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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The Cygnus 'superbubble' - A supernova explosion in a tenuous intercloud medium

Cash et al. (1980) observed an incomplete X-ray shell in the Cygnus region with a temperature of 2 x 10 to the 6th K and a density of 0.02 per cu cm. This feature closely resembles Loop I, a nearby supernova remnant expanding in a tenuous (less than 0.01 per cu cm) medium. A similar origin - remnant expansion in a tenuous intercloud medium with the bulk of the interstellar gas concentrated in clouds - is suggested for the Cygnus X-ray feature. This model greatly reduces the required initial thermal energy. Remnant shock interaction with ambient interstellar clouds produces the observed H-alpha filaments.

Higdon, J. C.↗
NASA NTRS1987

The history of gas in sprial galaxies

The general association of luminous young stars with spiral arms in galaxies has led to widespread acceptance of the idea that the formation of massive stars, at least, is somehow triggered by the interaction of interstellar gas clouds with a spiral density wave. A very simple model for the gas in a spiral galaxy, with a specified initial surface density and angular velocity is examined. Typical results from this simple model, with parameters appropriate to NGC 6946, are shown. The accuracy of the presumption that the molecular gas distributions in galaxies is based upon observations of CO J = 1-0 emission, is discussed.

Maloney, Philip↗
NASA NTRS1975

Charge transfer reactions in multiply charged ion-atom collisions

Charge-transfer reactions in collisions between highly charged ions and neutral atoms of hydrogen and/or helium may be rapid at thermal energies. If these reactions are rapid, they will suppress highly charged ions in H I regions and guarantee that the observed absorption features from such ions cannot originate in the interstellar gas. A discussion of such charge-transfer reactions is presented and compared with the available experimental data. The possible implications of these reactions for observations of the interstellar medium, H II regions, and planetary nebulae are outlined.

Steigman, G.↗
NASA NTRS1985

High dispersion observations of Epsilon Aur from Sept. 1982 to March 1983

Between September 1982 and March 1983 I obtained high dispersion spectra of epsilon Aur in selected regions using the Palomar 200-inch coude spectrograph and the Dominion Astrophysical Observatory 48-coude spectrograph. All spectra were taken with the 90-mm ITT image tube and IIa-D emulsion. Radial velocities are listed for the sodium D lines, KI lines, H alpha, and a few other features. While most of the sodium and potassium features are surely circumstellar there is certainly an interstellar component present. In the direction of epsilon Aur interstellar gas is seen mostly with radial velocities between +5 and +10 km s(-1). The sodium D lines and potassium lines show incipient resolution which may involve the interstellar components. The equivalent widths of the sodium and potassium lines are given. For potassium, blending with atmospheric O2 makes the line at lambda 7664 unmeasurable on the dates of these observations. The increase in equivalent widths already noted by Pathasarathy and Lambert is evident. Blending and partial resolution of the circumstellar and interstellar features may account for much of the velocity structure which is only partially discernable at the available resolution.

Wallterstein, G.↗
NASA NTRS2002

Exotic Molecules in Space: A Coordinated Astronomical Laboratory and Theoretical Study

This report details the work of NASA grant NAG5-9379 which is concerned with the discovery and characterization of new astrophysical molecules. Numerous papers have been or will be published on the laboratory detection of 21 molecules of astrophysical interest, nearly all not previously observed, and nearly all of astrophysical interest as plausible candidates for the interstellar gas and circumstellar shells. Also of interest include the laboratory detection of of optical molecular band exactly coinciding in frequency with the strongest and most widely studied optical diffuse interstellar band which remains an enigma in astrophysical spectroscopy. A new laser spectrometer has been developed and is now undergoing testing.

Thaddeus, Patrick↗
NASA NTRS1994

Hot gas in the interstellar medium: A reanalysis of O VI absorption data

The Copernicus O(+5) column densities toward 72 stars provide a rare and valuable tracer of 10(exp 5.5) K gas in the interstellar medium. The original analysis of the data by Jenkins provided important clues about the distribution of interstellar O(+5) ions, but our understanding of the local interstellar medium has since grown substantially. We revisit that work, including the possibility that local hot gas may contribute a significant O(+5) column density to most lines of sight. Our reanalysis also includes slight improvements in the statistics and was found to be reliable when tested on simulated data sets. In the end, we come to conclusions about the distribution of interstellar O(+5) ions that differ considerably from those of the original analysis. With our reanalysis, some theoretical models now show promise. For example, our Local Bubble column density compares favorably with the estimated quantity of O(+5) within the remnant of an ancient local explosion. Similarly, our mean O(+5) column density per feature in more distant regions is like that found in models of hot interstellar bubbles from either stellar winds or ancient supernova explosions in a warm diffuse interstellar environment, suggesting that the hot gas in interstellar space may exist primarily within discrete regions of modest volume occupation rather than in a continuous and pervasive phase.

Shelton, R. L.↗
NASA NTRS1994

ROSAT PSPC observations of NGC 4636: Interaction with Virgo gas ?

ROSAT Position Sensitive Proportional Counter (PSPC) observations of NGC 4636 have provided a deep image of the galaxy and its surroundings, which reveal the presence of emission well outside the optical galaxy. The source emission is measured out to r approximately 18 min, where the instrument support structure prevents us at this time from following it farther out. The nature of this emission is not fully understood, but could be evidence that the Virgo cluster gas extends as far out as this galaxy (greater than 3 Mpc from M87). Spectral analysis of the X-ray emission suggests a relatively cool (kT approximately 0.5 to 0.9 keV) interstellar medium, with temperatures increasing with radius. However, the detailed properties of the interstellar gas cannot be unambiguously determined with the present data, since the results we obtain depend strongly on the choice of the spectral model. Comparison of the spectral distributions in concentric annuli clearly indicates significant differences with radius, which can be parameterized as a general increase of the temperature. For low cosmic abundance models, kT varies from approximately 0.55 keV in the inner 1 min to approximately 0.8 keV at r approximately 6 to 8 min. Outside 8 min the average temperature is higher than in the inner region (kT approximately 0.8 to 1.2 keV) and the low-energy absorption is significantly lower. For 100% cosmic abundance and galactic line-of-sight absorption, multi-temperature fits are required, suggesting the possibility that the interstellar medi um is inhomogeneous.

Trinchieri, G.↗
NASA NTRS1982

Interstellar iron and manganese - UV oscillator strengths and abundances

Observations of 16 UV resonance lines of Fe II and six of Mn II in five stars are used to derive new f-values for the lines of these species at wavelengths lower than 1300 A. Values of forbidden lines Fe/H and Mn/H are derived. These new values are used to reassess mean depletions and range of variations in depletions for several lines of sight. On an integrated line-of-sight basis, depletions of Fe and Mn show larger variations than P, Cl, or Zn. The mean local depletion forbidden line Fe/H is 1.65, in interstellar gas. One Fe II line, 2366.864 A, has never been detected. Its f-value is shown to be much lower than previously thought. This line is therefore not useful for interstellar studies at the present time. It is suggested that the true wavelength of 1142 A of Fe II, from UV multiplet 10, is 1142.285 A.

Lugger, P.↗
NASA NTRS1985

High-latitude H I structure and the soft X-ray background

The paper presents 21 cm observations made with the NRAO 43 m (140 foot) telescope of 20 randomly selected intermediate and high galactic latitude regions. The data are examined for evidence of the neutral gas clumping required by models in which a substantial fraction of the diffuse soft X-ray background (hv = 0.1 - 0.284 keV) originates outside the galactic disk and is absorbed by interstellar gas. No such evidence is found, and it is concluded that the degree of clumping required by such models must, if it exists, have characteristic angular scales less than 14 arcmin. Furthermore, an analysis of other data indicates that the required clumping does not exist on smaller size scales. It is therefore unlikely that a significant fraction of the X-ray flux originates in a galactic corona, unless some other explanation of the anomalously small apparent absorption can be found.

Jahoda, K.↗
NASA NTRS1994

Hubble Space Telescope imaging of the Seyfert 2 galaxy NGC 2110

Hubble Space Telescope (HST) images of the Seyfert 2 galaxy NGC 2110 in the emission lines of (O III) lambda lambda-4959, 5007 and H-alpha + (N II) lambda lambda-6548, 6584 and the nearby continuum are presented. After deconvolution, the resolution of these images is approximately 0.1 sec, corresponding to a linear scale of approximately 23 pc at the assumed distance (46.8 Mpc) to this galaxy. The dominant line emission is associated with a strongly curved, narrow, 1 sec (230 pc) long feature emanating from the nucleus to the north. The morphology of this feature suggests that it may represent gas flowing outward from the nucleus (perhaps as a 'jet'). While this optical emission-line feature and the jetlike radio emission extend along a similar P.A., their detailed brightness distributions are loosely anticorrelated. In particular, there is no line emission associated with the off-nuclear 6 cm peaks and only weak radio emission along the optical 'jet'. On a larger scale, there is an S-shaped distribution of ionized gas (seen best in H-alpha) extending approximately 4 sec north and south of the nucleus. Ground-based kinematical data suggest this larger scale component represents normally rotating, ambient, interstellar gas photoionized by the central source. A continuum color map derived from HST observations shows evidence for an unresolved region (scale less than 23 pc) of very strong reddening at the location of the optical and radio nucleus. The location and size of the reddened region are consistent with obscuration by a dusty torus, but the observed reddening provides only a lower limit (A(sub V) greater than or equal to 4.6(sub -1.7 sup +1.2) mag) on the amount of obscuration to the nucleus. Nevertheless, this obscuration is sufficient to account for the 'energy deficit' previously reported in this object.

Mulchaey, John S.↗
NASA NTRS1991

Preliminary spectral observations of the Galaxy with a 7 deg beam by the Cosmic Background Explorer (COBE)

The FIR absolute spectrophotometer (FIRAS) on the Cosmic Background Explorer (COBE) has carried out the first all-sky spectral line survey in the FIR region, as well as mapping spectra of the Galactic dust distribution at below 100 microns. Lines of forbidden C I, C II, and N II, as well as of CO are all clearly detected. The mean line intensities are interpreted in terms of the heating and cooling of the multiple phases of the interstellar gas. In addition, an average spectrum of the galaxy is constructed and searched for weak lines. The spectrum of the galaxy observed by FIRAS has two major components: a continuous spectrum due to interstellar dust heated by starlight, and a line spectrum dominated by the strong 158-micron line from singly ionized carbon, with a spatial distribution similar to the dust distribution, and a luminosity of 0.3 percent of the dust luminosity. There are in addition moderately strong 122- and 205.3-micron lines, identified as coming from singly-ionized nitrogen. Maps of the emission by dust and forbidden C II and N II are presented.

Wright, E. L.↗
NASA NTRS1984

X-ray nebular models. II - Constant pressure clouds

Models are presented for the ionization and temperature structure of X-ray illuminated gas clouds under the assumption that the clouds' pressure is fixed. Models are considered which have a variety of different combinations of X-ray source spectrum and cloud pressure, characteristic of galactic X-ray sources and interstellar gas. It is shown that optically thick constant pressure clouds obey scaling laws for their ionized column densities which are analogous to the scaling behavior of constant density models. The results of constant pressure models are contrasted with constant density model results, and it is shown that the constant pressure assumption leads to enhanced thermal instability effects and also causes important differences in the line spectra emergent from X-ray illuminated clouds. Observable consequences for X-ray illuminated interstellar clouds are discussed.

Kallman, T. R.↗
NASA NTRS2012

Organic Chemistry of Low-Mass Star-Forming Cores. I. 7 mm Spectroscopy of Chamaeleon MMSl

Observations are presented of emission lines from organic molecules at frequencies 32-50 GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about 5000 AU from the protostar, whereas methanol peaks about 15,000 AU away. Averaged over the telescope beam, the molecular hydrogen number density is calculated to be 10(exp 6) / cubic cm and the gas kinetic temperature is in the range 5-7 K. The abundances of long carbon chains are very large and are indicative of a nonequilibrium carbon chemistry; C6H and HC7N column densities are 5.9(sup +2.9) (sub -1.3) x 10(exp 11) /cubic cm and 3.3 (sup +8.0)(sub -1.5) x 10(exp 12)/sq cm, respectively, which are similar to the values found in the most carbon-chain-rich protostars and prestellar cores known, and are unusually large for star-forming gas. Column density upper limits were obtained for the carbon chain anions C4H(-) and C6H(-), with anion-to-neutral ratios [C4H(-)]/[C4H] < 0.02% and [C6H(-l)]/[C6H] < 10%, consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC,3 and c-C3H2 were detected. The [DC3N]/[HC,N] ratio of approximately 4% is consistent with the value typically found in cold interstellar gas.

Cordiner, Martn A.↗
NASA NTRS1984

Absorption and Emission of EUV Radiation by the Local ISM

The Berkeley extreme ultraviolet radiation (EUV) telescope flown on the Apollo Soyuz mission in July, 1975 established the existence of a measurable flux of EUV (100 lambda or = or = 1000 A) originating from sources outside the solar system. White dwarfs, flare stars and cataclysmic variables were dicovered to be relatively intense compact sources of EUV photons. Moreover, this and other subsequent experiments have strongly suggested the presence of a truly diffuse component of the FUV radiation field possibly due to thermal emission from hot interstellar gas located in the general vicinity of the Sun. Closer to the H1, 912 A edge, the effect of a few hot O and B stars has been shown to be very important in establishing the interstellar flux density. All these results imply that the local interstellar medium (ISM) is immersed in a non-negligible EUV radiation field which, because of the strong coupling between EUV photons and matter, will play a crucial role in determining its physical structure. The available information on the local ISM derived from the limited EUV observations carried out so far is assembled and analyzed. These include measurements of the spectra of bright EUV sources that reveal clear evidence of H photo absorption at lambda 400 A and of the He ionization edge at 228 A.

Paresce, F.↗
NASA NTRS1980

Observations of interstellar helium with a gas absorption cell - Implications for the structure of the local interstellar medium

A photometer sensitive at the 584 A line of He 1, incorporating a helium gas resonance absorption cell, was flown on the Apollo-Soyuz Test Project in July 1975. The instrument observed much of the night-time sky, and returned 42 min of usable data. The data were analyzed by fitting to a model of resonant scattering of solar 584 A flux from nearby interstellar helium. Good model fits were obtained for an interstellar gas bulk velocity vector pointing toward alpha = 72 deg, delta = +15 deg, with speed 20 km/s, with interstellar medium temperatures from 5000 to 20,000 K and with neutral interstellar helium density (8.9 plus or minus 10 to the -3rd/cu cm). In the context of theoretical studies of the interstellar medium by McKee and Ostriker (1977), the results may indicate that the sun lies in the warm, partially ionized periphery of a cold interstellar cloud, surrounded by a high-temperature gas heated by old supernova remnants.

Freeman, J.↗
NASA NTRS1994

Neutral gas and diffuse interstellar bands in the LMC

Tracing the dynamics of the neutral gas and observing diffuse interstellar bands in the LMC (Large Magellanic Cloud) was the focus of this study. The S/N values, a Quartz lamp exposure, a T horium Argon Comparision lamp exposure, and spectral plots for each star observed were taken. The stars observed were selected to sample the 30 Dor vicinty. NaI absorption profiles are included.

Danks, Anthony C.↗
NASA NTRS1992

The separation between gas and dust filaments at the edge of the expanding shell in Eridanus

Observations obtained from IRAS for a 120 sq deg region at the boundary of a large expanding shell in Eridanus are presented. It is found that the separation between the structures in the H I and IR emission is not due to a transition of the gas into molecular hydrogen at the location of the IR filaments. The molecular hydrogen column density of these filaments is at least two orders of magnitude below what is typically seen in high-latitude molecular clouds. As the H I and dust in this region are associated with a large expanding shell (or superbubble), the action of shocks and radiation fields may be responsible for the separations of gas and dust. Unless the gas and dust structures are resolved and lie in a favorable viewing geometry, the effect tends to be hidden. The results indicate that it is not always evident, from observations with spatial resolutions coarser than a few arcminutes, how interstellar gas and dust are related.

Verschuur, G. L.↗
NASA NTRS1980

Molecular diagnostics of interstellar shocks

The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

Hartquist, T. W.↗