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Re: [mesa-users] solar calibration with Asplund abundances
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From: Tomasz P. <tom...@gm...> - 2014-01-15 15:57:39
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<tt>Do I remember correctly that the Asplund et al. work actually
does rely on a certain theoretical/computational model? This means
the errors are not only measrumement- but also model-dependent.<br>
<br>
Tomek<br>
--<br>
</tt>
<div class="moz-cite-prefix">On 01/14/14 16:45, David Arnett wrote:<br>
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<div class="gmail_quote">On Tue, Jan 14, 2014 at 1:44 PM,
Grant Newsham <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:new...@gm..." target="_blank">new...@gm...</a>></span>
wrote:<br>
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<div dir="ltr">I haven't read much about this in recent
times - but at least the models mesh with
helioseismology.</div>
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<div> </div>
<div>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.<br>
</div>
<div> </div>
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<div dir="ltr"> Put in the Aslpund abundances and they do
not. And aren't the Asplun abundances still based on
iffy 3-D modelling?</div>
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<div><br>
</div>
<div>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.<br>
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<div class="h5">On Tue, Jan 14, 2014 at 7:17 PM,
David Arnett <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:wda...@gm..."
target="_blank">wda...@gm...</a>></span>
wrote:<br>
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<div>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.<br>
<br>
</div>
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). <br>
<br>
3. This leaves us no further adjustments to
fit the helio-seismological data (Rcz),
except for the metalicity. <br>
The conventional conclusion is that the
Asplund metalicity is too low because of the
above discrepancy with Rcz. <br>
<br>
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<br>
<a moz-do-not-send="true"
href="http://www.nasa.gov/mission_pages/sdo/news/coronal-rain.html"
target="_blank">http://www.nasa.gov/mission_pages/sdo/news/coronal-rain.html</a><br>
</div>
<div>and see if you thinks a one-parameter
model fits solar convection ;-)<br>
<br>
</div>
<div>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.<br>
<br>
</div>
<div>I hope this helps.<span><font
color="#888888"><br clear="all">
</font></span></div>
<span><font color="#888888">
<div>
<div>
<div>
<div><br>
-- <br>
David Arnett<br>
Regents Professor<br>
Steward Observatory<br>
University of Arizona<br>
<br>
Facts are stubborn, but statistics
are more pliable. Mark Twain<br>
Facts do not cease to exist
because they are ignored. Aldous
Huxley<br>
</div>
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<br clear="all">
<br>
-- <br>
David Arnett<br>
Regents Professor<br>
Steward Observatory<br>
University of Arizona<br>
<br>
Facts are stubborn, but statistics are more pliable. Mark
Twain<br>
Facts do not cease to exist because they are ignored. Aldous
Huxley<br>
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