[Mesa-users] Ideal gas law

[Jason Wright]

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>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20210216/7c763376/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Screen Shot 2021-02-16 at 1.14.25 PM.png
Type: image/png
Size: 84673 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20210216/7c763376/attachment.png>