Re: [mesa-users] solar calibration with Asplund abundances

[Grant N. <new...@gm...>]

I haven't read much about this in recent times - but at least the models
mesh with helioseismology. Put in the Aslpund abundances and they do not.
And aren't the Asplun abundances still based on iffy 3-D modelling?


On Tue, Jan 14, 2014 at 7:17 PM, David Arnett <wda...@gm...> wrote:

> 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
>
>
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