Author name code: feldman ADS astronomy entries on 2022-09-14 author:"Feldman, Uri" ------------------------------------------------------------------------ Title: Transition Region Abundance Measurements During Impulsive Heating Events Authors: Warren, Harry P.; Brooks, David H.; Doschek, George A.; Feldman, Uri Bibcode: 2016ApJ...824...56W Altcode: 2015arXiv151204447W It is well established that elemental abundances vary in the solar atmosphere and that this variation is organized by first ionization potential (FIP). Previous studies have shown that in the solar corona, low-FIP elements such as Fe, Si, Mg, and Ca, are generally enriched relative to high-FIP elements such as C, N, O, Ar, and Ne. In this paper we report on measurements of plasma composition made during impulsive heating events observed at transition region temperatures with the Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these events the intensities of O IV, v, and VI emission lines are enhanced relative to emission lines from Mg v, VI, and vii and Si VI and vii, and indicate a composition close to that of the photosphere. Long-lived coronal fan structures, in contrast, show an enrichment of low-FIP elements. We conjecture that the plasma composition is an important signature of the coronal heating process, with impulsive heating leading to the evaporation of unfractionated material from the lower layers of the solar atmosphere and higher-frequency heating leading to long-lived structures and the accumulation of low-FIP elements in the corona. Title: Anomalous Relative Ar/Ca Coronal Abundances Observed by the Hinode/EUV Imaging Spectrometer Near Sunspots Authors: Doschek, G. A.; Warren, H. P.; Feldman, U. Bibcode: 2015ApJ...808L...7D Altcode: In determining the element abundance of argon (a high first ionization potential; FIP element) relative to calcium (a low FIP element) in flares, unexpectedly high intensities of two Ar xiv lines (194.40, 187.96 Å) relative to a Ca xiv line (193.87 Å) intensity were found in small (a few arcseconds) regions near sunspots in flare spectra recorded by the Extreme-ultraviolet Imaging Spectrometer on the Hinode spacecraft. In the most extreme case the Ar xiv line intensity relative to the Ca xiv intensity was 7 times the value expected from the photospheric abundance ratio, which is about 30 times the abundance of argon relative to calcium in active regions, i.e., the measured Ar/Ca abundance ratio is about 10 instead of 0.37 as in active regions. The Ar xiv and Ca xiv lines are formed near 3.4 MK and have very similar contribution functions. This is the first observation of the inverse FIP effect in the Sun. Other regions show increases of 2-3 over photospheric abundances, or just photospheric abundances. This phenomenon appears to occur rarely and only over small areas of flares away from the regions containing multi-million degree plasma, but more work is needed to quantify the occurrences and their locations. In the bright hot regions of flares the Ar/Ca abundance ratio is coronal, i.e., the same as in active regions. In this Letter we show three examples of the inverse FIP effect. Title: Assessing atomic data accuracy along isoelectronic sequences Authors: Young, Peter R.; Feldman, Uri Bibcode: 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. Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico Bibcode: 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. 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. Bibcode: 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. Title: Redshifts, Widths, and Radiances of Spectral Lines Emitted by the Solar Transition Region Authors: Feldman, U.; Dammasch, I. E.; Doschek, G. A. Bibcode: 2011ApJ...743..165F Altcode: A long-standing problem in understanding the physics of the transition region has been the ubiquitous redshifts of transition region ultraviolet spectral lines relative to chromospheric emission lines, a result known since the Skylab era. Extended spectral scans performed for various regions of the solar disk by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer on the Solar and Heliospheric Observatory contain thousands of line profiles per study and allow a thorough investigation of the redshift phenomenon. In using these data from seven distinct disk areas made in lines spanning the chromosphere to coronal temperature range, we derive a relationship between Doppler wavelength shifts and radiances and a relationship between line widths and radiances. While chromospheric and coronal lines emitted by very bright plasmas may in some cases show pronounced redshifts, transition-region lines predominantly show redshifts everywhere in the quiet Sun and in active regions. In coronal holes, however, they display a reduced shift, which at times altogether disappears. The observations and the findings will be described, and possible explanations will be considered. Title: Forbidden and Intercombination Lines of RR Telescopii: Wavelength Measurements and Energy Levels Authors: Young, P. R.; Feldman, U.; Lobel, A. Bibcode: 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. Title: Atomic Data for Solar Corona Studies Authors: Feldman, Uri Bibcode: 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. Title: TOPICAL REVIEW The solar UV-x-ray spectrum from 1.5 to 2000 Å Authors: Doschek, G. A.; Feldman, U. Bibcode: 2010JPhB...43w2001D Altcode: This review illustrates the potential of UV-x-ray spectroscopy for determining the physical conditions in the solar chromosphere, transition region and corona, and how spectroscopy can be used as a tool to understand the physical mechanisms governing the atmosphere. It also illustrates the potential for understanding transient events such as solar flares. This is a vast topic, and therefore the review is necessarily not complete, but we have tried to be as general as possible in showing in particular how solar spectra are currently being used to understand the solar upper atmosphere. The review is intended for non-solar physicists with an interest in spectroscopy as well as for solar physicists who are not specialists in spectroscopy. Title: 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. Bibcode: 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) Title: Elemental Abundance Variations in a Decaying EUV-Bright Region Authors: Ko, Yuan-Kuen; Landi, E.; Feldman, U.; Young, P. Bibcode: 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. Title: A new approach for deriving the solar irradiance from nonflaring solar upper atmosphere plasmas at 2 × 104 ≤ T ≤ 2 × 107 K Authors: Feldman, U.; Brown, C. M.; Seely, J. F.; Dammasch, I. E.; Landi, E.; Doschek, G. A.; Colgan, J.; Abdallah, J.; Fontes, C. J.; Sherrill, M. E. Bibcode: 2010JGRA..115.3101F Altcode: 2010JGRA..11503101F We propose a new approach for deriving the solar irradiance due to the emission by solar upper atmosphere plasmas at 2 × 104 ≤ T ≤ 2 × 107 K for wavelengths shorter than 800 Å. Our approach is based on a new understanding of the properties of the solar upper atmosphere; specifically, the discovery that the majority of emission from the nonflaring solar upper transition region and corona in the temperature range 3 × 105 ≤ T ≤ 3 × 106 K arises from isothermal plasmas that have four distinct temperatures: 0.35, 0.9, 1.4, and 3 × 106 K. Although the lower transition region (2 × 104 ≤ T ≤ 2 × 105 K) of coronal holes, quiet regions or active regions, is multithermal and variable in brightness, the shape of emission measure versus temperature curves in this region is almost constant. At any given time, flaring plasmas are for the most part isothermal, although their emission measure and temperature continuously change. In this paper we review these recent results and propose a set of simple spectrometers for recording the solar spectrum in several narrow bands. The solar emission measure, average plasma temperature, and composition can be derived using the measured line fluxes. By combining the emission measure and other plasma properties with the output of a suite of atomic physics codes, which are also described here, the solar irradiance at wavelengths shorter than 800 Å can be calculated. Title: The Effect of Hot Coronal Electrons on Extreme-Ultraviolet Spectral Lines of He II Emitted by Solar Transition Region Plasmas Authors: Feldman, U.; Ralchenko, Yu.; Doschek, G. A. Bibcode: 2010ApJ...708..244F Altcode: The cause of the lower intensities of extreme-ultraviolet (EUV) He II lines emitted by coronal hole (CH) plasmas compared with quiet Sun (QS) plasmas has been the subject of many studies dating back over half a century. In this paper, we study the effect of small amounts of "hot" electrons at coronal temperatures (Te = 1.4 × 106 K) on the intensities of EUV He II lines, as well as on the intensities of EUV lines of C III, C IV, O III, and O IV emitted by 1.5 × 104 K-1.5 × 105 K (4.2 <= log Te <= 5.2) plasmas in the QS. We show that although the influence of a fraction as small as 10-4-10-3 of hot electrons on the intensities of the C and O lines is noticeable, the effect on the intensities of the He lines is much larger, to the extent that it could explain the excess brightness of He II lines emitted by QS regions relative to CH plasmas. Title: The thermal structure of the solar upper atmosphere Authors: Landi, Enrico; Feldman, Uri Bibcode: 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. Title: Can the Composition of the Solar Corona Be Derived from Hinode/Extreme-Ultraviolet Imaging Spectrometer Spectra? Authors: Feldman, U.; Warren, H. P.; Brown, C. M.; Doschek, G. A. Bibcode: 2009ApJ...695...36F Altcode: Elemental abundances appear to be the same everywhere in the photosphere, but in the solar corona they vary in different regions. Abundances in quiet Sun (closed) flux tubes are different from those in coronal hole (CH, open) magnetic field regions, and therefore abundance variations might possibly be used to determine locations of slow and fast solar wind in the corona. In active regions, abundances can change from region to region and can vary with the age of the region. In the present paper, we evaluate the feasibility of determining relative elemental abundances in the corona using spectra acquired by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. As test cases, we attempt to evaluate the coronal composition above the limb in an equatorial quiet region and in a polar CH. We also determine the elemental composition of coronal regions with moderate activity on the disk and at the limb. To estimate the accuracy of the instrumental calibration and the atomic physics used in the calculations, we compare the derived composition with earlier derivations from spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer in similar regions. We find that EIS can be used to determine relative abundance variations in the inner solar corona. The determination of absolute abundances can also be attempted after additional calibrations in space are accomplished. Title: The Emission Measure of the Solar Lower Transition Region (2 × 104-2 × 105 K) Authors: Feldman, U.; Dammasch, I. E.; Landi, E. Bibcode: 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. Title: Radiative Losses of Solar Coronal Plasmas Authors: Colgan, J.; Abdallah, J., Jr.; Sherrill, M. E.; Foster, M.; Fontes, C. J.; Feldman, U. Bibcode: 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. 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 Bibcode: 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. Title: Solar Observations of High-Temperature Emission with the Extreme-Ultraviolet Imaging Spectrometer on Hinode Authors: Warren, Harry P.; Feldman, Uri; Brown, Charles M. Bibcode: 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. Title: Nonthermal Electron Measurements in Solar Flares with Hinode EIS Authors: Feldman, Uri; Ralchenko, Yuri; Landi, Enrico Bibcode: 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. Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico Bibcode: 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. 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. Bibcode: 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. Title: Line Intensity Ratios in the EIS Range Sensitive to Electron Densities in 107 K Plasmas Authors: Feldman, U.; Landi, E.; Doschek, G. A. Bibcode: 2008ApJ...679..843F Altcode: Electron density variations during the rise, maximum, and decay phases of flaring plasmas at T simeq 10 MK are important quantities to be used to test flare models. To date, electron density values measured in solar flares are, with few exceptions, only lower limits. With the launch of the EUV Imaging Spectrometer (EIS) on Hinode, it has become possible for the first time to measure electron densities and their time evolution during flares. In this paper we discuss electron density diagnostics in the 1010-1013 cm-3 range by means of intensity ratios of lines emitted by Ti, Cr, and Mn ions within the Hinode/EIS wavelength range. Title: The temperature structure of solar coronal plasmas Authors: Feldman, Uri; Landi, Enrico Bibcode: 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>0.7 MK) are isothermal and their temperature can have only a small set of fixed values. Title: Ultra-Hot Plasma in Active Regions Observed by the Extreme-ultraviolet Imaging Spectrometer on Hinode Authors: Doschek, G. A.; Warren, H. P.; Feldman, U. Bibcode: 2008AGUSMSP43C..01D Altcode: The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft obtains high resolution spectra of the solar atmosphere in two wavelength ranges: 170 - 210 and 250 — 290 Angstroms. These wavelength regions contain a wealth of emission lines covering temperature regions from the chromosphere/transition region (e.g., He II, Si VII) up to soft X-ray flare temperatures (Fe XXIII, Fe XXIV). EIS can obtain line profiles and intensities for the spectral lines in these wavelength regions. Of particular interest for understanding coronal heating is a line of Ca XVII, formed near a temperature of 6 MK. This line is blended with lines of Fe XI and O V. However, by using unblended lines of these ions, the Ca XVII line can be deconvolved from the blended emission. EIS has obtained many raster observations of active regions by stepping the slit in small increments across the active region, producing monochromatic images of the active region. The Ca XVII blend has been included in many of these rasters. In this paper we discuss the appearance and frequency of 6 MK plasma in active regions in the absence of strong flaring activity. This temperature region is not well-observed by normal incidence imaging spectrometers and therefore the EIS data shed light on higher temperature areas of active regions than normally available from imaging instruments alone. We discuss how to deconvolve the blend and show examples of 6 MK plasma emission in several active regions. Title: An EUV narrow band imaging technique for diagnosing 10-30 keV ITER plasmas Authors: Feldman, U.; Seely, J. F.; Landi, E.; Ralchenko, Y. Bibcode: 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 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. Bibcode: 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. Title: The Thermal Structure of an Active Region Observed Outside the Solar Disk Authors: Landi, E.; Feldman, U. Bibcode: 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. Bibcode: 2008cosp...37..866F Altcode: 2008cosp.meet..866F The solar irradiance in the far ultraviolet (FUV) and extreme ultraviolet (EUV) and its time variability are important inputs to geospace models. It provides the primary mechanism for heating the earth's upper atmosphere and creating the ionosphere. Understanding various space weather phenomena requires reliable detailed knowledge of the solar EUV irradiance. Ideally one would like to have a single well-calibrated, high-resolution spectrometer that can continuously monitor the solar irradiance over the relevant wavelengths range. Since this is much too difficult to accomplish, a number of monitoring instruments were constructed in the past, each covering a fraction of the required wavelength range. Assembling solar irradiance from measurements by a number of instruments is extremely difficult and is usually plagued by large uncertainties. To overcome some of the difficulties resulting from such procedures, empirical models have been developed that rely in large part on solar activity levels as proxies. In recent years a different approach has been established for the determination of the solar irradiance, an approach independent of irradiance observations. The new approach is based on the line intensities calculated from emission measure (EM) distributions across the solar surface. The EM distributions are derived from spatially and spectrally resolved measurements of line intensities and describe the temperature and density structure of the basic large scale features of the solar atmosphere, specifically coronal holes, quiet Sun, and active regions. Recently, as a result of detailed analysis of solar upper atmosphere (SUA) spectra recorded by SUMER/SoHO it was discovered that, in contrast to earlier beliefs, the solar EM in 3x105 -4x106 K plasmas does not appear to vary continuously with temperature as previously assumed. Instead it appears to be composed of isothermal structures where each can attain but one of the following four main temperatures: 5x105 , 9x105 , 1.4x106 and 3x106 K. At the transition region (2x104 -2x105 K) where the structures are not isothermal the slopes of the emission measure vs. temperature stay the same independent of the solar activity. In our talk we will propose a variation to the EM method for the determination of the solar irradiance described above. The modified method will be based on line intensity calculations from the actual solar EM values at the above specified discrete temperatures. The EM in those temperatures could in principle be derived from solar observations spanning a fairly limited wavelengths range. Title: 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 Bibcode: 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. Bibcode: 2007PASJ...59S.865B Altcode: A wavelength calibration of solar lines observed by the high resolution EUV Imaging Spectrometer (EIS) on the Hinode satellite is reported. Spectral features of the quiet sun and of two mildly active areas were measured and calibrated. A listing of the stronger observed lines with identification of the leading contributor ions is presented. 41 lines are reported, with 90% identified. Wavelength precisions (2σ) of ±0.0031Å for the EIS short band and ±0.0029Å for the EIS long band are obtained. These lines, typical of 1-2 ×106 K plasmas, are recommended as standards for the establishment of EIS wavelength scales. The temperature of EIS varies by about 1D.5 C around the orbit and also with spacecraft pointing. The correlation of these temperature changes with wavelength versus pixel number scale changes is reported. Title: Comparison of solar spectra from the Hinode extreme-ultraviolet imaging spectrometer (EIS) to preflight calibrations Authors: Seely, John; Feldman, Uri; Brown, Charles; Doschek, George; Hara, H. Bibcode: 2007SPIE.6688E..0WS Altcode: 2007SPIE.6688E..29S The Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode satellite records high-resolution solar spectra in the 170-210 Å and 246-290 Å wavelength ranges. The EIS optics operate at near normal incidence and consist of an off-axis parabolic mirror, a toroidal diffraction grating, two CCD detectors, and two thin aluminum filters. To increase the normal incidence efficiency, high-reflectance multilayer interference coatings were deposited on the mirror and the grating. Prior to launch, each of the optical components was calibrated using synchrotron radiation, and the spectral and spatial resolution of the complete instrument were measured. In this paper, we compare the preflight calibrations with the first-light spectra recorded in space. Title: Improved low-lying energy levels determined from solar coronal forbidden and spin-forbidden lines in the 500 1500 Å range Authors: Feldman, U.; Doschek, G. A. Bibcode: 2007ADNDT..93..779F Altcode: We list observed parity-forbidden and spin-forbidden lines in the 500 1600 Å range emitted by solar coronal plasmas and derive improved energy levels from their wavelengths. The lines, emitted by astrophysical abundant elements, belong to transitions within the ground configurations of the type ns2npk, for n = 2, 3 and k = 0 5, and between the lowest term of the first excited configuration 2s2pk+1 and the 2s22pk ground configurations for k = 0, 1, 2. For each line we give the newly measured wavelength, and the measured or predicted wavelength from the NIST Atomic Spectra Database (ASD) (which except for a few cases includes the previously reported compilation of Kaufman and Sugar [J. Phys. Chem. Ref. Data 15 (1986) 321]), and the values of the transition probability taken from the ASD and CHIANTI database. The list contains measured wavelengths of 136 lines of which over 100 were not available for the Kaufman and Sugar compilation. In addition we provide energy levels that were derived from the reported lines. Title: Spectroscopic Measurement of Coronal Compositions Authors: Feldman, U.; Widing, K. G. Bibcode: 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. Bibcode: 2007ApJ...660.1674F Altcode: In the present paper we use UV lines emitted by He-like ions as a tool to test the presence of nonthermal high-energy electrons and to quantify their number and energy. The He-like lines we consider are the He-like 1s2s3S-1s2p3P lines observed in the UV, and their use capitalizes on the high excitation energies for the 1s2p3P levels and on the near-unity ion abundances of the He-like ions for large temperature ranges. We investigate the presence of nonthermal high-energy electrons in solar active regions, placing upper limits on the presence of electrons capable of exciting the upper levels of Ne IX, Mg XI, and Si XIII. Title: Neon and Oxygen Absolute Abundances in the Solar Corona Authors: Landi, E.; Feldman, U.; Doschek, G. A. Bibcode: 2007ApJ...659..743L Altcode: In the present work we use the UV spectrum of a solar flare observed with SOHO SUMER to measure the absolute abundance of Ne in the solar atmosphere. The measurement is carried out using the intensity ratio between the allowed 1s2s3S1-1s2p3P2 Ne IX line at 1248.28 Å and the free-free continuum radiation observed close to the Ne IX line. We find a value of the absolute Ne abundance ANe=8.11+/-0.12, in agreement with previous estimates but substantially higher than the very recent estimate by Asplund et al. based on the oxygen photospheric abundance and the Ne/O relative abundance. Considering our measured ANe value, we argue that the absolute oxygen abundance of Asplund et al. is too low by a factor 1.9. This result has important consequences for models of the solar interior based on helioseismology measurements, as well as on the FIP bias determination of the solar upper atmosphere, solar wind, and solar energetic particles. Title: Is There a High-Energy Particle Population in the Quiet Solar Corona? Authors: Ralchenko, Yu.; Feldman, U.; Doschek, G. A. Bibcode: 2007ApJ...659.1682R Altcode: A study of spectra emitted by the quiet solar corona indicates that the majority of line intensities originating in low-lying levels are consistent with isothermal plasma of ~1.3×106 K. Nevertheless, a number of line intensities and, in particular, those belonging to ions that are typical of higher temperatures are brighter than expected. We show in this paper that the excess brightness of the hotter lines may be satisfactorily accounted for by a two-Maxwellian electron distribution function. We have calculated the effects on the line intensities and ionization balance under the assumption of both single- and two-Maxwellian electron distribution functions. One Maxwellian is characterized by a temperature of about 110 eV (1.35×106 K). The second Maxwellian is assumed to be a high-energy component ranging in temperatures between 150 and 1000 eV, with electron fractions relative to the total electron density that vary from 0.5% to 10%. We found that a good match to the quiet-Sun intensities could be achieved by adding ~5% electrons with a 300-400 eV Maxwellian temperature to the cooler component at 110 eV. We also found that the calculated line intensities become inconsistent with the quiet solar corona measurements if more than 3% of a Te=500 eV plasma or more than 1% of a Te=1000 eV plasma is added to the cooler Maxwellian. Title: Spectroscopic Measurement of Coronal Compositions Authors: Feldman, U.; Widing, K. G. Bibcode: 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. Bibcode: 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. Bibcode: 2006ApJ...643.1258L Altcode: In the present work we analyze the physical properties of the quiet-Sun plasma measured in a 0.5×1.8 Rsolar region above the west solar limb (Rsolar=solar radius). We make use of large scans obtained with the SUMER spectrometer on board SOHO to construct two-dimensional spatial maps of line intensities, electron temperature, emission measure, element abundances, line widths and nonthermal velocities, and photoexcitation effects covering the entire field of view. Electron densities were measured in a more limited portion of the field of view. The aim of the paper is to identify tracers of coronal hole and quiet-Sun plasma at high altitudes that allow us to measure the position of the coronal hole/quiet-Sun boundaries, and to provide a comprehensive, empirical picture of the off-limb solar corona that can provide theoreticians with experimental constraints to their models of the large-scale coronal structure, coronal heating, and solar wind acceleration. Title: X-Ray Observations of Solar Long-Duration Flares Authors: Phillips, K. J. H.; Feldman, U.; Harra, L. K. Bibcode: 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. Bibcode: 2005A&A...441.1211F Altcode: We introduce a new technique for the measurement of the in-flight relative intensity calibration of high resolution spectrometers. This technique makes use of the free-free radiation in hot, dense active regions and flares, and combines it with spectral line intensities in an iterative procedure. After a few iterations, the relative intensity calibration and the temperature of the emitting plasma are determined. The application of this technique to the EIS instrument on board the Solar-B satellite (launch in 2006) is discussed. Title: Evidence for In Situ Heating in Active Region Loops Authors: Curdt, W.; Landi, E.; Wang, T. J.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2005AGUSMSP21B..08D Altcode: We discuss the analysis of 36 spectral observations recorded by the SUMER spectrometer on SOHO on April 22-23, 1998, at the onset of the new solar cycle. The observations were made with the 4" x 300" slit, and are distributed over the west hemisphere between 1.02 and 1.5 solar radii along the equatorial direction and between -0.9 solar radii south of the equator and +0.9 solar radii north of it. At the far corners of the studied region the solar distance was 1.74 solar radii. We have found that the physical characteristics of the central part of the region are typical of quiet Sun coronal plasmas. The regions furthest from the equator resemble coronal hole plasmas and the intermediate regions are consistent with a transition between the two. We believe that this is the most comprehensive work of its kind undertaken thus far using UV spectral lines. We use the recorded line intensities and line shapes to describe, as a function of coronal position, electron temperatures, electron densities, elemental abundances, line-of-sight emission measures (EM), nonthermal mass motions, and mass dependent elemental settling. By using intensity ratios between the two component resonance lines of Li-like O VI, Ne VIII and Mg X, we determine the fractional excitation in the Li-like lines produced by electron collisions and the fractional excitation produced by photo-excitation of transition region radiation emitted just above the photosphere. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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&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 Bibcode: 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 > 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. Bibcode: 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. Bibcode: 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. Bibcode: 2004ApJ...609..439F Altcode: We discuss a set of flare observations obtained at a position of 0.10 Rsolar above the solar northwest limb. The data were acquired by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO). We derive time-dependent comparisons of physical properties, such as electron temperature and density, between flare plasma and background coronal plasma observed along the same lines of sight. In addition to temperature and density, we discuss emission measures, elemental abundances, nonthermal mass motions (from line widths), and bulk mass motions (from Doppler shifts). The observations appear to indicate that the flaring plasmas (4×106K<=Te<=1×107K) along the lines of sight were formed by in situ heating and possibly by compression of the ambient coronal material (Te<=2×106 K). Title: 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. Bibcode: 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 Bibcode: 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. Bibcode: 2004ApJ...600.1061D Altcode: The widths of spectral lines in the ultraviolet (UV) and extreme ultraviolet (EUV) spectral regions that are formed in the solar transition region and corona are usually greater than the optically thin widths due to thermal Doppler broadening calculated under the assumption of ionization equilibrium. Although opacity can explain the widths of some lines, there are a host of optically thin lines for which the excess widths are attributed to nonthermal motions. Interest in these motions for coronal heating theories has led to the measurement and comparison of spectral line profiles/widths throughout the solar UV and EUV spectrum. We find that for the quiet Sun the widths of some optically allowed lower transition region lines, deduced from spectra obtained by the Solar Ultraviolet Measurements of Ultraviolet Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft, are considerably larger than predicted from simply scaling previously measured wavelengths of other lines from the same ion. For example, the O III lines of the multiplet near 834 Å are considerably wider than predicted from the previously measured (from Skylab) width of the optically thin O III 1666.15 Å intersystem line. The excess widths are not due to nonthermal motions, as these are already included in the width of the 1666.15 Å line. In this paper, we analyze the widths of some prominent optically allowed lines and discuss possible causes for discrepancies with previous measurements of intersystem lines. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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<=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. Bibcode: 2003ApJ...593.1226F Altcode: We report the detection of free-free (bremsstrahlung) emission near 1200 Å from a flare at the solar limb observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The observations consist of a time series of slit spectra at a fixed pointing that lasted almost 2 hr, during which the observed solar region produced a C8 flare. Using the free-free continuum intensities in conjunction with intensities of high-temperature (106-107 K) emission lines that appear in the same wavelength range, we derive the flare plasma electron density, electron temperature, emission measure, and nonthermal mass motions before, during, and after the flare. We describe a new diagnostic method for determining the temperature of cooling plasmas. Because the free-free radiation is emitted primarily by the interaction of electrons with nuclei of H and He atoms, we are also able to derive the Fe/H, Al/H, and Ca/H abundance ratios from the line intensities of highly ionized Fe, Al, and Ca lines and the intensities of the free-free emission, assuming a He abundance. The present work demonstrates the exceptional plasma diagnostic potential of ultraviolet free-free continuum radiation when coupled with emission-line intensities. We demonstrate that a similar technique could be employed to diagnose plasma properties of stellar flares using a high-resolution spectrometer with a sufficiently large effective collecting area. Title: Properties of Solar Plasmas near Solar Maximum above Two Quiet Regions at Distances of 1.02-1.34 Rsolar Authors: Landi, E.; Feldman, U. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2003ApJ...590.1121D Altcode: UV emission from B-like N and O ions offers a rather rare opportunity for recording spectral lines in a narrow wavelength range that can potentially be used to derive temperatures relevant to the solar transition region. In these ions, the line intensity ratios of the type (2s2p2-2p3)/(2s22p-2s2p2) are very sensitive to the electron temperature. In addition, the lines involving the ratios fall within a range of only ~12 Å in N III the lines fall in the 980-992 Å range, and in O IV in the 780-791 Å range. In this work, we explore the use of these atomic systems, primarily in N III, for temperature diagnostics of the transition region by analyzing UV spectra obtained by the Solar Ultraviolet Measurement of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory. The N III temperature-sensitive line ratios are measured in more than 60 observations. The mean measured ratios are lower by ~30% than those predicted in the typical quiet Sun. Assuming an isothermal plasma, most of the measured ratios correspond to temperatures in the range 5.7×104-6.7×104 K. This range is considerably lower than the calculated temperature of maximum abundance of N III, which is ~7.6×104 K. Detailed analysis of the spectra further indicates that the measured ratios are probably somewhat overestimated because of resonant scattering effects in the 2s22p-2s2p2 lines and small blends in the 2s2p2-2p3 lines. Actual lower ratios would only increase the discrepancy between the ionization balance calculations and present temperature measurements based on a collisional excitation model. In the case of the O IV spectra, we determine that because of the close proximity in wavelength of the weak line (2s2p2-2p3 transitions) to a strong Ne VIII line, sufficiently accurate ratio measurements cannot be obtained. Title: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 2002AIPC..636..125D Altcode: This work addresses two topics important for the appropriate interpretation of astrophysical spectra. The first is the effect of high-lying levels on the atomic models and the second is the importance of ionization and recombination processes in forming line emission. In the first part of the work we study the influence of high-lying configurations on the calculated intensities of UV lines, particularly of O-like ions, observed by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer aboard the SOHO satellite. The high-lying configurations alter the line intensities through radiative cascades and configuration interaction effects. We find that cascades can significantly enhance the intensities of some lines of the considered ions by up to 65% at temperatures of the ion maximum fractional abundance. The enhancement due to cascades increases with increasing temperature and charge state. The configuration mixing effects can either enhance or reduce the line intensities. In a second study, we calculate the theoretical intensities of the soft X-ray Fe16+ lines arising from 2l-3l' transitions using a three-ion collisional-radiative model that includes the contribution of recombination and ionization processes to line formation. Dielectronic recombination is found to be particularly important. The newly calculated line intensities can explain the high values of the 2p-3s / 2p-3d intensity ratios, which are often obtained in astrophysical observations. Observed intensity ratios among the 2p-3s lines are also better reproduced. Title: 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. Bibcode: 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. Bibcode: 2002ApJ...574..504D Altcode: In this work we investigate the effect of including high-lying configurations in the collisional-radiative models used to calculate spectral line intensities recorded by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on board the SOHO satellite. Many of the emission lines observed by SUMER are attributed to transitions within the L and M electronic shells of ions isoelectronic to sequences from Li I to Na I. By using atomic data that are mostly generated by the Hebrew University Lawrence Livermore Atomic Code (HULLAC), we incorporate in the atomic models configurations from higher shells and systematically study their effect on the calculated line intensities in selected ions. The high-lying configurations alter the line intensities through radiative cascades and configuration interaction effects. We find that cascades can significantly enhance the line intensities of the considered ions by up to 60% at temperatures of the ion maximum fractional abundance. The enhancement due to cascades increases with increasing temperature and charge state. The configuration mixing effects can either enhance or reduce the line intensities. Generally, the mixing effect becomes less important for higher charge states. Title: The new picture of the transition region and corona from SUMER Authors: Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 2002ApJS..139..297D Altcode: Observatories such as Chandra, XMM-Newton, and more likely future instruments with higher effective collecting area of radiation will offer the opportunity to study the nature of chemically peculiar sources using observations in the X-ray and EUV range. In the present work we explore the possibility to observe the spectral signature of highly stripped Hg ions that might be present in possible coronae or winds of HgMn stars. A systematic theoretical survey of the most intense X-ray spectral features predicted to be emitted by H-like to Pd-like Hg ions (Hg+79-Hg+34) is performed. The calculated intensities (photons s-1 ion-1) of the various spectral features of the Hg ions are compared to the intensities calculated for the lines of Fe ions that may be observed in the same range of the X-ray spectrum, but not necessarily from the same temperature domain. Fe lines corresponding to transitions from the L electronic shell were already observed in the coronae of stars, e.g., by Chandra in Capella. Assuming a similar abundance for Hg and Fe ions, many of the calculated Hg lines are found to be of comparable intensity to the Fe lines and in some cases stronger by about a factor of 20. We also discuss possible density and temperature diagnostic applications for some of the Hg lines. Title: CHIANTI-An Atomic Database for Emission Lines. V. Comparison with an Isothermal Spectrum Observed with SUMER Authors: Landi, E.; Feldman, U.; Dere, K. P. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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<3 105 b: Te~3 105 c: Te~4 105 d: 6 105<Te <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. Bibcode: 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. Bibcode: 2001ApJ...556..912L Altcode: We investigate the relative intensities of the two moderately bright Be-like 2s2 1S0-2s2p 3P1 and 2s2p 1P1-2p2 1D2 lines as a function of electron temperature. We show that the intensity ratios of the lines in the beryllium isoelectronic sequence from C III to Ni XXV ions can serve as sensitive temperature indicators for a large variety of solar plasmas. While the C III-Ne VII lines can be used to diagnose unresolved fine structures in relatively cold solar atmosphere plasmas [(1-5)×105 K], the Na VIII-Ar XV ions can be used to diagnose coronal plasmas [(0.8-3)×106 K], and Ca XVII-Ni XXV lines are useful to measure the temperature in flaring plasmas [(5-16)×107 K]. We investigate the effects on the temperature determination caused by varying the number of energy levels that are included in the atomic model for the considered ions. It is found that a model that includes the 2l2l' and 2l3l' configurations is sufficient for adequately describing the relevant level populations of the Be-like ions in coronal conditions. We compare theoretical ratios obtained using collisional cross section and transition probability values derived by different theoretical methods. The atomic data are obtained from the CHIANTI database, the Hebrew University Lawrence Livermore Atomic Code (HULLAC) suite of programs, and other available sources in the literature. Finally, we use spectra of an apparently isothermal coronal plasma observed by the Solar Ultraviolet Measurement of Emitted Radiation instrument on the Solar and Heliospheric Observatory to determine the electron temperature of streamer plasma using the HULLAC and CHIANTI atomic data sets. The result is compared with the temperature derived in an earlier study using different methods. Title: The SUMER spectral atlas of solar-disk features Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi, B. N.; Schühle, U.; Lemaire, P. Bibcode: 2001A&A...375..591C Altcode: A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of the Sun between 670 Å and 1609 Å in the 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). The atlas contains spectra of the average quiet Sun, a coronal hole and a sunspot on the 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 almost 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. These lines are clearly marked in the atlas. The spectra include emissions from atoms and ions in the temperature range 6*E3 K to 2*E6 K, i.e., continua and emission 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 to study 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. Brief descriptions of the data reduction and calibration procedures are given. The spectral radiances are determined with a relative uncertainty of 0.15 to 0.30 (1sigma ) and the wavelength scale is accurate to typically 10 mÅ. The atlas is also available in a machine readable form. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/591 Title: On the Rate of Abundance Modifications versus Time in Active Region Plasmas Authors: Widing, K. G.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2001ApJ...546..559D Altcode: We determine the line-of-sight emission measure distribution and nonthermal motions as a function of height above the limb in the north and south polar coronal holes. These quantities are derived from extreme-ultraviolet (EUV) spectra obtained from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The SUMER slit was oriented along the north-south direction for all the observations, and the spatial resolution is about 1". The spectra were obtained from a number of different types of observations in 1996. We select a group of emission lines for analysis for which, under the usual assumption of ionization equilibrium, the maximum emissivities span the temperature range from about 3×105 K up to about 1.1×106 K. We compare our results with recently published similar observations of a west limb quiet-Sun streamer region, with other coronal hole results based on SUMER spectra, and with earlier observations of the quiet Sun and coronal holes obtained from Skylab and rocket spectra. We find that the electron temperature in the polar holes increases with height above the limb, that the emission measure distribution of plasma located at line-of-sight heights less than about 60" peaks at a temperature of about 9×105 K, and that nonthermal motions sometimes, but not always, increase slightly with height above the limb. When observed, these increases level off above the limb at about 120". We speculate that the increases with height above the limb may be a manifestation of the fast solar wind. They may also be due to the reduction in transition region structures with increasing limb height. We also discuss wave heating as a cause of the line width increases. Title: 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>=3×106 K) and Their Potential Use in Plasma Diagnostics Authors: Feldman, U.; Curdt, W.; Landi, E.; Wilhelm, K. Bibcode: 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>=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. Bibcode: 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. Bibcode: 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 <=20 mÅ(1σ), and in one case <=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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2000SPD....31.1307D Altcode: 2000BAAS...32Q.846D We discuss nonthermal motions, line-of-sight emission measures, and relative element abundances as a function of height in the solar polar coronal holes. The data pertain to the upper transition region and coronal regions of the atmosphere at heights ranging from the solar limb to about 150'' above the limb. The spatial resolution is 1\arcsec. The physical quantities are derived from spectral line intensities and profiles obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The line width information is important for wave theories of coronal heating. We find that the electron temperature in the polar holes increases with height above the limb, that the emission measure distribution of plasma at line-of-sight heights less than 60'' peaks at a temperature of about 9 x 105 K, and that nonthermal motions sometimes, but not always, increase slightly with height above the limb. When observed, these increases level off above the limb at about 120\arcsec. We speculate that the line width increases with height above the limb may be a manifestation of the fast solar wind. Finally, we find that increases of a Mg VI/Ne VI line ratio with height above the north polar limb are probably due to the increase of electron temperature with height, and not due to a relative element abundance variation caused by the first ionization potential (FIP) effect. This work was supported by NASA SR&T Grant W-19,329 and by the ONR/NRL Research Option, Solar Magnetism and the Earth's Environment. Title: The Solar Helium Abundance in the Outer Corona Determined from Observations with SUMER/SOHO Authors: Laming, J. M.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 < 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 < Te < 1.4 W 106 K Temperature Regime Authors: Feldman, U.; Widing, K. G.; Warren, H. P. Bibcode: 2000ApJ...529.1145F Altcode: No abstract at ADS Title: Extreme-Ultraviolet Spectral Line Widths in Quiet-Sun Coronal Plasmas at Distances of 1.03<=Rsolar<=1.45 along the Solar Equatorial Plane Authors: Doschek, G. A.; Feldman, U. Bibcode: 2000ApJ...529..599D Altcode: We measure the full width at half-maximum intensity (FWHM) of extreme-ultarviolet (EUV) spectral line profiles as a function of height in the Sun's equatorial west limb streamer region using EUV spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The spectra were recorded on 1996 November 21 and 22, during a special ``roll'' maneuver in which the SUMER slit was oriented in the east-west direction. Because the SUMER spectrometer is stigmatic along the slit length, the spectra are spatially resolved in the east-west direction. The spectra we discuss cover an effective distance range outside the west limb from 1.03 to 1.45 Rsolar the maximum spatial resolution is 1''. We select a group of emission lines for analysis that under the usual ionization equilibrium assumption have maximum fractional abundances at temperatures ranging from 3×105 up to 2×106 K. We determine nonthermal motions as a function of position in the streamer region from the FWHMs under the assumption that the ion temperature equals the electron temperature of the streamer plasma. The electron temperature was derived previously by Feldman and coworkers. Title: 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 Bibcode: 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<=Te<=107 K) Authors: Laming, J. M.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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<Te<1.4×106 K Temperature Regime Authors: Feldman, U.; Widing, K. G.; Warren, H. P. Bibcode: 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<=Te<=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<=Te<=1.4×106 K temperature domain of the solar upper atmosphere consists of a hierarchy of isothermal loop structures. While at the Te<8×105 K temperature regime the looplike structures are more abundant along the chromospheric network, at higher temperatures (Te>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. Bibcode: 1999ApJ...518..909D Altcode: Atomic data for ionized atoms are important for many astrophysical applications. The launch of the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) extreme-ultraviolet (EUV) spectrometer aboard the Solar and Heliospheric Observatory (SOHO) allows us to test the accuracy of certain computed relative excitation rate coefficients and transition probabilities for a number of important astrophysical ions. We use spectral line intensity ratios derived from SUMER spectra to compare these quantities with the best available theoretical calculations for transitions within the ions C II, N III, N IV, O III, O IV, O V, S III, S IV, and S V. The results of this work are important for many current and upcoming NASA astrophysics missions. In addition to the published atomic data, we calculate some new atomic data using the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Our comparison of measured intensity ratios with theoretical predictions reveals significant discrepancies between the predicted and measured intensity ratios for several ions, particularly for S III, S IV, and S V. S III and S IV produce strong line emission in the Io torus. We discuss the methods we used to ensure that our ratios are accurate, the possible effects of Lyman continuum absorption on our data, and the ramifications of ignoring dielectronic capture resonances in certain transitions as a possible explanation for some of the discrepancies. Title: The Off-Limb Behavior of the First Ionization Potential Effect in T>5×105 K Solar Plasmas Authors: Laming, J. M.; Feldman, U.; Drake, J. J.; Lemaire, P. Bibcode: 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<=Rsolar<=1.50 along the Solar Equatorial Plane Authors: Feldman, U.; Doschek, G. A.; Schühle, U.; Wilhelm, K. Bibcode: 1999ApJ...518..500F Altcode: We determine the physical properties, i.e., electron temperature, density, line-of-sight emission measure, and element-abundance variation with height, in the Sun's equatorial west limb streamer region from extreme-ultraviolet (EUV) spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The spectra were recorded on 1996 November 21-22 during a special ``roll'' maneuver in which the SUMER slit was oriented in the east-west direction. Because the SUMER spectrometer is stigmatic along the slit length, the spectra are spatially resolved in the east-west direction. The spectra we discuss cover an effective distance range outside the west limb from 1.03 to 1.50 solar radii (Rsolar) the maximum spatial resolution is 1''. We select a group of emission lines for analysis that under the usual ionization equilibrium assumption span the temperature range from 3×105 up to 2×106 K. However, we note that above the limb a major fraction of a line intensity may arise at a temperature that is far from the temperature of maximum emitting efficiency in ionization equilibrium. In this paper we assume ionization equilibrium in deriving plasma parameters. Readers can redo our analysis without this assumption if desired, because the line intensities we present in this paper are simply the measured photon production rates in the lines. Assuming ionization equilibrium, we determine the electron temperature, electron density, line-of-sight emission measure, and abundance variation with height above the limb from the line intensities and line intensity ratios. The spatial resolution has allowed us to detect an apparent element-abundance variation as a function of height above the west limb that is strong evidence for gravitational settling of ``heavy'' elements. Title: Properties of the Quiet Sun Corona in the West Limb Equatorial Streamer Region Authors: Doschek, G. A.; Feldman, U. Bibcode: 1999AAS...19410005D Altcode: 1999BAAS...31..997D We determine physical properties, such as electron temperature and density, in the Sun's west limb equatorial streamer region from spectra recorded by the SUMER spectrometer on SOHO. The spectra were recorded on 1996 November 21-22 during a special roll maneuver in which the stigmatic SUMER slit was oriented in the east-west direction. Results are obtained as a function of height from close to the limb out to about 1.5 solar radii. We find that the streamer region is well-represented by an isothermal plasma at 1.3 x 10(6) K between 1.03 and 1.5 solar radii. The electron density falls from 1.8 x 10(8) cm(-3) near the limb to about 1.6 x 10(7) cm(-3) at 1.3 solar radii. For ions with similar atomic weights, we find that the typical quiet Sun FIP enhancement of about a factor of 4 does not vary with height above the limb. Perhaps of most interest, we find strong evidence for gravitational settling of Fe relative to the lighter elements such as Ne, Mg, and Si. This adds a complicating factor in determining physical parameters in the corona. The above results are discussed in detail in Feldman et al. 1999, ApJ, 518, June 10 issue. We also measure the full width at half maximum intensity of spectral line profiles for lines of several upper transition region and coronal ions formed in the streamer. If we adopt our measured electron temperature and assume that the electron and ion temperatures are equal, we obtain typical nonthermal speeds of about 33 km s(-1) and in addition find that the speed does not increase with height between about 1.03 and 1.3 solar radii. The line profile results are discussed in detail in Doschek & Feldman 1999, ApJ, submitted. This work was funded by the 6.1 NRL/ONR Solar Magnetism and the Earth's Environment Research Option. Title: 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. Bibcode: 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. Bibcode: 1999ApJ...511L..61F Altcode: In recent years, multilayer-coated optics have been used in solar-soft X-ray and extreme-ultraviolet telescopes to record high-resolution, full Sun images. The multilayer coatings reflect efficiently over rather narrow wavelength bands that are selected to contain spectral emission lines considered to have plasma diagnostic importance for determining approximate electron temperatures. The purpose of this Letter is to discuss the effect of continuum emission on the response of multilayer passbands and the effect of this response on temperature determinations in the 4×106-2×107 K range. Significant effects are largely confined to continuum emission from flare plasma. The flare free-free continuum in the EUV range is nearly temperature and wavelength insensitive and dominates the emission in passbands that are centered on quiet- to active-Sun coronal lines emitted by ions such as Fe IX-Fe XV. Title: On the Unresolved Fine Structures of the Solar Atmosphere. III. Elemental Abundances Consideration Authors: Feldman, Uri Bibcode: 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 <= Te <= 8 × 106 K. In a recent paper Wikstøl, Judge, & 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. Bibcode: 1998ApJ...507..991D Altcode: We determine the electron density at the temperatures of formation of O+4 and Si+2 ions, which are about 2.5 × 105 and 3.2 × 104 K in ionization equilibrium, respectively. These temperatures occur in the lower transition region of the Sun's atmosphere and allow a test of the often invoked assumption of constant pressure in quiet-Sun models. The O+4 density is determined from a density-sensitive spectroscopic O V line ratio involving 2s2p3P-2p23P transitions that fall near 760 Å. The Si+2 density is determined from a density-sensitive Si III line ratio within the 3s3p3P-3p23P multiplet near 1300 Å. There are few available line ratio techniques for determining the density and hence electron pressure in the quiet-Sun and coronal hole transition regions using lines emitted by the same ion, and determining these quantities is the principal motivation for this work. The spectra used in our analysis were obtained from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the Solar and Heliospheric Observatory (SOHO). We determine the electron density and pressure in typical quiet-Sun/coronal hole regions, and densities in active region brightenings and in an explosive event. Our O V and Si III results indicate that constant pressure is valid or nearly valid in quiet-Sun lower transition regions, although there are complications arising from the weakness of a key Si III line in the quiet-Sun disk spectra. We also discuss our results in light of other density measurements and theories regarding the structure and heating of the transition region. Title: 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. Bibcode: 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. Bibcode: 1998ApJ...504..573D Altcode: Using spectra obtained from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory (SOHO) spacecraft, we determine the Si/Ne abundance ratio in diffuse, interplume polar coronal hole regions, as well as the ratio relative to quiet-Sun coronal regions. Ne has the second highest first ionization potential (FIP) of solar abundant elements, and Si is a low-FIP element. Thus the Si/Ne ratio is a sensitive indicator of abundance variations due to the FIP effect. We develop new spectroscopic diagnostics for the determination of the Si/Ne abundance ratio. Assuming ionization equilibrium, we find that the Si/Ne abundance ratio in interplume polar coronal hole regions is about a factor of 2 greater than the photospheric value and is close to or the same as in coronal quiet-Sun regions. This result pertains to the electron temperature range 5-8 × 105 K. However, the combined atomic physics, instrumental, and statistical uncertainty in this result is about a factor of 2, and therefore this observed enhancement is consistent with no enhancement in the polar hole abundances. Nevertheless, our results follow the same trend, i.e., a greater than photospheric abundance ratio of low-FIP elements in the corona relative to high-FIP elements, as found from other abundance measurements in the corona that involve different atomic physics and different instruments. Therefore we feel that our results reflect an actual abundance enhancement, despite being within an uncertainty level bar that encompasses photospheric abundances. We also examine the Ne/Mg abundance ratio over a 24.5 hr observation and find no significant abundance variations. (Mg is a low-FIP element.) Thus, no large transient abundance variations appear to occur on timescales shorter than about a day, although this result is based on only one observation. From lines of Mg VII, Mg VIII, Mg IX, and Mg X we find that the electron temperature along the line of sight increases with height above the limb over the polar coronal holes, as has been previously reported. We determine the emission measure distribution as a function of height from Mg VII, Mg VIII, and Mg X lines. We determine average temperatures along the line of sight over the polar holes from Ne VIII/Ne VII, Mg VIII/Mg VII, and Si VIII/Si VII line ratios. We also discuss the temperature properties of the coronal hole and quiet-Sun regions using forbidden lines of Fe X and Fe XI. We comment on the possibility that ionization equilibrium is not valid in polar coronal hole regions, a possible scenario in light of recent observations that show outflows in coronal holes beginning at about the temperature of formation of Ne VIII. Title: High-Temperature Lines in SUMER Spectra Recorded Above a Bright Solar Active Region Authors: Feldman, U.; Curdt, W.; Doschek, G. A.; Schühle, U.; Wilhelm, K.; Lemaire, P. Bibcode: 1998ApJ...503..467F Altcode: We identify spectral lines emitted by solar abundant elements due primarily to transitions within the 2s22pk and 3s23pk (where k = 1, 5) ground configurations of ions that are formed in ionization equilibrium between 2 × 106 and 8 × 106 K. The transitions were identified in spectra of a bright active region recorded 1997 September 6, by the Solar Ultraviolet Measurements of Emitted Radiation Spectrometer (SUMER) flown on the Solar and Heliospheric Observatory (SOHO). Some of these lines provide useful plasma diagnostic tools for measuring the physical conditions in the solar corona. Title: A Compact Spectral Range and Matching Extreme-Ultraviolet Spectrometer for the Simultaneous Study of 1 × 104-2 × 107 K Solar Plasmas Authors: Feldman, U.; Brown, C. M.; Laming, J. M.; Seely, J. F.; Doschek, G. A. Bibcode: 1998ApJ...502..997F Altcode: An EUV spectral range of less than 100 Å in first order has been found that includes sufficient spectral lines and critical combinations of lines in first and second order to permit dynamic and diagnostic investigations of the solar atmosphere with a relatively simple spectrometer. An optical design of such a spectrometer, based on the performance of the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft, and sample stigmatic solar spectra for the range 1334-1428 Å from SUMER are presented to illustrate the utility of this range. Lines of almost all abundant solar elements except H and He are present within this wavelength band in first or second order. The lines cover the large temperature range from 1 × 104 K (chromosphere) to 2 × 107 K (flares). The spectrometer's resolution is sufficiently high to permit measuring line profiles and wavelength shifts which allows plasma dynamical studies of individual solar structures from the chromosphere up into the corona. In addition, electron density diagnostics are available within the spectral range that cover the temperature range from 8 × 104 to 1 × 106 K and an electron density range from 108 to 1013 cm-3. Title: FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results Authors: Feldman, U. Bibcode: 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 < 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. Bibcode: 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. Bibcode: 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. Bibcode: 1998ASSL..229..341P Altcode: 1998opaf.conf..341P No abstract at ADS Title: FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results Authors: Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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 < 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 > 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, & 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 {<atop >} 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1997ApJ...474..511F Altcode: In this paper we investigate the occurrence rate of soft X-ray solar flares observed by the Geostationary Operational Environmental Satellites (GOES). The analysis includes all flares classified as equal to or brighter than A1 and covers the time period from 1993 November to 1995 July. We find a power-law relationship between the number of flares per hour and peak X-ray brightness in the 1-8 Å range. The average power-law index for dN/dF, where N is the number of events per hour and F, the GOES flux, is about -1.88 +/- 0.21. A similar result was found from previous work based on uncollimated GOES-type observations concerning flares brighter than about C2. This index is independent of the background flux level (which is related to the solar activity level) to within our statistical uncertainties. We obtain the FWHM distribution of flare lifetimes from our sample and find that the distribution is independent of X-ray brightness class. We extrapolate the soft X-ray flare occurrence rate obtained for the Sun to other very active solar-like stars. Title: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1996ApJ...460.1034F Altcode: In this paper we present a statistical analysis of soft X-ray flare class and emission measure as a function of electron temperature determined for the time of maximum flare X-ray flux. The study includes 868 flares of X-ray class A2 to X2. Our work shows that their properties are very different, although large and small flares as seen by the 1-8 Å detector aboard the Geostationary Operational Environmental Satellite (GOES) records have similar appearances. The peak temperature of intense (major) flares is much higher than the peak temperature of weak (minor) flares. This finding has important implications on the nature of the flare-heating mechanism. For example, if a flare is a collection of elementary bursts, the plasma properties of the elementary-bursts occurring during peak emission of large flares and small flares must be different.

Using the relationship between electron temperature and emission measure in solar flares, we provide an estimate of the electron temperature during the peak emission of large stellar flares. Title: Electron Temperature and Emission Measure Determinations of Very Faint Solar Flares Authors: Feldman, U.; Doschek, G. A.; Behring, W. E. Bibcode: 1996ApJ...461..465F Altcode: We have studied 28 flares in the X-ray magnitude range of A2-A9 using high-resolution Bragg crystal spectrometer data obtained from instrumentation flown on the Yohkoh spacecraft. Flares in the A-class category can be detected in spectral lines of He-like ions formed at low temperatures. Their average temperature is approximately 5 x 106 K, and their emission measure as determined from the S XV resonance line near 5 Å varies between 2 x 1046 and 1 x 1048 cm-3. Title: The Temperature of the Bright Knots at the Tops of Solar Flare Loops Authors: Doschek, G. A.; Feldman, U. Bibcode: 1996ApJ...459..773D Altcode: The Japanese Yohkoh spacecraft has revealed the pervasive presence of confined bright regions at the tops of solar flare magnetic flux tubes. The physical parameters in the bright regions, such as temperature and density, are of considerable interest for attempting to understand the nature and longevity of these regions. We have found an example of such a source in spectroheliograms of a flare observed by the Naval Research Laboratory slitless spectroheliograph on Skylab. This instrument offers better temperature discrimination than possible with a broadband X-ray telescope such as flown on Yohkoh We determine the temperature of the Skylab source using the most recent atomic data. From the Skylab extreme-ultraviolet images of this flare in spectral lines of Fe XXII, Fe XXIII, and Fe XXIV, we find that the confined bright region can be described as an isothermal source at a temperature of about 11 x 106 K. However, this conclusion generally contradicts temperatures measured from uncollimated Bragg crystal spectrometer spectra from Yohkoh and other spacecraft for similar X-ray class flares. There is also emission at the same location from Ca XVII ions formed at about 6 x 106 K, implying that the source might be multithermal A multithermal source would indicate that the bright regions are composed of structures below the spatial resolution of the Skylab and Yohkoh instrumentation and could possibly resolve the discrepancies between Bragg spectrometer and imaging data. Title: Ultra Low Temperature Sulfur X-Ray Spectra Authors: Doschek, G. A.; Feldman, U.; Dubau, J. Bibcode: 1996ASPC..111..122D Altcode: 1997ASPC..111..122D The BCS experiment on Yohkoh was designed to be about an order of magnitude more sensitive than previously flown Bragg crystal X-ray spectrometers. Because of this sensitivity the authors have attempted to detect X-ray sulfur line emission emitted from temperatures as low as 2×106K. This attempt failed, in part because of possible scattered radiation from cosmic X-ray sources! Nevertheless, the authors investigated the plasma diagnostic possibilities and present some preliminary results. Title: Properties of Thermal Flares (4-30 MK) Derived from Observations: Does a Reconnection Mechanism Have a Role in the Flare Process? Authors: Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1995ApJ...451L..79F Altcode: We discuss an extrapolation of a recently discovered correlation between temperature and emission measure derived from X-ray spectra for the peak of solar flares to temperatures and emission measures characteristic of stellar flares. We find surprisingly good agreement between the parameters derived for stellar flares by various authors and the extrapolation of the results from the survey of solar flares. Title: Relationships between Temperature and Emission Measure in Solar Flares Determined from Highly Ionized Iron Spectra and from Broadband X-Ray Detectors Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Brown, C. M. Bibcode: 1995ApJ...450..441F Altcode: We compare the electron temperature and emission measure of flares at the time of maximum soft X-ray intensity derived using two different techniques: (1) from the ratio of a dielectronic Fe XXIV line to the resonance line of Fe XXV, combined with the absolute intensity of the Fe XXV line, and (2) from the ratio of the 0.5-4.0 Å and 1-8 Å broadband X-ray fluxes, combined with the absolute flux in one of the broadband spectral regions. The high-resolution Fe spectra are obtained with the Bragg Crystal Spectrometer experiment flown on the Japanese Yohkoh spacecraft. The broadband fluxes are obtained from Geostationary Operational Environmental Satellites (GOES). A data set of 540 X-ray magnitude C2 or brighter flares, observed by both spacecraft, is used for the analysis. Both techniques assume an isothermal plasma. The broadband temperatures are substantially lower than the Fe xxv temperatures. We find that the maximum temperature of flares brighter than MS exceeds 2 × 107 K and that the maximum temperature of flares fainter than C4 is substantially lower than 2 × 107 K. We find that the Fe XXV emission measure is linearly proportional to the GOES flux in the 0.5-4.0 Å detector. Title: Relationship between Cold and Hot Post--Solar Flare Loops and the Impact on the Reconnection Flare Model Authors: Feldman, U.; Seely, J. F. Bibcode: 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 Bibcode: 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. Bibcode: 1995ApJ...446..860F Altcode: We have analyzed the Yohkoh soft X-ray telescope images and Bragg crystal spectrometer spectra of two long-duration X-class events (LDEs), obtained from instruments on the Japanese Yohkoh spacecraft. The two events are a limb flare that occurred on 1992 November 2 near 03 UT and a disk flare that occurred on 1992 February 27 near 10 UT. The spatial resolution of the images is about 2"5, and the time resolution is 2 s. The emission originates from plasma at temperatures ≥ 107 K.

The morphology of the LDEs is quite complicated, but the most intense emission consists of a small number of loops (usually one or two prominent loops). The brightest emission regions are located at the tops of loops for most of the flares' duration, as was found in earlier studies of compact flares observed by Yohkoh In the case of the 1992 November 2 limb flare, the brightening at the loop top is visible for a period of 24 hr after flare onset. This implies that the heating mechanism must act over a period of tens of hours for these long-duration events, that the energy is deposited at the top of the loop, and that the hot plasma is confined at the top of the loop.

We derive emission measures and temperatures from the soft X-ray telescope and Bragg crystal spectrometer data. Lower limit estimates of electron density of the bright regions at the loop tops are derived from the morphology of the regions and the emission measures. Fractional ion abundances for highly ionized iron are deduced from the spectrometer data.

We relate the Yohkoh observations to previous observations from the solar instruments on the Skylab manned space station. Title: VizieR Online Data Catalog: Cool X-ray flares of Sun with GOES (Phillips+, 1995) Authors: Phillips, K. J. H.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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 >=10 6 K and the Properties of the T E <=7 x10 5 K Solar Plasmas Authors: Feldman, U.; Laming, J. M. Bibcode: 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. Bibcode: 1994kofu.symp..177S Altcode: The SXT images of over fifty C, M, and X type flares which occurred between October 1991 and February 1993 were analyzed. For each flare, the 10 million degree emitting region was typically found to be located at the loop top in the first well-exposed flare image recorded during the rise phase (within 1 to 2 minutes after flare onset), in images recorded near the intensity peak, and in images recorded during most of the decay phase. For the November 2 1992 limb flare, the loop top was bright for 24 hours. For a few flares, the brightness of the footpoints in the onset images was comparable to the brightness of the loop top, but the loop top brightness rapidly increased relative to the footpoints and remained intense for the duration of the flare. The brightest region at the loop top was very small throughout the flare, often as small as a single pixel (1800x1800 km). The conclusions are that the energy is deposited in a small volume at the top of the flaring loop structure, the heating mechanism acts over a period of up to tens of hours, and the hot plasma is confined at the top of the loop structure. These results are not explained by the traditional chromospheric evaporation model of solar flares. Title: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1994ApJ...424..444F Altcode: In this paper we have analyzed images of 48 C-, M-, and X-type flares which occurred between 1991 October and 1993 February. The images were recorded by the soft X-ray telescope (SXT) flown on the Japanese Yohkoh spacecraft. The spatial resolution of the recorded images is about 2.5 sec. In each of the recorded flares the brightest regions emitting the 107 K radiation were analyzed and evaluate. The 107 K emitting region was found to be located at loop tops in the first well-exposed flare image recorded during the rise phase (within 1-2 minutes after flare onset), in images recorded near intensity peak, and in those recorded during most of the decay phase. Occasionally, in the begining of the event when the total flare intensity is low, the brightness of the footpoints may rival the brightness of the loop top. However, in these cases it is expected that the temperature of the loop top is considerably higher. The emitting region, even during flare peak, is very small (often smaller than a single SXT pixel 1800 x 1800 km). Title: Very Impulsive Solar Flares Observed with the YOHKOH Spacecraft Authors: Feldman, U.; Hiei, E.; Phillips, K. J. H.; Brown, C. M.; Lang, J. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1993SPIE.1945..164K Altcode: A program is underway at the Naval Research Laboratory (NRL) to develop a high-resolution spectrometer for the study of astrophysical sources at EUV/soft X-ray wavelengths. The spectrometer design is simple in that the sole optic is a multilayer-coated spherical grating or mosaic of co-aligned gratings used at near-normal incidence, allowing large effective collecting area without the strict tolerance requirements of grazing incidence optics. Therefore, both high resolution and high throughput can be obtained over several selected narrow bandpasses. We present efficiency and resolving power measurements of spherical gratings which have parameters similar to that intended for our flight instrument. Two gratings were replicated from the same ruled master and then coated with a multilayer of molybdenum and silicon. A third sister grating was used as a control and over-coated with gold. Title: Nonphotospheric Abundances in a Solar Active Region Authors: Widing, K. G.; Feldman, U. Bibcode: 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 Bibcode: 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 > 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 >= 100 eV) astrophysically abundant [n(X)/n(H) >= 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^ <= n_e_ (cm^-3^) <= 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 1993ApJ...404..394S Altcode: The abundance of calcium relative to hydrogen in soft X-ray-emitting solar flare plasmas is determined. Results were obtained for 25 flares. An average calcium-to-hydrogen abundance of about 5 x 10 exp -6, which is about a factor of 2 greater than measured for the photosphere, is found. This result is consistent with an enhancement of low first ionization elements in soft X-ray flare plasmas. For one flare, the calcium abundance was higher, at about 1.6 times the average results. It is inferred that the calcium abundance can vary among flares. Significant variations of the calcium abundance during the course of a flare were not detected. Title: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 1992PASJ...44L.141W Altcode: Helium-like sulphur spectra (formation temperature, T_m ~ 18times 10(6) K) from coronal active regions are being obtained by the Bragg Crystal Spectrometer onboard the Yohkoh mission. The average electron temperatures of the quiescent active regions deduced from the full-disk integrated sulphur spectra are 3.5--4 times 10(6) K. The temporal behavior of the emission lines in the sub-C level events shows that hot plasmas (T > 10(7) K) can be produced in these weak events. Title: The Morphology of 20times 10(6) K Plasma in Large Non-Impulsive Solar Flares Authors: Acton, Loren W.; Feldman, Uri; Bruner, Marilyn E.; Doschek, George A.; Hirayama, Tadashi; Hudson, Hugh S.; Lemen, James R.; Ogawara, Yoshiaki; Strong, Keith T.; Tsuneta, Saku Bibcode: 1992PASJ...44L..71A Altcode: We have examined images of 10 flares observed by the Soft X-ray Telescope on-board the Yohkoh spacecraft. These images show that the hottest portion of the soft X-ray flare is located in compact regions that appear to be situated at the tops of loops. These compact regions form at, or shortly after, flare onset, and persist well into the decay phase of the flares. In some cases, the compact regions are only a few thousand kilometers in size and are small compared to the lengths of flaring loops. This is inconsistent with the smoother intensity distribution along the loops expected from models of chromospheric evaporation. Title: 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. Bibcode: 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 Bibcode: 1992PASJ...44L.181K Altcode: It has been suggested that observed coronal loops have constant thicknesses. However, if plasma loops coincide with magnetic loops, then we might expect many loops to be significantly broader at their tops than at their footpoints (since, on average, magnetic fields must diverge with height in the solar corona). It is important to understand how the thicknesses of loops vary along their lengths, since such a variation is related to the distribution of electric currents in the corona and is therefore relevant to solar flares and coronal heating. We here present preliminary results of our investigation of thickness variations along coronal loops observed with the Soft X-ray Telescope (SXT) on board the Yohkoh satellite. Title: YOHKOH Bragg Crystal Spectrometer Observations of the Dynamics and Temperature Behavior of a Soft X-Ray Flare Authors: Doschek, George A.; Mariska, John T.; Watanabe, Tetsuya; Hiei, Eijiro; Lang, James; Culhane, J. Leonard; Bentley, Robert D.; Brown, Charles M.; Feldman, Uri; Phillips, Andrew T.; Phillips, Kenneth J. H.; Sterling, Alphonse C. Bibcode: 1992PASJ...44L..95D Altcode: We describe X-ray spectra of an M1.5 flare that occurred on 1991 November 9, starting at about 0313 UT. This flare is unusual in that very intense blueshifted components are observed in the resonance lines of Fe XXV, Ca XIX, and S XV. During the onset of the flare, the resonance lines of Ca XIX and Fe XXV are primarily due to this blueshifted component, which from the Doppler effect indicates line-of-sight speeds and turbulent motions that in combination extend up to 800 km s(-1) . Title: 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. Bibcode: 1992AAS...181.9803G Altcode: 1992BAAS...24.1274G No abstract at ADS Title: Elemental abundances in the upper solar atmosphere Authors: Feldman, Uri Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1992ApJS...81..387F Altcode: A description of the lines from the most abundant ions in the EUV spectrum in the range 50-500 A that have special diagnostic significance is presented. These lines are from plasmas in the temperature range from 10 exp 5 to 10 exp 7 K. Their utility for determining temperature, density, and abundances is demonstrated. An objective grating spectrometer, based on the Skylab slitless spectrograph, for making celestial observations in the EUV spectral region with high spectral resolution is also described. Such an instrument, if equipped with a multilayer grating, can achieve efficiencies over limited EUV wavelength ranges that rival much larger telescope-spectrometer instruments for the observation of stars and other celestial objects. Title: Element Abundances and Plasma Properties in a Coronal Polar Plume Authors: Widing, K. G.; Feldman, U. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1991SoPh..136...89C Altcode: The Bragg Crystal Spectrometer (BCS) is one of the instruments which makes up the scientific payload of the SOLAR-A mission. The spectrometer employs four bent germanium crystals, views the whole Sun and observes the resonance line complexes of H-like FeXXVI and He-like FeXXV, CaXIX, and SXV in four narrow wavelength ranges with a resolving power (λ/Δλ) of between 3000 and 6000. The spectrometer has approaching ten times better sensitivity than that of previous instruments thus permitting a time resolution of better than 1 s to be achieved. The principal aim is the measurement of the properties of the 10 to 50 million K plasma created in solar flares with special emphasis on the heating and dynamics of the plasma during the impulsive phase. This paper summarizes the scientific objectives of the BCS and describes the design, characteristics, and performance of the spectrometers. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1991PhRvA..43.2565D Altcode: We present relative spectral line intensities for 16 3s-3p and 3p-3d transitions in the neonlike ion Fe16+, obtained from solar-flare spectra. The spectra were obtained by a Naval Research Laboratory slitless spectrograph flown on the Skylab manned space station. The results are of relevance to x-ray-laser experiments involving collisional pumping of excited states of neonlike ions, and to the analysis of solar-flare spectra. The relative line intensities are measured to an accuracy of about 30%. The measured line intensities are compared with theoretical line intensities calculated assuming electron collisional excitation within the Fe16+ ion followed by deexcitation and radiative decay. The measured and theoretical intensities agree to within less than a factor of 2 for all but one line. The important J=0 lines (3 1S0-3s 1P1,3s 3P1) at 254.87 and 204.65 Å are about a factor of 1.4 weaker than predicted, which is almost within experimental error. The 3s 3P2-3p 3S1 line at 409.69 Å is 2.3 times weaker than predicted, and this is unexplained. Title: The Solar Spectrum between 914 and 1177 Angstrom Authors: Feldman, U.; Doschek, G. A. Bibcode: 1991ApJS...75..925F Altcode: A spectral line list with wavelengths and identifications for the 914-1177 A region is presented. The list is based on a Naval Research Laboratory (NRL) solar spectrum obtained from a rocket flight in 1966 and on spectra recorded by the NRL S082-B slit spectrograph flown in 1973 on the Skylab manned space station as part of the Apollo Telescope Mount. Three Skylab spectra were used for this work: a limb spectrum recorded at a position of arcsec outside the white-light limb, and two flare spectra. The wavelength list should be useful in analyzing some spectra to be obtained from the planner NASA Lyman Far Ultraviolet Spectroscopic Explorer mission. A separate table listing observed or predicted forbidden lines that fall in the 914-1177 A range is presented, and some of the plasma diagnostic possibilities for spectral lines in this range are discused. Title: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1991AdSpR..11e..77C Altcode: 1991AdSpR..11...77C A Bragg Crystal spectrometer is one of the instruments on the Solar-A mission. Using bent crystals, the spectrometer will observe the resonance line complexes of the H-like Fe XXVI, and He-like Fe XXV and Ca XIX ions with a sensitivity 5 to 10 times that of the SMM Bent Crystal Spectrometer. It will also study the lower temperature lines of He-like S XV. The improved sensitivity will allow observations much earlier in the impulsive phase of flares than has previously been possible. The new observations should help to answer questions about plasma heating and dynamics. As well as providing information on line profiles and shifts, the selected spectral lines will also provide electron temperature and emission measure estimates over a range from 5 to 50 MK. The onboard microprocessor will permit spectral resolution to be traded against time resolution during an observation. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1989ApJ...345.1079D Altcode: Blueshifted X-ray spectral line components in Fe and Ca spectra of a large long-duration flare observed on June 5, 1979. It is found that blueshifted emission exists for a time interval of at least 28 minutes indicating upflowing plasma at about 250 km/s. Emission measures for both the blueshifted and stationary plasma are derived and the results are interpreted in terms of chromospheric evaporation. The total amount of hot upflowing plasma during the flare rise time exceeds the amount of stationary plasma contained in the loop close to the time of the peak of the flare. This result contradicts the simplest version of the evaporation model. Evaporation can account for the observations only if some of the upflowing plasma cools on time scales much shorter than the rise time of the event, which was about 40 minutes. Title: Measurement of relative electron-impact-excitation cross sections for Fe(24+) Authors: Brown, C. M.; Feldman, U.; Doschek, G. A.; Seely, J. F.; Lavilla, R. E. Bibcode: 1989PhRvA..40.4089B Altcode: We present measurements of the relative electron-impact-excitation cross sections for the 1s2 1S0-1s2p 1P1, 1s2 1S0-1s2p 3P2, 1s2 1S0-1s2p 3P1, and 1s2 1S0-1s2s 3S1 transitions for the He-like ion, Fe24+. The measurements were made at two electron energies: 6.86 and 9.94 keV. The cross-section measurements are compared with theoretical calculations. Title: Abundance Variations in the Outer Solar Atmosphere Observed in SKYLAB Spectroheliograms Authors: Widing, K. G.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 1989BAAS...21..850D Altcode: No abstract at ADS Title: Element Abundances in the Sun Observed on SKLAB Spectroheliograms Authors: Widing, K. G.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1988JOSAB...5.2237F Altcode: 1988OSAJB...5.2237F The authors review the status and prospects of solar spectroscopy in the far-UV - X-ray wavelength regions between approximately 1.7 and 2000 Å. They divide the solar spectrum into a number of wavelength regions, determined by characteristics of spectroscopic instrumentation. The quality of the available spectra obtained in each region is discussed, concentrating on spectral resolution, wavelength coverage and accuracy, and line intensity and line-profile information. Title: Generation of XUV Spectra by Powerful Picosecond Laser Authors: Nam, C. H.; Tighe, W.; Suckewer, S.; Feldman, U.; Seely, J. Bibcode: 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. Bibcode: 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. Bibcode: 1987ApJ...319..541S Altcode: The Fe XXV resonance line and dielectronic satellite intensities have been measured as functions of time for several flares recorded by the Naval Research Laboratory crystal spectrometer (SOLFLEX) flown on the US Air Force P78-I spacecraft. The intensity ratios of the Fe XXV resonance line, the Fe XXIV n = 2 satellite line j, and the Fe XXIV n = 3 satellite line d13 indicate that nonthermal electron energy distributions occur during the impulsive phase of the flares. For the electron energies at which the j and d13 satellites are formed (4.7 and 5.8 keV, respectively), the electron energy distributions during the impulsive phase are observed to have a bump or to be nearly flat. For all of the flares that were studied, hard X-ray bursts occurred near the time of the nonthermal distributions observed in the SOLFLEX data. Title: Ultraviolet AL III Emission Lines and the Physics of the Solar Transition Region Authors: Doschek, G. A.; Feldman, U. Bibcode: 1987ApJ...315L..67D Altcode: Two lines of the solar UV spectrum were identified as due to 3p-3d Al III transitions near 1612 A; the ratios of these lines to the 3s-3p Al III doublet near 1855 A were found to be very sensitive to temperature. Thus, the temperatures of formation of the Al III lines could be determined by using one of the line ratios in two quiet sun regions, a coronal hole, and an active region. The results were found to be consistent with expectations based on the assumption of ionization equilibrium for Al III. It is suggested that S III lines near 1350 A and 1200 A may also serve as a temperature diagnostic. Title: The Temperature of Solar Flares Determined from X-Ray Spectral Line Ratios Authors: Doschek, G. A.; Feldman, U. Bibcode: 1987ApJ...313..883D Altcode: The effect on derived solar flare plasma temperatures of (1) a power-law distribution of emission measure as a function of temperature, (2) a high-temperature isothermal source coupled to a low-temperature power-law distribution of emission measure, and (3) two isothermal sources is calculated for line ratios involving the ions S XV, Ca XIX, Ca XX, Fe XXV, Ni XXVII, and Fe XXVI. It is shown that if the Fe XXV temperature is less than about 25 million K, as is true for the majority of flares, then about 75 percent or more of the emission measure is produced by plasma at temperatures equal to or less than the Fe XXV temperature plus about 3 million K. If the Fe XXV temperature is 20 million K or higher, this percentage can be larger. This result is obtained even if a superhot component exists that extends up to several hundred million degrees. Temperatures determined from Fe XXVI demonstrate the presence of a superhot component. Title: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1985MNRAS.217..317D Altcode: Ratios of solar element abundances are determined for Ar/Ca, K/Ca, and Ca/Fe, from high-resolution solar flare X-ray spectra obtained from Bragg spectrometers flown on the P78-1 spacecraft. Values of the ratios are: Ar/Ca = 0.65, K/Ca = 0.10, and Ca/Fe = 0.10. If the abundance of iron is taken to be coronal, i.e. log A(Fe) = 7.65 log A(H) = 12, then the abundances are: log A(Ca) = 6.62, log A(Ar) = 6.44, log A(K) = 5.62. If the iron abundance is assumed to be photospheric, i.e., log A(Fe) = 7.50, then the abundances are: log A(Ca) = 6.47, log A(Ar) = 6.29, log A(K) = 5.47. The uncertainties in abundance ratios are + or - 25 percent. The abundance results are discussed in terms of the possibility of varying abundances in the solar atmosphere. Title: High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection Authors: Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Sheeley, N. R., Jr.; Seely, J. F. Bibcode: 1985ApJ...292..309K Altcode: It has been recognized that very long duration X-ray events (lasting several hours) are frequently associated with coronal mass ejection. Thus, Sheeley et al. (1983) found that the probability of the occurrence of a coronal mass ejection (CME) increases monotonically with the X-ray event duration time. It is pointed out that the association of long-duration, or long-decay, X-ray events (LDEs) with CMEs was first recognized from analysis of solar images obtained by the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL) slitless spectroheliograph. Recently high-resolution Bragg crystal X-ray spectrometers have been flown on three spacecraft, including the Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission (SMM), and the Japanese Hinotori spacecraft. In the present paper, P78-1 X-ray spectra of an LDE which had its origin behind the solar west limb on November 14, 1980 is presented. The obtained data make it possible to estimate temperatures of the hottest portion of the magnetic loops in which the emission arises. Title: 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. Bibcode: 1985PhRvA..31.2534S Altcode: Measured relative intensities of a number of allowed 2s22pk-2s2pk+1 transitions (60-200 A&#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. Bibcode: 1985STIN...8528908M Altcode: Solar X-ray spectra in the wavelength range 5.5-12 a have been measured by the SOLEX spectrometers aboard the USAF p78-1 satellite. The spectra were measured under a variety of flaring and nonflaring conditions. High sensitivity, attained by summing data from several successive spectral scans, enabled the detection of 85 lines, 22 of which remain unidentified, in this wavelength range. In addition, observations of many strong lines were possible with individual scans during the course of the flare evolution. This capability, coupled with the availability of nonflare spectra, facilitated the identification of several lines. The lines of Fe XXII-XXIV are especially important in this wavelength range. For many of these lines, theoretical and observed line strengths Title: Element Abundances from Solar Flare Spectra Authors: Doschek, G. A.; Feldman, U.; Seely, J. F. Bibcode: 1985BAAS...17..629D Altcode: No abstract at ADS Title: Precision measurement of transition energies and Lamb shifts in two-electron argon and potassium in solar-flare spectra Authors: Seely, J. F.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 1985MNRAS.212P..41F Altcode: The authors review the identifications of Fe XVII transitions between the 2s22p53s, 3p, and 3d configurations recently published by Jupén. The review is based on examining spectroheliograms of solar flares obtained by a Naval Research Laboratory instrument on Skylab (S082-A). The authors agree with the majority of identifications given by Jupén, but find different wavelengths for a few of the lines. The relative intensities of the lines are qualitatively in agreement with calculations. The authors also identify a broad line at 1153.20 Å with the 2p53s3P0→2p53s3P1 forbidden transition of Fe XVII. This line was found in flare spectra obtained by the NRL slit spectrograph on Skylab (S082-B). Title: The solar coronal X-ray spectrum from 5.5 to 12 A Authors: McKenzie, D. L.; Landecker, P. B.; Feldman, U.; Doschek, G. A. Bibcode: 1985ApJ...289..849M Altcode: A compilation of spectral lines in the 5.5-12 A wavelength region is presented from observations under a variety of solar conditions, including flare onset, flares, and nonflaring active regions. The line fluxes and wavelengths of Fe XXII-XXIV are compared with theory, and the results for Fe XXIII-XXIV are shown to agree with theoretical determinations. When only the strongest lines are considered, some relative strengths agree with theory and some do not. Diagnostically useful line ratios of Mg XI, Al XII, and Si XIII are also examined. The density-sensitive line ratio R measured for Mg XI and Si XIII agree with theoretical calculations of R(0) the low-density limit of R. For Mg XI in a flare-onset spectrum, R is lower than R(0), but the statistical significance of the result is not high. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1984ApJ...276L..53F Altcode: The rise phases of solar soft X-ray flares observed by X-ray crystal spectrometers on P78-1 are discussed in terms of the rate of change of X-ray flux as a function of time. It is shown that the flux increases exponentially over most of the rise time. The e-folding time (tau) has a cutoff at approximately 13 s. Soft X-ray flares with smaller values of tau are not observed. It is suggested that this phenomenon is due to the ability of the solar atmosphere to absorb the input energy and convert it into a typical soft X-ray flare, when the value of tau is greater than about 13 s. For energy input rates with tau greater than about 13 s, the temperature attained by the plasma is typically around 2 x 10 to the 7th K, but for values of tau less than 13 s, the gas is heated to much higher temperatures (about 10 to the 8th K), producing a certain class of hard X-ray flares. Title: Measurement of Wavelengths and Abundances from Solar Flare X-Ray Spectra Authors: Seely, J. F.; Feldman, U.; Doschek, G. A. Bibcode: 1984uxsa.coll..151S Altcode: 1984IAUCo..86..151S; 1984uxsa.conf..151S No abstract at ADS Title: Measurement of the Increase in Altitude of the Soft X-Ray Emission Regions of Solar Flares (short Abstract) Authors: Seely, J. F.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1983STIN...8423548F Altcode: The rise phases of solar soft X-ray flares observed by X-ray crystal spectrometers on p78-1 are discussed in terms of the rate of change of X-ray flux as a function of time. It is shown that the flux increased exponentially over most of the rise time. The e-folding time TAU has a cut-off at 13 s. Soft X-ray flares with smaller values of TAU are not observed. It is suggested that this phenomenon is due to the ability of the solar atmosphere to absorb the input energy and convert it into a typical soft X-ray flare. For energy input rates that are below a certain critical value the temperature attained by the plasma is around 20,000,000 K, but for values above the critical value, the gas is heated to much higher temperatures Te > or = 10 to the 8th K, producing a certain class of hard X-ray events. Title: Lines of Fe XII sensitive to coronal electron density Authors: Feldman, U.; Doschek, G. A.; Cohen, L. Bibcode: 1983ApJ...273..822F Altcode: Lines of Fe XII sensitive to coronal electron density are discussed. The lines appear in solar spectra obtained by the Naval Research Laboratory (NRL) slit spectograph flown on Skylab. These lines are due to transitions between levels of the 3s 2 3p 3 configuration and fall at the wavelengths 1242.03 A, 1349.38 A, 2169.03 A, 2405.71 A, and 2565.99 A. It is shown that the line at 2169.03 A is severely blended by a line of Ni II at heights less than 12 arcsec outside the solar limb. Above 12 arcsec the lines at 2169.03 and 2405.71 A are apparently unblended and can be used to derive electron densities. An average coronal electron pressure of 6 x 10 to the 14th/cu cm K is obtained. However, the emitting path lengths of the Fe XII lines, deduced using the electron densities and absolute intensities, are unrealistically large. The reason for this difficulty is unclear. Title: He D3 as a diagnostic for the hard and soft X-rays from solar flares Authors: Feldman, U.; Liggett, M.; Zirin, H. Bibcode: 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. Bibcode: 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 > 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. Bibcode: 1982ApJ...260..885F Altcode: Doschek et al. (1980) and Feldman et al. (1980) have discussed high-resolution soft X-ray spectra of solar flares. The present investigation is concerned with the characteristics of the impulsive events as observed in soft X rays and the cooling of the flare plasma in terms of energy loss processes. A class of intense, short-lived solar flares which appear to be characterized by very high densities at high temperatures is found. For the 1979 November 6 event, the cooling time is so rapid that the density obtained may be a lower limit. The main cooling mechanism for the flares is found to be radiative. Two of the events are associated with strong gamma-ray emission and both of these events are very unusual in their soft X-ray emission. The 1979 November 9 flare shows extremely broad X-ray emission lines during the rise phase, indicative of nonthermal velocities of the order of 300 km/s. Title: Observational constraints for a theoretical model describing the soft X-ray flare Authors: Feldman, U.; Cheng, C. -C.; Doschek, G. A. Bibcode: 1982ApJ...255..320F Altcode: High-resolution solar flare X-ray spectra have recently been obtained from X-ray spectrometer experiments flown on an Air Force spacecraft (P78-1) launched on 1979 February 24. Interpretation of the spectra has produced new results concerning the physical conditions and time behavior of the thermal soft X-ray emitting plasma at temperatures near 20,000,000 K. It is argued that soft and hard X-ray events are not causally related to each other, but are simply two different manifestations of flare energy release. They probably occur in different plasma volumes. The source of the preflare plasma appears to be in the cooler parts of the solar atmosphere, perhaps transition region loops with initial temperatures of 100,000 K and densities of 10 to the 11th per cu cm. Continuous energy input, rather than sequential activation of loops, is required to explain the observations. Compression coupled with chromospheric ablation may produce the high densities in coronal flare loops. Title: Doppler wavelength shifts of ultraviolet spectral lines in solar active regions Authors: Feldman, U.; Doschek, G. A.; Cohen, L. Bibcode: 1982ApJ...255..325F Altcode: Doppler shifts are measured for solar UV emission lines formed in the lower transition region of active regions. Doppler shifts in different regions at the same solar location, variations of Doppler shift with position of an active region on the disk, and variations of Doppler shift with time at the same solar location in the same active region were studied. Observations were made with the NRL slit spectrograph on Skylab. Excluding flare and flare-related phenomena, only redshifts are found whose magnitudes correspond to downflow velocities between about 4 and 17 km/s. Shifts are largest for lines formed between about 50,000 and 100,000 K, and are distinctly less for lines formed above 100,000 K. The shifts persist out to the limb, but not above it. There is no obvious change in redshift for lines measured at the same solar location over time intervals of about 20 minutes. Title: Ultraviolet continuum absorption /less than about 1000 A/ above the quiet sun transition region Authors: Doschek, G. A.; Feldman, U. Bibcode: 1982ApJ...254..371D Altcode: Lyman continuum absorption shortward of 912 A in the quiet sun solar transition region is investigated by combining spectra obtained from the Apollo Telescope Mount experiments on Skylab. The most recent atomic data are used to compute line intensities for lines that fall on both sides of the Lyman limit. Lines of O III, O IV, O V, and S IV are considered. The computed intensity ratios of most lines from O IV, O V, and S IV agree with the experimental ratios to within a factor of 2. However, the discrepancies show no apparent wavelength dependence. From this fact, it is concluded that at least part of the discrepancy between theory and observation for lines of these ions can be accounted for by uncertainties in instrumental calibration and atomic data. However, difficulties remain in reconciling observation and theory, particularly for lines of O III, and one line of S IV. The other recent results of Schmahl and Orrall (1979) are also discussed in terms of newer atomic data. Title: Electron densities in a solar flare derived from X-ray spectra Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge, H. R.; Young, R. M.; Doschek, G. A.; Feldman, U. Bibcode: 1982STIN...8325647M Altcode: A major solar flare was observed with the RAP crystal of the SOLEX B spectrometer. The spectra were obtained by scanning back and forth between Bragg angles of 17.4 deg and 61.7 deg (7.8 to 23 A) at a rate of 0.525 degrees-.15. A full scan took 84.5 sec. A line list identifying more than 100 lines observed in this flare was compiled. Measurements of the density sensitive O 7 lines near 22 A are discussed. Title: On ionization equilibrium in solar flares as determined from X-ray emissionlines of CA XVIII and CA XIX Authors: Doscher, G. A.; Feldman, U. Bibcode: 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. Bibcode: 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. Bibcode: 1981ApJ...250..799F Altcode: High resolution solar observations of the S v intersystem line at 1199.18 A are available from Skylab. This line is potentially useful as a density diagnostic for high density plasmas expected in solar flares. S v lines are also prominent in solar spectra at wavelengths below 1000 A. Collision strengths and radiative decay rates are calculated for levels of the configurations 3 s2, 3s3p, 3p2, and 3s3d. Level populations for the five lowest energy levels have been calculated as a function of electron density. These calculations are carried out assuming the temperature at which S v is most abundant in solar plasmas. The calculated population of the 3s3p 3P1 level reaches a pseudo-Boltzmann equilibrium at a density which is about five times higher than is derived from solar spectra and previous density determinations. It is believed that the discrepancy is due to a significant contribution from resonances to the 3s2-3s3p 3P excitation rate coefficient. It is suggested that the contribution of the resonances to the S v excitation rate coefficient can be estimated from a comparison of the experimental results and the theoretical calculations. Title: High resolution solar flare X-ray spectra - The temporal behavior of electron density, temperature, and emission measure for two class M flares Authors: Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L. Bibcode: 1981ApJ...249..372D Altcode: High resolution soft X-ray flare spectra recorded by Naval Research Laboratory (NRL) and Aerospace Corporation Bragg crystal spectrometers flown on an orbiting spacecraft (P78-1) are combined and analyzed. The instruments were launched on t979 February 24 by the U.S. Air Force, and the data discussed in this paper cover the wavelength ranges, 1.82-1.97 Å, 3.143.24 Å, and 18.423.0 Å. The NRL experiment (SOLFLEX) covers the two short wavelength ranges (highly ionized Fe and Ca lines) and the Aerospace experiment (SOLEX) covers the t8.4-23.O Å range, which includes the Lyα O VIII line and the resonance, intercombination, and forbidden lines of O VII. We analyze the spectra of two flares which occurred on 1980 April 8 and May 9. Temporal coverage is fairly complete for both flares, including the rise and decay phases. Measurements of electron density Ne with rather high time resolution (about 1 minute) have been obtained throughout most of the lifetimes of the two flares. These measurements were obtained from the O VII lines and pertain to flare plasma at temperatures near 2 × 106 K. Peak density seems to occur slightly before the times of peak X-ray flux in the resonance lines of Fe XXV, Ca XIX, and O VII, and for both flares the peak density is about 1012 cm-3. Electron temperature Te as a function of time is determined from the Fe and Ca spectra. Peak temperature for both flares is about 18 × 106 K. Differential emission measures and volume emission measures are determined from the resonance lines of O VII, Ca XIX, and Fe XXV. The number of electrons NeΔV and the volume ΔV over which the O VII lines are formed are determined from the O VII volume emission measure Ne2ΔV and the density Ne. These quantities are determined as a function of time. The relationship of the low and high temperature regions is discussed. Title: The use of spectral emission lines in the diagnostics of hot solar plasma. Authors: Feldman, U. Bibcode: 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. Bibcode: 1981MNRAS.196..517F Altcode: Several sets of ionization equilibrium calculations exist for use in interpreting X-ray and EUV spectra of astrophysical plasmas. In particular, the calculations of Jordan (1969, 1970), Jacobs et al. (1977, 1978) and Summers (1974) are well known. The temperatures of maximum fractional abundance calculated by Summers for the more highly ionized and heavier elements such as iron are about a factor of two higher than the temperatures calculated by Jordan and Jacobs et al. By the use of recently obtained X-ray spectra of solar flares, it is shown that the temperatures calculated by Summers (1974) for iron are incorrect. The temperatures calculated by Jordan or Jacobs et al. should be used until further improvements become available. Title: High resolution solar flare X-ray spectra: The temporal behavior of electron density, temperature, and emission measure for two class M flares Authors: Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L. Bibcode: 1981STIN...8225073D Altcode: High resolution soft X-ray flare spectra recorded by crystal spectrometers flown on an orbiting spacecraft (P78-1) are combined and analyzed. The spectra of two flares are analyzed. Temporal coverage for both flares, including the rise and decay phases, is discussed. Measurements of electron density were obtained throughout most of the lifetimes of the two flares. Electron temperature as a function of time is determined from the Fe and Ca spectra. Differential emission measures and volume emission measures are determined for the low and high temperature (Fe, Ca) plasma. The relationship of the low and high temperature regions is discussed. Title: On the relationship between soft X-rays and H-alpha-emitting structures during a solar flare Authors: Zirin, H.; Feldman, U.; Doschek, G. A.; Kane, S. Bibcode: 1981ApJ...246..321Z Altcode: Based on data obtained during a solar flare on March 31, 1979, soft X-ray (SXR) and hard X-ray (HXR) bursts are analyzed and compared with other available data in order to identify structures in H-alpha that may correspond to the SXR-emitting site. Measurements taken with the X-ray telescope and the XUV spectroheliograph flown on Skylab, have shown that the SXR emission from many flares comes from rather small structures of about 10-20 arcsec across. These structures appear to be loops that cross the magnetic neutral line. Understanding of the morphology of SXR was based on data of the solar flare of June 15, 1973, observed from Skylab, and the work of Moore et al., (1980). Dense, highly emissive coronal structures, not suggested to be the X-ray source, were forming, lost energy rapidly by emission and conduction, and finally formed the loops. It is concluded that bright H-alpha loops form rapidly as the SXR emission rises, and the overall decay (cooling rate) of SXR emission is much slower than the formation time of individual loops. Title: High resolution X-ray spectra of solar flares. V - Interpretation of inner-shell transitions in Fe XX-Fe XXIII Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D. Bibcode: 1981ApJ...245..315D Altcode: The paper examines high-resolution solar flare iron line spectra recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval Research Laboratory on an Air Force spacecraft launched on 1979 February 24. The emission line spectrum is due to inner-shell transitions in the ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line intensities obtained by methods discussed by Merts, Cowan, and Magee (1976), electron temperatures as a function of time for two large class X flares are derived. These temperatures are deduced from intensities of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the differential emission measure between about 12-million and 20-million K using these temperatures is considered. The possibility of determining electron densities in flare and tokamak plasmas using the inner-shell spectra of Fe XXI and Fe XX is discussed. Title: Mass motions in optically thin solar transition zone lines Authors: Doschek, G. A.; Mariska, John T.; Feldman, U. Bibcode: 1981MNRAS.195..107D Altcode: The widths of optically thin EUV spectral lines formed at temperatures between ≃ 3 × 104 and 2 × 105 K in the solar transition zone are larger than expected assuming ionization equilibrium. This result has been interpreted as due to non-thermal mass motions, characterized by a parameter ξ(km s-1) In this paper we discuss observations of spectral line recorded mostly at +2 arcsec outside the limb of the north and south polar coronal holes, and compare the derived values of ξ to values deduced from spectra of quiet Sun regions. These spectra were recorded by the NRL spectrograph on Skylab (1100-2000 Å). Systematic differences in line widths between coronal holes and quiet Sun region spectra are probably no larger than 0.01 Å, for the optically thin lines used in the analysis. -sight path lengths of the emitting plasma at 2 arc sec above the limb are calculated from the intensity ratios of optically thick lines of C IV, N V, Al III, and Si IV. These ratios should be 2:1 in the optically thin limit, but they are around 1.5 at 2 arcsec above the solar limb. The derived path lengths range from ≃1000 to 5000km. Title: What produces the high densities observed in solar flare plasmas Authors: Cheng, C. -C.; Feldman, U.; Doschek, G. A. Bibcode: 1981A&A....97..210C Altcode: Attention is drawn to the implications of the high densities observed in flare plasmas in the wide temperature range from 10 to the 4th K to more than 10 to the 7th K. The chromospheric evaporation theory for the decay phase is discussed, and it is found that it is not consistent with the observations. It is pointed out that all the flare mechanisms proposed so far, e.g., magnetic field reconnection in various geometries, have entirely ignored the fundamental problem of how the high densities arise in the first place, and, in fact, they are unable to answer this question. It is suggested that compressional heatings of a flaring loop might be responsible for the density and emission measure (EM) increases observed in flare plasmas. Chromospheric evaporation associated with local heating in the initial rising phase of the flare, in distinction to the existing evaporation theory which assumes a coronal heating source, is also discussed. Possible observational tests, utilizing the newly launched Solar Maximum Mission (SMM) satellite, are presented. Title: Solar flare X-ray spectra between 7.8 and 23.0 angstroms Authors: McKenzie, D. L.; Landecker, P. B.; Broussard, R. M.; Rugge, H. R.; Young, R. M.; Feldman, U.; Doschek, G. A. Bibcode: 1981STIN...8225072M Altcode: High resolution X-ray spectra taken during a large solar flare on 10 June 1979 are presented. Many lines of highly ionized iron were resolved and identified for the first time in solar spectra. Lines with a wide range of excitation temperatures are found to have a similar time development during the flare's rapid rise phase. The density-sensitive line ratios in Fe(XXI) and Fe(XXII) are discussed. Title: The detection of companion stars to the Cepheid variables Eta Aquilae and T Monocerotis. Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U. Bibcode: 1981NASCP2171..209M Altcode: 1981NASCP3171..209M; 1980IUE80......209M; 1981uviu.nasa..209M Ultraviolet spectra of the classical Cepheid variables eta Aq1 and T Mon at several phases in their periods were obtained with IUE. For eta Aq1 significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1600 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the nonvariable emission is consistent with the flux expected from a main sequence companion star with an effective temperature of about 9500 K (AO V - A1 V). For T Mon a nonvarying component to the ultraviolet emission is observed for wavelengths less than 2600 A. Comparison with model atmosphere flux distributions suggests that the companion has an effective temperature of around 10,000 K (AO) and is near the main sequence. Title: The detection of a companion star to the Cepheid variable T Monocerotis Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U. Bibcode: 1980ApJ...242.1083M Altcode: We have obtained ultraviolet spectra with the International Ultraviolet Explorer (IUE) spacecraft of the classical Cepheid T Mon at several phases in the 27 day period. Significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1900 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the emission is consistent with the flux expected from a companion star with an effective temperature of about 10,000 K (approximately A0) near the main sequence. Title: High-resolution X-ray spectra of solar flares. IV - General spectral properties of M type flares Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.; Mariska, J. T. Bibcode: 1980ApJ...241.1175F Altcode: The spectral characteristics in selected narrow regions of the X-ray spectrum of class M solar flares are analyzed. High-resolution spectra in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which contain lines important for the determination of electron temperature and departure from ionization equilibrium, were recorded by spaceborne Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are obtained from line ratios during flare rise phases in M as well as X flares, while in the decay phase the calcium temperature can be as low as 8,000,000 K, which is significantly lower than in X flares. Large nonthermal motions (on the order of 130 km/sec at most) are also observed in M as well as X flares, which are largest during the soft X-ray rise phase. Finally, it is shown that the method proposed by Gabriel and Phillips (1979) for detecting departures of electrons from Maxwellian velocity distributions is not sufficiently sensitive to give reliable results for the present data. Title: Solar flare X-ray spectra between 7.8 and 23.0 Angstroms. Authors: McKenzie, D. L.; Landecker, P. B.; Broussard, R. M.; Rugge, H. R.; Young, R. M.; Feldman, U.; Doschek, G. A. Bibcode: 1980ApJ...241..409M Altcode: The high-resolution X-ray spectra taken during a large solar flare on 1979 June 10 are presented. Many lines of highly ionized iron are resolved and identified for the first time in solar spectra. Lines with a wide range of excitation temperatures have similar time development during the flare's rapid rise phase. The density sensitive line ratios in Fe XXI and Fe XXII are discussed. Title: Simultaneous Observations of Solar Flares Obtained by the SOLEX AND SOLFLEX High Resolution X-Ray Spectrometers Authors: Landecker, P. B.; McKenzie, D. L.; Doschek, G. A.; Feldman, U. Bibcode: 1980BAAS...12Q.906L Altcode: No abstract at ADS Title: Physical conditions in the solar atmosphere above an active region Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A. Bibcode: 1980ApJ...240..300M Altcode: From a series of EUV spectra obtained at several heights above the limb in a solar active region, the volume emission measure is derived as a function of the electron temperature in the temperature range 70,000-1,500,000 K and the electron density at two locations. The emission measure from the coronal material (temperature greater than 700,000 K) is nearly the same everywhere and represents most of the material in the line of sight, while the emission measure from the transition region material (temperature between 70,000 and 250,000 K) fluctuates by two orders of magnitude from position to position above the active region. This is in agreement with the picture of this active region as consisting of a number of well-defined loops or lower portions of loops at transition region temperatures that are inhomogeneously distributed in much larger and more diffuse loop structures at coronal temperatures. The coronal data are in reasonable agreement with simple coronal models. Emission measures near 1,000,000 K evaluated using different ions differ by a factor of 4, suggesting difficulties with the atomic physics data. Title: High-resolution X-ray spectra of solar flares. III - General spectral properties of X1-X5 type flares Authors: Doschek, G. A.; Feldman, U.; Kreplin, R. W.; Cohen, L. Bibcode: 1980ApJ...239..725D Altcode: High-resolution X-ray spectra of six class X1-X5 solar flares are discussed. The spectra were recorded by spaceborne Bragg crystal spectrometers in the ranges 1.82-1.97, 2.98-3.07 and 3.14-3.24 A. Electron temperatures derived from dielectronic satellite line to resonance line ratios for Fe XXV and Ca XIX are found to remain fairly constant around 22,000,000 and 16,000,000 K respectively during the rise phase of the flares, then decrease by approximately 6,000,000 K during the decay phase. Nonthermal motions derived from line widths for the April 27, 1979 event are found to be greatest during the rise phase (approximately 130 km/sec) and decrease to about 60 km/sec during decay. Volume emission measures for Fe XXV, Ca XIX and Ca XX are derived from photon fluxes as a function of temperature, and examination of the intensity behavior of the Fe K alpha emission as a function of time indicates that it is a result of fluorescence. Differences between the present and previous observations of temperature variation are discussed, and it is concluded that the flare plasmas are close to ionization equilibrium for the flares investigated. Title: Atomic data for S IV and solar observations of the 3x/2/3p /2/P-3s3p/2/ /4/P multiplet Authors: Bhatia, A. K.; Doschek, G. A.; Feldman, U. Bibcode: 1980A&A....86...32B Altcode: High resolution observations of intersystem lines of S IV near 1400 A are available from Skylab. These lines are potentially useful as density diagnostics for the solar atmosphere. Energy levels, transition probabilities and collision strengths have, therefore, been calculated for S IV, including the configurations 3x(2)3p, 3s3p(2), and 3s(2)3d. Line intensities and level populations have been calculated as a function of electron density. The calculated population of the 3s3p(2) (4)P(5/2) level is found to reach a pseudo-Boltzmann equilibrium at a density which is four times higher than is inferred from solar spectra and level population calculations of lighter ions such as O IV. Title: Observations of the O I 1355.6 A and C I 1355.8 A lines in solar flares Authors: Cheng, C. C.; Feldman, U.; Doschek, G. A. Bibcode: 1980A&A....86..377C Altcode: The paper presents observations of the intersystem line O I 1355.6 A and the allowed line C I 1355.8 A in solar flares. In flares, the intersystem O I line is weaker than the allowed C I line and the intensity ratio O I/C I is 0.3-0.7. On the other hand, in active regions, O I line is stronger than the C I line and O I/C I is about 1-2, while in quiet sun regions, the O I line is much stronger than the C I line and O I/C I not in excess of 20. The variation of the intensity ratio from quiet sun region to flares may be due to an electron density enhancement of a factor of about 50 in flares. Title: The detection of a companion star to the Cepheid variable eta Aql. Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U. Bibcode: 1980ApJ...238L..87M Altcode: Ultraviolet spectra have been obtained with IUE of the classical Cepheid Eta Aquilae at several phases in the 7.18 day period. Significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1600 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the nonvariable emission is consistent with the flux expected from a main-sequence companion star with an effective temperature of about 9500 K (A0 V). The observed ultraviolet flux and spectral type are used to compute a distance of 300 pc to the system, in agreement with the distance predicted using the period luminosity relation. Title: High-resolution X-ray spectra of the 1979 March 25 solar flare Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W. Bibcode: 1980ApJ...238..365F Altcode: High-resolution X-ray spectra of a solar flare that occurred on 1979 March 25 are discussed. The spectra were obtained from four Bragg crystal spectrometers (SOLFLEX = solar flare X-rays) flown by NRL on a spacecraft launched by the Air Force. The wavelength ranges discussed here are: 1.82-1.97 A, 2.98-3.07 A, and 3.14-3.24 A. Electron temperatures ranging between 12 x 10 to the 6th K and 30 x 10 to the 6th K are derived from dielectronic satellite to resonance line ratios. The apparent departure from ionization equilibrium indicated by intensities of other satellite lines is discussed. Wavelengths and identifications are given for the strongest lines observed. It is proposed that the soft X-ray flare radiation is caused by the slow compression of a single or multiple set of magnetic flux tubes. Experimental methods of confirming or refuting this hypothesis are given. Title: Electron densities in a solar flare derived from X-ray spectra Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge, H. R.; Young, R. M.; Doschek, G. A.; Feldman, U. Bibcode: 1980ApJ...238L..43M Altcode: A major solar flare was observed with the rubidium acid phthalate crystal of the satellite-borne SOLEX B spectrometer and high-resolution solar X-ray spectra were obtained during the rising phase of the flare. Measurements of the density-sensitive line ratio of the O VII 1s2 1S(0) - 1s2s 3S(1) (22.10 A) flux to the O VII 1s2 1S(0) - 1s2p 3P(1) (21.80 A) flux indicate that the density of the plasma at around 2,000,000 K exceeded 10 to the 11th per cu cm near the peak of the flare. This corresponds to an electron pressure of about 30 dynes per sq cm. Title: Mass Motions in the Transition Zone of Coronal Holes Authors: Doschek, G. A.; Mariska, J. T.; Feldman, U. Bibcode: 1980BAAS...12S.518D Altcode: No abstract at ADS Title: High resolution solar flare X-ray spectra. Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W. Bibcode: 1980BAAS...12..529F Altcode: No abstract at ADS Title: The Detection of an Early Type Companion Star to the Classical Cepheid T Mon Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U. Bibcode: 1980BAAS...12Q.462M Altcode: No abstract at ADS Title: 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. Bibcode: 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. Bibcode: 1979BAAS...11..687M Altcode: No abstract at ADS Title: Solar Flare Electron Densities Derived from X-ray Spectra Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge, H. R.; Young, R. M.; Doschek, G. A.; Feldman, U. Bibcode: 1979BAAS...11..676M Altcode: No abstract at ADS Title: SOLEX Solar Flare X-ray Spectra from 5 to 23 Å Authors: Landecker, P. B.; McKenzie, D. L.; Broussard, R. M.; Rugge, H. R.; Young, R. M.; Doschek, G. A.; Feldman, U. Bibcode: 1979BAAS...11Q.709L Altcode: No abstract at ADS Title: New atomic data for Si/6+/, S/8+/ and Ar/10+/ Authors: Bhatia, A. K.; Feldman, U.; Doschek, G. A. Bibcode: 1979A&A....80...22B Altcode: The paper gives new atomic data, populations of excited levels, and line intensity ratios for the ions Si VII, S IX, and Ar XI of the O I isoelectronic sequence. Ten levels are included in the calculations, i.e., the levels of the 2s/2/2p/4/ and 2s2p/5/ and 2p/6/ configurations. It is noted that the calculations are done for applications to solar plasmas. The line ratios (2s/2/2p/4/3P1 - 2s2p/5/3P0) / (2s/2/2p/4/3P1 - 2s2p/5/3P1) and (2s/2/2p/4/1D2 - 2s2p/5/1P/1/) / (2s/2/2p/4/3P/1/ - 2s1p/5/3P/1/) are two of the ratios useful for electron density determination. Finally, density sensitive line ratios of Ca XIII and Fe XIX are also discussed. Title: The N III and O IV intersystem multiplets as density indicators for solar plasmas. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1979A&A....79..357F Altcode: The usefulness of the relative intensities of lines within the N III intersystem multiplet near 1750 A as an electron density indicator for solar plasmas is discussed. Although the relative intensities of lines in the multiplet are density sensitive, the intensity ratios should at present be used with caution. Errors of the order of 20% in transition probabilities and excitation rate coefficients can lead to order of magnitude errors in density determinations. It is demonstrated that the intensity ratio of one of the N III intersystem lines and an allowed line from a different ion may also be used as a density indicator in the 10 to the 9th to 10 to the 11th per cu cm regime. Title: High-resolution solar flare X-ray spectra. Authors: Doschek, G. A.; Kreplin, R. W.; Feldman, U. Bibcode: 1979ApJ...233L.157D Altcode: High-spectral-resolution solar flare spectra have been recorded by four Bragg crystal spectrometers flown by the Naval Research Laboratory on a spacecraft. The wavelength ranges are 1.82-1.97 A, 2.98-3.07 A, and 3.14-3.24 A. Electron temperatures ranging between 12 million and 30 million K are derived from dielectronic satellite to resonance-line ratios for an X9 flare that occurred on March 25, 1979. Nonthermal motions varying between about 70 and 160 km/s are derived from line profiles. Equilibrium conditions in the plasma are investigated by using lithium-like satellite lines excited by electron impact excitation. Emission measures of about 5 x 10 to the 50th per cu cm are determined for the times of maximum X-ray flux. Title: EUV limb spectra of a surge observed from Skylab. Authors: Doschek, G. A.; Feldman, U.; Mason, H. E. Bibcode: 1979A&A....78..342D Altcode: The EUV spectra of a surge observed at plus 8 in. and plus 20 in. above the white light limb from Skylab are examined. The shape of the differential emission measure determined at 8 in. and 20 in. is nearly the same as for a quiet Sun spectrum at 8 in., but the emission measure of the surge at 8 in. is about an order of magnitude greater than for the quiet Sun. At 20 in. the emission measure of the surge is initially close to the quiet Sun distribution, but decreases by a factor of 4 within 6 min. The optically thin lines formed near 10 to the 5th power K show nonthermal broadening at 8 in., and electron densities near this temperature are derived from intersystem to resonance ratios. The volume of the emitting plasma at 8 in. above the limb was determined, concluding that a continuous energy input is required to explain the observations. Title: The Fe XXI lambda 1354 line in solar flares observed from Skylab and its implications on ionization equilibrium calculations. Authors: Cheng, C. -C.; Feldman, U.; Doschek, G. A. Bibcode: 1979ApJ...233..736C Altcode: We have measured the line width of the forbidden line Fe xxi Al 354 in flare spectra observed from Skylab. The measured line widths are examined using three sets of ionization equilibrium calculations by Jordan, Summers, and Jacobs et al. The results indicate that the ionization equilibrium temperature of Fe xxi is more likely to be 1.0 x 10 K, a value given by Jacobs et al. and Jordan, rather than the higher value of 2.0 x 10 K given by Summers. Subject headings: Sun: flares - Sun: spectra Title: Extreme-ultraviolet limb spectra of a prominence observed from Skylab. Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U. Bibcode: 1979ApJ...232..929M Altcode: Line profiles of extreme ultraviolet emission lines observed in a solar prominence at positions above the white-light limb with the NRL slit spectrograph on Skylab are discussed. Absolute line intensities and full widths at half-maximum are presented, and emission measures, electron densities, and mass motions are derived at several locations within the prominence. For electron temperatures less than 40,000 K, the calculated mass motions are found to be near zero, while for electron temperatures greater than 40,000 K, the nonthermal velocity decreases with increasing height in the prominence. It is suggested that falling material is responsible for the fact that the measured electron density decreases with height less rapidly than the decrease predicted for a hydrostatic gas. In addition, from the He II 1640 A line profile, an average temperature of 27,000 K is derived for the region in which He II is emitted. Title: New atomic data for O+2. Authors: Bhatia, A. K.; Doschek, G. A.; Feldman, U. Bibcode: 1979A&A....76..359B Altcode: New atomic data are tabulated for the ion O(2+). Collision strengths are calculated for several energies of the exciting electron. The populations of the levels of O(2+) are calculated as a function of electron density under conditions appropriate for the solar atmosphere. The available solar data are compared with theoretical predictions of relative line intensities. Title: Solar flare spectroscopic diagnostics for wavelengths less than 2000 angstroms Authors: Doschek, G. A.; Feldman, U. Bibcode: 1979nrl..reptQ....D Altcode: We discuss the use of intensity ratios of emission lines for determining the electron density and temperature in flare plasmas. The availability diagnostics cover the temperature range from about 40,000 K to about 10,000,000 K. We summarize the current work on flare density diagnostics and review the applications of this theory to available flare spectra. We discuss the importance of line profiles for determining nonthermal mass motions in the plasma and for estimating path lengths along the line of sight. We review the current information on line profiles in flare spectra. We comment on determining departures from ionization equilibrium using line ratios in the X-ray and EUV regions. Title: On the structure of the solar transition zone and lower corona. Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T. Bibcode: 1979ApJ...229..369F Altcode: Recent observations of the solar transition zone and corona obtained primarily from NRL spectrographs on Skylab are summarized and used to examine the structure of the transition zone. The transition zone is revealed to be more inhomogeneous than is apparent from spectroheliograms with spatial resolution of about 3 arcsec. Transition-zone emission appears to arise in spicularlike structures. The effective area covered by the emitting structures at lower transition-zone temperatures (about 100,000 K) is only about 1% of the total surface area of the sun. The transition zone is highly inhomogeneous even over cell interior regions, where fluctuations in brightness by factors of 25 can occur. It is shown that homogeneous coronal models are not valid for the inner corona. Most of the higher-density inner corona is concentrated into looplike structures that extend down to the white-light limb. These structures are unrelated to the spicular-type structures that produce most of the transition-zone emission. Title: Fe XXI as an electron density diagnostic in solar flares. Authors: Mason, H. E.; Bhatia, A. K.; Doschek, G. A.; Feldman, U. Bibcode: 1979A&A....73...74M Altcode: Atomic data have been calculated for Fe XXI, and the theoretical intensity ratios for many transitions are tabulated. Fe XXI lines in wavelength regions 1-25 A, 90-200 A, and 300-2500 A are discussed with reference to presently available solar and laboratory spectra. It is found that Fe XXI is an excellent density diagnostic for solar-flare and tokamak plasmas, when densities are in the range from 10 to the 11th to 10 to the 15th per cu cm. The theoretical calculations are applied to flare spectra obtained from OSO 5, and an electron density of less than 10 to the 13th per cu cm is deduced for a temperature of 10,000,000 K. The results are somewhat ambiguous in several cases because of the limited spectral and temporal resolution of these earlier spectrometers. However, the calculations will be important for forthcoming solar projects, such as the Solar Maximum Mission. Title: High Resolution Solar Flare X-Ray Spectra Authors: Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Bell, W. D.; Wassam, W. W. Bibcode: 1979BAAS...11..421K Altcode: No abstract at ADS Title: Nonthermal broadening of extreme ultraviolet emission lines near the solar limb. Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A. Bibcode: 1979A&A....73..361M Altcode: Summary. Line profiles of optically thin extreme ultraviolet emission lines observed in quiet-Sun regions at 8', 12', and 20' above the white light limb with the NRL slit spectrograph (5082-B) on Skylab are discussed. Random mass-motion velocities are calculated. The velocity is found to increase with increasing height above the white light limb for all the lines regardless of the temperature of formation between 4 l0 K and 2l0 K. At +12' a typical velocity is about 33km -1 Key words: Sun - transition zone - EUV spectra Title: The dynamical properties of the solar corona from intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII. Authors: Cheng, C. -C.; Doschek, G. A.; Feldman, U. Bibcode: 1979ApJ...227.1037C Altcode: We have studied the line profiles of the solar coronal forbidden lines Si viii 1445.76 A, Fe XI 1467.08 A, and Fe xii 1242.03 A in quiet and active coronal regions from a survey of available limb spectra in the NRL Skylab data. The results show that the line widths of these lines are essentially the same in quiet-Sun regions as in active regions. For some active regions, however, the line widths are systematically narrower than those in quiet-Sun regions. In addition, the line widths are about the same in the height range from 0" to 30 . The widths are wider than the thermal Doppler widths at the ionization equilibrium temperature given by Jordan. The additional widths correspond to a nonthermal mass-motion velocity of 10-25 km -1 at 1.7 x 106 K (Fe xii), 10-17 km -1 at 1.5 x 10 K (Fe xi), and 10-20 km -1 at 9.3 x 10 K (Si viii). The intensities of the forbidden lines in active regions are about an order of magnitude greater than those in quiet-Sun regions. The distribution of column density calculated for the three different lines indicates that more plasma is near 1.7 x 106 K than near 9.3 x 10 K at a given height. The observational results are discussed in terms of coronal heating mechanisms. The dissipation of acoustic waves does not provide a sufficient heating rate. The dissipation of three modes of hydromagnetic waves-the slow mode, the fast mode, and the AlfVe'n mode-also cannot satisfactorily explain the observational results. It is difficult for heating by hydromagnetic waves to meet simultaneously the requirements of a large enough heating rate, a dissipation length comparable to the length of a coronal loop, and a velocity amplitude that agrees with observations. Subject headings: line profiles - Sun: corona - Sun: spectra - ultraviolet: spectra Title: L-series satellite spectra in Ti XII and Fe XVI. Authors: Burkhalter, P. G.; Cohen, L.; Cowan, R. D.; Feldman, U. Bibcode: 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. Bibcode: 1978ApJ...226..674F Altcode: Electron densities are derived in the solar inner corona from forbidden lines of S x near 1100 A. The density-sensitive line ratio considered is (4S0312-2D0312)/(4S0312-2D0612). The ratio is calculated as a function of density for four ions of the N I isoelectronic sequence, i.e., Mg VI, Si VIII, S x, and Ar XII. The variation of the ratio (4S0312-2P0312)/(4S0312-2D0312) with density is also calculated. The results are applied to off-limb spectra recorded by the NRL Skylab spectrograph. Densities were found to be the same in five quiet Sun regions and four active regions observed at heights > 8" outside the white-light limb. The average density derived from the S x lines for all regions considered is 1.0 x 10 cm -3. This result applies to plasma at the temperature of formation of S x, i.e., 1.3 x 106 K. At heights greater than 20" outside the limb the average density is 7.7 x 108 cm -3, and between 8" and 12" above the limb the average density is 1.0 x 10 cm 3, for both quiet Sun and active regions. Subject heading: Sun: corona Title: Densities in the quiet sun and polar coronal holes from EUV line ratios involving O III (1666.15 Å). Authors: Doschek, G. A.; Feldman, U.; Bhatia, A. K.; Mason, H. E. Bibcode: 1978ApJ...226.1129D Altcode: The EUV line intensity ratios C iii (1908.73 A)/o iii (1666.15 A), 0 iii (1666.15 A)/Si iv (1402.77 A), and C iii (1908.73 A)ISi iv (1402.77 A) are shown to be sensitive to variations in the electron density at densities typical of the quiet Sun ( 1010 cm - at 6 x 10 K). Using the 0 iii line, the above ratios can be normalized to observational data and densities in quiet-Sun regions and coronal holes can be determined. The average value of the density determined for three quiet-Sun regions is 1.9 x 1010 cm - . The densities determined from several observations of the north and south polar coronal holes are about the same as in the quiet Sun, with the exception of one set of observations of the north polar hole that indicates a density about a factor of 2 less than that of the quiet Sun. Subject headings: Sun: corona - Sun: spectra - ultraviolet: spectra Title: Measurements of extreme-ultraviolet emission-line profiles near the solar limb. Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A. Bibcode: 1978ApJ...226..698M Altcode: Line profiles of optically thin extreme-ultraviolet emission lines observed in a quiet sun region at positions within and above the white-light limb with the NRL slit spectrograph (S082-B) on Skylab are discussed. Absolute line intensities and full widths at half-maximum are presented for lines formed over the temperature range from about 10,000 to 22,000 K. The line intensities are compared with the predictions of simple atmospheric models consisting of a spicule component and a thin spherically symmetric or network models, but can be explained by assuming that the emission arises from spicule-like inhomogeneities. Random mass-motion velocities are calculated. The velocity increases with increasing temperature of line formation. Near the limb and above about 4000 K the calculated velocity is consistent with the predictions of a constant acoustic flux passing through the transition zone. For the ions formed at temperatures not less than about 63,000 K, the velocity is found to increase with increasing height above the white-light limb. Title: Electron densities in stellar atmospheres determined from IUE spectra. Authors: Doschek, G. A.; Feldman, U.; Mariska, J. T.; Linsky, J. L. Bibcode: 1978ApJ...226L..35D Altcode: No abstract at ADS Title: EUV spectra from Skylab (1175 - 1940 Å). Mass motions in the transition zone in regions of solar activity. Authors: Doschek, G. A.; Feldman, U. Bibcode: 1978A&A....69...11D Altcode: The profiles of spectral lines in the 1100-2000-A range emitted by transition-zone ions in regions of solar activity are discussed. The data were recorded by the NRL spectrograph on Skylab. At the spatial resolution of the Skylab spectrograph (2 x 60 arcsec), it is shown that the line profiles result from the superposed emission of a number of physically distinct regions at different electron densities and with different mass motions. Although high densities are found for some surgelike phenomena at transition-zone temperatures, the densities can also be comparable to normal active-region densities. Line profiles, as well as spectral line intensities, must be considered if meaningful theoretical models of dynamic activity in the transition zone are to be constructed. Title: 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. Bibcode: 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. Bibcode: 1978ApJS...37..443F Altcode: Skylab emission-line spectra (1175 to 1940 A) of two active regions on the solar limb are examined. Electron densities for the active regions are derived using the intensity ratios of selected intersystem and allowed lines. The intensity ratios in the active regions are compared with those observed previously in quiet-sun and coronal-hole regions. The behavior of coronal forbidden lines relative to transition-zone lines is discussed along with the solar continuum intensities near and above the limb. These continuum intensities are then compared with those at similar slit positions for the quiet sun and the previously studied coronal hole. The active-region data are found to be consistent with either (1) multithermal loops with the high-temperature plasma occupying the tops of the loops or (2) nearly isothermal loops with the hotter loops extending to higher altitudes. Title: XUV spectra of the 1973 June 15 solar flare observed from Skylab. III. A list of spectral lines from 1000 to 1940 Å. Authors: Cohen, L.; Feldman, U.; Doschek, G. A. Bibcode: 1978ApJS...37..393C Altcode: A wavelength list of spectral lines between 1000 and 1940 A is presented for the solar flare that occurred on June 15, 1973. The spectra were recorded by the NRL spectrograph on Skylab. The spectral resolution is 0.06 A. Intensities, identifications, and estimates of line widths are given. The intensity of the continuum is also given at 50-A intervals between 1400 and 1900 A. The wavelength list includes about 1400 lines; about 30% of these lines are not indentified. Because of the high wavelength resolution, this line list will be useful as a source of identification for some stellar as well as solar spectra. In particular, the list should be a useful aid in the identification of lines in the spectra of stars with classifications close to that of the sun. Spectra of such stars may be obtained from the recently launched IUE spacecraft. It is also interesting to compare the list with some of the spectra of early-type stars recorded by Copernicus. Title: The importance of spectroscopy in the 80 800 å region for plasma diagnostics in the solar atmosphere Authors: Feldman, U.; Doschek, G. A.; Behring, W. E. Bibcode: 1978SSRv...22..191F Altcode: We discuss the importance of the spectral range from about 80 to 800 Å for determining physical conditions in different regions of the solar atmosphere. We give examples of line ratios that may be used to determine electron densities in quiet Sun regions, active regions, and flares. We discuss the possibility of determining electron temperatures from line ratios in the EUV. We show that profiles as well as intensities of spectral lines must be obtained for a proper interpretation of the spectra. We give approximate parameters for a solar grazing incidence spectrograph suitable for the study of the 80 800 Å wavelength region. Title: The electron density at 105K in different regions of the solar atmosphere derived from an intersystem line of O IV. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1978A&A....65..215F Altcode: Summary. Electron densities are derived for typical solar active regions and flares from EUV spectral lines of 0 IV, N V, C iv and Si iv. The densities pertain to electron temperatures near 10 K. The spectra were recorded by the NRL spectrograph flown on Skylab. Typical densities found for active regions are 1011 . The density in flares can range from 1011 to above 1013 . The volumes of high density emitting plasma in active regions and flares are quite small, with values ranging from 1.5 1(Y cm3 to less than 2.2 1020 cm3. Also, the density in a polar coronal hole is about one-half of the density in a typical quiet Sun region, at a temperature near 6 1 K. Key words: Sun-transition zone-electron density Title: Nonthermal Broadening of Extreme Ultraviolet Emission Lines near the Solar Limb Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A. Bibcode: 1978BAAS...10..432M Altcode: No abstract at ADS Title: The Dynamical Properties of the Solar Corona from Intensities and Line Widths of EUV Forbidden Lines of Si VIII, Fe XI, and Fe XII. Authors: Cheng, C. C.; Doschek, G. A.; Feldman, U. Bibcode: 1978BAAS...10Q.439C Altcode: No abstract at ADS Title: Electron densities in solar flare and active region plasmas from a density-sensitive line ratio of Fe IX. Authors: Feldman, U.; Doschek, G. A.; Widing, K. G. Bibcode: 1978ApJ...219..304F Altcode: We demonstrate that the intensity ratio of the two lines of Fe IX at 241.739 and 244.911 A (3p53d 3P2 2p6 `So and 3p53d 3P, 2p6 `So) is sensitive to electron density above about 1010 . We calculate the intensity ratio as a function of density, and apply the result to two spectroheliograms of flares and surrounding plage regions recorded by the Naval Research Laboratory spectroheliograph on Skylab. We find that the densities at coronal temperatures of 106K vary considerably from region to region and can be at least as high as 2 x 10" cm 3. Subject headings: Sun: flares - Sun: spectroheliograms - ultraviolet: spectra Title: High-resolution spectra of the solar Mg II h and k lines from Skylab. Authors: Doschek, G. A.; Feldman, U. Bibcode: 1977ApJS...35..471D Altcode: Spectra of the Mg II h and k lines emitted by different regions in the solar atmosphere have been recorded by the NRL slit spectrograph on Skylab. The spectral resolution is 0.12 A, and the spatial resolution is 2 by 60 arcsec. Several examples are presented, including spectra of a chromospheric supergranulation cell boundary and interior and of a quiet-sun region above the limb, as well as selected active-region spectra on the disk and above the limb. Obvious differences among these spectra are noted and qualitatively discussed. Title: The solar spectrum in the vicinity of the Si IV lines at 1122 and 1128 Å. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1977A&A....61..295F Altcode: Summary. The extreme ultraviolet solar spectrum in the vicinity of the Si iv lines at 1122 and 1128 A is presented with a wavelength resolution of 0.06 A. The Si iv line at 1122.486 A is blended with an unresolved line of Fe "I at 1122.526 A. The Siiv line at 1128.340A is near two faint Fe iii lines. However, these lines will contribute little to the intensity of the Si iv line, even when the intensity is recorded with a wide spectrograph slit. Key words: extreme ultraviolet solar spectrum solar transition zone Title: A search for a turbulent-free region in the solar transition zone. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1977ApJ...216L.119F Altcode: A search for a turbulence-free transition-zone region was conducted. The data used were spectra recorded by a slit spectrograph on Skylab. It was found that the nonthermal turbulent motions are smallest in certain active regions and quiescent prominences. The spectra of one such region, a quiescent prominence, are discussed. The nonthermal turbulence in the region is between about 2 and 7 km/s. Therefore, the widths of lines emitted by transition-zone ions are determined primarily by the ion temperature. To within the experimental error, temperatures derived from the line widths are equal to the temperatures of maximum emitting efficiency obtained using the ionization equilibrium calculations of Jordan (1969). Title: Electron densities in solar flares from line ratios of Ca XVII. Authors: Doschek, G. A.; Feldman, U.; Dere, K. P. Bibcode: 1977A&A....60L..11D Altcode: Summary. We show that the intensity ratios of certain extreme ultraviolet spectral lines of Ca XVII are sensitive to electron density in solar flares. Calculations of the line ratios as functions of density are presented. These calculations are based on published atomic data for Ca XVII and for other ions of the beryllium isoelectronic sequence. For a flare that occurred on 9 August 1973, we derive a density of about 5 x 101 from the Ca XVII line ratios. Key words: solar flares - Be I sequence Title: XUV spectra of the 1973 June 15 solar flare observed from Skylab. I. Allowed transitions in chromospheric and transition zone ions. Authors: Doschek, G. A.; Feldman, U.; Rosenberg, F. D. Bibcode: 1977ApJ...215..329D Altcode: Spectra between 1100 and 1940 A of the 1973 June 15 solar flare are discussed. The spectra were recorded by the NRL normal-incidence slit spectrograph on Skylab. In this paper we discuss allowed transitions in ions formed in the chromosphere and transition zone. We give the power (ergs s-1) in the emission lines produced by the plasma viewed by the instrument, and we give the widths and shapes of the line profiles as a function of time during the flare. We calculate emission measures and volumes of the flare plasma for lines of Si iv, C iv, and N V. The characteristic lengths (= V113) are quite small, ranging between 0' 1 to 1'.'0. The smaller values are the more reliable. The flare can be qualitatively divided into two distinct phases. An eruptive phase occurs near the beginning of the flare and lasts for about 2 minutes. Plasma is observed moving toward the observer at velocities as high as km 1 during this phase. A continuous energy input is necessary to account for the lifetime of the moving plasma. A much longer lived quiescent phase follows the eruptive phase and lasts for about 23 minutes. Subject headings: Sun: chromosphere - Sun: flares - Sun: spectra - ultraviolet: spectra Title: XUV spectra of the 1973 June 15 solar flares observed from Skylab. II. Intersystem and forbidden transitions in transition zone and coronal ions. Authors: Feldman, U.; Doschek, G. A.; Rosenberg, F. D. Bibcode: 1977ApJ...215..652F Altcode: An analysis is given of the intersystem lines of transition zone ions and high-temperature forbidden lines for the 1973 June 15 flare. The electron density in the erupting part of the plasma is at least 1013 at temperatures of 1.3 x l0 K. The density of the stationary component of the flare plasma at similar temperatures varies between 1.5 x 1011 and 1012 . A density decrease observed in the stationary component occurs nearly simultaneously with an intensity enhancement of forbidden coronal lines such as Fe xii. These lines are believed to originate in arch-type structures. The electron density in the temperature regions 1.5 x 106K is between 2 x 1010 cm-3 and 2 x 1011 cm-3. These regions appear to be stationary. Their motion relative to the observer is less than 4 km 1 A continuous energy input is necessary to account for the transition zone emission. The transition zone emission arises in small regions, perhaps filaments. Subject headings: plasmas - Sun: flares - Sun: spectra - ultraviolet: spectra Title: On the problem of density diagnostics for the EUV spectrum of the solar transition zone. Authors: Doschek, G. A.; Feldman, U. Bibcode: 1977A&A....58L..13D Altcode: Spectral-line ratios that may be used to determine the electron temperature and density in the solar transition zone and corona are identified. The problem of interpreting the intensity ratios of C III lines observed in Skylab EUV limb spectra is considered. It is shown that the intensity distribution with height above the solar limb of the 1176-A C III lines is different from that of the 1909-A C III lines in the Skylab spectra, suggesting that model atmospheres must be folded into the C III calculations for proper interpretation of the data. Possible reasons for the differences in the intensity distributions and widths of the 1176-A and 1909-A lines are discussed along with an application to the analogous lines of Si III. Title: The 3s-3p and 3p-3d lines of Mg II observed above the solar limb from Skylab. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1977ApJ...212L.147F Altcode: No abstract at ADS Title: The emission spectrum of the hydrogen Balmer series observed above the solar limb from Skylab. I. A quiet Sun and a polar coronal hole. Authors: Rosenberg, F. D.; Feldman, U.; Doschek, G. A. Bibcode: 1977ApJ...212..905R Altcode: The hydrogen Balmer emission-line spectrum (H9 [3835 A] to the series limit at 3646 A) above the limb of the quiet Sun and above the north polar coronal hole is discussed. The data were obtained by the NRL XUV spectrograph aboard Skylab, with the slit tangent to the limb at 2" (1450 km) and at 4" (2900 km) above the limb. Electron densities of 2 x 1011 cm - , 2" above the limb of both the quiet Sun and coronal hole, are calculated from the Stark broadening of the higher series member lines, and the related merging of the higher member lines. The widths of the lines with principal quantum number m < 15 are broadened by opacity, and the opacities are estimated from the line widths. The widths of lines of m 15 are not appreciably affected by either opacity or Stark broadening. The combined ion temperature and nonthermal mass motion determined from the widths of these lines are consistent with previously determined values. The intensities of the lines indicate that the upper levels (>9) are populated in statistical equilibrium with each other. Absolute intensities are given, as well as the decrease of the intensity of the lines as a function of height above the limb. The Balmer emission-line spectrum above the limb over three active regions is discussed in the following paper. Subject headings: Sun: corona - Sun: spectra Title: The Emission Spectrum of the Hydrogen Balmer Series Observed above the Solar Limb from SKYLAB. II. Active Regions . . . . Authors: Feldman, U.; Doschek, G. A. Bibcode: 1977ApJ...212..913F Altcode: Electron densities are determined from the Stark broadening of Balmer hydrogen lines at 2" above the limb over three active regions. The spectra were recorded by the NRL slit spectrograph on Skylab. The density was found to be the same for all three regions and is 2 x 1011 with an error of less than 15% in fitting the theoretical curves to the data. The intensity falloff of the hydrogen lines above the limb over the active regions is compared with previous results obtained over a quiet Sun region and a polar coronal hole. The falloff is also compared with the intensity falloff of optically thin lines of Si II, Mg II, C II, singly ionized metals, and the neutral element, O I, recorded over a quiet Sun region. From this comparison, the temperature of the hydrogen plasma in all of the quiet and active regions that we observed is no more than about 8000 K. The intensity decrease of the hydrogen lines is the same as the intensity falloff of intersystem lines of 01. Nonthermal velocities of the hydrogen lines over the active regions are also derived. At 2" above the limb, these range from 0 km 1 to about 15 km s - . The lines of high members of the Balmer series are in Boltzmann equilibrium. The hydrogen observations are combined with our previous observations of singly ionized elements and are compared with observations of spicule s. Subject headings: Sun: chromosphere - Sun: corona - Sun: spectra Title: The coronal temperature and nonthermal motions in a coronal hole compared with other solar regions. Authors: Doschek, G. A.; Feldman, U. Bibcode: 1977ApJ...212L.143D Altcode: The coronal lines Si VIII (1446 A), Fe X (1463 A), Fe XI (1467 A), and Fe XII (1242 A and 1349 A) were observed above the limb over a quiet region, a coronal hole, and two active regions. The lines emitted at temperatures greater than 1 million K; i.e., the iron lines, are not observed in the coronal-hole spectra, so the indication is that in the coronal hole most of the plasma is at a temperature of less than 1 million K. The emission measures and column densities of the lines are derived from available atomic cross-section data, and the results are discussed. The nonthermal velocities in the coronal hole and quiet region are about 20 km/s. The velocities in the active regions are substantially less. Title: Observations of a Radiatively Cooling Subflare. Authors: Antiochos, S. K.; Underwood, J. H.; Feldman, U. Bibcode: 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. Bibcode: 1977ApJS...33..101D Altcode: Chromospheric limb spectra of a quiet-sun region between 2000 and 3200 A recorded by the normal-incidence spectrograph on Skylab are discussed. The spectral resolution is 0.12 A, and the projected slit area on the sun is 2 by 60 arcsec. A list of lines with wavelengths, identifications, and absolute intensities is given for the spectrum recorded at +4 arcsec outside the white-light limb. The intensity behavior outside the limb is shown for lines of the ions C II, Si II, Cr II, Mn II, Fe II, Fe III, Co II, and Ni II. The widths of the intersystem lines of Si II and C II increase monotonically with height above the limb. The full width at half-maximum of the Si II lines increases from 0.034 A at the limb to 0.27 A at +12 arcsec above the limb. The widths of the C II lines increase from 0.17 A at +2 arcsec to 0.31 A at +12 arcsec. Title: EUV Spectroscopy of Solar Transition-Zone Plasmas. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1977uxsa.coll...11F Altcode: 1977IAUCo..43...11F No abstract at ADS Title: Plasma diagnostics using high-resolution spectroscopic techniques. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1977JOSA...67..726F Altcode: 1977OSAJ...67..726F No abstract at ADS Title: Recent High Spectral and Spatial Resolution Spectroscopy of Laser-Produced Plasmas and Electron-Ion Beam Plasmas. Authors: Doschek, G. A.; Feldman, U.; Johnson, D. J.; Nagel, D. J. Bibcode: 1977uxsa.coll...18D Altcode: 1977IAUCo..43...18D No abstract at ADS Title: The emission-line spectrum of a sunspot in the far-ultraviolet. Authors: Cheng, C. -C.; Doschek, G. A.; Feldman, U. Bibcode: 1976ApJ...210..836C Altcode: The emission-line spectrum between 1200 and 1817 A from a sunspot in McMath region 12510 near the solar center is discussed. The spectrum was obtained by the normal-incidence spectrograph on Skylab. The principal results are: (1) the widths of emission lines originating in the chromosphere and lower transition region over the sunspot are much narrower than those previously reported for a polar coronal hole observed above the limb and a quiet chromospheric network observed near the solar center, indicating that the mass motions in the sunspot are less than in these other regions; (2) the sunspot spectrum, aside from the narrow widths of emission lines, is similar to spectra from the chromospheric network boundary. The intensities of lines in the sunspot are much enhanced relative to the network interior. From the full-width at half-maximum of the 1207-A Si III line, an optical depth at line center of 3.6 is deduced. Comparison with Parker's (1974) theory of sunspots shows that, if the enhancement of emission lines is due to enhanced transport of hydromagnetic waves generated in the sunspot convective zone, the mode of the waves is predominately Alfvenic. Title: The quiet sun chromospheric network observed from Skylab. Authors: Feldman, U.; Doschek, G. A.; Patterson, N. P. Bibcode: 1976ApJ...209..270F Altcode: The paper analyzes spectra of a supergranulation cell interior and cell boundary obtained near the solar center at wavelengths between 1200 and 1560 A with a normal-incidence spectrograph aboard Skylab. Absolute intensities, relative intensities, and profiles are given for selected optically thin and optically thick lines over the cell interior, the boundary, and intermediate positions; the results are compared with spectra obtained at the limb. Characteristic lengths along the line of sight are derived for the Si III emitting region, and these are compared with the predictions of Gabriel's (1975) model. It is concluded that the present data are representative of a fairly typical cell interior and boundary, that nonthermal motions are isotropic and the same for the interior and boundary, and that the electron-density ratio between the interior and the boundary is about a factor of two or less. Title: EUV Spectra of the 15 June 1973 Solar Flare Observed from Skylab. Authors: Doschek, G. A.; Feldman, U.; Rosenberg, F. Bibcode: 1976BAAS....8..555D Altcode: No abstract at ADS Title: The Solar Mg II h and k Lines Observed from Skylab. Authors: Feldman, U.; Doschek, G. A. Bibcode: 1976BAAS....8..523F Altcode: No abstract at ADS Title: Exploring plasmas: in the Sun and in the laboratory. Authors: Doschek, G. A.; Feldman, U. Bibcode: 1976AsAer..14...24D Altcode: 1976AsAau..14...24D In recent years, high-resolution spectroscopy in the X-ray, extreme-ultraviolet, ultraviolet, and visible spectral regions has found increasing application for the study of conditions in solar plasmas. The use of spectroscopic techniques in the X-ray and extreme-ultraviolet spectral regions to determine such physical quantities as electron and ion temperature, electron and ion density, turbulence or anisotropic motions, and the departure of the ionic species from kinetic equilibrium in solar and laboratory plasmas is discussed. Solar-flare spectra are compared to the spectra of active solar regions. Title: XUV spectrum of CI observed from Skylab during a solar flare. Authors: Feldman, U.; Brown, C. M.; Doschek, G. A.; Moore, C. E.; Rosenberg, F. D. Bibcode: 1976JOSA...66..853F Altcode: 1976OSAJ...66..853F A list of 193 neutral carbon lines observed in the XUV spectrum of a solar flare between 100 and 2000 A using the normal incidence spectrograph flown on Skylab is presented. Of these, 69 are newly identified lines arising from transitions from upper levels of high quantum number where the quantum number is not less than six. The new lines have allowed the determination of 63 new energy levels. Wavelengths for an additional 109 transitions were calculated by polynomial fitting using reference wavelengths of unblended neutral carbon, Si, N, and S lines emitted in the same atmospheric regions of the flare. The calculated lines falling between 1102 and 1140 A were not observed due to low instrumental efficiency at these wavelengths. The calculated wavelengths are in excellent agreement with those of Johansson (1965). It appears that in solar spectra recombination processes are dominant, enhancing the populations of the high quantum levels relative to the populations of levels with small quantum numbers. Title: The emission-line spectrum above the limb of a solar coronal hole: 1175 - 1940 Å. Authors: Feldman, U.; Doschek, G. A.; Vanhoosier, M. E.; Purcell, J. D. Bibcode: 1976ApJS...31..445F Altcode: Emission-line spectra of a coronal hole that coincided with the north pole of the sun are discussed which were obtained with a slit spectrograph aboard Skylab at positions within and above the solar white-light limb in the wavelength range from 1175 to 1940 A. Relative line intensities, line profiles, and full widths at half-maximum are presented for selected chromospheric and transition-zone lines observed above the present polar coronal hole. Average mass motions in the transition zone are determined as a function of electron temperature from the widths of the optically thin lines by assuming ionization equilibrium. The line intensities and profiles are compared with corresponding results deduced from spectra obtained above a quiet solar region. The coronal-hole spectra are found to imply an angular dependence for the source function as well as a radial dependence such that the source function is the smallest at the south pole and increases with decreasing solar latitude. Title: The emission-line spectrum above the limb of the quiet sun: 1175 - 1940 Å. Authors: Doschek, G. A.; Feldman, U.; Vanhoosier, M. E.; Bartoe, J. -D. F. Bibcode: 1976ApJS...31..417D Altcode: Spectra of a quiet solar region obtained at positions within and above the solar white-light limb in the wavelength region from 1175 to 1940 A are discussed. The spectra were obtained by the slit spectrograph (SO82-B) on Skylab. The spectral resolution is 0.06 A, and the projected slit area on the sun was 2 x 60 arcsec (1450 x 43500 km). Relative line intensities are presented for lines formed in the temperature region of the solar atmosphere from about 8000 to 220,000 K. Representative line profiles of both optically thin and optically thick lines are shown as a function of height above the limb. Random mass-motion velocities are deduced from the optically thin lines, and the relative intensities and profiles of the lines are discussed in terms of current theoretical models. A wavelength list with identifications is given for the spectrum obtained at +4 arcsec above the white-light limb. Title: Spectroscopy from Laser-produced Plasmas at Flare Temperatures Authors: Feldman, U. Bibcode: 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. Bibcode: 1976ApJ...205L.177D Altcode: Wavelengths of lines of the transition-zone ions Si IV, C IV, O IV, N V, and O V are observed to be redshifted relative to the wavelengths of chromospheric lines in XUV spectra obtained from the normal-incidence spectrograph on Skylab. The spectra cover the wavelength range from 1200 to 1565 A and were obtained with the slit positioned over chromospheric network and cell regions, on coronal holes, and above the limb. The network-area and coronal-hole spectra were obtained near the disk center. Only some of the spectra show redshifted transition-zone lines. The observed shifts are between 0.03 and 0.08 A, implying velocities of 15 km/s or less. The amount of wavelength shift does not always appear to be the same for lines of different ions. The shifts imply that descending plasma in the solar atmosphere produces more emission than ascending plasma at temperatures between approximately 70,000 and 200,000 K. Title: Densities in the Solar Chromosphere above the Quiet sun and a Coronal Hole Derived from the Hydrogen Balmer Lines Authors: Rosenberg, F. D.; Feldman, U.; Doschek, G. A. Bibcode: 1976BAAS....8..338R Altcode: No abstract at ADS Title: The solar spectrum: wavelengths and identifications from 160 to 770 Ångstroms. Authors: Behring, W. E.; Cohen, L.; Feldman, U.; Doschek, G. A. Bibcode: 1976ApJ...203..521B Altcode: The full-Sun solar spectrum from 160 to 770 A was photographed under quiet solar conditions by a rocket-borne spectrograph flown in 1973 September. The spectral resolution is 0.06 A or better. We present a composite list of spectral lines, including wavelengths, identifications, and approximate intensities that were obtained from the present flight and from a previous flight in 1969 May. This line list contains the most accurate solar wavelengths yet obtained in this spectral region. One result is improved energy levels which are given for the two lowest energy configurations of Fe ix through Fe xvi. No detectable relative mass motions of more than 4 km s ' exist between transition zone and coronal regions averaged over the visible disk of the Sun. The wavelengths of emission lines in this spectrum were determined with indicated accuracies ranging between 2 and 20 mA. The spectrograph employed a 3 m radius, 600 grooves mm ' gold grating used at grazing incidence. Subject headings: line identifications - Sun: corona - Sun: spectra - ultraviolet: spectra Title: Limb-brightening curves of XUV transition zone lines in the quiet sun and in a polar coronal hole observed from Skylab. Authors: Doschek, G. A.; Feldman, U.; Tousey, R. Bibcode: 1975ApJ...202L.151D Altcode: Solar limb-brightening curves are discussed for XUV spectral lines formed in the upper chromosphere and transition zone of a quiet region and a polar coronal hole. The spectra were recorded with a slit spectrograph on Skylab. The lines considered are emitted from ions formed within the temperature range from 10,000 to 220,000 K. The limb-brightening curves cover a region from -4 sec within the limb to +20 sec above it. The data from 0 sec to +20 sec are compared with predictions based on both homogeneous and inhomogeneous models of the transition zone. The limb-brightening curve of the O I line at 1355.6 A indicates that O I is formed in spicules. The limb brightening of the He II line at 1640.4 A is consistent with a temperature of formation between about 40,000 and 90,000 K for He II. Title: The intensities and profiles of XUV transition zone lines in a quiet sun region compared to a polar coronal hole. Authors: Feldman, U.; Doschek, G. A.; Tousey, R. Bibcode: 1975ApJ...202L.147F Altcode: The intensities of XUV transition-zone lines from limb spectra of a quiet-sun region and a polar coronal hole are compared. The spectra were obtained with a slit spectrograph on Skylab and cover a region from -12 sec within the limb to 20 sec above it. The lines selected for comparison are formed at temperatures that range from 36,000 to 220,000 K. Lines of the higher-temperature ions, e.g. O v, are significantly less intense in the coronal hole, and lines of lower-temperature ions show little change. Profiles of selected optically thin transition-zone lines from the quiet-sun and coronal-hole spectra are also shown. The lines are broader than expected in ionization equilibrium, and bulk-motion velocities are deduced from the widths of the lines. There appears to be little, if any, statistically significant difference in the velocities obtained from the quiet-sun region and the coronal hole. Title: The spatial and temperature structure of vacuum spark plasmas. Authors: Feldman, U.; Goldsmith, S.; Schwob, J. L.; Doschek, G. A. Bibcode: 1975ApJ...201..225F Altcode: The spatial and temperature structures of the X-ray emitting components of low-inductance vacuum-spark plasmas are investigated. The plasmas produced by low-inductance vacuum sparks show striking resemblances to solar-flare plasmas. High-resolution photographs show that the spark plasmas are composed of hot (about 30 million K) compact sources (less than 20 microns) and cooler (about 10 million K) larger sources (of the order of 100 microns). Both types of sources may be produced by the same plasma at different times. The differences between the solar flare iron-line spectrum near 1.9 A and the spark iron-line spectrum are discussed and interpreted. Title: Density sensitive lines of highly ionized iron Authors: Doschek, G. A.; Feldman, U.; Davis, J.; Cowan, R. D. Bibcode: 1975PhRvA..12..980D Altcode: Spectral lines from ions in the nitrogen isoelectronic sequence due to transitions of the type, 2s2p42D32,52-2p52P32, and 2s2p42D32-2p52P12, are identified in the 100-Å region in laser-produced plasma spectra of titanium (Ti xvi) through cobalt (Co xxi). It is proposed that the intensities of these lines relative to the intensities of lines of the same ions due to transitions of the type 2s22p3-2s2p4 are sensitive to electron density in the range from ~ 1018 to ~ 1020 cm-3. Calculations are performed for Fe xx, and a similar calculation is performed for a density-sensitive line ratio of Fe xix, i.e., (2s2p51P1-2p61S0)(2s22p41S0-2s2p51P1). This line ratio is also sensitive to electron density between about 1018 and 1020 cm-3. The 2s2p51P1-2p61S0 line is newly indentified in Cr xvii, Co xx, and Ni xxi. Title: The 1640.4 Å Halpha line of He II observed from Skylab. Authors: Feldman, U.; Doschek, G. A.; Vanhoosier, M. E.; Tousey, R. Bibcode: 1975ApJ...199L..67F Altcode: Profiles obtained from NRL Skylab solar spectra of the 1640.4 A feature identified as the H-alpha line of He II are discussed and compared with theoretical profiles derived assuming (1) collisional excitation and (2) radiative recombination as the dominant excitation mechanism. Relative intensities of this line as a function of altitude above and below the solar white-light limb are also given for a representative quiet sun region and for a polar coronal hole. Title: Forbidden lines of highly ionized iron in solar flare spectra. Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.; Sandlin, G. D.; Vanhoosier, M. E.; Brueckner, G. E.; Purcell, J. D.; Tousey, R. Bibcode: 1975ApJ...196L..83D Altcode: No abstract at ADS Title: Transitions 2s'2pk -2s2p"I of the N i and C i Isoelectronic Sequences Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, Leonard Bibcode: 1975ApJ...196..613F Altcode: Transitions of the type +1 have been identified for the elements from titanium through iron for ions of the nitrogen isoelectronic sequence and for the elements titanium through nickel for ions of the carbon isoelectronic sequence. Wavelengths, intensity estimates and energies are given. The lines were identified from EUV spectra obtained from laser-produced plasmas. The energy differences of levels of the ground configuration for the C I isoelectronic sequence are compared with extrapolations based on semiempirical equations derived by Edlen. Wavelengths of forbidden Fe XXI lines that can be seen in low-density plasmas such as solar flare plasmas are predicted. The laser plasma spectrum is briefly compared with available solar flare spectra. Subject headings: flares, solar - line identifications - spectra, laboratory - spectra, ultraviolet Title: Transitions 2s22p-2s2p2 in the B I isoelectronic sequence. Authors: Doschek, G. A.; Feldman, U.; Cohen, L. Bibcode: 1975JOSA...65..463D Altcode: 1975OSAJ...65..463D No abstract at ADS Title: Meteorological Conditions near the Wise Observatory, Israel Authors: Vidal, N. V.; Feldman, U. Bibcode: 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. Bibcode: 1974ApJ...192..213F Altcode: We have obtained X-ray spectra of high-temperature plasmas produced by the 100 GW glass laser at the Naval Research Laboratory. In this paper, we discuss the satellite lines of hydrogen-like and helium-like ions, observed in the 2-12 A region for elements ranging from sodium through titanium. The satellite lines are due to transitions of the type, lsnl-2pnl, ls2nl-ls2pnl, n = 2, 3; and ls22l-ls2l3p. Physical conditions in the plasma are discussed in terms of relative line-intensity ratios and line profiles. Subject headings: plasmas - spectra, laboratory - spectra, X-ray Title: The Widths of the Solar he i and he II Lines at 584, 537, and 304 Å Authors: Doschek, G. A.; Behring, W. E.; Feldman, U. Bibcode: 1974ApJ...190L.141D Altcode: In this Letter we report direct measurements from a rocket spectrograph of the widths of the solar He I lines, 152 1s2p and 1s2-1s3p, at 584 and 537 A. We also report the width of the solar resonance line of He II at 304 A. The deduced full widths at hall-maximum intensity are 0.14,0.12, and 0.10 A for the 584, 537, and 304 A lines, respectively. These widths represent averages over the entire Sun. Line profiles corrected for the nonlinear film response are presented for the 584 and 304 A lines. Subject headings: line profiles - spectra, solar Title: Solar Coronal Line Profiles in the Extreme-Ultraviolet Authors: Feldman, U.; Behring, W. E. Bibcode: 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 Bibcode: 1974BAAS....6T.286D Altcode: No abstract at ADS Title: Transitions 2S22pk -2s2 pk+, of the F i, 0 I, and N i Isoelectronic Sequences Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.; Cohen, Leonard Bibcode: 1974ApJ...188..417D Altcode: Transitions of the type, 2s +1, have been identified for the elements from titanium through nickel for ions of the fluorine, oxygen, and nitrogen isoelectronic sequences. Wavelengths, visual intensity estimates, and energies are given. The energy differences of levels of the ground configuration are compared with predictions based on semiempirical equations derived by Edlen. Some of the lines of these isoelectronic sequences should be strong lines in solar-flare spectra. Subject headings: line identifications - spectra, laboratory - spectra, ultraviolet Title: The Width of the Solar 584 Å Line of Neutral Helium Authors: Behring, W. E.; Doschek, G. A.; Feldman, U.; Cohen, Leonard; Houston, James Bibcode: 1974BAAS....6R.284B Altcode: No abstract at ADS Title: X-ray Satellite Lines of Hydrogenlike and Heliumlike Ions Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Cowan, R. D.; Whitlock, R. R. Bibcode: 1974BAAS....6R.286F Altcode: No abstract at ADS Title: Laser-Plasma Spectra of Highly Ionized Fluorine Authors: Feldman, U.; Doschek, G. A.; Nagel, J.; Behring, W. E.; Cowan, R. D. Bibcode: 1974ApJ...187..417F Altcode: Lines between 11.3 A and 17.2 A of lithium-like, helium-like, and hydrogen-like fluorine have been observed in spectra of laser-produced plasmas. These lines include nine members of the Lyman series of F IX; eight members of the principal series of F VIII; and satellite lines arising from doubly excited configurations of F VII and F VIII. Similar satellite lines of the abundant solar elements have been identified in soft X-ray spectra of solar flares. A wavelength list of fluorine lines is given, and physical conditions in the plasma are discussed. Subject headings: flares, solar - line identifications - plasmas - spectra, laboratory - spectra, X-ray Title: Transitions of Fe XVIII and Fe XIX Observed in Laser-Produced Plasmas Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Behring, W. E.; Cohen, Leonard Bibcode: 1973ApJ...183L..43F Altcode: Lines of Fe xvm and Fe XIX near 100 A have been ohserved in spectra from plasmas produced by 5-joule laser pulses of 0.9 ns duration. These lines produced by transitions of the type 2s2 +1 Transitions of the type -131 are prominent in the spectra below 20 A observed during solar flares. The splittings of the ground levels are obtained and compared with isoelectronic extrapolations. The corresponding forbidden lines as well as the allowed lines near 100 A inay be observable in flare spectra with some of the instruments to be flown on Skylab. Subject headings: flares, solar - spectra, ultraviolet - spectra, X-ray Title: Fluorine isoelectronic sequence. Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, L. Bibcode: 1973JOSA...63.1445F Altcode: No abstract at ADS Title: High-resolution rocket EUV solar spectrograph. Authors: Behring, W. E.; Ugiansky, R. J.; Feldman, U. Bibcode: 1973JOSA...63R.484B Altcode: No abstract at ADS Title: High resolution rocket EUV solar spectrograph. Authors: Behring, W. E.; Ugiansky, R. J.; Feldman, U. Bibcode: 1973ApOpt..12..528B Altcode: No abstract at ADS Title: On I isoelectronic sequence: transitions 2p4-2p33s. Authors: Doschek, G. A.; Feldman, U.; Cohen, L. Bibcode: 1973JOSA...63.1463D Altcode: No abstract at ADS Title: Statistical Analysis of Multiple Absorption Spectra in QSO Authors: Shaviv, Giora; Feldman, Uri; Koslovsky, Ben-Zion Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Title: Improved Wavelengths and Identifications in the Solar Spectrum from 60-385 Å Authors: Behring, W. E.; Cohen, Leonard; Feldman, Uri Bibcode: 1972BAAS....4U.377B Altcode: No abstract at ADS Title: The Lithium-Like Spectra of K XVII Through MN XXIII in the Extremeultraviolet Region Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L. Bibcode: 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. 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. Bibcode: 1972JOSA...62..260G Altcode: No abstract at ADS Title: Extreme-ultraviolet spectra of Sc XIV, Ti XV, and V XVI. Authors: Goldsmith, S.; Feldman, U.; Cohen, L. Bibcode: 1971JOSA...61..615G Altcode: No abstract at ADS Title: Boron-like spectra: Mg VIII, Al IX, and Si X. Authors: Hoory, S.; Goldsmith, S.; Feldman, U.; Behring, W.; Cohen, L. Bibcode: 1971JOSA...61..504H Altcode: No abstract at ADS Title: Spectra of Fe, Co, Ni, and Cu isoelectronic with Na I and Mg I. Authors: Feldman, U.; Katz, L.; Behring, W.; Cohen, L. Bibcode: 1971JOSA...61...91F Altcode: No abstract at ADS Title: On the Rich Absorption Spectra of Three Quasi-Stellar Objects Authors: Bahcall, John N.; Feldman, Uri Bibcode: 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. 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. Bibcode: 1970ApJ...160..781H Altcode: In this work the identification and classification of the 3p63d-3p53d4s transitions are extended from Fe viii to Cu xi. Title: A Line List for an Iron-Spark Spectrum (10-18 Å) Authors: Cohen, Leonard; Feldman, Uri Bibcode: 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. Title: Lithium-like spectra in Mg, Al, and Si. Authors: Feldman, U.; Cohen, L.; Behring, W. Bibcode: 1970JOSA...60..891F Altcode: No abstract at ADS Title: C V Spectra Near the 1s-2p Line of C VI Authors: Feldman, Uri; Cohen, Leonard Bibcode: 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 Title: Round-the-Clock Photoheliography Authors: Zirin, Harold; Bohlin, J. David; Weart, Spencer; Feldman, Uri Bibcode: 1969BAAS....1..297Z Altcode: No abstract at ADS Title: Observations of the Sun and Laboratory Sources with a Three-Meter xuv Spectrograph Authors: Behring, W. E.; Cohen, L.; Saffer, K.; Feldman, U. Bibcode: 1969BAAS....1S.272B Altcode: No abstract at ADS Title: An Iron Spark Line List in the 10-18 Å Range and its Comparison with Flare Spectra Authors: Feldman, U.; Cohen, L. Bibcode: 1968ApJ...151L..55F Altcode: No abstract at ADS Title: Spectra of Solar Physics Interest Produced by a Vacuum Spark Source Authors: Feldman, U.; Cohen, L.; Underwood, J. H. Bibcode: 1968AJS....73Q..60F Altcode: No abstract at ADS Title: Newly Identified Lines in the NE i Isoelectronic Sequences Authors: Feldman, U.; Cohen, L. Bibcode: 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. Title: Newly Identified Resonance Lines of NI XIX, CU xx, and zn XXI Authors: Feldman, U.; Cohen, L.; Swartz, M. Bibcode: 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. Title: Unclassified 3p63d-3p53d4s Transition Lines of Fe VIII, Mn VII, and Cr VI Authors: Feldman, U.; Fraenkel, B. S. Bibcode: 1966ApJ...145..959F Altcode: No abstract at ADS 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. Bibcode: 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. Title: 3p6-3p53d Transitions of Fe IX and Ni XI in the Solar Spectrum Authors: Alexander, E.; Feldman, U.; Fraenkel, B. S.; Hoory, S. Bibcode: 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.