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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 505 records · Page 28
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NASA NTRS1975

Optical studies of 10 high galactic latitude X-ray sources

Optical studies are reported for a representative sample of 10 unidentified high galactic latitude X-ray sources that are north of declination minus 25 deg and that have 3U error boxes less than or of the order of 0.5 square degrees. The source 3U 1410-03 is identified with a peculiar emission-line spiral galaxy, NGC 5506, and a distance group 4 rich cluster of galaxies, Abell 2142, is suggested as a possible identification for 3U 1555+27. It is shown that very few of the unidentified high galactic latitude sources are quasi-stellar sources brighter than 17.5 mag, although one possible X-ray quasar, NAB 0137-01, is reported.

Bahcall, J. N.↗
NASA NTRS1976

The relationship between the galactic matter distribution, cosmic ray dynamics, and gamma ray production

Theoretical considerations and analysis of the results of gamma ray astronomy suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density should be enhanced where the matter density is greatest on the scale of galactic arms. This concept has been explored in a galactic model using recent 21 cm radio observations of the neutral hydrogen and 2.6 mm observations of carbon monoxide, which is considered to be a tracer of molecular hydrogen. The model assumes: (1) cosmic rays are galactic and not universal; (2) on the scale of galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3) the cosmic ray scale height is significantly larger than the scale height of the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of about 3:1.

Kniffen, D. A.↗
NASA NTRS1977

SAS-2 gamma-ray results from the galactic plane and their implications for galactic structure and galactic cosmic-ray dynamics

The final SAS-2 results related to high energy galactic gamma-ray emission show a strong correlation with galactic structural features seen at other wavelenghts, when the known gamma-ray sources are subtracted. Theoretical considerations and analysis of the gamma-ray data suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density is enhanced where the matter density is greatest on the scale of the galactic arms. This concept has been explored in a galactic model that assumes: (1) cosmic rays are galactic and not universal; (2)on the scale of the galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3)the cosmic ray scale height is significantly larger than the scale height to the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of over 2:1.

Fichtel, C. E.↗
NASA NTRS1980

Nature of type 1 Supernovae

The nature of type 1 supernovae (SN 1) is discussed through a comparison of observational evidence and theoretical perspectives relating to both type 1 and 2 supernovae. In particular two hypotheses relating to SN 1 phenomenon are examined: the first proposing that SN 1 are components of binary systems in which, at a comparatively late stage of evolution, overflow of the mass occurs; the second considers pre-SN 1 to be recently evolved stars with a mass greater than 1.4 solar mass (white dwarfs). In addition, an explanation of the reduced frequency of flares of SN 1 in spiral galaxies as related to that in elliptical galaxies is presented.

Shklovskiy, I. S.↗
NASA NTRS1979

Observations of three QSOs lying in the spiral arms of NGC 1073

Spectrophotometric observations of three QSOs lying in the field of the spiral galaxy NGC 1073 are presented. These objects have been reported by Arp and Sulentic (1979), who obtained redshifts for two of them. The present observations, made with the Shane telescope at Lick Observatory, extend the wavelength coverage, show L-alpha in BSO 1 at z = 1.945, yield a firm redshift of z = 0.599 for BSO 2, and confirm the redshift z = 1.41 of RSO obtained by Arp and Sulentic (1979).

Burbidge, E. M.↗
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 triple quasar Q1115+080A, B, C - A quintuple gravitational lens image

Spectroscopy and direct imaging of Q1115+080A, B, C with a CCD camera support the hypothesis that they are gravitational images of a single object. Spectroscopy of the semiforbidden C III 1909-A emission line shows all the images to have identical spectra and redshifts (to within 100 km/s), except that B is slightly redder. Gravitational lens imaging by a massive spiral galaxy is investigated, and a quintuple image model resembling Q1115+080A, B, C is found. In this model, Q1115+080A is a highly magnified close pair of images oriented in the position angle 23 deg. An elongation Q1115+080A at this angle is seen in the CCD pictures.

Young, P.↗
NASA NTRS1981

NGC 1097 - The structure of the central 3 kiloparsecs at 10 microns

It is found that the central, optically bright region of the spiral galaxy NGC 1097 is a strong 10 micron source. A striking correlation is seen between the optical and infrared surface brightnesses. The properties of these sources imply that young stars power the infrared emission. It is inferred that the central 30 arcsec of NGC 1097 has a large bolometric luminosity of about 10 to the 11th solar luminosities, most of which originates in a ring approximately 2 kpc in diameter. These observations strongly support the hypothesis that the infrared emission from galaxies is often associated with bursts of star formation.

Telesco, C. M.↗
NASA NTRS1981

Detection of Lyman continuum absorption in the BL Lacertae object PKS 0735+178

The detection of the Lyman edge in the BL Lac object PKS 0735+178 at the absorption red shift determined by optical measurements leads to a lower limit for the column density of atomic hydrogen, N(H I) not less than 4(17)/sq cm. The Lyman-alpha absorption line appears to have been detected, but only an approximate upper limit can be obtained from the data, of the order of 2(19)/sq cm. This amount of atomic hydrogen is less than that for a line of sight through the disk of a normal spiral galaxy. It is suggested that the absorbing material exists either in the halo of a galaxy or in the tenuous, extended, gaseous disk of a galaxy.

Bregman, J. N.↗
NASA NTRS1982

A comparative study of computational methods in cosmic gas dynamics

Many theoretical investigations of fluid flows in astrophysics require extensive numerical calculations. The selection of an appropriate computational method is, therefore, important for the astronomer who has to solve an astrophysical flow problem. The present investigation has the objective to provide an informational basis for such a selection by comparing a variety of numerical methods with the aid of a test problem. The test problem involves a simple, one-dimensional model of the gas flow in a spiral galaxy. The numerical methods considered include the beam scheme, Godunov's method (G), the second-order flux-splitting method (FS2), MacCormack's method, and the flux corrected transport methods of Boris and Book (1973). It is found that the best second-order method (FS2) outperforms the best first-order method (G) by a huge margin.

Van Albada, G. D.↗
NASA NTRS1983

The probable association of SN 1957d in NGC 5236 (M83) with an unresolved radio source

Astrometric measurements of the position of SN 1957d in the spiral galaxy NGC 5236 using archival plates indicate that it is within 2 arcsec of the position of a point radio source of approximately Cas A strength on a VLA map made by Cowan and Branch (1982). This coincidence strongly suggests that the radio source originated from the supernova. If further investigation shows this point source to indeed be a supernova remnant, then this would be the first reported detection of an intermediate-age supernova remnant.

Pennington, R. L.↗
NASA NTRS1983

A note on the oxygen gradient in NGC 628

The Kitt Peak 2.1-m telescope and Intensified Image Dissector Scanner have been used to gather spectrophotometric data in the 3600-5200 A spectral region for five H II regions in the spiral galaxy NGC 628. The Pagel et al (1979) technique was then applied to determine the relative number abundances of O to H in each of the H II regions. An examination of the abundance values obtained as a function of the radial coordinate yields an O gradient of -0.05 + or - 0.03 dex/kpc.

Talent, D. L.↗
NASA NTRS1984

Images in the rocket ultraviolet - Photometry of M101

It is pointed out that ultraviolet imagery of spiral galaxies is a sensitive probe of the large-scale morphology of the star-forming regions and the associated interstellar dust. A rocket-borne Ritchey-Chretien telescope was employed to obtain three ultraviolet images of the Sc 1 galaxy M101 (NGC 5457). The present investigation is concerned with the procedures for reduction and absolute calibration of the obtained images and an analysis in terms of discrete sources. Attention is also given to the radial variation and the azimuthal variation of disk and arms. It is found that the emission from M101 in the UV bandpass is dominated by extreme Population I, in the form of discrete OB/H II complexes.

Hill, J. K.↗
NASA NTRS1984

The formation of stellar systems from interstellar molecular clouds

The observational and theoretical study of regions of continuing star formation promises greater insight into the physical conditions and events associated with the formation of the solar system, and elucidates the role played by star formation in the evolutionary cycle which seems to dominate interstellar material's processing by successive generations of stars in the spiral galaxies. Novel astronomical methods incorporated by the new facilities scheduled for development in the 1980s may yield substantial advancements in star formation process theory; most significant among these efforts will be the identification and examination of the elusive protostellar collapse phase of both star and planetary system formation.

Gehrz, R. D.↗
NASA NTRS1984

Dust Reradiation from NGC 6946

Far infrared measurements of dust reradiation for the spiral galaxy NGC 6946 are presented. The measurements consist of maps and an energy distribution, all made with a resolution of 49 sec. Effective wavelengths are 120 and 170 microns for the maps and 60, 120, and 170 microns for the energy distribution. Much of the reradiating dust has a temperature of 20 K. The amount of starlight reradiated at far infrared wavelengths is approx. 6 x 10 to the 10th power L(solar) or about half the total amount of starlight produced by the nucleus and disk of NGC 6946. A bright nuclear peak centered on a 5' wide disk describes the reradiation morphology at 170 microns. The disk contributes approx. 90% of the total reradiation; the 49 sec diameter region centered on the nucleus gives the small remainder. The morphology of reradiated starlight is compared to the familiar starlight morphology observed at optical wavelengths.

Smith, J.↗
NASA NTRS1985

Halo of NGC 4631 and models of cosmic-ray transport

The halo of edge on spiral galaxy of NGC 4631 is studied from 327 MHz to 10700 MHz to delineate the models of cosmic ray transport. Preliminary studies show that the spectral steepening as a function of height above the plane can be understood in terms of the simplest cosmic ray transport models, viz., simple isotropic diffusion in an infinite medium.

Cowsik, R.↗
NASA NTRS1984

An unsuccessful search for very extended halos around NGC 1300 and M61

The results of a search for H and K absorption in the halos of the two spiral galaxies projected against background QSOs are presented. The search was carried out using the blue-sensitive spectrograph attached to the Multiple Mirror Telescope (MMT). Despite good sensitivity (S/N of about 20) and high spectral resolution (1 A), no H and K absorption was found. Schematic illustrations of the nuclear and halo spectra of M61 and NGC 1300 are provided.

Bothun, G. D.↗
NASA NTRS1985

2237 + 0305 - A new and unusual gravitational lens

A new gravitational lens system has been discovered which consists of a quasar at z = 1.695 nearly centered on a 15-mag spiral galaxy, 2237 + 0305, at z = 0.0394. At 2 arcsec resolution, only a single optical image of the quasar is visible; its centroid is located within approximately 0.3 arcsec of the center of the galaxy. 'Snapshot' observations at the VLA yielded no detectable radio radiation, placing an upper limit of about 0.5 mJy on the combined flux density of the galaxy and quasar at a wavelength of 6 cm. A simple gravitational lens model that accounts for these observations is discussed.

Huchra, J.↗