THE MERGER RATE OF BINARY WHITE DWARFS IN THE GALACTIC DISK

• Published in: Astrophysical journal. Letters Vol. 749; no. 1; pp. 1 - 5
• Main Authors: Badenes, Carles, Maoz, Dan
• Format: Journal Article
• Language: English
• Published: United States 10.04.2012
• Subjects: ASTRONOMY; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; Binary systems; Computer simulation; COMPUTERIZED SIMULATION; INDEXES; MASS; Mathematical models; MILKY WAY; MONTE CARLO METHOD; Monte Carlo methods; Phase shift; RADIAL VELOCITY; SPECTROSCOPY; Stellar mass; SUPERNOVAE; WHITE DWARF STARS
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/749/1/L11

(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We use multi-epoch spectroscopy of ~4000 white dwarfs in the Sloan Digital Sky Survey to constrain the properties of the Galactic population of binary white dwarf systems and calculate their merger rate. With a Monte Carlo code, we model the distribution of Delta RV sub(max), the maximum radial velocity shift between exposures of the same star, as a function of the binary fraction within 0.05 AU, f sub(bin), and the power-law index in the separation distribution at the end of the common-envelope phase, alpha . Although there is some degeneracy between f sub(bin) and alpha , the 15 high- Delta RV sub(max) systems that we find constrain the combination of these parameters, which determines a white dwarf merger rate per unit stellar mass of ... x 10 super(-13) yr super(?1) ... (1[sigma] limits). This is remarkably similar to the measured rate of Type Ia supernovae (SNe Ia) per unit stellar mass in Milky-Way-like Sbc galaxies. The rate of super-Chandrasekhar mergers is only ... x 10 super(-14) yr super(?1) ... We conclude that there are not enough close binary white dwarf systems to reproduce the observed SN Ia rate in the "classic" double degenerate super-Chandrasekhar scenario. On the other hand, if sub-Chandrasekhar mergers can lead to SNe Ia, as has been recently suggested by some studies, they could make a major contribution to the overall SN Ia rate. Although unlikely, we cannot rule out contamination of our sample by M-dwarf binaries or non-Gaussian errors. These issues will be clarified in the near future by completing the follow-up of all 15 high- Delta RV sub(max) systems.