Discovery of a Bright, Extremely Low Mass White Dwarf in a Close Double Degenerate System
Abstract
We report the discovery of a bright (V ~ 13.7), extremely low mass white dwarf in a close double degenerate system. We originally selected GALEX J171708.5+675712 for spectroscopic follow-up among a group of white dwarf candidates in an ultraviolet-optical reduced proper-motion diagram. The new white dwarf has a mass of 0.18 M sun and is the primary component of a close double degenerate system (P = 0.246137 days, K 1 = 288 km s-1) comprising a fainter white dwarf secondary with M 2 ≈ 0.9 M sun. Light curves phased with the orbital ephemeris show evidence of relativistic beaming and weaker ellipsoidal variations. The light curves also reveal secondary eclipses (depth ≈8 mmag) while the primary eclipses appear partially compensated by the secondary gravitational deflection and are below detection limits. Photospheric abundance measurements show a nearly solar composition of Si, Ca, and Fe (0.1-1 sun), while the normal kinematics suggest a relatively recent formation history. Close binary evolutionary scenarios suggest that extremely low mass white dwarfs form via a common-envelope phase and possible Roche lobe overflow.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2011
- DOI:
- 10.1088/2041-8205/737/1/L16
- arXiv:
- arXiv:1108.0335
- Bibcode:
- 2011ApJ...737L..16V
- Keywords:
-
- binaries: close;
- stars: individual: GALEX J171708.5+675712;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- published in ApJ Letters