Marius Dan, Stephan Rosswog, James Guillochon, Enrico Ramirez-Ruiz
Despite their unique astrophysical relevance, the outcome of white dwarf
binary mergers has so far only been studied for a very restricted number of
systems. Here we present the results of a survey with more than two hundred
simulations systematically scanning the white dwarf binary parameter space. We
consider white dwarf masses ranging from 0.2 to 1.2 $M_\odot$ and account for
their different chemical compositions. We find excellent agreement with the
orbital evolution predicted by mass transfer stability analysis. Much of our
effort in this paper is dedicated to determining which binary systems are prone
to a thermonuclear explosion just prior to merger or at surface contact. We
find that a large fraction of He-accreting binary systems explode: all
dynamically unstable systems with accretor masses below 1.1 $M_\odot$ and donor
masses above $\sim$ 0.4 $M_\odot$ are found to trigger a helium detonation at
surface contact. A substantial fraction of these systems could explode at
earlier times via detonations induced by instabilities in the accretion stream,
as we have demonstrated in our previous work. We do not find definitive
evidence for an explosion prior to merger or at surface contact in any of the
studied double carbon-oxygen systems. Although we cannot exclude their
occurrence if some helium is present, the available parameter space for a
successful detonation in a white dwarf binary of pure carbon-oxygen composition
is small. We demonstrate that a wide variety of dynamically unstable systems
are viable type Ia candidates. The next decade thus holds enormous promise for
the study of these events, in particular with the advent of wide-field synoptic
surveys allowing a detailed characterization of their explosive properties.
View original:
http://arxiv.org/abs/1201.2406
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