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  • ASTROPHYSICS  (6,235)
  • FLUID MECHANICS AND HEAT TRANSFER  (3,305)
  • 1990-1994  (9,540)
Collection
Keywords
Years
Year
  • 1
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    0108 + 388 - A compact double source with surprising properties (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: 49 cm, 6 cm, and 20 cm observations of the compact double ratio source 0108 + 388 are presented. Extended emission about 20 deg to the east of the core is detected which resembles a hot spot/lobe with a bridge of emission extending back to the core. This is the first detection of extended emission associated with such a source, and it is inconsistent with the suggestion that such sources are very young classical double radio sources. The inconsistency can be reconciled if the activity in this object is recurrent and the emission is the relic of a previous epoch of activity. Alternatively, the source may be a normal-aged radio galaxy in which most of the radio-emitting plasma is currently unable to escape the nuclear regions of the galaxy. The steep low-frequency spectrum of the core is probably related to the origin of the compact double and suggests that both components are very sharply confined on both their inner and outer edges.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 232; 1, Ju
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  • 2
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    1-D models of induced density enhancements in hot-star winds (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We present a 1-D dynamical model of large-scale flow structures induced in a hot-star wind by an initial density perturbation in the inner wind. The resulting wind response is very complex, but includes strong density enhancements that propagate slowly outward through the wind. These density structures exhibit a very slow outward acceleration reminiscent of the discrete absorption components frequently observed in unsaturated UV lines formed in hot-star winds.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 221; 2-Jan; p. 437-441
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  • 3
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    1.25-mm observations of luminous infrared galaxies (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Measurements at a wavelength of 1.25 mm have been obtained for 17 IRAS galaxies selected on the basis of high far-infrared luminosity. These measurements are used to estimate the lower and upper limits to the mass of cold dust in infrared galaxies. As a lower limit on dust mass, all of the galaxies can be successfully modeled without invoking any dust colder than the dust responsible for the 60 and 100 micron emission that was detected by IRAS. As an upper limit, it is possible that the dust mass in a number of the galaxies may actually be dominated by cold dust. This large difference between the lower and upper limits is due primarily to uncertainty in the long-wavelength absorption efficiency of the astrophysical dust grains.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 104; 681; p. 1086-1090.
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  • 4
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    10 AU scale halo structure around DG Tauri (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Lunar occultation observations of the active T Tauri star DG Tau show that in the infrared K band it has a core-halo structure: 20-25 percent of the flux comes from a region 10 AU in extent and the rest from an unresolved core smaller than an AU. These results are consistent with those reported by Leinert et al. from a separate observation. The results obtained here and those of Leinert et al., measuring the intensity distribution projected along directions spanning roughly 40 deg, indicate that the resolved structure is not highly elongated. The extended emission is interpreted as star light scattered by optically thin dust located in a halo surrounding the star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 387; L43-L46
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  • 5
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    10 micron detection of the hard X-ray transient GRO J0422+32: Free-free emission from an X-ray-driven accretion disk wind? (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We report the detection of 10 micrometer emission from the transient low-mass X-ray binary (LMXB) and optical nova GRO J0422+32 near the maximum of its outburst. We discuss this result in terms of (1) a 'standard' model according to which low-energy radiation of LMXB is caused by reprocessing of X-rays in an accretion disk; (2) emission from a cool secondary star; (3) emission from dust grains heated by the transient X-rays, and (4) free-free emission from an X-ray-driven wind from the accretion disk. Only the fourth alternative provides a viable explanation for the observed 10 micrometer emission, with a mass-loss rate in the disk wind that may be substantially higher than the rate of accretion onto the compact star. The presence of such a wind may have a profound effect on the evolution of the binary, and contribute to the solution of the 'birthrate problem' of millisecond ratio pulsars.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal (ISSN 0004-637X); 429; 1, pt; p. L19-L23
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  • 6
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    10 micron spectra of protostars and the solid methanol abundance (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A search has been made for the strong C-O stretching absorption of solid methanol near 9.8 microns toward the heavily obscured protostars AFGL 961, AFGL 2591, the BN object and Mon R2 IRS 3. There is no clear evidence for this feature in the spectra, resulting in very conservative upper limits to the methanol abundance of 6 percent to 17 percent relative to solid H2O toward these objects. This is well below previous estimates of 50-80 percent obtained toward W33 A, NGC 7538 IRS 9, AFGL 2136, and W3 IRS 5, which were based on the assignment of the interstellar 6.85 microns absorption feature to the methanol C-H bending mode. This study shows that such high methanol abundances are not a characteristic of all interstellar ices.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 382; 523-529
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  • 7
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    12 and 20 micron imaging of the starburst galaxy NGC 253 (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The study presents 12- and 20-micron imaging of the starburst galaxy NGC 253 with a spatial resolution of 0.8 arcsec. A positional uncertainty of 1.6 arcsec in these images is estimated on the basis of previous ground-based mid-IR studies to determine the absolute position of the images. It is concluded that the proposed 'nucleus' of NGC 253, i.e., the dominant, bright, flat-spectrum radio source identified by Turner & Ho (1985) (TH 2), is not associated with the mid-IR peak, but rather is located 2.2 arcsec to the northeast. The mid-IR peak, IRS 1, is placed midway between TH 6 and TH 7. Several coincidences with the present 12-micron image are found: IRS 1 falls within 1 arcsec of the 2-micron peak; a second significantly weaker IR source, IRS 2, coincides with TH 2; and the brightest steep-spectrum 6-cm radio source, TH 9, coincides with a 'tongue' of emission extending to the southwest of IRS 1.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 401; 2; p. L75-L78.
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  • 8
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    15 GHz compact structure in galactic nuclei (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 362; 434-442
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  • 9
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    158 micrometers (CII) mapping of NGC 6946: Probing the atomic medium (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The strong 158 micrometers (C2) cooling line of the NGC 6946 galaxy is investigated. The data was acquired with a far infrared imaging Fabry-Perot interferometer with 55 minutes resolution. About 1 percent of the total far infrared luminosity of the galaxy is analyzed. The (C2) emission comes from a mizture of components of interstellar gas. The brightest emission is associated with the nucleus, a second component traces the spiral arms and the largest star forming/H2 regions contained within them, and a third extended component of low brightness can be detected at least 12 kpc from the nucleus. The nuclear and spiral arm components are most likely associated with dense photon dominated regions at molecular cloud surfaces that are exposed to ultraviolet radiation produced by young massive stars. The (C2) emission is analyzed and the cooling rate in the atomic medium is consistent with photoelectric heating by diffuse ultraviolet radiation.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-193463 , NAS 1.26:193463 , MPE-PREPRINT-222
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  • 10
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    158 micrometers (CII) mapping of the Orion molecular cloud (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Data from the inner regions of the Orion nebula in the 157.7409 micrometers (CII) fine structure line is investigated. Large scale strip maps in (CII) across the face of the Orion molecular cloud, and CO spectra at selected positions in the Orion HII region/molecular cloud interface were obtained. The total (CII) luminosity from the Orion molecular cloud is estimated to be approximately 1500 of the solar luminosity or 0.3 of the far infrared luminosity. The overall properties of the Orion molecular cloud deduced are: the photodissociated gas to molecular gas mass fraction, the (CII) line to far infrared continuum intensity ratio and the (CII)/CO(12) (1 to 0) line intensity ratio are the same for the Orion molecular cloud and the nuclei of non-starburst galaxies. The observations provide an important link between (CII) emission from galactic molecular clouds and the nuclei of external galaxies.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-193464 , NAS 1.26:193464 , MPE-PREPRINT-224
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