feldman

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Author name code: feldman
ADS astronomy entries on 2022-09-14
author:"Feldman, Uri"

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Title: Transition Region Abundance Measurements During Impulsive
Heating Events
Authors: Warren, Harry P.; Brooks, David H.; Doschek, George A.;
Feldman, Uri
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.

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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.
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.

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Title: Assessing atomic data accuracy along isoelectronic sequences
Authors: Young, Peter R.; Feldman, Uri
2014AAS...22410603Y Altcode:
The CHIANTI atomic database provides radiative decay rates and electron
excitation rates for modeling collisionally-excited emission lines from
242 ions. We present a new method for assessing atomic data accuracy
whereby level populations for specific atomic levels are plotted
along isoelectronic sequences. Results are presented for the helium
through fluorine isoelectronic sequences. Generally a smooth variation
of population with atomic number is found and so anomalies, often due
to problems with atomic data, can be identified. One exception is for
the iron ions, which can show level populations an order of magnitude
larger than neighboring ions. These can be demonstrated to be due to
the much larger atomic models that are typically run for iron ions.

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Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere
Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico
2012uxss.book.....P Altcode:
1. The solar atmosphere; 2. Fundamentals of solar radiation;
3. Fundamentals of atomic physics; 4. Mechanisms of formation of the
solar spectrum; 5. Plasma diagnostic techniques; 6. Ultraviolet and
X-ray emission lines; 7. Spectrometers and imagers for observing the
solar ultraviolet and X-ray spectrum; 8. Quiet Sun and coronal holes;
9. Active regions; 10. Solar flares; 11. Element abundances; Appendices;
References; Index.

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Title: The Ne VII 465.22 Å to Ca IX 466.23 Å Intensity Ratio
Abundance Diagnostic in Solar Observations
Authors: Widing, K. G.; Feldman, U.
2011ApJ...742...71W Altcode:
The Ne VII 465.22 Å, and the Ca IX 466.23 Å, lines appear side by
side in spectra of solar atmosphere regions. Although the two ions are
formed at nearly the same temperature, the relative intensities of the
two lines show great variations from typical cases where Ne VII 465.23
Å is 20-30 times stronger than Ca IX 466.23 Å to spectra where the two
lines are almost equal. The relative Ne VII/Ca IX intensity variation
is correlated with the presence of the first ionization potential
effect on elemental abundances in the outer solar atmosphere. Using
published observational results, we derive the abundances of a number
of regions and show that on occasion the enrichment of Ca in the solar
atmosphere exceeds a factor of 30.

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Title: Redshifts, Widths, and Radiances of Spectral Lines Emitted
by the Solar Transition Region
Authors: Feldman, U.; Dammasch, I. E.; Doschek, G. A.
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.

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Title: Forbidden and Intercombination Lines of RR Telescopii:
Wavelength Measurements and Energy Levels
Authors: Young, P. R.; Feldman, U.; Lobel, A.
2011ApJS..196...23Y Altcode: 2011arXiv1102.3101Y
Ultraviolet and visible spectra of the symbiotic nova RR Telescopii
are used to derive reference wavelengths for many forbidden and
intercombination transitions of ions +1 to +6 of elements C, N, O,
Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca. The wavelengths are then
used to determine new energy values for the levels within the ions'
ground configurations or first excited configuration. The spectra
were recorded by the Space Telescope Imaging Spectrograph of the
Hubble Space Telescope and the Ultraviolet Echelle Spectrograph of the
European Southern Observatory in 2000 and 1999, respectively, and cover
1140-6915 Å. Particular care was taken to assess the accuracy of the
wavelength scale between the two instruments. An investigation of the
profiles of the emission lines reveals that the nebula consists of at
least two plasma components at different velocities. The components
have different densities, and a simple model of the lines' emissions
demonstrates that most of the lines principally arise from the high
density component. Only these lines were used for the wavelength study.

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Title: Atomic Data for Solar Corona Studies
Authors: Feldman, Uri
2011AIPC.1344..239F Altcode:
In recent years due to the increased sophistication of space
instrumentation ever more detailed observations of a large variety
of coronal structures became available. Nevertheless, thus far no
credible model emerged that describes the means by which the solar upper
atmosphere is created and maintained. Nevertheless, while interpreting
such spectra, some unexpected properties of coronal plasmas were
discovered. Although there are many cases where agreements between
observations and calculations are found, there are cases were clear
discrepancies do exist. I discuss some of the unexpected observational
results that were recently discovered, and suggest some observations
that if successfully executed could help explain the processes that
form and maintain the solar upper atmosphere.

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Title: TOPICAL REVIEW The solar UV-x-ray spectrum from 1.5 to 2000 Å
Authors: Doschek, G. A.; Feldman, U.
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.

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Title: Spectroscopy of positron annihilation gamma rays from
laser-exited media
Authors: Szabo, C. I.; Feldman, U.; Seely, J.; Hudson, L.; Chen, Hui;
Tommasini, R.; Hazi, A.; Shepherd, R.; Zulick, C.; Dollar, F.; Falk,
K.; Murphy, C. D.
2010APS..DPPXO6014S Altcode:
Motivated by calculations for gamma ray yields and results of positron
beam measurements from laser irradiated high Z targets [1], a Gamma-ray
Crystal Spectrometer (GCS) was built by Artep Inc. and fielded at the
Titan laser facility of LLNL. The spectrometer is equipped with heavy
shielding around a cylindrically bent Ge crystal in a transmission
geometry. The Bremsstrahlung continuum and the 511 keV annihilation
gamma rays are dispersed by the Ge(440) crystal and detected by an
image plate placed on the Rowland circle. The gamma rays originate
inside the thick target material (1 to 3 mm Au disks) where positrons
are produced in the intense field of the high energy (350 J) short
pulse (10 ps) laser irradiation. In addition to the spectrometer,
two different electronic detection systems also recorded the gamma
ray spectra using the single hit per pixel technique. The first gamma
ray spectra recorded with the crystal spectrometer and the electronic
detectors will be reported. [4pt] [1] Hui Chen et al., PRL 105, 015003
(2010)

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Title: Elemental Abundance Variations in a Decaying EUV-Bright Region
Authors: Ko, Yuan-Kuen; Landi, E.; Feldman, U.; Young, P.
2010AAS...21640515K Altcode: 2010BAAS...41..891K
The EIS instrument on Hinode observed an EUV-bright region at N15 as it
evolved during a course of four days on December 7-11, 2009. Although
containing no sunspots, this region was associated with a weak magnetic
concentration and exhibited large variations in loop and footpoint
brightening. It was in a decay phase with dispersing magnetic field
and weakening high-temperature emission. We present the variations of
elemental abundances in this region among different spatial structures
and with time. Implications in factors that can be associated with
the First Ionization Potential (FIP) effect will be discussed.

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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.
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.

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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.
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 &lt;=
log Te &lt;= 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.

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Title: The thermal structure of the solar upper atmosphere
Authors: Landi, Enrico; Feldman, Uri
2009AIPC.1161..142L Altcode:
In the present work we review the thermal structure of the solar
atmosphere. We first discuss the main diagnostic techniques used
to measure it, outlining their pitfalls and limitations. Then, we
review the recent measurements of the thermal structure of the solar
atmosphere carried out with the SOHO spectrometers CDS and SUMER. The
review shows that the solar upper atmosphere is made by an ensemble of
few, nearly isothermal plasmas with fixed temperatures, disconnected
from the colder, thermally continuous lower atmosphere.

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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.
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.

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Title: The Emission Measure of the Solar Lower Transition Region
(2 × 104-2 × 105 K)
Authors: Feldman, U.; Dammasch, I. E.; Landi, E.
2009ApJ...693.1474F Altcode:
We analyze Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectra in the 750-790 Å wavelength range from 12 different solar
regions on the disk to measure the thermal structure of the lower
transition region (LTR). We considered four coronal hole (CH), four
quiet Sun (QS), and four active region (AR) data sets observed by
SUMER during the rising phase of the solar cycle, and we analyzed the
emission of seven different ions formed between 2 × 104
and 2 × 105 K. We study the spatial variation of line
radiances along the slit within each observation, as well as their
relative radiances in different data sets. We also use them to determine
the differential emission measure of the LTR. We find that all lines
behave in the same way both along the slit within the same observation,
and between different data sets from different regions of the Sun. We
also find that while the absolute value of the differential emission
measure of LTR plasmas changes from region to region, its distribution
with temperature is fairly constant, suggesting that the thermal
structure of LTR plasmas is the same in CH, QS, and AR regions, and as
a function of time along the solar cycle. We discuss the implications
of our results for studies of coronal heating and of the solar cycle.

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Title: Radiative Losses of Solar Coronal Plasmas
Authors: Colgan, J.; Abdallah, J., Jr.; Sherrill, M. E.; Foster, M.;
Fontes, C. J.; Feldman, U.
2008ApJ...689..585C Altcode:
A comprehensive set of calculations of the radiative losses of solar
coronal plasmas is presented. The Los Alamos suite of atomic structure
and collision codes is used to generate collisional data for 15 coronal
elements. These data are used in the Los Alamos plasma kinetics code
ATOMIC to compute the radiative power loss as a function of electron
temperature. We investigate the sensitivity of the loss curves to
the quality of the atomic data and changes in the coronal elemental
abundances, and we compare our results with previous work.

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Title: High-resolution imaging spectrometer for recording absolutely
calibrated far ultraviolet spectra from laser-produced plasmas
Authors: Brown, Charles M.; Seely, John F.; Feldman, Uri; Holland,
Glenn E.; Weaver, James L.; Obenschain, Steven P.; Kjornrattanawanich,
Benjawan; Fielding, Drew
2008RScI...79j3109B Altcode:
An imaging spectrometer was designed and fabricated for recording far
ultraviolet spectra from laser-produced plasmas with wavelengths as
short as 155 nm. The spectrometer implements a Cassegrain telescope
and two gratings in a tandem Wadsworth optical configuration that
provides diffraction limited resolution. Spectral images were
recorded from plasmas produced by the irradiation of various target
materials by intense KrF laser radiation with 248 nm wavelength. Two
pairs of high-resolution gratings can be selected for the coverage
of two wavebands, one grating pair with 1800 grooves/mm and covering
approximately 155-175 nm and another grating pair with 1200 grooves/mm
covering 230-260 nm. The latter waveband includes the 248 nm KrF
laser wavelength, and the former waveband includes the wavelength
of the two-plasmon decay instability at 23 the KrF laser wavelength
(165 nm). The detection media consist of a complementary metal
oxide semiconductor imager, photostimulable phosphor image plates,
and a linear array of 1 mm2 square silicon photodiodes
with 0.4 ns rise time. The telescope mirrors, spectrometer gratings,
and 1 mm2 photodiode were calibrated using synchrotron
radiation, and this enables the measurement of the absolute emission
from the laser-produced plasmas with temporal, spatial, and spectral
resolutions. The spectrometer is capable of measuring absolute spectral
emissions at 165 nm wavelength as small as 5×10-7 J/nm
from a plasma source area of 0.37 mm2 and with 0.4 ns
time resolution.

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Title: Solar Observations of High-Temperature Emission with the
Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Warren, Harry P.; Feldman, Uri; Brown, Charles M.
2008ApJ...685.1277W Altcode:
We present an analysis of solar coronal emission lines formed above 2.5
MK observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
during a small flare. Our main purpose is to evaluate the internal
consistency of the atomic data available for the observed emission. We
find that the observed emission from high-temperature Ca lines (Ca XIV,
XV, XVI, and XVII) is generally consistent with the available atomic
data. The observed Fe XVII emission at these wavelengths, in contrast,
is more difficult to reconcile with current atomic calculations. The
energy levels tabulated in the CHIANTI atomic physics database generally
do not correspond to the observed wavelengths. After associating the
calculated emissivities with the observed emission by hand, we find
that the observed intensities are roughly consistent with what is
predicted. However, the intensity of the strongest unblended line, Fe
XVII 254.87 Å, is not consistent with the intensities of the other Fe
XVII lines at these wavelengths. Several of the Ca XV emission lines,
which are formed at about 4 MK, form density-sensitive line ratios in
the range log ne = 9-11 cm-3. Density measurements
at these temperatures are potentially important for understanding
the coronal heating mechanism. Our initial analysis suggests that
high-temperature active region plasma is underdense relative to the
predictions of steady heating models.

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Title: Nonthermal Electron Measurements in Solar Flares with
Hinode EIS
Authors: Feldman, Uri; Ralchenko, Yuri; Landi, Enrico
2008ApJ...684..707F Altcode:
The spectral range of the Hinode EIS (EUV Imaging Spectrometer)
instrument is 170-211 Å and 245-291 Å lines emitted by low-energy
levels in highly ionized Mn, Fe, Co, and Ni, as well as the very
energetic 1s2s3S1-1s2p3P2
transition in Fe XXV, appear in the EIS range. In this paper, we
investigate the use of these lines for detecting the presence of
nonthermal, high-energy electrons in flares. We first calculate line
fluxes among the various lines expected in the EIS range, assuming
that the electron velocity distribution is strictly Maxwellian. Then,
we calculate line fluxes using a velocity distribution composed of a
Maxwellian distribution plus an additional population of electrons with
a temperature of 10 keV (1.2 × 108 K) providing 1%, 2%, 4%,
7%, and 10% of the total free electrons. The calculations indicate that
flux ratios between the highly excited Fe XXV line and lines originating
in low-lying levels of other highly ionized ions in the EIS range could
shed light on the electron velocity distribution in hot flare plasmas.

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Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere
Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico
2008uxss.book.....P Altcode:
1. The solar atmosphere; 2. Fundamentals of solar radiation;
3. Fundamentals of atomic physics; 4. Mechanisms of formation of the
solar spectrum; 5. Plasma diagnostic techniques; 6. Ultraviolet and
X-ray emission lines; 7. Spectrometers and imagers for observing the
solar ultraviolet and X-ray spectrum; 8. Quiet Sun and coronal holes;
9. Active regions; 10. Solar flares; 11. Element abundances; Appendices;
References; Index.

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Title: Wavelengths and Intensities of Spectral Lines in the 171-211
and 245-291 Å Ranges from Five Solar Regions Recorded by the
Extreme-Ultraviolet Imaging Spectrometer (EIS) on Hinode
Authors: Brown, C. M.; Feldman, U.; Seely, J. F.; Korendyke, C. M.;
Hara, H.
2008ApJS..176..511B Altcode:
We present spectral line wavelengths, identifications, and intensities
in the 171-211 and 245-291 Å ranges from five solar plasma regions
recorded by the Extreme-Ultraviolet Imaging Spectrometer (EIS)
on Hinode. The recorded data were emitted from a quiet region,
two active areas on the solar disk, a limb region, and a region
20” above the limb. The line list contains 500 lines of which 55%
were identified with previously known transitions. Although the EIS
spectral coverage is limited to two ranges approximately 40 Å wide,
the identified lines belong to a total of 56 ions from 15 elements.

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Title: Line Intensity Ratios in the EIS Range Sensitive to Electron
Densities in 107 K Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
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.

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Title: The temperature structure of solar coronal plasmas
Authors: Feldman, Uri; Landi, Enrico
2008PhPl...15e6501F Altcode:
In the early 1940s it was at last accepted that the temperature of
the solar corona is at least 1 MK and varies considerably from region
to region throughout the solar activity cycle. It was recognized that
during solar minimum periods the electron temperatures of plasmas in
polar regions do not exceed 1 MK, but during solar maximum periods
the plasma temperatures of highly active regions could be as high as 3
MK. Nevertheless, until recently the consensus among the solar physics
community was that coronal temperatures vary among the different
regions in a continuous manner. In the present paper we review the
evidence showing that solar coronal plasmas (Te&gt;0.7 MK)
are isothermal and their temperature can have only a small set of
fixed values.

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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.
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.

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Title: An EUV narrow band imaging technique for diagnosing 10-30
keV ITER plasmas
Authors: Feldman, U.; Seely, J. F.; Landi, E.; Ralchenko, Y.
2008AIPC..988..205F Altcode:
In this paper we investigate the use of lines from tungsten (W)
ions to measure the properties of W impurities in ITER plasmas. We
calculate the intensities of the brightest spectral lines expected to
be radiated by W ions with wavelengths longer than 45 Å, abundance of
10-4 and at densities of 1020 m3. Using
the calculated wavelengths and intensities we propose a concept for
segmented multilayer-coated imaging telescopes that could be used to
investigate the properties of W impurities as a function of time and
space using spectral lines from highly ionized W

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Title: Calcium-to-Argon and Nickel-to-Argon Abundance Ratios as
Tracers of the Source Region of Postflare Loop System Material
Authors: Widing, K. G.; Feldman, U.
2008ApJ...675..863W Altcode:
Intensities of abundance diagnostic lines of Ca XV, Ca XVI, Ni XVII,
Ar XIII, and Ar XV have been derived for a classic flare loop system
observed during the Skylab mission. These have been used to test
for photospheric or coronal origin of the flare loop material. The
resulting FIP-bias factors are between 1.7 and 4.6 with a majority of
the values around 4.5 indicating a source with material modified by the
FIP effect. The loop system bias factors are similar to those observed
in a sample of Skylab prominences, suggesting that the disrupted mass
of the preflare embedded filament provided the loop system material.

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Title: The Thermal Structure of an Active Region Observed Outside
the Solar Disk
Authors: Landi, E.; Feldman, U.
2008ApJ...672..674L Altcode:
In the present work we analyze an extensive active region spectrum
observed by the SUMER instrument on board SOHO with the aim of
determining the thermal structure of the emitting plasma. We found
that the plasma is made of three distinct, isothermal components,
whose physical properties are similar to coronal hole, quiet-Sun,
and active region plasmas. The temperatures of the coronal hole-like
and quiet-Sun-like plasmas are in excellent agreement with previous
measurements obtained outside active regions. We also used a DEM
diagnostic technique to check the robustness of our results and
found that the DEM curves are compatible with the presence of three
distinct nearly isothermal plasmas if the individual DEM measurements
are smoothed over a small temperature interval. Larger intervals lead
the resulting DEM curves to a more multithermal behavior, raising the
question of whether multithermal active region DEM curves available in
the literature are real or an artifact of oversmoothing. The results
are compared with measurements of the temperature of individual loop
structures in the literature and discussed in light of a new picture
of the solar corona.

---------------------------------------------------------
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.
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: Observations of the Sun at Vacuum-Ultraviolet Wavelengths
from Space. Part II: Results and Interpretations
Authors: Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N.; Feldman,
Uri
2007SSRv..133..103W Altcode:
In Part I of this review, the concepts of solar vacuum-ultraviolet
(VUV) observations were outlined together with a discussion of
the space instrumentation used for the investigations. A section on
spectroradiometry provided some quantitative results on the solar VUV
radiation without considering any details of the solar phenomena leading
to the radiation. Here, in Part II, we present solar VUV observations
over the last decades and their interpretations in terms of the plasma
processes and the parameters of the solar atmosphere, with emphasis
on the spatial and thermal structures of the chromosphere, transition
region and corona of the quiet Sun. In addition, observations of
active regions, solar flares and prominences are included as well as
of small-scale events. Special sections are devoted to the elemental
composition of the solar atmosphere and theoretical considerations on
the heating of the corona and the generation of the solar wind.

---------------------------------------------------------
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.
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: 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.
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.
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: Spectroscopic Measurement of Coronal Compositions
Authors: Feldman, U.; Widing, K. G.
2007SSRv..130..115F Altcode: 2007SSRv..tmp...94F
Although the elemental composition in all parts of the solar photosphere
appears to be the same this is clearly not the case with the solar
upper atmosphere (SUA). Spectroscopic studies show that in the corona
elemental composition along solar equatorial regions is usually
different from polar regions; composition in quiet Sun regions is
often different from coronal hole and active region compositions and
the transition region composition is frequently different from the
coronal composition along the same line of sight. In the following two
issues are discussed. The first involves abundance ratios between the
high-FIP O and Ne and the low-FIP Mg and Fe that are important for
meaningful comparisons between photospheric and SUA compositions and
the second involves a review of composition and time variability of
SUA plasmas at heights of 1.0≤ h≤1.5 R ⊙.

---------------------------------------------------------
Title: Diagnostics of Suprathermal Electrons in Active-Region Plasmas
Using He-like UV Lines
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
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.
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.
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: Spectroscopic Measurement of Coronal Compositions
Authors: Feldman, U.; Widing, K. G.
2007coma.book..115F Altcode:
Although the elemental composition in all parts of the solar photosphere
appears to be the same this is clearly not the case with the solar
upper atmosphere (SUA). Spectroscopic studies show that in the corona
elemental composition along solar equatorial regions is usually
different from polar regions; composition in quiet Sun regions is
often different from coronal hole and active region compositions and
the transition region composition is frequently different from the
coronal composition along the same line of sight. In the following two
issues are discussed. The first involves abundance ratios between the
high-FIP O and Ne and the low-FIP Mg and Fe that are important for
meaningful comparisons between photospheric and SUA compositions and
the second involves a review of composition and time variability of
SUA plasmas at heights of 1.0≤h≤1.5R ⊙.

---------------------------------------------------------
Title: Plasma Diagnostics of the Large-Scale Corona with SUMER
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
2006ESASP.617E..12L Altcode: 2006soho...17E..12L
No abstract at ADS

---------------------------------------------------------
Title: Plasma Diagnostics of the Large-Scale Corona with
SUMER. I. Measurements at the West Limb
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
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: X-Ray Observations of Solar Long-Duration Flares
Authors: Phillips, K. J. H.; Feldman, U.; Harra, L. K.
2005ApJ...634..641P Altcode:
Yohkoh X-ray observations during the several-hour decay of six
large solar flares show that the main emitting region is in the
form of a bright loop-top source whose spatial extent well after
the impulsive stage explains most of the broadening of S XV and Ca
XIX X-ray lines, which would otherwise imply nonthermal velocities
of 100 km s-1 or more. During the decay of each event,
the electron temperature and emission measure decline slowly. For the
nearly disk center event of 1992 February 27, the volume increases and
the deduced lower limit to the electron density Ne decreases
from ~1011 cm-3 to just below 1010
cm-3. The nonuniform emission along the loops indicates
that Spitzer heat conduction does not operate. If radiation is the
only or main energy-loss mechanism, the lower limits to Ne
imply upper limits to radiation cooling times of up to 10 hr, less
than the flare decay time, so necessitating a continuing energy
input. Although magnetic reconnection of previous broken open loops
(the Kopp-Pneuman model) has been widely regarded as the source of
energy in such flares, the small nonthermal velocities-only 20-50
km s-1 as indicated by SUMER observations-and the lack of
spectroscopic indicators of large inflows or outflows argue against
it. Other flare models must also explain the relatively small nonthermal
velocities. An alternative picture of loop oscillations recently seen
in TRACE and Yohkoh data is proposed for the production of observed
nonthermal velocities.

---------------------------------------------------------
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.
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: Evidence for In Situ Heating in Active Region Loops
Authors: Curdt, W.; Landi, E.; Wang, T. J.; Feldman, U.
2005ESASP.592..475C Altcode: 2005soho...16E..85C; 2005ESASP.592E..85C
No abstract at ADS

---------------------------------------------------------
Title: On the nature of the unidentified solar emission near 117 nm
Authors: Wilhelm, K.; Schühle, U.; Curdt, W.; Hilchenbach, M.;
Marsch, E.; Lemaire, P.; Bertaux, J. -L.; Jordan, S. D.; Feldman, U.
2005A&A...439..701W Altcode:
Spectral observations of the Sun in the vacuum-ultraviolet wavelength
range by SUMER on SOHO led to the discovery of unusual emission
features - called humps here - at 116.70 nm and 117.05 nm on either
side of the He i 58.43 nm line. This resonance line is seen in the
second order of diffraction, whereas the humps are recorded in the
first order with the SUMER spectrometer. In its spectra both orders
are superimposed. Two less pronounced humps can be detected at 117.27
nm and near 117.85 nm. After rejecting various possibilities of an
instrumental cause of the humps, they are studied in different solar
regions. Most of the measurements, in particular those related to the
limb-brightening characteristics, indicate that the humps are not part
of the background continuum. An assembly of spectrally-unresolved atomic
or ionic emission lines might be contributing to the hump at 117.05
nm, but no such lines are known near 116.7 nm. It is concluded that we
detect genuine radiation, the generation of which is not understood. A
two-photon emission process, parametric frequency down conversion,
and molecular emissions are briefly considered as causes of the humps,
but a final conclusion could not be reached.

---------------------------------------------------------
Title: On the sources of fast and slow solar wind
Authors: Feldman, U.; Landi, E.; Schwadron, N. A.
2005JGRA..110.7109F Altcode: 2005JGRA..11007109F
The slow speed solar wind as measured at the Earth orbit and beyond
is characterized by its velocity of ≃400 km s-1, by its
coronal composition and by its frozen-in temperature (from carbon
charge-states) of 1.4-1.6 × 106 K. In contrast the
fast speed solar wind is characterized by its velocity of ≃750
km s-1, its nearly photospheric composition and its
frozen-in temperature of ≃8 × 105 K. The solar wind is
believed to originate very close to the solar surface, but since it
is accelerated significantly above the solar surface, its velocity
cannot be correlated with remote observations to trace its origin. In
contrast, elemental abundances and freeze-in temperatures can be used
as tracers for locating the sources from which the slow and fast solar
winds emerge. By comparing remote observations with properties of the
solar wind observed in situ, the most likely structures from which solar
wind plasmas emerge can be identified. In the present paper we review
the current understanding of the morphological features present in the
solar upper atmosphere and their physical properties such as electron
temperature, electron density and elemental abundances. In addition, we
discuss these observations in the context of recent theories describing
the emergence of new magnetic flux to power the solar wind, and more
traditional models that treat the background field and solar wind as
a steady phenomenon.

---------------------------------------------------------
Title: Properties of the Solar Corona Outside the West Solar Limb
Authors: Doschek, G. A.; Feldman, U.; Landi, E.
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: Coronal Element Comparison Observed by SOHO SUMER in the
Quiet Southeast and Northwest Limb Regions at 1.04 Rsolar
above the Solar Disk
Authors: Widing, K. G.; Landi, E.; Feldman, U.
2005ApJ...622.1211W Altcode:
The composition in an isothermal region at 1.04 Rsolar above
a diffuse, quiet coronal region on the northwest limb is studied and
compared with a similar region above the southeast limb analyzed by
Warren in 1999. Elemental abundances relative to H in the corona are
measured and normalized to the abundance ratios in the photosphere. The
enrichment factors of the low first ionization potential elements are
comparable above both limbs, but are significantly smaller than the
factor of 4 in SUMER spectra obtained 2 years earlier at solar minimum
in a diffuse, quiet equatorial region.

---------------------------------------------------------
Title: Helium Abundance in High-Temperature Solar Flare Plasmas
Authors: Feldman, U.; Landi, E.; Laming, J. M.
2005ApJ...619.1142F Altcode:
In the present work we use emission from dense plasmas late in the decay
phase of flares, while the plasmas are still hot [(2-4)×106
K], to determine the absolute helium abundance in flaring solar
corona. To achieve this, we make use of intensity ratios of H I
and He II lines and of intensity ratios between the He II lines
and the bremsstrahlung continuum radiation emitted by the local
postflare plasmas. These ratios are very sensitive to the electron
temperature, which is measured by using two different techniques:
intensity ratios from lines emitted by heavier elements and from the
line width of H I and He II lines. The latter method is made possible
by the low atomic weight of H and He and by the high temperature of
the plasma, which causes the widths of these lines to exceed 0.6 Å
(He) and 1.1 Å (H). Such values significantly exceed the broadening
due to nonthermal mass motions, so line widths can provide accurate
temperature measurements. The average helium absolute abundance was
found to be 12.2%+/-2.4%.

---------------------------------------------------------
Title: In-Situ Heating in Active Region Loops
Authors: Curdt, W.; Landi, E.; Wang, T.; Feldman, U.
2005HvaOB..29..157C Altcode:
We report new observational results and insights in the energy release
during transient events on sub-flare level in active region coronal
loops. Our work is based on multi-temperature observations obtained
high above the limb by the SUMER spectrometer on SOHO. We conclude
that the energy is impulsively injected into the loop system from
one and only one foot point. This asymmetric injection does not seem
to be connected with any bulk flow and there is no indication that
the plasma in the loop is replenished or replaced. Therefore the
chromospheric evaporation model is not applicable for this type of
events. The electron density, Ne, however, increases by up
to two orders of magnitude during such events. If no new material is
added to the local plasma, then the Ne increase can only be
explained by a rapid volume decrease, i.e., by a in-situ pinch effect,
compressing and heating the affected plasma.

---------------------------------------------------------
Title: The SUMER spectral atlas of solar coronal features
Authors: Curdt, W.; Landi, E.; Feldman, U.
2004A&A...427.1045C Altcode:
We present a spectral atlas of the solar corona in the far-ultraviolet
(FUV) and extreme ultraviolet (EUV) wavelength range. The atlas is based
on observations obtained between 670 Å and 1609 Å in first order of
diffraction and between 465 and 670 Å in second order with the SUMER
(Solar Ultraviolet Measurements of Emitted Radiation) spectrograph
on SOHO (Solar and Heliospheric Observatory). This paper complements
the SUMER Spectral Atlas of Solar Disk Features, also published in
A&amp;A. The atlas contains off-limb spectra of the corona above a
coronal hole, a quiet region, the active corona, and a flare. We provide
wavelengths of all detected lines and identification, if available; 311
out of 507 coronal emission lines could be identified or reconfirmed,
including several new identifications. Brief descriptions of the
data reduction and calibration procedures are given. The spectral
radiances are determined with a relative uncertainty of 0.15 to 0.40
(1σ) and the wavelength scale is accurate to typically ≃30 mÅ. The
atlas is also available in a machine readable format. Table
\ref{tab3} and Fig. \ref{fig3} are only available in electronic form
at http://www.edpsciences.org

---------------------------------------------------------
Title: Role of Closed Magnetic Fields in Solar Wind Flow
Authors: Woo, Richard; Habbal, Shadia Rifai; Feldman, Uri
2004ApJ...612.1171W Altcode:
In this paper we demonstrate how closed magnetic fields appear to be
playing a significant role in solar wind flow. Confinement or trapping
of plasma is the physical process, while confinement duration, as
characterized by the first ionization potential (FIP) bias, is the
attribute that divides the fast- and slow-wind regions. The trapped
plasma is released along ubiquitous and predominantly radial open
field lines, presumably by continual reconnection at the base of the
corona, with evidence for this process coming from the appearance of
the imprint of polar coronal holes, quiet Sun, and active regions
in the outer corona and interplanetary space. When trapping is not
long enough to enrich the elemental abundance (FIP bias near 1), the
coronal radial density gradient is steep, coronal temperature is low,
and a fast wind flows in the overlying corona. However, the presence of
closed fields still influences the flow of the fast wind, as revealed
by the fact that flow speed is anticorrelated with, or characterized
by, the density at the base of the corona. When trapping is long
enough to enrich the abundance (FIP bias &gt; 1), a slow wind flows,
and FIP bias characterizes its properties. Enhanced FIP bias gives
rise to a decreased coronal radial density gradient, as manifested
by the extension of coronal streamers in white-light coronal images,
increased coronal temperature, and decreased solar wind speed in the
overlying corona.

---------------------------------------------------------
Title: Resolving X-Ray Sources from B Stars Spectroscopically:
The Example of μ Leporis
Authors: Behar, Ehud; Leutenegger, Maurice; Doron, Rami; Güdel,
Manuel; Feldman, Uri; Audard, Marc; Kahn, Steven M.
2004ApJ...612L..65B Altcode: 2004astro.ph..7338B
We present high-resolution X-ray observations of the chemically peculiar
late-type B star μ Lep. However, we find spectroscopic and astrometric
evidence, which shows that the X-rays are not traced back to the B
star itself but rather to a previously unresolved companion, μ Lep-B,
whose X-ray spectrum resembles that of a coronally active source. We
discuss the possibility that μ Lep-B is a pre-main-sequence companion,
most likely of the nonaccreting magnetically active type.

---------------------------------------------------------
Title: Models for Solar Magnetic Loops. IV. On the Relation between
Coronal and Footpoint Plasma in Active Region Loops
Authors: Landi, E.; Feldman, U.
2004ApJ...611..537L Altcode:
In the present work we analyze several SUMER intensity maps of active
region solar loops in order to compare the relative brightnesses of
the footpoints and the coronal section of active region loops. We
find that the former are barely distinguishable from the background
emission of the active region, while the coronal emission of loops is
confined in well-identifiable structures that are significantly brighter
than the background. This result means that the vast majority of the
active region emission in chromospheric and transition region lines
is generated by plasma not directly connected with the coronal plasma
that constitutes the observed coronal loops. We determine the observed
intensities of coronal lines relative to the observed transition
region and chromospheric emission and compare them with predictions
from loop models having uniform cross section and different heating
functions. We find that the loop models overestimate the footpoint
emission by orders of magnitude. We discuss the discrepancy in light
of the heating function and of the loop cross section. We speculate
that nonuniformity in the loop cross section, more specifically a
significant decrease of the cross section near the footpoints, is the
most likely solution to the discrepancy.

---------------------------------------------------------
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.
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&lt;=Te&lt;=1×107K)
along the lines of sight were formed by in situ heating
and possibly by compression of the ambient coronal material
(Te&lt;=2×106 K).

---------------------------------------------------------
Title: Newly Identified Forbidden Transitions within the Ground
Configuration of Ions of Very Low Abundance P, Cl, K, and Co
Authors: Feldman, U.; Landi, E.; Curdt, W.
2004ApJ...607.1039F Altcode:
Forbidden lines from transitions within the ground configuration
of highly ionized atoms occupy an important role in diagnosing the
properties of astrophysical plasmas. In this paper we report the
identification of forbidden lines in the 500-1500 Å range from
transitions within the ground configuration of highly ionized ions
of the very low abundance phosphorus, chlorine, potassium, and
cobalt recorded by SOHO SUMER. For the newly identified lines we
provide upper level fractional populations multiplied by relevant
spontaneous decay rates. Aided by the newly identified lines, the
coronal composition of elements with photospheric abundances of
5×10-7-1×10-8 relative to hydrogen could
be established.

---------------------------------------------------------
Title: Observations of the Sun at Vacuum- Ultraviolet Wavelengths
from Space. Part I: Concepts and Instrumentation
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.; Marsch, Eckart; Feldman,
Uri
2004SSRv..111..415W Altcode:
Studies of the high-temperature solar atmosphere are to a large extent
based on spectroscopic observations of emission lines and continuum
radiation in the vacuum-ultraviolet (VUV) wavelength range of the
electromagnetic spectrum. In addition, important contributions stem
from soft X-ray measurements. Most of the VUV radiation is produced
by transitions of atoms and ions. The resulting atomic and ionic
spectral lines have formation temperatures between 10 000 K and 20 MK,
representative of the chromosphere, transition region, corona, and
solar flares. Some molecular lines and the continua originate in cooler
regions of the Sun, around and below the temperature minimum between
the photosphere and the chromosphere. Radiation at VUV wavelengths
is strongly absorbed by the Earth's atmosphere. Consequently, it can
only be detected with instruments on sounding rockets and spacecraft
operating above the atmosphere. The progress in this field of research,
in particular over the last 25 years, will be presented in the first
part of this review by describing the concepts and instrumentation
of modern spectrographs and imaging telescopes. This presentation
is accompanied by some examples of high-resolution solar images
and a discussion of radiometric-calibration aspects and wavelength
measurements. A second part will follow in the near future, summarizing
important results obtained on the plasma conditions in the solar
atmosphere.

---------------------------------------------------------
Title: Properties of the Lower Transition Region: The Widths of
Optically Allowed and Intersystem Spectral Lines
Authors: Doschek, G. A.; Feldman, U.
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: What do Measurements of Abundance Variations Tell us About
the Origin and Evolution of the Solar Wind
Authors: Woo, R.; Habbal, S. R.; Feldman, U.
2003AGUFMSH41B0470W Altcode:
Connections between the Sun and solar wind have recently been made based
on observations of density, velocity, and magnetic field. These have
led to fundamental changes in our understanding of coronal magnetic
topology and the origin and evolution of the solar wind. During solar
minimum, polar coronal holes are neither the only regions of open
magnetic field lines nor the sole source of fast solar wind. Instead,
open magnetic field lines thread the entire corona, and solar wind
flowing along them carries the imprint of coronal holes, quiet Sun, and
active regions into interplanetary space. The purpose of this paper is
to show how measurements of abundance variations in the corona and solar
wind reinforce and complete this picture, providing key insight into
where and how the solar wind, especially the slow wind, is produced.

---------------------------------------------------------
Title: New Identifications of Mn VI and Fe VII Vacuum Ultraviolet
Lines
Authors: Ekberg, J. O.; Feldman, U.
2003ApJS..148..567E Altcode:
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer aboard the Solar and Heliospheric Observatory (SOHO)
recorded a large number of spectra in the 500-1600 Å region. Although
many of the detected lines have already been identified, the origins
of a substantial fraction of the lines remain unknown. In this paper
we report on a study of Mn VI and Fe VII in laboratory-generated
vacuum spark spectra. Some of the Fe VII identified lines belonging
to transitions of the type 3d4s-3d4p and 3d4p-3d4d were also observed
in SUMER quiet-Sun and sunspot spectra. Because of the much lower
manganese abundance in the solar atmosphere, none of the Mn VI lines
were observed in the SUMER spectra.

---------------------------------------------------------
Title: New Identifications of Mn VII and Fe VIII Lines Belonging
to Transitions of the Type 3p64p-3p64d and
3p53d2-3p64d
Authors: Ekberg, J. O.; Feldman, U.
2003ApJ...595..517E Altcode:
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer aboard the Solar and Heliospheric Observatory (SOHO)
recorded a large number of spectra in the 500-1600 Å region. Many of
the detected spectral lines have been identified as transitions in ions
from elements with low-to-moderate atomic numbers (Z&lt;=20). However,
a substantial number of lines remained unidentified. We postulated
that some of the unidentified lines are transitions between excited
configurations in Fe+7. Unfortunately, Cr+5 was
the last ion in the K I isoelectronic sequence where the envisioned
types of transitions were previously identified. In this paper we report
new identifications, in laboratory-generated spectra, of transitions
between excited configurations in Mn+6 and Fe+7,
two additional ions along the K I isoelectronic sequence. Since the
elemental abundance of manganese in the solar atmosphere is very low,
no Mn VII lines were identified in the SUMER spectra; however, the
laboratory-identified Fe VIII lines were found to be present in the
SUMER quiet-Sun spectra recorded above the solar limb and in sunspot
spectra recorded on the solar disk.

---------------------------------------------------------
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.
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: Properties of Solar Plasmas near Solar Maximum above Two
Quiet Regions at Distances of 1.02-1.34 Rsolar
Authors: Landi, E.; Feldman, U.
2003ApJ...592..607L Altcode:
In the present work we have analyzed the spectra emitted by two quiet
solar regions observed off the solar disk by the SUMER instrument on
board the SOHO satellite. The two complete spectra were recorded when
the SOHO north-south axis was rotated relative to the Sun north-south
axis by ~=150° clockwise. As a result, the SUMER slit could be placed
so that it is perpendicular to the solar limb in an intermediate
orientation between the equator and the poles. The SUMER fields of
view consisted of two 1" wide radial strips of the solar corona from
1.02 to 1.34 Rsolar. The aim of the present work was to
measure the physical properties of the emitting plasma, namely, the
electron density and temperature, the plasma emission measure, and
the nonthermal mass motions, as a function of the distance from the
solar limb. The measurement of the plasma absolute element abundances
is deferred to a future paper. In measuring the nonthermal velocities
of both source regions, we have discovered a residual instrumental
systematic effect to line widths. The plasma in the SUMER field of
view is nearly isothermal. The measurements of electron density and
temperature allow us to check the hydrostatic assumption commonly
adopted in the literature and to find that the plasma is denser than
predicted. The wide wavelength range covered by the SUMER instrument
includes several Li-like ions, allowing us to investigate the relative
contribution of the radiative and collisional excitation mechanisms
in the Li-like resonance doublet formation. We confirm the earlier
findings that a significant radiative excitation occurs for O VI and
Ne VIII resonance lines even at low altitudes.

---------------------------------------------------------
Title: The Variability of the Solar Coronal Helium Abundance: Polar
Coronal Holes Compared to the Quiet Sun
Authors: Laming, J. Martin; Feldman, Uri
2003ApJ...591.1257L Altcode:
We report on measurements of the abundance ratio He/H in solar polar
coronal holes and neighboring quiet coronal regions, using the SUMER
spectrometer on board SOHO. In coronal holes we find He abundances
smaller than or equal to the value found in the fast solar wind,
5% by number relative to H, suggesting that the flow speed of He up
into the wind is equal to or greater than the flow speed for H in the
regions we observe. Going to regions above quiet solar corona, we find
similar He abundances at altitudes of 50" or more, with some indication
that the He abundance is increased toward its photospheric value of
8.5% relative to H lower down. We take this to indicate that the He
abundance in open-field regions of the corona is never higher than 5%
(as observed in the solar wind), but that in low-lying, closed magnetic
field regions higher abundances may result.

---------------------------------------------------------
Title: Elemental Abundances in the Solar Upper Atmosphere Derived
by Spectroscopic Means
Authors: Feldman, U.; Widing, K. G.
2003SSRv..107..665F Altcode:
The composition of the solar photosphere is believed to be
uniform. Indeed a quantity that does not vary with solar surface
location or with a particular solar feature, i.e., no observational
evidence is available to indicate that the photospheric composition near
the solar equator is different from the photospheric composition near
the solar poles or that the photospheric composition in quiet regions
is different from the composition in active regions. In contrast, the
composition of the solar upper atmosphere is not well defined. Solar
composition work in recent decades has brought the recognition that
there are systematic differences between the composition of the
corona and the photosphere and revealed evidence for spatial and time
variability in the composition of various coronal features. We review
the spectroscopic techniques used and the progress that was made in
recent years in deriving the plasma compositions of various solar
upper atmosphere structures.

---------------------------------------------------------
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.
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: Images of the solar upper atmosphere from SUMER on SOHO
Authors: Feldman, Uri; Dammasch, Ingolf E.; Wilhelm, Klaus; Lemaire,
Philippe; Hassler, Donald M.; Battrick, Bruce
2003ESASP1274.....F Altcode: 2003isua.book.....F
During the first year of SOHO operations and later in 1999, SUMER
acquired several thousand images of the solar upper atmosphere. This
atlas includes most of the full-Sun images that SUMER recorded
and the majority of its images acquired during the Whole-Sun Month
campaign. One of our main tasks while selecting the atlas format has
been the implementation of our desire to maintain the high spatial
resolution that SUMER achieved. In particular we hope that people
with average vision will be able to see the finest details of the
plasma structures that SUMER can resolve. Thus the page size has
been chosen such that the finest resolution element in the images
corresponds to approximately 250 μm in this atlas. The images in
the atlas were recorded in spectral lines or in continuum radiation
emitted by plasmas spanning the electron temperature domain from
1×104K to 1.4×106K. Some of the images were
recorded simultaneously in radiation emitted by plasmas of different
temperatures. Due to substantial differences of the plasma properties
from which the radiation originated, the atlas provides a unique source
for studying many aspects of the solar upper atmosphere.

---------------------------------------------------------
Title: Nonthermal Mass Motions within the High-Temperature Plasmas
above a Complex Solar Active Region
Authors: Feldman, U.; Landi, E.; Curdt, W.
2003ApJ...585.1087F Altcode:
We report on mass motions in high-temperature plasmas at
radial distances of 1.06-1.20 Rsolar corresponding
to 3.3×104-1.3×105 km above the west
solar limb. The observations were conducted over a 53 hr time
period while a complex active region moved across the west
solar limb. We found that the nonthermal mass motions in the
2.6×106-6.6×106 K plasmas that were
imaged along the slit were in the 20-35 km s-1
velocity range. The magnitude of the nonthermal mass motions
was independent of the plasma temperature or its height above the
limb. We also found that the emission measure distribution within the
2.6×106-6.6×106 K plasma regimes did not change
during most of the observations, an indication that on the average
the temperature distribution among the various plasma volumes along
the line of sight stayed unchanged.

---------------------------------------------------------
Title: Mass Motions and Plasma Properties in the 107
K Flare Solar Corona
Authors: Landi, E.; Feldman, U.; Innes, D. E.; Curdt, W.
2003ApJ...582..506L Altcode:
In the present work, we analyze Solar Ultraviolet Measurement of
Emitted Radiation (SUMER) observations of a solar limb flare that
occurred on 1999 May 9. The analyzed data cover a time span of around
6.4 hr, during which an M-7.6 flare erupted and decayed in the field of
view. Two selected regions along the SUMER slit have been considered
for quantitative analysis. The main purpose of the present analysis
is to measure the mass motions and the nonthermal velocities of the
postflare plasmas and their temporal evolution. To achieve this we
use lines having formation temperatures in the 2.5×106
to 2×107 K range from which we derive net mass motions
and nonthermal velocities and compare them with the properties of the
surrounding plasma not affected by the flare activity. To understand
the physical conditions of the flaring plasma and of the surrounding
material, we derive electron temperature, electron density, and emission
measures of the emitting plasma. We find that bulk motions, initially
of the order of several hundreds of kilometers per second in both
directions, decay within 10 minutes from the flare onset; nonthermal
velocities decay to preflare values of around 30 km s-1 in
less than 2 hr from the maximum value of around 100 km s-1
at flare onset. The measured electron density does not seem to change
during activity, while the flare plasma temperature steadily decays
to preflare values. The temperature evolution is consistent with a
radiatively cooling plasma, although the uncertainties associated to
the measurement of the variation of thermal energy of the flare plasma
prevent a definitive conclusion on possible continuous heating of the
flaring plasma.

---------------------------------------------------------
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.
2002ASPC..277..461D Altcode: 2002sccx.conf..461D
No abstract at ADS

---------------------------------------------------------
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
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: A Comparison between Coronal Emission Lines from an Isothermal
Spectrum Observed with the Coronal Diagnostic Spectrometer and
CHIANTI Emissivities
Authors: Landi, E.; Feldman, U.; Dere, K. P.
2002ApJ...574..495L Altcode:
The present paper compares off-disk spectral observations of the
solar corona in the ranges 307-379 and 513-633 Å with theoretical
emissivities calculated using the CHIANTI database. The observed spectra
were recorded by the Coronal Diagnostic Spectrometer instrument on
board the Solar and Heliospheric Observatory using the normal-incidence
portion of the instrument. Using line-ratio techniques, we first measure
the electron temperature and density in the emitting region, verifying
that it is nearly isothermal. Next, we use an emission-measure analysis
to compare measured spectral line intensities with predictions from the
CHIANTI database. This comparison allows us to assess the quality of
the CHIANTI data for the brightest coronal lines in the 307-379 and
513-633 Å spectral ranges. As a result, we are able to (1) select
lines and ions for which the agreement between theory and observation
is good, (2) identify a few lines that are blended, and (3) stress
inconsistencies between a few lines and theory, thus showing where
improvements to atomic data and transition probabilities are necessary.

---------------------------------------------------------
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.
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: The new picture of the transition region and corona from SUMER
Authors: Feldman, U.
2002ESASP.508..531F Altcode: 2002soho...11..531F
The solar upper atmosphere (SUA) is defined as the volume above the
photosphere occupied by plasmas at electron temperatures greater than
2×104K. Until the Skylab era, little was known about
the morphology of the SUA. As a result, the early models assumed
a continuous atmosphere in which the temperature increased with
height. With the advances in spectroscopic measurements it became
apparent that most of the radiation from plasmas at temperatures of
3×104 - 6×105K is not coming from the interface
between the chromosphere and corona but rather from unrelated plasma
structures that I chose to name Unresolved Fine Structures (UFS). Recent
results obtained by instruments on SOHO and on TRACE support the earlier
conclusions and provide additional insight into the makeup of the SUA
plasma structures of quiet Sun and coronal-hole regions.

---------------------------------------------------------
Title: SOHO/SUMER Measurements of the Solar Coronal Helium Abundance
Authors: Laming, J. M.; Feldman, U.
2002AAS...200.5716L Altcode: 2002BAAS...34R.739L
We report on the progress of work to measure the helium abundance in
various regions of the solar corona. Concentrating on polar coronal
holes, we find similar helium abundances to those measured in the fast
solar wind, i.e. 4-5% by number relative to hydrogen at an altitude
approximately 100 arcseconds above the limb. This suggests that the
flows of hydrogen and helium up into the fast solar wind must be locked
together, presumably by plasma waves, since otherwise large variations
of the He/H abundance ratio could result. This work is supported by
the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research
Option and by NASA Contract S137836.

---------------------------------------------------------
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.
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: CHIANTI-An Atomic Database for Emission Lines. V. Comparison
with an Isothermal Spectrum Observed with SUMER
Authors: Landi, E.; Feldman, U.; Dere, K. P.
2002ApJS..139..281L Altcode:
CHIANTI is a database consisting of critically evaluated atomic data and
transition probabilities necessary to analyze spectral observations
of optically thin plasmas. Previous papers described the content
of the database and compared it to a solar active region spectrum
between 170 and 450 Å. The aim of the present paper is to compare
CHIANTI predictions to off-disk spectral observations of the solar
corona between 500 and 1500 Å. The observed spectra were recorded by
the SUMER instrument on board the Solar and Heliospheric Observatory
using the full spectral range allowed by the instrument. Earlier works
have demonstrated that the particular emitting plasma is isothermal
at a temperature of 1.35×106 K, making it ideal for the
assessment of the accuracy of the CHIANTI database. This assessment of
the CHIANTI database allowed us (1) to select lines and ions for which
the agreement between theory and observation is good, (2) to identify
several lines which are blended, and (3) to stress inconsistencies
between a few lines and theory, thus showing where improvements to
atomic data and transition probabilities are necessary.

---------------------------------------------------------
Title: A review of the first ionization potential effect on elemental
abundances in the solar corona and in flares
Authors: Feldman, U.; Widing, K. G.
2002PhPl....9..629F Altcode:
The elemental composition of solar upper atmosphere plasmas was
studied from spectra obtained by instruments aboard all major
solar observatories that were launched into space in the last three
decades. The studies show that the first ionization potential (FIP)
of the elements has a profound effect on their abundance in the various
solar upper atmosphere regions. In this paper we review properties of
the FIP effect as they relate to coronal holes, quiet regions, active
regions and flares and we show that although the derived compositions
vary considerably with the type of plasma observed regularities in
their behavior are emerging. The observed behavior may help identify
the energy deposition mechanism that fuels the corona and solar flares.

---------------------------------------------------------
Title: Electric Currents as the Main Cause of Coronal and Flare
Activity in the Sun and in Many Late-Type Stars
Authors: Feldman, U.
2002PhyS...65..185F Altcode:
Coronal temperatures of late type stars are hundreds to thousands of
times higher than the temperatures of their photospheres. Attempts
to account for the existence of high coronal temperature in the Sun,
by invoking wave heating of various kinds and/or by the annihilation
of parts of the magnetic field above the surface and using the resulted
energy to heat coronal activity, seem to be unsuccessful. In this paper,
I suggest that electric currents are the means by which the Sun and
most likely many late type stars produce their coronal activity. To
support this idea, I bring evidence from observations occurring in
solar and stellar upper atmosphere plasmas that resemble in their
appearance phenomena that are the consequence of electric currents
flowing in highly ionized plasmas.

---------------------------------------------------------
Title: The Solar Helium Abundance in Polar Coronal Holes as Measured
by SOHO/SUMER
Authors: Laming, J. M.; Feldman, U.
2001AAS...199.8806L Altcode: 2001BAAS...33.1434L
The solar helium abundance measured in situ in the fast solar wind is
typically 0.05 by number relative to hydrogen, whereas in the solar
envelope it is measured by helioseismology to be 0.085. We report on
analyses of spectra taken by SOHO/SUMER of solar polar coronal holes
to determine the abundance of helium by emission line spectroscopy. In
comparison with our earlier measurement in an equatorial streamer,
coronal hole spectra are less intense, which makes determining
the intensities of hydrogen lines to adequate precision much more
difficult. Using other strong lines in the spectrum, e.g. C IV, N V,
O VI we find helium abundance values more consistent with those in the
fast solar wind than the photospheric value. This work is supported by
the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research
Option and by NASA Contract S137836.

---------------------------------------------------------
Title: The SUMER spectral atlas of solar-disk features
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schühle, U.; Lemaire, P.
2001AIPC..598...45C Altcode: 2001sgc..conf...45C
A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas
of the Sun between 670 Å and 1609 Å in first order of diffraction
has been derived from observations obtained with the SUMER (Solar
Ultraviolet Measurements of Emitted Radiation) spectrograph on
the spacecraft SOHO (Solar and Heliospheric Observatory) [1]. The
atlas contains spectra of the average quiet Sun, a coronal hole and
a sunspot on disk. Different physical parameters prevalent in the
bright network (BN) and in the cell interior (CI)-contributing in a
distinct manner to the average quiet-Sun emission-have their imprint
on the BN/CI ratio, which is also shown for the entire spectral
range. With a few exceptions, all major lines are given with their
identifications and wavelengths. Lines that appear in second order
are superimposed on the first order spectra, but below 500 Å the
responsivity of the normal-incidence optical system is very low. The
spectra include emissions from atoms and ions in the temperature range
6 103 K to 2 106 K, i.e., continua and mission
lines emitted from the lower chromosphere to the corona. This spectral
atlas, with its broad wavelength coverage, provides a rich source
of new diagnostic tools for studying the physical parameters in the
chromosphere, the transition region and the corona. In particular,
the wavelength range below 1100 Å as observed by SUMER represents
a significant improvement over the spectra produced in the past. In
view of the manifold appearance and temporal variation of the solar
atmosphere it is obvious that our atlas can only be a-hopefully
typical-snapshot. The spectral radiances are determined with a
relative uncertainty of 0.15 to 0.30 (1σ), and the wavelength scale
is accurate to typically 10 mÅ, which is the level achievable with
semi-automatic processing. The SUMER solar-disk spectral atlas will
be published in the near future by Curdt et al. [2]. It includes
profiles of the average quiet Sun, an equatorial coronal hole, and
a sunspot. As an example we show in Fig. 1 the spectral range from
1300 Å to 1342 Å with the prominent O I and C II lines. Resolved
emission lines are indicated by a mark, the measured wavelength in
angstrom, and the identification, if available. Marks point to line
lists available in the literature, where additional information about
a specific line can be found [3-7]. New lines or identifications
are indicated. Lines observed in first order and in second-order of
diffraction are distinguished. Only the three least-significant digits
of the wavelength values are given. If available, unidentified lines
are characterized by the temperature classification defined in [3] (a:
Te&lt;3 105 b: Te~3 105 c:
Te~4 105 d: 6 105&lt;Te
&lt;9 105 e: Te~1.4 106 f:
Te~1.8 106). The vertical axes are scaled
to spectral radiance in units of mW sr-1 m-2
Å-1 on the left the radiometric calibration for first
order lines is given, on the right for second order lines. Note,
that second order lines are always superimposed on a first order
background. We have taken care of the type of photocathode (bare or KBr)
when applying the radiometric calibration to different sections of the
spectrum. Also displayed in green is the BN/CI ratio in an attempt
to characterize the quiet-Sun chromospheric network structure. A
pre-print of the SUMER spectral atlas and a line list is available at
http://www.linmpi.mpg.de/~curdt. .

---------------------------------------------------------
Title: On the Unresolved Fine Structures of the Solar Upper
Atmosphere. IV. The Interface with the Chromosphere
Authors: Feldman, U.; Dammasch, I. E.; Wilhelm, K.
2001ApJ...558..423F Altcode:
An important objective of the solar physics community is the
unambiguous determination of the morphology of the fine structures of
the solar upper atmosphere in quiet-Sun and coronal hole regions and
the relationship of the cold chromosphere to the hot corona. Recently
the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
on board the Solar and Heliospheric Observatory succeeded in obtaining
observations that can be used to achieve this goal. In this paper
we study the spatial relationship between previously unresolved fine
structures and the chromospheric emissions that underlie them. The main
result is that looplike structures seen in transition region lines
with length scales of 10"-20" straddle the chromospheric network and
have no chromospheric counterpart near their apparent footpoints.

---------------------------------------------------------
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.
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: On the Rate of Abundance Modifications versus Time in Active
Region Plasmas
Authors: Widing, K. G.; Feldman, U.
2001ApJ...555..426W Altcode:
Four emerging and developing active regions observed on Skylab
spectroheliograms (300-600 Å) have been studied over intervals of 3
to 7 days to determine the change in their Mg/Ne abundance ratio. The
Mg/Ne abundance ratio is used as a measure of the FIP effect on element
abundances in the solar upper atmosphere. Mg/Ne abundance ratios were
derived from diagnostic intensity ratios of Mg VI lines at 400 Å
relative to adjacent Ne VI lines. Intensity ratios were estimated from
the active region images in the Skylab Atlas of Extreme-Ultraviolet
Spectroheliograms. The resulting abundance ratios expressed in terms
of the FIP bias β (see text) are plotted as a function of elapsed
time since emergence. After emergence the newborn region shows
photospheric composition: i.e., the abundance ratio of Mg/Ne=0.296,
β=1. Thereafter, the developing regions show a progressive increase
in the Mg/Ne abundance ratio with the value of β reaching after 2
days coronal-type abundances: Mg/Ne=1.43, β~4.8. In the later stages,
the bias increases to values between 7 and 9 after 3 to 7 days. Some
implications of the abundance modifications are briefly discussed.

---------------------------------------------------------
Title: VizieR Online Data Catalog: SUMER Spectral Atlas of Solar
Disk Features (Curdt+, 2001)
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schuhle, U.; Lemaire, P.
2001yCat..33750591C Altcode:
List of spectral lines in the wavelength range from 668Å to 1611Å
identified in SUMER (Solar Ultraviolet Measurements of Emitted
Radiation, spectrograph on the spacecraft SOHO) spectra of the average
quiet Sun (QS), a coronal hole (CH) and a sunspot on disk (SS). Spectral
lines observed in second order of diffraction which are also given
here, extend the lower wavelength limit to below 500Å. For each entry
we give the observed wavelengths in angstrom, the identification,
the transition, the peak of spectral radiance, Lpeak, in
mW/(sr*m2*Å) (incl. background), and a cross-reference
to other line lists available in the literature (cf., Sect. 5.1). For
second-order lines radiance entries are generally not provided, since
the background separation in both orders of diffraction is a non-trivial
task, which can not be automated. Only a few radiance values of strong
second-order lines with negligible first-order contribution are given,
which are marked by an asterisk (*). (1 data file).

---------------------------------------------------------
Title: FIP Effect Measurements in the Solar Corona and in Flares
Authors: Feldman, U.
2001AGUSM..SH52C04F Altcode:
The compositions of solar upper atmosphere plasmas were studied from
spectra obtained by instruments aboard all major solar observatories
that were launched into space in the last three decades. During my talk
I will review FIP effect results that were obtained from instruments
on some of the observatories as they relate to coronal holes, quiet
regions, active regions and flares. I will shaw that although the
derived compositions vary considerably with the type of plasma observed
some regularities in their behavior begin to emerge.

---------------------------------------------------------
Title: The Solar Helium Abundance in the Outer Corona Determined
from Observations with SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.
2001ApJ...546..552L Altcode: 2000astro.ph..8427L
At altitudes of about 1.05 Rsolar or more, the corona above
quiet solar regions becomes essentially isothermal. This obviates many
of the difficulties associated with the inverse problem of determining
emission measure distributions and allows for fairly straightforward
relative element abundance measurements. We present new values for the
He abundance. The first is based on a reanalysis of the He/O ratio
studied previously using data acquired by SUMER. A more thorough
evaluation of the atomic physics for He II, including a detailed
treatment of radiative recombination, increases the predicted emission
in the He II Balmer series compared with earlier analyses. We use a
recently revised value of the O abundance to derive an He/H abundance
ratio of 0.038 (mass fraction, Y=0.13), with an error of ~17% coming
mainly from the O abundance uncertainty. We demonstrate that this result
may be affected by gravitational settling of O relative to He. We also
derive an abundance for He by direct comparison with emission lines of
the H I Lyman series, with the result He/H=0.052+/-0.005 (Y=0.17), a
value similar to He abundances determined in the slow-speed solar wind.

---------------------------------------------------------
Title: Spectroscopic features in the EUV emission of a M8 flare
observed by SUMER
Authors: Curdt, W.; Landi, E.; Feldman, U.; Innes, D.; Dwivedi, B.;
Wilhelm, K.
2001IAUS..203..260C Altcode:
On May 9, 1999 a flare of size M8 occurred while SUMER obtained a
spectral scan above the active region NOAA 8537 at the west limb. We
recorded spectra during the pre-flare phase, at flare onset, and during
the decay phase. More than 60 flare lines were observed during this
event, which include Fe XVIII - Fe XXIII lines that provide evidence
of 107 K plasmas. We also recorded lines from He-like ions,
such as Ne IX, Na X, Mg XI or Si XIII. Accurate wavelength measurements
of such lines are of interest in basic atomic physics studies. Using
plasma diagnostic techniques, we investigated the temporal evolution
of the electron densities and temperatures during the event. Since
the spectra contain lines from many different elements, we were able
to determine elemental abundances in the flaring plasma.

---------------------------------------------------------
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.
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: Identification of Spectral Lines in the 500-1600 Å Wavelength
Range of Highly Ionized Ne, Na, Mg, Ar, K, Ca, Ti, Cr, Mn, Fe, Co,
and Ni Emitted by Flares (Te&gt;=3×106 K)
and Their Potential Use in Plasma Diagnostics
Authors: Feldman, U.; Curdt, W.; Landi, E.; Wilhelm, K.
2000ApJ...544..508F Altcode:
On 1999 May 9 the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on the Solar and Heliospheric Observatory
(SOHO) recorded spectra from a high-temperature region located
in the solar corona above the west limb. These spectra contain
lines from rather less-abundant elements in solar plasmas. In
this paper we present identifications of the high-temperature
(Te&gt;=3×106 K) Ne, Na, Mg, Ar, K, Ca, Ti,
Cr, Mn, Fe, Co, and Ni lines that were detected in the 500-1600 Å
spectral range of SUMER. In addition, accurate wavelength measurements
have been obtained with uncertainties varying between 0.015 and 0.040
Å (1 σ). Making use of the newly measured wavelengths, we derive
energy levels in the ground configuration of a number of highly
charged ions. We present intensity ratio calculations of lines in
the SUMER range that could be used to measure electron densities in
high-temperature solar plasmas. We also provide emissivities for Ca
XIII-Ca XV and Fe XVIII-Fe XXIII lines that could be used to determine
emission measures and electron temperatures of high-temperature
plasmas. We discuss a method for measuring elemental abundance
variations in high-temperature solar plasmas using lines presented
in the paper. A list of spectral lines spanning the 300-30000 Å
wavelength range and their branching ratios that are suitable for
efficiency calibration of space-borne spectrographs is provided.

---------------------------------------------------------
Title: The Morphology of the Solar Upper Atmosphere During the
Sunspot Minimum
Authors: Feldman, U.; Dammasch, I. E.; Wilhelm, K.
2000SSRv...93..411F Altcode:
The solar upper atmosphere (SUA) is defined as the volume above the
photosphere occupied by plasmas with electron temperatures, T_e,
above ~ 2×10^4 K. Until the Skylab era, only little was known about
the morphology of the SUA, while the quality of the spectroscopic
observations was continually improving. A spherically symmetric
atmosphere was assumed at that time, in which the temperature increased
with height. With advances in the observational techniques, it became
apparent that the morphology of the SUA was very complex even during the
minimum of the magnetic activity cycle. In particular, spectroscopic
measurements with high spectral and spatial resolution, which were
made in the light of ultraviolet emission lines representing a variety
of temperatures, led to the conclusion that most of the radiation
from the solar transition region could not be explained by assuming
a continuous chromosphere-corona interface, but rather by a region of
unresolved fine structures. Recent observational results obtained by
modern instruments, such as the Extreme-ultraviolet Imaging Telescope
(EIT), the Large Angle Spectroscopic Coronagraph (LASCO), and the
Solar Ultraviolet Measurements of (SUMER) spectrograph on the Solar and
Heliospheric Observatory (SOHO), as well as the Transition Region and
Coronal Explorer (TRACE), and their interpretations will be presented
in this review of our understanding of the morphology of the SUA.

---------------------------------------------------------
Title: Wavelength measurements of heliumlike 1s2s
3S1-1s2p 3P0,2
transitions in Ne8+, Na9+, Mg10+,
and Si12+ emitted by solar flare plasmas
Authors: Curdt, W.; Landi, E.; Wilhelm, K.; Feldman, U.
2000PhRvA..62b2502C Altcode:
With the Solar Ultraviolet Measurements of Emitted Radiation
instrument-a high-resolution normal-incidence telescope and spectrometer
on board the Solar and Heliospheric Observatory-heliumlike 1s2s
3S1-1s2p 3P0,2 transitions
in the highly ionized species Ne8+, Na9+,
Mg10+, and Si12+ were observed. The spectral
lines were emitted by high-temperature solar flare plasmas. In this
paper, we report on wavelength measurements of the He-like lines
identified in the recorded spectra. The wavelength uncertainties
we obtained from the solar measurements are &lt;=20 mÅ(1σ),
and in one case &lt;=30 mÅ. This is comparable to or better than
the best determinations so far achieved for these heliumlike 1s2s
3S1-1s2p 3P0,2 transitions
with instrumentation in the laboratory. For the Na9+
3S1-3P2 transition we
report what is to our knowledge the first wavelength measurement. The
knowledge of the accurate wavelengths can provide important checks on
atomic structure calculations.

---------------------------------------------------------
Title: Wavelengths of Forbidden Transitions Arising from Levels Within
the Fe+19 2S22P3 Ground Configuration
Authors: Kucera, T. A.; Feldman, U.; Widing, K. G.; Curdt, W.
2000ApJ...538..424K Altcode:
In this paper we report the identification of all remaining unidentified
forbidden lines arising from transitions within levels of the
Fe+19 ground configuration. These lines were identified using
data from the SOHO/SUMER spectrograph and Skylab. Adjusted wavelength
values are also given for some previously observed lines. Forbidden
lines that are the result of transitions within levels of the ground
configuration of a highly ionized astrophysically abundant element
generally have longer wavelengths than resonance lines emitted by
the same ion. Many of these forbidden lines are fairly prominent in
low-density plasmas and traditionally have been used in determining
properties of high-temperature astrophysical plasmas. The identified
Fe+19 forbidden lines span the 300-2665 Å wavelength
range. Since spontaneous decay rates of forbidden transitions arising
from the same upper level are known quite accurately, these lines can
be used for calibrating spectrometers over wide wavelength ranges.

---------------------------------------------------------
Title: The EUV Spectrum of Sunspot Plumes Observed by SUMER on SOHO
Authors: Curdt, W.; Dwivedi, B. N.; Feldman, U.
2000JApA...21..397C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The solar helium abundance in the outer corona determined
from observations with SUMER/SOHO.
Authors: Laming, J. M.; Feldman, U.
2000BAAS...32Q.815L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Properties of Solar Polar Coronal Hole Plasmas Observed Above
the Limb
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.
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&amp;T Grant
W-19,329 and by the ONR/NRL Research Option, Solar Magnetism and the
Earth's Environment.

---------------------------------------------------------
Title: The Solar Helium Abundance in the Outer Corona Determined
from Observations with SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.
2000SPD....31.0224L Altcode:
At altitudes of about 1.05 solar radii or more, the corona above quiet
solar regions becomes essentially isothermal. This obviates many of
the difficulties associated with the inverse problem of determining
emission measure distributions, and allows for fairly straightforward
relative element abundance measurements. We present new values for
the He abundance. The first is based on a reanalysis of the He/O ratio
studied by previously by Feldman (1998) using data acquired by SUMER. We
use a revised value of the O abundance, and a more thorough evaluation
of the atomic physics for He II to derive an He/H abundance ratio of
0.092, (mass fraction, Y=0.27), with an error of ~ 17% coming mainly
from the O abundance uncertainty. We demonstrate that this result
may be affected by gravitational settling of O relative to He. We
also derive an abundance for He by direct comparison to emission
lines of the H I Lyman series, with the result He/H =0.083 +/- 10%
(Y=0.25). Gravitational settling, if present, has the opposite effect
on this result to that above. Combining the two measurements leads
to a final result of He/H =0.084+/- 0.008. This work was supported by
the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research
Option and by NASA Contract W19473. The SUMER project is financially
supported by DARA, CNES, NASA and the ESA PRODEX program (Swiss
contribution). SUMER is a part of SOHO, the Solar and Heliospheric
Observatory, of ESA and NASA.

---------------------------------------------------------
Title: Newly Discovered Fe XX lines in Flares Observed by SOHO/SUMER
and Skylab.
Authors: Kucera, T. A.; Feldman, U.; Widing, K. G.; Curdt, W.; Khan,
J. I.
2000SPD....31.0264K Altcode: 2000BAAS...32..822K
We have used UV spectra from solar flares observed with SOHO/SUMER and
Skylab to identify all of the all remaining unidentified forbidden
lines arising from transitions within levels of the Fe XX ground
configuration. We have also obtained more accurate wavelengths for
previously observed lines. Forbidden lines resulting from transitions
within levels of the ground configuration of highly ionized elements
generally have longer wavelengths than resonance lines emitted by
the same ions. Many of these forbidden lines are fairly prominent in
low-density plasmas, and have traditionally been used in determining
properties of high temperature astrophysical plasmas. The identified Fe
XX forbidden lines span the 300-2665 Angstroms wavelength range. Since
spontaneous decay rates of forbidden transitions arising from the same
upper level are known quite accurately, these lines can be used for
calibrating spectrometers over wide wavelength ranges.

---------------------------------------------------------
Title: Observations: The case for unresolved fine structures
Authors: Feldman, U.
2000SPD....31.1201F Altcode: 2000BAAS...32..843F
The solar upper atmosphere (SUA) is defined as the volume above the
photosphere occupied by plasma with electron temperature above 20,000
K. Until the Skylab era, only little was known about the morphology
of the SUA. As a result early models assumed a continuous atmosphere
in which the temperature increased with height. With the advances in
spectroscopic measurements it became apparent that most of the radiation
from the 30,000-500,000 K temperature region could not be explained as
coming from a continuous chromosphere-corona interface, but rather from
unrelated plasma structures named unresolved fine structures. Recent
results obtained by the Extreme Ultraviolet Imaging telescope (EIT),
the Solar Ultraviolet Measurements of Emitting Radiation (SUMER) and
the Transition Region and Coronal Explorer (TRACE) support the earlier
conclusions. An account of observations that were made, over the last
three decades, to identify the morphology of the 30,000-500,000 K plasma
structures above quiet and coronal hole regions will be given. This
work was supported by the NRL/ONR Solar Magnetism and the Earth's
Environment 6.1 Research Option.

---------------------------------------------------------
Title: Element Abundances in the Upper Atmospheres of the Sun and
Stars: Update of Observational Results
Authors: Feldman, U.; Laming, J. M.
2000PhyS...61..222F Altcode:
We review observational progress in the determination of element
abundances in the solar corona, largely due to the new capabilities
offered by the instrumentation on the SOHO satellite. Many new facets
to coronal abundance anomalies with respect to the photosphere are
revealed. This includes new results on the FIP (First Ionization
Potential) Effect, whereby elements with FIP &lt; 10 eV are enriched
in the corona by a factor ∼4 with respect to the photosphere, and
the first evidence for gravitational settling of heavy elements in the
corona. Advances in EUV and X-ray astronomy instrumentation have also
yielded the first spectra of stellar coronae of sufficient quality to
allow element abundance measurements. We survey these new results and
compare the various stellar cases to the solar corona.

---------------------------------------------------------
Title: Erratum: Morphology of the Quiet Solar Upper Atmosphere in
the 4 W 104 &lt; Te &lt; 1.4 W 106 K Temperature Regime
Authors: Feldman, U.; Widing, K. G.; Warren, H. P.
2000ApJ...529.1145F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Extreme-Ultraviolet Spectral Line Widths in Quiet-Sun Coronal
Plasmas at Distances of 1.03&lt;=Rsolar&lt;=1.45 along
the Solar Equatorial Plane
Authors: Doschek, G. A.; Feldman, U.
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: Radiometric Calibration of the Vacuum-Ultraviolet Spectrograph
SUMER on the SOHO Spacecraft with the B Detector
Authors: Schühle, Udo; Curdt, Werner; Hollandt, Jörg; Feldman, Uri;
Lemaire, Philippe; Wilhelm, Klaus
2000ApOpt..39..418S Altcode:
The Solar Ultraviolet Measurement of Emitted Radiation (SUMER)
vacuum-ultraviolet spectrograph was calibrated in the laboratory
before the integration of the instrument on the Solar and Heliospheric
Observatory (SOHO) spacecraft in 1995. During the scientific operation
of the SOHO it has been possible to track the radiometric calibration
of the SUMER spectrograph since March 1996 by a strategy that employs
various methods to update the calibration status and improve the
coverage of the spectral calibration curve. The results for the A
Detector were published previously Appl. Opt. 36, 6416 (1997) . During
three years of operation in space, the B detector was used for two
and one-half years. We describe the characteristics of the B detector
and present results of the tracking and refinement of the spectral
calibration curves with it. Observations of the spectra of the stars and
Leonis permit an extrapolation of the calibration curves in the range
from 125 to 149.0 nm. Using a solar coronal spectrum observed above
the solar disk, we can extrapolate the calibration curves by measuring
emission line pairs with well-known intensity ratios. The sensitivity
ratio of the two photocathode areas can be obtained by registration of
many emission lines in the entire spectral range on both KBr-coated and
bare parts of the detector s active surface. The results are found to be
consistent with the published calibration performed in the laboratory
in the wavelength range from 53 to 124 nm. We can extrapolate the
calibration outside this range to 147 nm with a relative uncertainty
of 30% (1 ) for wavelengths longer than 125 nm and to 46.5 nm with 50%
uncertainty for the short-wavelength range below 53 nm.

---------------------------------------------------------
Title: Relationships among the Intensities of LI-, BE-, and NA-like
Resonance Lines in Collisionally Ionized Astrophysical Plasmas
(105&lt;=Te&lt;=107 K)
Authors: Laming, J. M.; Feldman, U.
1999ApJ...527..461L Altcode:
The strongest lines emitted from optically thin collisionally ionized
astrophysical plasmas are usually those of the Li-, Be-, and Na-like
sequences. When numerous other weaker lines are also measurable in the
spectrum, the derivation of relative element abundances is reasonably
straightforward. However, for many sources only the strongest lines
will be observed, so here we explore under what conditions it may be
possible to determine relative element abundances in this case. We find
that several temperature regions exist in which the ratios of these
strong lines can be fairly insensitive to temperature. We discuss
applications to solar/stellar coronae, the interstellar medium, and
SN 1987A. Additionally under certain conditions in the solar corona
ratios of Li-like line intensities to those of He II are found to
allow relatively straightforward determinations of the He abundance.

---------------------------------------------------------
Title: SOHO EIT Observations of Coronal Holes
Authors: Norton, H.; Newmark, J. S.; Feldman, U.
1999ESASP.446..509N Altcode: 1999soho....8..509N
We present a study of coronal holes (not including the polar holes)
using observations from SOHO EIT during 1996 and 1997. EIT obtains
daily full disk observations of the Sun at spectral emission lines from
FeIX,X (171 A), FeXII (195 A), FeXV (284 A), and HeII (304 A). Previous
studies (mainly He I 10830 A and ground based magnetograms) have
demonstrated the role that bipolar magnetic regions play in their
evolution as well as rotation rates for recurrent coronal holes. We
further the correlation between coronal holes and bipolar fields by
presenting definitive symbiotic relationships between coronal holes
and active regions. Comparisons of EUV observations and magnetograms
plus potential field extrapolations are shown.

---------------------------------------------------------
Title: Molecular Hydrogen Lines Observed with SUMER in the Spectrum
of a Sunspot
Authors: Schüehle, U.; Brown, C. M.; Curdt, W.; Feldman, U.
1999ESASP.446..617S Altcode: 1999soho....8..617S
No abstract at ADS

---------------------------------------------------------
Title: Measuring the Solar He Abundance in the Outer Corona with
SUMER.
Authors: Laming, J. Martin; Feldman, Uri
1999ESASP.446..405L Altcode: 1999soho....8..405L
We outline new spectroscopic methods for measuring relative element
abundances in the solar corona, with special emphasis on the He
abundance. At altitudes of about 1.05 solar radius or more, the solar
corona becomes essentially isothermal. This is not unexpected in view
of the quiescent nature of the plasma at these heights, and the long
radiative cooling times at densities below log ne = 8.0. The
isothermal nature of the plasma obviates many of the difficulties
associated with the inverse problem of determining an emission
measure distribution. This is particularly true in the cases of Li-
and Na-like ions whose ionization balance fractions have long tails
extending to high temperatures, making the inversion problem especially
difficult. We present new calculations of intensity ratios as a function
of temperature that can be used to determine element abundance ratios in
the solar corona. The He abundance may be determined from He II lines
relative to, for example, O VI, and we present an extensive analysis
of the He II spectrum. In order to predict accurate line intensities,
large close-coupling calculations are required. One special feature
is that in order to get the excitation cross sections correct, impact
ionization channels also need to be included in the calculation,
for the temperatures relevant to the solar corona. The model ion also
needs to include the many highly excited levels from which the Balmer
series originates.

---------------------------------------------------------
Title: Morphology of the Quiet Solar Upper Atmosphere in the
4×104&lt;Te&lt;1.4×106 K
Temperature Regime
Authors: Feldman, U.; Widing, K. G.; Warren, H. P.
1999ApJ...522.1133F Altcode:
Studies on the morphology of the solar upper atmosphere began over
three decades ago. Early models assumed that the temperature structure
of the solar upper atmosphere was continuous with a thin transition
region connecting the chromosphere with the corona. Over the years
it became apparent that the original depiction of the solar upper
atmosphere was too simplistic. In this paper we present a morphological
study of the solar upper atmosphere over a wide range of temperatures
(4×104&lt;=Te&lt;=1.4×106 K)
using high-resolution images (1”-2”)
taken by TRACE, the SUMER spectrometer on SOHO, and the NRL
spectroheliograph on Skylab. The images clearly show that the
4×104&lt;=Te&lt;=1.4×106
K temperature domain of the solar upper atmosphere consists
of a hierarchy of isothermal loop structures. While at the
Te&lt;8×105 K temperature regime the looplike
structures are more abundant along the chromospheric network, at higher
temperatures (Te&gt;9×105 K) no association
between them and the chromospheric network is apparent. The hottest
(Te~1.4×106 K), which are also the longest among
the quiet-Sun loop structures, form a canopy over the lower temperature
loop structures. We discuss in the paper possible relationships between
the morphology of the solar upper atmosphere, its elemental abundance,
and ideas regarding the origin of the slow-speed solar wind.

---------------------------------------------------------
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.
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: The Off-Limb Behavior of the First Ionization Potential Effect
in T&gt;5×105 K Solar Plasmas
Authors: Laming, J. M.; Feldman, U.; Drake, J. J.; Lemaire, P.
1999ApJ...518..926L Altcode:
We investigate the behavior of the solar first ionization potential
(FIP) effect (the abundance enhancement of elements with first
ionization potential of less than 10 eV in the corona with respect
to photospheric values) with height above the limb in a region of
diffuse quiet corona observed by the SUMER instrument on SOHO, with
emphasis on so-called upper transition region lines. Previous disk
observations have shown different abundance patterns in emission
from lines at temperatures above and below ~8×105 K,
with an FIP effect clearly visible at the higher temperatures and
less so at the lower temperatures. Our initial aim is to determine
whether such a difference is also visible in off-limb observations. We
find a low-FIP element enhancement of a factor of 3-4 indicated in
all line ratios. The Mg VII 868.11/Ne VII 895.17 ratio is also seen
to decrease toward a photospheric value when tracked down from the
corona to the limb. This is markedly different from the behavior of
higher temperature line ratios and may be related to the differing
heating and mass supply mechanisms for plasmas at temperatures above
and below ~8×105 K. An additional unexpected feature
of our observations is that in low-FIP/high-FIP line ratios formed
at temperatures close to the freeze-in temperature of the fast solar
wind (~106 K), there is also a small diminution of the FIP
enhancement at the highest altitudes observed in this study. We discuss
the possible relevance of this to the origin of the fast solar wind.

---------------------------------------------------------
Title: Properties of Quiet-Sun Coronal Plasmas at Distances of
1.03&lt;=Rsolar&lt;=1.50 along the Solar Equatorial Plane
Authors: Feldman, U.; Doschek, G. A.; Schühle, U.; Wilhelm, K.
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.
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 &amp; Feldman 1999, ApJ,
submitted. This work was funded by the 6.1 NRL/ONR Solar Magnetism
and the Earth's Environment Research Option.

---------------------------------------------------------
Title: New Identifications of Si VIII and S X Lines in the Solar
Coronal Spectrum Measured by SOHO/SUMER
Authors: Kink, I.; Engström, L.; Feldman, U.
1999ApJ...512..496K Altcode:
This paper reports the identification of 14 lines
in the solar coronal spectrum as high-excitation
2s22p23s-2s22p23p
and 2s22p23p-2s22p23d
transitions in Si VIII and S X (N I isoelectronic sequence). The
analysis combines solar spectra, recorded by the SUMER (Solar
Ultraviolet Measurement of Emitted Radiation) instrument on board the
Solar and Heliospheric Observatory (SOHO) satellite, with laboratory
data obtained with the beam-foil technique. Theoretical gA values
and branching ratios for the observed lines, based on semiempirical
calculations, are also presented. Intensity ratios between the newly
identified high-excitation transitions and known forbidden transitions
within the 2s22p3 ground configuration can be
used in determining coronal plasma temperatures in the 70-120 eV range.

---------------------------------------------------------
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.
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: On the Unresolved Fine Structures of the Solar
Atmosphere. III. Elemental Abundances Consideration
Authors: Feldman, Uri
1998ApJ...507..974F Altcode:
Results from high-quality solar upper atmosphere observations in the
104-106 K range contradict predictions made
by models that assume that a single class of structures stretching
throughout the entire temperature domain, from the cold chromosphere
to the hot corona, is responsible for all the radiation we see. As a
result, I proposed that new types of structures--the unresolved fine
structures (UFSs)--are responsible for most of the detected emission in
the 3 × 106 &lt;= Te &lt;= 8 × 106
K. In a recent paper Wikstøl, Judge, &amp; Hansteen challenged the
presence of UFSs by claiming that the interpretation of the data
in terms of UFSs is not unique and is likely to be incorrect in the
presence of plasmas with unresolved dynamics. Further, they claim that
most or all of the evidence that was brought in support of the UFSs is
amenable to a different, equally reasonable interpretation in which the
transition region emission is at all times formed in the time-varying
thermal interface between the corona and chromosphere. In this paper I
discuss some of the assertions made by Wikstøl and collaborators. I
also bring evidence from elemental abundance studies that would
be difficult to support with the Wikstøl model. In contrast, the
existence of UFSs is not contradicted by any of the new observations.

---------------------------------------------------------
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.
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: Coronal Composition above the Solar Equator and the North Pole
as Determined from Spectra Acquired by the SUMER Instrument on SOHO
Authors: Feldman, U.; Schühle, U.; Widing, K. G.; Laming, J. M.
1998ApJ...505..999F Altcode:
Using spectra obtained by the SUMER instrument on the Solar and
Heliospheric Observatory (SOHO) we have determined the composition of
the bulk of the coronal plasma in the vicinity of the solar surface
over a polar coronal hole and an equatorial region. Our measurements
show that although low first ionization potential (FIP) elements are
enriched by about a factor of 4 in the corona above the quiet equatorial
region, little or no enrichment exists above the north polar coronal
hole. These observations are in good agreement with the Ulysses in
situ observations in both fast speed and slow speed winds.

---------------------------------------------------------
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.
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.
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.
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: FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results
Authors: Feldman, U.
1998SSRv...85..227F Altcode:
Recent spectroscopic measurements from instruments on the Solar and
Heliospheric Observatory (SOHO) find that the coronal composition above
a polar coronal hole is nearly photospheric. However, similar SOHO
observations show that in coronal plasmas above quiet equatorial regions
low-FIP elements are enhanced by a factor of ≈ 4. In addition, the
process of elemental settling in coronal plasmas high above the solar
surface was shown to exist. Measurements by the Ulysses spacecraft,
which are based on non-spectroscopic particle counting techniques,
show that, with the exception of He, the elemental composition of
the fast speed solar wind is similar to within a factor of 1.5 to
the composition of the photosphere. In contrast, similar measurements
in the slow speed wind show that elements with low first ionization
potential (FIP &lt; 10 eV) are enhanced, relative to the photosphere,
by a factor of 4-5. By combining the SOHO and Ulysses results, ideas
related to the origin of the slow speed solar wind are presented. Using
spectroscopic measurements by the Solar Ultraviolet Measurement of
Emitted Radiation (SUMER) instrument on SOHO the photospheric abundance
of He was determined as 8.5 ± 1.3% (Y = 0.248).

---------------------------------------------------------
Title: The Neon-to-Magnesium Abundance Ratio as a Tracer of the
Source Region of Prominence Material
Authors: Spicer, D. S.; Feldman, U.; Widing, K. G.; Rilee, M.
1998ApJ...494..450S Altcode:
A survey of all 1000 spectroheliograms in the Skylab spectroheliograph
plate collection was made to identify prominences above the limb and
prominence-like features. The Ne/Mg abundance ratios obtained from
the measurements have been determined from relative intensities of Ne
VI and Mg VI lines at 400 Å of seven prominences and prominence-like
features observed above the solar limb. The derived abundance ratios
have values intermediate between the photosphere and corona, while none
are as low as the ratio of 0.7 expected in the corona, which implies
that the material found in prominences is photospheric in origin. The
significance of these results for the formation of prominences is
briefly discussed.

---------------------------------------------------------
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.
1998ESASP.417..289S Altcode: 1998cesh.conf..289S
No abstract at ADS

---------------------------------------------------------
Title: Using the YOHKOH BCS to Check Element Abundances and Ionization
Fractions
Authors: Phillips, K. J. H.; Feldman, U.
1998ASSL..229..341P Altcode: 1998opaf.conf..341P
No abstract at ADS

---------------------------------------------------------
Title: FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results
Authors: Feldman, U.
1998sce..conf..227F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The solar disk spectrum between 660 and 1175 Anstroms (first
order) obtained by SUMER on SOHO
Authors: Curdt, W.; Feldman, U.; Laming, J. M.; Wilhelm, K.; Schuehle,
U.; Lemaire, P.
1997A&AS..126..281C Altcode:
SUMER -- Solar Ultraviolet Measurements of Emitted Radiation -- onboard
of SOHO -- Solar and Heliospheric Observatory -- obtained its first
spectrum on January 25, 1996 near the north polar limb. The range
from 660 Angstroms to 1175 Angstroms which has never before been
observed with such a good spectral resolution contains a wealth of
spectroscopic details. Identification of about 400 lines in this
spectral range is given. We list the wavelengths of identified
transitions and provide their absolute peak intensities. General
spectral features of the most abundant elements H, He, C, N, O,
Ne, Mg, Si, S, Ar, and Fe are described. In this spectral range
many density- and temperature-sensitive line pairs are found. It is
shown in examples how they can be used as diagnostic tools. Table
1 and Fig.nearlimb are also available in digital form at the CDS
via anonymous ftp to cdsarc.u-strasbg. fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/Abstract.html

---------------------------------------------------------
Title: The Off-Limb Behaviour of the Solar Transition Region FIP
Effect
Authors: Laming, J. M.; Feldman, U.; Drake, J. J.; Schuhle, U.; Curdt,
W.; Wilhelm, K.; Lemaire, P.
1997AAS...191.7301L Altcode: 1997BAAS...29.1320L
We investigate the behaviour of the solar FIP effect (the abundance
enhancement of elements with first ionization potential &lt; 10 eV by
factor of 3-4 in the corona with respect to photospheric values) with
height above the limb in a region of diffuse quiet corona observed
by the SUMER instrument on SOHO. Line ratios formed at log T &gt;
5.8 show coronal abundances for all heights. Line ratios formed at
lower temperatures are consistent with coronal abundances well off the
limb, with the apparent magnitude of the FIP enhancement decreasing
by a factor of 1.5 - 2 as one approaches the solar limb. Thus our
observations support a spatial variation in the quiet sun transition
region FIP effect inferred previously from studies of the full disk
solar spectrum (Laming, Drake, &amp; Widing 1995, ApJ, 443, 416
and references therein). This result adds to the probability that
emission from the solar disk transition region and corona originates
from qualitatively different structures for values of log T {&lt;atop
&gt;} 5.8, having different FIP effects.

---------------------------------------------------------
Title: A Coronal Spectrum in the 500--1610 Angstrom Wavelength Range
Recorded at a Height of 21,000 Kilometers above the West Solar Limb
by the SUMER Instrument on Solar and Heliospheric Observatory
Authors: Feldman, U.; Behring, W. E.; Curdt, W.; Schühle, U.; Wilhelm,
K.; Lemaire, P.; Moran, T. M.
1997ApJS..113..195F Altcode:
We present a solar coronal spectrum recorded by the extreme UV
spectrometer SUMER on the Solar and Heliospheric Observatory. The
spectrum was taken between 21:28 UT on 1996 June 25 and 02:47 UT on
1996 June 26, at a height of 21,000 km above the west equatorial limb
with the slit oriented in the north-south direction. At the time of
the observations the Sun was rather quiet, and the west limb appeared
“devoid of any activity.” The spectrum, which covers the 500-1610
Å wavelength range, originates from plasmas with temperatures
ranging between 1.5 × 104 and 1.5 × 106
K. Identification of lines originating from different temperature
regimes is facilitated by the appearance of their intensity along the
300" long slit. Well over 800 lines have been found, many of which
were not previously observed. We present the entire spectrum and discuss
line identifications. A table of the wavelengths of lines observed,
with their identifications and peak intensities, is provided. Although
we have identified lines previously detected in laboratory plasmas and
a number of new lines not previously observed, over 40% of the SUMER
lines remain unidentified. Among the newly detected lines, some have
a potential as plasma density diagnostics.

---------------------------------------------------------
Title: Laboratory Identification of Temperature Diagnostic Si VII and
S IX Lines Present in the Solar Coronal Spectra Measured by SUMER/SOHO
Authors: Kink, I.; Jupén, C.; Engström, L.; Feldman, U.; Laming,
J. M.; Schühle, U.
1997ApJ...487..956K Altcode:
The solar coronal spectrum between 500 and 1610 Å and at a
height of 21,000 km above the west equatorial limb has recently
been recorded by the SUMER instrument on SOHO. Using laboratory
spectra obtained with the beam-foil technique, we report
the identification of 32 lines observed in this spectrum as
2s22p33s-2s22p33p and
2s22p33p-2s22p33d
transitions in Si VII and S IX. Theoretical gA-values
and branching ratios for the observed lines, obtained from
semiempirical configuration interaction calculations, are also
presented. Intensity ratios between the 2s22p4
3P1-2s22p4
1S0 forbidden transition and transition from
the newly identified high-excitation lines that appear in the same
wavelength range are temperature sensitive. Calculations of the
intensity ratios between the forbidden line and the high-excitation
lines for three temperatures are presented. A comparison between the
calculations and some of the SUMER observations is provided.

---------------------------------------------------------
Title: Radiometric calibration of SUMER: refinement of the laboratory
results under operational conditions on SOHO
Authors: Wilhelm, Klaus; Lemaire, Philippe; Feldman, Uri; Hollandt,
Jörg; Schühle, Udo; Curdt, Werner
1997ApOpt..36.6416W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electron Density Diagnostics for the Solar Upper Atmosphere
from Spectra Obtained by SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.; Schühle, U.; Lemaire, P.; Curdt,
W.; Wilhelm, K.
1997ApJ...485..911L Altcode:
We evaluate the electron density in various solar regions above the
limb observed by the Solar Ultraviolet Measurement of Emitted Radiation
(SUMER) instrument on SOHO. We find in general good agreement among
line ratios from Be-, B-, N-, and Mg-like ions, giving densities of
order 108 cm-3.

---------------------------------------------------------
Title: Turbulent Velocities and Ion Temperatures in the Solar Corona
Obtained from SUMER Line Widths
Authors: Seely, J. F.; Feldman, U.; Schühle, U.; Wilhelm, K.; Curdt,
W.; Lemaire, P.
1997ApJ...484L..87S Altcode:
Turbulent plasma velocities and ion temperatures were determined from
the line widths recorded by the Solar Ultraviolet Measurements of
Emitted Radiation instrument on the Solar and Heliospheric Observatory
spacecraft. From the widths of the lines of five light elements
(Ne, Na, Mg, Si, and S) and a heavy element (Fe), it was possible
to determine the contributions of turbulent plasma motion and ion
thermal motion to the line widths. The results indicated that the
turbulent velocity was approximately 22 km s-1 at 30"
above the limb and decreased to less than 10 km s-1 at 109"
and 209" above the limb. At 30" above the limb, the ion temperatures
of the hotter lines were comparable to the electron temperatures for
ionization equilibrium. The ion temperatures of the cooler lines were
higher than the ionization equilibrium temperatures; at 109" and 209"
above the limb, the ion temperatures were at least a factor of 2.5
higher than the ionization equilibrium temperatures.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Solar disk spectrum (660-1175A)
(Curdt+ 1997)
Authors: Curdt, W.; Feldman, U.; Laming, J. M.; Wilhelm, K.; Schuehle,
U.; Lemaire, P.
1997yCat..41260281C Altcode:
The near-limb quiet-Sun spectrum recorded on January 25, 1996
near the solar North pole is presented in tabular form and in
graphical form. Table 1 - the line list - lists all lines found
in the spectrum providing absolute peak intensities, measured and
literature wavelengths, identification, and classification of the
transition. Fig. 4 is a display the composite spectrum. The most
prominent lines are labelled. In this figure intensities are given in
instrumental units and logarithmic scale. (1 data file).

---------------------------------------------------------
Title: Yohkoh Observations as a Means of Checking S, Ca, and Fe
Coronal Abundances and He-like Ionization Fractions
Authors: Phillips, K. J. H.; Feldman, U.
1997ApJ...477..502P Altcode:
Electron temperatures are derived from X-ray spectra observed by
the Bragg crystal spectrometer on board the Yohkoh satellite during
long-duration solar flares, and it is found that in the late stages
of such events the emitting plasma is nearly isothermal. This fact
enables us to examine the accuracy of the fractional abundances of
He-like S, Ca, and Fe ions, as well as the ratios of coronal element
abundances. Using currently accepted values for ionization fractions
and our own values of element abundances, we find that adjustments of
50% or less are needed.

---------------------------------------------------------
Title: The Occurrence Rate of Soft X-Ray Flares as a Function of
Solar Activity
Authors: Feldman, U.; Doschek, G. A.; Klimchuk, J. A.
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: First Results of the SUMER Telescope and Spectrometer on SOHO -
I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
1997SoPh..170...75W Altcode:
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) - observed
its first light on January 24, 1996, and subsequently obtained a
detailed spectrum with detector B in the wavelength range from 660
to 1490 Å (in first order) inside and above the limb in the north
polar coronal hole. Using detector A of the instrument, this range
was later extended to 1610 Å. The second-order spectra of detectors
A and B cover 330 to 805 Å and are superimposed on the first-order
spectra. Many more features and areas of the Sun and their spectra
have been observed since, including coronal holes, polar plumes and
active regions. The atoms and ions emitting this radiation exist at
temperatures below 2 × 106 K and are thus ideally suited
to investigate the solar transition region where the temperature
increases from chromospheric to coronal values. SUMER can also be
operated in a manner such that it makes images or spectroheliograms
of different sizes in selected spectral lines. A detailed line profile
with spectral resolution elements between 22 and 45 mÅ is produced for
each line at each spatial location along the slit. From the line width,
intensity and wavelength position we are able to deduce temperature,
density, and velocity of the emitting atoms and ions for each emission
line and spatial element in the spectroheliogram. Because of the high
spectral resolution and low noise of SUMER, we have been able to detect
faint lines not previously observed and, in addition, to determine
their spectral profiles. SUMER has already recorded over 2000 extreme
ultraviolet emission lines and many identifications have been made on
the disk and in the corona.

---------------------------------------------------------
Title: Properties of thermal flare plasmas (3 × 106-3
× 107 K): Observational results
Authors: Feldman, Uri
1996PhPl....3.3203F Altcode:
One of the most violent while best observed phenomena occurring in
the solar upper atmosphere is flare emission in the 3×106
to 3×107 K temperature range. This emission, commonly
called thermal flare emission, can vary in intensity by more than
five orders of magnitude, and exhibits regular and predictable
properties. A wealth of observational data regarding thermal solar
flares has been collected. Through these data the morphological
properties of thermal flares have been determined. Plasma properties
such as electron temperatures, electron densities, mass motions, and
variations in elemental abundances during the course of the flare are
well established. Observational data have also been used to determine
relationships between peak fluxes and maximum flare temperatures as
well as general properties of the light curve of flares.

---------------------------------------------------------
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.
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.
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: The Temperature of the Bright Knots at the Tops of Solar
Flare Loops
Authors: Doschek, G. A.; Feldman, U.
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.
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: Properties of Thermal Flares (4-30 MK) Derived from
Observations: Does a Reconnection Mechanism Have a Role in the
Flare Process?
Authors: Feldman, U.
1996ASPC..111..145F Altcode: 1997ASPC..111..145F
One of the most violent and best observed phenomena occurring in the
solar upper atmosphere is flare emission in the 4 - 30 MK temperature
range. This emission can vary in intensity by more than five orders
of magnitude, yet exhibits regular and predictable properties. A
wealth of observational data regarding 4 - 30 MK solar flares has been
collected. Any credible flare model must account for the observations
described.

---------------------------------------------------------
Title: Possibility of infrared coronal line laser emission in
Seyfert nuclei.
Authors: Greenhouse, M. A.; Smith, H. A.; Feldman, U.
1996amli.conf..295G Altcode:
The following topics were dealt with: stimulated emission in Seyfert
Nuclei, population inversions and gain lengths, observational tests.

---------------------------------------------------------
Title: Relationship between Cold and Hot Post-Flare Loops and the
Impact on the Reconnection Flare Model
Authors: Seely, J. F.; Feldman, U.
1996mpsa.conf..517S Altcode: 1996IAUCo.153..517S
No abstract at ADS

---------------------------------------------------------
Title: Properties of cool flare with GOES class B5 to C2.
Authors: Phillips, K. J. H.; Feldman, U.
1995A&A...304..563P Altcode:
Observed parameters for 208 small flares with GOES classification
B5 to C2 are discussed using data from the broad-band detectors
on the Geostationary Operational Environmental Satellites (GOES)
and the Bragg Crystal Spectrometer (BCS) on the Yohkoh solar flare
spacecraft. Peak temperatures derived from He-like sulfur spectra are in
the range 8+/-2x10^6^K and are similar to those derived from the ratio
of the 1-8A and 0.5-4A GOES channels, but a little less than those
from He-like calcium spectra, showing that even these small flares
are non-isothermal. The absence of He-like iron emission shows that
the temperatures are less than 14x10^6^K. There is a slight positive
correlation between temperature and emission measure from the calcium
and sulfur data. Differences in this distribution and that derived
for larger flares in a separate study can be reconciled in terms of
the fact that temperatures were measured from He-like iron spectra for
the larger flares. The emission measure of the flares in our sample are
correlated with GOES class. A detailed study of a subset of 20 flares
shows that the temperatures generally reach peak flux slightly before
(up to 30s) or coincident with the light curve maximum. It is found
that even small flux enhancements which are frequently present are
associated with temperature enhancements.

---------------------------------------------------------
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.
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.
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: Relationship between Cold and Hot Post--Solar Flare Loops
and the Impact on the Reconnection Flare Model
Authors: Feldman, U.; Seely, J. F.
1995ApJ...450..902F Altcode:
The relationship between cold and hot postflare loops has been studied
using the 1973 September 7 and 1974 January 15 flare images recorded
by the Skylab S082 spectroheliograph. The images are of intense
emission lines in the extreme ultraviolet region that span the 1 ×
104 (He I) to 3.2 × 106 K (Ni XVIII) temperature
range. The analysis of the images does not support the widely held
notion that cold loops are always smaller than hot loops, lie below
hot loops, and are similar in shape. It is found that the coldest and
hottest loops often differ significantly in size and shape. Based on
the analysis of a time sequence of Skylab images of cold and hot loops,
there is no evidence that the loop system expands in a discontinuous
manner, as would be the case if higher loops were sequentially formed
and activated by reconnection of the magnetic field. It is found
that the individual coronal loops expand in a gradual manner. These
conclusions are consistent with images of postflare loop systems in the
107 K range that were recorded by the soft X-ray telescope
on the Yohkoh spacecraft. Previous observations and interpretations of
postflare loop systems, which led to the formulation of the reconnection
flare model, are reexamined. In light of recent high-quality imagery
that spans the temperature range from 104 to 107
K, it is concluded that the observations do not support all aspects
of the reconnection flare model as presently articulated. Elements
of the reconnection flare model that are inconsistent with the modern
observations should be reconsidered.

---------------------------------------------------------
Title: Infrared Coronal Emission Lines and the Possibility of Their
Laser Emission in Seyfert Nuclei: Erratum
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Avi
1995ApJS...99..743G Altcode:
In the paper "Infrared Coronal Emission Lines and the Possibility of
Their Laser Emission in Seyfert Nuclei" by Matthew A. Greenhouse, Uri
Feldman, Howard A. Smith, Marcel Klapisch, Anand K. Bhatia, and Avi
Bar- Shalom (ApJS, 88,23-48[1993]), the wavelength of the 2s2ρ^3^P1-
^3^P_2_ transition of Ne VII is listed incorrectly as 10.6 microns. The
correct value is 10.06 microns. This error is typographical and does
not affect the results of the paper.

---------------------------------------------------------
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.
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: VizieR Online Data Catalog: Cool X-ray flares of Sun with GOES
(Phillips+, 1995)
Authors: Phillips, K. J. H.; Feldman, U.
1995yCat..33040563P Altcode:
Observed parameters for 208 small flares with GOES classification B5
to C2 are discussed using data from the broad-band detectors on the
Geostationary Operational Environmental Satellites (GOES) and the Bragg
Crystal Spectrometer (BCS) on the Yohkoh solar flare spacecraft. Peak
temperatures derived from He-like sulfur spectra are in the range
8+/-2x106K and are similar to those derived from the ratio
of the 1-8A and 0.5-4A GOES channels, but a little less than those
from He-like calcium spectra, showing that even these small flares
are non-isothermal. The absence of He-like iron emission shows that
the temperatures are less than 14x106K. There is a slight
positive correlation between temperature and emission measure from
the calcium and sulfur data. Differences in this distribution and that
derived for larger flares in a separate study can be reconciled in terms
of the fact that temperatures were measured from He-like iron spectra
for the larger flares. The emission measure of the flares in our sample
are correlated with GOES class. A detailed study of a subset of 20
flares shows that the temperatures generally reach peak flux slightly
before (up to 30s) or coincident with the light curve maximum. It is
found that even small flux enhancements which are frequently present
are associated with temperature enhancements. (1 data file).

---------------------------------------------------------
Title: Abundance Ratios of Oxygen, Neon, and Magnesium in Solar
Active Regions and Flares: The FIP Effect
Authors: Widing, K. G.; Feldman, U.
1995ApJ...442..446W Altcode:
Relative abundances of oxygen, neon, and magnesium have been
derived for a sample of nine solar active regions, flares, and
an erupting prominance by combining plots of the ion differential
emission measures. The observations were photographed in the 300-600
A range by the Naval Research Laboratory (NRL) spectroheliograph on
Skylab. Methods for deriving the Mg/Ne abundance ratio-which measures
the separation between the low- first ionization potential (FIP) and
high-FIP abundnace plateaus-have been described in previous papers. In
this paper we describe the spectroscopic methods for deriving the
O/Ne abundance ratio, which gives the ratio between two high-FIP
elements. The plot of the O/Ne ratio versus the Mg/Ne ratio in the
sample of nine Skylab events is shown. The variation in the Mg/Ne ratio
by a factor of 6 is associated with a much smaller range in the O/Ne
ratio. This is broadly consistent with the presence of the standard
FIP pattern of abundances in the outer atmosphere of the Sun. However,
a real change in the relative abundances of oxygen and neon by a factor
of 1.5 cannot be excluded.

---------------------------------------------------------
Title: Can the state of ionization equilibrium in the solar upper
atmosphere be determined by means of atomic physics?
Authors: Feldman, U.
1995CoAMP..31...11F Altcode:
The solar upper atmosphere (SUA) is an intriguing body of plasma
spanning the 3×104≤Te≤2×107K
electron temperature and
1×109≤ne≤1×1013cm-3
electron density ranges. After some fifty years of research into
the mechanism sustaining the SUA, no satisfactory solution has been
found. It seems that some of the assumptions describing SUA properties
are invalid, in particular the assumption stating that SUA plasmas
are in steady state coronal ionization equilibrium (SSCIE) is in
question. Atomic physics properties of the SUA based on the state of
ionization equilibrium are reviewed. Discrepancies between predictions
based on SSCIE calculations and observations are presented. It is
shown that by assuming transient ionization conditions some of the
discrepancies disappear.

---------------------------------------------------------
Title: On the Absence of a Relationship between the Properties of
the T E &gt;=10 6 K and the Properties of the T E &lt;=7 x10 5 K
Solar Plasmas
Authors: Feldman, U.; Laming, J. M.
1994ApJ...434..370F Altcode:
When accounting for coronal heat losses (based on previous models)
three mechanisms are considered: (1) radiation by coronal plasma;
(2) thermal conductivity between the 106 K corona and the
104 K chromosphere and (3) mass motions, mostly into the
solar wind. According to these models, thermal conductivity is the
most efficient among the coronal heat loss mechanisms. In this paper,
we describe studies of the relationships between structures having
temperatures of Te greater than or = 1 x 106 and
those with temperatures of Te less than 7 x 105
K. We show that effects of thermal conduction between the hot and cold
regions are not seen at the expected levels, implying that unimpaired
continuity is not being maintained between the 106 and
104 K plasma regions. As a consequence of these findings,
we stress that no conclusion on the properties of Te greater
than or = 1 x 106 K plasmas can be drawn from properties
of the so-called transition region (3 x 104 less than or =
Te less than or = 7 x 105 K) plasmas.

---------------------------------------------------------
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.
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: The plasma properties of the solar upper atmosphere determined
from high resolution observations and the nature of the physical
processes sustaining it
Authors: Feldman, Uri
1994PhPl....1.1390F Altcode:
Half a century ago, it was established that the temperature of the
“quiescent” solar corona is ≊106 K (≊100 eV). Wave
theories have been used to explain the means by which the Sun
keeps the corona about 200 times hotter than the 5000 K (≊0.5 eV)
photosphere. In recent years, it has been suggested that a mechanism
other than wave dissipation heats the “quiescent” corona and other
transient phenomena that occur in the upper solar atmosphere. It is
postulated by some that the solar upper atmosphere is heated by small
bursts of energy resulting from magnetic reconnection. In this paper,
the plasma properties of the upper solar atmosphere, a domain that,
when flares are included, encompasses about three orders of magnitude
in temperature (3×104-3×107 K) and four orders
of magnitude in electron density (3×108—3×1012
cm-3), are described. It is shown that conventional scenarios
based on magnetic reconnections may not adequately explain the observed
plasma properties of the solar upper atmosphere. However, a model,
consisting of electric currents flowing along magnetic field lines may
have a better chance simulating the observed properties. For quiescent
solar upper atmosphere phenomena, constant currents are needed to
simulate the observations, while for flares, currents supplied by an
exponentially decaying storage media are required.

---------------------------------------------------------
Title: The Solar Abundance of Helium Determined from a Redshifted
Plasma Flow over a Sunspot
Authors: Laming, J. M.; Feldman, U.
1994ApJ...426..414L Altcode:
The ultraviolet spectrum of a redshifted plasma flow appearing over a
sunspot in data obtained during the Naval Research Laboratory (NRL) High
Resolution Telescope and Spectrograph (HRTS I) flight is interpreted
as a radiatively cooling plasma. For most lines emitted from this
plasma, the assumption of ionization equilibrium during the cooling
is good; however, for He II this is not the case. In order to get the
helium abundance by comparison with other lines, one must integrate
differential equations for the various He ionization fractions, and
the temperature, and then calculate the radiation emitted. Our result
for the solar helium abundance is in the range 0.078-0.22 relative
to hydrogen, with the uncertainty arising from lack of knowledge of
model parameters.

---------------------------------------------------------
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.
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: Very Impulsive Solar Flares Observed with the YOHKOH Spacecraft
Authors: Feldman, U.; Hiei, E.; Phillips, K. J. H.; Brown, C. M.;
Lang, J.
1994ApJ...421..843F Altcode:
Using X-ray data from two instruments aboard the Yohkho spacecraft,
launched in 1991 August to study solar high-energy phenomena, some 38
extremely impulsive flares of X-ray importance greater than C1 have
been identified and studied. Electron temperatures of these flares,
derived from Yohkoh Bent Crystal Spectrometer data, appear to decline
immediately after the intensity maximum is attained, implying that
energy input into the flaring plasma is reduced or possibly ceases
after this time. Images of these flares with the high-resolution Yohkoh
Soft X-ray Telescope show that, contrary to expectation if thermal
conduction is a significant cooling mechanism, the emitting regions of
tiny pointlike sources (volumes less than or = 3 x 1024cc)
within a loop structure. With mass loss along field lines eliminated
also, from a previous study, the chief energy-loss mechanism is
likely to be radiation, and if so a lower limit for the electron
density of approximately 1012/cc is imposed. This is only
compatible with values of the emission measure if the flare volume
is 3 x 1024cc, corresponding to a sphere of only 1790 km
in diameter.

---------------------------------------------------------
Title: Absorption spectroscopy of radiatively-heated low-Z foils
Authors: Seely, J. F.; Feldman, U.; Brown, C. M.; Hammel, B. A.;
Back, C. A.; Hsieh, E.; Lee, R. W.
1994JQSRT..51..349S Altcode:
High-resolution absorption spectra of radiatively-heated low-Z foils
(CH and BN) have been recorded at the Nova II laser facility by a
grazing-incidence spectrograph. Using a calibration curve for Kodak
101 photographic plates, the plate density was converted to relative
intensity transmitted by the foil. Absorption spectra are presented
for the elements B, C, and N. The absoprtion features near the nickel
L edge in the wavelength region 11-15 A are also presented.

---------------------------------------------------------
Title: Infrared Coronal Emission Lines and the Possibility of their
Laser Emission in Seyfert Nuclei
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Avi
1994IAUS..159..447G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Very Impulsive Flares Observed with YOHKOH
Authors: Feldman, U.; Hiei, E.; Phillips, K. J. H.; Lang, J.; Brown,
C. M.
1994xspy.conf..269F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Very Impulsive Flares Observed with Yohkoh
Authors: Lang, J.; Feldman, U.; Hiei, E.; Phillips, K. J. H.; Brown,
C. M.
1994emsp.conf..191L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: What have we Learned from YOHKOH about Flares and what Should
BE done from Solar B
Authors: Feldman, U.
1994xspy.conf..139F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Coronal Abundances of Elements with Low First Ionization
Potential: Chromium, Calcium, and Aluminum
Authors: McKenzie, D. L.; Feldman, U.
1994ApJ...420..892M Altcode:
We have used X-ray spectra obtained by the SOLEX spectrometers on the
P78-1 satellite to study coronal abundances of three elements with low
first ionization potential (FIP): Cr, Ca, and Al. The Cr/O abundance
ratio was determined from the ratio of the Cr XV 2p6
(1)S0-2p5 3d (1)P1 line to the O VIII
1s (2)S-2p (2)P unresolved doublet, a ratio that is almost independent
of temperture. In a scenario in which the ratio of an element's
coronal to its photospheric abundance is largely determined by its
FIP, the Cr/O ratio should be reflective of the absolute Cr abundance,
because the FIPs of O and H are nearly equal. We find that the Cr/O
abundance ratio in coronal active regions varies by a factor of 2.7
and is probably always enhanced by at least a factor of 3 over the
photospheric ratio. The Ca/O abundance ratio was determined from the
ratio of a blend of Ca XV lines at around 22.75 A to the O VIII 1s
(2)S-2P (2)P doublet. Because this ratio is temperature dependent,
only lower limits are derived for the Ca/O abundance ratio. The lower
limits range from 3.0 to 9.7 times the photospheric ratio. Hence, it
is likely that both Ca and Cr are always enriched by at least a factor
of 3 in coronal active regions and flares. The Al/Mg abundance ratio
determination was based on the line ratio (Al XII 1 S2
(i)S0-s2p (1)P1/(Mg XI 1s2
(1)S0-1s 3p (1)P1). Because this ratio is
temperature sensitive and we have only six Al/Mg spectra, the results
of this study are somewhat equivocal. The evidence indicates that Al
is enriched in coronal active regions, but it is uncertain whether,
as expected, it is enriched as much as is Ca, which has a slightly
higher FIP. In order to account for these observations, as well as
previously reported determinations of the Fe/O, O/Ne, and Fe/Mg coronal
abundance ratios, in terms of a mechanism that moves ions much more
easily than neutrals form the chromosphere to the corona, we have
calculated the fraction of ionization for the abundant elelments
in the chromosphere. Photoionization by blackbody radiaiton from
just below the temperature minimum region, by locally produced Ly
alpha radiation, and by line and continuum radiation emitted at high
temperatures play and important role in determining the chromospheric
ionization structure. In particular, photoionization of O I by EUV
radiation from above must be invoked to account for variations in
the coronal O/Ne abundance ratio. Because H I strongly absorbs this
radiation, O is unionized at chromospheric depths of more than a few
hundred kilometers. The ionization pattern, as a function of FIP,
in the part of the upper chromosphere where the temperature is in
the range 6000-8000 K, may account for the observed coronal abundance
variations and enrichments. A mechanism that imparts a few tens of eV
to ions, but not to neutrals, in this region could be responsible for
the coronal enrichment of low-FIP elements.

---------------------------------------------------------
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.
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: Nonphotospheric Abundances in a Solar Active Region
Authors: Widing, K. G.; Feldman, U.
1993ApJ...416..392W Altcode:
Element abundances have been determined for a solar active region
observed to have a highly nonphotospheric Ne/Mg abundance ratio
associated with an open magnetic field. This active region is an
example of a class of relatively inconspicuous features with open
magnetic fields which contrast with brighter, more compact emission
regions with less anomalous abundance ratios. The study is based
on images of the active region in Ne VI, VII, Mg VI-VIII, Na VIII,
Si VIII, and Ca VIII, IX photographed in the 300-600 Å range by the
NRL spectroheliograph on Skylab. Element abundances relative to
magnesium were determined by combining plots of the ion differential
emission measures. The electron density was bracketed in the range 4 ×
109 to 2 × 1010 cm-3, and ionization
equilibrium was assumed. The Ne/Mg abundance ratio was also derived
from the Ne VI to Mg VI intensity ratios observed at 400 Å. We
find that the Ne/Mg abundance ratio is 15 times smaller than in the
photosphere, whereas the abundances of Na, Si, and Ca relative to
magnesium are not different by more than a factor of 2 from the ratios
in the photosphere. From other evidence we conclude that the abundances
of the low first ionization potential group of elements (Na, Mg, Si,
and Ca) are enriched more than tenfold relative to high FIP neon in
this region with open magnetic fields. Properties of a similar group
of solar features are summarized.

---------------------------------------------------------
Title: Infrared Coronal Emission Lines and the Possibility of Their
Laser Emission in Seyfert Nuclei
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Avi
1993ApJS...88...23G Altcode:
Infrared coronal emission lines are providing a new window for
observation and analysis of highly ionized gas in such Galactic
and extragalactic sources as Seyfert nuclei and classical novae
shells. These lines are expected to be primary coolants in colliding
galaxies, galaxy cluster cooling flows, cometary-compact H II regions,
and supernova remnants. In this paper, we compile a complete list
of infrared (λ &gt; 1 micron) lines due to transitions within
the ground configurations 2S^2^2p^k^ and 3S^2^3p^k^ (k = 1-5) or
the first excited configurations 2s2p and 3s3p of highly ionized
(χ &gt;= 100 eV) astrophysically abundant [n(X)/n(H) &gt;= 10^-6^]
elements. Included are approximately 74 lines in ions of O, Ne, Na,
Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of
approximately 1-280 microns. We present results from detailed balance
calculations, critical densities for collisional deexcitation, intrinsic
photon rates, branching ratios, and excitation temperatures for the
majority of the compiled transitions. The temperature and density
parameter space for dominant cooling via infrared coronal lines is
presented, and the relationship of infrared and optical coronal lines
is discussed. We find that under physical conditions found in Seyfert
nuclei, 14 of 70 transitions examined have significant population
inversions in levels that give rise to infrared coronal lines. Laser
gain lengths and corresponding column densities are calculated for
dense [10^6^ &lt;= n_e_ (cm^-3^) &lt;= 10^9^] collisionally ionized
plasmas. Application of these results to cooler plasmas photoionized
by power-law continuum radiation fields is also discussed. We find that
several infrared coronal line transitions have laser gain lengths that
correspond to column densities of 10^24-25^ cm^-2^ which are modeled
to exist in Seyfert nuclei. Observations that can reveal inverted level
populations and laser gain in infrared coronal lines are also suggested.

---------------------------------------------------------
Title: Elemental Abundances in the Upper Solar Atmosphere of Quiet
and Coronal Hole Regions (T E 4.3 X 10 5 K)
Authors: Feldman, U.; Widing, K. G.
1993ApJ...414..381F Altcode:
Detailed examination of the sun's upper atmosphere reveals that
elemental abundances vary between different solar regions. Some solar
regions exhibit the well-established photospheric abundances, while in
other regions the abundances of some elements diverge from photospheric
by an order of magnitude, and perhaps even more. Elemental abundances
in the solar wind (SW) are also different from elemental abundances
in the photosphere. It is postulated that elemental abundances in the
SW reflect the elemental abundances of their place of origin near the
solar surface. The solar surface is covered, predominantly, by quiet
and coronal hole regions. In this paper we measure the intensities of
limb-brightening rings over quiet and coronal hole regions in lines
of Mg VI and Ne VI (Te is approximately equal to 4.3 x 10 exp 5 K) and
determine the relative elemental abundances of the features producing
the rings. The rings are formed by a plasma component occupying only
a small fraction of the immediate volume above the solar surface.

---------------------------------------------------------
Title: Is It Justified to Assume that “Everywhere in the Sun's
Photosphere-Corona Domain the Electric Conductivity Is High”?; or,
What Drives the Solar Upper Atmosphere?
Authors: Feldman, Uri
1993ApJ...411..896F Altcode:
For many years, solar scientists have recognized the extreme complexity
of the upper solar atmosphere. However, in order to construct a valid
theoretical model they have formulated a set of simplified assumptions
governing the makeup of the sun's upper atmosphere. In previous papers
a number of assumptions used to construct the models were shown not
to be valid. In this Paper I bring evidence to question the validity
of the last and most important of the assumptions, the assertion that
'Everywhere in the photosphere-corona domain the electric conductivity
is HIGH'. The consequences of the finding are briefly discussed. A
laboratory measurement of the electrical conductivity versus temperature
in a gas with photospheric composition would resolve this important
issue and seem to be feasible.

---------------------------------------------------------
Title: Non-Photospheric Abundances in a Solar Active Region
Authors: Widing, K. G.; Feldman, U.
1993BAAS...25.1201W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Atomic Transition Probabilities of Fe II Lines Determined from
Solar Emission Spectra. I. The 2000--2800 Angstrom Wavelength Range
Authors: Ekberg, J. O.; Feldman, U.
1993ApJS...86..611E Altcode:
Intensities of Fe II lines were measured at a number of positions
above the white light limb of the quiet sun, using photographic spectra
obtained by the Naval Research Laboratory normal incidence spectrometer
on Skylab. With the aid of experimental spontaneous decay rates
previously published in the scientific literature we have calculated the
spontaneous decay rates of over 550 Fe II transitions in the 2000-2800 A
wavelength range. Two-hundred twenty of the measured spontaneous decay
rates are published for the first time. It was determined that the Fe
II levels in the solar chromosphere achieve a Boltzmann population
corresponding to a about 0.78 eV temperature. The accuracy of the
new rates is comparable to the accuracy of the previously published
experimental rates.

---------------------------------------------------------
Title: The He II 1640 Angstrom Multiplet Observed from Solar
Prominences: Erratum
Authors: Laming, J. M.; Feldman, U.
1993ApJ...409..869L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Burst Model for Line Emission in the Solar Atmosphere. III. A
Reassessment of the Assumptions of Constant Pressure and Steady
State Coronal Equilibrium in the Solar Transition Region
Authors: Feldman, U.; Laming, J. M.
1993ApJ...404..799F Altcode:
We investigate the temperature dependence of the electron densities
inferred from various spectral line diagnostics for the quiet sun,
two active regions, and the 1973 June 15 flare, all observed by
NRL instruments on Skylab. We find that the common assumption of
constant pressure in these solar regions is very poor, especially
for the quiet sun and the active regions, and that a constant density
assumption is much closer to the observations. Such a conclusion is not
contradicted by the morphology of these regions, as observed by the
HRTS instrument. We also investigate the variation of the nonthermal
mass motion with departures of the line formation temperature from
that corresponding to ionization equilibrium.

---------------------------------------------------------
Title: On the Absolute Abundance of Calcium in Solar Flares
Authors: Sterling, Alphonse C.; Doschek, George A.; Feldman, Uri
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: Infrared coronal emission lines and the possibility of their
maser emission in Seyfert nuclei
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Abi
1993egte.conf..303G Altcode:
Energetic emitting regions have traditionally been studied via x-ray,
UV and optical emission lines of highly ionized intermediate mass
elements. Such lines are often referred to as 'coronal lines' since
the ions, when produced by collisional ionization, reach maximum
abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6)
K typical of the sun's upper atmosphere. However, optical and UV
coronal lines are also observed in a wide variety of Galactic and
extragalactic sources including the Galactic interstellar medium,
nova shells, supernova remnants, galaxies and QSOs. Infrared coronal
lines are providing a new window for observation of energetic emitting
regions in heavily dust obscured sources such as infrared bright
merging galaxies and Seyfert nuclei and new opportunities for model
constraints on physical conditions in these sources. Unlike their
UV and optical counterparts, infrared coronal lines can be primary
coolants of collisionally ionized plasmas with 10(exp 4) less than
T(sub e)(K) less than 10(exp 6) which produce little or no optical or
shorter wavelength coronal line emission. In addition, they provide
a means to probe heavily dust obscured emitting regions which are
often inaccessible to optical or UV line studies. In this poster,
we provide results from new model calculations to support upcoming
Infrared Space Observatory (ISO) and current ground-based observing
programs involving infrared coronal emission lines in AGN. We present
a complete list of infrared (lambda greater than 1 micron) lines due to
transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k)
(k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly
ionized (x greater than or equal to 100 eV) astrophysically abundant
(n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included
are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar,
Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280
microns. We present new results from detailed balance calculations,
new critical densities for collisional de-excitation, intrinsic photon
rates, branching ratios, and excitation temperatures for the majority
of the compiled transitions. The temperature and density parameter
space for dominant cooling via infrared coronal lines is presented,
and the relationship of infrared to optical coronal lines is discussed.

---------------------------------------------------------
Title: The He II 1640 Angstrom Multiplet Observed from Solar
Prominences
Authors: Laming, J. M.; Feldman, U.
1993ApJ...403..434L Altcode:
We describe an analysis of EUV spectra of solar prominences taken with
the SO82-B instrument on Skylab, with special attention to the 1640 A
2l-3l arcmin multiplet of He II. It appears that the line intensities
emitted from plasma at temperatures between 2 x 10 exp 4 and 4 x 10 exp
4 K can be explained by an ionization equilibrium model, incorporating
photoexcitation and photoionization by incident radiation from the
solar disk. With this interpretation, the data are consistent with an
abundance for He of 0.1 relative to H. Some problems remain, however,
in predicting the relative intensities of the components of the 1640
A multiplet.

---------------------------------------------------------
Title: Highly ionized atoms: what do they teach us about the solar
atmosphere?
Authors: Feldman, U.
1993PhST...47..128F Altcode:
Solar atmosphere models are based primarily on six assumptions designed
to describe the properties and the fashion by which solar plasmas
behave. Over the years atomic physics methods were used to investigate
the above assumptions. In the course of this paper comments on each
of the six assumptions will be made and conclusions will be drawn.

---------------------------------------------------------
Title: Highly ionized atoms in space; or highly ionized atoms,
what are they teaching us about the solar coronal heating processes?
Authors: Feldman, U.
1993PhST...46...34F Altcode:
Dedicated to Professor Bengt Edlén on the 50. anniversary of the
publication of his paper on the identification of the solar coronal
lines.

---------------------------------------------------------
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
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 &gt; 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
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: A Burst Model for Line Emission in the Solar
Atmosphere. II. Coronal Extreme Ultraviolet Lines
Authors: Feldman, U.; Laming, J. M.; Mandelbaum, P.; Goldstein, W. H.;
Osterheld, A.
1992ApJ...398..692F Altcode:
We review the spectroscopic evidence for explosive events - bursts -
occurring in solar coronal plasmas. Problems in the interpretation
of extreme ultraviolet spectra from Mg-like ions, particularly Fe XV
in solar flares can be obviated to certain extent if these ions are
produced in an ionizing plasma, with the 3s3p 3P levels being excited
directly by inner shell ionization of the Al-like ion. We believe that a
similar mechanism should apply to Be-like ions. The excitation following
inner shell ionization can become important compared to electron impact
excitation at a temperature corresponding to approximately twice the
ionization potential of the ion concerned, but to be properly effective,
it requires some deviation of the electron distribution function from
a Maxwellian. The model we present produces a coronal heating rate
from these bursts that is somewhat larger than current estimates.

---------------------------------------------------------
Title: Thickness Variations along Coronal Loops Observed by the Soft
X-Ray Telescope on YOHKOH
Authors: Klimchuk, James A.; Lemen, James R.; Feldman, Uri; Tsuneta,
Saku; Uchida, Yutaka
1992PASJ...44L.181K Altcode:
It has been suggested that observed coronal loops have constant
thicknesses. However, if plasma loops coincide with magnetic loops,
then we might expect many loops to be significantly broader at their
tops than at their footpoints (since, on average, magnetic fields
must diverge with height in the solar corona). It is important to
understand how the thicknesses of loops vary along their lengths, since
such a variation is related to the distribution of electric currents
in the corona and is therefore relevant to solar flares and coronal
heating. We here present preliminary results of our investigation of
thickness variations along coronal loops observed with the Soft X-ray
Telescope (SXT) on board the Yohkoh satellite.

---------------------------------------------------------
Title: 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.
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: Infrared Coronal Emission Lines and the Possibility of Their
Maser Emission In Seyfert Nuclei
Authors: Greenhouse, M. A.; Feldman, U.; Smith, H. A.; Klapisch, M.;
Bhatia, A. K.; Bar-Shalom, A.
1992AAS...181.9803G Altcode: 1992BAAS...24.1274G
No abstract at ADS

---------------------------------------------------------
Title: Elemental abundances in the upper solar atmosphere
Authors: Feldman, Uri
1992PhST...46..202F Altcode:
A previous reassessment of spectroscopic abundance measurements from
high temperature solar plasmas showed that, on the average, the solar
upper atmosphere possesses a composition that is similar in nature to
the composition of the solar wind and solar energetic particles. In
recent years, an examination of spectra of the upper solar atmosphere
has confirmed these results and proceeded to demonstrate that elemental
substances change from region to region by as much as an order of
magnitude. An account of these changes, a description of the regions
in which they occur, and a possible elemental enrichment model are
presented.

---------------------------------------------------------
Title: Elemental abundances in the upper solar atmosphere.
Authors: Feldman, U.
1992PhyS...46..202F Altcode:
Elemental abundances in the solar wind (SW) and in solar energetic
particles (SEP) are different from abundances in the photosphere. A
reassessment of spectroscopic abundance measurements from high
temperature solar plasmas showed that, indeed, on the average, the solar
upper atmosphere possesses a composition which is similar in nature
to the composition of SW and SEP's. In the last few years a detailed
examination of spectra of the upper solar atmosphere has confirmed the
above results and proceeded to show that elemental abundances change
from region to region by as much as an order of magnitude. An account
of these changes, a description of the regions in which the changes
occur, and a possible elemental enrichment model is given.

---------------------------------------------------------
Title: Observation of Upflows during Soft X-Ray Solar Flares
Authors: Seely, J. F.; Feldman, Uri
1992ApJ...394..697S Altcode:
Upflows of the soft X-ray emission regions of four flares located near
sun center have been determined from the blueshift of the absolute
wavelength of the Ca XIX resonance lines recorded by the SOLFLEX
spectrometer on the P-78 spacecraft. Peak upward velocities were 35-90
km/s and occurred during the time of gradual increase in the Ca XIX
count rate and prior to the peak H-alpha emission. Rises in altitude
of 7000-80,000 km were inferred from the upward velocities.

---------------------------------------------------------
Title: Absolute O and O 2 concentrations in the
thermosphere from SKYLAB occultation data
Authors: Meier, R. R.; Feldman, U.; Brown, C. M.; Picone, J. M.
1992P&SS...40.1153M Altcode:
High resolution far u.v. spectra of the Sun observed during the
SKYLAB mission exhibited both broadband extinction by O 2
and narrowband self-absorption by O as the spacecraft passed through
sunset. The data were analyzed using Discrete Inverse Theory to retrieve
the O 2 and O concentrations. Excellent agreement with the
MSIS-86 model was found for O 2 and moderate agreement
for O. Both determinations were made with high absolute accuracy,
thereby demonstrating the power of absorption experiments.

---------------------------------------------------------
Title: The Potential for Plasma Diagnostics from Stellar
Extreme-Ultraviolet Observations
Authors: Feldman, U.; Mandelbaum, P.; Seely, J. F.; Doschek, G. A.;
Gursky, H.
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: Element Abundances and Plasma Properties in a Coronal Polar
Plume
Authors: Widing, K. G.; Feldman, U.
1992ApJ...392..715W Altcode:
The paper determines element abundances in a coronal polar plume
previously observed to have a low Ne/Mg abundance ratio associated with
an open magnetic field. This study is based on images of the plume in
Ne VI, VII, Mg VI-VIII, Na VIII, and Ca IX, X photographed between 300
and 600 A by the NRL spectroheliograph on Skylab. The density variation
with height derived from MG VIII 436.7 A is satisfactorily fitted with
a temperature of 843,000 K in hydrostatic equilibrium, close to the
temperature expected in ionization equilibrium. The electron density
derived from the MG VIII doublet ratio is 1 x 10 exp 9/cu cm. Element
abundances relative to magnesium at several altitudes are derived
by combining plots of the ion differential emission measures. The
relative abundances of Na, Mg, and Ca in the plume are found to be the
same (within a factor of 2) as those in the photosphere, whereas the
abundance of neon relative to magnesium is only 1/10 of this ratio in
the photosphere.

---------------------------------------------------------
Title: Thickness Variations Along Coronal Loops Observed by Yohkoh
Authors: Klimchuk, J. A.; Kluge, K.; Lemen, J. R.; Feldman, U.;
Uchida, Y.
1992AAS...180.2304K Altcode: 1992BAAS...24Q.760K
No abstract at ADS

---------------------------------------------------------
Title: The variability of elemental abundances in the upper solar
atmosphere
Authors: Feldman, Uri
1992AIPC..257..171F Altcode:
Coronal elemental abundances are found to change by as much as
an order of magnitude relative to those present in the solar
photosphere. Observations of modifications in coronal elemenal
abundances are reviewed and a tentative model governing the changes
is discussed.

---------------------------------------------------------
Title: Variations in the Relative Elemental Abundances of Oxygen,
Neon, Magnesium, and Iron in High-Temperature Solar Active-Region
and Flare Plasmas
Authors: McKenzie, D. L.; Feldman, U.
1992ApJ...389..764M Altcode:
X-ray line ratios that are weakly dependent on temperature are
used here to search for coronal abundance variations of O, Ne, Mg,
and Fe. Significant variations are found for the following abundance
ratios: Fe/Ne (a factor of 4.1-4.3), Fe/O (2.4-3.1), and O/Ne(2.4). The
mechanism, that enhances the coronal abundances of low first ionization
potential (FIP) elements apparently operates to a decreasing extent with
increasing FIP up to at least 13.6 eV, the FIP of oxygen. The data also
indicate that significant abundance changes in the course of a flare
are rare, but that changes on a time scale of days are not unusual. It
is argued that the minimum observed coronal abundance ratios of Fe/Ne,
Fe/O, and O/Ne should be no lower than the photospheric ratios, unless a
process that favors the population of the corona with high-FIP elements
over lower FIP elements is operative.

---------------------------------------------------------
Title: A Burst Model for Line Emission in the Solar Atmosphere. I. XUV
Lines of He i and He II in Impulsive Flares
Authors: Laming, J. M.; Feldman, U.
1992ApJ...386..364L Altcode:
A model in which the solar chromosphere is heated by explosive events
is developed and used to interpret XUV spectra of He I and He II in
impulsive flares observed by the Skylab spectroheliograph. From a
comparison of relative line intensities from He I and He II emitted
within the flares, the model establishes sizes, durations, and
frequencies for the individual events and, by comparison with lines
from other elements observed in the same flares, is demonstrated to
be consistent with a helium abundance relative to hydrogen of 0.1 for
burst temperatures of 15-18 eV.

---------------------------------------------------------
Title: Transitions from Metastable Levels Emitted during
Short-Duration Bursts: How Valid Are Their Calculated Intensities?
Authors: Feldman, Uri
1992ApJ...385..758F Altcode:
Recent spectroscopic studies of the quiescent and transient phenomena
that take place in the sun's atmosphere suggest that short-duration
bursts may play a significant role in the heating processes of
the upper solar atmosphere. Accepting bursts as working processes,
concepts of electron density diagnostics in the upper solar atmosphere,
and element abundance determinations, methods which are based mostly
on line ratios formed in steady state coronal equilibrium are being
reexamined. A review of the Fe IX density diagnostics and the effects
of high-temperature short-lived bursts on this unique atomic system
is given. An account of some of the metastable emission lines used
in solar plasma diagnostics, and the electron densities at which they
may become affected as a result of short-lived bursts, is also given.

---------------------------------------------------------
Title: Elemental abundances and their variations in the upper solar
atmosphere
Authors: Widing, K. G.; Feldman, U.
1992sws..coll..405W Altcode:
In the standard FIP pattern of element abundances observed in the bulk
corona and solar wind, elements with first ionization potential (FIP)
below about 10 eV are enriched relative to elements with higher FIP. We
have surveyed element abundances in a variety of emitting structures
on the sun using imaged spectra of the sun in the 200-600 A range
from SKYLAB and diagnostic flux ratios of soft X-ray lines between
10 and 20 A. The resulting element abundances show the imprint of the
FIP effect, but the characteristics of this pattern are variable and
greatly enhanced in some features, and are correlated with the magnetic
morphology. The enrichment factor reaches values of 10 to 15 in diffuse
features with open magnetic fields. The O/Ne abundance ratio is constant
in the SKYLAB sample (in agreement with the standard FIP pattern), but
shows variations up to a factor of two in soft X-ray flares. Soft X-ray
abundance ratios involving Fe suggest that the photospheric abundance
of iron is equal to the meteoritic rather than the spectroscopic ratio.

---------------------------------------------------------
Title: Fe II Emission Lines. II. Excitation Mechanisms in Cool Stars
Authors: Judge, P. G.; Jordan, C.; Feldman, U.
1992ApJ...384..613J Altcode:
Excitation mechanisms are discussed for the 'resonance' transitions
(between the 3d(6)4s, 3d7, and 3d(6)4p configurations) of Fe II observed
in emission in the near-UV spectra of cool stars. The analysis is
based upon: (1) emission measure analysis of previously measured
lines in IUE spectra of cool giants; (2) discussion of the behavior
of Fe II lines observed above the solar limb from Skylab spectra; (3)
approximate radiative-transfer calculations in a 59 level Fe-II model
atom using mean escape probabilities and a parameterization of optical
radiation fields; and (4) accurate radiative transfer calculations in
a smaller atomic model. The solar spectra show unambiguous evidence
that electron collisions are responsible for most of the Fe-II emission
observed above the white-light limb. The terms leading to UV multiplets
3-6, 34-36, and 61-64 are excited by electron excitation of metastable
quartet terms below about 4 eV, followed by photoexcitation in lines at
optical wavelengths by photospheric radiation. A 'cool-star' diagnostic
diagram is constructed showing the regimes in which electron collisions
and continuum photoexcitation are important in the chromospheres of
cool stars.

---------------------------------------------------------
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.
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: The Iron-to-Calcium Abundance Ratio in the 20 X 10 6 K Plasma
of Medium and Large Solar Flares
Authors: Phillips, K. J. H.; Feldman, U.
1991ApJ...379..401P Altcode:
The iron-to-calcium abundance ratio during several flares observed
by instruments on the P78-1 and Solar Maximum Mission spacecraft are
determined using the intensity ratio of a dielectronic satellite line
of Fe XXIV and the resonance line of Ca XIX. Values of A(Fe)/A(Ca)
equal to 6.8 +/- 1.0 and 6.0 +/- 1.5 were derived from these data sets,
respectively, the small difference being attributable to errors in the
calculated instrument sensitivities. These values fall between two other
determinations from X-ray spectra, but are less than the photospheric
value. They are fairly constant from flare to flare, contrasting with
other recent work which indicates strong flare-to-flare variations.

---------------------------------------------------------
Title: Analysis of the Solar O ii/O III Multiplets at 834 Angstrom :
Implications for the Emission Measure Distribution in the Vicinity
of 40,000 K
Authors: Meier, R. R.; Widing, K. G.; Feldman, U.
1991ApJ...369..570M Altcode:
A previously unpublished very high resolution solar spectrum has
been analyzed to determine the relative contributions of O II and
O III at 834 Å. The resulting ratio of O II to O III emissions is
found to be 0.35, which is lower than derived from lower resolution
data or expected from calculations based on standard emission measure
theory. In order to reproduce the ratio observed in the high-resolution
spectrum, it is proposed to lower the emission measure in the vicinity
of 40,000 K by a factor of 2. This would also reconcile differences
among apparently discrepant lines of C II and is consistent with the
physical interpretation that the emission measure between 104
and 105 K is comprised of components arising from physically
different regimes in the solar atmosphere.

---------------------------------------------------------
Title: Element Abundances in a Coronal Polar Plume
Authors: Widing, K. G.; Feldman, U.
1991BAAS...23.1046W 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.
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.
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: Wavelengths and Energy Levels for the Na I Isoelectronic
Sequence Y28+ through U81+
Authors: Seely, J. F.; Brown, C. M.; Feldman, U.; Ekberg, J. O.;
Keane, C. J.; MacGowan, B. J.; Kania, D. R.; Behring, W. E.
1991ADNDT..47....1S Altcode:
Na-like transitions from the n = 3, 4, and 5 excited levels of the
ions Cd 37+, In 38+, Sn 39+, and Gd
53+ were identified in the extreme ultraviolet spectra from
plasmas produced by one or two beams of the Nova laser at the Lawrence
Livermore National Laboratory. The currently observed wavelengths and
the previously observed wavelengths for lower Z ions were compared with
the wavelengths calculated using Grant's multiconfiguration Dirac-Fock
program. Based on this comparison, semiempirical corrections to the
wavelengths were made, and the corrected wavelengths were determined
for the ions Y 28+ through U 81+. The excitation
energies for the n = 3, 4, and 5 levels and the ionization energies
of the ground states were also derived for the ions Y 28+
through U 81+.

---------------------------------------------------------
Title: The beam driven chromospheric evaporation model of large
solar flares: a model getting “no respect” from the sun
Authors: Feldman, Uri
1991LNP...387..146F Altcode: 1991fpsa.conf..146F
Since before the last solar maximum, theoretical and to some extent
observational, flare physics were dominated by beam driven chromospheric
evaporation models. Comparisons between theoretical predictions and
observations from soft and hard X-ray radiations point to major model
inconsistencies. An account of some of the inconsistencies as well as
the requirements for a better soft X-ray model are presented.

---------------------------------------------------------
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.
1991LNP...387...22C Altcode: 1991fpsa.conf...22C
No abstract at ADS

---------------------------------------------------------
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.
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: On the Anomalous Abundances of the 2 x10 4--2 10 5 K Solar
Atmosphere above a Sunspot
Authors: Feldman, U.; Widing, K. G.; Lund, P. A.
1990ApJ...364L..21F Altcode:
The EUV spectrum (1175-1710 A) of a sunspot is compared with the EUV
spectrum of two nearby plage regions. The observations were obtained
during the July 21, 1975 rocket flight of the Naval Research Laboratory
High Resolution Telescope and Spectrograph (HRTS). It is shown that
the silicon-to-carbon elemental abundance ratios in the 20,000-200,000
K temperature regions observed in the plage are enhanced by a factor
of about 3 relative to the same ratios in the sunspot. By comparing
lines from C II, Si II, and Si III with H I Ly-alpha and O I, it is
shown that above active regions the abundance of ionized silicon is
enhanced relative to its value in the photosphere.

---------------------------------------------------------
Title: Photospheric Abundances of Oxygen, Neon, and Argon Derived
from the XUV Spectrum of an Impulsive Flare
Authors: Feldman, U.; Widing, K. G.
1990ApJ...363..292F Altcode:
Relative elemental abundances of O, Ne, Na, Mg, Ar, and Ca are
determined from detailed analysis of XUV spectra emitted by an
impulsive flare. The electron density measured from three diagnostic
line ratios is 2-3 x 10 to the 12th/cu cm. It was found that the
relative abundances in the flare are similar to values obtained from
or proposed for photospheric material. The ratios of O/Mg, Ne/Mg,
and Ar/Mg are about four times higher in the impulsive flare than the
values typically observed in the average corona. It is suggested that
electric fields above the photosphere may be responsible for the order
of magnitude variations between the abundances of the group of elements
with high first ionization potentials (FIP) and the group with low FIP.

---------------------------------------------------------
Title: The Beam-driven Chromospheric Evaporation Model of Solar
Flares: A Model Not Supported by Observations from Nonimpulsive
Large Flares
Authors: Feldman, U.
1990ApJ...364..322F Altcode:
Most large solar flares exhibit hard X-ray emission which is usually
impulsive, as well as thermal soft X-ray emission, which is gradual. The
beam-driven chromospheric evaporation model of solar flares was proposed
to explain the origin of the soft X-ray emitting flare plasma. A careful
evaluation of the issue under discussion reveals contradictions between
predictions from the theoretical chromospheric evaporation model and
actual observations from a set of large X- and M-type flares. It is
shown that although the soft X-ray and hard X-ray emissions are a
result of the same flare, one is not a result of the other.

---------------------------------------------------------
Title: Spectral Line Intensities for the Carbon Isoelectronic Sequence
(Kr XXXI through Xe IL)
Authors: Seely, J. F.; Feldman, U.; Rozzi, S.; Goldstein, W. H.;
Klapisch, M.
1990ADNDT..45..321S Altcode:
The intensities of transitions in the C-like ions Kr XXXI, Sr XXXIII,
Zr XXXV, Mo XXXVII, Ru XXXIX, Pd XLI, Cd XLIII, Sn XLV, Te XLVII,
and Xe IL have been calculated. Included in the calculation were 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. The intensities were calculated for
the electron densities 10 12, 10 13, and 10
14 cm -3 that are appropriate for tokamak plasmas.

---------------------------------------------------------
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.
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.
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: Abundance Variations in the Outer Solar Atmosphere Observed
in SKYLAB Spectroheliograms
Authors: Widing, K. G.; Feldman, U.
1989ApJ...344.1046W Altcode:
Relative abundances of neon, magnesium, silicon, and oxygen have
been derived from emission measure analyses of a prominence, flare,
and active region observed in the 315-625 A range on NRL Skylab
spectroheliograms. The neon-to-magnesium abundance ratio changes from
a value of 2.2 in the prominence to 0.64 in the active region, while
the magnesium to silicon ratio does not vary, suggesting that neon is
the variable element. Neon-to-magnesium abundance ratios in a larger
sample of solar features have been estimated using eye estimates of
line ratios in the Ne VI and Mg VI multiplets at 400 A. The abundance
variations are strongly correlated with the magnetic field morphology,
ranging from Ne/Mg = 0.1 or 0.2 in some diffuse, open-field structures
to values of 2 or 3 in some active, closed-field structures. Large
Ne/Mg ratios of approximately 3 observed in impulsive flares may be
representative of the abundance distribution in the photosphere. It
is suggested that the well-known weakening of helium lines in coronal
holes may be caused by an abundance deficiency of helium, similar to
the abundance of depletions of neon observed in open-field regions.

---------------------------------------------------------
Title: Photospheric Abundances of Oxygen, Neon, and Argon Derived
from XUV Spectra of an Impulsive Flare
Authors: Feldman, U.; Widing, K. G.
1989BAAS...21.1151F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Mass Upflow in the Long Duration Flare of 5 June 1979
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.; McKenzie, D. L.
1989BAAS...21..850D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Element Abundances in the Sun Observed on SKLAB
Spectroheliograms
Authors: Widing, K. G.; Feldman, U.
1989BAAS...21..833W Altcode:
No abstract at ADS

---------------------------------------------------------
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.
1989JOSAB...6..379F Altcode: 1989OSAJB...6..379F
No abstract at ADS

---------------------------------------------------------
Title: Atomic Data and Spectral Line Intensities for the Nitrogen
Isoelectronic Sequence (Ar XII through Kr XXX)
Authors: Bhatia, A. K.; Seely, J. F.; Feldman, U.
1989ADNDT..43...99B Altcode:
Oscillator strengths, radiative decay rates, and electron collision
strengths have been calculated for the N-like ions Ar XII, Ti XVI,
Fe XX, Zn XXIV, and Kr XXX. Included in the calculation are the 72
levels of the configurations 2 s22 p3, 2 s2
p4, 2 p5, 2 s22 p23 s,
2 s22 p23 d. and 2 s22 p23
d. The level populations are calculated for the electron densities 10
13, 10 14, and 10 15 cm -3,
and the spectral line intensities of the transitions from these levels
are presented. The calculated intensities are in good agreement with
the relative intensities observed in the spectra from the PLT tokamak.

---------------------------------------------------------
Title: Wavelengths and Energy Levels for the Cu I Isoelectronic
Sequence Ru15+ through U63+
Authors: Seely, J. F.; Brown, C. M.; Feldman, U.
1989ADNDT..43..145S Altcode:
The observed wavelengths for the 18 strongest transitions of types
n = 4-4 and n = 4-5 in the Cu I isoelectronic sequence were compared
to the wavelengths calculated using the optimal-level option of the
multiconfiguration Dirac-Fock program of Grant et al. On the basis
of this comparison semiempirical corrections to the wavelengths were
made, and corrected wavelengths for the ions Ru 15+ through U
63+ were determined. The semiempirically corrected excitation
energies for all of the n = 4 and n = 5 levels were also derived.

---------------------------------------------------------
Title: Solar spectroscopy in the far-ultraviolet - X-ray wavelength
regions:status and prospects.
Authors: Feldman, U.; Doschek, G. A.; Seely, J. F.
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: Generation of XUV Spectra by Powerful Picosecond Laser
Authors: Nam, C. H.; Tighe, W.; Suckewer, S.; Feldman, U.; Seely, J.
1988JPhys..49..203N Altcode: 1988IAUCo.102..203N
No abstract at ADS

---------------------------------------------------------
Title: On the Unresolved Fine Structures of the Solar
Atmosphere. II. The Temperature Region 2 x10 5 K--5 x10 5 K
Authors: Feldman, U.
1987ApJ...320..426F Altcode:
It was shown previously (Feldman, 1983) that the 30,000-200,000 K
temperature solar plasmas behave differently than the chromosphere and
corona, and it was concluded that while a small part of the emission
detected may consist of 'classical' transition zone plasma, most of
the emissions from these temperatures belong to a different entity
termed 'unresolved fine structures'. In this paper these conclusions
are extended to plasma emitted at higher temperatures, in the range of
Te between 200,000 to 500,000 K. Using the Skylab spectrometer data on
the Lyman continuum, C II, C III, O IV, O VI, and Mg X, it is shown that
the properties of the solar atmosphere in these two temperature regions
(30,000-200,000 K and 200,000-500,000 K, respectively) are similar.

---------------------------------------------------------
Title: Observations of Nonthermal Energy Distributions during the
Impulsive Phase of Solar Flares
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.
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: Ultraviolet AL III Emission Lines and the Physics of the
Solar Transition Region
Authors: Doschek, G. A.; Feldman, U.
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.
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: Atomic Data and Spectral Line Intensities for the Carbon
Isoelectronic Sequence (Ar XIII through Kr XXXI)
Authors: Bhatia, A. K.; Seely, J. F.; Feldman, U.
1987ADNDT..36..453B Altcode:
Oscillator strengths, radiative decay rates, and electron collision
strengths have been calculated for the C-like ions Ar XIII, Ti XVII,
Fe XXI, Zn XXV, Se XXIX, and Kr XXXI. The corresponding atomic data
for the ions Ca XV, Cr XIX, Ni XXIII, and Ge XXVII are determined by
interpolation. The configurations included in the calculation are 2
s22 p2, 2 s2 p3, 2 p4,
2 s22 p3 s, 2 s22 p3 p, and 2 s22 p3
d. The populations of the 46 levels belonging to these configurations
are calculated for electron densities equal to 10 13,
10 14, and 10 15 cm -3, and the
spectral line intensities of the transitions from these levels are
also presented.

---------------------------------------------------------
Title: Atlas of extreme ultraviolet spectroheliograms from 170 to
625 A. Volume 1; Volume 2
Authors: Feldman, Uri
1987aeus.book.....F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Extreme-Ultraviolet Spectrum (300--630 Angstrom ) of an
Errupting Prominence Observed from SKYLAB
Authors: Widing, K. G.; Feldman, U.; Bhatia, A. K.
1986ApJ...308..982W Altcode:
The eruptive-spray event of 1974 January 17 observed from Skylab was
an energetic limb event in which the expansion of a prominence arch
with velocities of the order of 400 km s-1 was accompanied
by heating to coronal temperatures. The authors have studied the
prominence images photographed in the 300 - 630 Å wavelength range by
the NRL spectroheliograph on Skylab. From the spectrum they have derived
thermal properties for the brightest portion of the nearly straightened
leg of the arch. Wavelengths, identifications, and intensities are
presented for approximately 90 emission lines formed at temperatures
between 105K and 106K. The emission measure
plot is similar to those observed for the quiet Sun. From this plot
the authors derive a neon to magnesium abundance ratio of 2.2 and an
oxygen to neon ratio of 8.

---------------------------------------------------------
Title: Measurement of Wavelengths and Lamb Shifts for Inner-Shell
Transitions in Fe xviii--xxiv
Authors: Seely, J. F.; Feldman, U.; Safronova, U. I.
1986ApJ...304..838S Altcode:
The wavelengths of inner-shell 1s-2p transitions in the ions Fe
XVIII-XXIV have been measured in solar flare spectra recorded by the
Naval Research Laboratory crystal spectrometer (SOLFLEX) on the Air
Force P78-1 spacecraft. The measurements are compared with previous
measurements and with recently calculated wavelengths. It is found that
the measured wavelengths are systematically larger than the wavelengths
calculated using the Z-expansion method by up to 0.65 mA. For the more
highly charged ions, these differences can be attributed to the QED
contributions to the transition energies that are not included in the
Z-expansion calculations.

---------------------------------------------------------
Title: Measured wavelengths for N = 4 to 2 transitions in Fe XXIV
and Fe XXIII
Authors: Seely, J. F.; Feldman, U.
1986PhyS...33..110S Altcode:
Accurate wavelength measurements for Fe XXIV and Fe XXIII
transitions near 8 A and of the type N = 4 to 2 from solar spectra
are presented. The resonance transition in the hydrogenlike ion Mg
XII is used as a reference. The measured wavelengths are compared with
previous ones and with ab initio and semiempirical calculations that
include screening parameters in the nonrelativistic, relativistic,
and radiative terms.

---------------------------------------------------------
Title: Atomic Data and Spectral Line Intensities for the Beryllium
Isoelectronic Sequence (Ar XV through Kr XXXIII)
Authors: Bhatia, A. K.; Feldman, U.; Seely, J. F.
1986ADNDT..35..449B Altcode:
Oscillator strengths, radiative decay rates, and electron collision
strengths are calculated for the ions Ar XV, Ti XIX, Ni XXV, Ge XXIX,
and Kr XXXIII in the Be I isoelectronic sequence. The corresponding
atomic data for the ions Ca XVII, Cr XXI, Fe XXIII, Zn XXVII, and Se
XXXI are determined by interpolation. The configurations included
in the calculation of the atomic data are 2 s2, 2 s2 p,
2 p2, 2 s3 s, 2 s3 p, 2 s3 d, 2 p3 s, 2 p3 p, and 2 p3
d. The intensities for transitions between the lowest 20 levels of
these configurations are calculated for an electron temperature equal
to half the ionization potential and for electron densities equal to 10
13, 10 14, and 10 15 cm -3.

---------------------------------------------------------
Title: Atomic Data and Spectral Line Intensities for the Boron
Isoelectronic Sequence (Ar XIV through Kr XXXII)
Authors: Bhatia, A. K.; Feldman, U.; Seely, J. F.
1986ADNDT..35..319B Altcode:
We have calculated the oscillator strengths, radiative decay rates,
and the electron collision strenghts for the B-like ions Ar XIV, Ti
XVIII, Fe XXII, Ge XXVIII, and Kr XXXII. The corresponding atomic data
for the ions Ca XVI, Cr XX, Ni XXIV, Zn XXVI, and Se XXX are determined
by interpolation. The configurations included in the calculation are 2
s22 p, 2 s2 p2, 2 p3, 2 s23
s, 2 s23 p, and 2 s23 d. Using both the computed
and the interpolated atomic data, we calculated the populations of
the 20 levels belonging to these configurations. The intensities of
the transitions are presented for electron densities of interest for
the diagnosis of tokamak plasmas (10 13, 10 14,
and 10 15 cm -3).

---------------------------------------------------------
Title: High-resolution observations of X-ray transitions in Fe
XXV-XXIII
Authors: Seely, J. F.; Feldman, U.
1985JPhB...18L.797S Altcode:
The wavelengths of X-ray transitions in Fe XXV-XXIII have been measured
using a high-resolution spectrum reflected from the Ge(13-1) planes. A
number of transitions have been resolved for the first time in solar
flare spectra, and the contributions of the Fe XXIV n = 3 satellites
to the Fe XXV parent lines are discussed. The QED contributions to
the wavelengths of the Fe XXIV n = 3 satellite transitions have been
determined.

---------------------------------------------------------
Title: Element abundances from solar flare spectra
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.
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.
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: Relative intensities of 2s22pk-2s2pk
+ 1 transitions in F i- to B i-like Ti, Cr, Fe, Ni, and Ge in
a tokamak plasma: A comparison of experiment and theory
Authors: Stratton, B. C.; Moos, H. W.; Suckewer, S.; Feldman, U.;
Seely, J. F.; Bhatia, A. K.
1985PhRvA..31.2534S Altcode:
Measured relative intensities of a number of allowed
2s22pk-2s2pk+1 transitions (60-200
A&amp;#778) in the F i- to B i-like ions of titanium, chromium, iron,
nickel, and germanium are compared with values from level-population
calculations. The measurements are from Princeton Large Torus (PLT)
tokamak plasmas with electron densities of ~2.5×1013
cm-3. For titanium and chromium, data from plasmas
with densities of ~5×1012 cm-3 are also
presented; a number of density-dependent line-intensity ratios are
found. The spectra were obtained with use of a grazing-incidence
time-resolving spectrograph which was radiometrically calibrated with
use of synchrotron radiation from the National Bureau of Standards
Synchrotron Ultraviolet Radiation Facility (SURF II). The measured
relative intensities are therefore reliable. For the majority of the
observed lines, agreement between the measured and calculated relative
intensities is within 30%, the estimated accuracy of the measurements;
significant discrepancies are found in the titanium ions at the
low density. The discrepancies, some of which are due to blends,
are discussed. Thus, the level-population calculations may be used
with some confidence for spectroscopic plasma diagnostics. In the C
i-like ions, there is some evidence that calculations which include
proton-collisional excitation and deexcitation between the levels of
the ground configuration are in better agreement with the measurements
than those that do not, indicating that proton collisions should be
included in the calculations for these ions.

---------------------------------------------------------
Title: The solar coronal X-ray spectrum 5.5-12 A
Authors: McKenzie, D. L.; Landecker, P. B.; Feldman, U.; Doschek, G. A.
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.
1985BAAS...17..629D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Precision measurement of transition energies and Lamb shifts
in two-electron argon and potassium in solar-flare spectra
Authors: Seely, J. F.; Feldman, U.
1985PhRvL..54.1016S Altcode:
The wavelengths of 1s2 1S0-1snp
1P1 transitions in the two-electron ions Ar
xvii and K xviii have been measured in solar-flare spectra. The QED
contributions to the transition energies are determined by comparison
of the measured transition energies to the calculated values. The
ionization limit of Ar xvii is also determined.

---------------------------------------------------------
Title: Population mechanisms for the He(+) N = 3 levels determined
from measurements of the solar 1640 A emission
Authors: Seely, J. F.; Feldman, U.
1985MNRAS.213..417S Altcode:
The intensities of the 3s-2p, 3p-2s, and 3d-2p components of the He II
1640 Å line have been measured from solar data taken by the NRL slit
spectrograph on Skylab. The relative and absolute population densities
of the 3s, 3p, and 3d levels of He+ are determined near
the white-light limb in various solar regions (coronal hole, quiet
Sun, active regions, and a prominence) and in a flare region on the
solar disc. The population density measurements are interpreted using
a rate equation model for the He+ ion. It is found that
self-absorption of the 3p-1s radiation contributes to the population
of the 3p level in all the solar regions that are studied and is
particularly important in the active regions, the prominence and the
flare. Recombination contributes to the population of the 3d level in
the active regions near the limb and in the prominence. In all the
solar regions that are studied, the 3p-2s component of the 1640 Å
line is more intense than the 3d-2p and 3s-2p components.

---------------------------------------------------------
Title: New identifications of Fe XVII spectral lines in solar flares
Authors: Feldman, U.; Doschek, G. A.; Seely, J. F.
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.
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: Atomic Data and Spectral Line Intensities for the Neon
Isoelectronic Sequence (Si V through Kr XXVII)
Authors: Bhatia, A. K.; Feldman, U.; Seely, J. F.
1985ADNDT..32..435B Altcode:
The electron impact collision strengths and the spontaneous radiative
decay rates are presented for the following ions of the Ne isoelectronic
sequence: Si V, Ar IX, Ti XIII, Fe XVII, Ge XXIII and Kr XXVII. Data are
given for the 27 levels that belong to four different configurations
(2 s22 p6, 2 s22 p53 s,
2 s22 p53 p, and 2 s22 p53
d). By use of the atomic data calculations of the above-mentioned
ions, the atomic data for all the ions with 14 ⩽ Z ⩽ 36 have
been interpolated. Energy levels and level populations are presented
for all the even- Z ions with 14 ⩽ Z ⩽ 36 (Si V, S VII, Ar IX,
Ca XI, Ti XIII, Cr XV, Fe XVII, Ni XIX, Zn XXI, Ge XXIII, Se XXV,
and Kr XXVII). The level populations are given for the three electron
densities 10 13, 10 14, and 10 15
cm -3. Spectral line intensities are also presented for
all transitions with intensities within two orders of magnitude of
the most intense line in each ion.

---------------------------------------------------------
Title: Spectral Line Intensities for the O I, N I, C I, B I, and Be
I Isoelectronic Sequences, Z = 26-36
Authors: Feldman, U.; Seely, J. F.; Bhatia, A. K.
1985ADNDT..32..305F Altcode:
The spectral line intensities for the O I, N I, C I, B I, and Be
I isoelectronic sequences and for Z = 26, 28, 30, 32, 34, and 36
are presented. The transitions are of the types 2 s22
pk-2 s2 pk+1 , 2 s2 pk+1 -2 pk+2
, 2 s22 pk-2 s22 pk,
and 2 s2 pk+1 -2 s2 pk+1 . The simulated spectra
are useful for the identification of allowed and forbidden transitions
in the wavelength range 40 to 2300 Å in tokamak plasmas. The
line intensities are calculated for an electron density of 2.5 ×
10 13 cm -3 and for an electron temperature
approximately equal to the temperature for maximum abundance of each
ion in the case of coronal equilibrium.

---------------------------------------------------------
Title: The relation of electron temperature to emission measure and
limits of increase in emission measure in soft X-ray flares
Authors: Denton, R. E.; Feldman, U.
1984ApJ...286..359D Altcode:
A sample of 126 soft X-ray flares (ranging in X-ray class from C3
up to X3) is studied in order to look for possible correlations
between various parameters of the flare plasma. It is found that
the emission measure (N2V) correlates positively with the electron
temperature (T) determined from the Ca XIX resonance line and nearby
satellites. Measured values of the maximum value of T (TM) range
from 8 to 18 x 10 to the 6th K. Increases in N2V of no more than a
factor of 400 from X-ray onset to soft X-ray maximum are observed. The
largest increases result from the most intense flares. The limit on
the increase of N2V may be important in determining the relative roles
of chromospheric evaporation and compression in producing the observed
high densities in soft X-ray flare plasmas.

---------------------------------------------------------
Title: The Large Flare November 7, 1980: A Test of Chromospheric
Evaporation Theories?
Authors: Karpen, J. T.; Doschek, G. A.; Feldman, U.
1984BAAS...16.1003K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Direct measurement of the increase in altitude of the soft
X-ray emission region during a solar flare
Authors: Seely, J. F.; Feldman, U.
1984ApJ...280L..59S Altcode:
The upward motions of the hot thermal regions of several large (M
type) solar flares have been determined from the soft X-ray spectral
data recorded by the scanning spectrometer (SOLFLEX) on the P78-1
spacecraft. For the limb flares that are studied, the centroid of the
Ca XIX emission region moves to a higher altitude with an apparent
speed of 20-40 km/s for a period of 20-30 minutes following onset of
the flare and reaches an altitude of 30,000-40,000 km. Although brief
periods of downward motion of the emission centroid are observed,
substantial decreases in altitude are not observed in any of the flares.

---------------------------------------------------------
Title: On the rate of energy input in thermal solar flares
Authors: Feldman, U.; Doschek, G. A.; McKenzie, D. L.
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.
1984uxsa.coll..151S Altcode: 1984IAUCo..86..151S; 1984uxsa.conf..151S
No abstract at ADS

---------------------------------------------------------
Title: Measurement of the Increase in Altitude of the Soft X-Ray
Emission Regions of Solar Flares (short Abstract)
Authors: Seely, J. F.; Feldman, U.
1984uxsa.coll...12S Altcode: 1984IAUCo..86...12S; 1984uxsa.conf...12S
No abstract at ADS

---------------------------------------------------------
Title: Transitions of the Type 2s-2p in Highly-Ionized CA Through RB
Authors: Behring, W. E.; Cohen, L.; Seely, J. F.; Feldman, U.;
Goldsmith, S.; Richardson, M.
1984uxsa.coll..225B Altcode: 1984uxsa.conf..225B; 1984IAUCo..86..225B
No abstract at ADS

---------------------------------------------------------
Title: Relative Intensities of Lines in Fi-Bi ti, cr, fe, ni, and Ge:
a Comparison of Theory and Experiment
Authors: Stratton, B. C.; Moos, H. W.; Feldman, U.; Seely, J. F.;
Suckewer, S.; Finkenthal, M.
1984uxsa.coll..175S Altcode: 1984uxsa.conf..175S; 1984IAUCo..86..175S
No abstract at ADS

---------------------------------------------------------
Title: On the unresolved fine structures of the solar atmosphere in
the 30,000-200,000 K temperature region
Authors: Feldman, U.
1983ApJ...275..367F Altcode:
The solar atmospheres from the chromosphere through the transition
zone and all the way up into the corona usually are considered to be
parts of one continuous structure. Now that stellar measurements in the
far-ultraviolet have become available, an attempt is being made to apply
solar physics ideas to solar type stars. The intention of this paper is
to reexamine the experimental facts concerning the relations between the
solar chromosphere, transition zone, and corona. Experimental evidence
is presented to argue that the solar plasma in the temperature region
40,000-220,000 K occurs in structures magnetically isolated from the
chromosphere and corona. It is suggested that while a small part of the
emission detected in the 40,000-220,000 K region consists of the 'true'
transition zone plasma, i.e., the interface between chromospheric and
coronal temperature, most of it belongs to an altogether different
entity. It is also suggested that this particular entity be called
unresolved fine structures.

---------------------------------------------------------
Title: On the rate of energy input in thermal solar flares
Authors: Feldman, U.; Doschek, G. A.; McKenzie, D. L.
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 &gt; or =
10 to the 8th K, producing a certain class of hard X-ray events.

---------------------------------------------------------
Title: Lines of Fe XII sensitive to coronal electron density
Authors: Feldman, U.; Doschek, G. A.; Cohen, L.
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: He D3 as a diagnostic for the hard and soft X-rays from
solar flares
Authors: Feldman, U.; Liggett, M.; Zirin, H.
1983ApJ...271..832F Altcode:
The time comparison of He D3 and X-ray emission has been studied
in a number of medium-sized flares. In most cases there is a good
agreement between the time histories of the He D3 emission and the
high-temperature (about 2 keV) thermal source. The most intense He D3
emission comes from two small regions on either side of the neutral
line, which are identified with the footpoints of magnetic structures
in which a hot (2.3 x 10 to the 7th K) thermal plasma is formed. The
impulsive X-ray event is marked by the transient brightening of a
number of (usually weaker) He D3 sources. The two types of sources are
well displaced from each other, which is an indication that they are
produced in two different volumes. In some cases a long-lived third
He D3 source is seen.

---------------------------------------------------------
Title: X-Rays from Laboratory and Astrophysical Plasmas
Authors: Feldman, U.
1982AIPC...94..447F Altcode:
X-ray spectra of highly ionized elements are widely used in diagnosing
high temperature plasmas from astrophysical as well as from laboratory
sources. The emission lines in the X-ray region are produced primarily
from two different types of transitions. One type involves the
transitions 1s-2p in hydrogen-like ions, helium-like ions and their
associated satellites. The second type involves the transitions 2l - nl'
for n &gt; 2. These transitions are sensitive to electron temperature,
electron density and the ionization balance. High quality spectrometers
in the X-ray region have instrumental line widths that in many cases
are significantly less than the true line widths. As a result, it is
quite convenient to use the physical information in the line profiles to
determine additional properties of the plasma under investigation. In the course of my talk I will describe results from recent
experiments concerning solar plasmas as well as laboratory sources.

---------------------------------------------------------
Title: High-resolution X-ray spectra of solar flares. VI - Impulsive
soft X-ray flares
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
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: Observational constraints for a theoretical model describing
the soft X-ray flare
Authors: Feldman, U.; Cheng, C. -C.; Doschek, G. A.
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: Doppler wavelength shifts of ultraviolet spectral lines in
solar active regions
Authors: Feldman, U.; Doschek, G. A.; Cohen, L.
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: Ultraviolet continuum absorption /less than about 1000 A/
above the quiet sun transition region
Authors: Doschek, G. A.; Feldman, U.
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.
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: On ionization equilibrium in solar flares as determined from
X-ray emissionlines of CA XVIII and CA XIX
Authors: Doscher, G. A.; Feldman, U.
1981ApJ...251..792D Altcode:
A diagnostic capable of determining the state of ionization equilibrium
in flare plasmas is important for the determination of the physical
conditions in flares. An experiment on the Air Force satellite P78-1
has provided high-resolution X-ray spectra which make it possible
to determine the state of the ionization equilibrium in coronal flare
plasmas. The considered investigation has the objective to show that the
interpretation of the calcium results is complicated by several possible
blends to line q, and to point out a variation in the observed ratios
which seems difficult to account for. Possible explanations for the
observations are discussed, taking into account the possibility that
the ionization equilibrium calculations have to be improved. Another
possible explanation is related to a suggestion made by Urnov (1981)
and Karev et al. (1980) concerning the effects produced by the presence
of high-energy nonthermal electrons.

---------------------------------------------------------
Title: A Solar Extreme Ultraviolet Telescope and Spectrograph for
Shuttle / Spacelab
Authors: Neupert, W. M.; Epstein, G. L.; Thomas, R. J.; Feldman, U.
1981SSRv...29..425N Altcode:
An instrument for advanced studies of the solar corona is described. Its
optical system provides nearly stigmatic imaging of selected portions
of the Sun over the spectral range from 22.5 to 44.0 nm. Both
spectroheliograms and emission line profiles of coronal features will
be obtained over a wide range of coronal temperatures.

---------------------------------------------------------
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.
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.
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: The use of spectral emission lines in the diagnostics of hot
solar plasma.
Authors: Feldman, U.
1981PhyS...24..681F Altcode:
A summary of spectroscopic and atomic physics results that were
obtained in the last 30 years and are closely related to diagnostics
of solar plasmas will be presented. The article will not review the
very extensive work that was done on the theoretical determinations of
energy levels, transition probabilities, or calculations of excitation
ionization and recombination cross sections, but with the end results of
these calculations. In other words it deals with line intensities, line
shapes and their changes as a result of the properties of the plasma
from which they are emitted. The emission lines under discussion are
optically thin and the spectral range covered is primarily from 2000
A down to 1.8 A. The review is divided into several sections according
to the typical wavelength ranges covered by the different spectrometers.

---------------------------------------------------------
Title: A discussion of theoretical ionization equilibrium calculations
based on solar flare X-ray spectra
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.
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.
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.
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.
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.
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.
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.
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 detection of companion stars to the Cepheid variables
Eta Aquilae and T Monocerotis.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
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.
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.
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.
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: 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.
1980BAAS...12Q.906L 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.
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.
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.
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.
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.
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.
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.
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.
1980BAAS...12S.518D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High resolution solar flare X-ray spectra.
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
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.
1980BAAS...12Q.462M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Impulsive phase of solar flares
Authors: Kane, S. R.; Crannell, C. J.; Datlowe, D.; Feldman, U.;
Gabriel, A.; Hudson, H. S.; Kundu, M. R.; Maetzler, C.; Neidig, D.;
Petrosian, V.
1980sfsl.work..187K Altcode: 1980sofl.symp..187K
The present understanding of the impulsive phase of a solar flare,
characterized by short-duration bursts of impulsive hard X-ray,
EUV, optical and radio emission indicating the release of energetic
electrons is reviewed. Observations of the spectral distribution
of impulsive hard X-ray bursts and of Type III and radio continuum
bursts are presented and interpreted in terms of energetic electron
distributions, and impulsive EUV, XUV, soft X-ray and optical
observations, which provide a lower limit to total energy release
during the impulsive phase, are discussed. The role of energetic
electrons in exciting the hard X-ray, EUV and microwave emissions is
considered, and thin-target, thick-target, partial-precipitation and
thermal models of impulsive phase electron acceleration are evaluated
in light of the observations. It is noted that available data do
not allow discrimination between a thermal or a nonthermal electron
distribution, on which depends the proportion of flare energy supplied
by the energetic electrons, and that data favors models which permit
at least partial electron precipitation. Future observational and
theoretical work is indicated.

---------------------------------------------------------
Title: The Detection of a Companion Star to the Cepheid Variable
Eta Aquilae
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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: L-series satellite spectra in Ti XII and Fe XVI.
Authors: Burkhalter, P. G.; Cohen, L.; Cowan, R. D.; Feldman, U.
1979JOSA...69.1133B Altcode: 1979OSAJ...69.1133B
Transitions in Na-like Ti and Fe ions, which appear as satellites
to 2p-3s and 2p-3d transitions in Ne-like ions, were studied. The
soft X-ray spectra produced by a focused-laser source and a
vacuum-spark device were obtained with the same grazing-incidence
spectrograph. Atomic structure calculations agreed with the observed
2p-3s spectral patterns and made possible line identifications in Ti
XII and Fe XVI.

---------------------------------------------------------
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.
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 &gt; 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.
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.
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.
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.
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: Evolution of the coronal and transition-zone plasma in a
compact flare: the event of 1973 August 9.
Authors: Underwood, J. H.; Antiochos, S. K.; Feldman, U.; Dere, K. P.
1978ApJ...224.1017U Altcode:
X-ray and extreme ultraviolet observations of a compact flare were
analyzed to determine the relative importance of radiation, thermal
conduction, and 'evaporation' in the evolution of the temperature and
density structure of the plasma. In the event studied (1973 August 9),
the electron density was relatively high (5 x 10 to the eleventh to 1 x
10 to the twelfth) and radiation was evidently an important energy-loss
and cooling mechanism. The light curves of ultraviolet lines formed at
temperatures between 10 to the fifth to 10 to the seventh K indicate a
time-varying emission measure gradient, and hence temperature gradient,
during the flare. Radiative instability evidently played an important
role in determining the steepness of these gradients during the rise
and fall phases, and caused strong downward motions of material during
the cooling phase. Toward the end of the event, the coronal electron
density decreased and the temperature gradient relaxed toward that
expected from a conduction-dominated plasma. For this flare, evaporative
cooling did not appear to be a significant factor.

---------------------------------------------------------
Title: Emission-line spectra of two active regions on the solar limb:
1175 - 1940 Å.
Authors: Feldman, U.; Doschek, G. A.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 &lt; 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 (&gt;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.
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.
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: Observations of a Radiatively Cooling Subflare.
Authors: Antiochos, S. K.; Underwood, J. H.; Feldman, U.
1977BAAS....9..329A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Chromospheric limb spectra from Skylab: 2000 to 3200 Å-.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
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.
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.
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.
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.
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.
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.
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.
1976BAAS....8..523F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Exploring plasmas: in the Sun and in the laboratory.
Authors: Doschek, G. A.; Feldman, U.
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.
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.
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.
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: Spectroscopy from Laser-produced Plasmas at Flare Temperatures
Authors: Feldman, U.
1976Ap&SS..41..155F Altcode:
A discussion of laboratory spectra similar in temperatures and ion
abundances to solar flare spectra is given. The laboratory spectra were
obtained from high temperature plasmas produced by high power lasers and
low inductance vacuum sparks. The current state of knowledge regarding
line identifications in laboratory spectra is reviewed, and some of the
results are used to identify lines in the high temperature solar flare
spectrum in the 100 Å region and in the 1000 Å region. In addition,
the physical dimensions and temperatures of the hot regions in the
plasmas produced by the low inductance spark were recently measured,
and a short summary of the results is given.

---------------------------------------------------------
Title: Doppler wavelength shifts of transition zone lines measured
in Skylab solar spectra.
Authors: Doschek, G. A.; Feldman, U.; Bohlin, J. D.
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.
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.
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.
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.
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.
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.
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.
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.
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
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: Transitions 2s22p-2s2p2 in the B I
isoelectronic sequence.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
1975JOSA...65..463D Altcode: 1975OSAJ...65..463D
No abstract at ADS

---------------------------------------------------------
Title: Meteorological Conditions near the Wise Observatory, Israel
Authors: Vidal, N. V.; Feldman, U.
1974QJRAS..15..462V Altcode:
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.
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.
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 Coronal Line Profiles in the Extreme-Ultraviolet
Authors: Feldman, U.; Behring, W. E.
1974ApJ...189L..45F Altcode:
We report here the first direct measurements of the widths of the lines
emitted by the solar corona from 170 to 370 A. The transitions 1s-2p and
in He ii are wider than 0.1 A, perhaps showing the effect of optical
depth. The lines of highly ionized 0, Mg, Si, S, and Fe have widths
which may be ascribed to a mean random turbulent velocity of about 30
km Sri in addition to thermal Doppler broadening. Subject headings:
corona, solar - line profiles - ultraviolet

---------------------------------------------------------
Title: Solar Flare Emission Lines of Highly-Ionized Iron and Nickel
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.; Cohen, Leonard
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
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
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.
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.
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
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: Fluorine isoelectronic sequence.
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, L.
1973JOSA...63.1445F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-resolution rocket EUV solar spectrograph.
Authors: Behring, W. E.; Ugiansky, R. J.; Feldman, U.
1973JOSA...63R.484B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High resolution rocket EUV solar spectrograph.
Authors: Behring, W. E.; Ugiansky, R. J.; Feldman, U.
1973ApOpt..12..528B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On I isoelectronic sequence: transitions
2p4-2p33s.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
1973JOSA...63.1463D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Statistical Analysis of Multiple Absorption Spectra in QSO
Authors: Shaviv, Giora; Feldman, Uri; Koslovsky, Ben-Zion
1972Ap&SS..19..159S Altcode:
A detailed statistical analysis was carried out for several quasars
with multiple red-shifts systems. The most important results are (a) The
statistical test of the reliability of az-system is very sensitive toz,
the total number of absorption lines, the selected set of reference
lines and the number of identified lines (b) The standard deviation
σ from μ, the average number of randomz-systems per random spectra
is larger than μ. Consequently, the reliability of any system depends
predominately on σ and not on μ.

---------------------------------------------------------
Title: Energy levels and spectra of the Li i and Be i isoelectronic
sequences in the fourth row
Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L.
1972SSRv...13..560G Altcode: 1972IAUCo..14..560G
No abstract at ADS

---------------------------------------------------------
Title: Wavelengths of solar lines in the 50 380Å region and their
identifications
Authors: Feldman, U.; Behring, W.; Cohen, L.
1972SSRv...13..608F Altcode: 1972IAUCo..14..608F
No abstract at ADS

---------------------------------------------------------
Title: Erratum: the Lithium-Like Spectra of K XVII Through MN XXIII
in the Extreme-Ultraviolet Region
Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L.
1972ApJ...175..589G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Spectrum: Wavelengths and Identifications from 60
TO 385 Angstroms
Authors: Behring, W. E.; Cohen, Leonard; Feldman, Uri
1972ApJ...175..493B Altcode:
The solar spectrum from 60 to 158 A and 163 to 385 - was photographed
at a resolution of 004 A or better on glass plates The wavelengths
of emission lines in these records were determined with a typical
accuracy of 0.008 A above 100 A and 0.004 A below 100 A. The
spectrograph employed a 3-meter radius, 1200 grooves gold grating at
graxing incidence The design considerations and limitations of this
instrument are presented along with a description of the Aerobee 130
flight mission on 1969 May t6. The wavelengths for the 370 observed
lines are listed together with intensity estimates. Of these, the 180
identified lines are due to ions of lle, 0, Ne, Mg, Si, S, Ar, Ca,
Fe, and Ni. These identified lines are also tabulated separately foi
each isoelectronic sequence from Li I to K I. The solar lines are well
enough resolved that wavelength determinations to t 0.004 A can be made
whenever better laboratory wavelengths become available. The reliability
of the solar line "Mentifications" could then be much improved.

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Title: Improved Wavelengths and Identifications in the Solar Spectrum
from 60-385 Å
Authors: Behring, W. E.; Cohen, Leonard; Feldman, Uri
1972BAAS....4U.377B Altcode:
No abstract at ADS

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Title: The Lithium-Like Spectra of K XVII Through MN XXIII in the
Extremeultraviolet Region
Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L.
1972ApJ...174..209G Altcode:
Identifications and classifications of spectral lines in the
lithium-like spectra of the elements K through n is presented for
the first time. The extrapolation procedures used to calculate these
spectra are presented in detail. The excellent agreement between the
predicted and measured lines establish the longrange extrapolation.

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Title: Carbon-like spectra of Sc XVI, Ti XVII, and V XVIII in the
range 16 - 22 Å.
Authors: Goldsmith, S.; Feldman, U.; Crooker, A.; Cohen, L.
1972JOSA...62..260G Altcode:
No abstract at ADS

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Title: Extreme-ultraviolet spectra of Sc XIV, Ti XV, and V XVI.
Authors: Goldsmith, S.; Feldman, U.; Cohen, L.
1971JOSA...61..615G Altcode:
No abstract at ADS

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Title: Boron-like spectra: Mg VIII, Al IX, and Si X.
Authors: Hoory, S.; Goldsmith, S.; Feldman, U.; Behring, W.; Cohen, L.
1971JOSA...61..504H Altcode:
No abstract at ADS

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Title: Spectra of Fe, Co, Ni, and Cu isoelectronic with Na I and Mg I.
Authors: Feldman, U.; Katz, L.; Behring, W.; Cohen, L.
1971JOSA...61...91F Altcode:
No abstract at ADS

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Title: On the Rich Absorption Spectra of Three Quasi-Stellar Objects
Authors: Bahcall, John N.; Feldman, Uri
1970ApJ...161..389B Altcode:
The absorption spectra of PHL 938, TON 1530, and PKS 0237-23 have
been searched in a systematic way for redshifts that may include lines
arising from metastable states, interstellar lines, and Balmer lines. A
search for blueshifts was also carried out for the first time. The
statistical significance of the redshift system I = 0.6128 in PIlL
938 was established by analyzing random-number spectra. It is shown
that the electron density is less than 50 T4112 in the vicinity of
this absorption system and that the minimum separation between PHL 938
and the absorption system is about 100 pc. A critical test of the idea
that normal galaxies produce the absorption lines is described. Nine
interstellar lines observed in the spectra of stars in the galaxy might
appear in the.observationally accessible region between 4956 and 6400
A for the redshift system I = 0.6128 of PHL 938.

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Title: Identification and Classification of the 3p^{6}3d-3p^{5}3d4s;
Transitions in CO ix, NI x, and CU XI
Authors: Hoory, S.; Goldsmith, S.; Fraenkel, B. S.; Feldman, U.
1970ApJ...160..781H Altcode:
In this work the identification and classification of the 3p63d-3p53d4s
transitions are extended from Fe viii to Cu xi.

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Title: A Line List for an Iron-Spark Spectrum (10-18 Å)
Authors: Cohen, Leonard; Feldman, Uri
1970ApJ...160L.105C Altcode:
A low-inductance 17-19 kV vacuum spark was used to generate spark
spectra of iron electrodes. Wavelengths and visually estimated
intensities are given for the region A.

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Title: Lithium-like spectra in Mg, Al, and Si.
Authors: Feldman, U.; Cohen, L.; Behring, W.
1970JOSA...60..891F Altcode:
No abstract at ADS

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Title: C V Spectra Near the 1s-2p Line of C VI
Authors: Feldman, Uri; Cohen, Leonard
1969ApJ...158L.169F Altcode:
We have measured seven lines of C v near the ls-2p line of C
vi. The lines were first reported by Edlén and Tyr~n. Six of them
are identified as belonging to transitions of the types ls2s-2s2p,
ls2p-2p2, and ls3s-2p3s

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Title: Round-the-Clock Photoheliography
Authors: Zirin, Harold; Bohlin, J. David; Weart, Spencer; Feldman, Uri
1969BAAS....1..297Z Altcode:
No abstract at ADS

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Title: Observations of the Sun and Laboratory Sources with a
Three-Meter xuv Spectrograph
Authors: Behring, W. E.; Cohen, L.; Saffer, K.; Feldman, U.
1969BAAS....1S.272B Altcode:
No abstract at ADS

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Title: An Iron Spark Line List in the 10-18 Å Range and its
Comparison with Flare Spectra
Authors: Feldman, U.; Cohen, L.
1968ApJ...151L..55F Altcode:
No abstract at ADS

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Title: Spectra of Solar Physics Interest Produced by a Vacuum
Spark Source
Authors: Feldman, U.; Cohen, L.; Underwood, J. H.
1968AJS....73Q..60F Altcode:
No abstract at ADS

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Title: Newly Identified Lines in the NE i Isoelectronic Sequences
Authors: Feldman, U.; Cohen, L.
1967ApJ...149..265F Altcode:
Using a graxing-incidence spectrometer and a low inductance, 14- F,
12-17 kV spark source, the authors have observed spectra of Sc xu,
Ti xiii, and V xiv. The lines have been identified as arising from
transitions between the ground level 2s2 2p6 iS0 and the following
electronic configurations: 2s 2p6 3p, and 2s2 2p5 4s, 4d, 5d. The
transitions of the type 2s2 2p8-2s2 2p5 4d have been observed also in
Co xviii, Ni xix, and Cu xx.

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Title: Newly Identified Resonance Lines of NI XIX, CU xx, and zn XXI
Authors: Feldman, U.; Cohen, L.; Swartz, M.
1967ApJ...148..585F Altcode:
By using a grazing-incidence spectrometer and a lowAnductance
condensed-spark source, the authors have observed spectra of Ni xix, Cu
xx, and Zn xxi By extrapolating the known data of the Ne i isoelectronic
sequence, the new lines have been identified as belonging to transition
arrays between the ground level 2s22p6 15o and the following electronic
configurations: 2s22p53s, 2s22p53d, and 2s2p63p Some of these lines
may be emitted from the solar corona.

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Title: Unclassified 3p63d-3p53d4s Transition
Lines of Fe VIII, Mn VII, and Cr VI
Authors: Feldman, U.; Fraenkel, B. S.
1966ApJ...145..959F Altcode:
No abstract at ADS

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Title: Identification of Solar Ultraviolet Lines Resulting from a
Study of the AR i and K i Isolelctronic Sequences.
Authors: Feldman, U.; Fraenkel, B. S.; Hoory, S.
1965ApJ...142..719F Altcode:
The classification of the 3p5 3d level in Ar I isoelectronic spectra
and the interaction between configurations 3p6 and 3p5 are discussed
Solar lines of transitions 3p6-3p5nl, 3p6 3d-3p6nl and 3p6 3d-3p5 3d3
are identified.

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Title: 3p6-3p53d Transitions of Fe IX and Ni
XI in the Solar Spectrum
Authors: Alexander, E.; Feldman, U.; Fraenkel, B. S.; Hoory, S.
1965Natur.206..176A Altcode:
USING rocket spectroscopy, Hinteregger et al.1 obtained
interesting new solar lines, the majority of which could not
be classified up to now. Among these lines, two strong lines
at 171.1 Å and at 148.5 Å have been seen. We have been able,
using the technique of differentiation between different degrees
of ionization2,3, to classify these two lines as
the 3p6 1S0 - 3p53d
1P1 transition of Fe IX and Ni XI. This line
was found to be very prominent in the isoelectronic sequence of A I
(Table 1). The foregoing classification is based on the assumption of
LS coupling.