Mass transfer and mergers in double white dwarf binaries

Abstract

We have developed a self consistent field (SCF) technique similar to the one described by Hachisu, Eriguchi, & Nomoto (1986b) that can be used to construct detailed force-balanced models of synchronously rotating, double white dwarf (DWD) binaries. This SCF technique can be used to construct model sequences that mimic the last portion of the detached inspiral phase of DWD binary evolutions, and semi-detached model sequences that mimic a phase of conservative mass transfer. In addition, the SCF models can be used to provide quiet initial starts for dynamical studies of the onset of mass transfer in DWD systems. We present multiple dynamical simulations of interacting DWD binaries using these improved initial models and a modified version of the hydrodynamics code developed originally by Motl et al. (2002) to investigate the stability of mass transfer and the possibility that DWD binary mergers serve as progenitors for Type Ia supernovae. These are among the first white dwarf merger simulations carried out using a grid-based hydrodynamics technique and a realistic equation of state. Where there is overlap, our results compare favorably to simulations that have been previously published by other groups but carried out using smooth particle hydrodynamics (SPH) techniques.