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From: YKhan on 18 Mar 2010 14:15
On Mar 17, 2:43 am, Andrew Usher <k_over_hb...(a)yahoo.com> wrote:
> Dan Birchall wrote:
> > bbb...(a)spammenot.yahoo.com (Yousuf Khan) wrote:
> > >  Just as we were talking about the possibility of dual white dwarf star
> > >  mergers being the cause of some Type Ia supernovas in another thread,
> > >  there is now confirmation that at least one of them was definitely like
> > >  this. SN 2007if is believed to have been a mass explosion of about 2.1
> > >  Msun +/- 10%, well above the normal Chandrasekhar Limit Type Ia
> > >  explosions of about 1.4 Msun.
> > [snip]
> > >  "Scalzo believes there's a good chance that SN 2007if resulted from the
> > >  merging of two white dwarfs, rather than the explosion of a single white
> > >  dwarf and hopes to study the other super-Chandrasekhar supernovae to
> > >  determine whether they, too, could have involved a merger of two white
> > >  dwarfs."
>
> > Argh!  It figures.  The very day I fly out for a weekend in Paris,
> > this hits ArXiv!  http://arxiv.org/pdf/1003.2217v1is presumably
> > where RedOrbit picked it up.
>
> The paper gives the combined progenitor mass of 2.4 +/- 0.2 Msun. So
> one of the WDs must have been ONe, but as I stated both can't be
> (oxygen/neon does not ignite soon enough; hence ECSNe), so the maximum
> mass is ~2.45 Msun. The paper, however, ignores that. I suppose one
> could have accreted more mass later, though, so it's not a hard limit.

Well, then it's possible that they both could've accreted more mass
later on. It's possible that this was not just a binary WD system, but
it could've been a trinary, with a three-way merger. If there was a
third star, perhaps one less massive than the dual WD's progenitors,
and it was just going red giant at this point in time. It's expanded
envelope could've engulfed both WD's, and the resulting aerodynamic
friction made all three spiral inward.

Yousuf Khan
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