Most Double Degenerate Low-mass White Dwarf Binaries Merge
Abstract
We estimate the merger rate of double degenerate binaries containing extremely low mass (ELM; \lt 0.3 M ⊙) white dwarfs (WDs) in the Galaxy. Such WDs are detectable for timescales of 0.1-1 Gyr in the ELM Survey; the binaries they reside in have gravitational wave merger times of 0.001-100 Gyr. To explain the observed distribution requires that most ELM WD binary progenitors detach from the common envelope phase with <1 hr orbital periods. We calculate the local space density of ELM WD binaries and estimate a merger rate of 3 × 10-3 yr-1 over the entire disk of the Milky Way; the merger rate in the halo is 10 times smaller. The ELM WD binary merger rate exceeds by a factor of 40 the formation rate of stable mass transfer AM CVn binaries, marginally exceeds the rate of underluminous supernovae, and is identical to the formation rate of R CrB stars. On this basis, we conclude that ELM WD binaries can be the progenitors of all observed AM CVn and possibly underluminous supernovae; however, the majority of He+CO WD binaries go through unstable mass transfer and merge, e.g., into single massive ∼1 M ⊙ WDs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2016
- DOI:
- 10.3847/0004-637X/824/1/46
- arXiv:
- arXiv:1604.04269
- Bibcode:
- 2016ApJ...824...46B
- Keywords:
-
- binaries: close;
- Galaxy: stellar content;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 13 pages, ApJ accepted