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  • 1
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    Are there detectable infrared arcs around supernova 1987A? (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The possibility is examined that the recently discovered arcs of reflected light in the LMC around SN 1987A may be accompanied by detectable arcs of thermal IR emission from dust heated by the UV-visual output of the supernova. Detectability depends on the ratio Zeta = Q(a)/Q(p)P, where Q(a) and Q(s) are the visual absorption and scattering efficiencies of the dust and P is the small-angle scattering phase function. Calculations for spherical grains of graphite and silicate are presented. A Mathis-Rumpl-Nordsieck distribution of grain sizes has an effective Zeta of roughly 0.1. Some grain size distributions more heavily weighted toward small grains in the Galaxy have values of Zeta roughly one to two. With current instrumentation, the flux is below or at best close to the detection limit.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 342; 300-305
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  • 2
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    Mystery spot in supernova 1987A - Reflection or fluorescence by an interstellar cloud? (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper explores fluorescence and reflection models of the companion to SN 1987A obseved by speckle interferometry, recalling a 1901 precedent. The apparent small angular size of the companion is a severe constraint. A fluorescence model cannot reach the observed brightness unless the ultraviolet burst from the supernova contained as many as 2 x 10 to the 58th ionizing photons. This is about 25 times stronger than generous current models. Even then, the expected line ratios and widths do not fit the observations. The absence of narrow H-alpha and H-beta lines in the supernova spectrum, the ratio of fluxes of the companion in H-alpha and forbidden N II line filters, the invisibility of the companion at 4861 (H-beta), and its detection at 5330 fail to agree with theory. A dust-reflection model is more promising, and the color can be reddened by the evaporation of small grains, but the model still falls more than about 1 mag short in brightness. Furthermore, a dust reflection should have increased in relative brightness in May-June 1987, rather than disappearing as the mystery spot did. If all the observations are correct, neither model is likely to work.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 340; 943-949
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  • 3
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    Infrared and optical evidence for a dust cloud behind supernova 1987A (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A substantial increase in the 8-13 micron flux from SN1987A since May 1988 has been attributed to reradiation by an asymmetric circumstellar dust cloud located mainly behind the supernova at a distance of about 200 light days. The calculations of Roche et al. (1989) are extended here to consider the implications of such a cloud. It is concluded that the expected optical echo from the cloud should be resolvable and this, rather than an internal energy source, may cause the observed slowdown in dimming of the supernova. The reflected light may contribute substantially to the current optical luminosity. Observations should be made as soon as possible, for the phenomenon may be evanescent. The dust spectrum suggests that the dust is carbonaceous rather than silicaceous. The cloud behind the supernova may be truly interstellar.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 339; 123-125
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  • 4
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    Spatially resolved flares in RS CVn systems (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Mg II k emission-line profiles arising solely from the flaring region during flares on AR Lac and V 711 Tau have been isolated. From several high-resolution spectra obtained during the lifetime of the flare, the size and position of the flaring regions have been determined, and the decay of the emission line width, radial velocity, and integrated line flux has been studied.
    Keywords: ASTROPHYSICS
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  • 5
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    A study of ten quasars with redshifts greater than four (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Four quasars with redshifts greater than four were detected in a low-resolution CCD grism survey. CCD photometry and high S/N, moderate resolution spectra are presented for these quasars and the six other known quasars with redshifts above 4. The M sub B values of nine of the objects are between -27.5 and -25, with the tenth quasar having an M sub B value of -29. The emission lines and shapes of the continua of these ten quasars are similar to those of lower-redshift quasars. The results suggest that the C IV emission lines in high-redshift quasars may be weaker than those in lower-redshift quasars. The continua of all of the high-redshift quasars display strong depressions blueward of the Ly-alpha emission line.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 98; 1507-152
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  • 6
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    PC 1158 + 4635 - An optically selected quasar with a redshift of 4.73 (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Photometric and spectroscopic observations of PC 1158 + 4635, a quasar with a redshift of 4.73, are presented. This object was discovered by the detection of its Ly-alpha emission line in a low-resolution CCD grism survey. The apparent magnitude of the quasar is r = 20.2; its absolute magnitude is similar to that of 3C 273 (for q0 = 0.5). The spectrum of PC 1158 + 4635 reveals prominent emission lines of Ly-alpha and C IV and a sharp, approximately one magnitude drop in the continuum level across the Ly-alpha emission line (features seen in most greater than 4 quasars). The redshift-continuum depression relation for quasars requires a dramatic change in the 'Lymann alpha clouds' (either in number or intrinsic properties) at a redshift of about 3.5 or else the presence of a new source that is responsible for the majority of the absorption at redshifts obove four.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 98; 1951-195
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  • 7
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    Intrinsic integrated UBVRI colors of Galactic globular clusters (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Published observational data on 50 Galactic globular clusters, including spectral classifications, homogenized colors, and color excesses, are compiled in extensive tables, graphs, and diagrams and analyzed to determine the intrinsic-color/integrated-spectral-type relationship in the UBVRI system. These relationships are found to exhibit significant slopes, although the RI colors do not contribute substantially to the intrinsic-color determination. The values of a(B-V) for the northern and southern Galactic hemispheres are found to be 0.068 + or - 0.006 and 0.039 + or - 0.003 mag, respectively.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 100; 545-567
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  • 8
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    Spectroscopic CCD surveys for quasars at large redshift. II - A Pfuei transit survey (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A CCD transit survey has been carried out with the 200 in. telescope of a strip of sky 5 arcmin wide and 9 hr long. Direct images and slitless spectra of over 43,000 objects were obtained on two successive nights. An automatic search for emission lines of given minimum equivalent width and signal-to-noise ratio yielded 52 candidate sources. Slit spectra revealed that 24 were emission-line galaxies with z less than 0.4 and eight were quasars with 2 between 1.00 and 2.76. The number of quasars detect agrees with that predicted from luminosity function models for z less than 2.9. The models also indicate that between 30 and 62 quasars with z less than 2.9 should have been found in this survey, but none were detected. This result reconfirms that there is a redshift cutoff near or below redshift three. The apparent conflict of this measurement with the known existence of dozens of quasars with redshifts larger than three is discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 310; 518-533
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  • 9
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    Nine optically selected quasars with redshifts larger than 3 (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The detection of nine quasars with redshifts between 3.0 and 3.8 is reported. The quasars were all found in a grism survey from their Lyman-alpha emission line. The r magnitudes of the quasars range from 18.5 to 21.7. The strengths of the Lyman-alpha lines are comparable to the values observed in other quasars (rest equivalent widths from 40 to 160 A). The spectrum of one of the objects possesses complex broad absorption features, similar to those seen in PHL 5200. A preliminary evaluation of these findings suggests that the comoving quasar density declines gradually beyond z = 3.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 316; L1-L3
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