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  • 1
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    New insight into the physical state of galaxies and quasars (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Data from the International Ultraviolet Explorer satellite have revolutionized many concepts in extragalactic astronomy. These include the physical processes at work in the emitting gas characteristic of active objects, the nature of the continuum source itself in those objects, and the constituent hot stellar and gaseous components of normal galaxies. Several problems of extragalactic research investigated with IUE were reviewed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 711-723
    Format: application/pdf
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  • 2
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    Spectrophotometric and model-atmosphere analyses of the hot DO and DAO white dwarfs from the Palomar-Green survey (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Recent optical and spectrophotometric observations of all currently known DAO and DO hot white dwarf candidates from the Palomar-Green Survey are presented. The optical observations were carried out using the Kitt Peak National Observatory Intensified Image Dissector Scanner (IIDS) system, the Multiple Mirror Telescope (MMT), and two photon-counting Reticon systems. Ultraviolet spectrophotometry was obtained using the International Ultraviolet Explorer (IUE) short-wavelength and long-wavelength cameras. The following spectroscopic subgroups were identified in the observations: the cool DO stars with spectra showing H I features together with He II + H blends; the hot DO stars, with spectra exhibiting weak He II (+H) lines; and hydrogen-rich DAO stars with broad H lines and sharp H II lines at 4686 A. A fourth subgroup of stars resembling PG 1159 with He at He II lines at 4686, and a C, N ion blend in the optical spectrum were also found. The spectroscopic data were analyzed in terms of a grid of hot, high-gravity LTE model atmospheres composed of a mixture of hydrogen and helium, and atmospheric parameters are deduced for each class of objects. On the basis of the model atmosphere analysis, the local space density of the DO stars is estimated to be 1.9-3.0 x 10 to the -7th per cubic pc, depending on the scale height.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 58; 379-411
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  • 3
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    Observations of quasars with the International Ultraviolet Explorer satellite (1980)
    In:  Other Sources
    Details
    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
    Format: text
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  • 4
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    IUE observations of high-redshift quasars (1984)
    In:  Other Sources
    Details
    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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  • 5
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    A spectroscopic investigation of the nebulosity around low-luminosity quasars (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 263
    Format: text
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  • 6
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    Two hot, low-field magnetic DA white dwarfs (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two hot stars discovered in the Palomar Green survey which were found to exhibit peculiarly broad and strong Balmer lines possibly indicative of low magnetic fields are discussed. The stars, PG 1658+441 and PG 0136+251, were found to have extended trough-shaped Balmer and Lyman-alpha line profiles when compared to nonmagnetic dwarfs of similar temperatures. Further observations of PG 1658+441 show it to correspond to a 30,000 K pure hydrogen atmosphere and confirm its nature as a magnetic object with a longitudinal field strength of about 0.7 megagauss and a mean surface field of about 2.3 megagauss. PG 0136+251 is found to be a hotter star (40,000-50,000 K) with weaker lines. Although no strong evidence for magnetic line splitting was obtained, it is argued that neither a high surface gravity nor very rapid rotation can account for the Balmer line shapes. Results thus extend the range of magnetic degenerates to include very hot white dwarfs, and demonstrate the usefulness of line-widths as indicators of possible low-field magnetic sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
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  • 7
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    Two new color-selected magnetic DA white dwarfs (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The discovery of two magnetic white dwarfs culled from blue star surveys is reported. The surveys were carried out with the Mount Lemnon 1.5-meter reflecting telescope attached to a two-holer polarimeter/photometer. Spectral observations of the objects, (PG 1533 - 057, and K813 - 14), indicate the presence of hydrogen and Zeeman components. On the basis of dipolar field simulations, it is shown that PG 1533 - 057 has a polar field strength of 31 megagauss (MG) while K813 - 14 has a polar field strength of 29 MG. A third known white dwarf has a polar field strength of 18 MG. All the dwarfs had temperatures in the 11,000-20,000 K range. The possibility that a significant fraction of isolated magnetic degenerate stars could be the progeny of magnetic accreting binary systems is considered.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 97; 158-164
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  • 8
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    Two new extremely hot pulsating white dwarfs (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.
    Keywords: ASTROPHYSICS
    Type: AD-A144474 , AFOSR-TR-84-0652 , Astrophysical Journal, Part 1 (ISSN 0004-637X); 279; 751-757
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  • 9
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    PG 1012-029 - A high-excitation eclipsing cataclysmic variable (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The paper presents a photometric and spectrophotometric analysis of a new eclipsing cataclysmic variable, PG 1012-029, with an orbital period of 3 hr 14 minutes 18.7 s. The eclipse depth reaches 1.9 mag, is rounded at minimum, and shows a prolonged egress 'shoulder', as found for UX UMa and some other eclipsing systems. The spectrum shows strong high-excitation lines at optical and UV wavelengths. A large fraction of the He II flux disappears during the eclipse, when the hydrogen spectrum fits a cooler temperature, and the continuum reddens. This behavior is attributed to eclipse of the hotter inner disk region.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 276; 233-242
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  • 10
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    The spectrum of the halo surrounding the quasar PHL 1070 (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The quasar PHL 1070 and its surrounding halo of light have been observed with the Palomar multichannel spectrophotometer using circular and annular apertures. The central quasar has a magnitude of 16.6 and an emission-line redshift of 0.076 + or - 0.002. The halo light has a magnitude of 19.0 and a possible absorption-line system with an absorption redshift of 0.067 + or - 0.008. The magnitude, possible absorption lines, and probable spectral energy distribution of the halo are consistent with those of a normal galaxy at the redshift of the quasar.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 219
    Format: text
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