Discovery of a white dwarf companion of the "hybrid" K giant HD 81817.

Abstract

IUE observations show that the bright K giant HD 81817 has a faint blue companion which is identified as a white dwarf. A fit of theoretical DA model atmosphere fluxes to the observed energy distribution in the wavelength range λλ1250 Å to 1600 Å yields an effective temperature T_e = 20000±2000K for the WD companion and places the WD at the same distance as the red giant. On the basis of an estimate of the giant's mass, it is argued that the white dwarf must have had a progenitor with an initial mass above ≡4 M_sun;. Finally, it is shown by comparison with θ Her that HD 81817 is a member of the 'hybrid star' class.