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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Infrared emission from hydrogenated amorphous carbon and amorphous carbon grains in the interstellar medium

The correlations deduced by Boulanger et al. (1990) from IRAS maps of the Chamaeleon, Taurus and Ursa Major molecular cloud complexes are interpreted in terms of the evolutionary hydrogenated amorphous carbon model of interstellar dust. In particular, regions of relatively strong 12-micron emission may be regions where recently accreted carbon is being converted by ambient UV to small PAHs in situ. Regions of weak 12-micron emission are probably quiescent regions where carbon has been annealed to amorphous carbon. Observational consequences of these inferences are briefly described.

Duley, W. W.↗
NASA NTRS2002

A Multi-Wavelength Study of the Hot Component of the Interstellar Medium

The goals of this research are as follows: (1) Using the large number of lines of sight available in the ME database, identify the lines of sight with high-velocity components in interstellar lines, from neutral species through Si VI, C IV, and N V; (2) Compare the column density of the main components (i.e. low velocity components) of the interstellar lines with distance, galactic longitude and latitude, and galactic radial position. Derive statistics on the distribution of components in space (e.g. mean free path, mean column density of a component). Compare with model predictions for the column densities in the walls of old SNR bubbles and superbubbles, in evaporating cloud boundaries and in turbulent mixing layers; (3) For the lines of sight associated with multiple high velocity, high ionization components, model the shock parameters for the associated superbubble and SNR to provide more accurate energy input information for hot phase models and galactic halo models. Thus far 49 lines of sight with at least one high velocity component to the C IV lines have been identified; and (4) Obtain higher resolution data for the lines of sight with high velocity components (and a few without) to further refine these models.

Nichols, Joy↗
NASA NTRS1990

Galactic H I and the interstellar medium in Ursa Major

Sensitive neutral hydrogen measurements have been made over a 100 square degree field in Ursa Major. The observations cover the area which has the least neutral hydrogen and probably the least interstellar matter of any direction in the sky. It is likely that this data set contains every line of sight that intersects a total H I column density of less than 6.5 x 10 to the 19th/sq cm. The smallest colum density is estimated to be 4.4 + or - 0.5 x 10 to the 19th/sq cm. Observations at 10 arcmin angular resolution reveal little structure that is not seen at 21 arcmin resolution, and it is believed that the estimates of the total H I column density are accurate on yet smaller angular scales. The lowest N(H I) area is also extremely deficient in H-alpha emission, and shows no evidence for significant amounts of H2.

Jahoda, Keith↗
NASA NTRS1984

Local Interstellar Medium. International Astronomical Union Colloquium No. 81

Helium and hydrogen backscattering; ultraviolet and EUV absorption spectra; optical extinction and polarization; hot gases; soft X-ray observations; infrared and millimeter wavelengths; radio wavelengths and theoretical models of the interstellar matter within about 150 parsecs of the Sun were examined.

Kondo, Y.↗
NASA NTRS1985

The kinematics of cool metal-line white dwarfs and accretion in the local interstellar medium

The data base of spectroscopically identified white dwarfs is used to isolate a sample of cool degenerates with trace metals. The spatial distribution and space velocity components of the white dwarfs projected onto and perpendicular to the galactic plane are compared with the distribution of local interstellar hydrogen. The results are consistent with the metals having been accreted during recent encounters with local density enhancements. However, the limited availability of radial velocities, coupled with uncertainties in the derived abundances, the diffusion times, and in the three-dimensional structure of the local medium, prevent a definitive test of the accretion hypothesis at this time.

Aannestad, P. A.↗
NASA NTRS1987

IUE observations of hydrogen and deuterium in the local interstellar medium

High-resolution Ly-alpha spectra of the late-type stars Epsilon Eri, Procyon, Altair, Capella, and HR 1099 taken with the short-wavelength camera on IUE are presented. The density, velocity dispersion, and bulk velocity of the interstellar H I toward each of the stars is derived from the spectra. Lower limits on the deuterium-to-hydrogen ratio toward these stars are obtained.

Murthy, J.↗
NASA NTRS1988

The hydrogen density of the local interstellar medium and an upper limit to the galactic glow determined from Pioneer 10 ultraviolet photometer observations

Pioneer 10 Lyman-alpha data obtained beyond the heliocentric distance of 30 AU are used here to determine the local ISM hydrogen density and downwind Galactic glow. The resulting asymptotic interstellar hydrogen density obtained using a conventional interplanetary model is 0.06/cu cm, and the Galactic Lyman-alpha glow is found to be negligible in the downwind direction. Discrepancies are found between observations and the conventional theoretical predictions of the glow dependence on radial distance. Based solely on data obtained between 30 and 39 AU, a better fit is obtained with a constant density distribution beyond 30 AU. In this case, a density of 0.05/cu cm and Galactic glow of 1.5 R is obtained. These results suggest that a complex density distribution may be more appropriate than either the conventional exponential distribution or the constant distribution.

Wu, F. M.↗
NASA NTRS1975

Cosmic ray antiproton and positron production in the interstellar medium

We have calculated the energy spectra of cosmic ray secondary antiprotons and positrons using the latest available data on inclusive reactions. Using the measured positron spectrum, we have found that the amount of matter traversed by the cosmic rays in the few GeV region to be 4.7 (+ or - 1.5) g/sq cm of interstellar hydrogen. The computed antiproton to proton ratio is about .0004 for energies 5-10 GeV. This is sufficient to make observations of antiprotons feasible from balloon flights. We have also pointed out the type of information that can be obtained if accurate information of the spectra of these two components becomes available.

Badhwar, G. D.↗
NASA NTRS1993

The hot interstellar medium in NGC 1399

The first two high signal-to-noise, broad bandpass x-ray spectra of elliptical galaxies were obtained with the Broad Band X-ray Telescope (BBXRT) as part of the December 1990 Astro mission. These observations provided unprecedented information on the thermal and metallicity structure of the hot interstellar media in two ellipticals: NGC 1399, the central galaxy in the Fornax cluster, and NGC 4472, the brightest galaxy in the Virgo cluster. The finalized analysis and interpretation of the approximately 4000 sec of BBXRT data on NGC 1399 is reported.

Loewenstein, Michael↗
NASA NTRS2017

Organics and Ices in the Outer Solar System: Connections to the Interstellar Medium

The solar nebula, that aggregate of gas and dust that formed the birthplace of the Sun, planets and plethora of small bodies comprising the Solar System, originated in a molecular cloud that is thought to have spawned numerous additional stars, some with their own planets and attendant small bodies. The question of the chemical and physical reprocessing of the original interstellar materials in the solar nebula has challenged both theory and observations. The acquisition and analysis of samples of comet and asteroid solids, and a growing suite of in-situ and close-up analyses of relatively unaltered small Solar System bodies now adds critical new dimensions to the study of the origin and evolution of the early solar nebula. Better understanding the original composition of the material from which our solar nebula formed, and the processing that material experienced, will aid in formulations of chemistry that might occur in other solar systems. While we seek to understand the compositional history of planetary bodies in our own Solar System, we will inevitably learn more about the materials that comprise exoplanets and their surrounding systems.

SOLAR NEBULA↗
NASA NTRS1985

Meteoritic evidence that graphite is rare in the interstellar medium

Carbonaceous material from several distinct astrophysical environments that has been identified in primitive meteorites is discussed. Most of this material is not well crystallized graphite, but ranges from kerogenlike macromolecular organic matter to poorly graphitized carbon. Of the small fraction of the carbonaceous material which is graphite, most may have resulted from the graphitization of macromolecular precursors in the solar nebula. Since graphite is more stable than those precursors, preexisting interstellar graphite should have survived in meteorites to at least the same extent as did other forms of carbon. It is concluded from this dearth of graphite that graphitic carbon was not a major component of the interstellar dust at the time of the formation of the solar system.

Nuth, J. A.↗
NASA NTRS1987

Diffuse and dark clouds in the interstellar medium

Observations of clouds in the ISM of the Galaxy and the Magellanic Clouds, obtained with the IUE satellite since its launch in 1978, are reviewed. Consideration is given to the techniques used to analyze IUE Maxwellian growth curves and oscillator strengths, the general structure of the Galactic ISM, the high-velocity clouds, heavy-element depletion, and observations toward strongly reddened stars in the outer portions of dark clouds. Theoretical models of interstellar dust formation and selective and nonselective removal of elements from dust grains are discussed; observations of reflection nebulae and their implications for light scattering by dust are examined; the dynamics and ionization structure of the Galactic halo ISM are described; and the Magellanic Cloud observations are briefly characterized. Diagrams, graphs, and tables of numerical data are provided.

De Boer, Klaas S.↗
NASA NTRS1990

The dense interstellar medium and the birthplaces of OB stars

A review is presented of Stromgren's research on the relationships among atomic, ionized, and molecular hydrogen in the Galaxy and the spatial distribution and kinematics of OB stars. Particular attention is given to the development of density-wave theory, the implication that the pattern of the formation of OB stars in a spiral galaxy should rotate at a constant angular speed, which differs generally from the mean material speed of the interstellar gas. Other theories involving the mechanical support of molecular clouds; triggered star formation; and the relationships among H2, H I, and H II are discussed.

Shu, Frank H.↗
NASA NTRS1986

A molecular cloud in the local, hot interstellar medium

Echelle spectra recorded at the D lines of Na I are reported for nine A or F stars. Lying at approximate distances ranging from 25 to 230 pc, the stars are projected on or near the high-latitude molecular cloud MBM 12 at l = 159 deg, b = -34 deg. Among a subgroup of five of these stars separated by no more than 1.2 deg on the sky, four which are located at distances d more than 70 pc show strong interstellar D line absorption near the radial velocity of the CO emission observed in this general direction. The fifth star, at roughly 60 pc, shows no detectable absorption. MBM 12 therefore probably lies at roughly 65 pc, within the local region filled primarily by very hot, low-density gas, a conclusion supported by the large internal velocity dispersion of the molecular cloud complex.

Hobbs, L. M.↗
NASA NTRS1985

The role of cosmic rays in magnetic hydrodynamics of interstellar medium

Cosmic ray (CR) propagation in the Galaxy and generally in the cosmic plasma is usually considered in the diffusion approximation. The diffusion is regarded to result from CR scattering due to their interaction with a magnetic and an electric field. In most cases the fields are assumed to be given. Meanwhile, in the Galaxy the CR energy density w sub cr is similar to I eV/cm, i.e., it is comparable with the energy densities of the magnetic field and turbulent motions in the interstellar gas. Therefore, for the Galaxy it becomes necessary to take into account the influence of CR on the gas dynamics and on the magnetic fields in this gas. The simplest way to this is to use the hydrodynamic approximation, but this is possible only on scales greatly exceeding the CR free path lambda before scattering and only for times larger than lambda/v approx. equals lambda/c. One should thus obtain corresponding MHD equations and establish the limits of their applicability.

Ginzburg, V. L.↗
NASA NTRS1986

High-resolution X-ray spectroscopy of the Crab Nebula and the oxygen abundance of the interstellar medium

The measurement and analysis of a high-resolution soft X-ray spectrum of the Crab Nebula obtained with the Focal Plane Crystal Spectrometer on the Einstein Observatory are reported. A hydrogen column density of 3.45 + or - 0.42 x 10 to the 21st/sq cm and an oxygen column density of 2.78 + or - 0.55 x 10 to the 18th/sq cm, corresponding to an oxygen abundance of 1.1 + or - 0.3 times solar, were obtained. The absence of any evident oxygen depletion effects suggests that most interstellar grains are reasonably transparent to soft X-rays, implying sizes of less than 0.4 micron. The detailed spectrum in the vicinity of the oxygen edge gives marginal evidence for a resonant absorption line and suggests an edge from singly ionized oxygen.

Schattenburg, M. L.↗
NASA NTRS1989

Star formation and the interstellar medium in two peculiar, nonspiral galaxies - NGC 1569 and NGC 3593

This paper discusses far-IR and optical observations aimed at investigating the far-IR energy distribution of two peculiar galaxies without spiral arms which are actively forming stars: NGC 1569, a Magellanic irregular galaxy, and NGC 3593, a dusty S0/a galaxy. The data are used to determine the characteristic temperatures of the dust and to infer dust and molecular gas masses which are combined with other data to explore the characteristics of the interstellar media. Visual-wavelength continuum and H-alpha images are presented and used to estimate current and past star formation rates and the efficiency of stellar creation.

Hunter, Deidre A.↗