The Spacelab-1 very wide field survey of UV-excess objects. I. CPD -71 172 AB, a new binary with a hot subdwarf.

Abstract

The images taken with the Very Wide Field Camera aboard Spacelab-1 have revealed a variety of stellar objects with strong UV excess. UV(IUE) and ground-based observations of the first object identified (CPD -71°172) have demonstrated a binary system comprising a cool, moderately-evolved star (F3-F4 IV), and a hot OB subdwarf with T_eff ≈ 60000K. From the cool primary, and using optical multicolour data, the authors derive a distance modulus of 9.2±0.3 for the system, yielding a bolometric flux for the hot secondary of log (L/L_sun;) = 2.8±0.2 and a radius of (0.24±0.04)R_sun;. Its gross chemical composition, estimated by comparisons with UV data on several known subdwarfs, indicates that it belongs to the rare He-poor sdO's with T_eff > 40000K.