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Astron. Astrophys. 324, L53-L56


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Letter to the Editor

Helium line profile variations in the DAB white dwarf HS 0209+0832

U. Heber, R. Napiwotzki, M. Lemke*, and H. Edelmann

Dr. Remeis-Sternwarte, Universität Erlangen-Nürnberg, Sternwartstr. 7, D-96049 Bamberg, Germany

Received 12 June 1997 / Accepted 27 June 1997

Abstract

HS0209+0832, the only white dwarf known to show helium lines in the DB gap region, is reported to display profile variations of helium lines. A quantitative spectroscopic analysis using NLTE model atmospheres reveals that the line profile variations are consistent with a constant Teff = 36100 K and log g = 7.91 but with a varying helium abundance. It decreased from a high abundance state (He/H = 0.012, by number) by a factor of 2 to 3 in 1995 and recovered back to the high abundance state in 1996. The previously suggested possibility that HS 0209+0832 is a composite spectrum (DA+DB) object is ruled out by the spectral analysis. Hence HS 0209+0832 is the first DAB star to be unambigously near the middle of the DB gap and appears to be explainable by a homogeneous He/H atmosphere with the helium abundance lower by a factor of 2-3 in one observation.

Key words: stars: white dwarfs - stars: atmospheres - stars: abundances - stars: variables: other - stars: individual: HS0209+0832 - Diffusion

Send offprint requests to: U. Heber
* Visiting Astronomer, German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy.


© European Southern Observatory (ESO) 1997

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