Theta Hya: Spectroscopic identification of a second B star + white dwarf binary

TL;DR

This paper reports the spectroscopic identification of a second B star plus white dwarf binary system, providing insights into white dwarf progenitor masses and the initial-final mass relation.

Contribution

It is the first to conclusively identify a white dwarf companion to Theta Hya, expanding understanding of B star + white dwarf binaries.

Findings

White dwarf temperature constrained between 25,000K and 31,000K.

First conclusive identification of a white dwarf companion to Theta Hya.

Potential white dwarf companion in the B9.5V star 16 Dra.

Abstract

We report the identification, in an Extreme Ultraviolet Explorer (EUVE) spectrum, of a hot white dwarf companion to the 3rd magnitude late-B star Theta Hya (HR3665, HD79469). This is the second B star + white dwarf binary to be conclusively identified; Vennes, Berghofer and Christian (1997), and Burleigh and Barstow (1998) had previously reported the spectroscopic discovery of a hot white dwarf companion to the B5V star y Pup (HR2875). Since these two degenerate stars must have evolved from main sequence progenitors more massive than their B star companions, they can be used to place observational lower limits on the maximum mass for white dwarf progenitors, and to investigate the upper end of the initial-final mass relation. Assuming a pure hydrogen composition, we constrain the temperature of the white dwarf companion to Theta Hya to lie between 25,000K and 31,000K. We also predict that a third bright B star, 16 Dra (B9.5V), might also be hiding an unresolved hot white dwarf companion.