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  • ASTROPHYSICS  (7)
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  • 1
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    The unusual cometary star-forming region G110-13 (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We present far-IR, radio continuum, and spectral line observations of an unusual, highly elongated, comet-shaped molecular cloud, located about 100 pc from the Galactic plane. The presence of three late B-type stars embedded within, or adjacent to, this low-mass cloud implies a star-forming efficiency that may be as high as 30 percent. Several mechanisms that may have been responsible for its unusual morphology and high star-forming efficiency will be described and evaluated. Although ram-pressure resulting from the rapid motion of this cloud through the interstellar medium could explain its streamlined appearance, there is evidence that G110-13 is the compression front formed by a recent cloud collision.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 397; 1; p. 174-186.
    Format: text
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  • 2
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    Galactic H I and the interstellar medium in Ursa Major (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: 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.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 354; 184-189
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  • 3
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    Ultraviolet and radio observations of Milky Way halo gas (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Interstellar-absorption-line and 21-cm emission-line data for sight lines to 56 stars are combined in order to study the kinematics and spatial distribution of the gas that is at great distances from the Galactic plane. Measurements of the interstellar velocities and H I column densities from the 21-cm emission and Ly-alpha absorption are included. The problem of contamination of the interstellar Ly-alpha absorption line by stellar Ly-alpha absorption is analyzed, and this information is used to reevaluate the vertical distribution of H I. A new method for determining lower limits on the vertical distribution of gas by including information on the velocity structure in the gas is presented. The data for individual sight lines are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 81; 1 Ju
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  • 4
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    Accurate galactic N(H) values towards quasars and AGN (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Integrated Galactic 21-cm column densities toward about 174 quasars and AGN are presented. The data are corrected for stray radiation, using the technique of Lockman et al. (1986). Because of the 21-arcmin beam size of the 140-ft telescope used in the study, the uncertainty in N(H) due to angular variations in the H I of the Galaxy at high latitudes is minimized. The column densities are accurate to about 1 X 10 to the 19th atoms/sq cm, or 5 percent, whichever is larger. Errors above N(H) of about 4 X 10 to the 20th atoms/sq cm are dominated by opacity uncertainties.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 97; 777-782
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  • 5
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    The prevalence of supernova remnants among unidentified Galactic radio sources (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Nine Galactic radio sources were mapped to identify new Crab-like and composite supernova remnants. The sources were selected on the basis of existing stringent upper limits on their hydrogen recombination line fluxes. One new Cracb-like remnant, one new composite remnant, at least one, and probably two, new shell-like remnants, and a compact H II region were found, along with the expected collection of extragalactic objects. The results suggest that there are several hundred SNRs in the Galaxy which are detectable with current instruments, but which have yet to be identified.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 341; 151-162
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  • 6
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    Soft X-ray and H I surveys of the low N(sub H) region in Ursa Major (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A region of almost 300 deg squared in Ursa Major around the direction of the lowest neutral hydrogen column density in the sky has been surveyed in the 1/4 keV X-ray band (approximately 0.12 to 0.284 keV at 10% of the peak response) using the ROSAT position sensitive proportional counter (PSPC) and has been fully mapped in the 21 cm line of neutral hydrogen with an angular resolution of 21' or better. We present maps of these two data sets and an analysis of the spatial correlation between them. Over the entire field, the 1/4 keV band X-ray count rate shows a strong negative correlation with the column density of Galactic neutral hydrogen. We discuss the local, extragalactic, and halo contributions to the observed diffuse X-ray intensity and derive an upper limit to the Galactic X-ray emission originating beyond this H I distribution that is more than a factor of 7 smaller than the inferred flux beyond the Draco nebula, an apparent halo object located approximately 41 degs away. This implies that while there may be significant amounts of hot gas in the Galactic halo, its properties must vary strongly across the sky.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal (ISSN 0004-637X); 430; 2 pt; p. 601-609
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  • 7
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    Small-scale H I structure and the soft X-ray background (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The observed anticorrelation between diffuse soft X-ray flux and H I column density has been explained as absorption of soft X-rays produced in a hot Galactic halo, assuming that the neutral interstellar material is sufficiently clumped to reduce the soft X-ray absorption cross section by a factor of two to three. A 21-cm emission-line study of H I column density variations at intermediate and high Galactic latitudes is extended to 10 arcmin spatial resolution. The results confirm conclusions from preliminary work at coarser resolution, and, in combination with other data, appear to rule out, on any angular scale, the hypothesis that clumping of neutral interstellar matter significantly reduces X-ray absorption cross sections in the 0.13-0.28 keV energy range. It is concluded therefore that the observed anticorrelation is not primarily a consequence of absorption of soft X-rays produced in a hot Galactic halo.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 311; L57-L61
    Format: text
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