[Mesa-users] Stationary model

[Pablo Marchant]

Hi,

depending on what exactly you're trying to do your message could be
interpreted in different ways. Something that might be close to what you're
looking, is to fix the composition of the star by setting

dxdt_nuc_factor = 0d0
mix_factor = 0d0

the first option will keep the energy input from nuclear reactions, while
ignoring the corresponding changes in composition. The second one will
remove composition changes due to mixing. You don't want to turn off
nuclear reactions, because if you do that the star will simply lose energy
and evolve to higher central temperatures in a Kelvin-Helmholtz timescale.
If you use these option, you will freeze the evolution of the star if you
are dealing with phases in thermal equilibrium. If the starting model is
not in thermal equilibrium, then it's trickier.

If this does not work for you, then you'll have to describe your problem
better. What changes do you want to explore on four "fixed" model? In
particular, if you literally want to fix the structure variables of the
star, how do you expect to perturb it at all?

Cheers



On Mon, Nov 12, 2018 at 7:54 PM g.mirouh--- via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear MESA users,
>
> I am new at using the code and to test some specific physics, I would
> like to stop the nuclear reactions in the core while keeping the
> luminosities to the value they had before stopping the reactions.
> Basically I want to create a stationary model and let time go on with no
> changes in the composition or the structure.
>
> I tried by setting
>
> s%rate_factors=0d0
> s%weak_rate_factor = 0d0
>
> which keeps my composition constant, but obviously my "star" collapses
> and cools slowly. How can I "force" the luminosity/radiation
> pressure/etc. to keep my structure invariant with time?
>
> Thanks a lot for your help, and apologies to whom is not concerned.
> Best.
> --
> Giovanni Mirouh.
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>

-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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