[mesa-users] solar calibration with Asplund abundances

[David A. <wda...@gm...>]

1. The He abundance is not known to that accuracy (0.2447). By slightly
adjusting it (less He, so more opacity) you can get L to fit the observed
value.

2. Both Teff and Rcz depend upon the convective model. At present MESA uses
mixing-length theory in a one-parameter form. That parameter is the
mixing-length alpha, and it is adjusted to fix the radius (Teff plus L).

3. This leaves us no further adjustments to fit the helio-seismological
data (Rcz), except for the metalicity.
The conventional conclusion is that the Asplund metalicity is too low
because of the above discrepancy with Rcz.

An alternative possibility is that mixing-length theory is not accurate
enough. For example, it ignores Reynolds stresses, an error that must be
absorbed by the choice of alpha; it is not obvious that this is the same
physics that determines the deep convection at the lower boundary (Rcz).
This, or some other aspect of turbulent convection not included in
mixing-length theory, may be the root of the problem.  Look at
http://www.nasa.gov/mission_pages/sdo/news/coronal-rain.html
and see if you thinks a one-parameter model fits solar convection ;-)

I am inclined to the view that the Asplund abundances are correct and the
stellar models are wrong, but that is just my opinion. Don't forget, the
models are not so VERY wrong even with MLT.

I hope this helps.

-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona

Facts are stubborn, but statistics are more pliable.  Mark Twain
Facts do not cease to exist because they are ignored.  Aldous Huxley