On WD-WD Mergers in Triple Systems: The Role of Kozai Resonance with Tidal Friction

Snezana Prodan, Norman Murray, Todd A. Thompson

Published 2013-05-09, updated 2013-11-26Version 2

White dwarf-white dwarf (WD-WD) mergers may lead to type Ia supernovae events. Thompson (2011) suggested that many such binaries are produced in hierarchical triple systems. The tertiary induces eccentricity oscillations in the inner binary via the Kozai-Lidov mechanism, driving the binary to high eccentricities, and significantly reducing the gravitational wave merger timescale (T_GW) over a broad range of parameter space. Here, we investigate the role of tidal forces in these systems. We show that tidal effects are important in the regime of moderately high initial relative inclination between the inner binary and the outer tertiary. For 85 < i_0 < 90 degrees (prograde) and 97 < i_0 < 102 degrees (retrograde), tides combine with GW radiation to dramatically decrease T_GW. In the regime of high inclinations between 91 < i_0 < 96 degrees, the inner binary likely suffers a direct collision, as in the work of Katz & Dong (2012) and tidal effects do not play an important role.