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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Heat and ionization sources in the interstellar medium

This is a review of the astrophysical sources of heat and ionization in interstellar clouds and in the intercloud medium. Observational data on density, ionization, and temperatures of H I regions are summarized, and the heat and ionization requirements are specified in terms of heat input and hydrogen ionization rate. A wide variety of sources and mechanisms are reviewed and contrasted, and corresponding estimates of heat input and hydrogen ionization rate are presented in tabular form.

Silk, J.↗
NASA NTRS2012

The Atomic to Molecular Transition in the Interstellar Medium

Study of H2 in UV and IR continues to surprise us with complexity of excitation state, OPR, and role in astrochemistry. Atomic H in molecular clouds is a very powerful tool suggesting that they are not "young" but that it takes millions of years to convert primarily atomic hydrogen clouds to 99.9% molecular form. Laboratory data suggests that H2 formation is efficient over broader range of temperatures than thought to be the case a few years ago, but range is still limited. Issues of complex grain morphology and surface structure make this a very difficult field in which to obtain definitively meaningful results. Ongoing and future observations of CI and CII will improve our understanding of the structure of clouds, their total mass, and how they have evolved and will continue to do so.

interstellar medium↗
NASA NTRS1990

High-resolution sodium absorption-line observations of the local interstellar medium

High-resolution observations of the sodium D1 and D2 interstellar absorption lines have been made toward 19 stars in the local ISM at distances ranging from 20 to 220 pc. A least-squares absorption line-fitting analysis is carried out on 10 of the stars that show detectable sodium. The velocity structure, velocity dispersions, and column densities of the various interstellar cloud components are derived. For the majority of stars, the best-fit dispersion parameter is about 2 km/s, corresponding to an upper limit for the kinetic temperature of the interstellar gas of about 5500 K. No sodium is detected toward stars with distances less than 42 pc, placing an upper limit 2.5 x 10 to the 18th/sq cm to the hydrogen column density in these lines of sight.

Welsh, Barry Y.↗
NASA NTRS1993

Photoabsorption and photodissociation of molecules important in the interstellar medium

The photo absorption, photo dissociation, and fluorescence cross sections of interstellar molecules and radicals were measured in the vacuum ultraviolet region. These quantitative optical data are useful for understanding of the formation and destruction processes of molecules under the intense interstellar W radiation field. Infrared (IR) emissions from W excitation of aromatic molecules were also observed in this research program. The research results are useful for studying the sources of the 'unidentified' interstellar infrared (UIR) emission bands.

Lee, Long C.↗
DOE OSTI2024

Low-temperature gas-phase formation of cyclopentadiene and its role in the formation of aromatics in the interstellar medium

The cyclopentadiene (C 5 H 6 ) molecule has emerged as a molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures such as corannulene (C 20 H 10 ), nanobowls (C 40 H 10 ), and fullerenes (C 60 ) in deep space. However, the underlying elementary gas-phase processes synthesizing cyclopentadiene from acyclic hydrocarbon precursors have remained elusive. Here, by merging crossed molecular beam experiments with rate coefficient calculations and comprehensive astrochemical modeling, we afford persuasive testimony on an unconventional low-temperature cyclization pathway to cyclopentadiene from acyclic precursors through the reaction of the simplest diatomic organic radical—methylidyne (CH)—with 1,3-butadiene (C 4 H 6 ) representing main route to cyclopentadiene observed in TaurusMolecular Cloud. This facile route provides potential solution for the incorporation of the cyclopentadiene moiety in complex aromatic systems via bottom–up molecular mass growth processes and offers an entry point to the low-temperature chemistry in deep space leading eventually to nonplanar PAHs in our carbonaceous Universe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1981

A semiempirical model for heavy element depletion in the interstellar medium

An empirical relationship is derived which reproduces the observed depletion factors in interstellar gas by relating them to some preshock distribution factor and the binding energy of the elements in appropriate compounds. By fitting this equation to the data, estimates are obtained for both the distribution factor and the critical binding energy, which is related to the shock strength at which grains are completely destroyed. The critical binding energy value therefore provides an estimate of the energy involved in the most recent shock event, while the preshock distribution factor is related to the preshock elemental distribution between gas and dust. It is noted that the minerals most likely to survive are the refractory ones with the largest binding energies.

Trivedi, B. M. P.↗
NASA NTRS1984

Ultraviolet studies of the interstellar medium

Copernicus satellite and IUE investigations of the chemical composition and physical condition of interstellar gas and dust in our Galaxy, and in external systems are reviewed. The local interstellar environment, dust, and the distribution of gas away from the plane of our Galaxy are covered.

Blades, J. C.↗
NASA NTRS2009

Chemical Evolution in the Interstellar Medium: From Astrochemistry to Astrobiology

Great strides have been made in our understanding of interstellar material thanks to advances in infrared astronomy and laboratory astrophysics. Ionized polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier astrochemical standards, are widespread and very abundant throughout much of the Universe. In cold molecular clouds, the birthplace of planets and stars, interstellar molecules freeze onto dust and ice particles forming mixed molecular ices dominated by simple species such as water, methanol, ammonia, and carbon monoxide. Within these clouds, and especially in the vicinity of star and planet forming regions, these ices and PAHs are processed by ultraviolet light and cosmic rays forming hundreds of far more complex species, some of biogenic interest. Eventually, these are delivered to primordial planets by comets and meteorites. Astrochemical evolution, highlights of this field from a chemist's perspective, and the astronomer's infrared toolbox will be reviewed.

Allamandola, Louis J.↗
NASA NTRS2017

Radiation Chemistry of Solid Acetone in the Interstellar Medium - A New Dimension to an Old Problem

A laboratory investigation of acetone, an interstellar and cometary molecule, has produced new results concerning its decomposition in a radiation environment. Mid-infrared spectroscopy has been used to follow amorphous acetone’s destruction by ionizing radiation (1 MeV protons) at 20 K. Radiation products identified are the CH4, CO, and CO2 usually made in such experiments, along with ketene, allene, and the acetonyl radical, all identified here for the first time in irradiated solid acetone. Evidence for the reduction product 2-propanol was suggestive, but a firm identification could not be made either for it or for the C2 hydrocarbons (i.e., C2H6, C2H4, C2H2). The acetyl radical was not observed as a radiation product. Isotopically labeled reagents were used to demonstrate ketene formation and to emphasize that multiple approaches are needed for robust assignments of infrared spectral features of irradiated icy solids. Results from a supporting radiation experiment with isotopically labeled acetic acid are described. Comparisons are made to a previous study of acetone’s stability in extraterrestrial radiation environments, and caution is urged in measuring and interpreting CO abundances in irradiated icy solids.

R. L. Hudson↗
NASA NTRS1979

The interstellar medium near the sun. II - The line of sight to Alpha Virginis

Measurements of the UV interstellar lines in Alpha Vir between 935 and 2960 A are reported. The derived abundances indicate significant depletion of Al, Si, Mn, Fe, and possibly Mg, whereas S, C, Ar, and O appear to be essentially undepleted. About half the gas is shown to be ionized, with a mean electron density of no more than 1 per cu cm, and the remainder is neutral, though both regions have the same velocity to within 2 km/s. A small fraction of the gas is apparently at a temperature of 400,000 K. The possibility of measuring the temperature of the H I gas is discussed, using the observed relationship between Doppler width and mass. A detailed discussion is included of the data analysis useful for comparatively simple lines of sight in terms of density, temperature, and extent of the possible physical regions, and of the relevant radiation field. An unidentified feature at 1063.2 A is reported.

York, D. G.↗
NASA NTRS1984

Feii and Mgii in the Nearby Interstellar Medium

Ultraviolet spectra with 15 km/s resolution of bright stars were searched for FeII and MgII interstellar lines. Equivalent widths of absorption for 8 stars are presented and average line-of-sight densities n(FeII) = 4 x 10(-8) and n(MgII) = 2 x 10(-7)/cubic cm are calculated. This represents approximately n(H) = 0.03/cuib cm.

Deboer, K. S.↗
NASA NTRS1980

Supernova radio remnants and the filling factor of the hot interstellar medium

If a hot (temperature of about one-million K), tenuous gas fills about 90% of interstellar space, then the observed number and surface brightness distribution of galactic radio remnants implies a galactic supernova rate of once about every 30 years. This is consistent with estimates based on observations of historical supernovae, pulsars, and supernovae in other spiral galaxies.

Higdon, J. C.↗
NASA NTRS1981

The nearby interstellar medium

The high dispersion spectrometer on board the International Ultraviolet Explorer (IUE) satellite was used to observe interstellar absorption lines in Rasalhague (Alpha Oph). This star is located 18 pc from the sun in the direction of the North Polar Spur, a prominent radio continuum feature in the Ophiuchus region of the sky. The satellite results, combined with previous interstellar line data and observations of the 'local interstellar wind' and soft X-ray emission, support earlier suggestions that the sun is immersed in a supernova remnant which may be an extension of the 'Loop I' or 'North Polar Spur' supernova remnant seen in the Scorpius-Ophiuchus region of the sky.

Frisch, P. C.↗
NASA NTRS1981

The interstellar medium and galactic structure

High energy gamma rays are produced by the interaction of cosmic rays with the interstellar matter in the galaxy. By combining the gamma ray information with radio data, a picture of the galaxy is presented with regard to the general structure and the effects of cosmic ray pressure. The interaction processes and galactic matter distribution are discussed. Galactic cosmic ray distribution and current gamma ray results are reported.

Source record↗
NASA NTRS1991

The dissipation of magnetohydrodynamic turbulence responsible for interstellar scintillation and the heating of the interstellar medium

The present reexamination of the problem of ISM heating via the damping of plasma irregularities responsible for interstellar scintillations of radio sources gives attention to the effects of recent observational results on the hot plasma of the irregularities and on developments of in the theory of MHD waves. The damping mechanisms considered are linear Landau damping, ion-neutral collisional damping, nonlinear steepening of wave packets, a parametric decay instability, and nonlinear Landau damping. The heat input from all damping mechanisms can be accommodated by the 'fluctifer' region containing the irregularities, if it has features similar to the extended H II envelopes.

Spangler, Steven R.↗