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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Spectroscopy from 2 to 200 keV

The astrophysical processes responsible for line and continuum emission in the spectra range 2 keV to 200 keV are examined from the viewpoint of designing a spectrometer which would operate in this regime. Phenomena considered include fluorescent line radiation in X-ray binaries, magnetically shifted iron lines and cyclotron emission from neutron star surfaces, line emission from cosmically abundant elements in thermal plasmas, and nuclear deexcitation lines in fresh nucleosynthetically produced matter. An instrument consisting of a approximately 10 sq cm array of planar germanium detectors surrounded by a large sodium-iodide anticoincidence shield is described and projected background rates and sensitivities are considered. A sample observing program for a two-day shuttle-based mission is included as an example of the wide range of scientific questions which could be addressed by such an instrument.

Helfand, D. J.↗
NASA NTRS2004

Hydrogen emission in meteors as a potential marker for the exogenous delivery of organics and water

We detected hydrogen Balmer-alpha (H(alpha)) emission in the spectra of bright meteors and investigated its potential use as a tracer for exogenous delivery of organic matter. We found that it is critical to observe the meteors with high enough spatial resolution to distinguish the 656.46 nm H(alpha) emission from the 657.46 nm intercombination line of neutral calcium, which was bright in the meteor afterglow. The H(alpha) line peak stayed in constant ratio to the atmospheric emissions of nitrogen during descent of the meteoroid. If all of the hydrogen originates in the Earth's atmosphere, the hydrogen atoms are expected to have been excited at T = 4400 K. In that case, we measured an H(2)O abundance in excess of 150 +/- 20 ppm at 80-90 km altitude (assuming local thermodynamic equilibrium in the air plasma). This compares with an expected <20 ppm from H(2)O in the gas phase. Alternatively, meteoric refractory organic matter (and water bound in meteoroid minerals) could have caused the observed H(alpha) emission, but only if the line is excited in a hot T approximately 10000 K plasma component that is unique to meteoric ablation vapor emissions such as Si(+). Assuming that the Si(+) lines of the Leonid spectrum would need the same hot excitation conditions, and a typical [H]/[C] = 1 in cometary refractory organics, we calculated an abundance ratio [C]/[Si] = 3.9 +/- 1.4 for the dust of comet 55P/Tempel-Tuttle. This range agreed with the value of [C]/[Si] = 4.4 measured for comet 1P/Halley dust. Unless there is 10 times more water vapor in the upper atmosphere than expected, we conclude that a significant fraction of the hydrogen atoms in the observed meteor plasma originated in the meteoroid.

Water↗
NASA NTRS1992

Spatially resolved ultraviolet spectroscopy of the LINER galaxy NGC 3998

Results of recent IUE observations of the LINER galaxy NGC 3998 are reported. Spatial structure in the LW emission is apparent; the spatial profiles in the longwave primary (LWP) images show a two-component structure, with an unresolved central component superposed on extended underlying emission. New software, which exploits a knowledge of the LWP point spread function and its variation with wavelength, is used to model the spatial profiles and to separate the LWP emission into component spectra. The unresolved component spectrum is found to be considerably flatter than the spectrum of the extended component, which is dominated by fairly late-type stars. The unresolved component exhibits strong semiforbidden C II 2326 and broad Mg II 2800 emission. The width of the Mg II emission is about 8000 km/s, and its profile agrees quite well with the broad wings of the H-alpha emission.

Reichert, G. A.↗
NASA NTRS1987

EX56a study of extended X-ray emission around isolated galaxies EX56b identification and spectra of bright X-ray sources at high galactic latitude

The EXOSAT observations confirmed the identification and extended nature of PKS 2345-35. It gave a good 2 to 10 keV X-ray spectrum and a detailed spatial profile indicating asymmetry of the structure. In the high galactic latitidue investigation, the BL Lac object identified with the HEAO-1 source 1430+423 was detected, and the first X-ray spectrum was obtained. Several simulataneous observations of H0323+022 were obtained over a broad range of electromagnetic spectrum. Studies of luminous active galactic nuclei have given significant information on the spectrum of the quasar PKS 0558-504. In a study of Southern sky cataclysmic variables, the EXOSAT was used to determine the X-ray spectrum and search for periodicities in two objects. Studies of complete identifications have revealed that X-ray sources in two high galactic latitude fields are stars, and therefore are to be excluded from the Piccinotti extragalactic sample. Only one Piccinotti source remains to be identified.

Schwartz, Daniel A.↗
NASA NTRS1993

The magnetic field in the corona above sunspots at the eclipse of 1991 July 11

A partial solar eclipse and an X-ray image are used to study the magnetic field as a function of height in the corona above an active region during the solar eclipse of July 11, 1991. The dominant features of AR 6718 are two leading spots of positive polarity followed by two spots of negative polarity about 3 arcmin to the east. Bright radio emission coincides with the positions of the sunspots, attributable to a gyroresonance radiation from ambient electrons above the spots. A simplified model of the source as a function of frequency based on the interferometer fringe amplitudes is used to obtain brightness temperature spectra for the emission associated with the sunspots. It is deduced that the magnetic field strength at the base of the corona above the leading spots was 1200 G, and about 1100 G above the following spots. The soft X-ray brightness above the sunspots was very low, about 30 times lower than that of the adjacent plage-associated emission.

Gary, D. E.↗
NASA NTRS1994

Camera artifacts in IUE spectra

This study of emission line mimicking features in the IUE cameras has produced an atlas of artifiacts in high-dispersion images with an accompanying table of prominent artifacts and a table of prominent artifacts in the raw images along with a medium image of the sky background for each IUE camera.

Bruegman, O. W.↗
NASA NTRS1994

High-resolution spectra of Jupiter's northern auroral ultraviolet emission with the Hubble Space Telescope

The first spectroscopic observations of planetary aurora with the Hubble Space Telescope (HST) are reported. These include spectral regions centered on the H2 Lyman and Werner bands of a region of Jupiter's northern aurora. The observations were made with the Goddard High Resolution Spectrograph (GHRS) using the Large Science Aperture as part of a campaign to study Jupiter at the time of the Ulysses flyby. The individual rotational-vibrational bands are resolved and the observed emissions are essentially all from H2. A rotational-vibrational temperature for H2 of 530 +/- 100 K is derived, a value significantly less than the 850-1100 K reported for Jovian H3(+) in the near-infrared but consistent with the temperature reported for fundamental-band quadrupole H2 emission. Comparison with the Faint Object Camera (FOC) images shows that the observed region was not one of the hot spots of the aurora. The results are interpreted in trms of electron impact excitation of H2 from secondary particles generated by primaries precipitating into Jupiter's atmsophere from the magnetosphere. In the region of the aurora observed, the homopause level is found to be significantly hotter but not necessarily higher than observed at nonauroral latitudes. The equatorial H2 dayglow spectrum was also detected; its intensity was 3.2 kR or 13% of the strength of the observed auroral emission.

Trafton, L. M.↗
NASA NTRS2017

Hardware Demonstration: Frequency Spectra of Transients

Radiated emissions measurements as specified by MIL-STD-461 are performed in the frequency domain, which is best suited to continuous wave (CW) types of signals. However, many platforms implement signals that are single event pulses or transients. Such signals can potentially generate momentary radiated emissions that can cause interference in the system, but they may be missed with traditional measurement techniques. This demonstration provides measurement and analysis techniques that effectively evaluate the potential emissions from such signals in order to evaluate their potential impacts to system performance.

EMI↗
NASA NTRS1980

The ultraviolet dayglow. I - Far UV emissions of N and N2

Far ultraviolet rocket spectra of N I and N2 dayglow emissions have been analyzed by using AE-E photoelectron spectra, laboratory-measured excitation cross sections, and photochemical models of atomic nitrogen. A self-consistent picture of both optically thick and thin emission features is found by using a model in which the principal production mechanism for N I 1200-A and 1493-A photons is photodissociative excitation of N2. The aeronomic data require that 50-70% of the excited 4 P atoms produced dissociatively have velocities within the Doppler core of the ambient nitrogen atoms, contrary to the expectation that those atoms are produced with large excess kinetic energy. The derived atomic nitrogen density has a maximum density of 2.7 x 10 to the 7th per cu cm at 170 km, a value that is within 40% of that from recent models of odd nitrogen photochemistry.

Meier, R. R.↗
NASA NTRS1992

IRAS LRS spectroscopy of galaxies

The study presents IRAS LRS data for 350 galaxies with pointlike IRAS sources having either S(12) or S(25) not less than 1.5 Jy. Techniques are presented which form the mean of an ensemble of LRS spectra, ll of which are only of low signal-to-noise ratio, by quantitative evaluation of the significance of the individual spectra for each object rather than mere acceptance of the 'average spectrum' present in the complete LRS data base. Average LRS spectra for groups of galaxies with distinct optical nuclear properties are formed. Average LRS spectra for several categories of objects are presented and interpreted. H II region galaxies show the polycyclic aromatic hydrocarbon spectrum of bands in emissions; type 2 Seyferts present a broad emission feature parking near 16 microns; LINERs and galaxies without optical emission lines have LRS spectra that decline with wavelength, whereas type 1 Seyferts and WR galaxies have red spectra suggestive of nonthermal emission processes.

Cohen, M.↗
NASA NTRS1973

Mariner 9 infrared interferometer spectrometer (IRIS) reduced data records documentation

The Mariner 9 spacecraft was successfully inserted into orbit around Mars. One of the five instruments on board, an infrared interferometer spectrometer is used to record the thermal emission spectrum of Mars between 200 and 2000 cm/1. The spatial resolution for vertical viewing is a circular area of approximately 110 km diameter for a periapsis height of 1400 km. The total number of calibrated spectra included in the final data set is 21167. The final calibrated thermal emission spectra contained in the reduced data records are reported.

Source record↗
NASA NTRS1994

Survey of emission-line galaxies: Universidad Complutense de Madrid list

A low-dispersion objective-prism survey for low-redshift emission-line galaxies (ELGs) is being carried out by the University Complutense de Madrid with the Schmidt telescope at the German-Spanish Observatory of Calar Alto (Almeria, Spain). A 4 deg full aperture prism, which provides a dispersion of 1950 A/mm, and IIIaF emulsion combination has been used to search for ELGs selected by the presence of H-alpha emission in their spectra. Our survey has proved to be able to recover objects already found by similar surveys with different techniques and, what is more important, to discover new objects not previously cataloged. A compilation of descriptions and positions, along with finding charts when necessary, is presented for 160 extragalactic emission-line objects. This is the first list, which contains objects located in a region of the sky covering 270 sq deg in 10 fields near alpha = 0(sup h) and delta = 20 deg.

Zamorano, J.↗
NASA NTRS1988

A catalog of chromospherically active binary stars

A catalog of 168 chromospherically active binary stars is presented, including the class of RS CVn, BY Dra binaries, and other binaries which show strong Ca II H and K emission in their spectra. The catalog contains information on the photometric, spectroscopic, orbital, and physical properties of the systems as well as the space motions and positions. Summarized in a candidate list are in additional 37 stars having similar characteristics but which are not definitely known binaries or have not had H and K emission observed. The catalog contains stars in both the northern and the southern sky.

Strassmeier, K. G.↗
NASA NTRS1981

Search for optical coronal line emission from the X-ray sources Epsilon Orionis /B0 Ia/ and Kappa Orionis /B0.5 Ia/

A search was conducted for evidence of a coronal region at the base of the winds of Epsilon Ori and Kappa Ori, by means of high signal-to-noise observations at the forbidden lines of Fe X, at 6574 A, and Fe XIV, 5303 A. Both stars have been detected as soft X-ray sources, and show anomalously strong O VI lines in their UV spectra. Large coronal emission measures were expected from the total X-ray flux and Auger-enhanced ionization, but the fact that the iron coronal lines were not detected places new limits on the emission measure if the total temperature is in the range of 700,000-3,000,000 or more than 1,000,000 for Kappa Ori and 2,000,000 for Epsilon Ori. It is suggested that at least some of the X-rays arise, not from the base corona, but from source features farther out in the wind.

Nordsieck, K. H.↗
NASA NTRS1982

Magnesium emission variability among late-type giant stars

Profiles of the Mg II h and k emission features in the spectra of 21 late-type giant stars were obtained. Emission strengths were separately measured in the shortward (S) and longward (L) components. Variations in total emission intensity (S + L) can be interpreted as evidence for variations in the rate of mechanical energy deposition in the chromosphere. Mass loss processes in the corona/outer atmosphere may be strong enough to affect the ratio of S/L: thus, rapid mass loss causes S/L to be less than unity. Rapid mass loss is likely caused by deposition of mechanical energy by stellar wind. Variations in S/L are a measure of variations in the rate of mechanical energy deposition in the corona/outer atmosphere. The stellar sample variations were divided into four classes: (1) variations in S/L; (2) variations in the circumstellar absorption components; (3) variations in the total flux; and (4) no evidence for variations found on the time scales used.

Mullan, D. J.↗
NASA NTRS1990

Camera artifacts in IUE low-dispersion spectra

Sky-background images obtained by the International Ultraviolet Explorer (IUE) were analyzed to study artificial spectral features (camera artifacts) in low-dispersion spectra. The artifacts mimic emission features and have been present in long-exposure spectra since the launch of the IUE satellite. The camera artifacts are strong in spectra characterized by long exposure times because they scale in time-integrated flux with the background level, which increases during the exposure due to camera phosphorescence. The artifacts cannot be detected in spectra obtained from short, direct exposures of flat-field lamps or standard stars. Plots of average sky-background spectra for the three operational IUE cameras (SWP, LWP, and LWR) are given to aid scientists in the identification of artifacts in their spectra.

Crenshaw, D. Michael↗
NASA NTRS1987

Detection of neutral oxygen and sulfur emissions near Io using IUE

IUE spectra have shown several O I and S I emissions near Io. The optical thickness of the S I 1814 A multiplet indicates that the S column density is greater than about 2 x 10 to the 12th/sq cm. The presence of an S I 1479 A feature suggests that electron collisions with SO2 could be a major source of the emissions. It is likely that particle excitation in the denser collision-dominated part of the atmosphere is also responsible for a substantial part of the observed emissions.

Ballester, G. E.↗
NASA NTRS1978

Gamma-ray line emission above 8 MeV

The spectra of energetic nuclei within astrophysical sources may be determined by studying gamma-ray line emissions above 8 MeV. Excited states which can be produced by inelastic scattering, charge exchange, and spallation reactions in the abundant nuclear species were considered in order to identify nuclear lines which may contribute to the gamma spectrum. The cross sections for production of most high-energy states are sparsely measured. Those which were determined are comparable to the cross section for production of the 15.11 MeV level in C-12 with few exceptions. The branching ratios for gamma-ray and particle emission are, however, better known. Of those states considered, 44 measured branching ratios greater than 40% for emission of a gamma-ray with energy above 8 MeV. For twelve more states the branching ratios, although not yet determined, are expected to be small. The gamma-ray emission from other individual nuclear states is not likely to be as great as that that for the 15.11 MeV state in C-12.

Crannell, C. J.↗