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  • ASTROPHYSICS  (7)
  • ASTRONOMY  (5)
  • 2010-2014
  • 1985-1989  (5)
  • 1980-1984  (3)
  • 1975-1979  (4)
  • 1960-1964
  • 1
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: Analytic approximations and numerical simulations are used to derive the characteristic behavior of star counts in a galactic spheroidal population, whose visible stars' stellar luminosity function is obtainable for galactocentric distances between about 4 and 12 kpc from star count observations above 30 deg galactic latitude. The total densities of stars and of mass in the spheroid at the solar position are evaluated using different assumed luminosity functions, in order to extrapolate the measured values to a wider range of absolute magnitudes. The upper limits to the frequency of intermediate population stars are derived for the absolute visual magnitude range of 5-8. If such stars occur in either a flat disk with a scale height of 3 kpc or a spheroid with an ellipticity of 0.5, their local surface density is less than 1.8 times that of the spheroid.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 265
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  • 2
    Publication Date: 2019-06-27
    Description: The paper deals with the spectra of six quasars, ranging in redshift from 0.23 to 2.04, obtained with the 45-cm telescope mounted on the IUE satellite. The average emission-line intensity ratio for L-alpha to H beta and the detection of higher-order Lyman emission lines in two objects are found to be inconsistent with a simple optically thick recombination model. The Lyman and Balmer line velocity profiles are identical. The emission lines in 3C 351 can be decomposed into sharp and broad components, with the sharp lines consistent with the recombination model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 239
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  • 3
    Publication Date: 2019-06-28
    Description: Attention is given to the spectral energy distributions of nine high-redshift quasars between 1250 and 10,000 A. The distributions steepen shortward of about 1200 A in all but one object. The steepening's lack of correlation with QSO luminosity suggests that it arises from absorption by intervening material along the line of sight. Reddening may contribute to the steepening of the QSO continua, if dust lies along the line of sight to the continuum source, and is difficult to assess quantitatively. In QSOs with redshift sufficiently high for Lyman-alpha to be observed at high resolution, it is possible to account for the observed continuum steepening by the Lyman continuum absorption corresponding to the narrow Lyman-alpha absorption lines seen.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 76-89
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  • 4
    Publication Date: 2019-06-27
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 202; Dec. 1
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  • 5
    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 217
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  • 6
    Publication Date: 2019-06-27
    Description: 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.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 199; July 1
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  • 7
    Publication Date: 2019-06-27
    Description: IUE observations indicate that the spectrum of 3C 273 is similar to that of other large-redshift quasars. There is a large excess of flux in the range 2400 A to 5300 A, which encompasses the Balmer jump region but which does not appear to be explainable by Balmer emission. The intensity ratio of Lyman-alpha to H-beta is 5.5, in agreement with other measures and a factor 6 smaller than the recombination value. The only absorption lines in the spectrum are due to our Galaxy. There is marginal evidence for a depression of the continuum shortward of the Lyman-alpha emission line, but the errors are too large to warrant any conclusion that 3C 273 has a rich absorption-line spectrum such as that seen in large-redshift quasars. The absence of emission and absorption lines of Fe II leads to the conclusion that resonance fluorescence probably produces the visual Fe II emission lines.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 230
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  • 8
    Publication Date: 2019-07-12
    Description: Images of the gravitational lens 2237+0305 acquired in good seeing have resolved the system into at least five components within the central few arsec of the object: the galaxy nucleus and four point sources in a ringlike formation approximately centered on the galaxy. It is found that the four point sources are distinctly bluer than the galaxy, but that they do not have identical colors. The observed configuration is well reproduced by a simple model that assumes that the four objects are images of the quasar and that the lens is a constant mass-to-light ratio, elliptical, de Vaucouleurs bulge.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 95; 1619-162
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  • 9
    Publication Date: 2019-07-12
    Description: Moderate-resolution slit spectroscopy of the extended emission-line objects A1 and B1 located within 5 arcsec of the triple radio source 2016 + 112 shows that at least one is physically associated with the z = 3.273 quasar thought to be multiply imaged by a foreground galaxy. The data and theoretical models unanimously favor the identification of A1 and B1 with two separate clouds of ionized gas that lie within a few kiloparsecs of the primary A/B QSO and radio source. The available evidence does not support the view that they are multiple images of a single object or their classification as separate (companion) galaxies.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 94; 12-15
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  • 10
    Publication Date: 2019-07-12
    Description: This paper presents optical photometry and spectroscopy of SN 1987D, a Type Ia supernova in the nearby galaxy UGC 7370, during the period immediately subsequent to its discovery. The distance modulus of the galaxy, independently determined by the redshift and the Tully-Fisher (1977) relation, is 32.3 + or - 1.0. The maximum brightness of SN 1987D was V about 13.2 and occurred on April 18, 1987, + or - 4 days; the absolute luminosity is about 0.6 mag brighter than the average for SNe Ia. The spectrum of SN 1987D is typical of SNe Ia, but the expansion velocity (9600 km/s) is considerably lower than average.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 1167-117
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