Circumstellar MG II absorption in UV spectra of hot companions of red giants and the meaning of the MG II asymmetry dividing line.
Abstract
High-resolution lUE spectra of the Mg II 2800 Å doublet of 28 red giant/hot main-sequence binary systems have been investigated for circumstellar (wind-) material of the red giant in the line of sight of the hot companion. The aim was to define more clearly a "wind dividing line" by means of Mg II absorption. Special care is taken to determine temperatures, colours, spectral types and absolute magnitudes of both components in order to locate the red giants correctly in an HR diagram. It turned out that in several cases spectral classifications from composite spectra were quite inaccurate.
We find a Mg II wind dividing line close to the circumstellar Ca II wind dividing line (Reimers 1977). It appear that a Mg II asymmetry V/R < 1 cannot be used to predict the occurrence of cool winds in the HR diagram.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- September 1993
- Bibcode:
- 1993A&A...276..161H
- Keywords:
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- stars: atmospheres;
- stars: binaries: spectroscopic;
- stars: circumstellar matter;
- stars: late type;
- stars: mass-loss