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  • ASTROPHYSICS  (150)
  • 1980-1984  (150)
  • 1960-1964
  • 1983  (150)
  • 1963
  • 11
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    A far-infrared study of the N/O abundance ratio in galactic H II regions (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: New measurements are presented for W43 (G30.8-0.0), Orion A, and G75.84+0.4, which are located at widely varying distances from the galactic center. The combination of the forbidden N III 57.3 microns and forbidden O III 88.4 and 51.8 microns yields measurements of N(++)/O(++) that are for the most part insensitive to electron temperature and density uncertainties and to clumping of the ionized gas. This is due to the similarity of the critical densities for these transitions. It is contended that for the observed nebulae, N(++)/O(++) should be indicative of N/O, a ratio that is of signal importance in nucleosynthesis theory. The measurements are compared with previous measurements of M17 and W51, which lie at intermediate galactocentric distances. For nebulae in the solar circle, it is found that N(++)/O(++) is greater than the N/O values derived from optical studies of N(+)/O(+) in low-ionization zones of the same nebulae. Possible sources of this discrepancy are considered. It is found that N(++)/O(++) in W43 is significantly higher than for the other H II regions in the sample. Since W43 is located at R = 5 kpc, which is the smallest galactocentric distance in the sample, the data are seen as consistent with the presence of a negative abundance gradient d(N/O)/dR.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 15
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  • 12
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    Peculiar ultraviolet interstellar extinction (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In connection with investigations of the physical characteristics of interstellar dust, a study of objects with peculiar extinction might provide new insights about the composition, size distribution, formation, and destruction of the particulate matter. Meyer and Savage (1981) have found that the dust toward many stars exhibits peculiar UV extinction. The present investigation is concerned with International Ultraviolet Explorer (IUE) spectrophotometric measurements for a sample of stars judged by Meyer and Savage to have highly anomalous UV extinction as inferred from the broad-band Astronomical Netherlands Satellite (ANS) data. The reported IUE measurements provide the opportunity to determine if the ANS photometry measurements of Meyer and Savage are anomalous because of peculiar extinction.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
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  • 13
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    Interstellar abundances of oxygen and nitrogen (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Neutral nitrogen and oxygen column densities or limits are derived for 53 path lengths through the diffuse interstellar medium and compared with column densities of neutral hydrogen. For neither N nor O is a systematic increase of depletion found as reddening increases. The value found for forbidden O/N is 8, and the abundances of N and O are both between 40% and 70% of the solar values. Implications of these results for models of interstellar grains are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
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  • 14
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    Chemical state of pre-solar matter (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Consideration is given to several features of the chemical state of interstellar matter that may be relevant to the observed properties of chondrules if they are formed from aggregates of pre-existing particles. First, a brief summary of the numbers and types of interstellar particles as indicated by the extinction of starlight is given. Second, a model of the free decay interval required by the low solar abundance of 129-I is advanced. This model can support variations in the 129-I/127-I ratio that are larger than typical isotopic anomalies. Third, a new steady-state model of the chemical state of the interstellar medium is presented as a first step toward a quantitative distribution of the abundances among different chemical forms. Last, the advantages of fusing chondrules from aggregates of pre-solar dust by the action of exothermic chemistry are enumerated.
    Keywords: ASTROPHYSICS
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  • 15
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    The nature of R136a, the superluminous central object of the 30 Doradus nebula (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: UV data show R136a to be an extremely luminous object having spectral characteristics similar to that of O3 stars. It is suggested that the bright component of R136a is either a single, supermassive hydrogen-burning star, or a compact multiple system of supermassive stars. In the former case, the observational data imply a mass exceeding that of the most massive stars known by a factor of 20 and raise important theoretical problems concerning stellar formation and stability. Formation may occur through ordinary collapse in a region with peculiar dust properties, or through coalescence in the core of a compact cluster.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 273; 597-623
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  • 16
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    Far-infrared detection of low-luminosity star formation in the Bok globule B335 (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Measurements of far-infrared intensities in the Bok globule B335, made with higher spatial and spectral resolution than two earlier studies, are described. The NASA 3-m Infrared Telescope Facility was used in February 1981 and the Kuiper Airborne Observatory 0.9-m telescope was used in October 1981 and August 1982 for the observations. The far-infrared source in B335 was revealed to be more compact than previously assumed, ruling out the interstellar radiation field as the dominant heat source. The new far-infrared size, luminosity, and temperature derived suggest that these may be the first observations of low-mass star formation embedded deeply within a Bok globule. The far-infrared source does not have a near-infrared or radio continuum counterpart. High angular resolution at submillimeter wavelengths will be critical in further studies of low-mass star formation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L43-L47
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  • 17
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    The photometric variability of solar-type stars. III - Results from 1981-82, including parallel observations of thirty-six Hyades stars (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A photometric survey of main-sequence stars in the Pleiades, Hyades, and Malmquist Field, to investigate variability among solar-type stars, had been continued at Cloudcroft Observatory for a second season. Possibly six of 40 Pleiades stars, two (possibly six) of 49 Hyades stars and possibly four of 42 stars in the Malmquist Field are found to be variable. Parallel observations of Hyades stars were obtained also at Lowell Observatory. These measurements, which achieved better precision, reveal significiant variations in eleven (possibly 16) of 36 Hyades stars, all of spectral type F7 V-K2 V. Agreement between the two surveys is acceptable. The two seasons of the Cloudcroft survey show that changes in the mean annual brightness of the Hyades stars accompany changes in the amplitude of their short-term variability, in the sense that a star tends to become fainter as its variability increases and vice versa. Color effects are absent.
    Keywords: ASTROPHYSICS
    Type: AD-A135037 , AFGL-TR-83-0303 , Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 621-634
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  • 18
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    The discovery of S2 in comet IRAS-Araki-Alcock 1983d (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Ultraviolet spectra of comet IRAS-Araki-Alcock 1983d, obtained with the International Ultraviolet Explorer spacecraft when the comet was only 0.032 AU from earth, show strong emission bands due to S2, the first detection of this species in an astronomical object. The spatial profiles imply that the S2 is released directly from the nucleus and has a lifetime of the order of 450 s. The derived production rate of S2 was 2 x 10 to the 25th per s. It is suggested that the S2 can be formed by cosmic-ray irradiation of other sulfurous compounds in the ices and that it need not be primordial. It has been also determined that the scale length of the parent of CS (presumably CS2) is 300 km and that the CS production is approximately equal to that of S2, both near 5 x 10 to the -4th that of OH and comparable to that of other trace species observed in comets.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L99-L103
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  • 19
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    Possible contributions of supernova remnants to the soft X-ray diffuse background (0.1 - 1 keV) (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Almost all of the B band (0. 10-0.19 keV) and C band (0.15-0.28 keV) X-rays probably originate in a hot region surrounding the sun, which Cox and Anderson modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5-1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra galactic power law flux and any large-scale-height stellar (or galactic halo) emission.
    Keywords: ASTROPHYSICS
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  • 20
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    Corequake and shock heating model of the 5 March 1979 gamma-ray burst (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Ramaty et al. (1980) have proposed a model of a neutron-star corequake and subsequent shock heating of the atmosphere to account for the gamma-ray burst of March 5, 1979. This model is elaborated by examining the overall energetics and characteristics of the radiation-dominated gas shocks under the assumption of thermodynamic equilibrium, taking into account the electron-positron pair production behind the shock. Using values for the density typical of those expected for neutron-star crusts (100-10,000 g/cu cm) and shock velocities characteristic of the sound speed (40,000-100,000), shock luminosities are obtained comparable to those required if the burst originated in the LMC. In addition, the fraction of energy deposited in electron-positron pairs is in good agreement with observation. Uneven shock heating between the polar and equatorial regions of the neutron star due to the presence of a dipole magnetic field, coupled with a rotation rate of 8 s, can also naturally account for the pulsating phase of the burst.
    Keywords: ASTROPHYSICS
    Type: International Cosmic Ray Conference; Aug 22, 1983 - Sep 03, 1983; Bangalore; India
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