Subject:
Re: Reminder
From:
Rollin Thomas <rthomas@panisse.lbl.gov>
Date:
Wed, 25 Feb 2004 15:47:24 -0800 (PST)
To:
Alex Kim <AGKim@lbl.gov>
CC:
Natalia Kuznetsova <NVKuznetsova@lbl.gov>, Eric Linder <EVLinder@lbl.gov>, Ramon Miquel <RMiquel@lbl.gov>, Tony Spadafora <ALSpadafora@lbl.gov>, John Bercovitz <JHBercovitz@lbl.gov>, larry gladney <larryg@hep.upenn.edu>, "Brian C. Lee" <BCLee@lbl.gov>, Gary Kushner <GEKushner@lbl.gov>, Natalie Roe <NARoe@lbl.gov>, Jodi Lamoureux <JILamoureux@lbl.gov>, Carl Pennypacker <pennypacker@lbl.gov>, Brian McGinnis <BJMcGinnis@lbl.gov>, kamarnold@hotmail.com, "Brian C. Lee" <BCLee@lbl.gov>, RAScalzo@lbl.gov, "Rachel G." <RAGibbons@lbl.gov>, "Lafever, Robin" <RELafever@lbl.gov>

Journal club people, I contacted Eddie Baron to get some clarification
on this flash stuff mentioned in the Yoon and Langer paper.  During
the discussion we were left wondering why some accretion rates are
unstable, others less so, and what the difference is if you have H and
not He.  I have included the exchange below.

In short, it doesn't matter what the accreted material is, but just
how degenerate it is.  Slower accretion permits more degeneracy,
robbing the material of a way out of runaway in the face of
temperature fluctuations in the shell.

Still, even though Yoon and Langer say they arrived at their IC's by
some simple binary evolution considerations, we don't know how
critical that particlar choice of IC's is.

Rollin


>> From rthomas@plearn.lbl.gov Wed Feb 25 15:34:27 2004
>> Date: Wed, 25 Feb 2004 14:12:44 -0800 (PST)
>> From: Rollin Thomas <rthomas@plearn.lbl.gov>
>> To: E. Baron <baron@nhn.ou.edu>
>> Subject: Re: Dumb questions.
>> 
>> 
>> On Wed, 25 Feb 2004, E. Baron wrote:
>> 
>
>>> > If you accrete slowly, the stuff cools, electrons become degenerate and no
>>> > matter what the fuel you get flashes.
>
>> 
>> Oh it's easy then.  In normal matter, if you heat a gas it will expand
>> because it's dominated by the thermal pressure term.  So in such a gas
>> the thermonuclear cross-sections will not increase and the reaction
>> rate stays low.
>> 
>> But in a degenerate gas, you can heat it all you want (mostly) and it
>> won't react by expanding; the thermonuclear cross-sections can go up
>> until *they* do the job of expanding the gas you you get a flash.
>> 
>> So is it just a question of how degenerate the accreted material can
>> become?
>> 
>> Rollin


>> From baron@nhn.ou.edu Wed Feb 25 15:34:35 2004
>> Date: Wed, 25 Feb 2004 17:02:51 -0600 (CST)
>> From: E. Baron <baron@nhn.ou.edu>
>> To: Rollin Thomas <rthomas@panisse.lbl.gov>
>> Subject: Re: Dumb questions.
>> 
>> On Wed, 25 Feb 2004, Rollin Thomas wrote:
>> 
>
>>> >
>>> > So is it just a question of how degenerate the accreted material can
>>> > become?
>
>> 
>> yep!
>> 
>> of course if you accrete too fast the WD will puff up into a red giant
>> and choke off accretion (and you lose the envelope to tidal friction).
>> 
>> -eddie
>> --
>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> For additional contact info, etc, see http://www.nhn.ou.edu/~baron/
>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++