[Mesa-users] Ideal gas law

[mutlu yildiz]

Dear Jason,

It is due to the Coulomb pressure. Another view of this effect can be seen
in figure 1 of Yıldız & Kızıloğlu (1997) for the present Sun:

https://ui.adsabs.harvard.edu/abs/1997A%26A...326..187Y/abstract
or
https://arxiv.org/abs/astro-ph/9706228

Best Regards,
Mutlu Yıldız

On Tue, Feb 16, 2021 at 9:29 PM Jason Wright via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> I'm using MESA in a graduate course and I've managed to stump myself with
> a problem I assigned.
>
> I am looking at the profile of an ordinary 1 solar mass ZAMS star. I
> assigned the students the task of testing the perfect gas law.  We find a
> large, smooth violation of the law in the convective zone, with anomalies
> up to 7%.  I attach the anomalies here (I hope this image comes through the
> mailing list, if not you should be able to see the image at
> https://sites.psu.edu/astrowright/files/2021/02/hw3.9.1b.pdf).
>
> [image: Screen Shot 2021-02-16 at 1.14.25 PM.png]
> Note that I'm plotting the x axis using the logit function to
> logarithmically stretch out both the core and envelope (core on the left,
> envelope on the right). m = M/2 is at abscissa value 0.
>
> I can't fathom why the perfect gas law does not hold in the envelope.  The
> negative anomaly in the core I understand (electron degeneracy pressure)
> but the rest has me baffled. It roughly lines up with the ionization of He,
> but not perfectly and anyway, why would that matter?
>
> I am plotting using the variables logrho, pgas, mu, and logT.  I've tried
> using cell boundaries vs. centers, but that's not it (these things should
> all be defined in the cell anyway).  I've tried using logP (total pressure
> and get almost the same answer.  mlt_turb = 0 everywhere.  Radiation
> pressure is not important anywhere.
>
> Thanks for any ideas!
>
> --
>                                                 -
> ---------------
> Jason T Wright
> Professor of Astronomy & Astrophysics
> Director, Penn State Extraterrestrial Intelligence Center
> Acting Director, Center for Exoplanets and Habitable Worlds
> NEID Instrument Team Project Scientist <http://neid.psu.edu/>
> he/him/his
> *https://sites.psu.edu/astrowright/ <https://sites.psu.edu/astrowright/>*
> @Astro_Wright
>
> <http://twitter.com/Astro_Wright>
> _______________________________________________
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>

-- 
Ege Üniversitesi Fen Fakültesi
Astronomi UBB 35100 Bornova İzmir
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