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  • 1
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    An interactive companion to the S star HD 35155 (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Low-dispersion UV spectra taken by the IUE satellite of an S star HD 35155 are presented. It is shown that the spectra contain strong emission lines of multiply ionizes species and an excess continuous emission shortward of 2000 A. Because neither the photospheres nor chromospheres of S stars are expected to produce multiply ionized ions, the emission lines and the excess short-wave emission seen in the HD 35155 spectra are interpreted as an evidence of the presence of a hot nearby compact companion. Some inferences regarding the compact companion and the possible location of the source of the emission lines of multiply ionized ions are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 383; 842-852
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  • 2
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    Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. IV - Further IUE detections (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We have obtained IUE spectra for 31 middle and late-type giant and supergiant stars whose TD-1 fluxes or ground-based spectra indicate the presence of a hot component, or whose radial velocities indicate an unseen component. Stellar components earlier than type F1 were detected in 22 cases. While 20 of the hot secondaries are seen weakly in optical spectra, two are UV discoveries: HD 58134 and HD 183864. The hot companions are classified accurately by temperature class from their far-UV spectra. The interstellar extinction of each system and the relative luminosities of the components are derived from the UV and optical fluxes, using a new grid of UV intrinsic colors for hot dwarfs. We find that many giant stars apparently have companions which are too hot and hence too luminous for consistency with the primary's spectral classification.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 412; 2; p. 814-826.
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  • 3
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    Companions to bright S and MS stars - Technetium deficiency and binarity (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: To test the popular hypothesis that technetium-deficient stars of spectral types S and MS are mass-transfer binaries, we have searched for ultraviolet light from the putative hot secondaries in spectra taken with the SWP spectrograph of IUE. Although most S and MS stars are apparently thermally pulsing AGB (asymptotic giant branch) stars whose surfaces have been enriched with s-process elements and carbon dredged up from the interior, those stars whose spectra show enhanced s-process elements but no Tc are widely believed to be cooler analogs of the Ba II stars, which apparently owe their unusual abundances to prior mass transfer, the Tc from which has decayed away. We report IUE observations of 15 S and MS stars with the SWP, including the identification of six hot companions. Assembling all the IUE observations made to date, we find clear support for the mass-transfer hypothesis, confirming evidence from other lines of research. We further discuss the ages of the companions and the implications of these discoveries for stellar evolution.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 402; 2; p. 667-679.
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  • 4
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    First results from the Goddard High-Resolution Spectrograph - The chromosphere of Alpha Tauri (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The K5 III star Alpha Tau was observed with the Goddard High Resolution Spectrograph on November 27, 1990 as part of the Science Assessment Program for the HST. The spectra show intersystem and permitted chromospheric emission lines of semiforbidden C II and Si II, Fe II, Fe I, Ni II, and Co II. Resolved profiles of the semiforbidden C II lines indicate a complex chromospheric turbulent velocity distribution with mean value of roughly 24 km/s, while their observed wavelengths indicate a 4 km/s downflow of the semiforbidden C II plasma. Twenty-five new emission lines have been found in the 2320-2370 A region, 17 of which have been identified with the aid of Skylab data obtained above the solar limb, including four lines from Co II (UV 8) and an Fe I (UV 12) line.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 377; L45-L48
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  • 5
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    HD 51956 - A supergiant in an interacting binary (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: IUE ultraviolet spectral observations reveal that the F supergiant HD 51956 contains a hot companion star partially obscured by warm plasma. Variable absorption features are analogous to those in the strongly interacting system HD 207739. The F type component is apparently transferring matter to a subluminous B type star which originally was the primary component.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 364; L13-L15
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