[mesa-users] Thermal timescale

[Ehsan Moravveji]

Hi Rene,
If you proceed to $MESA_DIR/star/defaults/history_columns.defaults, line 324, you find a rich menu of timescales to help yourself with.
In case you want to compute that yourself, and perhaps compare the integral with the value that is stored in your history file, then,in  run_star_extras.f90, 
how_many_extra_history_columns() and data_for_extra_history_columns() are your friends.
There is an excellent documentation here:
http://mesa.sourceforge.net/run_star_extras.html <http://mesa.sourceforge.net/run_star_extras.html>

Good luck,
Ehsan.

> On 26 Jul 2015, at 21:44, Rene Breton <R.Breton at soton.ac.uk> wrote:
> 
> Hi,
> 
> I'm looking into calculating the thermal timescale in the envelope of a star and I was wondering how to go about it. The goal is basically to investigate possible thermal instabilities. As far as I know, MESA does not store any variable directly related to timescales pertaining to various shells of the star, either in the history file or in the profile.
> 
> I know that for the star as a whole, the Kelvin-Holmholtz timescale would be:
> t_{KH} = \Omega / (2L) \approx GM^2 / (2RL)
> 
> with \Omega the gravitational binding energy.
> 
> It is less clear to me how I would calculate it for, say, the envelope of a star (or a certain layer within it) in terms of whatever variables are available from MESA. Presumably the timescale would go like:
> t_{KH,s} = \Omega / (2L) = - \int_{R_in}^{R_out} G m(r) dm(r) / r / (2L)
> 
> i.e. the integral of the binding energy from R_in to R_out divided by 2L.
> 
> This integral could always be recast in terms of pressure I suppose but perhaps I'm just overcomplicating it.
> 
> Would anyone have a clue?
> 
> Thanks,
> 
> Rene
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