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

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

On Tue, Jan 14, 2014 at 1:44 PM, Grant Newsham <new...@gm...> wrote:

> I haven't read much about this in recent times - but at least the models
> mesh with helioseismology.
>

If you twist all the knobs the disagreement is still much larger than the
observational errors. This is not as good agreement as I would expect, so I
would not say that they mesh with helio-seismology. Perhaps this is a
reasonable issue to debate in the community.


> Put in the Aslpund abundances and they do not. And aren't the Asplun
> abundances still based on iffy 3-D modelling?
>

The "iffy" 3D models solve the Navier-Stokes and the radiative transfer
equations, subject to increasingly diminishing numerical error as computers
become more powerful. The MLT solar models are 1D and solve fairly
heavy-handed approximations to the Navier-Stokes equations (steady state,
no turbulence, homogeneous structure on radial surfaces), and the radiative
transfer equations. I tend to find the 3D models more physical. Again, this
deserves discussion.

>
>
> 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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>


-- 
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