[mesa-users] freeeos

[Jean-Claude Passy]

Hi Jing,
> It is a very interesting paper:-) I have two questions.
Thanks for your interest. I was indeed wondering if you were interested 
in this problem, in particular when I saw your last email about how to 
change the energy transport and generation equations.
> 1, May I ask why you choose to use freeeos as the eos? MESA has its own
> eos tables. Does freeeos make the run faster or make the large mass loss
> rate tolerable numerically? If yes, why? If not, why not use MESA's own
> eos tables? Because I want to reproduce the high-mass-loss-rate examples
> in your paper, I would like to know whether I need to apply freeeos too.
> If the eos is not subtle for high mass loss rate, then I would use MESA's
> own tables.
You are right, MESA has its own tables but if you look at Figure 1 in 
the instrumental paper (Paxton et al. 2011), you will see that MESA uses 
different tables depending on where you are in the rho-T diagram. Some 
inconsistencies can arise just at the boundaries between these tables. 
For instance, a 0.3 Msun ZAMS lies right on the eos boundary of OPAL and 
SCVH. If you plot its entropy profile, you will obtain the profile 
attached instead of a flat profile as it is expected (the star is fully 
convective). Even though there was no problem for the giant stars, I 
wanted to be consistent between the MS and giants models so I decided to 
use the FreeEos tables for all models.
Also, I should mention that building the FreeEoS tables is a little bit 
tedious and I found it hard to compile with the recent versions of MESA. 
An interesting alternative would be to try the MacDonald tables, which 
Nate Bode has successfully used recently. May be he can tell you more.
> 2, It claims in the paper that an artificial viscosity is applied to
> prevent shocks. Is it subtle to fulfill the high mass loss rate? Why?
For the high mass loss rates, the evolution can be slightly transonic so 
you need artificial viscosity to deal with shocks. Without it, the 
reconstruction scheme is not stable and some unphysical oscillations 
will occur.

Hope that helps. Let me know off-list if you have other specific 
questions about the paper.
Cheers,

JC


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