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  • 1
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    The CI pressure shift and gravitational redshift of the cool DBQA5 white dwarf LDS678A (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A high resolution ultraviolet spectrum of the helium rich degenerate LDS 678A, obtained with the International Ultraviolet Explorer (IUE) satellite is presented. LDS 678A is the coolest metallic line generate (DQ or DZ) yet observed with the IUE scale. These observations provide a detailed line profile of the strong C I 2479 absorption line with equivalent width (W sub 2479 = 2.35 plus or minus 0.06 angstroms) from which theoretical line profile fits yield a C abundance (log C/He = 6.4). The presence of carbon in a helium rich atmosphere lends credence to the notion that LDS 678A is a transitional case between the DB white dwarfs with nearly pure helium atmospheres and the helium rich DQ white dwarfs which exhibit carbon bands. Corrected for an inferred pressure shift for the C I line, a gravitational redshift is deduced from which a most probable mass of 0.55 solar mass is derived.
    Keywords: ASTROPHYSICS
    Type: ESA, Evolution in Astrophysics: IUE Astronomy in the Era of New Space Missions; p 467-470
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  • 2
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    Ultraviolet carbon lines in the spectrum of the white dwarf BPM 11668 (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The southern hemisphere DC white dwarf BPM 11668 has been found to show strong ultraviolet lines of neutral carbon using observations from the IUE satellite. This star seems typical of the growing number of DC white dwarfs found to be of this type and appears to have a carbon abundance near C:He = 0.0001, with an effective temperature of 8500 K.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 128; 1; 258
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  • 3
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    The cool DC white dwarf Stein 2051B (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Visual scans from the Kitt-Peak 2.1-m telescope and UV spectra from the IUE satellite are combined in a spectroscopic study of the bright DC white dwarf, Stein 2051B. With a cooling age near 2 billion years, and a resulting atmospheric mass of hydrogen of the order of 6 x 10 to the 17th g, the accretion rate over the star's lifetime is less than 2 x 10 to the -25th solar masses/year. This is far below the predictions of standard accretion theories, and requires unreasonably strong suppression of hydrogen accretion in this star if the accretion-diffusion theory is to account for the carbon abundance found. It is suggested that the carbon may have been brought to the surface by convective mixing.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 275; 240-246
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  • 4
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    Observations of ultraviolet carbon lines in the spectra of three DC white dwarfs (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 268; May 1
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  • 5
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    Variations in the mass flow from Zeta Puppis (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Detailed simultaneous visible and ultraviolet spectroscopy of Zeta Puppis was carried out in order to study the time scale of variations in its stellar wind and to assess the relationship between fluctuations in lines of ions formed at different heights. The observed variations were most striking in the He II 4686 A profile, but were also seen in H alpha and in the resonance doublets of Si IV and O VI. Fluctuations in the visible features occurred in times of about one hour, while the ultraviolet profiles showed changes which took several hours to develop. No evidence of periodicity was seen, but the time coverage is not sufficiently complete to preclude it. Specific changes, particularly in H alpha and 4686 A, may have been caused by the passage of density enhancements from the stellar surface outward through the wind. The profile variations, when compared with recent model calculations, imply changes in the mass-loss rate by no more than a factor of two in times of a few hours.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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  • 6
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    Observations of the strong ultraviolet absorptions in the spectrum of the DC white dwarf G218-8 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The spectrum of the 14th magnitude DC white dwarf G218-8 (EG 245) is described. In the visible spectral region the star has been observed with the IIDS scanner attached to the Kitt Peak National Observatory 2.1 m telescope, where it shows a featureless spectrum. However, the ultraviolet observations using the IUE satellite show that strong absorption lines attributable to neutral carbon are present. G218-8 has an effective temperature near 11,500 K and a helium dominated atmosphere with a carbon-to-helium abundance ratio less than or approximately equal to 0.005.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 248
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  • 7
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    An analysis of the bright white dwarf CD - 38 deg 10980 (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The bright DA white dwarf CD - 38 deg 10980 is comprehensively analyzed using all available data. Detailed comparisons of the overall energy distribution and Lyman-alpha and Balmer profiles are made with theoretical predictions based on a homogeneous grid of model atmospheres. These comparisons yield a consistent, well-defined effective temperature and surface gravity for this star of 24,700 + or - 250 K and log g = 7.95 + or - 0.15, respectively. A new gravitational redshift of 28.4 + or - 4.8 km/s is derived from an IUE high-dispersion spectrum. Conclusions regarding the mass and radius of CD - 38 deg 10980 are also presented.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 294-302
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  • 8
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    Identification of the 1400 and 1600 A features observed in the ultraviolet spectra of DA white dwarfs (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The 600 A absorption feature in the spectra of cool DA white dwarf stars has been identified as a resonance broadening of Ly-alpha due to the hydrogen quasi molecule. Likewise, the 1400 A absorption feature in the spectra of cool and moderately warm DA white dwarf stars appears to be due to a Ly-alpha satellite line arising from the hydrogen ion quasi molecule. The strength of both features is gravity sensitive and therefore promises to be an excellent indicator of surface gravity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 289; L31-L33
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  • 9
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    The discontinuity near 1600 A in the spectra of DA white dwarfs (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Ultraviolet spectroscopic observations of two relatively cool DA white dwarfs, L481 - 60 (= WD 1544 - 37) and BPM 1266 ( = WD 2105 - 82), with the International Ultraviolet Explorer (IUE) satellite show a strong drop in their spectral energy distributions below 1600 A. Published model atmospheres and thier visual spectra suggest that these two stars have effective temperatures in the vicinity of 9,000-10,000 K, and it is proposed that the 1600 A feature could be due to the 342(1S) 3s2(1S) photoionization edge of Mg I.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 284; L43-L46
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  • 10
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    Simultaneous visible and ultraviolet spectroscopy of stellar wind variability in Zeta Puppis (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Spectra of He II 4686 A and H-alpha in Zeta Pup were obtained simultaneously with Copernicus ultraviolet scans of several P Cygni profiles in this O4 If supergiant with strong mass loss. The visible-wavelength data show significant variations in the profiles of both lines, consisting of doubling of the emission over times of less than a day. Recent theoretical calculations show that the observed profile variations in 4686 A can be produced by significant fluctuations in the wind density. The Copernicus data show less variability, although in one scan of the 1400-A Si IV doublet there appears to be a significant enhancement of the emission which may be correlated with one of the doublings observed in 4686 A and H-alpha, as though a density enhancement formed at low levels and then moved outward in the wind.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 226
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