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NASA NTRS1985

Rocket observation of the ultraviolet spectrum of Comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on Feb. 26, 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 x 10 to the 29th/s and the volume mixing ratio of CO to H2O is 21 percent. The predicted brightness distribution from a radial outflow model with H2O and CO as parent molecules are in accordance with the measured spatial profiles of O I and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker C I emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3 percent of the water production rate is included in the model.

Woods, T. N.↗

NASA NTRS1987

X-ray and ultraviolet radiation from accreting white dwarfs. IV - Two-temperature treatment with electron thermal conduction

Results are reported from two-temperature calculations of the structures and X-ray spectra of radiation shocks generated by accretion onto nonmagnetic white dwarfs. The approach was necessitated by the domination of bremsstrahlung in the emission region by Compton cooling. Features of the shock model, which includes steady, spherical infall of fully ionized plasma and dominance of the stand-off shock by collisional processes, are summarized. A maximum hard X-ray temperature of about 50 keV and a maximum hard X-ray luminosity of 2 x 10 to the 36th ergs/sec were obtained. The results prove that the bulk of accretion energy cannot be transported to the star by electron thermal conduction, provided that bremsstrahlung cooling is dominant over cyclotron cooling.

Imamura, J. N.↗

NASA NTRS1990

Ultraviolet observations of NGC 205

Low-resolution IUE observations of the dwarf elliptical galaxy NGC 205 show that the UV spectral energy distribution of the galaxy is relatively flat. Spectra centered on the nucleus and on a region north of the nucleus show evidence of recent 'bursts' of star formation which contribute strongly to the UV spectral energy distribution. The UV spectra are fit with a composite spectrum based on a Miller-Scalo initial mass function, an underlying older population and an extinction based on a SMC-like extinction curve. This fit implies that the total mass of young stars in the galaxy is about 700,000 solar mass, which can be compared to the total mass of Population II stars in the galaxy of about 100 million solar mass.

Wilcots, Eric M.↗

NASA NTRS1993

The hot stellar component in elliptical galaxies and spiral bulges. I - The far-ultraviolet spectrum of the bulge of M31

An analysis of the M31 spectrum is presented and compared to the spectrum of NGC 1399. There are significant differences between the two spectra that cannot easily be explained by uncertainties in extinction. The M31 spectrum requires a contribution from stars hotter than those that dominate the NGC 1399 spectral energy distribution. It is found that an acceptable fit to the M31 spectrum can be produced by assuming that it consists of stars like those in NGC 1399, combined with a much higher proportion of classical post-asymptotic giant branch stars. This result is not completely conclusive because of uncertainties in extinction, but it agrees with the idea that as metallicity increases, so does the contribution from extreme horizontal branch stars, post-early-AGB stars, and AGB-Manque stars.

Ferguson, Henry C.↗

NASA NTRS1994

The Fe XIV spectrum: Predicted line intensities and solar identifications

Level populations and line intensities have been calculated in a 40-level model of Fe XIV which includes the configuations 3p(exp 3) and 3s3p3d. The results have been compared against intensities of weaker, unidentified, or tentatively classified lines in published solar line lists including a recent Goddard Space Flight Center/Solar Extreme Ultraviolet Telescope and Spectrograph (GSFC/SERTS) high-resolution list, and in presently measured archival Naval Research Laboratory (NRL)/S082A active region spectra. Seven new lines are identified as Fe XIV transitions; five other observed, unidentified lines are considered to be Fe XIV transitions on the basis of wavelength coincidence, but require further observations to obtain photometric intensities for verification; one line at 216.93 A is shown to be due to some other ion than Fe XIV. In addition, a unique forbidden infrared (approx. equal to 1.25 micrometer(s)) line originating in the high metastable level 3s3p3d(F(sub 9/2)-4) is found to have an unusual intensity dependence on electron density.

Bhatia, A. K.↗

NASA NTRS2003

Laboratory Studies of Thermal Energy Charge Transfer of Multiply Charged Ions in Astrophysical Plasmas

The laser ablation/ion storage facility at the UNLV Physics Department has been dedicated to the study of atomic and molecular processes in low temperature plasmas. Our program focuses on the charge transfer (electron capture) of multiply charged ions and neutrals important in astrophysics. The electron transfer reactions with atoms and molecules is crucial to the ionization condition of neutral rich photoionized plasmas. With the successful deployment of the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Chandra X-ray Observatory by NASA high resolution VUV and X-ray emission spectra fiom various astrophysical objects have been collected. These spectra will be analyzed to determine the source of the emission and the chemical and physical environment of the source. The proper interpretation of these spectra will require complete knowledge of all the atomic processes in these plasmas. In a neutral rich environment, charge transfer can be the dominant process. The rate coefficients need to be known accurately. We have also extended our charge transfer measurements to KeV region with a pulsed ion beam. The inclusion of this facility into our current program provides flexibility in extending the measurement to higher energies (KeV) if needed. This flexibility enables us to address issues of immediate interest to the astrophysical community as new observations are made by high resolution space based observatories.

Kwong, Victor H. S.↗

NASA NTRS2004

Undersampling Correction for Array Detector-Based Satellite Spectrometers

Array detector-based instruments are now fundamental to measurements of ozone and other atmospheric trace gases from space in the ultraviolet, visible, and infrared. The present generation of such instruments suffers, to a greater or lesser degree, from undersampling of the spectra, leading to difficulties in the analysis of atmospheric radiances. We provide extended analysis of the undersampling suffered by modem satellite spectrometers, which include Global Ozone Monitoring Experiment (GOME), Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), Ozone Monitoring Instrument (OMI), and Ozone Mapping and Profiler Suite (OMPS). The analysis includes basic undersampling, the effects of binning into separate detector pixels, and the application of high-resolution Fraunhofer spectral data to correct for undersampling in many useful cases.

Chance, Kelly↗

NASA NTRSDate not supplied

Experimental and Theoretical Needs for the JWST Early Release Science Program on Radiative Feedback from Massive Stars (PDRs4ALL): III. A Quantum Chemistry Perspective

Massive stars disrupt their natal molecular cloud material by dissociating molecules, ionizing atoms and molecules, and heating the gas and dust. These processes drive the evolution of interstellar matter in our Galaxy and throughout the Universe from the era of vigorous star formation at z=1-3 to the present day. Much of this interaction occurs in Photo- Dissociation Regions (PDRs) where far-ultraviolet photons of these stars create a largely neutral, but warm region of gas and dust. PDR emission dominates the IR spectra of starforming galaxies and provides a unique tool to study the physical and chemical processes that are relevant for inter- and circumstellar media including diffuse clouds, molecular cloud and protoplanetary disk surfaces, and starburst galaxies. The ERS program ID1288 is dedicated to provide template data as well as data processing and analysis tools for PDRs. To this end, it will observe the Orion Bar, the proto-typical PDR situated in the nearby Orion Nebula, using NIRSpec IFU, MIRI IFU, and NIRCAM and MIRI imaging. These observations will, for the first time, spatially resolve and perform a tomography of the PDR, revealing the individual IR spectral signatures from the key zones and sub-regions within the ionized gas, the PDR, and the molecular cloud. Quantum chemistry can be used to determine molecular data such as ionization potentials, chemical reaction rates, electronic spectra, dissociation energies, channels, and branching ratios, etc. These are often used in synergy with experiment to take advantage of the strengths of each approach. An area of active research is modeling the infrared (IR) emission spectra produced by PAH molecules, including the effects of anharmonicity. This will be important in the interpretation of JWST data which will yield higher-resolution spectral data compared to Spitzer or ISO. Quantum chemistry methods can compute accurate anharmonic IR absorption spectra of PAH molecules up to about 25 C atoms, and the results have been benchmarked against high-resolution experimental spectra. These feed into a quantum Monte Carlo (QMC) approach to generate temperature-dependent anharmonic IR emission spectra and then used to generate fully anharmonic cascade emission IR spectra of PAH molecules -- the very type of spectra that JWST will observe. Work continues to extend these methods to larger PAH molecules. We will discuss the current state of this work, as well as

Timothy Lee↗

NASA NTRS1988

Carbon and nitrogen lines in the spectra of Wolf-Rayet stars

The one-representative-point radiative transfer theory of Castor and van Blerkom (1970) is used to predict the relative energies in emission lines of the ions of carbon and nitrogen in Wolf-Rayet atmospheres for a wide range of parameters. The predicted ratios are compared with observed relative energies of lines in the visible and ultraviolet spectral ranges of six Wolf-Rayet stars. It is found that the lower levels of C II, C III, N III, and N IV are strongly overpopulated relative to their populations in LTE. The differences between WC and WN spectra appear to be due chiefly to a difference in electron temperature in the line-emitting regions. The typical volume of stars studied is estimated to be in the range of 10 to the 41st to 10 to the 44th cu cm. Possible ways in which the line-emitting regions may be arranged around the star are discussed, noting that the high-temperature line-emitting plasma may lie in a thin annular disk approximately 10 to the 15th cm from the star.

Bhatia, A. K.↗

NASA NTRS2004

Reflectance Experiment Laboratory (RELAB) Description and User's Manual

Spectroscopic data acquired in the laboratory provide the interpretive foundation upon which compositional information about unexplored or unsampled planetary surfaces is derived from remotely obtained reflectance spectra. The RELAB is supported by NASA as a multi-user spectroscopy facility, and laboratory time can be made available at no charge to investigators who are in funded NASA programs. RELAB has two operational spectrometers available to NASA scientists: 1) a near- ultraviolet, visible, and near-infrared bidirectional spectrometer and 2) a near- and mid- infrared FT-IR spectrometer. The overall purpose of the design and operation of the RELAB bidirectional spectrometer is to obtain high precision, high spectral resolution, bidirectional reflectance spectra of earth and planetary materials. One of the key elements of its design is the ability to measure samples using viewing geometries specified by the user. This allows investigators to simulate, under laboratory conditions, reflectance spectra obtained remotely (i.e., with spaceborne, telescopic, and airborne systems) as well as to investigate geometry dependent reflectance properties of geologic materials. The Nicolet 740 FT-IR spectrometer currently operates in reflectance mode from 0.9 to 25 Fm. Use and scheduling of the RELAB is monitored by a 4-member advisory committee. NASA investigators should direct inquiries to the Science Manager or RELAB Operator.

Pieters, Carle M.↗

NASA NTRS1990

Fluorescence from excitation of CH4, CH3OH and CH3SH by extreme vacuum ultraviolet radiation

The photoabsorption and fluorescence cross sections of CH4, CH3OH, and CH3SH were measured in the wavelength regions of 52-106, 48-106, and 48-106 nm, respectively. The fluorescence spectra were dispersed to identify the emitting species. Emissions from the excited species of H(asterisk) and CH(asterisk) are commonly observed for all three molecules. Emission from the excited CH2(asterisk) is observed from CH4, OH(asterisk) from CH3OH and CS(asterisk) from CH3SH. The photoexcitation processes that may produce the observed emission bands are discussed.

Ma, Guang↗

NASA NTRS1982

The remarkable spectrum of some material ejected by Eta Carinae

Some of the outer condensations of the very massive star Eta Carinae have emission-line spectra which convey clues to the nature of the star from which they were ejected. Ground-based spectrograms as well as ultraviolet IUE data on the brightest such condensation is described. Excess nitrogen presumably resulting from the C/N/O cycle implies that the star is at least moderately evolved. The facts seem consistent with recent suggestions that turbulent mixing, combined with mass loss, causes a very massive star like Eta Carinae to evolve quasi-homogeneously.

Davidson, K.↗

NASA NTRS1984

Interstellar O2. II - VUV oscillator strengths of Schumann-Runge lines and prospects for Space Telescope observations

Interstellar molecular oxygen should be detectable in interstellar clouds through observation of its absorption lines in the spectra of background stars. This paper describes and presents the results of measurements of oscillator strengths for some lines in the vacuum ultraviolet (VUV) spectrum of O2. Lines of the (13, 0) through (16, 0) bands of the B 3Sigma(-)u - X 3Sigma(-)g, Schumann-Runge system between 1760 A and 1790 A will be the most suitable for searches for absorption by interstellar O2 with the High Resolution Spectrograph on Space Telescope. The strongest lines in these bands have oscillator strengths of about 3 x 10 to the -5th.

Smith, P. L.↗

NASA NTRS1988

Spectral images of HD 199178

High-resolution IUE spectra of the Mg II k line of HD 199178 were analyzed, applying spectral imaging techniques to derive an image of the chromospheric structure and to study the transient behavior of the chromosphere. All spectra in the IUE archives were uniformly reduced and analyzed. Results are compared with ground-based observations of the photosphere. Four ultraviolet flares on HD 199178 are observed; 3 of these occurred at roughly the same rotational phase. There is no clear phase-dependence of the SWP line fluxes, but there is for the Mg II k flux. The emission centroid of the Mg II k line varies in a quasi-sinusoidal fashion, presumably due to the rotation of a nonuniform chromosphere.

Neff, J. E.↗

NASA NTRS1990

Late stages in the evolution of classical novae

The long term evolution of novae in outburst is studied in order to determine the means by which they return to quiescence when nuclear burning has ended is described. The project involves both International Ultraviolet Explorer (IUE) and optical observations and theoretical predictions. In the initial observational part of this project, IUE SWP (Short Wavelength Prime) spectra of GQ Mus 1983 and QU Vul 1984 are obtained. Each spectrum was a 16 hour exposure using a combined US1 plus Vilspa shift. No novae were sudied in the UV for as long as QU Vul and GQ Mus and observations of their spectral evolution provides unique data on the turnoff time scale. The spectra of old novae from the IUE archives are used to compare the existing spectra with those of GQ Mus and QU Vul. The theoretical prediction is that a nova should be very hot just before turnoff but x ray observations from EXOSAT do not confirm this prediction.

Starrfield, Sumner G.↗

NASA NTRS1994

The NASA/JPL Evaluation of Oxygen Interactions with Materials-3 (EOIM-3)

The deleterious effects of hyperthermal atomic oxygen (AO) found in low-earth-orbit (LEO) environments on critical flight materials has been known since early shuttle flights. This corrosive effect is of considerable concern because it compromises the performance and longevity of spacecraft/satellite materials deployed for extended periods in LEO. The NASA Evaluation of Oxygen Interactions with Materials-3 (EOIM-3) experiment served as a testbed for a variety of candidate flight materials for space assets. A total of 57 JPL test specimens were present in six subexperiments aboard EOIM-3. In addition to a number of passive exposure materials for flight and advanced technology programs, several subexperiments were included to provide data for understanding the details of atomic oxygen interactions with materials. Data and interpretations are presented for the heated tray, heated strips, solar ultraviolet exposure, and scatterometer subexperiments, along with a detailed description of the exposure conditions experienced by materials in the various experiments. Mass spectra of products emerging from identical samples of a (sup 13)C-enriched polyimide polymer (chemically equivalent to Kapton) under atomic oxygen bombardment in space and in the laboratory were collected. Reaction products unambiguously detected in space were (sup 13)CO, NO, (sup 12)CO2, and (sup 13)CO2. These reaction products and two others, H2O and (sup 12)CO, were detected in the laboratory, along with inelastically scattered atomic and molecular oxygen. Qualitative agreement was seen in the mass spectra taken in space and in the laboratory; the agreement may be improved by reducing the fraction of O2 in the laboratory molecular beam.

Brinza, David E.↗

NASA NTRS2006

Accurate VUV Laboratory Measurements of Fe III Transitions for Astrophysical Applications

We report preliminary measurements of Fe III spectra in the 1150 to 2500 A wavelength interval. Spectra have been recorded with an iron-neon Penning discharge lamp (PDL) between 1600 and 2500 A at Imperial College (IC) using high resolution Fourier (FT) transform spectroscopy. These FT spectrometer measurements were extended beyond 1600 A to 1150 A using high-resolution grating spectroscopy at the National Institute of Standards and Technology (NIST). These recorded spectra represent the first radiometrically calibrated measurements of a doubly-ionized iron-group element spectrum combining the techniques of vacuum ultraviolet FT and grating spectroscopy. The spectral range of the new laboratory measurements corresponds to recent HST/STIS observations of sharp-lined B stars and of Eta Carinae. The new improved atomic data can be applied to abundance studies and diagnostics of astrophysical plasmas.

Blackwell-Whitehead, R. J.↗

NASA NTRS2017

Space Telescope and Optical Reverberation Mapping Project. VI. Reverberating Disk Models for NGS 5548

We conduct a multi-wavelength continuum variability study of the Seyfert 1 galaxy NGC 5548 to investigate the temperature structure of its accretion disk. The 19 overlapping continuum light curves (1158 Angstrom to 9157 Angstrom) combine simultaneous Hubble Space Telescope, Swift, and ground-based observations over a 180 day period from 2014 January to July. Light-curve variability is interpreted as the reverberation response of the accretion disk to irradiation by a central time-varying point source. Our model yields the disk inclination i = 36deg +/- 10deg, temperature T(sub 1) = (44+/-6) times 10 (exp 3)K at 1 light day from the black hole, and a temperature radius slope (T proportional to r (exp -alpha)) of alpha = 0.99 +/- 0.03. We also infer the driving light curve and find that it correlates poorly with both the hard and soft X-ray light curves, suggesting that the X-rays alone may not drive the ultraviolet and optical variability over the observing period. We also decompose the light curves into bright, faint, and mean accretion-disk spectra. These spectra lie below that expected for a standard blackbody accretion disk accreting at L/L(sub Edd) = 0.1.

accretion↗