectrograph (S082-B) on the Skylab space
station. The spectra were obtained from a quiet Sun region, a polar
coronal hole, and two active regions. The major goal of this work is
to determine electron densities and emission measures for transition
region lines formed between about 3 x 10(4) K and 2.5 x 10(5) K, using
the best available atomic data. The majority of these data were not
available during the Skylab era. Electron densities are determined
from density sensitive line ratios involving lines of C III, N III,
O IV, O V, and Si III. The densities and inferred electron pressures
show considerable variation with temperature. The overall shape of the
differential emission measure distribution with temperature derived in
this analysis is similar to that found from other data sets. However,
as found recently by others, there are significant discrepancies in
emission measures obtained for ions that should be formed at the
same temperature. These discrepancies are not caused by variable
element abundances. Apart from inaccuracies in atomic physics, some
of the discrepancies in emission measures and electron pressures may
be real and reflect the unresolved fine structure of the transition
region. No indications of non-Maxwellian distributions were found from
the lines analyzed. The temperature of Al III is consistent with the
predicted temperature based on ionization equilibrium. These results are
directly relevant to analysis of spectra from the SUMER spectrometer
on SOHO. This work was supported by a NASA SR&T Grant (W-18218)
from the Solar Physics Branch of the Space Physics Division.
Title: Observations of Thermal Plasma in a Solar Limb Flare
Authors: Mariska, J. T.; Doschek, G. A.
Bibcode: 1996AAS...188.7004M
Altcode: 1996BAAS...28R.938M
While the earliest phases of a solar flare are characterized mainly by
nonthermal emissions, such as hard X-rays, the remainder of the event
manifests itself primarily as thermal emissions at wavelengths ranging
from X-rays through optical. This radiation comes from flare plasma
covering a wide range of temperatures. Yohkoh Soft X-Ray Telescope
(SXT) observations show that in soft X-rays this emission often
comes from complex emitting structures, with temperatures that vary
from feature to feature. These temperatures, however, are based on
filter ratios and are thus difficult to interpret for a multithermal
plasma. Yohkoh Bragg Crystal Spectrometer (BCS) observations also
provide a temperature diagnostic for the soft X-ray emitting flare
plasma. These temperatures often differ from those obtained using
filter ratios, again demonstrating that flare plasma is multithermal. We
report on observations of a limb flare observed on 1991 October 21 in
which the temperatures measured using emission lines of CaXIX and FeXXV
agreed, suggesting that this flare contained substantial amounts of
isothermal plasma. We use SXT and BCS data from this flare to verify
SXT filter ratio temperatures and to determine relative ion fractions
of FeXXII, FeXXIII, FeXIV, and FeXXV for comparison with ionization
balance calculations. This work was supported by the NASA Office of
Space Science and the Naval Research Laboratory.
Title: Electron Temperature, Emission Measure, and X-Ray Flux in A2
to X2 X-Ray Class Solar Flares
Authors: Feldman, U.; Doschek, G. A.; Behring, W. E.; Phillips,
K. J. H.
Bibcode: 1996ApJ...460.1034F
Altcode:
In this paper we present a statistical analysis of soft X-ray flare
class and emission measure as a function of electron temperature
determined for the time of maximum flare X-ray flux. The study includes
868 flares of X-ray class A2 to X2. Our work shows that their properties
are very different, although large and small flares as seen by the 1-8
Å detector aboard the Geostationary Operational Environmental Satellite
(GOES) records have similar appearances. The peak temperature of intense
(major) flares is much higher than the peak temperature of weak (minor)
flares. This finding has important implications on the nature of the
flare-heating mechanism. For example, if a flare is a collection of
elementary bursts, the plasma properties of the elementary-bursts
occurring during peak emission of large flares and small flares must
be different. Using the relationship between electron temperature
and emission measure in solar flares, we provide an estimate of the
electron temperature during the peak emission of large stellar flares.
Title: Electron Temperature and Emission Measure Determinations of
Very Faint Solar Flares
Authors: Feldman, U.; Doschek, G. A.; Behring, W. E.
Bibcode: 1996ApJ...461..465F
Altcode:
We have studied 28 flares in the X-ray magnitude range of A2-A9
using high-resolution Bragg crystal spectrometer data obtained from
instrumentation flown on the Yohkoh spacecraft. Flares in the A-class
category can be detected in spectral lines of He-like ions formed
at low temperatures. Their average temperature is approximately 5 x
106 K, and their emission measure as determined from the S
XV resonance line near 5 Å varies between 2 x 1046 and 1
x 1048 cm-3.
Title: Soft X-Ray Flare Dynamics
Authors: Doschek, G. A.; Mariska, John T.; Sakao, T.
Bibcode: 1996ApJ...459..823D
Altcode:
We discuss the dynamics of four soft X-ray flares as revealed by the
X-ray resonance line profiles of the He-like ions, Fe xxv, Ca xix,
and S xv. The flares chosen for analysis belong to a subclass of
events that have intense Doppler blueshifted spectral signatures
during the rise phase. The spectra were obtained froin the Bragg
crystal spectrometer (BC S) experiment flown on the Japanese Yohkoh
spacecraft. We deconvolve the line profiles into a flare decay phase
component (stationary component) produced by nonmoving plasma with
little or no turbulent motions, and a flare rise phase component
(dynamic component) produced by bulk plasma motion and turbulence. The
dynamic component is further deconvolved into a high-speed component
(greater than 400 km s 1) and a lower speed, more turbulent
component. We find that the dynamic and stationary components have
approximately the same electron temperature. The dynamic and stationary
component fluxes are compared with hard X-ray fluxes obtained from the
hard X-ray telescope (HXT) on Yohkoh We find that the onset time of
the high-speed dynamic component corresponds closely to the onset of
hard X-rays. We discuss the X-ray morphology of the flares as revealed
by the soft X-ray telescope (SXT) and hard X-ray telescope (HXT) on
Yohkoh. From analysis of the X-ray light curves of individual pixels in
the SXT images, we believe we have been able to determine at least some
of the locations of the dynamic component in the images. Although the
observations support many aspects of chromospheric evaporation models,
there are significant problems. No obvious rising fronts of plasma
are observed for any of the flares. There are apparent footpoint hard
X-ray sources that cannot be physically related in an obvious manner
with the main sources of soft X-ray emission. The flares are complex,
and therefore there are some ambiguities in interpretation of the
morphology.
Title: Timing of the soft X-ray blue-wing and the hard X-ray burst
from observations by YOHKOH
Authors: Bentley, R. D.; Doschek, G. A.; Mariska, J. T.
Bibcode: 1996AdSpR..17d..55B
Altcode: 1996AdSpR..17...55B
A knowledge of the relative timing of the hard X-ray burst and emission
in soft X-rays is helpful in deciding between a number of theoretical
models that describe the mechanism of a solar flare. Here we continue
a study of this relationship using observations from the Yohkoh Bragg
Crystal Spectrometer and Hard X-ray Telescope, together with supporting
observations from the CGRO Batse experiment. The enhanced capabilities
of the instruments onboard Yohkoh have made it possible to study the
problem in a way that was not previously possible. A study of the
timing, intensity and evolution of the soft X-ray blue-wing shows that
there is no simple relationship between hard and soft X-ray emissions;
strong blue-wings sometimes result from relatively weak hard X-ray
bursts; the burst responsible for the blue wing need not be the first
or most intense burst associated with the flare; the blue-wing is found
to follow very closely after the hard X-ray burst. We also discuss
timing issues and why other researchers may have reached different
conclusions on this matter.
Title: The Temperature of the Bright Knots at the Tops of Solar
Flare Loops
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1996ApJ...459..773D
Altcode:
The Japanese Yohkoh spacecraft has revealed the pervasive presence
of confined bright regions at the tops of solar flare magnetic
flux tubes. The physical parameters in the bright regions, such as
temperature and density, are of considerable interest for attempting
to understand the nature and longevity of these regions. We have
found an example of such a source in spectroheliograms of a flare
observed by the Naval Research Laboratory slitless spectroheliograph on
Skylab. This instrument offers better temperature discrimination than
possible with a broadband X-ray telescope such as flown on Yohkoh We
determine the temperature of the Skylab source using the most recent
atomic data. From the Skylab extreme-ultraviolet images of this flare
in spectral lines of Fe XXII, Fe XXIII, and Fe XXIV, we find that the
confined bright region can be described as an isothermal source at a
temperature of about 11 x 106 K. However, this conclusion generally
contradicts temperatures measured from uncollimated Bragg crystal
spectrometer spectra from Yohkoh and other spacecraft for similar
X-ray class flares. There is also emission at the same location from
Ca XVII ions formed at about 6 x 106 K, implying that the source might
be multithermal A multithermal source would indicate that the bright
regions are composed of structures below the spatial resolution of
the Skylab and Yohkoh instrumentation and could possibly resolve the
discrepancies between Bragg spectrometer and imaging data.
Title: Ultra Low Temperature Sulfur X-Ray Spectra
Authors: Doschek, G. A.; Feldman, U.; Dubau, J.
Bibcode: 1996ASPC..111..122D
Altcode: 1997ASPC..111..122D
The BCS experiment on Yohkoh was designed to be about an order of
magnitude more sensitive than previously flown Bragg crystal X-ray
spectrometers. Because of this sensitivity the authors have attempted
to detect X-ray sulfur line emission emitted from temperatures as
low as 2×106K. This attempt failed, in part because of
possible scattered radiation from cosmic X-ray sources! Nevertheless,
the authors investigated the plasma diagnostic possibilities and
present some preliminary results.
Title: Recent Advances in EUV Solar Astronomy
Authors: Doschek, G. A.
Bibcode: 1996aeu..conf..503D
Altcode: 1996IAUCo.152..503D
No abstract at ADS
Title: Atomic Data and Spectral Line Intensities for Fe XI
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1996ADNDT..64..183B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for Fe XI. The data pertain to the 48 levels of
the configurations 3s23p4, 3s3p5,
3s23p33d, and 3p6. Collision
strengths are calculated at three incident electron energies, 8.0,
16.0, and 24.0 Ry. Relative spectral line intensities are calculated
for all astrophysically important transitions. These are obtained
by computing the excitation rate coefficients, i.e., the collision
strengths integrated over a Maxwellian electron distribution, and
then solving the equations of detailed balance for the populations of
the 48 energy levels, assuming a collisional excitation model and an
electron temperature of 1.3 × 106K. This temperature is
typical for Fe XI when formed in equilibrium by collisional ionization
and recombination. Using the excitation rate coefficients and the
radiative decay rates, level populations are computed for several
electron densities and are given in this paper. We also investigate
the effects of proton excitation and solar radiative excitation on
the level populations and line intensities. Finally, the calculated
relative line intensities are compared with experimental solar
intensities where available.
Title: EUV Line Intensities of Fe X
Authors: Young, P. R.; Mason, H. E.; Bhatia, A. K.; Doschek, G. A.;
Thomas, R. J.
Bibcode: 1996aeu..conf..583Y
Altcode: 1996IAUCo.152..583Y
No abstract at ADS
Title: Temperature diagnostics of solar flare plasmas.
Authors: Doschek, G. A.
Bibcode: 1996uxsa.conf...69D
Altcode: 1996uxsa.coll...69D
The physical characteristics of soft X-ray solar flare plasmas, such
as electron temperature, density, and composition, are important for
understanding flare energy release and transport processes. Plasma
diagnostics in the X-ray and extreme ultraviolet spectral ranges are
particularly useful for determining these characteristics. However,
the derived results frequently depend on the type of instrumentation
used, as well as on assumptions regarding the temperature distribution
within the source, the degree of ionization and/or thermal equilibrium,
and the filling factor, etc. In this paper the author discusses
the determination of electron temperature using different types of
instrumentation, including both high spectral resolution Bragg crystal
spectrometers and broadband X-ray detectors.
Title: The Correlation of Solar Flare Temperature and Emission
Measure Extrapolated to the Case of Stellar Flares
Authors: Feldman, U.; Laming, J. M.; Doschek, G. A.
Bibcode: 1995ApJ...451L..79F
Altcode:
We discuss an extrapolation of a recently discovered correlation
between temperature and emission measure derived from X-ray spectra
for the peak of solar flares to temperatures and emission measures
characteristic of stellar flares. We find surprisingly good agreement
between the parameters derived for stellar flares by various authors
and the extrapolation of the results from the survey of solar flares.
Title: Relationships between Temperature and Emission Measure in
Solar Flares Determined from Highly Ionized Iron Spectra and from
Broadband X-Ray Detectors
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Brown, C. M.
Bibcode: 1995ApJ...450..441F
Altcode:
We compare the electron temperature and emission measure of flares at
the time of maximum soft X-ray intensity derived using two different
techniques: (1) from the ratio of a dielectronic Fe XXIV line to
the resonance line of Fe XXV, combined with the absolute intensity
of the Fe XXV line, and (2) from the ratio of the 0.5-4.0 Å and 1-8
Å broadband X-ray fluxes, combined with the absolute flux in one of
the broadband spectral regions. The high-resolution Fe spectra are
obtained with the Bragg Crystal Spectrometer experiment flown on
the Japanese Yohkoh spacecraft. The broadband fluxes are obtained
from Geostationary Operational Environmental Satellites (GOES). A
data set of 540 X-ray magnitude C2 or brighter flares, observed by
both spacecraft, is used for the analysis. Both techniques assume an
isothermal plasma. The broadband temperatures are substantially lower
than the Fe xxv temperatures. We find that the maximum temperature
of flares brighter than MS exceeds 2 × 107 K and that the
maximum temperature of flares fainter than C4 is substantially lower
than 2 × 107 K. We find that the Fe XXV emission measure
is linearly proportional to the GOES flux in the 0.5-4.0 Å detector.
Title: Morphology and Physical Parameters for Two Long-Duration
Solar Flares: Observations from YOHKOH
Authors: Feldman, U.; Seely, J. F.; Doschek, G. A.; Brown, C. M.;
Phillips, K. J. H.; Lang, J.
Bibcode: 1995ApJ...446..860F
Altcode:
We have analyzed the Yohkoh soft X-ray telescope images and Bragg
crystal spectrometer spectra of two long-duration X-class events (LDEs),
obtained from instruments on the Japanese Yohkoh spacecraft. The two
events are a limb flare that occurred on 1992 November 2 near 03 UT
and a disk flare that occurred on 1992 February 27 near 10 UT. The
spatial resolution of the images is about 2"5, and the time resolution
is 2 s. The emission originates from plasma at temperatures ≥
107 K. The morphology of the LDEs is quite complicated,
but the most intense emission consists of a small number of loops
(usually one or two prominent loops). The brightest emission regions
are located at the tops of loops for most of the flares' duration,
as was found in earlier studies of compact flares observed by Yohkoh
In the case of the 1992 November 2 limb flare, the brightening at
the loop top is visible for a period of 24 hr after flare onset. This
implies that the heating mechanism must act over a period of tens of
hours for these long-duration events, that the energy is deposited at
the top of the loop, and that the hot plasma is confined at the top
of the loop. We derive emission measures and temperatures from
the soft X-ray telescope and Bragg crystal spectrometer data. Lower
limit estimates of electron density of the bright regions at the loop
tops are derived from the morphology of the regions and the emission
measures. Fractional ion abundances for highly ionized iron are deduced
from the spectrometer data. We relate the Yohkoh observations to
previous observations from the solar instruments on the Skylab manned
space station.
Title: The Bright Knots at the Tops of Soft X-Ray Loops: Quantitative
Results from YOHKOH
Authors: Doschek, G. A.; Strong, K. T.; Tsuneta, S.
Bibcode: 1995ApJ...440..370D
Altcode:
Soft X-ray Telescope (SXT) observations from the Japanese Yohkoh
spacecraft have shown that confined bright regions are common features
at the tops of flare loops throughout most of the duration of the
flares. In this paper we present quantitative results for these
flare knots, in relation to other flare regions, for four relatively
'simple' flares. Emission measure distributions, electron temperatures,
and electron densities are derived from SXT and Yohkoh Bragg Crystal
Spectrometer (BCS) observations. The four flares selected are dominated
by what appear to be single-loop structures, with bright knots at
the loop tops. The flares are neither long-duration nor impulsive
events. The spatial distributions of brightness and emission measure
in the flares are found to be quite similar for all four events, even
though there are significant differences in dynamical behavior between
at least two of the events. Temperatures and densities calculated for
these flares are consistent with previous results from many solar
experiments. An investigation of intensity correlations between
adjacent pixels at the tops of the loops suggests the existence of
local disturbances in the magnetic loops that occur on spatial scales
less than the radii of the loops.
Title: Atomic Data and Spectral Line Intensities for C-like Mg VII
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1995ADNDT..60..145B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for the C-like ion Mg VII. The data pertain to the
46 levels of the configurations 2 s22 p2, 2 s2
p3, 2 p4, 2 s22 p3 s, 2 s22
p3 p, and 2 s22 p3 d. Collision strengths are calculated at
three incident electron energies: 12.0, 24.0, and 36.0 Ry. Spectral line
intensities are calculated for all transitions with intensities within
two orders of magnitude of the most intense Mg VII line. These are
obtained by computing the excitation rate coefficients (cm 3
s -1), i.e., the collision strengths integrated over a
Maxwellian electron distribution, and then solving the equations of
detailed balance for the populations of the 46 energy levels, assuming
a collisional excitation model and an electron temperature of 6.31 × 10
5 K. This temperature is typical for Mg VII in solar and some
other astrophysical plasmas. Using the excitation rate coefficients
and the radiative decay rates, level populations are computed for
several electron densities and are also given in this paper.
Title: Atomic Data and Spectral Line Intensities for Fe X
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1995ADNDT..60...97B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for the important astrophysical ion Fe X. The
data pertain to the 54 levels of the configurations 3 s23
p5, 3 s3 p6, 3 s23 p43 d,
and 3 s3 p53 d. Collision strengths are calculated at five
incident electron energies: 9.0, 18.0, 27.0, 36.0, and 45.0 Ry. Relative
spectral line intensities are calculated for all astrophysically
important transitions. These are obtained by computing the excitation
rate coefficients (cm 3 s -1), i.e., the collision
strengths integrated over a Maxwellian electron energy distribution,
and then solving the equations of detailed balance for the populations
of the 54 energy levels, assuming a collisional excitation model and an
electron temperature of 1.0 × 10 6 K. This temperature is
typical for Fe X when formed in equilibrium by collisional ionization
and recombination. Using the excitation rate coefficients and the
radiative decay rates, level populations are computed for several
electron densities and are given in this paper. We also investigate the
effects of proton excitation and solar radiative excitation on the level
populations and line intensities. Finally, the calculated relative
line intensities are compared with experimental solar intensities
where available, and two good electron-density-sensitive line ratios
are discussed. One result of the comparison is the identification of
four unidentified solar spectral lines as Fe X transitions: 220.86,
226.32, 238.71, and 324.71 Å.
Title: The NASA High-Energy Solar Physics Mission (HESP)
Authors: Dennis, B. R.; Emslie, A. G.; Canfield, R.; Doschek, G.;
Lin, R. P.; Ramaty, R.
Bibcode: 1994AIPC..294..230D
Altcode: 1994hesp.conf..230D
The NASA High Energy Solar Physics (HESP) mission offers the opportunity
for major breakthroughs in our understanding of the fundamental energy
release and particle acceleration processes at the core of the solar
flare problem. HESP's primary strawman instrument, the High Energy
Imaging Spectrometer (HEISPEC), will provide X-ray and gamma-ray
imaging spectroscopy, i.e., high-resolution spectroscopy at each
spatial point in the image. It has the following unique capabilities:
(1) high-resolution (~keV) spectroscopy from 2 keV-20 MeV to resolve
flare gamma-ray lines and sharp features in the continuum; (2) hard
X-ray imaging with 2` angular resolution and tens of millisecond
temporal resolution, commensurate with the travel times and stopping
distances for the accelerated electrons; (3) gamma-ray imaging with 4-8`
resolution with the capability of imaging in specific lines or continuum
regions; (4) moderate resolution measurements of energetic (20 MeV to
~1 GeV) gamma-rays and neutrons. Addtional strawman instruments
include a Bragg crystal spectrometer for diagnostic information
and a soft X-ray/XUV/UV imager to map the flare coronal magnetic
field and plasma structure. The HESP mission also includes extensive
ground-based observational and supporting theory programs. Recently,
the HESP mission has been adapted to ``lightsats''-lighter, smaller,
cheaper spacecraft that can be built faster-and the baseline plan now
includes two Taurus-class and one Pegasus-class spacecraft. A launch
by the end of the year 2000 is desirable to be in time for the next
solar activity maximum.
Title: Fe XXV Temperatures in Flares from the YOHKOH Bragg Crystal
Spectrometer
Authors: Sterling, Alphonse C.; Doschek, George A.; Pike, C. David
Bibcode: 1994ApJ...435..898S
Altcode:
Studies by Doschek et al. using P78-1 and Solar Maximum Misson
(SMM) data have shown that the ratio of intensities of the Fe XXV
and Ca XIX resonance lines can be expressed as a function of Fe XXV
temperature. Using a more recent data set consisting of 13 flares
observed by the Bragg crystal spectrometer (BCS) experiment on board
Yohkoh, we find a nearly identical functional relationship between
the same resonance line ratios and Fe XXV temperatures. We use this
functional relationship to obtain resonance line ratio temperatures
(TRLR) for each flare in our data set, and compare them
with temperatures resulting from application of a simple spectral
fitting method. (TSSF) to individal Fe XXV spectra. We also
use a more involved free-parameter spectral fitting method to deduce
temperatures (TFSF) from some of these spectra. On average,
agreement between TRLR and TSSF improves as a
flare progresses in time, with average agreements of 10.0% +/- 5.2%,
6.4% +/- 5.4%, and 5.0% +/- 3.9% over the rise, peak, and decay phases,
respectively. Deviations between TRLR and TFSF
are about the same or smaller. Thus, for most analysis purposes, all
three methods yield virtually identical temperatures in flares. The
somewhat poorer agreement between TSSF and TRLR
during the earlier phases may be partially a result of difficulties
in obtaining precise values for temperatures from spectral fits
when blueshifts and large nonthermal broadenings are present in the
spectra. Because of the high sensitivity of the Yohkoh BCS compared
to that of BCS experiments on earlier spacecraft, we can for the first
time consistently observe the heating phase of flares in Fe XXV.
Title: The Determination of Electron Densities in the Solar Atmosphere
from the 1718.56 Angstrom /1486.51 Angstrom Emission-Line Ratio in
N IV
Authors: Keenan, F. P.; Harra, L. K.; Doschek, G. A.; Cook, J. W.
Bibcode: 1994ApJ...432..806K
Altcode:
The theoretical electron density sensitive emission-line ratio
R = I(1718.56 a)/I(1486.51 A) in N IV is presented for a range of
Ne(approximately equals 1010 - 1012/cu
cm) applicable to higher density solar plasmas, such as active
regions. A comparison of these calculations with the observed values
of R of several solar features obtained with the Naval Research
Laboratory's S082B spectrograph on board Skylab reveals general
agreement between theory and observation at pointings just above the
limb, where line blends with N IV 1718.56 A should be insignificant,
which provides experimental support for the accuracy of the line
ratio calculations.
Title: Yohkoh observations of the creation of high-temperature plasma
in the flare of 16 December 1991
Authors: Culhane, J. L.; Phillips, A. T.; Inda-Koide, M.; Kosugi,
T.; Fludra, A.; Kurokawa, H.; Makishima, K.; Pike, C. D.; Sakao, T.;
Sakurai, T.; Doschek, G. A.; Bentley, R. D.
Bibcode: 1994SoPh..153..307C
Altcode:
Yohkoh observations of an impulsive solar flare which occurred on 16
December, 1991 are presented. This flare was a GOES M2.7 class event
with a simple morphology indicative of a single flaring loop. X-ray
images were taken with the Hard X-ray Telescope (HXT) and soft X-ray
spectra were obtained with the Bragg Crystal Spectrometer (BCS)
on board the satellite. The spectrometer observations were made at
high sensivity from the earliest stages of the flare, are continued
throughout the rise and decay phases, and indicate extremely strong
blueshifts, which account for the majority of emission in CaXIX during
the initial phase of the flare. The data are compared with observations
from other space and ground-based instruments. A balance calculation
is performed which indicates that the energy contained in non-thermal
electrons is sufficient to explain the high temperature plasma which
fills the loop. The cooling of this plasma by thermal conduction
is independently verified in a manner which indicates that the loop
filling factor is close to 100%. The production of `superhot' plasma
in impulsive events is shown to differ in detail from the morphology
and mechanisms appropriate for more gradual events.
Title: The 1991 November 9 Flare at 03.2 UT: Observations from YOHKOH
Authors: Doschek, G. A.; Mariska, J. T.; Strong, K. T.; Bentley, R. D.;
Brown, C. M.; Culhane, J. L.; Lang, J.; Sterling, A. C.; Watanabe, T.
Bibcode: 1994ApJ...431..888D
Altcode:
We discuss X-ray spectra and soft X-ray images of an M1.9 flare that
occurred on 1991 November 9 near 03.2 UT. These data were obtained with
instrumentation on the Japanese Yohkoh spacecraft. They cover the entire
rise phase and peak flare emission, and the beginning of the decay
phase. We determine the dynamics, temperature, and emission measure
of the flare as inferred from the X-ray line profiles of resonance
lines of Fe XXV, Ca XIX, and S XV. We discuss the morphology of the
flare as inferred from the soft X-ray images. The November 9 flare is
atypical in that a stronger than usual blueshifted emission component
(relative to the stationary component) is observed for the resonance
lines at flare onset. We discuss several methods for deconvolving the
blueshifted component from the stationary component. The X-ray line
profiles are consistent with predictions of numerical simulations
of chromospheric evaporation. The X-ray images reveal a flare with a
complicated loop geometry that is not fully understood. Many of the
features in the images are moving upwards at speeds ranging from a
few km/s to about 800 km/s. The blueshifted emission begins near the
onset of hard X-ray emission, implying that particle acceleration and
upflowing plasma have a common energy source.
Title: The Electron Density in the Localized Bright Regions at the
Tops of Flare Loops
Authors: Doschek, G. A.
Bibcode: 1994kofu.symp..173D
Altcode:
A technique for determining the electron density in the localized
bright regions at the tops of flare loops is discussed, and some
preliminary results are given. The technique utilizes SXT flare images
obtained with the Be filter, and S XV spectra obtained by the BCS. The
densities are derived under the assumption of a filling factor of unity,
and are therefore lower limits.
Title: Morphology of the 10 Million Degree Plasma in Solar Flares
and the Failure of the Chromospheric Evaporation Model
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.; Strong, K. T.;
Acton, L. W.; Uchida, Y.; Tsuneta, S.
Bibcode: 1994kofu.symp..177S
Altcode:
The SXT images of over fifty C, M, and X type flares which occurred
between October 1991 and February 1993 were analyzed. For each flare,
the 10 million degree emitting region was typically found to be located
at the loop top in the first well-exposed flare image recorded during
the rise phase (within 1 to 2 minutes after flare onset), in images
recorded near the intensity peak, and in images recorded during most of
the decay phase. For the November 2 1992 limb flare, the loop top was
bright for 24 hours. For a few flares, the brightness of the footpoints
in the onset images was comparable to the brightness of the loop top,
but the loop top brightness rapidly increased relative to the footpoints
and remained intense for the duration of the flare. The brightest region
at the loop top was very small throughout the flare, often as small as
a single pixel (1800x1800 km). The conclusions are that the energy is
deposited in a small volume at the top of the flaring loop structure,
the heating mechanism acts over a period of up to tens of hours, and
the hot plasma is confined at the top of the loop structure. These
results are not explained by the traditional chromospheric evaporation
model of solar flares.
Title: EUVE Spectra of Alpha Aurigae (Capella) at Different Phases
Authors: Dupree, A. K.; Brickhouse, N. S.; Doschek, G. A.; Hanson,
G. J.; Raymond, J. C.
Bibcode: 1994AAS...184.0508D
Altcode: 1994BAAS...26..864D
Extreme ultraviolet spectra (lambda 70 -- lambda 740) of the bright
spectroscopic binary system, Capella (Alpha Aurigae; G5 III+G0 III)
were obtained at three different orbital phases (phi = 0.84, 0.45,
and 0.97) using the spectrometers on the Extreme Ultraviolet Explorer
satellite (EUVE) in December 1992, December 1993, and February 1994. All
of the spectra show rich emission dominated by iron emission lines:
Fe IX, Fe XV -- XXIV. The emission measure for the system generally
maintains a continuous distribution of plasma temperatures between
10(5) and 10(7.8) \ K, with a clear minimum near 10(6\) K and a local
maximum at 6 times 10(6\) K; these features were established from
the first spectrum (cf. Dupree et al., 1993, ApJ, 418, L41). However
the relative fluxes of ion species have varied significantly from
the December 1992 observations, indicating a modification of the
apparent structure of the atmosphere of the Capella system when
viewed at different orbital phases. Emission measure distributions,
spectral syntheses, and density diagnostics will be presented for
the the observations. These spectra were obtained through the Guest
Observer Program for the EUVE satellite; this research is supported
in part by NASA Grant NAG5-2330 to the Smithsonian Institution.
Title: The Morphology of the 10 7 K Plasma in Solar
Flares. I. Nonimpulsive Flares
Authors: Feldman, U.; Seely, J. F.; Doschek, G. A.; Strong, K. T.;
Acton, L. W.; Uchida, Y.; Tsuneta, S.
Bibcode: 1994ApJ...424..444F
Altcode:
In this paper we have analyzed images of 48 C-, M-, and X-type
flares which occurred between 1991 October and 1993 February. The
images were recorded by the soft X-ray telescope (SXT) flown on the
Japanese Yohkoh spacecraft. The spatial resolution of the recorded
images is about 2.5 sec. In each of the recorded flares the brightest
regions emitting the 107 K radiation were analyzed and
evaluate. The 107 K emitting region was found to be located
at loop tops in the first well-exposed flare image recorded during the
rise phase (within 1-2 minutes after flare onset), in images recorded
near intensity peak, and in those recorded during most of the decay
phase. Occasionally, in the begining of the event when the total
flare intensity is low, the brightness of the footpoints may rival the
brightness of the loop top. However, in these cases it is expected that
the temperature of the loop top is considerably higher. The emitting
region, even during flare peak, is very small (often smaller than a
single SXT pixel 1800 x 1800 km).
Title: Sleuthing the Dynamo: HST/FOS Observations of UV Emissions
of Solar-Type Stars in Young Clusters
Authors: Ayres, T.; Basri, G.; Simon, T.; Stauffer, J.; Stern, R.;
Antiochos, S.; Bookbinder, J.; Brown, A.; Doschek, G.; Linsky, J.;
Ramsey, L.; Walter, F.
Bibcode: 1994ASPC...64...53A
Altcode: 1994csss....8...53A
No abstract at ADS
Title: A Far-Ultraviolet Flare on a Pleiades G Dwarf
Authors: Ayres, T. R.; Stauffer, J. R.; Simon, Theodore; Stern, R. A.;
Antiochos, S. K.; Basri, G. S.; Bookbinder, J. A.; Brown, A.; Doschek,
G. A.; Linsky, J. L.; Ramsey, L. W.; Walter, F. M.
Bibcode: 1994ApJ...420L..33A
Altcode:
The Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) recorded
a remarkable transient brightening in the C IV lambda lambda 1548,50
emissions of the rapidly rotating Pleiades G dwarf H II 314. On the one
hand the 'flare' might be a rare event luckily observed; on the other
hand it might be a bellwether of the coronal heating in very young
solar-mass stars. If the latter, flaring provides a natural spin-down
mechanism through associated sporadic magnetospheric mass loss.
Title: A Resonance Line Rations Method for Determining Flare
Temperatures Using YOHKOH BCS Spectra
Authors: Sterling, A. C.; Doschek, G.; Mariska, J. T.; Hiei, E.;
Watanabe, T.
Bibcode: 1994xspy.conf..127S
Altcode:
No abstract at ADS
Title: The Correlation of Solar Flare Hard X-Ray Bursts with Doppler
Blueshifted Soft X-Ray Flare Emission
Authors: Bentley, R. D.; Doschek, G. A.; Simnett, G. M.; Rilee, M. L.;
Mariska, J. T.; Culhane, J. L.; Kosugi, T.; Watanabe, T.
Bibcode: 1994ApJ...421L..55B
Altcode:
We have investigated the temporal correlation between hard X-ray
bursts and the intensity of Doppler blueshifted soft X-ray spectral
line emission. We find a strong correlation for many events that have
intense blueshifted spectral signatures and some correlation in events
with modest blueshifts. The onset of hard X-rays frequently coincides to
within a few seconds with the onset of blueshifted emission. The peak
intensity of blueshifted emission is frequently close in time to the
peak of the hard X-ray emission. Decay rates of the blueshifted and hard
X-ray emission are similar, with the decay of the blueshifted emission
tending to lag behind the hard X-ray emission in some cases. There
are, however, exceptions to these conclusions, and, therefore, the
results should not be generalized to all flares. Most of the data for
this work were obtained from instruments flown on the Japanese Yohkoh
solar spacecraft.
Title: The NASA High Energy Solar Physics (HESP) mission for the
next solar maximum.
Authors: Lin, R. P.; Dennis, B. R.; Ramaty, R.; Emslie, A. G.;
Canfield, R.; Doschek, G.
Bibcode: 1994GMS....84..283L
Altcode:
The NASA High Energy Solar Physics (HESP) mission offers the opportunity
for major breakthroughs in the understanding of the fundamental energy
release and particle acceleration processes at the core of the solar
flare problem. Recently, the HESP mission has been adapted to Lightsats,
lighter, smaller, cheaper spacecraft: the baseline HESP mission now
includes two Pegasus-class spacecraft. A launch by the end of the year
2000 is desirable to be in time for the next solar activity maximum.
Title: Flare Plasma Dynamics Observed with the YOHKOH Bragg Crystal
Spectrometer. I. Properties of the CA XIX Resonance Line
Authors: Mariska, John T.; Doschek, G. A.; Bentley, R. D.
Bibcode: 1993ApJ...419..418M
Altcode:
Using data from the Bragg crystal spectrometer on the Yohkoh spacecraft
we have computed measures of the total intensity, centroid position,
and line width for the resonance line of Ca xix during the rise phase
and after maximum for 219 solar flares. The difference between the
centroid positions early and late in each flare yields a measure
of the line-of-sight velocity shift of the line centroid. We find
a trend in the average value of the centroid shift with distance
from Sun center suggesting radial mass motions with a characteristic
velocity of 58 km s-1. There is a correlation between the
rise-phase line widths and the centroid shift. We find no correlation
between the centroid shift and the peak intensity, rise time, and
total flare duration; and no correlation between the line width and
the distance from Sun center, the peak intensity, rise time, and total
flare duration. These results do not conclusively support or refute
the simple electron-beam-driven model or the thermal model for the
rise phase of a solar flare.
Title: New Atomic Data for the Astrophysically Important Ion, Fe X
Authors: Doschek, G. A.; Bhatia, A. K.
Bibcode: 1993AAS...18311201D
Altcode: 1993BAAS...25.1458D
New atomic data for Fe X have been calculated using the distorted
wave approximation. These data should be useful for analysis of EUVE
and HST high resolution stellar spectra. The calculations include
the 54 levels of the 3s(2) 3p(5) , 3s3p(6) , 3s(2) 3p(4) 3d, and
3s3p(5) 3d configurations. Electron impact collision strengths were
calculated at five incident electron energies: 9.0, 18.0, 27.0, 36.0
and 45.0 Ry. Spontaneous radiative decay probabilities have also been
computed. Relative spectral line intensities were calculated for all
astrophysically important transitions, for an ion temperature of 10(6)
K and electron densities ranging from 10(8) to 10(12) cm(-3) . The line
intensities were obtained by computing excitation rate coefficients
assuming a Maxwellian electron velocity distribution, and solving the
equations of detailed balance for the level populations. In addition,
the effects of proton excitation and radiative excitation from a
photosphere have been considered. The relative line intensities
have been compared to available solar observations in the UV and
EUV wavelength regions. Four previously unidentified EUV lines in
solar spectra are classed as Fe X transitions as a result of this
comparison. While there is general agreement between calculated
and experimental line intensities, there are also some interesting
discrepancies. This work is supported by a NASA grant from the
Ultraviolet and Visible Astrophysics Branch of the Astrophysics Division
under Contract No. W17,362.
Title: Atomic Data and Spectral Line Intensities for C-like Ne V
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1993ADNDT..55..315B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for the C-like ion, Ne V. The data pertain to
the 46 levels of the configurations 2s22p2,
2s2p3, 2p4, 2s22p3s,
2s22p3p, and 2s22p3d. Collision strengths are
calculated at three incident electron energies: 10.0, 15.0 and 20.0
Ry above threshold. Spectral line intensities are calculated for all
transitions with intensities within two orders of magnitude of the
most intense Ne V line. These are obtained by computing the excitation
rate coefficients, that is, the collision strengths integrated over
a Maxwellian electron distribution, and then solving the equations of
detailed balance for the populations of the 46 energy levels, assuming
a collisional excitation model and an electron temperature of 3.16 ×
105 K. This temperature is typical for Ne V in solar and some
other astrophysical plasmas. Using the excitation rate coefficients
and the radiative decay rates, level populations are computed for
several electron densities and are also given in this paper.
Title: High-resolution EUV spectroscopy: performance of spherical
multilayer-coated gratings operated at near normal incidence
Authors: Kowalski, Michael P.; Seely, John F.; Cruddace, Raymond G.;
Rife, Jack C.; Brown, C. M.; Doschek, G. A.; Feldman, Uri; Barbee,
Troy W.; Hunter, William R.; Holland, G. E.; Boyer, Craig N.
Bibcode: 1993SPIE.1945..164K
Altcode:
A program is underway at the Naval Research Laboratory (NRL) to develop
a high-resolution spectrometer for the study of astrophysical sources
at EUV/soft X-ray wavelengths. The spectrometer design is simple in
that the sole optic is a multilayer-coated spherical grating or mosaic
of co-aligned gratings used at near-normal incidence, allowing large
effective collecting area without the strict tolerance requirements
of grazing incidence optics. Therefore, both high resolution and high
throughput can be obtained over several selected narrow bandpasses. We
present efficiency and resolving power measurements of spherical
gratings which have parameters similar to that intended for our flight
instrument. Two gratings were replicated from the same ruled master
and then coated with a multilayer of molybdenum and silicon. A third
sister grating was used as a control and over-coated with gold.
Title: The Extreme Ultraviolet Spectrum of Alpha Aurigae (Capella)
Authors: Dupree, A. K.; Brickhouse, N. S.; Doschek, G. A.; Green,
J. C.; Raymond, J. C.
Bibcode: 1993ApJ...418L..41D
Altcode:
No abstract at ADS
Title: Atomic Data and Spectral Line Intensities for C-Like Si IX
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1993ADNDT..55..281B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for the C-like ion, Si IX. The data pertain to
the 46 levels of the configurations 2s22p2,
2s2p3, 2p4, 2s22p3s,
2s22p3p, and 2s22p3d. Collision strengths are
calculated at three incident electron energies: 20.0, 40.0 and 60.0
Ry. Spectral line intensities are calculated for all transitions with
intensities within two orders of magnitude of the most intense Si IX
line. These are obtained by computing the excitation rate coefficients,
that is, the collision strengths integrated over a Maxwellian electron
distribution, and then solving the equations of detailed balance for the
populations of the 46 energy levels, assuming a collisional excitation
model and an electron temperature of 1.26 × 106 K. This
temperature is typical for Si IX in solar and some other astrophysical
plasmas. Using the excitation rate coefficients and the radiative decay
rates, level populations are computed for several electron densities
and are also given in this paper.
Title: The 1992 January 5 Flare at 13.3 UT: Observations from YOHKOH
Authors: Doschek, G. A.; Strong, K. T.; Bentley, R. D.; Brown, C. M.;
Culhane, J. L.; Fludra, A.; Hiei, E.; Lang, J.; Mariska, J. T.;
Phillips, K. J. H.; Pike, C. D.; Sterling, A. C.; Watanabe, T.; Acton,
L. W.; Bruner, M. E.; Hirayama, T.; Tsuneta, S.; Rolli, E.; Kosugi,
T.; Yoshimori, M.; Hudson, H. S.; Metcalf, T. R.; Wuelser, J. -P.;
Uchida, Y.; Ogawara, Y.
Bibcode: 1993ApJ...416..845D
Altcode:
We discuss X-ray spectra and soft X-ray images of an M1.9 flare that
occurred on 1992 January 5 near 13.3 UT. These data were obtained
with instrumentation on the Japanese Yohkoh spacecraft. They cover
the entire rise phase of the flare. To supplement these data we have
ground-based magnetograms and Hα spectroheliograms. We calculate
the electron temperature and emission measure of the flare as a
function of time during the early rise phase using X-ray spectral
line intensities and line ratios. Using spectral line widths, line
profile asymmetries, and wavelength shifts due to the Doppler effect,
we calculate the dynamical properties of the flare. The time development
of the morphology of the flare, as revealed by the soft X-ray images
and the Hα spectroheliograms, and the physical quantities inferred
from the X-ray spectra, are compared with chromospheric evaporation
models. There is an enhancement of blueshifted emission that is closely
correlated with the hard X-ray bursts. Heating of one loop in the flare
is consistent with a conduction-evaporation model, but heating is found
in several structures that do not appear to be physically associated
with each other. No standard evaporation model can adequately explain
all of the observations.
Title: The NASA high energy solar physics (HESP) mission for the
next solar maximum
Authors: Lin, R. P.; Dennis, B. R.; Emslie, A. G.; Ramaty, R.;
Canfield, R.; Doschek, G.
Bibcode: 1993AdSpR..13i.401L
Altcode: 1993AdSpR..13..401L
The NASA High Energy Solar Physics (HESP) mission offers the opportunity
for major breakthroughs in our understanding of the fundamental energy
release and particle acceleration processes at the core of the solar
flare problem. HESP's primary strawman instrument, the High Energy
Imaging Spectrometer (HEISPEC), will provide X-ray and γ-ray imaging
spectroscopy, i.e., high-resolution spectroscopy at each spatial
point in the image. It has the following unique capabilities; (1)
high-resolution (~keV) spectroscopy from 2 keV - 20 MeV to resolve flare
gamma-ray lines and sharp features in the continuum; (2) hard X-ray
imaging with 2'' angular resolution and tens of millisecond temporal
resolution, commensurate with the travel and stopping distances and
times for the accelerated electrons; (3) gamma-ray imaging with 4''-8''
resolution with the capability of imaging in specific lines or continuum
regions; (4) moderate resolution imaging of energetic (20 MeV to ~1 GeV)
gamma-rays and neutrons. Additional strawman instruments include a Bragg
crystal spectrometer for diagnostic information and a soft X-ray/XUV/UV
imager to map the flare coronal magnetic field and plasma structure. The
HESP mission also includes extensive ground-based observational and
supporting theory programs. Presently HESP is planned for a FY 1995 new
start and late 1999 launch, in time for the next solar activity maximum.
Title: Yohkoh observations of plasma upflows during solar flares
Authors: Culhane, J. L.; Phillips, A. T.; Pike, C. D.; Fludra, A.;
Bentley, R. D.; Bromage, B.; Doschek, G. A.; Hiei, E.; Inda, M.;
Mariska, J. T.; Phillips, K. J. H.; Sterling, A. C.; Watanabe, T.
Bibcode: 1993AdSpR..13i.303C
Altcode: 1993AdSpR..13..303C
Observations of two flares, an M 2.2 event on 16 December, 1991 and the
precursor to an X1 flare on 15 November, 1991 are presented. Spectra
obtained with the Bragg Crystal Spectrometer (BCS) are compared with
data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide
Band Spectrometer (WBS) on the satellite. For both events the creation
of upflowing plasma is detected. While the first event seems to conform
well to the chromospheric evaporation model for high temperature plasma
production, the behaviour for the second event is more complex.
Title: Determination of coronal abundances of sulphur, calcium and
iron using the yohkoh bragg crystal spectrometer
Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.;
Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T.
Bibcode: 1993AdSpR..13i.395F
Altcode: 1993AdSpR..13..395F
Using spectra from the Bragg Crystal Spectrometer on Yohkoh we have
derived coronal abundances of sulphur, calcium and iron during several
flares from the ratio of the flux in the resonance line to the nearby
continuum. Multi-thermal effects have been taken into account using
differential emission measure analysis. We have also determined the
abundance of S in cool active regions during a period of very low solar
activity. We compare the coronal abundances of S, Ca and Fe with their
photospheric values.
Title: An Improved Ultraviolet Spectral Line List for the Symbiotic
Star RR Telescopii
Authors: Doschek, G. A.; Feibelman, W. A.
Bibcode: 1993ApJS...87..331D
Altcode:
We have remeasured wavelengths and intensities of International
Ultraviolet Explorer (IUE) spectra of the symbiotic star, RR Tel. The
main work is centered on the long 820 minute exposure high-resolution
spectrum obtained on 1983 June 18. The list is intended to serve as
a source of improved intensities and wavelengths for the ultraviolet
spectrum of this star. A complete line list with intensities based on
this exposure has not been published previously. The strongest spectral
lines are saturated in the 820 minute exposure, and intensities for
these lines are mostly obtained from a 20 minute exposure obtained on
the same day. A few intensities are obtained from other exposures if
neither the 820 nor the 20 minute exposure is satisfactory. There are
111 lines in our list between 1168 and 1980 A. Some of the very weakest
lines may not be real. These are indicated by question marks. We also
discuss some of the plasma diagnostics available using spectral lines
of O v and O iv.
Title: Upflowing Multimillion Degree Plasma During Solar Flares
Authors: Doschek, G. A.; Mariska, J. T.; Rilee, M.
Bibcode: 1993BAAS...25R1177D
Altcode:
No abstract at ADS
Title: Flare Plasma Dynamics Observed with the Yohkoh Bragg Crystal
Spectrometer
Authors: Mariska, J. T.; Doschek, G. A.; Bentley, R. D.
Bibcode: 1993BAAS...25Q1178M
Altcode:
No abstract at ADS
Title: A Comparison of Solar Flare Hard X-Ray Bursts with Doppler
Blue-Shifted Soft X-Ray Emission
Authors: Rilee, M. L.; Bentley, R. D.; Culhane, J. L.; Doschek, G. A.;
Mariska, J. T.; Simnett, G. M.; Watanabe, T.
Bibcode: 1993BAAS...25.1189R
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: Invited Talk: (The NASA High Energy Solar Physics (HESP)
Mission for the Next Solar Maximum)
Authors: Lin, R. P.; Dennis, B. R.; Ramaty, R.; Emslie, A. G.;
Canfield, R.; Doschek, G.
Bibcode: 1993BAAS...25.1180L
Altcode:
No abstract at ADS
Title: EUVE Spectra of Capella (Alpha Aurigae)
Authors: Dupree, A. K.; Doschek, G. A.; Green, J. C.; Raymond, J. C.
Bibcode: 1993AAS...182.4125D
Altcode: 1993BAAS...25..864D
Under the Guest Observer Program for EUVE, extreme ultraviolet spectra
of the bright RSCVn binary system, Capella (HD 34029; G8 III + G0
III) were obtained between 10-13 Dec. 1992 during the calibration
program of the satellite. Spectra from the 3 spectrometers cover
the wavelength range lambda lambda 70 - 740. The total integration
time was approximately 20 hours. These data were reduced with the
``Fast-Track'' processing procedures. A rich spectrum of emission
lines is detected and identified including He II (lambda 304) which is
associated with the system. Many emission lines of ionized iron are
identified in the spectra: Fe XV, XVI, XVIII ...; apparently Fe XXIV
(lambda 192) is also present, indicative of temperatures of 2 times
10(7) \ K. Line identifications will be given, and emission measures
derived for the system and compared to previous distributions from
X-ray and ultraviolet spectra.
Title: A Remarkable FUV Flare on the Pleiades G Dwarf HZ 314
Authors: Ayers, T.; Basri, G.; Simon, T.; Stauffer, J.; Stern, R.;
Antiochon, S.; Bookbinger, J.; Brown, A.; Doschek, G.; Linsky, J.;
Ramsey, L.; Walter, F.
Bibcode: 1993AAS...182.4611A
Altcode: 1993BAAS...25..875A
No abstract at ADS
Title: Atomic Data and Spectral Line Intensities for C-like Ca XV
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1993ADNDT..53..195B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for the C-like ion, Ca XV. The data pertain to
the 46 levels of the configurations 2s22p2,
2s2p3, 2p4, 2s22p3s,
2s22p3p, and 2s22p3d. Collision strengths are
calculated at three incident electron energies: 45.0, 90.0 and 135.0
Ryd. Spectral line intensities are calculated for all transitions
with intensities within two orders of magnitude of the most intense
Ca XV line. These are obtained by computing the excitation rate
coefficients (cm3 s-1), that is, the collision
strengths integrated over a Maxwellian electron distnbution, and
then solving the equations of detailed balance for the populations
of the 46 energy levels, assuming a collisional excitation model and
an electron temperature of 4 × 106 K. This temperature is
typical for Ca XV in solar and some other astrophysical plasmas. Using
the excitation rate coefficients and the radiative decay rates, level
populations are computed for several electron densities and are also
given in this paper.
Title: On the Absolute Abundance of Calcium in Solar Flares
Authors: Sterling, Alphonse C.; Doschek, George A.; Feldman, Uri
Bibcode: 1993ApJ...404..394S
Altcode:
The abundance of calcium relative to hydrogen in soft X-ray-emitting
solar flare plasmas is determined. Results were obtained for 25
flares. An average calcium-to-hydrogen abundance of about 5 x 10
exp -6, which is about a factor of 2 greater than measured for the
photosphere, is found. This result is consistent with an enhancement
of low first ionization elements in soft X-ray flare plasmas. For
one flare, the calcium abundance was higher, at about 1.6 times the
average results. It is inferred that the calcium abundance can vary
among flares. Significant variations of the calcium abundance during
the course of a flare were not detected.
Title: Determination of element abundances using the Yohkoh Bragg
Crystal Spectrometer.
Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.;
Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T.
Bibcode: 1993uxrs.conf..542F
Altcode: 1993uxsa.conf..542F
No abstract at ADS
Title: Helium-Like Sulphur Emission Lines in Solar Active Regions
and Their Sub-C Class Variability
Authors: Watanabe, Tetsuya; Hiei, Eijiro; Lang, James; Culhane,
J. Leonard; Bentley, Robert D.; Doschek, George A.; Bromage, Barbara
J. I.; Brown, Charles M.; Feldman, Uri; Fludra, Andrzej; Kato, Takako;
Payne, Jeffrey
Bibcode: 1992PASJ...44L.141W
Altcode:
Helium-like sulphur spectra (formation temperature, T_m ~ 18times
10(6) K) from coronal active regions are being obtained by the Bragg
Crystal Spectrometer onboard the Yohkoh mission. The average electron
temperatures of the quiescent active regions deduced from the full-disk
integrated sulphur spectra are 3.5--4 times 10(6) K. The temporal
behavior of the emission lines in the sub-C level events shows that
hot plasmas (T > 10(7) K) can be produced in these weak events.
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: Observations of Several Small Flares with the Bragg Crystal
Spectrometer on YOHKOH
Authors: Culhane, J. Leonard; Fludra, Andrzej; Bentley, Robert D.;
Doschek, George A.; Watanabe, Tetsuya; Hiei, Eijiro; Lang, James;
Carter, Martin K.; Mariska, John T.; Phillips, Andrew T.; Phillips,
Kenneth J. H.; Pike, C. David; Sterling, Alphonse C.
Bibcode: 1992PASJ...44L.101C
Altcode:
We have analysed data from two flares of GOES class C7.1 and C8.5
observed by the Yohkoh Bragg Crystal Spectrometer. The high sensitivity
of the Yohkoh instrument allows us to observe the very early stages of
flare development and to study small events with a high signal-to-noise
ratio. Spectral fitting programs have been used to derive plasma
temperatures, emission measures and velocities from spectra of S XV,
Ca XIX and Fe XXV. Large plasma motions indicative of chromospheric
evaporation have been found. A more detailed analysis of a flare which
occurred on 1991 October 30 is presented.
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: YOHKOH Bragg Crystal Spectrometer Observations of the Dynamics
and Temperature Behavior of a Soft X-Ray Flare
Authors: Doschek, George A.; Mariska, John T.; Watanabe, Tetsuya;
Hiei, Eijiro; Lang, James; Culhane, J. Leonard; Bentley, Robert D.;
Brown, Charles M.; Feldman, Uri; Phillips, Andrew T.; Phillips,
Kenneth J. H.; Sterling, Alphonse C.
Bibcode: 1992PASJ...44L..95D
Altcode:
We describe X-ray spectra of an M1.5 flare that occurred on 1991
November 9, starting at about 0313 UT. This flare is unusual in that
very intense blueshifted components are observed in the resonance
lines of Fe XXV, Ca XIX, and S XV. During the onset of the flare,
the resonance lines of Ca XIX and Fe XXV are primarily due to
this blueshifted component, which from the Doppler effect indicates
line-of-sight speeds and turbulent motions that in combination extend
up to 800 km s(-1) .
Title: The Performance of the YOHKOH Bragg Crystal Spectrometer
Authors: Lang, James; Bentley, Robert D.; Brown, Charles M.; Culhane,
J. Leonard; Doschek, George A.; Watanabe, Tetsuya; Hiei, Eijiro;
Deslattes, Richard D.; Fludra, Andrzej; Guttridge, Philip R.; Magraw,
John E.; Payne, Jeffrey; Pike, C. David; Trow, Matthew W.
Bibcode: 1992PASJ...44L..55L
Altcode:
An overview of the Yohkoh Bragg Crystal Spectrometer is given,
complemented by details of the laboratory testing prior to launch. The
in-orbit performance of the instrument is described.
Title: The Potential for Plasma Diagnostics from Stellar
Extreme-Ultraviolet Observations
Authors: Feldman, U.; Mandelbaum, P.; Seely, J. F.; Doschek, G. A.;
Gursky, H.
Bibcode: 1992ApJS...81..387F
Altcode:
A description of the lines from the most abundant ions in the EUV
spectrum in the range 50-500 A that have special diagnostic significance
is presented. These lines are from plasmas in the temperature
range from 10 exp 5 to 10 exp 7 K. Their utility for determining
temperature, density, and abundances is demonstrated. An objective
grating spectrometer, based on the Skylab slitless spectrograph, for
making celestial observations in the EUV spectral region with high
spectral resolution is also described. Such an instrument, if equipped
with a multilayer grating, can achieve efficiencies over limited
EUV wavelength ranges that rival much larger telescope-spectrometer
instruments for the observation of stars and other celestial objects.
Title: Yohkoh BCS Observations of Doppler Shifts Early in Solar Flares
Authors: Mariska, J. T.; Doschek, G. A.; Sterling, A. C.; Culhane,
J. L.; Hiei, E.; Watanabe, T.; Lang, J.
Bibcode: 1992AAS...180.2308M
Altcode: 1992BAAS...24..761M
No abstract at ADS
Title: Solar Flare X-Ray Spectroscopy from YOHKOH
Authors: Doschek, G. A.; BCS Team; SXT Team
Bibcode: 1992AAS...180.2305D
Altcode: 1992BAAS...24..760D
No abstract at ADS
Title: Time Variation of Solar Flare Temperatures Determined from
YOHKOH BCS Spectra
Authors: Sterling, A. C.; Doschek, G. A.; Mariska, J. T.; Pike, C. D.;
Culhane, J. L.; Hiei, E.; Watanabe, T.; YOHKOH BCS Team
Bibcode: 1992AAS...180.3001S
Altcode: 1992BAAS...24..775S
Bragg Crystal Spectrometer (BCS) X-ray spectra analysis from past
satellite missions indicate that it is possible to estimate temperatures
in highly ionized flare plasmas to within about 12\ resonance lines
in different He-like ions. This procedure is particularly valuable
in cases where other temperature measuring methods are insufficient,
such as during the rise phase of flares with strong X-ray spectra
blue shifts. Here we examine this ratio variation in several flares
using data from the Fe XXV, Ca XIX, and S XV channels of the BCS
experiment onboard the Yohkoh satellite. We select flares for
which we have good rise phase data, and calibrate the ratios using
dielectronic-to-resonance line ratios in selected Fe XXV spectra
assuming constant elemental abundances in each event. The Yohkoh BCS is
about an order of magnitude more sensitive than previous X-ray flare
spectrometers, and is therefore able to examine the early stages of
flare development in greater detail than previously possible. For this
study we select events for which we have good rise phase data, but data
well into the decay phase is available for a number of the selected
events. This allows us, for the first time, to follow the evolution
of flare spectra from relatively cool temperatures (~ 12 MK in Fe XXV)
to previously quoted ``typical" flare temperatures (~ 17 MK in Fe XXV).
Title: Atomic Data and Spectral Line Intensities for Ne-like Fe XVII
Authors: Bhatia, A. K.; Doschek, G. A.
Bibcode: 1992ADNDT..52....1B
Altcode:
Electron impact collision strengths and spontaneous radiative decay
rates are calculated for the Ne-like ion Fe XVII. The data pertain to
the 37 levels of the configurations 2 s22 p6,
2 s22 p53 s, 2 s22 p53
p, 2 s22 p53 d, 2 s2 p63 s, 2 s2
p63 p, and 2 s2 p63 d. Collision strengths
are calculated at five energies. In Rydberg units these energies are
76.83, 91.53, 120.93, 179.73, and 253.23. Spectral line intensities
are calculated for all transitions with intensities within two orders
of magnitude of the most intense line in each ion. These are obtained
by computing the excitation rate coefficients (cm 3 s
-1), that is, the collision strengths integrated over a
Maxwellian electron distribution, and then solving the equations of
detailed balance for the populations of the 37 energy levels, assuming
a collisional excitation model. The level populations are computed
for several electron densities and are also given in this paper.
Title: Relative Abundances in the Lower Solar Transition Region
Authors: Doschek, G. A.; Dere, K. P.; Lund, P. A.
Bibcode: 1991ApJ...381..583D
Altcode:
Properties of the lower solar transition region as determined from
UV spectral lines recorded by the Naval Research Laboratory HRTS
are investigated. The spectra were obtained from a rocket flight in
July 1975. Variations of intensity ratios of strong lines of C IV,
Si IV, C II, Si III, and O IV over the entire field of view of the
HRTS instrument, which extends from disk center to the solar limb are
discussed. The largest apparent abundance variations appear to be in
the active regions surrounding a sunspot. The C/Si ratio is lower in
the active regions than anywhere else in the instrument field of view,
implying a lower C/Si abundance ratio in the active regions. There
is a possible correlation of line intensity variation in the active
region with Doppler shift of the lines; the explanation for this is
unclear. The magnitude and reality of intensity ratio variations of
all observed solar features are discussed, and monotonic center-to-limb
intensity ratio variations due to the opacity of some of the spectral
lines are measured.
Title: The Bragg Crystal Spectrometer for SOLAR-A
Authors: Culhane, J. L.; Hiei, E.; Doschek, G. A.; Cruise, A. M.;
Ogawara, Y.; Uchida, Y.; Bentley, R. D.; Brown, C. M.; Lang, J.;
Watanabe, T.; Bowles, J. A.; Deslattes, R. D.; Feldman, U.; Fludra,
A.; Guttridge, P.; Henins, A.; Lapington, J.; Magraw, J.; Mariska,
J. T.; Payne, J.; Phillips, K. J. H.; Sheather, P.; Slater, K.;
Tanaka, K.; Towndrow, E.; Trow, M. W.; Yamaguchi, A.
Bibcode: 1991SoPh..136...89C
Altcode:
The Bragg Crystal Spectrometer (BCS) is one of the instruments which
makes up the scientific payload of the SOLAR-A mission. The spectrometer
employs four bent germanium crystals, views the whole Sun and observes
the resonance line complexes of H-like FeXXVI and He-like FeXXV,
CaXIX, and SXV in four narrow wavelength ranges with a resolving power
(λ/Δλ) of between 3000 and 6000. The spectrometer has approaching
ten times better sensitivity than that of previous instruments thus
permitting a time resolution of better than 1 s to be achieved. The
principal aim is the measurement of the properties of the 10 to 50
million K plasma created in solar flares with special emphasis on the
heating and dynamics of the plasma during the impulsive phase. This
paper summarizes the scientific objectives of the BCS and describes
the design, characteristics, and performance of the spectrometers.
Title: On the Absolute Abundance of Ca in Solar Flares
Authors: Sterling, A. C.; Doschek, G. A.
Bibcode: 1991BAAS...23.1467S
Altcode:
No abstract at ADS
Title: Intensities of the neonlike iron
(Fe16+) 2p53s-2p53p and
2p53p-2p53d transitions in solar-flare spectra
Authors: Doschek, G. A.; Feldman, U.; Bhatia, A. K.
Bibcode: 1991PhRvA..43.2565D
Altcode:
We present relative spectral line intensities for 16 3s-3p and 3p-3d
transitions in the neonlike ion Fe16+, obtained from
solar-flare spectra. The spectra were obtained by a Naval Research
Laboratory slitless spectrograph flown on the Skylab manned space
station. The results are of relevance to x-ray-laser experiments
involving collisional pumping of excited states of neonlike ions,
and to the analysis of solar-flare spectra. The relative line
intensities are measured to an accuracy of about 30%. The measured line
intensities are compared with theoretical line intensities calculated
assuming electron collisional excitation within the Fe16+
ion followed by deexcitation and radiative decay. The measured and
theoretical intensities agree to within less than a factor of 2 for all
but one line. The important J=0 lines (3 1S0-3s
1P1,3s 3P1) at 254.87 and
204.65 Å are about a factor of 1.4 weaker than predicted, which is
almost within experimental error. The 3s 3P2-3p
3S1 line at 409.69 Å is 2.3 times weaker than
predicted, and this is unexplained.
Title: The Solar Spectrum between 914 and 1177 Angstrom
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1991ApJS...75..925F
Altcode:
A spectral line list with wavelengths and identifications for the
914-1177 A region is presented. The list is based on a Naval Research
Laboratory (NRL) solar spectrum obtained from a rocket flight in 1966
and on spectra recorded by the NRL S082-B slit spectrograph flown
in 1973 on the Skylab manned space station as part of the Apollo
Telescope Mount. Three Skylab spectra were used for this work: a limb
spectrum recorded at a position of arcsec outside the white-light
limb, and two flare spectra. The wavelength list should be useful in
analyzing some spectra to be obtained from the planner NASA Lyman Far
Ultraviolet Spectroscopic Explorer mission. A separate table listing
observed or predicted forbidden lines that fall in the 914-1177 A
range is presented, and some of the plasma diagnostic possibilities
for spectral lines in this range are discused.
Title: The SOLAR-A Bragg Crystal Spectrometer (Extended Abstract)
Authors: Culhane, J. L.; Hiei, E.; Bentley, R. D.; Brown, C. M.;
Doschek, G. A.; Feldman, U.; Lang, J.; Watanabe, T.
Bibcode: 1991LNP...387...22C
Altcode: 1991fpsa.conf...22C
No abstract at ADS
Title: Solar astronomy
Authors: Rosner, Robert; Noyes, Robert; Antiochos, Spiro K.; Canfield,
Richard C.; Chupp, Edward L.; Deming, Drake; Doschek, George A.;
Dulk, George A.; Foukal, Peter V.; Gilliland, Ronald L.
Bibcode: 1991aap..reptR....R
Altcode:
An overview is given of modern solar physics. Topics covered include
the solar interior, the solar surface, the solar atmosphere, the Large
Earth-based Solar Telescope (LEST), the Orbiting Solar Laboratory, the
High Energy Solar Physics mission, the Space Exploration Initiative,
solar-terrestrial physics, and adaptive optics. Policy and related
programmatic recommendations are given for university research and
education, facilitating solar research, and integrated support for
solar research.
Title: UV-optical from space
Authors: Illingworth, Garth; Savage, Blair; Angel, J. Roger; Blandford,
Roger D.; Boggess, Albert; Bowyer, C. Stuart; Carruthers, George R.;
Cowie, Lennox L.; Doschek, George A.; Dupree, Andrea K.
Bibcode: 1991aap..rept.....I
Altcode:
The following subject areas are covered: (1) the science program (star
formation and origins of planetary systems; structure and evolution
of the interstellar medium; stellar population; the galactic and
extragalactic distance scale; nature of galaxy nuclei, AGNs, and QSOs;
formation and evolution of galaxies at high redshifts; and cosmology);
(2) implementation of the science program; (3) the observatory-class
missions (HST; LST - the 6m successor to HST; and next-generation 16m
telescope); (4) moderate and small missions (Delta-class Explorers;
imaging astrometric interferometer; small Explorers; optics development
and demonstrations; and supporting ground-based capabilities);
(5) prerequisites - the current science program (Lyman-FUSE; HTS
optimization; the near-term science program; data analysis, modeling,
and theory funding; and archives); (6) technologies for the next
century; and (7) lunar-based telescopes and instruments.
Title: Heating and Flows in Flares
Authors: Doschek, G. A.
Bibcode: 1991LNP...387..121D
Altcode: 1991LNP...387..119D; 1991fpsa.conf..121D
A review is presented of some unresolved problems in high resolution
soft X-ray spectroscopy of solar flares. The main emphasis is on the
dynamics of the multi-million degree thermal plasma, as revealed by line
broadening and blueshifted components of spectral lines. I discuss some
of the most recent results obtained from analysis of X-ray spectra. I
also discuss some problems related to the temperature distribution and
ionization balance in the flare plasma. The data from SOLAR-A should
provide substantial new insight into all of these problems.
Title: Extreme Ultraviolet Spectroscopy as a Probe of Astrophysical
Plasmas - Learning from the Sun
Authors: Doschek, G. A.
Bibcode: 1991eua..coll...94D
Altcode:
No abstract at ADS
Title: High-temperature plasma in solar flares.
Authors: Doschek, G. A.
Bibcode: 1991psf..conf..451D
Altcode:
The thermal soft X-ray flare plasma is at temperatures ranging from
a few million degrees up to about 40×106K. The author
discusses some current problems in our understanding of the physical
conditions in this plasma, particularly the ionization balance and
the possible detection of non-thermal electrons. He discusses X-ray
spectroscopic diagnostics that might help in resolving some of the
issues.
Title: Plasma diagnostics with the Solar-A Bragg Crystal Spectrometer
Authors: Culhane, J. L.; Hiei, E.; Bentley, R. D.; Brown, C. M.;
Doschek, G. A.; Feldman, U.; Lang, J.; Watanabe, T.
Bibcode: 1991AdSpR..11e..77C
Altcode: 1991AdSpR..11...77C
A Bragg Crystal spectrometer is one of the instruments on the Solar-A
mission. Using bent crystals, the spectrometer will observe the
resonance line complexes of the H-like Fe XXVI, and He-like Fe XXV
and Ca XIX ions with a sensitivity 5 to 10 times that of the SMM Bent
Crystal Spectrometer. It will also study the lower temperature lines
of He-like S XV. The improved sensitivity will allow observations
much earlier in the impulsive phase of flares than has previously been
possible. The new observations should help to answer questions about
plasma heating and dynamics. As well as providing information on line
profiles and shifts, the selected spectral lines will also provide
electron temperature and emission measure estimates over a range from
5 to 50 MK. The onboard microprocessor will permit spectral resolution
to be traded against time resolution during an observation.
Title: X-rays and inner-shell transitions in the solar atmosphere
Authors: Doschek, G. A.
Bibcode: 1990AIPC..215..603D
Altcode:
During the 1980's, very high spectral resolution solar X-ray spectra
were obtained from a number of Bragg crystal spectrometer experiments
on orbiting spacecraft. Taken together, these instruments covered the
solar X-ray spectrum from about 1.8 A˚ up to about 25 A˚. Inner-shell
transitions in highly ionized ions were observed for several solar
abundant elements, such as iron and calcium. Most of the spectra
were obtained from solar flare plasmas at temperatures of about 1-3.5
keV. It was possible to study the time-behavior of line intensities
and line profiles for all phases of a solar flare. From these spectra,
the accuracy of certain atomic physics calculations can be determined,
and parameters in the solar flare plasma such as electron temperature
and density can be measured. The most significant results from
these space missions are reviewed, and a new Bragg crystal spectrometer
experiment is described. The solar spectra will also be related to some
recent laboratory measurements involving tokamak spectra and spectra
obtained from the Electron Beam Ion Trap (EBIT) at Lawrence Livermore
National Laboratory.
Title: On the Dependence of Solar Flare X-Ray Spectral Line Intensity
Ratios of Highly Ionized Sulfur, Calcium, and Iron on Electron
Temperature, Differential Emission Measure, and Atomic Physics
Authors: Doschek, G. A.; Fludra, A.; Bentley, R. D.; Lang, J.;
Phillips, K. J. H.; Watanabe, T.
Bibcode: 1990ApJ...358..665D
Altcode:
This paper focuses on what can be learned about the emission measure
distribution and certain atomic physics parameters from spectral lines
of highly ionized ions of sulfur, calcium, and iron that appear in
solar flare spectra. The particular lines chosen for analysis allow the
electron temperature to be determined independently of the assumption
of ionization equilibrium. An attempt is made to find emission measure
models based on selected functional dependences of emission measure
on temperature that reproduce the observed temperatures deduced from
spectral line ratios as well as the relative intensities of resonance
lines of different elements.
Title: Solar Coronal Ar/Fe and Ne/Mg Abundance Ratios Derived from
Ultraviolet Forbidden Line Spectra
Authors: Doschek, G. A.; Bhatia, A. K.
Bibcode: 1990ApJ...358..338D
Altcode:
An Ar/Fe abundance ratio of 0.031 + or - 35 percent and an upper limit
of 0.4 to the Ne/Mg abundance ratio are determined for solar coronal
active regions using solar spectra. Forbidden lines occur at 1324.45 A
for Mg V, 1349.38 A for Fe XII, 1375.98 A for Ca XV, and 1392.12 A for
Ar XI. The unobserved Ne V line is predicted to fall at 1574.68 A. These
abundance ratios are consistent with lower abundances of Ne and Ar in
the corona relative to low first ionization potential elements.
Title: Soft X-Ray Spectroscopy of Solar Flares: an Overview
Authors: Doschek, G. A.
Bibcode: 1990ApJS...73..117D
Altcode:
An overview of the current status of high spectral resolution soft
X-ray observations of solar flares is given. The review concentrates
primarily on recent results and interpretations of results obtained from
orbiting Bragg crystal spectrometers flow during the last solar maximum
on the US DoD P78-1 spacecraft, the NASA SMM, and the ISAS Hinotori
spacecraft. Results and several key issues regarding interpretation
of the spectra are presented. Specifically, the dynamics of coronal
flare plasmas as revealed by X-ray line profiles and wavelength shifts
are discussed. Recent results concerning the theory of chromospheric
evaporation are given. The temperature of coronal flare plasma is
discussed within the context of a differential mission measure. Results
concerning electron density measurements, nonequilibrium processes,
and relative element abundances are also reviewed.
Title: Solar Flares - Present Status and Future Prospects
Authors: Doschek, G. A.
Bibcode: 1990BAAS...22..838D
Altcode:
No abstract at ADS
Title: The Ar/Ca Abundance Ratio in Solar Flares
Authors: Doschek, George A.; Seely, John F.
Bibcode: 1990ApJ...348..341D
Altcode:
An Ar/Ca abundance ratio of at least 0.56 is derived using the X-ray
spectra of solar flares recorded by the SOLFLEX spectrometers on the
P78-1 spacecraft. The method involves determining the contribution
of the Ar XVII 1s2 1S0-1s4p 1P1 line to a blended feature at 3.2005
A. This contribution is determined by considering the relationship of
the other component of the blended feature, namely the Ca XVIII 1s2 2s
2S(1/2)-1s2p2s 2P(3/2) line, to the dielectronic satellite lines of
Ca XVII that fall between 3.215 and 3.24 A. It is demonstrated that
a broad-wavelength coverage solar X-ray spectrometer experiment is
necessary for precise abundance measurements.
Title: High-Resolution X-Ray Spectra of Solar Flares. IX. Mass Upflow
in the Long-Duration Flare of 1979 June 5
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.; McKenzie, D. L.
Bibcode: 1989ApJ...345.1079D
Altcode:
Blueshifted X-ray spectral line components in Fe and Ca spectra of a
large long-duration flare observed on June 5, 1979. It is found that
blueshifted emission exists for a time interval of at least 28 minutes
indicating upflowing plasma at about 250 km/s. Emission measures for
both the blueshifted and stationary plasma are derived and the results
are interpreted in terms of chromospheric evaporation. The total amount
of hot upflowing plasma during the flare rise time exceeds the amount
of stationary plasma contained in the loop close to the time of the
peak of the flare. This result contradicts the simplest version of the
evaporation model. Evaporation can account for the observations only
if some of the upflowing plasma cools on time scales much shorter than
the rise time of the event, which was about 40 minutes.
Title: Measurement of relative electron-impact-excitation cross
sections for Fe(24+)
Authors: Brown, C. M.; Feldman, U.; Doschek, G. A.; Seely, J. F.;
Lavilla, R. E.
Bibcode: 1989PhRvA..40.4089B
Altcode:
We present measurements of the relative
electron-impact-excitation cross sections for the 1s2
1S0-1s2p 1P1, 1s2
1S0-1s2p 3P2, 1s2
1S0-1s2p 3P1, and
1s2 1S0-1s2s 3S1
transitions for the He-like ion, Fe24+. The measurements
were made at two electron energies: 6.86 and 9.94 keV. The cross-section
measurements are compared with theoretical calculations.
Title: Solar Coronal Abundance Ratios Ar/Fe and Ne/Mg Derived from
Ultraviolet Forbidden Line Spectra
Authors: Doschek, G. A.; Bhatia, A. K.
Bibcode: 1989BAAS...21.1187D
Altcode:
No abstract at ADS
Title: Effects of initial-state population variations on the 2p
--> 1s K alpha dielectronic satellite spectra of highly ionized
iron ions in high-temperature astrophysical and laboratory plasmas
Authors: Jacobs, V. L.; Doschek, G. A.; Seely, J. F.; Cowan, R. D.
Bibcode: 1989PhRvA..39.2411J
Altcode:
Theoretical predictions for the iron K-alpha X-ray emission spectra
of high-temperature plasmas have been obtained under the assumption
of steady-state optically thin excitation conditions. The study
takes into account the fine-structure components of the 2p-to-1s
inner-shell-electron radiative transitions in the iron ions from Fe
XVIII to Fe XXIV. In addition to an electron-temperature variation,
the present spectra are found to exhibit an electron-density sensitivity
which is the result of the density-dependent distribution of populations
among the different fine-structure levels of the initial ions in the
dielectronic recombination, and of inner-shell electron collisional
excitation processes.
Title: Nonlocal Thermal Transport in Solar Flares. II. Spectroscopic
Diagnostics
Authors: Karpen, Judith T.; Cheng, Chung-Chieh; Doschek, George A.;
DeVore, C. Richard
Bibcode: 1989ApJ...338.1184K
Altcode:
Physical parameters obtained for a flaring solar atmosphere in an
earlier paper are used here to predict time-dependent emission-line
profiles and integrated intensities as a function of position for
two spectral lines commonly observed during solar flares: the X-ray
resonance lines of Ca XIX and Mg XI. Considerations of ionization
nonequilibrium during the rise phase of the flare are addressed,
and the effects on the predicted spectral-line characteristics are
discussed. It is concluded that some spectroscopic diagnostics favor
the nonlocal model, but other long-standing discrepancies between the
numerical models and the observations remain unresolved.
Title: Mass Upflow in the Long Duration Flare of 5 June 1979
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.; McKenzie, D. L.
Bibcode: 1989BAAS...21..850D
Altcode:
No abstract at ADS
Title: Measurement of Wavelengths for Inner-Shell Transitions in
CA xvii--xix
Authors: Seely, J. F.; Doschek, G. A.
Bibcode: 1989ApJ...338..567S
Altcode:
The wavelengths of transitions in solar flare spectra in the region
3.12-3.24 A have been measured using data recorded by a crystal
spectrometer on the Air Force P78-1 spacecraft. Appearing in this
wavelength region are inner-shell transitions of the type n = 1-2 in
Ca XVII-XIX and resonance transitions in Ar XVII, Ar XVIII, and Fe
XXV. The hydrogenic Ar XVIII 1s-1p transition was used to establish
an absolute wavelength scale with an estimated uncertainty of 0.3 mA,
and the relative wavelengths were measured to an uncertainty that
is typically less than 0.1 mA. The presently measured wavelengths
are compared with previously measured and calculated wavelengths,
and the observed flare spectra are compared with synthetic spectra.
Title: Erratum: Solar spectroscopy in the far-ultraviolet-x-ray
wavelength regions: status and prospects: errata
Authors: Feldman, Uri; Doschek, G. A.; Seely, John F.
Bibcode: 1989JOSAB...6..379F
Altcode: 1989OSAJB...6..379F
No abstract at ADS
Title: Chromospheric explosions.
Authors: Doschek, G. A.; Antiochos, S. K.; Antonucci, E.; Cheng,
C. -C.; Culhane, J. L.; Fisher, G. H.; Jordan, C.; Leibacher, J. W.;
MacNiece, P.; McWhirter, R. W. P.; Moore, R. L.; Rabin, D. M.; Rust,
D. M.; Shine, R. A.
Bibcode: 1989epos.conf..303D
Altcode:
The work of this team addressed the question of the response and
relationship of the flare chromosphere and transition region to the
hot coronal loops that reach temperatures of about 107K
and higher. Flare related phenomena such as surges and sprays were
also discussed. The team members debate three main topics: 1) whether
the blue-shifted components of X-ray spectral lines are signatures of
"chromospheric evaporation"; 2) whether the excess line broadening of UV
and X-ray lines is accounted for by "convective velocity distribution"
in evaporation; and 3) whether most chromospheric heating is driven by
electron beams. These debates illustrated the strengths and weaknesses
of our current observations and theories.
Title: CDS: The Coronal Diagnostic Spectrometer
Authors: Patchett, B. E.; Harrison, R. A.; Sawyer, E. C.; Aschenbach,
B.; Culhane, J. L.; Doschek, G. A.; Gabriel, A. H.; Huber, M. C. E.;
Jordan, C.; Kjeldseth-Moe, O.
Bibcode: 1988sohi.rept...39P
Altcode:
The prime objective of the Coronal Diagnostic Spectrometer (CDS) is to
obtain intensity ratios of selected extreme-ultraviolet line pairs, with
spatial and temporal scales appropriate to the fine-scale features of
the solar atmosphere. This will be done simultaneously across a large
portion of the solar atmosphere. From this, density and temperature
information will be derived which coupled with a modest capability for
the detection of flows will be used to study the energy and mass balance
of the atmosphere. Understanding the heating of the solar corona and the
acceleration of the solar wind are the ultimate goals of this research.
Title: LASCO: A wide-field white light and spectrometric coronagraph
for SOHO
Authors: Michels, D. J.; Schwenn, R.; Howard, R. A.; Bartoe, J. -D. F.;
Antiochos, S. K.; Brueckner, G. E.; Cheng, C. -C.; Dere, K. P.;
Doschek, G. A.; Mariska, J. T.
Bibcode: 1988sohi.rept...55M
Altcode:
The scientific objectives of the LASCO (light and spectrometric
coronagraph) project in the SOHO (solar and heliospheric observatory)
mission are described. These include investigation of mechanisms
for heating of the corona and acceleration of the solar wind, causes
of coronal transients, and their role in development of large scale
coronal patterns and interplanetary disturbances. The distribution
and properties of dust particles, including those released from
sun-grazing comets are investigated. Interactions of coronal plasma
with the dust are studied. The corona is analyzed spectroscopically
by a high-resolution scanning, imaging interferometer. The spectral
profiles of three emission lines and one Fraunhofer line are measured
for each picture point, giving temperatures, velocities, turbulent
motions and volume densities. Polarization analysis yields the direction
of coronal magnetic fields.
Title: Solar spectroscopy in the far-ultraviolet - X-ray wavelength
regions:status and prospects.
Authors: Feldman, U.; Doschek, G. A.; Seely, J. F.
Bibcode: 1988JOSAB...5.2237F
Altcode: 1988OSAJB...5.2237F
The authors review the status and prospects of solar spectroscopy in
the far-UV - X-ray wavelength regions between approximately 1.7 and 2000
Å. They divide the solar spectrum into a number of wavelength regions,
determined by characteristics of spectroscopic instrumentation. The
quality of the available spectra obtained in each region is discussed,
concentrating on spectral resolution, wavelength coverage and accuracy,
and line intensity and line-profile information.
Title: The Bragg Crystal Spectrometer Experiment on SOLAR-A
Authors: Hiei, E.; Culhane, J. L.; Doschek, G. A.
Bibcode: 1988BAAS...20..710H
Altcode:
No abstract at ADS
Title: Atomic Physics and the Emission Measure Distribution of
Solar Flares
Authors: Doschek, G. A.
Bibcode: 1988BAAS...20..687D
Altcode:
No abstract at ADS
Title: Extreme Ultraviolet Solar Spectroscopy
Authors: Doschek, G. A.
Bibcode: 1988als..conf..265D
Altcode:
No abstract at ADS
Title: Introduction to Solar Spectroscopy
Authors: Doschek, G. A.
Bibcode: 1988als..conf..237D
Altcode:
Contents: 1. Introduction to solar spectroscopy. 2. UV solar
spectroscopy. 3. XUV solar spectroscopy. 4. The solar X-ray spectrum.
Title: Ultraviolet Solar Spectroscopy
Authors: Doschek, G. A.
Bibcode: 1988als..conf..251D
Altcode:
No abstract at ADS
Title: The Solar X-Ray Spectrum
Authors: Doschek, G. A.
Bibcode: 1988als..conf..279D
Altcode:
No abstract at ADS
Title: Calcium ionization balance and argon/calcium abundance in
solar flares
Authors: Antonucci, E.; Marocchi, D.; Gabriel, A. H.; Doschek, G. A.
Bibcode: 1987A&A...188..159A
Altcode:
An earlier analysis of solar flare calcium spectra from XRP and P78-1
aimed at measuring the calcium ionization balance resulted in an
ambiguity due to a line blend between the calcium q line and an Ar
XVII line. In the present work the calcium line 'r' is included in
the analysis in order to resolve this problem. It is shown that the
correct calcium ionization balance is that indicated in the earlier
paper as corresponding to an argon/calcium abundance ratio of 0.2. The
argon/calcium abundance ratio in the group of solar flares studied
is shown to be 0.2 + or - 0.2. It is further argued that while the
abundance of heavy elements may be enhanced in energetic flare events,
this enhancement is less for argon than for calcium, leading to an
argon/calcium ratio smaller than that present in the quiet sun.
Title: Transient Ionization and Solar Flare X-Ray Spectra
Authors: Doschek, G. A.; Tanaka, K.
Bibcode: 1987ApJ...323..799D
Altcode:
In this paper the effects of a transiently ionizing solar flare
plasma on the X-ray spectrum of iron between 1.85 and 1.92 A are
considered. The atomic physics of the nonequilibrium spectrum is
discussed, and reasons for differences in appearance from ionization
equilibrium spectra are explained. The effect of spectral resolution on
the ability to detect transient ionization in the iron X-ray spectrum
is illustrated by synthetic spectra. A synthetic transiently ionizing
spectrum is applied to the interpretation of spectra obtained from the
SOX 1 spectrometer on the Japanese Hinotori spacecraft. Some indications
of transient ionization are found, although counting statistics negate
a strong conclusion. A hypothetical spectrometer with about one order
of magnitude more sensitivity than the SOX 1 Hinotori or the bent
crystal spectrometer flown on the Solar Maximum Mission (SMM) is also
considered. The ranges of plasma parameters such as plasma emission
measure and density that are necessary for transient ionization to be
detected by such an instrument are discussed.
Title: What's needed in the UV and EUV.
Authors: Doschek, G. A.
Bibcode: 1987NASCP2483...37D
Altcode: 1987tphr.conf...37D
High spectral and spatial resolution UV and EUV spectroscopy is
discussed with emphasis on the spectroscopic observations that are
required in order to increase our understanding of the physics of
the lower transition region. The properties of the lower transition
region are reviewed, and the available lower transition region plasma
diagnostics are reviewed for the wavelength range between about 1150 and
2000 Å. One important conclusion is that comprehensive spectroscopic
coverage over a rather broad temperature range is necessary in order
to observe satisfactorily small transition region structures. This
is illustrated by two examples from the recent NRL Spacelab 2 HRTS
experiment.
Title: Observations of Nonthermal Energy Distributions during the
Impulsive Phase of Solar Flares
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.
Bibcode: 1987ApJ...319..541S
Altcode:
The Fe XXV resonance line and dielectronic satellite intensities
have been measured as functions of time for several flares recorded
by the Naval Research Laboratory crystal spectrometer (SOLFLEX) flown
on the US Air Force P78-I spacecraft. The intensity ratios of the Fe
XXV resonance line, the Fe XXIV n = 2 satellite line j, and the Fe
XXIV n = 3 satellite line d13 indicate that nonthermal electron energy
distributions occur during the impulsive phase of the flares. For the
electron energies at which the j and d13 satellites are formed (4.7 and
5.8 keV, respectively), the electron energy distributions during the
impulsive phase are observed to have a bump or to be nearly flat. For
all of the flares that were studied, hard X-ray bursts occurred near
the time of the nonthermal distributions observed in the SOLFLEX data.
Title: The Search for Transient Ionization in Solar Flare X-ray
Spectra of Iron
Authors: Doschek, G. A.; Tanaka, K.
Bibcode: 1987BAAS...19..922D
Altcode:
No abstract at ADS
Title: Ultraviolet AL III Emission Lines and the Physics of the
Solar Transition Region
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1987ApJ...315L..67D
Altcode:
Two lines of the solar UV spectrum were identified as due to 3p-3d
Al III transitions near 1612 A; the ratios of these lines to the
3s-3p Al III doublet near 1855 A were found to be very sensitive to
temperature. Thus, the temperatures of formation of the Al III lines
could be determined by using one of the line ratios in two quiet
sun regions, a coronal hole, and an active region. The results were
found to be consistent with expectations based on the assumption of
ionization equilibrium for Al III. It is suggested that S III lines
near 1350 A and 1200 A may also serve as a temperature diagnostic.
Title: The Temperature of Solar Flares Determined from X-Ray Spectral
Line Ratios
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1987ApJ...313..883D
Altcode:
The effect on derived solar flare plasma temperatures of (1) a power-law
distribution of emission measure as a function of temperature, (2)
a high-temperature isothermal source coupled to a low-temperature
power-law distribution of emission measure, and (3) two isothermal
sources is calculated for line ratios involving the ions S XV, Ca
XIX, Ca XX, Fe XXV, Ni XXVII, and Fe XXVI. It is shown that if the
Fe XXV temperature is less than about 25 million K, as is true for
the majority of flares, then about 75 percent or more of the emission
measure is produced by plasma at temperatures equal to or less than the
Fe XXV temperature plus about 3 million K. If the Fe XXV temperature
is 20 million K or higher, this percentage can be larger. This result
is obtained even if a superhot component exists that extends up to
several hundred million degrees. Temperatures determined from Fe XXVI
demonstrate the presence of a superhot component.
Title: Chromospheric explosions
Authors: Doschek, G. A.; Antiochos, S. K.; Antonucci, E.; Cheng,
C. -C.; Culhane, J. L.; Fisher, G. H.; Jordan, C.; Leibacher, J. W.;
MacNeice, P.; McWhirter, R. W. P.
Bibcode: 1986epos.conf..4.1D
Altcode: 1986epos.confD...1D
Three issues relative to chromospheric explosions were debated. (1)
Resolved: The blue-shifted components of x-ray spectral lines are
signatures of chromospheric evaporation. It was concluded that
the plasma rising with the corona is indeed the primary source of
thermal plasma observed in the corona during flares. (2) Resolved:
The excess line broading of UV and X-ray lines is accounted for by a
convective velocity distribution in evaporation. It is concluded that
the hypothesis that convective evaporation produces the observed
X-ray line widths in flares is no more than a hypothesis. It is
not supported by any self-consistent physical theory. (3) Resolved:
Most chromospheric heating is driven by electron beams. Although it
is possible to cast doubt on many lines of evidence for electron
beams in the chromosphere, a balanced view that debaters on both
sides of the question might agree to is that electron beams probably
heat the low corona and upper chromosphere, but their direct impact
on evaporating the chromosphere is energetically unimportant when
compared to conduction. This represents a major departure from the
thick-target flare models that were popular before the Workshop.
Title: High-Resolution X-Ray Spectra of Solar Flares. VIII. Mass
Upflow in the Large Flare of 1980 November 7
Authors: Karpen, J. T.; Doschek, G. A.; Seely, J. F.
Bibcode: 1986ApJ...306..327K
Altcode:
The large flare of November 7, 1980 provides a unique opportunity to
investigate the upward-moving plasma seen during the early stages of
many flares. Soft X-ray spectroscopic data obtained by the Solar Flare
X-ray (SOLFLEX) instruments on board the Air Force P78-1 satellite
have been used to determine the spatial extent, turbulent velocity,
temperature, and emission measure of the blueshifted and stationary
plasmas, as well as the upward velocity of the blueshifted component
alone. Two geometries are considered in calculating the resultant
mass and energy balance. In addition, coincident hard X-ray data
was acquired from the HXRBS instrument on board the SMM satellite
to determine the relative timing and enertics of the hard and soft
X-ray flare plasmas. These results are compared with the predictions
of the chromospheric evaporation hypothesis. It is concluded that
electron-induced evaporation plays a minor role in this flare, and that
another mechanism must account for the observed blueshifted emission.
Title: Solar High-energy Astrophysical Plasmas Explorer
(SHAPE). Volume 1: Proposed concept, statement of work and cost plan
Authors: Dennis, Brian R.; Martin, Franklin D.; Prince, T.; Lin,
R.; Bruner, M.; Culhane, L.; Ramaty, R.; Doschek, G.; Emslie, G.;
Lingenfelter, R.
Bibcode: 1986STIN...8725983D
Altcode:
The concept of the Solar High-Energy Astrophysical Plasmas Explorer
(SHAPE) is studied. The primary goal is to understand the impulsive
release of energy, efficient acceleration of particles to high energies,
and rapid transport of energy. Solar flare studies are the centerpieces
of the investigation because in flares these high energy processes
can be studied in unmatched detail at most wavelenth regions of the
electromagnetic spectrum as well as in energetic charged particles
and neutrons.
Title: S V Line Ratios in the Sun
Authors: Dufton, P. L.; Hibbert, A.; Keenan, F. P.; Kingston, A. E.;
Doschek, G. A.
Bibcode: 1986ApJ...300..448D
Altcode:
In the present prediction of level populations and emission line
intensity ratios for electron densities and temperatures appropriate to
the sun, on the basis of new atomic data for S V, the electron impact
collision rates for spin-forbidden transitions, and the intercombination
transition spontaneous radiative rate, are noted to be substantially
larger than previously ascertained. The S V intensity ratio is shown
to be a useful electron density diagnostic for log N(e) greater than
11.5 ratios deduced from observations obtained with a slit spectrograph
aboard Skylab generally agree with the theoretical values presented.
Title: Chromospheric explosions.
Authors: Doschek, G. A.; Antiochos, S. K.; Antonucci, E.; Cheng,
C. -C.; Culhane, J. L.; Fisher, G. H.; Jordan, C.; Leibacher, J. W.;
MacNiece, P.; McWhirter, R. W. P.; Moore, R. L.; Rabin, D. M.; Rust,
D. M.; Shine, R. A.
Bibcode: 1986NASCP2439....4D
Altcode:
The work of this team addressed the question of the response and
relationship of the flare chromosphere and transition region to the
hot coronal loops that reach temperatures of about 107K
and higher. Flare related phenomena such as surges and sprays are
also discussed. The team members debated three main topics: 1. whether
the blue-shifted components of X-ray spectral lines are signatures of
"chromospheric evaporation"; 2. whether the excess line broadening of UV
and X-ray lines is accounted for by "convective velocity distribution"
in evaporation; and 3. whether most chromospheric heating is driven
by electron beams.
Title: Element abundances from solar flare spectra
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.
Bibcode: 1985MNRAS.217..317D
Altcode:
Ratios of solar element abundances are determined for Ar/Ca, K/Ca,
and Ca/Fe, from high-resolution solar flare X-ray spectra obtained from
Bragg spectrometers flown on the P78-1 spacecraft. Values of the ratios
are: Ar/Ca = 0.65, K/Ca = 0.10, and Ca/Fe = 0.10. If the abundance
of iron is taken to be coronal, i.e. log A(Fe) = 7.65 log A(H) = 12,
then the abundances are: log A(Ca) = 6.62, log A(Ar) = 6.44, log A(K)
= 5.62. If the iron abundance is assumed to be photospheric, i.e.,
log A(Fe) = 7.50, then the abundances are: log A(Ca) = 6.47, log A(Ar)
= 6.29, log A(K) = 5.47. The uncertainties in abundance ratios are +
or - 25 percent. The abundance results are discussed in terms of the
possibility of varying abundances in the solar atmosphere.
Title: High-resolution X-ray spectra of solar flares. VII - A
long-duration X-ray flare associated with a coronal mass ejection
Authors: Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Sheeley, N. R.,
Jr.; Seely, J. F.
Bibcode: 1985ApJ...292..309K
Altcode:
It has been recognized that very long duration X-ray events
(lasting several hours) are frequently associated with coronal mass
ejection. Thus, Sheeley et al. (1983) found that the probability of the
occurrence of a coronal mass ejection (CME) increases monotonically
with the X-ray event duration time. It is pointed out that the
association of long-duration, or long-decay, X-ray events (LDEs) with
CMEs was first recognized from analysis of solar images obtained by
the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL)
slitless spectroheliograph. Recently high-resolution Bragg crystal
X-ray spectrometers have been flown on three spacecraft, including the
Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission
(SMM), and the Japanese Hinotori spacecraft. In the present paper,
P78-1 X-ray spectra of an LDE which had its origin behind the solar
west limb on November 14, 1980 is presented. The obtained data make
it possible to estimate temperatures of the hottest portion of the
magnetic loops in which the emission arises.
Title: The solar coronal X-ray spectrum 5.5-12 A
Authors: McKenzie, D. L.; Landecker, P. B.; Feldman, U.; Doschek, G. A.
Bibcode: 1985STIN...8528908M
Altcode:
Solar X-ray spectra in the wavelength range 5.5-12 a have been measured
by the SOLEX spectrometers aboard the USAF p78-1 satellite. The
spectra were measured under a variety of flaring and nonflaring
conditions. High sensitivity, attained by summing data from several
successive spectral scans, enabled the detection of 85 lines, 22 of
which remain unidentified, in this wavelength range. In addition,
observations of many strong lines were possible with individual scans
during the course of the flare evolution. This capability, coupled with
the availability of nonflare spectra, facilitated the identification
of several lines. The lines of Fe XXII-XXIV are especially important
in this wavelength range. For many of these lines, theoretical and
observed line strengths
Title: Element Abundances from Solar Flare Spectra
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.
Bibcode: 1985BAAS...17..629D
Altcode:
No abstract at ADS
Title: New identifications of Fe XVII spectral lines in solar flares
Authors: Feldman, U.; Doschek, G. A.; Seely, J. F.
Bibcode: 1985MNRAS.212P..41F
Altcode:
The authors review the identifications of Fe XVII transitions between
the 2s22p53s, 3p, and 3d configurations
recently published by Jupén. The review is based on examining
spectroheliograms of solar flares obtained by a Naval Research
Laboratory instrument on Skylab (S082-A). The authors agree with
the majority of identifications given by Jupén, but find different
wavelengths for a few of the lines. The relative intensities of
the lines are qualitatively in agreement with calculations. The
authors also identify a broad line at 1153.20 Å with the
2p53s3P0→2p53s3P1
forbidden transition of Fe XVII. This line was found in flare spectra
obtained by the NRL slit spectrograph on Skylab (S082-B).
Title: The solar coronal X-ray spectrum from 5.5 to 12 A
Authors: McKenzie, D. L.; Landecker, P. B.; Feldman, U.; Doschek, G. A.
Bibcode: 1985ApJ...289..849M
Altcode:
A compilation of spectral lines in the 5.5-12 A wavelength region
is presented from observations under a variety of solar conditions,
including flare onset, flares, and nonflaring active regions. The
line fluxes and wavelengths of Fe XXII-XXIV are compared with theory,
and the results for Fe XXIII-XXIV are shown to agree with theoretical
determinations. When only the strongest lines are considered, some
relative strengths agree with theory and some do not. Diagnostically
useful line ratios of Mg XI, Al XII, and Si XIII are also examined. The
density-sensitive line ratio R measured for Mg XI and Si XIII agree with
theoretical calculations of R(0) the low-density limit of R. For Mg XI
in a flare-onset spectrum, R is lower than R(0), but the statistical
significance of the result is not high.
Title: Diagnostics of solar and astrophysical plasmas - Dependent
on autoionization phenomena
Authors: Doschek, G. A.
Bibcode: 1985arda.book..171D
Altcode:
The application of autoionization calculations to problems in solar
and astrophysical plasma diagnostics is discussed. Attention is given
to space plasmas having high spectral resolution, particularly in
the wavelength region between about 300 and 1100 A. It is shown that
atomic resonance data can be used to calculate many of the spectral
line intensities in solar plasmas in order to obtain information
concerning the physical properties of the emitting gas, including
temperature, density, ionization balance, and atmospheric structure
and dynamics. Recent spectral observations of nonsolar plasmas are
also discussed. A list of the major high-resolution astrophysical
plasma spectrometers and spectrographs is provided.
Title: Numerical simulations of loops heated to solar flare
temperatures. III - Asymmetrical heating
Authors: Cheng, C. -C.; Doschek, G. A.; Karpen, J. T.
Bibcode: 1984ApJ...286..787C
Altcode:
A numerical model is defined for asymmetric full solar flare loop
heating and comparisons are made with observational data. The Dynamic
Flux Tube Model is used to describe the heating process in terms of
one-dimensional, two fluid conservation equations of mass, energy
and momentum. An adaptive grid allows for the downward movement of
the transition region caused by an advancing conduction front. A
loop 20,000 km long is considered, along with a flare heating system
and the hydrodynamic evolution of the loop. The model was applied to
generating line profiles and spatial X-ray and UV line distributions,
which were compared with SMM, P78-1 and Hintori data for Fe, Ca and
Mg spectra. Little agreement was obtained, and it is suggested that
flares be treated as multi-loop phenomena. Finally, it is concluded
that chromospheric evaporation is not an effective mechanism for
generating the soft X-ray bursts associated with flares.
Title: A solar spectral line between 10 and 200 A modified for
application to high spectral resolution X-ray astronomy.
Authors: Doschek, G. A.; Cowan, R. D.
Bibcode: 1984ApJS...56...67D
Altcode:
A spectral line list for the 10-200 A range is developed from existing
solar spectra for application to high spectral resolution measurements
of astrophysical plasmas. The solar spectral line lists are merged into
a single comprehensive list. The effect of the solar emission measure
distribution is removed from the line intensities, which results in
a set of emission rates for the lines that can be applied to many
optically thin, low density high temperature plasmas in ionization
equilibrium. In addition to the measured solar lines, 250 theoretical
lines are added to this list. These lines fall in wavelength regions
where the existing solar lists have few lines because of limitations
in instrumental sensitivity. Also, some lines have been added because
the sun has very little plasma at temperatures of about one million K,
and consequently these lines are weak or absent in solar spectra. The
entire list contains about 600 lines. Finally, predicted spectra of
the two RS CVn stars, alpha Aur (Capella) and UX Ari, are presented at
1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at
1 A resolution, and the emission rate spectrum (spectrum not modified
by an emission measure distribution) is shown at very high spectral
resolution. The predicted spectra for Capella and UX Ari are based
on results obtained from the Einstein and International Ultraviolet
Explorer (IUE) spacecraft.
Title: What the Sun Can Tell Us Concerning Phenomena and Spectroscopy
Authors: Doschek, G. A.
Bibcode: 1984BAAS...16R.984D
Altcode:
No abstract at ADS
Title: The Large Flare November 7, 1980: A Test of Chromospheric
Evaporation Theories?
Authors: Karpen, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1984BAAS...16.1003K
Altcode:
No abstract at ADS
Title: The possibility of steady state nonionization equilibrium
conditions in soft X-ray flare plasmas
Authors: Doschek, G. A.
Bibcode: 1984ApJ...283..404D
Altcode:
The possibility of the existence in soft X-ray flare plasmas of
conditions that result in a steady state departure of ion abundances
from ionization equilibrium values is considered. The observed flare
plasma is assumed to be a result of many small 'elementary bursts' that
occur on time scales comparable to the ionization and recombination
times of highly ionized atoms of iron and calcium. Specific models are
adopted, the time-dependent equations for ion abundances are solved
numerically, and X-ray line intensities and line ratios are computed
and averaged over the effective time of a single burst. The computed
results are compared to observed variations for a number of different
line ratios. Although the behavior of certain line ratios can be
explained in the context of the burst models considered in this paper,
the behavior of the set of all the available line ratios cannot be
explained in this manner. The observed departures of line ratios from
equilibrium values that can be explained in terms of a burst scenario
can also be accounted for by uncertainties in the atomic physics.
Title: The effects of a multidensity plasma on ultraviolet
spectroscopic electron density diagnostics
Authors: Doschek, G. A.
Bibcode: 1984ApJ...279..446D
Altcode:
Spectroscopic electron density diagnostics have been developed for
interpretation of UV, EUV, and X-ray emission line spectra of solar
and other astrophysical plasmas, and tokamak plasmas. In principle,
accurate electron densities can be determined. However, in practice,
a number of difficulties arise with respect to the determination of
very accurate electron densities in the 1100-3000 A region. The present
study has the objective to investigate one of these difficulties, taking
into account the effect on line ratios produced by a source composed of
several regions of substantially different densities, all at the same
temperature. The study is in particular concerned with a source in which
small high density knots are embedded in low-density plasma. Attention
is given to line ratios involving the O IV multiplet near 1400 A,
obtained from the spectrum of a surge observed outside the solar limb.
Title: X-Ray Spectroscopy of Solar Flares
Authors: Doschek, G. A.
Bibcode: 1984BAAS...16R.483D
Altcode:
No abstract at ADS
Title: On the rate of energy input in thermal solar flares
Authors: Feldman, U.; Doschek, G. A.; McKenzie, D. L.
Bibcode: 1984ApJ...276L..53F
Altcode:
The rise phases of solar soft X-ray flares observed by X-ray crystal
spectrometers on P78-1 are discussed in terms of the rate of change of
X-ray flux as a function of time. It is shown that the flux increases
exponentially over most of the rise time. The e-folding time (tau) has
a cutoff at approximately 13 s. Soft X-ray flares with smaller values
of tau are not observed. It is suggested that this phenomenon is due
to the ability of the solar atmosphere to absorb the input energy and
convert it into a typical soft X-ray flare, when the value of tau is
greater than about 13 s. For energy input rates with tau greater than
about 13 s, the temperature attained by the plasma is typically around
2 x 10 to the 7th K, but for values of tau less than 13 s, the gas is
heated to much higher temperatures (about 10 to the 8th K), producing
a certain class of hard X-ray flares.
Title: Measurement of Wavelengths and Abundances from Solar Flare
X-Ray Spectra
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.
Bibcode: 1984uxsa.coll..151S
Altcode: 1984IAUCo..86..151S; 1984uxsa.conf..151S
No abstract at ADS
Title: Ultraviolet and x-ray spectroscopy of astrophysical and
laboratory plasmas
Authors: Doschek, G. A.
Bibcode: 1984uxsa.coll.....D
Altcode: 1984IAUCo..86......
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: On the rate of energy input in thermal solar flares
Authors: Feldman, U.; Doschek, G. A.; McKenzie, D. L.
Bibcode: 1983STIN...8423548F
Altcode:
The rise phases of solar soft X-ray flares observed by X-ray crystal
spectrometers on p78-1 are discussed in terms of the rate of change of
X-ray flux as a function of time. It is shown that the flux increased
exponentially over most of the rise time. The e-folding time TAU has a
cut-off at 13 s. Soft X-ray flares with smaller values of TAU are not
observed. It is suggested that this phenomenon is due to the ability
of the solar atmosphere to absorb the input energy and convert it into
a typical soft X-ray flare. For energy input rates that are below
a certain critical value the temperature attained by the plasma is
around 20,000,000 K, but for values above the critical value, the
gas is heated to much higher temperatures Te > or =
10 to the 8th K, producing a certain class of hard X-ray events.
Title: SI III line ratios in the Sun.
Authors: Dufton, P. L.; Hibbert, A.; Kingston, A. E.; Doschek, G. A.
Bibcode: 1983ApJ...274..420D
Altcode:
New atomic data for Si III have been used to predict level populations
and emission-line intensity ratios for electron densities and
temperatures appropriate to the solar transition region. The electron
impact collision rates used here are substantially larger than those
previously published owing to delineation of the complex resonance
structures in the low-energy collision strengths. This together with
small changes in the spontaneous radiative rates produces significant
changes in the calculated intensity ratios. Generally good agreement is
found with observations obtained using the Naval Research Laboratory
slit spectrograph aboard Skylab, electron densities from three Si III
ratios and from other methods normally agreeing to 0.2 dex or better for
a wide variety of solar features. For a fourth ratio, incorporating
lines with a wide wavelength separation, the agreement is less
satisfactory, possibly owing to uncertainties in the observational data.
Title: Lines of Fe XII sensitive to coronal electron density
Authors: Feldman, U.; Doschek, G. A.; Cohen, L.
Bibcode: 1983ApJ...273..822F
Altcode:
Lines of Fe XII sensitive to coronal electron density are discussed. The
lines appear in solar spectra obtained by the Naval Research
Laboratory (NRL) slit spectograph flown on Skylab. These lines are
due to transitions between levels of the 3s 2 3p 3 configuration and
fall at the wavelengths 1242.03 A, 1349.38 A, 2169.03 A, 2405.71 A,
and 2565.99 A. It is shown that the line at 2169.03 A is severely
blended by a line of Ni II at heights less than 12 arcsec outside the
solar limb. Above 12 arcsec the lines at 2169.03 and 2405.71 A are
apparently unblended and can be used to derive electron densities. An
average coronal electron pressure of 6 x 10 to the 14th/cu cm K is
obtained. However, the emitting path lengths of the Fe XII lines,
deduced using the electron densities and absolute intensities, are
unrealistically large. The reason for this difficulty is unclear.
Title: A Solar X-ray Spectral Line List Modified for Application to
X-ray Astronomy
Authors: Doschek, G. A.; Cowan, R. D.
Bibcode: 1983BAAS...15R1002D
Altcode:
No abstract at ADS
Title: Mass Transport and the Interaction of Loops
Authors: Doschek, G.
Bibcode: 1983SoPh...86..454D
Altcode:
No abstract at ADS
Title: Solar Flare X-Ray Spectra from the P78 - 1 Spacecraft
Authors: Doschek, G. A.
Bibcode: 1983SoPh...86...49D
Altcode:
Results from the high resolution solar X-ray spectrometer experiments
on the P78-1 spacecraft are discussed. These results concern physical
quantities such as electron temperature and density, turbulence, mass
motions, and state of ionization equilibrium, characteristic of the
thermal soft X-ray emitting flare plasma, and the time behavior of
these quantities during flares. In addition, a brief description of
the instruments is given, the plasma diagnostics used in interpreting
the spectra are summarized, and the origin of the thermal soft X-ray
emitting plasma is discussed in light of the P78-1 results, earlier
data, and numerical simulations of magnetic flux tubes heated to solar
flare temperatures.
Title: Solar instruments on the P78-1 spacecraft.
Authors: Doschek, G. A.
Bibcode: 1983SoPh...86....9D
Altcode:
The solar experiment package on the P78-1 spacecraft is described. The
satellite was launched on 24 February 1979 by the U.S. Air Force
and contains high resolution Bragg crystal spectrometers, hard
X-ray proportional counters, and a white light coronagraph. The high
resolution spectrometers were built by the Aerospace Corporation and the
Naval Research Laboratory. The hard X-ray spectrometers were built by
the Aerospace Corporation and the white light coronagraph was supplied
by the Naval Research Laboratory. Most of these instruments are still
returning data.
Title: Numerical Simulations of Solar Flare Hydrodynamics:
Asymmetrical Heatings
Authors: Cheng, C. C.; Karpen, J. T.; Doschek, G. A.; Boris, J. P.
Bibcode: 1983BAAS...15Q.708C
Altcode:
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: Numerical simulations of loops heated to solar flare
temperatures. I
Authors: Cheng, C. -C.; Oran, E. S.; Doschek, G. A.; Boris, J. P.;
Mariska, J. T.
Bibcode: 1983ApJ...265.1090C
Altcode:
The NRL's Dynamic Flux Tube Model is used to numerically simulate
the dynamic response of a coronal magnetic loop to an energy input of
the order encountered in solar flares. The coronal plasma is heated
by the deposition of flare energy at the top of the loop to more
than 10 million K, yielding a conduction front that moves toward
the chromosphere, where the plasma is heated by the large downward
conductive flux and ablates upward to the coronal part of the loop at
velocities of a few hundred km/sec. The conduction front simultaneously
produces chromospheric ablation and compresses the material ahead of
it. With the aid of compressional instabilities, the compressed plasma
grows throughout the flare heating phase, presenting a possible source
of the flare optical continuum emission which is correlated with soft
X-ray radiation. The observational consequences of rapidly heated
loop gas dynamic processes are discussed. In the second part of this
presentation, the dynamical calculation results previously obtained are
used to predict the spectral line intensities, profiles and wavelengths
of several X-ray lines and the UV line of Fe XXI at 1354.1 A. Three
different viewing orientations of the loop are considered.
Title: Numerical Simulations of Loops Heated to Solar Flare
Temperatures - Part Two - X-Ray and Ultraviolet Spectroscopy
Authors: Doschek, G. A.; Cheng, C. C.; Oran, E. S.; Boris, J. P.;
Mariska, J. T.
Bibcode: 1983ApJ...265.1103D
Altcode:
In the first paper in this series, numerical simulation techniques
were used to investigate the fluid dynamics of plasma that is confined
to a magnetic flux tube and is heated to solar flare temperatures of
about 2 × 107 K. The temperature, density, and velocity
of the plasma were derived as functions of position and time in the
flux tube or loop, after deposition of flare energy at the top of the
loop. In this paper the results of the dynamical calculations described
in the first paper in this series are used to predict the spectral
line intensities, profiles, and wavelengths of several X-ray lines
and the UV line of Fe XXI at 1354.1 Å. The distribution of emission
from these lines within the loop is computed, as well as the profiles
of the lines that would be recorded by a spectrometer that viewed
the entire loop. Three different viewing orientations of the loop are
considered. The computed spectra are compared with recent observations
obtained from orbiting spacecraft. The computed differential emission
measure is flatter than observed, and this result is similar to previous
analytical and numerical calculations. The computed X-ray profiles
of Fe xxv and Ca xix lines show a stationary component, i.e., no shift
in wavelength due to the Doppler effect, and shifted components produced
by ablated chromospheric plasma. These profiles qualitatively resemble
some of the X-ray observations. A large Doppler shift of about 0.7
Å is predicted for the Fe XXI line. Such a shift is unobserved in
spectra obtained from the Naval Research Laboratory spectrograph on
Skylab. Physically different flare models can apparently produce
markedly different spectroscopic results. Differences between computed
and observed spectra suggest modifications of the model that might
produce better agreement between these quantities and hence result in
a better understanding of flare morphology and heating mechanisms.
Title: The Best Possible UV Line List from RR TEL
Authors: Doschek, George A.
Bibcode: 1983iue..prop.1428D
Altcode:
The object of this proposal is to obtain the best possible high
dispersion spectra of the slow nova RR Tel. This strong emission line
source can provide an excellent line-list for UV astronomy, which may
also have important implications for atomic physics. Since the longest
current exposures are only 3 hours, there is scope for a considerably
deeper study.
Title: High-resolution X-ray spectra of solar flares. VI - Impulsive
soft X-ray flares
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
Bibcode: 1982ApJ...260..885F
Altcode:
Doschek et al. (1980) and Feldman et al. (1980) have discussed
high-resolution soft X-ray spectra of solar flares. The present
investigation is concerned with the characteristics of the impulsive
events as observed in soft X rays and the cooling of the flare plasma in
terms of energy loss processes. A class of intense, short-lived solar
flares which appear to be characterized by very high densities at high
temperatures is found. For the 1979 November 6 event, the cooling time
is so rapid that the density obtained may be a lower limit. The main
cooling mechanism for the flares is found to be radiative. Two of the
events are associated with strong gamma-ray emission and both of these
events are very unusual in their soft X-ray emission. The 1979 November
9 flare shows extremely broad X-ray emission lines during the rise
phase, indicative of nonthermal velocities of the order of 300 km/s.
Title: A Numerical Simulation of Cooling Coronal Flare Plasma
Authors: Doschek, G. A.; Boris, J. P.; Cheng, C. C.; Mariska, J. T.;
Oran, E. S.
Bibcode: 1982ApJ...258..373D
Altcode:
We have simulated the cooling of coronal flare plasma (Te
> 107 K) using a numerical model of a vertical magnetic
flux tube containing an idealized flare chromosphere, transition region,
and corona. The model solves the set of one-dimensional, two-fluid
hydrodynamic equations. The cooling of the flux tube is calculated for
a specific case beginning with an initial atmosphere in hydrostatic
equilibrium and a maximum temperature of about 18 × 106
K. The behavior of temperature, density, and velocity is calculated as
a function of height as the system cools. Early in the cooling, energy
is transported by conduction into the transition region and chromosphere
where it is radiated away. Later, the transition region-corona interface
moves upward into the tube at velocities of about 20 km s-1,
while the chromosphere cools and the coronal component cools by both
conduction and radiation. Coronal downflow velocities of about 60 km
s-1 are evident during this phase. The expected spectral
line emission from the system in X-ray lines of Fe XXV, Fe XXIV,
Fe XXII, O VIII, and O VII is also calculated and compared to recent
observational results. Some observational results can be explained
as a consequence of simple cooling of flare flux tubes. The expected
spectral line emission from certain transition region lines is also
briefly considered. The dependence of our results on flare size is
discussed, and our results are compared with similar previous work.
Title: S IV emission-line ratios in the sun
Authors: Dufton, P. L.; Hibbert, A.; Kingston, A. E.; Doschek, G. A.
Bibcode: 1982ApJ...257..338D
Altcode:
New atomic data are presented for transitions between the five lowest
levels in S IV, taking into account the fine-structure rates between
the individual J levels together with the electron impact mixing
rates within the levels. The values are found to differ significantly
from previously published values. Using the atomic data, ionic level
populations are deduced for a range of electron temperatures and
densities. The results are used to calculate theoretical line intensity
ratios for S IV. Excellent agreement is found with intensity ratios
for a variety of solar features observed with the NRL normal incidence
spectrograph on Skylab.
Title: Observational constraints for a theoretical model describing
the soft X-ray flare
Authors: Feldman, U.; Cheng, C. -C.; Doschek, G. A.
Bibcode: 1982ApJ...255..320F
Altcode:
High-resolution solar flare X-ray spectra have recently been obtained
from X-ray spectrometer experiments flown on an Air Force spacecraft
(P78-1) launched on 1979 February 24. Interpretation of the spectra
has produced new results concerning the physical conditions and time
behavior of the thermal soft X-ray emitting plasma at temperatures
near 20,000,000 K. It is argued that soft and hard X-ray events
are not causally related to each other, but are simply two different
manifestations of flare energy release. They probably occur in different
plasma volumes. The source of the preflare plasma appears to be in the
cooler parts of the solar atmosphere, perhaps transition region loops
with initial temperatures of 100,000 K and densities of 10 to the 11th
per cu cm. Continuous energy input, rather than sequential activation
of loops, is required to explain the observations. Compression coupled
with chromospheric ablation may produce the high densities in coronal
flare loops.
Title: Solar transition region response to variations in the
heating rate
Authors: Mariska, J. T.; Doschek, G. A.; Boris, J. P.; Oran, E. S.;
Young, T. R., Jr.
Bibcode: 1982ApJ...255..783M
Altcode:
The response of a numerical model for the upper chromosphere,
transition region, and corona to variations in the energy input has
been examined. The numerical model solves the set of one-dimensional
two-fluid hydrodynamic equations in a simple vertical magnetic flux
tube. The atmosphere responds to both the increase and decrease in
energy deposition by smoothly readjusting the temperature gradient and
the amount of material in the region of peak radiating efficiency to
radiate away energy being deposited. At no time during this readjustment
is a departure from a thin laminar transition region structure seen. In
addition, a time-dependent description of the nonequilibrium ionization
of all of the ionization stages of oxygen has been included. This
calculation is coupled with the self-consistent calculations of the
dynamical variables. It is found that the nonequilibrium ionization
balance calculations for both heating and cooling small loops in the
quiet sun predict relative ionic abundances which differ substantially
from those which would be predicted by an equilibrium calculation
Title: Doppler wavelength shifts of ultraviolet spectral lines in
solar active regions
Authors: Feldman, U.; Doschek, G. A.; Cohen, L.
Bibcode: 1982ApJ...255..325F
Altcode:
Doppler shifts are measured for solar UV emission lines formed in the
lower transition region of active regions. Doppler shifts in different
regions at the same solar location, variations of Doppler shift with
position of an active region on the disk, and variations of Doppler
shift with time at the same solar location in the same active region
were studied. Observations were made with the NRL slit spectrograph on
Skylab. Excluding flare and flare-related phenomena, only redshifts
are found whose magnitudes correspond to downflow velocities between
about 4 and 17 km/s. Shifts are largest for lines formed between about
50,000 and 100,000 K, and are distinctly less for lines formed above
100,000 K. The shifts persist out to the limb, but not above it. There
is no obvious change in redshift for lines measured at the same solar
location over time intervals of about 20 minutes.
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: Ultraviolet continuum absorption /less than about 1000 A/
above the quiet sun transition region
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1982ApJ...254..371D
Altcode:
Lyman continuum absorption shortward of 912 A in the quiet sun solar
transition region is investigated by combining spectra obtained from
the Apollo Telescope Mount experiments on Skylab. The most recent
atomic data are used to compute line intensities for lines that fall
on both sides of the Lyman limit. Lines of O III, O IV, O V, and S
IV are considered. The computed intensity ratios of most lines from
O IV, O V, and S IV agree with the experimental ratios to within a
factor of 2. However, the discrepancies show no apparent wavelength
dependence. From this fact, it is concluded that at least part of the
discrepancy between theory and observation for lines of these ions
can be accounted for by uncertainties in instrumental calibration and
atomic data. However, difficulties remain in reconciling observation
and theory, particularly for lines of O III, and one line of S IV. The
other recent results of Schmahl and Orrall (1979) are also discussed
in terms of newer atomic data.
Title: Electron densities in a solar flare derived from X-ray spectra
Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge,
H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1982STIN...8325647M
Altcode:
A major solar flare was observed with the RAP crystal of the SOLEX
B spectrometer. The spectra were obtained by scanning back and forth
between Bragg angles of 17.4 deg and 61.7 deg (7.8 to 23 A) at a rate of
0.525 degrees-.15. A full scan took 84.5 sec. A line list identifying
more than 100 lines observed in this flare was compiled. Measurements
of the density sensitive O 7 lines near 22 A are discussed.
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: Solar Flare X-Ray Spectra from the P78-1 Spacecraft.
Authors: Doschek, G. A.
Bibcode: 1982uxsa.coll....2D
Altcode: 1982IAUCo..73....2D
No abstract at ADS
Title: Solar observations and atomic data for the 3s2 1s0-3s3p 3P1
transition in S V
Authors: Feldman, U.; Doschek, G. A.; Bhatia, A. K.
Bibcode: 1981ApJ...250..799F
Altcode:
High resolution solar observations of the S v intersystem line at
1199.18 A are available from Skylab. This line is potentially useful
as a density diagnostic for high density plasmas expected in solar
flares. S v lines are also prominent in solar spectra at wavelengths
below 1000 A. Collision strengths and radiative decay rates are
calculated for levels of the configurations 3 s2, 3s3p, 3p2, and
3s3d. Level populations for the five lowest energy levels have been
calculated as a function of electron density. These calculations are
carried out assuming the temperature at which S v is most abundant
in solar plasmas. The calculated population of the 3s3p 3P1 level
reaches a pseudo-Boltzmann equilibrium at a density which is about
five times higher than is derived from solar spectra and previous
density determinations. It is believed that the discrepancy is due
to a significant contribution from resonances to the 3s2-3s3p 3P
excitation rate coefficient. It is suggested that the contribution of
the resonances to the S v excitation rate coefficient can be estimated
from a comparison of the experimental results and the theoretical
calculations.
Title: High resolution solar flare X-ray spectra - The temporal
behavior of electron density, temperature, and emission measure for
two class M flares
Authors: Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L.
Bibcode: 1981ApJ...249..372D
Altcode:
High resolution soft X-ray flare spectra recorded by Naval Research
Laboratory (NRL) and Aerospace Corporation Bragg crystal spectrometers
flown on an orbiting spacecraft (P78-1) are combined and analyzed. The
instruments were launched on t979 February 24 by the U.S. Air Force,
and the data discussed in this paper cover the wavelength ranges,
1.82-1.97 Å, 3.143.24 Å, and 18.423.0 Å. The NRL experiment (SOLFLEX)
covers the two short wavelength ranges (highly ionized Fe and Ca lines)
and the Aerospace experiment (SOLEX) covers the t8.4-23.O Å range,
which includes the Lyα O VIII line and the resonance, intercombination,
and forbidden lines of O VII. We analyze the spectra of two flares which
occurred on 1980 April 8 and May 9. Temporal coverage is fairly complete
for both flares, including the rise and decay phases. Measurements of
electron density Ne with rather high time resolution (about
1 minute) have been obtained throughout most of the lifetimes of the
two flares. These measurements were obtained from the O VII lines and
pertain to flare plasma at temperatures near 2 × 106 K. Peak
density seems to occur slightly before the times of peak X-ray flux in
the resonance lines of Fe XXV, Ca XIX, and O VII, and for both flares
the peak density is about 1012 cm-3. Electron
temperature Te as a function of time is determined from
the Fe and Ca spectra. Peak temperature for both flares is about 18 ×
106 K. Differential emission measures and volume emission
measures are determined from the resonance lines of O VII, Ca XIX,
and Fe XXV. The number of electrons NeΔV and the volume
ΔV over which the O VII lines are formed are determined from the
O VII volume emission measure Ne2ΔV and the
density Ne. These quantities are determined as a function
of time. The relationship of the low and high temperature regions
is discussed.
Title: A discussion of theoretical ionization equilibrium calculations
based on solar flare X-ray spectra
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.
Bibcode: 1981MNRAS.196..517F
Altcode:
Several sets of ionization equilibrium calculations exist for use
in interpreting X-ray and EUV spectra of astrophysical plasmas. In
particular, the calculations of Jordan (1969, 1970), Jacobs et
al. (1977, 1978) and Summers (1974) are well known. The temperatures
of maximum fractional abundance calculated by Summers for the more
highly ionized and heavier elements such as iron are about a factor
of two higher than the temperatures calculated by Jordan and Jacobs
et al. By the use of recently obtained X-ray spectra of solar flares,
it is shown that the temperatures calculated by Summers (1974) for
iron are incorrect. The temperatures calculated by Jordan or Jacobs
et al. should be used until further improvements become available.
Title: High resolution solar flare X-ray spectra: The temporal
behavior of electron density, temperature, and emission measure for
two class M flares
Authors: Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L.
Bibcode: 1981STIN...8225073D
Altcode:
High resolution soft X-ray flare spectra recorded by crystal
spectrometers flown on an orbiting spacecraft (P78-1) are combined
and analyzed. The spectra of two flares are analyzed. Temporal
coverage for both flares, including the rise and decay phases, is
discussed. Measurements of electron density were obtained throughout
most of the lifetimes of the two flares. Electron temperature as a
function of time is determined from the Fe and Ca spectra. Differential
emission measures and volume emission measures are determined for the
low and high temperature (Fe, Ca) plasma. The relationship of the low
and high temperature regions is discussed.
Title: On the relationship between soft X-rays and H-alpha-emitting
structures during a solar flare
Authors: Zirin, H.; Feldman, U.; Doschek, G. A.; Kane, S.
Bibcode: 1981ApJ...246..321Z
Altcode:
Based on data obtained during a solar flare on March 31, 1979, soft
X-ray (SXR) and hard X-ray (HXR) bursts are analyzed and compared with
other available data in order to identify structures in H-alpha that
may correspond to the SXR-emitting site. Measurements taken with the
X-ray telescope and the XUV spectroheliograph flown on Skylab, have
shown that the SXR emission from many flares comes from rather small
structures of about 10-20 arcsec across. These structures appear to
be loops that cross the magnetic neutral line. Understanding of the
morphology of SXR was based on data of the solar flare of June 15, 1973,
observed from Skylab, and the work of Moore et al., (1980). Dense,
highly emissive coronal structures, not suggested to be the X-ray
source, were forming, lost energy rapidly by emission and conduction,
and finally formed the loops. It is concluded that bright H-alpha
loops form rapidly as the SXR emission rises, and the overall decay
(cooling rate) of SXR emission is much slower than the formation time
of individual loops.
Title: High resolution X-ray spectra of solar flares. V -
Interpretation of inner-shell transitions in Fe XX-Fe XXIII
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.
Bibcode: 1981ApJ...245..315D
Altcode:
The paper examines high-resolution solar flare iron line spectra
recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval
Research Laboratory on an Air Force spacecraft launched on 1979 February
24. The emission line spectrum is due to inner-shell transitions in the
ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line
intensities obtained by methods discussed by Merts, Cowan, and Magee
(1976), electron temperatures as a function of time for two large class
X flares are derived. These temperatures are deduced from intensities
of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the
differential emission measure between about 12-million and 20-million K
using these temperatures is considered. The possibility of determining
electron densities in flare and tokamak plasmas using the inner-shell
spectra of Fe XXI and Fe XX is discussed.
Title: Mass motions in optically thin solar transition zone lines
Authors: Doschek, G. A.; Mariska, John T.; Feldman, U.
Bibcode: 1981MNRAS.195..107D
Altcode:
The widths of optically thin EUV spectral lines formed at temperatures
between ≃ 3 × 104 and 2 × 105 K in the
solar transition zone are larger than expected assuming ionization
equilibrium. This result has been interpreted as due to non-thermal
mass motions, characterized by a parameter ξ(km s-1) In
this paper we discuss observations of spectral line recorded mostly at
+2 arcsec outside the limb of the north and south polar coronal holes,
and compare the derived values of ξ to values deduced from spectra of
quiet Sun regions. These spectra were recorded by the NRL spectrograph
on Skylab (1100-2000 Å). Systematic differences in line widths between
coronal holes and quiet Sun region spectra are probably no larger than
0.01 Å, for the optically thin lines used in the analysis. -sight
path lengths of the emitting plasma at 2 arc sec above the limb are
calculated from the intensity ratios of optically thick lines of C IV,
N V, Al III, and Si IV. These ratios should be 2:1 in the optically thin
limit, but they are around 1.5 at 2 arcsec above the solar limb. The
derived path lengths range from ≃1000 to 5000km.
Title: What produces the high densities observed in solar flare
plasmas
Authors: Cheng, C. -C.; Feldman, U.; Doschek, G. A.
Bibcode: 1981A&A....97..210C
Altcode:
Attention is drawn to the implications of the high densities observed in
flare plasmas in the wide temperature range from 10 to the 4th K to more
than 10 to the 7th K. The chromospheric evaporation theory for the decay
phase is discussed, and it is found that it is not consistent with the
observations. It is pointed out that all the flare mechanisms proposed
so far, e.g., magnetic field reconnection in various geometries, have
entirely ignored the fundamental problem of how the high densities
arise in the first place, and, in fact, they are unable to answer this
question. It is suggested that compressional heatings of a flaring loop
might be responsible for the density and emission measure (EM) increases
observed in flare plasmas. Chromospheric evaporation associated with
local heating in the initial rising phase of the flare, in distinction
to the existing evaporation theory which assumes a coronal heating
source, is also discussed. Possible observational tests, utilizing
the newly launched Solar Maximum Mission (SMM) satellite, are presented.
Title: Solar flare X-ray spectra between 7.8 and 23.0 angstroms
Authors: McKenzie, D. L.; Landecker, P. B.; Broussard, R. M.; Rugge,
H. R.; Young, R. M.; Feldman, U.; Doschek, G. A.
Bibcode: 1981STIN...8225072M
Altcode:
High resolution X-ray spectra taken during a large solar flare on
10 June 1979 are presented. Many lines of highly ionized iron were
resolved and identified for the first time in solar spectra. Lines
with a wide range of excitation temperatures are found to have a
similar time development during the flare's rapid rise phase. The
density-sensitive line ratios in Fe(XXI) and Fe(XXII) are discussed.
Title: The Dynamics of Coronal Flare Loops: II. Comparison to
Observations
Authors: Doschek, G. A.; Cheng, C. -C.; Boris, J. P.; Mariska, J. T.;
Oran, E. S.
Bibcode: 1981BAAS...13..819D
Altcode:
No abstract at ADS
Title: The Dynamics of Coronal Flare Loops: I. Gasdynamics
Authors: Cheng, C. -C.; Doschek, G. A.; Boris, J. P.; Mariska, J. T.;
Oran, E. S.
Bibcode: 1981BAAS...13Q.819C
Altcode:
No abstract at ADS
Title: Solar Transition Region Response to Heating Rate Variations
Authors: Oran, E. S.; Mariska, J. T.; Boris, J. P.; Young, T. R.;
Doschek, G. A.
Bibcode: 1981BAAS...13..836O
Altcode:
No abstract at ADS
Title: The detection of companion stars to the Cepheid variables
Eta Aquilae and T Monocerotis.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1981NASCP2171..209M
Altcode: 1981NASCP3171..209M; 1980IUE80......209M; 1981uviu.nasa..209M
Ultraviolet spectra of the classical Cepheid variables eta Aq1
and T Mon at several phases in their periods were obtained with
IUE. For eta Aq1 significant ultraviolet emission is detected at
wavelengths less than 1600 A, where little flux is expected from
classical Cepheids. Furthermore, the emission at wavelengths less
than about 1600 A does not vary with phase. Comparison with model
atmosphere flux distributions shows that the nonvariable emission is
consistent with the flux expected from a main sequence companion star
with an effective temperature of about 9500 K (AO V - A1 V). For T Mon
a nonvarying component to the ultraviolet emission is observed for
wavelengths less than 2600 A. Comparison with model atmosphere flux
distributions suggests that the companion has an effective temperature
of around 10,000 K (AO) and is near the main sequence.
Title: The detection of a companion star to the Cepheid variable
T Monocerotis
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...242.1083M
Altcode:
We have obtained ultraviolet spectra with the International Ultraviolet
Explorer (IUE) spacecraft of the classical Cepheid T Mon at several
phases in the 27 day period. Significant ultraviolet emission is
detected at wavelengths less than 1600 A, where little flux is expected
from classical Cepheids. Furthermore, the emission at wavelengths
less than about 1900 A does not vary with phase. Comparison with model
atmosphere flux distributions shows that the emission is consistent with
the flux expected from a companion star with an effective temperature
of about 10,000 K (approximately A0) near the main sequence.
Title: High-resolution X-ray spectra of solar flares. IV - General
spectral properties of M type flares
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.; Mariska, J. T.
Bibcode: 1980ApJ...241.1175F
Altcode:
The spectral characteristics in selected narrow regions of the X-ray
spectrum of class M solar flares are analyzed. High-resolution spectra
in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which
contain lines important for the determination of electron temperature
and departure from ionization equilibrium, were recorded by spaceborne
Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are
obtained from line ratios during flare rise phases in M as well as X
flares, while in the decay phase the calcium temperature can be as low
as 8,000,000 K, which is significantly lower than in X flares. Large
nonthermal motions (on the order of 130 km/sec at most) are also
observed in M as well as X flares, which are largest during the soft
X-ray rise phase. Finally, it is shown that the method proposed by
Gabriel and Phillips (1979) for detecting departures of electrons
from Maxwellian velocity distributions is not sufficiently sensitive
to give reliable results for the present data.
Title: Solar flare X-ray spectra between 7.8 and 23.0 Angstroms.
Authors: McKenzie, D. L.; Landecker, P. B.; Broussard, R. M.; Rugge,
H. R.; Young, R. M.; Feldman, U.; Doschek, G. A.
Bibcode: 1980ApJ...241..409M
Altcode:
The high-resolution X-ray spectra taken during a large solar flare
on 1979 June 10 are presented. Many lines of highly ionized iron are
resolved and identified for the first time in solar spectra. Lines with
a wide range of excitation temperatures have similar time development
during the flare's rapid rise phase. The density sensitive line ratios
in Fe XXI and Fe XXII are discussed.
Title: Numerical Simulation of a Cooling Flare Loop for Application
to X-Ray Flare Spectra
Authors: Doschek, G. A.; Boris, J. P.; Mariska, J. T.; Oran, E. S.
Bibcode: 1980BAAS...12..912D
Altcode:
No abstract at ADS
Title: A Dynamic Flux-Tube Model for Compressible MHD Processes in
the Solar Atmosphere
Authors: Boris, J. P.; Mariska, J. T.; Book, D. L.; Oran, E. S.;
Young, T.; Doschek, G. A.
Bibcode: 1980BAAS...12..908B
Altcode:
No abstract at ADS
Title: Condensational Instability in Coronal Plasmas
Authors: Oran, E. S.; Boris, J. P.; Mariska, J. T.; Doschek, G. A.
Bibcode: 1980BAAS...12..910O
Altcode:
No abstract at ADS
Title: Simultaneous Observations of Solar Flares Obtained by the
SOLEX AND SOLFLEX High Resolution X-Ray Spectrometers
Authors: Landecker, P. B.; McKenzie, D. L.; Doschek, G. A.; Feldman, U.
Bibcode: 1980BAAS...12Q.906L
Altcode:
No abstract at ADS
Title: Some Aspects of Transition Zone Dynamics
Authors: Mariska, J. T.; Boris, J. P.; Oran, E. S.; Doschek, G. A.
Bibcode: 1980BAAS...12..908M
Altcode:
No abstract at ADS
Title: Physical conditions in the solar atmosphere above an active
region
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1980ApJ...240..300M
Altcode:
From a series of EUV spectra obtained at several heights above the
limb in a solar active region, the volume emission measure is derived
as a function of the electron temperature in the temperature range
70,000-1,500,000 K and the electron density at two locations. The
emission measure from the coronal material (temperature greater than
700,000 K) is nearly the same everywhere and represents most of the
material in the line of sight, while the emission measure from the
transition region material (temperature between 70,000 and 250,000
K) fluctuates by two orders of magnitude from position to position
above the active region. This is in agreement with the picture of
this active region as consisting of a number of well-defined loops
or lower portions of loops at transition region temperatures that
are inhomogeneously distributed in much larger and more diffuse loop
structures at coronal temperatures. The coronal data are in reasonable
agreement with simple coronal models. Emission measures near 1,000,000
K evaluated using different ions differ by a factor of 4, suggesting
difficulties with the atomic physics data.
Title: High-resolution X-ray spectra of solar flares. III - General
spectral properties of X1-X5 type flares
Authors: Doschek, G. A.; Feldman, U.; Kreplin, R. W.; Cohen, L.
Bibcode: 1980ApJ...239..725D
Altcode:
High-resolution X-ray spectra of six class X1-X5 solar flares are
discussed. The spectra were recorded by spaceborne Bragg crystal
spectrometers in the ranges 1.82-1.97, 2.98-3.07 and 3.14-3.24
A. Electron temperatures derived from dielectronic satellite line to
resonance line ratios for Fe XXV and Ca XIX are found to remain fairly
constant around 22,000,000 and 16,000,000 K respectively during the
rise phase of the flares, then decrease by approximately 6,000,000 K
during the decay phase. Nonthermal motions derived from line widths
for the April 27, 1979 event are found to be greatest during the rise
phase (approximately 130 km/sec) and decrease to about 60 km/sec during
decay. Volume emission measures for Fe XXV, Ca XIX and Ca XX are derived
from photon fluxes as a function of temperature, and examination of the
intensity behavior of the Fe K alpha emission as a function of time
indicates that it is a result of fluorescence. Differences between
the present and previous observations of temperature variation are
discussed, and it is concluded that the flare plasmas are close to
ionization equilibrium for the flares investigated.
Title: Atomic data for S IV and solar observations of the 3x/2/3p
/2/P-3s3p/2/ /4/P multiplet
Authors: Bhatia, A. K.; Doschek, G. A.; Feldman, U.
Bibcode: 1980A&A....86...32B
Altcode:
High resolution observations of intersystem lines of S IV near 1400
A are available from Skylab. These lines are potentially useful
as density diagnostics for the solar atmosphere. Energy levels,
transition probabilities and collision strengths have, therefore, been
calculated for S IV, including the configurations 3x(2)3p, 3s3p(2), and
3s(2)3d. Line intensities and level populations have been calculated as
a function of electron density. The calculated population of the 3s3p(2)
(4)P(5/2) level is found to reach a pseudo-Boltzmann equilibrium at a
density which is four times higher than is inferred from solar spectra
and level population calculations of lighter ions such as O IV.
Title: Observations of the O I 1355.6 A and C I 1355.8 A lines in
solar flares
Authors: Cheng, C. C.; Feldman, U.; Doschek, G. A.
Bibcode: 1980A&A....86..377C
Altcode:
The paper presents observations of the intersystem line O I 1355.6
A and the allowed line C I 1355.8 A in solar flares. In flares,
the intersystem O I line is weaker than the allowed C I line and
the intensity ratio O I/C I is 0.3-0.7. On the other hand, in active
regions, O I line is stronger than the C I line and O I/C I is about
1-2, while in quiet sun regions, the O I line is much stronger than
the C I line and O I/C I not in excess of 20. The variation of the
intensity ratio from quiet sun region to flares may be due to an
electron density enhancement of a factor of about 50 in flares.
Title: The detection of a companion star to the Cepheid variable
eta Aql.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...238L..87M
Altcode:
Ultraviolet spectra have been obtained with IUE of the classical Cepheid
Eta Aquilae at several phases in the 7.18 day period. Significant
ultraviolet emission is detected at wavelengths less than 1600 A,
where little flux is expected from classical Cepheids. Furthermore,
the emission at wavelengths less than about 1600 A does not vary with
phase. Comparison with model atmosphere flux distributions shows that
the nonvariable emission is consistent with the flux expected from a
main-sequence companion star with an effective temperature of about
9500 K (A0 V). The observed ultraviolet flux and spectral type are
used to compute a distance of 300 pc to the system, in agreement with
the distance predicted using the period luminosity relation.
Title: High-resolution X-ray spectra of the 1979 March 25 solar flare
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
Bibcode: 1980ApJ...238..365F
Altcode:
High-resolution X-ray spectra of a solar flare that occurred on
1979 March 25 are discussed. The spectra were obtained from four
Bragg crystal spectrometers (SOLFLEX = solar flare X-rays) flown by
NRL on a spacecraft launched by the Air Force. The wavelength ranges
discussed here are: 1.82-1.97 A, 2.98-3.07 A, and 3.14-3.24 A. Electron
temperatures ranging between 12 x 10 to the 6th K and 30 x 10 to the 6th
K are derived from dielectronic satellite to resonance line ratios. The
apparent departure from ionization equilibrium indicated by intensities
of other satellite lines is discussed. Wavelengths and identifications
are given for the strongest lines observed. It is proposed that the
soft X-ray flare radiation is caused by the slow compression of a
single or multiple set of magnetic flux tubes. Experimental methods
of confirming or refuting this hypothesis are given.
Title: Electron densities in a solar flare derived from X-ray spectra
Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge,
H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...238L..43M
Altcode:
A major solar flare was observed with the rubidium acid phthalate
crystal of the satellite-borne SOLEX B spectrometer and high-resolution
solar X-ray spectra were obtained during the rising phase of the
flare. Measurements of the density-sensitive line ratio of the O
VII 1s2 1S(0) - 1s2s 3S(1) (22.10 A) flux to the O VII 1s2 1S(0) -
1s2p 3P(1) (21.80 A) flux indicate that the density of the plasma at
around 2,000,000 K exceeded 10 to the 11th per cu cm near the peak of
the flare. This corresponds to an electron pressure of about 30 dynes
per sq cm.
Title: Mass Motions in the Transition Zone of Coronal Holes
Authors: Doschek, G. A.; Mariska, J. T.; Feldman, U.
Bibcode: 1980BAAS...12S.518D
Altcode:
No abstract at ADS
Title: High Resolution Solar Flare X-ray Spectra
Authors: Doschek, G. A.; Kreplin, R. W.
Bibcode: 1980BAAS...12..529D
Altcode:
No abstract at ADS
Title: High resolution solar flare X-ray spectra.
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
Bibcode: 1980BAAS...12..529F
Altcode:
No abstract at ADS
Title: The Detection of an Early Type Companion Star to the Classical
Cepheid T Mon
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980BAAS...12Q.462M
Altcode:
No abstract at ADS
Title: The chromosphere and transition region
Authors: Canfield, R. C.; Brown, J. C.; Craig, I. J. D.; Brueckner,
G. E.; Cook, J. W.; Doschek, G. A.; Emslie, A. G.; Machado, M. E.;
Henoux, J. -C.; Lites, B. W.
Bibcode: 1980sfsl.work..231C
Altcode: 1980sofl.symp..231C
The physical processes occurring as a result of the transfer of
energy and momentum from the primary solar flare energy release site
in the corona to the underlying chromosphere and transition region
during the course of the flare are investigated through a comparison
of theoretical models and observational data. Static, dynamic and
hydrodynamic models of the lower-temperature chromospheric flare are
reviewed. The roles of thermal conduction, radiation, fast particles
and mass motion in chromosphere-corona interactions are analyzed on
the basis of Skylab UV, EUV and X-ray data, and empirical and synthetic
models of the chromospheric and upper photospheric responses to flares
are developed. The canonical model of chromospheric heating during
flares as a result of primary energy release elsewhere is found to be
justified in the chromosphere as a whole, although not entirely as the
temperature minimum, and a simplified model of horizontal chromospheric
flare structure based on results obtained is presented.
Title: The Detection of a Companion Star to the Cepheid Variable
Eta Aquilae
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11..687M
Altcode:
No abstract at ADS
Title: Solar Flare Electron Densities Derived from X-ray Spectra
Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge,
H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11..676M
Altcode:
No abstract at ADS
Title: SOLEX Solar Flare X-ray Spectra from 5 to 23 Å
Authors: Landecker, P. B.; McKenzie, D. L.; Broussard, R. M.; Rugge,
H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11Q.709L
Altcode:
No abstract at ADS
Title: New atomic data for Si/6+/, S/8+/ and Ar/10+/
Authors: Bhatia, A. K.; Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....80...22B
Altcode:
The paper gives new atomic data, populations of excited levels,
and line intensity ratios for the ions Si VII, S IX, and Ar XI
of the O I isoelectronic sequence. Ten levels are included in the
calculations, i.e., the levels of the 2s/2/2p/4/ and 2s2p/5/ and
2p/6/ configurations. It is noted that the calculations are done
for applications to solar plasmas. The line ratios (2s/2/2p/4/3P1
- 2s2p/5/3P0) / (2s/2/2p/4/3P1 - 2s2p/5/3P1) and (2s/2/2p/4/1D2 -
2s2p/5/1P/1/) / (2s/2/2p/4/3P/1/ - 2s1p/5/3P/1/) are two of the ratios
useful for electron density determination. Finally, density sensitive
line ratios of Ca XIII and Fe XIX are also discussed.
Title: The N III and O IV intersystem multiplets as density indicators
for solar plasmas.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....79..357F
Altcode:
The usefulness of the relative intensities of lines within the N III
intersystem multiplet near 1750 A as an electron density indicator for
solar plasmas is discussed. Although the relative intensities of lines
in the multiplet are density sensitive, the intensity ratios should at
present be used with caution. Errors of the order of 20% in transition
probabilities and excitation rate coefficients can lead to order of
magnitude errors in density determinations. It is demonstrated that the
intensity ratio of one of the N III intersystem lines and an allowed
line from a different ion may also be used as a density indicator in
the 10 to the 9th to 10 to the 11th per cu cm regime.
Title: High-resolution solar flare X-ray spectra.
Authors: Doschek, G. A.; Kreplin, R. W.; Feldman, U.
Bibcode: 1979ApJ...233L.157D
Altcode:
High-spectral-resolution solar flare spectra have been recorded
by four Bragg crystal spectrometers flown by the Naval Research
Laboratory on a spacecraft. The wavelength ranges are 1.82-1.97 A,
2.98-3.07 A, and 3.14-3.24 A. Electron temperatures ranging between
12 million and 30 million K are derived from dielectronic satellite
to resonance-line ratios for an X9 flare that occurred on March 25,
1979. Nonthermal motions varying between about 70 and 160 km/s are
derived from line profiles. Equilibrium conditions in the plasma are
investigated by using lithium-like satellite lines excited by electron
impact excitation. Emission measures of about 5 x 10 to the 50th per
cu cm are determined for the times of maximum X-ray flux.
Title: EUV limb spectra of a surge observed from Skylab.
Authors: Doschek, G. A.; Feldman, U.; Mason, H. E.
Bibcode: 1979A&A....78..342D
Altcode:
The EUV spectra of a surge observed at plus 8 in. and plus 20
in. above the white light limb from Skylab are examined. The shape of
the differential emission measure determined at 8 in. and 20 in. is
nearly the same as for a quiet Sun spectrum at 8 in., but the emission
measure of the surge at 8 in. is about an order of magnitude greater
than for the quiet Sun. At 20 in. the emission measure of the surge is
initially close to the quiet Sun distribution, but decreases by a factor
of 4 within 6 min. The optically thin lines formed near 10 to the 5th
power K show nonthermal broadening at 8 in., and electron densities near
this temperature are derived from intersystem to resonance ratios. The
volume of the emitting plasma at 8 in. above the limb was determined,
concluding that a continuous energy input is required to explain the
observations.
Title: The Fe XXI lambda 1354 line in solar flares observed from
Skylab and its implications on ionization equilibrium calculations.
Authors: Cheng, C. -C.; Feldman, U.; Doschek, G. A.
Bibcode: 1979ApJ...233..736C
Altcode:
We have measured the line width of the forbidden line Fe xxi Al 354
in flare spectra observed from Skylab. The measured line widths are
examined using three sets of ionization equilibrium calculations
by Jordan, Summers, and Jacobs et al. The results indicate that the
ionization equilibrium temperature of Fe xxi is more likely to be 1.0
x 10 K, a value given by Jacobs et al. and Jordan, rather than the
higher value of 2.0 x 10 K given by Summers. Subject headings: Sun:
flares - Sun: spectra
Title: Extreme-ultraviolet limb spectra of a prominence observed
from Skylab.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1979ApJ...232..929M
Altcode:
Line profiles of extreme ultraviolet emission lines observed in a
solar prominence at positions above the white-light limb with the NRL
slit spectrograph on Skylab are discussed. Absolute line intensities
and full widths at half-maximum are presented, and emission measures,
electron densities, and mass motions are derived at several locations
within the prominence. For electron temperatures less than 40,000
K, the calculated mass motions are found to be near zero, while for
electron temperatures greater than 40,000 K, the nonthermal velocity
decreases with increasing height in the prominence. It is suggested
that falling material is responsible for the fact that the measured
electron density decreases with height less rapidly than the decrease
predicted for a hydrostatic gas. In addition, from the He II 1640 A
line profile, an average temperature of 27,000 K is derived for the
region in which He II is emitted.
Title: New atomic data for O+2.
Authors: Bhatia, A. K.; Doschek, G. A.; Feldman, U.
Bibcode: 1979A&A....76..359B
Altcode:
New atomic data are tabulated for the ion O(2+). Collision strengths
are calculated for several energies of the exciting electron. The
populations of the levels of O(2+) are calculated as a function
of electron density under conditions appropriate for the solar
atmosphere. The available solar data are compared with theoretical
predictions of relative line intensities.
Title: Solar flare spectroscopic diagnostics for wavelengths less
than 2000 angstroms
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1979nrl..reptQ....D
Altcode:
We discuss the use of intensity ratios of emission lines for determining
the electron density and temperature in flare plasmas. The availability
diagnostics cover the temperature range from about 40,000 K to about
10,000,000 K. We summarize the current work on flare density diagnostics
and review the applications of this theory to available flare
spectra. We discuss the importance of line profiles for determining
nonthermal mass motions in the plasma and for estimating path lengths
along the line of sight. We review the current information on line
profiles in flare spectra. We comment on determining departures from
ionization equilibrium using line ratios in the X-ray and EUV regions.
Title: On the structure of the solar transition zone and lower corona.
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.
Bibcode: 1979ApJ...229..369F
Altcode:
Recent observations of the solar transition zone and corona
obtained primarily from NRL spectrographs on Skylab are summarized
and used to examine the structure of the transition zone. The
transition zone is revealed to be more inhomogeneous than is
apparent from spectroheliograms with spatial resolution of about 3
arcsec. Transition-zone emission appears to arise in spicularlike
structures. The effective area covered by the emitting structures at
lower transition-zone temperatures (about 100,000 K) is only about 1%
of the total surface area of the sun. The transition zone is highly
inhomogeneous even over cell interior regions, where fluctuations in
brightness by factors of 25 can occur. It is shown that homogeneous
coronal models are not valid for the inner corona. Most of the
higher-density inner corona is concentrated into looplike structures
that extend down to the white-light limb. These structures are
unrelated to the spicular-type structures that produce most of the
transition-zone emission.
Title: Fe XXI as an electron density diagnostic in solar flares.
Authors: Mason, H. E.; Bhatia, A. K.; Doschek, G. A.; Feldman, U.
Bibcode: 1979A&A....73...74M
Altcode:
Atomic data have been calculated for Fe XXI, and the theoretical
intensity ratios for many transitions are tabulated. Fe XXI lines in
wavelength regions 1-25 A, 90-200 A, and 300-2500 A are discussed with
reference to presently available solar and laboratory spectra. It is
found that Fe XXI is an excellent density diagnostic for solar-flare
and tokamak plasmas, when densities are in the range from 10 to the
11th to 10 to the 15th per cu cm. The theoretical calculations are
applied to flare spectra obtained from OSO 5, and an electron density
of less than 10 to the 13th per cu cm is deduced for a temperature
of 10,000,000 K. The results are somewhat ambiguous in several cases
because of the limited spectral and temporal resolution of these
earlier spectrometers. However, the calculations will be important
for forthcoming solar projects, such as the Solar Maximum Mission.
Title: High Resolution Solar Flare X-Ray Spectra
Authors: Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Bell, W. D.;
Wassam, W. W.
Bibcode: 1979BAAS...11..421K
Altcode:
No abstract at ADS
Title: Nonthermal broadening of extreme ultraviolet emission lines
near the solar limb.
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....73..361M
Altcode:
Summary. Line profiles of optically thin extreme ultraviolet emission
lines observed in quiet-Sun regions at 8', 12', and 20' above the
white light limb with the NRL slit spectrograph (5082-B) on Skylab are
discussed. Random mass-motion velocities are calculated. The velocity
is found to increase with increasing height above the white light limb
for all the lines regardless of the temperature of formation between 4
l0 K and 2l0 K. At +12' a typical velocity is about 33km -1 Key words:
Sun - transition zone - EUV spectra
Title: The dynamical properties of the solar corona from intensities
and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII.
Authors: Cheng, C. -C.; Doschek, G. A.; Feldman, U.
Bibcode: 1979ApJ...227.1037C
Altcode:
We have studied the line profiles of the solar coronal forbidden lines
Si viii 1445.76 A, Fe XI 1467.08 A, and Fe xii 1242.03 A in quiet and
active coronal regions from a survey of available limb spectra in the
NRL Skylab data. The results show that the line widths of these lines
are essentially the same in quiet-Sun regions as in active regions. For
some active regions, however, the line widths are systematically
narrower than those in quiet-Sun regions. In addition, the line widths
are about the same in the height range from 0" to 30 . The widths are
wider than the thermal Doppler widths at the ionization equilibrium
temperature given by Jordan. The additional widths correspond to
a nonthermal mass-motion velocity of 10-25 km -1 at 1.7 x 106 K (Fe
xii), 10-17 km -1 at 1.5 x 10 K (Fe xi), and 10-20 km -1 at 9.3 x 10 K
(Si viii). The intensities of the forbidden lines in active regions are
about an order of magnitude greater than those in quiet-Sun regions. The
distribution of column density calculated for the three different lines
indicates that more plasma is near 1.7 x 106 K than near 9.3 x 10 K
at a given height. The observational results are discussed in terms
of coronal heating mechanisms. The dissipation of acoustic waves does
not provide a sufficient heating rate. The dissipation of three modes
of hydromagnetic waves-the slow mode, the fast mode, and the AlfVe'n
mode-also cannot satisfactorily explain the observational results. It
is difficult for heating by hydromagnetic waves to meet simultaneously
the requirements of a large enough heating rate, a dissipation length
comparable to the length of a coronal loop, and a velocity amplitude
that agrees with observations. Subject headings: line profiles - Sun:
corona - Sun: spectra - ultraviolet: spectra
Title: Electron densities in the solar corona from density-sensitive
line ratios in the N I isoelectronic sequence.
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Bhatia, A. K.;
Mason, H. E.
Bibcode: 1978ApJ...226..674F
Altcode:
Electron densities are derived in the solar inner corona from forbidden
lines of S x near 1100 A. The density-sensitive line ratio considered
is (4S0312-2D0312)/(4S0312-2D0612). The ratio is calculated as a
function of density for four ions of the N I isoelectronic sequence,
i.e., Mg VI, Si VIII, S x, and Ar XII. The variation of the ratio
(4S0312-2P0312)/(4S0312-2D0312) with density is also calculated. The
results are applied to off-limb spectra recorded by the NRL Skylab
spectrograph. Densities were found to be the same in five quiet Sun
regions and four active regions observed at heights > 8" outside
the white-light limb. The average density derived from the S x lines
for all regions considered is 1.0 x 10 cm -3. This result applies to
plasma at the temperature of formation of S x, i.e., 1.3 x 106 K. At
heights greater than 20" outside the limb the average density is 7.7 x
108 cm -3, and between 8" and 12" above the limb the average density is
1.0 x 10 cm 3, for both quiet Sun and active regions. Subject heading:
Sun: corona
Title: Densities in the quiet sun and polar coronal holes from EUV
line ratios involving O III (1666.15 Å).
Authors: Doschek, G. A.; Feldman, U.; Bhatia, A. K.; Mason, H. E.
Bibcode: 1978ApJ...226.1129D
Altcode:
The EUV line intensity ratios C iii (1908.73 A)/o iii (1666.15 A), 0 iii
(1666.15 A)/Si iv (1402.77 A), and C iii (1908.73 A)ISi iv (1402.77 A)
are shown to be sensitive to variations in the electron density at
densities typical of the quiet Sun ( 1010 cm - at 6 x 10 K). Using
the 0 iii line, the above ratios can be normalized to observational
data and densities in quiet-Sun regions and coronal holes can be
determined. The average value of the density determined for three
quiet-Sun regions is 1.9 x 1010 cm - . The densities determined from
several observations of the north and south polar coronal holes are
about the same as in the quiet Sun, with the exception of one set of
observations of the north polar hole that indicates a density about
a factor of 2 less than that of the quiet Sun. Subject headings: Sun:
corona - Sun: spectra - ultraviolet: spectra
Title: Measurements of extreme-ultraviolet emission-line profiles
near the solar limb.
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJ...226..698M
Altcode:
Line profiles of optically thin extreme-ultraviolet emission
lines observed in a quiet sun region at positions within and above
the white-light limb with the NRL slit spectrograph (S082-B) on
Skylab are discussed. Absolute line intensities and full widths at
half-maximum are presented for lines formed over the temperature range
from about 10,000 to 22,000 K. The line intensities are compared with
the predictions of simple atmospheric models consisting of a spicule
component and a thin spherically symmetric or network models, but can
be explained by assuming that the emission arises from spicule-like
inhomogeneities. Random mass-motion velocities are calculated. The
velocity increases with increasing temperature of line formation. Near
the limb and above about 4000 K the calculated velocity is consistent
with the predictions of a constant acoustic flux passing through the
transition zone. For the ions formed at temperatures not less than
about 63,000 K, the velocity is found to increase with increasing
height above the white-light limb.
Title: Electron densities in stellar atmospheres determined from
IUE spectra.
Authors: Doschek, G. A.; Feldman, U.; Mariska, J. T.; Linsky, J. L.
Bibcode: 1978ApJ...226L..35D
Altcode:
No abstract at ADS
Title: EUV spectra from Skylab (1175 - 1940 Å). Mass motions in
the transition zone in regions of solar activity.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1978A&A....69...11D
Altcode:
The profiles of spectral lines in the 1100-2000-A range emitted by
transition-zone ions in regions of solar activity are discussed. The
data were recorded by the NRL spectrograph on Skylab. At the spatial
resolution of the Skylab spectrograph (2 x 60 arcsec), it is shown that
the line profiles result from the superposed emission of a number of
physically distinct regions at different electron densities and with
different mass motions. Although high densities are found for some
surgelike phenomena at transition-zone temperatures, the densities can
also be comparable to normal active-region densities. Line profiles,
as well as spectral line intensities, must be considered if meaningful
theoretical models of dynamic activity in the transition zone are to
be constructed.
Title: Emission-line spectra of two active regions on the solar limb:
1175 - 1940 Å.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJS...37..443F
Altcode:
Skylab emission-line spectra (1175 to 1940 A) of two active
regions on the solar limb are examined. Electron densities for the
active regions are derived using the intensity ratios of selected
intersystem and allowed lines. The intensity ratios in the active
regions are compared with those observed previously in quiet-sun and
coronal-hole regions. The behavior of coronal forbidden lines relative
to transition-zone lines is discussed along with the solar continuum
intensities near and above the limb. These continuum intensities are
then compared with those at similar slit positions for the quiet sun
and the previously studied coronal hole. The active-region data are
found to be consistent with either (1) multithermal loops with the
high-temperature plasma occupying the tops of the loops or (2) nearly
isothermal loops with the hotter loops extending to higher altitudes.
Title: XUV spectra of the 1973 June 15 solar flare observed from
Skylab. III. A list of spectral lines from 1000 to 1940 Å.
Authors: Cohen, L.; Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJS...37..393C
Altcode:
A wavelength list of spectral lines between 1000 and 1940 A is
presented for the solar flare that occurred on June 15, 1973. The
spectra were recorded by the NRL spectrograph on Skylab. The spectral
resolution is 0.06 A. Intensities, identifications, and estimates of
line widths are given. The intensity of the continuum is also given at
50-A intervals between 1400 and 1900 A. The wavelength list includes
about 1400 lines; about 30% of these lines are not indentified. Because
of the high wavelength resolution, this line list will be useful as a
source of identification for some stellar as well as solar spectra. In
particular, the list should be a useful aid in the identification
of lines in the spectra of stars with classifications close to that
of the sun. Spectra of such stars may be obtained from the recently
launched IUE spacecraft. It is also interesting to compare the list
with some of the spectra of early-type stars recorded by Copernicus.
Title: The importance of spectroscopy in the 80 800 å region for
plasma diagnostics in the solar atmosphere
Authors: Feldman, U.; Doschek, G. A.; Behring, W. E.
Bibcode: 1978SSRv...22..191F
Altcode:
We discuss the importance of the spectral range from about 80 to 800
Å for determining physical conditions in different regions of the
solar atmosphere. We give examples of line ratios that may be used to
determine electron densities in quiet Sun regions, active regions,
and flares. We discuss the possibility of determining electron
temperatures from line ratios in the EUV. We show that profiles as
well as intensities of spectral lines must be obtained for a proper
interpretation of the spectra. We give approximate parameters for a
solar grazing incidence spectrograph suitable for the study of the 80
800 Å wavelength region.
Title: The electron density at 105K in different regions
of the solar atmosphere derived from an intersystem line of O IV.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1978A&A....65..215F
Altcode:
Summary. Electron densities are derived for typical solar active
regions and flares from EUV spectral lines of 0 IV, N V, C iv and
Si iv. The densities pertain to electron temperatures near 10 K. The
spectra were recorded by the NRL spectrograph flown on Skylab. Typical
densities found for active regions are 1011 . The density in flares
can range from 1011 to above 1013 . The volumes of high density
emitting plasma in active regions and flares are quite small, with
values ranging from 1.5 1(Y cm3 to less than 2.2 1020 cm3. Also, the
density in a polar coronal hole is about one-half of the density in
a typical quiet Sun region, at a temperature near 6 1 K. Key words:
Sun-transition zone-electron density
Title: Nonthermal Broadening of Extreme Ultraviolet Emission Lines
near the Solar Limb
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1978BAAS...10..432M
Altcode:
No abstract at ADS
Title: The Dynamical Properties of the Solar Corona from Intensities
and Line Widths of EUV Forbidden Lines of Si VIII, Fe XI, and Fe XII.
Authors: Cheng, C. C.; Doschek, G. A.; Feldman, U.
Bibcode: 1978BAAS...10Q.439C
Altcode:
No abstract at ADS
Title: Electron densities in solar flare and active region plasmas
from a density-sensitive line ratio of Fe IX.
Authors: Feldman, U.; Doschek, G. A.; Widing, K. G.
Bibcode: 1978ApJ...219..304F
Altcode:
We demonstrate that the intensity ratio of the two lines of Fe IX
at 241.739 and 244.911 A (3p53d 3P2 2p6 `So and 3p53d 3P, 2p6 `So)
is sensitive to electron density above about 1010 . We calculate the
intensity ratio as a function of density, and apply the result to two
spectroheliograms of flares and surrounding plage regions recorded by
the Naval Research Laboratory spectroheliograph on Skylab. We find that
the densities at coronal temperatures of 106K vary considerably from
region to region and can be at least as high as 2 x 10" cm 3. Subject
headings: Sun: flares - Sun: spectroheliograms - ultraviolet: spectra
Title: High-resolution spectra of the solar Mg II h and k lines
from Skylab.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1977ApJS...35..471D
Altcode:
Spectra of the Mg II h and k lines emitted by different regions in the
solar atmosphere have been recorded by the NRL slit spectrograph on
Skylab. The spectral resolution is 0.12 A, and the spatial resolution
is 2 by 60 arcsec. Several examples are presented, including spectra
of a chromospheric supergranulation cell boundary and interior and of
a quiet-sun region above the limb, as well as selected active-region
spectra on the disk and above the limb. Obvious differences among
these spectra are noted and qualitatively discussed.
Title: The solar spectrum in the vicinity of the Si IV lines at 1122
and 1128 Å.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977A&A....61..295F
Altcode:
Summary. The extreme ultraviolet solar spectrum in the vicinity of
the Si iv lines at 1122 and 1128 A is presented with a wavelength
resolution of 0.06 A. The Si iv line at 1122.486 A is blended with
an unresolved line of Fe "I at 1122.526 A. The Siiv line at 1128.340A
is near two faint Fe iii lines. However, these lines will contribute
little to the intensity of the Si iv line, even when the intensity is
recorded with a wide spectrograph slit. Key words: extreme ultraviolet
solar spectrum solar transition zone
Title: A search for a turbulent-free region in the solar transition
zone.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...216L.119F
Altcode:
A search for a turbulence-free transition-zone region was conducted. The
data used were spectra recorded by a slit spectrograph on Skylab. It
was found that the nonthermal turbulent motions are smallest in
certain active regions and quiescent prominences. The spectra of one
such region, a quiescent prominence, are discussed. The nonthermal
turbulence in the region is between about 2 and 7 km/s. Therefore,
the widths of lines emitted by transition-zone ions are determined
primarily by the ion temperature. To within the experimental error,
temperatures derived from the line widths are equal to the temperatures
of maximum emitting efficiency obtained using the ionization equilibrium
calculations of Jordan (1969).
Title: Electron densities in solar flares from line ratios of Ca XVII.
Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.
Bibcode: 1977A&A....60L..11D
Altcode:
Summary. We show that the intensity ratios of certain extreme
ultraviolet spectral lines of Ca XVII are sensitive to electron density
in solar flares. Calculations of the line ratios as functions of
density are presented. These calculations are based on published atomic
data for Ca XVII and for other ions of the beryllium isoelectronic
sequence. For a flare that occurred on 9 August 1973, we derive a
density of about 5 x 101 from the Ca XVII line ratios. Key words:
solar flares - Be I sequence
Title: XUV spectra of the 1973 June 15 solar flare observed from
Skylab. I. Allowed transitions in chromospheric and transition
zone ions.
Authors: Doschek, G. A.; Feldman, U.; Rosenberg, F. D.
Bibcode: 1977ApJ...215..329D
Altcode:
Spectra between 1100 and 1940 A of the 1973 June 15 solar flare are
discussed. The spectra were recorded by the NRL normal-incidence slit
spectrograph on Skylab. In this paper we discuss allowed transitions in
ions formed in the chromosphere and transition zone. We give the power
(ergs s-1) in the emission lines produced by the plasma viewed by the
instrument, and we give the widths and shapes of the line profiles as
a function of time during the flare. We calculate emission measures
and volumes of the flare plasma for lines of Si iv, C iv, and N V. The
characteristic lengths (= V113) are quite small, ranging between 0'
1 to 1'.'0. The smaller values are the more reliable. The flare can be
qualitatively divided into two distinct phases. An eruptive phase occurs
near the beginning of the flare and lasts for about 2 minutes. Plasma
is observed moving toward the observer at velocities as high as km 1
during this phase. A continuous energy input is necessary to account
for the lifetime of the moving plasma. A much longer lived quiescent
phase follows the eruptive phase and lasts for about 23 minutes. Subject
headings: Sun: chromosphere - Sun: flares - Sun: spectra - ultraviolet:
spectra
Title: XUV spectra of the 1973 June 15 solar flares observed from
Skylab. II. Intersystem and forbidden transitions in transition zone
and coronal ions.
Authors: Feldman, U.; Doschek, G. A.; Rosenberg, F. D.
Bibcode: 1977ApJ...215..652F
Altcode:
An analysis is given of the intersystem lines of transition zone ions
and high-temperature forbidden lines for the 1973 June 15 flare. The
electron density in the erupting part of the plasma is at least 1013
at temperatures of 1.3 x l0 K. The density of the stationary component
of the flare plasma at similar temperatures varies between 1.5 x 1011
and 1012 . A density decrease observed in the stationary component
occurs nearly simultaneously with an intensity enhancement of forbidden
coronal lines such as Fe xii. These lines are believed to originate in
arch-type structures. The electron density in the temperature regions
1.5 x 106K is between 2 x 1010 cm-3 and 2 x 1011 cm-3. These regions
appear to be stationary. Their motion relative to the observer is less
than 4 km 1 A continuous energy input is necessary to account for the
transition zone emission. The transition zone emission arises in small
regions, perhaps filaments. Subject headings: plasmas - Sun: flares -
Sun: spectra - ultraviolet: spectra
Title: On the problem of density diagnostics for the EUV spectrum
of the solar transition zone.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1977A&A....58L..13D
Altcode:
Spectral-line ratios that may be used to determine the electron
temperature and density in the solar transition zone and corona are
identified. The problem of interpreting the intensity ratios of C
III lines observed in Skylab EUV limb spectra is considered. It is
shown that the intensity distribution with height above the solar
limb of the 1176-A C III lines is different from that of the 1909-A
C III lines in the Skylab spectra, suggesting that model atmospheres
must be folded into the C III calculations for proper interpretation
of the data. Possible reasons for the differences in the intensity
distributions and widths of the 1176-A and 1909-A lines are discussed
along with an application to the analogous lines of Si III.
Title: The 3s-3p and 3p-3d lines of Mg II observed above the solar
limb from Skylab.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...212L.147F
Altcode:
No abstract at ADS
Title: The emission spectrum of the hydrogen Balmer series observed
above the solar limb from Skylab. I. A quiet Sun and a polar
coronal hole.
Authors: Rosenberg, F. D.; Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...212..905R
Altcode:
The hydrogen Balmer emission-line spectrum (H9 [3835 A] to the series
limit at 3646 A) above the limb of the quiet Sun and above the north
polar coronal hole is discussed. The data were obtained by the NRL XUV
spectrograph aboard Skylab, with the slit tangent to the limb at 2"
(1450 km) and at 4" (2900 km) above the limb. Electron densities of 2 x
1011 cm - , 2" above the limb of both the quiet Sun and coronal hole,
are calculated from the Stark broadening of the higher series member
lines, and the related merging of the higher member lines. The widths
of the lines with principal quantum number m < 15 are broadened
by opacity, and the opacities are estimated from the line widths. The
widths of lines of m 15 are not appreciably affected by either opacity
or Stark broadening. The combined ion temperature and nonthermal mass
motion determined from the widths of these lines are consistent with
previously determined values. The intensities of the lines indicate that
the upper levels (>9) are populated in statistical equilibrium with
each other. Absolute intensities are given, as well as the decrease of
the intensity of the lines as a function of height above the limb. The
Balmer emission-line spectrum above the limb over three active regions
is discussed in the following paper. Subject headings: Sun: corona -
Sun: spectra
Title: The Emission Spectrum of the Hydrogen Balmer Series Observed
above the Solar Limb from SKYLAB. II. Active Regions . . . .
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...212..913F
Altcode:
Electron densities are determined from the Stark broadening of Balmer
hydrogen lines at 2" above the limb over three active regions. The
spectra were recorded by the NRL slit spectrograph on Skylab. The
density was found to be the same for all three regions and is 2 x 1011
with an error of less than 15% in fitting the theoretical curves to the
data. The intensity falloff of the hydrogen lines above the limb over
the active regions is compared with previous results obtained over a
quiet Sun region and a polar coronal hole. The falloff is also compared
with the intensity falloff of optically thin lines of Si II, Mg II,
C II, singly ionized metals, and the neutral element, O I, recorded
over a quiet Sun region. From this comparison, the temperature of the
hydrogen plasma in all of the quiet and active regions that we observed
is no more than about 8000 K. The intensity decrease of the hydrogen
lines is the same as the intensity falloff of intersystem lines of
01. Nonthermal velocities of the hydrogen lines over the active regions
are also derived. At 2" above the limb, these range from 0 km 1 to
about 15 km s - . The lines of high members of the Balmer series are
in Boltzmann equilibrium. The hydrogen observations are combined with
our previous observations of singly ionized elements and are compared
with observations of spicule s. Subject headings: Sun: chromosphere -
Sun: corona - Sun: spectra
Title: The coronal temperature and nonthermal motions in a coronal
hole compared with other solar regions.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1977ApJ...212L.143D
Altcode:
The coronal lines Si VIII (1446 A), Fe X (1463 A), Fe XI (1467 A), and
Fe XII (1242 A and 1349 A) were observed above the limb over a quiet
region, a coronal hole, and two active regions. The lines emitted at
temperatures greater than 1 million K; i.e., the iron lines, are not
observed in the coronal-hole spectra, so the indication is that in
the coronal hole most of the plasma is at a temperature of less than
1 million K. The emission measures and column densities of the lines
are derived from available atomic cross-section data, and the results
are discussed. The nonthermal velocities in the coronal hole and quiet
region are about 20 km/s. The velocities in the active regions are
substantially less.
Title: Chromospheric limb spectra from Skylab: 2000 to 3200 Å-.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
Bibcode: 1977ApJS...33..101D
Altcode:
Chromospheric limb spectra of a quiet-sun region between 2000 and
3200 A recorded by the normal-incidence spectrograph on Skylab are
discussed. The spectral resolution is 0.12 A, and the projected slit
area on the sun is 2 by 60 arcsec. A list of lines with wavelengths,
identifications, and absolute intensities is given for the spectrum
recorded at +4 arcsec outside the white-light limb. The intensity
behavior outside the limb is shown for lines of the ions C II, Si
II, Cr II, Mn II, Fe II, Fe III, Co II, and Ni II. The widths of the
intersystem lines of Si II and C II increase monotonically with height
above the limb. The full width at half-maximum of the Si II lines
increases from 0.034 A at the limb to 0.27 A at +12 arcsec above the
limb. The widths of the C II lines increase from 0.17 A at +2 arcsec
to 0.31 A at +12 arcsec.
Title: EUV Spectroscopy of Solar Transition-Zone Plasmas.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977uxsa.coll...11F
Altcode: 1977IAUCo..43...11F
No abstract at ADS
Title: Plasma diagnostics using high-resolution spectroscopic
techniques.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977JOSA...67..726F
Altcode: 1977OSAJ...67..726F
No abstract at ADS
Title: Recent High Spectral and Spatial Resolution Spectroscopy of
Laser-Produced Plasmas and Electron-Ion Beam Plasmas.
Authors: Doschek, G. A.; Feldman, U.; Johnson, D. J.; Nagel, D. J.
Bibcode: 1977uxsa.coll...18D
Altcode: 1977IAUCo..43...18D
No abstract at ADS
Title: The emission-line spectrum of a sunspot in the far-ultraviolet.
Authors: Cheng, C. -C.; Doschek, G. A.; Feldman, U.
Bibcode: 1976ApJ...210..836C
Altcode:
The emission-line spectrum between 1200 and 1817 A from a sunspot in
McMath region 12510 near the solar center is discussed. The spectrum
was obtained by the normal-incidence spectrograph on Skylab. The
principal results are: (1) the widths of emission lines originating
in the chromosphere and lower transition region over the sunspot are
much narrower than those previously reported for a polar coronal hole
observed above the limb and a quiet chromospheric network observed
near the solar center, indicating that the mass motions in the sunspot
are less than in these other regions; (2) the sunspot spectrum, aside
from the narrow widths of emission lines, is similar to spectra from
the chromospheric network boundary. The intensities of lines in the
sunspot are much enhanced relative to the network interior. From the
full-width at half-maximum of the 1207-A Si III line, an optical depth
at line center of 3.6 is deduced. Comparison with Parker's (1974) theory
of sunspots shows that, if the enhancement of emission lines is due
to enhanced transport of hydromagnetic waves generated in the sunspot
convective zone, the mode of the waves is predominately Alfvenic.
Title: The quiet sun chromospheric network observed from Skylab.
Authors: Feldman, U.; Doschek, G. A.; Patterson, N. P.
Bibcode: 1976ApJ...209..270F
Altcode:
The paper analyzes spectra of a supergranulation cell interior and cell
boundary obtained near the solar center at wavelengths between 1200
and 1560 A with a normal-incidence spectrograph aboard Skylab. Absolute
intensities, relative intensities, and profiles are given for selected
optically thin and optically thick lines over the cell interior, the
boundary, and intermediate positions; the results are compared with
spectra obtained at the limb. Characteristic lengths along the line of
sight are derived for the Si III emitting region, and these are compared
with the predictions of Gabriel's (1975) model. It is concluded that
the present data are representative of a fairly typical cell interior
and boundary, that nonthermal motions are isotropic and the same for
the interior and boundary, and that the electron-density ratio between
the interior and the boundary is about a factor of two or less.
Title: EUV Spectra of the 15 June 1973 Solar Flare Observed from
Skylab.
Authors: Doschek, G. A.; Feldman, U.; Rosenberg, F.
Bibcode: 1976BAAS....8..555D
Altcode:
No abstract at ADS
Title: The Solar Mg II h and k Lines Observed from Skylab.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1976BAAS....8..523F
Altcode:
No abstract at ADS
Title: Exploring plasmas: in the Sun and in the laboratory.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1976AsAer..14...24D
Altcode: 1976AsAau..14...24D
In recent years, high-resolution spectroscopy in the X-ray,
extreme-ultraviolet, ultraviolet, and visible spectral regions has found
increasing application for the study of conditions in solar plasmas. The
use of spectroscopic techniques in the X-ray and extreme-ultraviolet
spectral regions to determine such physical quantities as electron and
ion temperature, electron and ion density, turbulence or anisotropic
motions, and the departure of the ionic species from kinetic equilibrium
in solar and laboratory plasmas is discussed. Solar-flare spectra are
compared to the spectra of active solar regions.
Title: XUV spectrum of CI observed from Skylab during a solar flare.
Authors: Feldman, U.; Brown, C. M.; Doschek, G. A.; Moore, C. E.;
Rosenberg, F. D.
Bibcode: 1976JOSA...66..853F
Altcode: 1976OSAJ...66..853F
A list of 193 neutral carbon lines observed in the XUV spectrum
of a solar flare between 100 and 2000 A using the normal incidence
spectrograph flown on Skylab is presented. Of these, 69 are newly
identified lines arising from transitions from upper levels of
high quantum number where the quantum number is not less than
six. The new lines have allowed the determination of 63 new energy
levels. Wavelengths for an additional 109 transitions were calculated
by polynomial fitting using reference wavelengths of unblended neutral
carbon, Si, N, and S lines emitted in the same atmospheric regions of
the flare. The calculated lines falling between 1102 and 1140 A were not
observed due to low instrumental efficiency at these wavelengths. The
calculated wavelengths are in excellent agreement with those of
Johansson (1965). It appears that in solar spectra recombination
processes are dominant, enhancing the populations of the high quantum
levels relative to the populations of levels with small quantum numbers.
Title: The emission-line spectrum above the limb of a solar coronal
hole: 1175 - 1940 Å.
Authors: Feldman, U.; Doschek, G. A.; Vanhoosier, M. E.; Purcell, J. D.
Bibcode: 1976ApJS...31..445F
Altcode:
Emission-line spectra of a coronal hole that coincided with the
north pole of the sun are discussed which were obtained with a slit
spectrograph aboard Skylab at positions within and above the solar
white-light limb in the wavelength range from 1175 to 1940 A. Relative
line intensities, line profiles, and full widths at half-maximum
are presented for selected chromospheric and transition-zone lines
observed above the present polar coronal hole. Average mass motions
in the transition zone are determined as a function of electron
temperature from the widths of the optically thin lines by assuming
ionization equilibrium. The line intensities and profiles are compared
with corresponding results deduced from spectra obtained above a quiet
solar region. The coronal-hole spectra are found to imply an angular
dependence for the source function as well as a radial dependence
such that the source function is the smallest at the south pole and
increases with decreasing solar latitude.
Title: The emission-line spectrum above the limb of the quiet sun:
1175 - 1940 Å.
Authors: Doschek, G. A.; Feldman, U.; Vanhoosier, M. E.; Bartoe,
J. -D. F.
Bibcode: 1976ApJS...31..417D
Altcode:
Spectra of a quiet solar region obtained at positions within and above
the solar white-light limb in the wavelength region from 1175 to 1940
A are discussed. The spectra were obtained by the slit spectrograph
(SO82-B) on Skylab. The spectral resolution is 0.06 A, and the projected
slit area on the sun was 2 x 60 arcsec (1450 x 43500 km). Relative line
intensities are presented for lines formed in the temperature region of
the solar atmosphere from about 8000 to 220,000 K. Representative line
profiles of both optically thin and optically thick lines are shown
as a function of height above the limb. Random mass-motion velocities
are deduced from the optically thin lines, and the relative intensities
and profiles of the lines are discussed in terms of current theoretical
models. A wavelength list with identifications is given for the spectrum
obtained at +4 arcsec above the white-light limb.
Title: Doppler wavelength shifts of transition zone lines measured
in Skylab solar spectra.
Authors: Doschek, G. A.; Feldman, U.; Bohlin, J. D.
Bibcode: 1976ApJ...205L.177D
Altcode:
Wavelengths of lines of the transition-zone ions Si IV, C IV, O IV,
N V, and O V are observed to be redshifted relative to the wavelengths
of chromospheric lines in XUV spectra obtained from the normal-incidence
spectrograph on Skylab. The spectra cover the wavelength range from 1200
to 1565 A and were obtained with the slit positioned over chromospheric
network and cell regions, on coronal holes, and above the limb. The
network-area and coronal-hole spectra were obtained near the disk
center. Only some of the spectra show redshifted transition-zone
lines. The observed shifts are between 0.03 and 0.08 A, implying
velocities of 15 km/s or less. The amount of wavelength shift does not
always appear to be the same for lines of different ions. The shifts
imply that descending plasma in the solar atmosphere produces more
emission than ascending plasma at temperatures between approximately
70,000 and 200,000 K.
Title: Densities in the Solar Chromosphere above the Quiet sun and
a Coronal Hole Derived from the Hydrogen Balmer Lines
Authors: Rosenberg, F. D.; Feldman, U.; Doschek, G. A.
Bibcode: 1976BAAS....8..338R
Altcode:
No abstract at ADS
Title: The solar spectrum: wavelengths and identifications from 160
to 770 Ångstroms.
Authors: Behring, W. E.; Cohen, L.; Feldman, U.; Doschek, G. A.
Bibcode: 1976ApJ...203..521B
Altcode:
The full-Sun solar spectrum from 160 to 770 A was photographed
under quiet solar conditions by a rocket-borne spectrograph flown
in 1973 September. The spectral resolution is 0.06 A or better. We
present a composite list of spectral lines, including wavelengths,
identifications, and approximate intensities that were obtained from
the present flight and from a previous flight in 1969 May. This line
list contains the most accurate solar wavelengths yet obtained in this
spectral region. One result is improved energy levels which are given
for the two lowest energy configurations of Fe ix through Fe xvi. No
detectable relative mass motions of more than 4 km s ' exist between
transition zone and coronal regions averaged over the visible disk
of the Sun. The wavelengths of emission lines in this spectrum were
determined with indicated accuracies ranging between 2 and 20 mA. The
spectrograph employed a 3 m radius, 600 grooves mm ' gold grating used
at grazing incidence. Subject headings: line identifications - Sun:
corona - Sun: spectra - ultraviolet: spectra
Title: Limb-brightening curves of XUV transition zone lines in the
quiet sun and in a polar coronal hole observed from Skylab.
Authors: Doschek, G. A.; Feldman, U.; Tousey, R.
Bibcode: 1975ApJ...202L.151D
Altcode:
Solar limb-brightening curves are discussed for XUV spectral lines
formed in the upper chromosphere and transition zone of a quiet region
and a polar coronal hole. The spectra were recorded with a slit
spectrograph on Skylab. The lines considered are emitted from ions
formed within the temperature range from 10,000 to 220,000 K. The
limb-brightening curves cover a region from -4 sec within the limb
to +20 sec above it. The data from 0 sec to +20 sec are compared with
predictions based on both homogeneous and inhomogeneous models of the
transition zone. The limb-brightening curve of the O I line at 1355.6 A
indicates that O I is formed in spicules. The limb brightening of the
He II line at 1640.4 A is consistent with a temperature of formation
between about 40,000 and 90,000 K for He II.
Title: The intensities and profiles of XUV transition zone lines in
a quiet sun region compared to a polar coronal hole.
Authors: Feldman, U.; Doschek, G. A.; Tousey, R.
Bibcode: 1975ApJ...202L.147F
Altcode:
The intensities of XUV transition-zone lines from limb spectra of a
quiet-sun region and a polar coronal hole are compared. The spectra
were obtained with a slit spectrograph on Skylab and cover a region
from -12 sec within the limb to 20 sec above it. The lines selected for
comparison are formed at temperatures that range from 36,000 to 220,000
K. Lines of the higher-temperature ions, e.g. O v, are significantly
less intense in the coronal hole, and lines of lower-temperature ions
show little change. Profiles of selected optically thin transition-zone
lines from the quiet-sun and coronal-hole spectra are also shown. The
lines are broader than expected in ionization equilibrium, and
bulk-motion velocities are deduced from the widths of the lines. There
appears to be little, if any, statistically significant difference in
the velocities obtained from the quiet-sun region and the coronal hole.
Title: The spatial and temperature structure of vacuum spark plasmas.
Authors: Feldman, U.; Goldsmith, S.; Schwob, J. L.; Doschek, G. A.
Bibcode: 1975ApJ...201..225F
Altcode:
The spatial and temperature structures of the X-ray emitting components
of low-inductance vacuum-spark plasmas are investigated. The plasmas
produced by low-inductance vacuum sparks show striking resemblances
to solar-flare plasmas. High-resolution photographs show that the
spark plasmas are composed of hot (about 30 million K) compact sources
(less than 20 microns) and cooler (about 10 million K) larger sources
(of the order of 100 microns). Both types of sources may be produced by
the same plasma at different times. The differences between the solar
flare iron-line spectrum near 1.9 A and the spark iron-line spectrum
are discussed and interpreted.
Title: Density sensitive lines of highly ionized iron
Authors: Doschek, G. A.; Feldman, U.; Davis, J.; Cowan, R. D.
Bibcode: 1975PhRvA..12..980D
Altcode:
Spectral lines from ions in the nitrogen
isoelectronic sequence due to transitions of the type,
2s2p42D32,52-2p52P32,
and
2s2p42D32-2p52P12,
are identified in the 100-Å region in laser-produced plasma
spectra of titanium (Ti xvi) through cobalt (Co xxi). It is
proposed that the intensities of these lines relative to the
intensities of lines of the same ions due to transitions of the
type 2s22p3-2s2p4 are sensitive
to electron density in the range from ~ 1018
to ~ 1020 cm-3. Calculations
are performed for Fe xx, and a similar calculation
is performed for a density-sensitive line ratio of Fe xix, i.e.,
(2s2p51P1-2p61S0)(2s22p41S0-2s2p51P1).
This line ratio is also sensitive to electron density between
about 1018 and 1020 cm-3. The
2s2p51P1-2p61S0
line is newly indentified in Cr xvii, Co xx, and Ni xxi.
Title: The 1640.4 Å Halpha line of He II observed from Skylab.
Authors: Feldman, U.; Doschek, G. A.; Vanhoosier, M. E.; Tousey, R.
Bibcode: 1975ApJ...199L..67F
Altcode:
Profiles obtained from NRL Skylab solar spectra of the 1640.4 A feature
identified as the H-alpha line of He II are discussed and compared with
theoretical profiles derived assuming (1) collisional excitation and (2)
radiative recombination as the dominant excitation mechanism. Relative
intensities of this line as a function of altitude above and below
the solar white-light limb are also given for a representative quiet
sun region and for a polar coronal hole.
Title: Forbidden lines of highly ionized iron in solar flare spectra.
Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.; Sandlin, G. D.;
Vanhoosier, M. E.; Brueckner, G. E.; Purcell, J. D.; Tousey, R.
Bibcode: 1975ApJ...196L..83D
Altcode:
No abstract at ADS
Title: Transitions 2s'2pk -2s2p"I of the N i and C i Isoelectronic
Sequences
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, Leonard
Bibcode: 1975ApJ...196..613F
Altcode:
Transitions of the type +1 have been identified for the elements
from titanium through iron for ions of the nitrogen isoelectronic
sequence and for the elements titanium through nickel for ions of
the carbon isoelectronic sequence. Wavelengths, intensity estimates
and energies are given. The lines were identified from EUV spectra
obtained from laser-produced plasmas. The energy differences of levels
of the ground configuration for the C I isoelectronic sequence are
compared with extrapolations based on semiempirical equations derived
by Edlen. Wavelengths of forbidden Fe XXI lines that can be seen in
low-density plasmas such as solar flare plasmas are predicted. The
laser plasma spectrum is briefly compared with available solar flare
spectra. Subject headings: flares, solar - line identifications -
spectra, laboratory - spectra, ultraviolet
Title: X-Ray and EUV Spectra of Solar Flares and Laboratory Plasmas
Authors: Doschek, G. A.
Bibcode: 1975IAUS...68..165D
Altcode:
Recent laboratory work on the spectroscopy of highly ionized atoms
relevant to solar flares is reviewed. Much of this work has concerned
the X-ray and EUV spectrum of iron ions, Fe XVIII-Fe XXIV, which produce
prominent emission lines in the spectra of solar flares. Also discussed
are recently obtained laboratory X-ray spectra of emission lines of
hydrogen-like and helium-like ions as well as associated satellite
lines due to transitions of the types 1s2l-2p2l, 1s(2)2l-1s2p2l, and
1s(2)2l-1s2l3p. Satellite lines have also been identified in spectra
of solar flares and can be used to determine the electron temperature
of the plasma. The laboratory work is important in the planning of
future experiments in solar-flare X-ray and EUV spectroscopy.
Title: Advances in X-ray and EUV spectroscopy of solar flares and
laboratory plasmas
Authors: Doschek, G. A.
Bibcode: 1975xris.conf..306D
Altcode:
Results are discussed for spectroscopic analyses of extremely hot
laboratory and solar plasmas, and their laboratory and astrophysical
applications are considered. The dominant lines in X-ray emission
line spectra of coronal flare plasmas are identified, and the quantum
mechanisms responsible for these lines and their satellites are
noted. Laboratory analysis of the satellite lines is summarized,
the spectra of laser-heated laboratory plasmas are discussed, and
the significance of iron line emission in high-temperature plasmas is
described in detail. It is noted that the Fe XVII lines are particularly
useful for diagnostic purposes since they are the only iron lines which
appear with appreciable intensity in active regions and can be used in
a Pottasch-type analysis of flare plasmas, giving the emission measure
as a function of temperature and time.
Title: Transitions 2s22p-2s2p2 in the B I
isoelectronic sequence.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
Bibcode: 1975JOSA...65..463D
Altcode: 1975OSAJ...65..463D
No abstract at ADS
Title: Satellite Line Spectra from Laser-Produced Plasmas
Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Cowan, R. D.;
Whitlock, R. R.
Bibcode: 1974ApJ...192..213F
Altcode:
We have obtained X-ray spectra of high-temperature plasmas produced by
the 100 GW glass laser at the Naval Research Laboratory. In this paper,
we discuss the satellite lines of hydrogen-like and helium-like ions,
observed in the 2-12 A region for elements ranging from sodium through
titanium. The satellite lines are due to transitions of the type,
lsnl-2pnl, ls2nl-ls2pnl, n = 2, 3; and ls22l-ls2l3p. Physical conditions
in the plasma are discussed in terms of relative line-intensity ratios
and line profiles. Subject headings: plasmas - spectra, laboratory -
spectra, X-ray
Title: The Widths of the Solar he i and he II Lines at 584, 537,
and 304 Å
Authors: Doschek, G. A.; Behring, W. E.; Feldman, U.
Bibcode: 1974ApJ...190L.141D
Altcode:
In this Letter we report direct measurements from a rocket spectrograph
of the widths of the solar He I lines, 152 1s2p and 1s2-1s3p, at 584 and
537 A. We also report the width of the solar resonance line of He II at
304 A. The deduced full widths at hall-maximum intensity are 0.14,0.12,
and 0.10 A for the 584, 537, and 304 A lines, respectively. These
widths represent averages over the entire Sun. Line profiles corrected
for the nonlinear film response are presented for the 584 and 304 A
lines. Subject headings: line profiles - spectra, solar
Title: Solar Flare Emission Lines of Highly-Ionized Iron and Nickel
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.; Cohen, Leonard
Bibcode: 1974BAAS....6T.286D
Altcode:
No abstract at ADS
Title: Transitions 2S22pk -2s2 pk+, of the F i, 0 I, and N i
Isoelectronic Sequences
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.; Cohen, Leonard
Bibcode: 1974ApJ...188..417D
Altcode:
Transitions of the type, 2s +1, have been identified for the
elements from titanium through nickel for ions of the fluorine,
oxygen, and nitrogen isoelectronic sequences. Wavelengths, visual
intensity estimates, and energies are given. The energy differences
of levels of the ground configuration are compared with predictions
based on semiempirical equations derived by Edlen. Some of the lines
of these isoelectronic sequences should be strong lines in solar-flare
spectra. Subject headings: line identifications - spectra, laboratory -
spectra, ultraviolet
Title: The Width of the Solar 584 Å Line of Neutral Helium
Authors: Behring, W. E.; Doschek, G. A.; Feldman, U.; Cohen, Leonard;
Houston, James
Bibcode: 1974BAAS....6R.284B
Altcode:
No abstract at ADS
Title: X-ray Satellite Lines of Hydrogenlike and Heliumlike Ions
Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Cowan, R. D.;
Whitlock, R. R.
Bibcode: 1974BAAS....6R.286F
Altcode:
No abstract at ADS
Title: Laser-Plasma Spectra of Highly Ionized Fluorine
Authors: Feldman, U.; Doschek, G. A.; Nagel, J.; Behring, W. E.;
Cowan, R. D.
Bibcode: 1974ApJ...187..417F
Altcode:
Lines between 11.3 A and 17.2 A of lithium-like, helium-like, and
hydrogen-like fluorine have been observed in spectra of laser-produced
plasmas. These lines include nine members of the Lyman series of F IX;
eight members of the principal series of F VIII; and satellite lines
arising from doubly excited configurations of F VII and F VIII. Similar
satellite lines of the abundant solar elements have been identified in
soft X-ray spectra of solar flares. A wavelength list of fluorine lines
is given, and physical conditions in the plasma are discussed. Subject
headings: flares, solar - line identifications - plasmas - spectra,
laboratory - spectra, X-ray
Title: Transitions of Fe XVIII and Fe XIX Observed in Laser-Produced
Plasmas
Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Behring, W. E.;
Cohen, Leonard
Bibcode: 1973ApJ...183L..43F
Altcode:
Lines of Fe xvm and Fe XIX near 100 A have been ohserved in spectra
from plasmas produced by 5-joule laser pulses of 0.9 ns duration. These
lines produced by transitions of the type 2s2 +1 Transitions of the
type -131 are prominent in the spectra below 20 A observed during solar
flares. The splittings of the ground levels are obtained and compared
with isoelectronic extrapolations. The corresponding forbidden lines
as well as the allowed lines near 100 A inay be observable in flare
spectra with some of the instruments to be flown on Skylab. Subject
headings: flares, solar - spectra, ultraviolet - spectra, X-ray
Title: Spectra of Solar Flares from 8.5 Å to 16 Å
Authors: Doschek, G. A.; Meekins, J. F.; Cowan, Robert D.
Bibcode: 1973SoPh...29..125D
Altcode:
X-ray spectra of solar flares in the spectral range from 8.5 Å to
∼ 16 Å have been obtained from a Naval Research Laboratory crystal
spectrometer flown on the sixth Orbiting Solar Observatory (OSO-6). A
list of emission features is presented and tentative identifications of
some of the features are suggested. The time-behavior of the emission
lines during flares is discussed, and the possibility of determining
electron densities in flare plasmas using density sensitive lines
of highly ionized iron is considered. Approximate calculations are
performed for a density sensitive line of FeXXII.
Title: Note on Heliumlike Silicon and Sulfur Lines Observed in the
X-Ray Spectra of Solar Flares (Erratum)
Authors: Doschek, G. A.; Meekins, J. F.
Bibcode: 1973SoPh...28..517D
Altcode:
No abstract at ADS
Title: Fluorine isoelectronic sequence.
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, L.
Bibcode: 1973JOSA...63.1445F
Altcode:
No abstract at ADS
Title: Spectra of highly ionized atoms from the laboratory and from
the sun.
Authors: Doschek, G. A.
Bibcode: 1973JOSA...63.1314D
Altcode:
No abstract at ADS
Title: Soft X-ray Flare Spectra
Authors: Doschek, G. A.; Meekins, J. F.
Bibcode: 1973NASSP.342..262D
Altcode: 1973heps.conf..262D
No abstract at ADS
Title: On I isoelectronic sequence: transitions
2p4-2p33s.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
Bibcode: 1973JOSA...63.1463D
Altcode:
No abstract at ADS
Title: Further Iron-Line Observations during Solar Flares
Authors: Doschek, G. A.; Meekins, J. F.; Cowan, Robert D.
Bibcode: 1972ApJ...177..261D
Altcode:
Transitions in Fe xxiv of the type 1s221 2L-1s241' 2L', and the Fe
xxiii transition, 1s22s2 1S0- 1s22s4p 1P1, are identified in soft X-ray
spectra of solar flares. The relative line strengths of Fe xxiv are
compared with theory, and the temporal behavior of the Fe xxiv lines
and the Fe xxiii line is discussed, particularly with reference to
the continuum emission near 8 A.
Title: The Solar Flare Plasma: Observation and Interpretation
(invited Paper)
Authors: Doschek, G. A.
Bibcode: 1972SSRv...13..765D
Altcode: 1972IAUCo..14..765D
In the past several years, X-ray observations of the Sun made
from rockets and satellites have demonstrated the existence of high
temperature (∼20 × 106 ∼100 × 106 K), low
density plasmas associated with solar flare phenomena. In the hard X-ray
range (λ < 1 Å), spectra of the flaring plasma have been obtained
using proportional and scintillation counter detectors. It is possible
from these data to determine the evolution of the hard X-ray flare
spectrum as the burst progresses; and by assuming either a non-thermal
or thermal (Maxwellian) electron distribution function, characteristic
plasma parameters such as emission measure and temperature (for a
thermal interpretation) can be determined. Thermal interpretations of
hard X-ray data require temperatures of ∼ 100 × 106 K. In
contrast, the soft X-ray flare spectrum (1 Å <λ<30 Å) exhibits
line emission from hydrogen-like and helium-like ions, e.g. Ne, Mg,
Al, Si,... Fe, that indicates electron energies more characteristic
of temperatures of ∼20 × 106 K. Furthermore, line
intensity ratios obtained during the course of an event show that the
flare plasma can only be described satisfactorily by assuming a source
composed of several different temperature regions; and that the emission
measures and temperatures of these regions appear to change as the flare
evolves. Temperatures are determined from line ratios of hydrogen-like
to helium-like ions for a number of different elements, e.g., S, Si,
and Mg, and from the slope of the X-ray continuum which is assumed to be
due to free-free and free-bound emission. There is no obvious indication
in soft X-ray flare spectra of non-thermal processes, although accurate
continuum measurements are difficult with the data obtained to date
because of higher order diffraction effects due to the use of crystal
spectrometers. Soft X-ray flare spectra also show satellite lines of
the hydrogen-like and helium-like ions, notably the 1s 22s
2 S-1s2s2p 2 P transition of the lithium-like ion,
and support the contention that in low density plasmas these lines are
formed by dielectronic recombination to the helium-like ion. Also,
series of allowed transitions of hydrogen-like and helium-like ions
are strong, e.g., the Lyman series of S up to Lyman-ɛ, and ratios
of the higher member lines to the Lyman-α line can be compared with
theoretical calculations of the relative line strengths obtained by
assuming various processes of line formation. This review will discuss
the X-ray spectrum of solar flares from ∼250 keV to ∼0.4 keV,
but will be primarily concerned with the soft X-ray spectrum and the
interpretation of emission lines and continuum features that lie in
this spectral range.
Title: The Soft X-Ray Flare of 12 August 1970
Authors: Doschek, G. A.; Meekins, J. F.
Bibcode: 1972BAAS....4Q.381D
Altcode:
No abstract at ADS
Title: Soft x-ray spectral studies of solar flare plasmas
Authors: Doschek, G. A.; Meekins, J. F.; Kreplin, R. W.; Chubb, T. A.;
Friedman, H.
Bibcode: 1972cpp..conf..165D
Altcode:
No abstract at ADS
Title: Iron-Line Emission during Solar Flares
Authors: Doschek, G. A.; Meekins, J. F.; Kreplin, R. W.; Chubb, T. A.;
Friedman, H.
Bibcode: 1971ApJ...170..573D
Altcode:
Iron-line emission 1.9 A recorded by NRL Bragg crystal spectrometers on
080-6 during intense solar soft X-ray flares is discussed. Individual
emission features are resolved in second order, and variability in
emission from Fe xxv relative to inner-shell emission from lower
ionization stages is considered. A feature at 1.932 A is attributed
to radiation from Fe ii in the photosphere. In the region of the
secondorder iron spectra, the two fine-structure components of the
first excited P state of hydrogenic argon are resolved.
Title: Discussion of Paper `On the Polarization and Anisotropy of
Solar X-Radiation During Flares', by G. Elwert and E. Haug
Authors: Kahler, S. W.; Doschek, G. A.; Meekins, J. F.; Horan, D. M.
Bibcode: 1971SoPh...20..422K
Altcode:
No abstract at ADS
Title: Iron-Line Emission During Solar Flares.
Authors: Doschek, G. A.; Meekins, J. F.; Cowan, R. D.
Bibcode: 1971BAAS....3..461D
Altcode:
No abstract at ADS
Title: Heliumlike Calcium Emission Observed during a Solar Flare
Authors: Doschek, G. A.; Meekins, J. F.; Kreplin, R. W.; Chubb, T. A.;
Friedman, H.
Bibcode: 1971ApJ...164..165D
Altcode:
An analysis is presented of X-ray line emission from heliumlike calcium
and related satellite lines produced by the large flare of 1969 November
2. The data were obtained from an NRL Bragg crystal spectrometer
aboard OSO-6. The inner-shell transition of Ca+17, 1s22s 2S-ls2s2p
P, and the forbidden transition of Ca+58, 1s2 5S-ls2s S, are clearly
resolved. The intercombination line of Ca+58 is numerically separated
into contributions from the 2 i and 2 3p2 levels. Time histories of the
flux of the resonance (1s 58-1s2p ii)), intercombination (lsi 5S-1s2p
3p), and forbidden (1s2 53-ls2s 25) lines of Ca+15, and the inner-shell
K-line of Ca+17 (1s22s 2S-1s2s2p ip), indicate that recombination is an
important process for line formation under flare conditions. For the
November 2 event, no statistically significant changes in the ratio
of the forbidden to intercombination lines occurred during the time
interval of observation.
Title: Emission Line Features of Solar Soft X-Ray Flare Spectra
Authors: Doschek, G. A.; Meekins, J. F.; Kreplin, R. W.
Bibcode: 1971BAAS....3....6D
Altcode:
No abstract at ADS
Title: Transport of Resonance Radiation in Optically Thick Media
Authors: Doschek, G. A.; Donahue, T. M.
Bibcode: 1970ApJ...161..737D
Altcode:
The mathematical assumption of complete frequency redistribution
(CFR) is investigated for the problem of the transport of resonance
radiation through gaseous media of large optical thicknesses. The
investigation is initiated by solving the CFR integral equation of
radiative transfer in a plane-parallel layer of gas. A steady-state
excited-atom density is maintained by plane-wave white-light radiation
produced by a source external to the medium. Computer solutions of the
CFR transfer equation are obtained for various values of the natural
damping coefficient and a range of total optical thicknesses. The CFR
source functions for large total optical thicknesses are then used as
trial solutions in the exact integral equation for the problem. Only
a first iteration is performed. The resultant intensity profiles for
various values of the damping coefficient are compared with CFR profiles
calculated from the CFR source functions. The orders of magnitude of
the total optical thicknesses and damping coefficients used in the
numerical computations approximate the values that are realized in
planetary nebulae. The non-CFR intensity profiles calculated by the
method described above deviate from the CFR profiles in the manner
predicted by qualitative argument.
Title: Recombination Edges Observed in Solar Soft X-Ray Flare Spectra
Authors: Meekins, J. F.; Doschek, G. A.
Bibcode: 1970SoPh...13..213M
Altcode:
Edges in the solar soft X-ray flare continuum have been observed
with the NRL Bragg crystal spectrometer aboard OSO-4. The edges
near 2.06 Å, 2.8 Å, and 4.46 Å are interpreted to be due to an
innershell dielectronic recombination process, details of which are
presented. Two other edges, 3.59 Å and 3.31 Å, are interpreted to be
due to recombination of the bare sulfur ion and innershell transitions
of calcium.
Title: Solar Soft X-Ray Flare Spectra from OSo-4
Authors: Meekins, J. F.; Doschek, G. A.; Friedman, H.; Chubb, T. A.;
Kreplin, R. W.
Bibcode: 1970SoPh...13..198M
Altcode:
Solar flare spectral data, covering the wavelength range 0.7-8.5 Å,
are derived from the NRL Bragg crystal spectrometers aboard OSO-4. A
detailed analysis of the soft X-ray spectra for the 3b flare of 16
November 1967 (2140 UT) is presented, and it is found that electron
temperatures derived from continua and emission lines are compatible
with a two or more component plasma, differing in temperature by 6-10
× 106K.
Title: The Helium-Like Calcium, Silicon, and Sulfur Lines During
the Decay of a Large Flare
Authors: Doschek, G. A.; Meekins, J. F.
Bibcode: 1970SoPh...13..220D
Altcode:
Helium-like resonance, intercombination, and forbidden transitions
of Ca, Si, and S were observed during the 3b solar flare of 16
November 1967, by means of the NRL Bragg crystal spectrometers
aboard OSO-4. During the decay of this flare, the forbidden lines
became enhanced relative to the intercombination and resonance
lines. Comparisons of the observed line ratios are made with theory
and mechanisms are proposed to explain the observations.
Title: A Large Apperature Confirmatory Service for A.L.P.O. Observers
Authors: Mullaney, J. J.; Doschek, G. A.
Bibcode: 1961StAst..15..155M
Altcode: 1961JALPO..15..155M
The purpose of this paper is to propose before the A.L.P.O., a
"confirmatory service" for its members, The availability of several
large aperture instruments, a shortage of available observing time,
and the frequent requests in The Strolling Astronomer for confirmation
of observations of "new" lunar and planetary features have all combined
to prompt me to bring forth this proposal.