[mesa-users] Fwd: tau=0.70...

[David Arnett]

---------- Forwarded message ----------
From: David Arnett <wdarnett at gmail.com>
Date: Fri, Mar 23, 2012 at 7:47 PM
Subject: tau=0.70...
To: jingluan at caltech.edu
Cc: Bill Paxton <paxton at kitp.ucsb.edu>


Hi Jing,

Good question, but the answer may not be what you expect.

For a stellar model, the outer boundary condition is virtually the same at
tau=2/3 (Eddington) and tau = 300.0. This is enough to get dT/dr and dP/dr,
as well as L and r correct.

There is little mass beyond this level, and the model is unchanged at a
level of 1e-6 (expect of course, in the atmosphere), so we accept this as a
converged model. If this bothers you, please consider that the REAL
atmosphere is 3D, dynamic, and not nearly so simple as the Eddington
boundary condition, tau = 2/3.

So, you are right in an important sense, but in another, it may be
irrelevant. To really do the full model we need 3D MHD in a dynamic sense,
and we can't do that yet for a full star :-(  Alas!

I hope this helps; it is just my take on the issue.

Dave Arnett

-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona



-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona
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