[Mesa-users] Star Mass Loss Question

Isaac Malsky isaacmalsky at uchicago.edu
Sun Aug 27 17:57:41 EDT 2017


Hi Mr. Schwab,

Thanks so much for your response!

I've attached the subroutine that I've been writing, although most of it
just just basic math that determines the escape of h1 and he4 so far.

I'm evolving sub-Neptune sized planets according to the paper I've
attached, which specifies the escape rates based on energy limited escape
and a couple other factors. If I could forcibly modify the abundances (and
maybe set max_dt quite small) I think it would save a lot of time. I
haven't looked into modifying the array that stores abundances, but I'll do
that right now.

I've created a set of inlists that that the model I'm evolving is about 10
earth masses and with helium fraction ~.25, and a metalicity of ~.02,
although the exact abundances change for different runs.

On Sun, Aug 27, 2017 at 4:36 PM, Josiah Schwab <jwschwab at ucsc.edu> wrote:

> Hi Isaac,
>
> > I was hoping to ask if anyone had a suggestion on how to modify the mass
> of
> > a small star in a particular way so that the model loses hydrogen and
> > helium in specific ways. I've written a hook in run_star_extras that
> > determines how much mass for each element should be lost, but I'm unsure
> of
> > how to modify the parameter in star_data.inc. Should I use something like
> >
> > s% star_mass_h1 = star_mass_h1 - escape_h1
> >
> > Similar to %s mstar_dot = blank_variable?
> >
> > I'd greatly appreciate any help/advice. This is all in the adjust_mdot
> and
> > mass_loss subroutine.
>
> Mass loss in MESA effectively removes material with the composition of
> the outermost layers of the star.
>
> Variables like star_mass_h1 are reported quantities derived from the
> chemical profile of the star, so modifying them won't affect how the
> model is evolving.
>
> Can you say a little more about the application you have in mind?  I
> assume this is modeling some process like Jeans escape?
>
> Do you have a surface convection zone?  The first thing that comes to
> mind is directly manipulating the model abundances within a well-mixed
> region such that at the end of the step, the total mdot and the
> forcibly-imposed abundance change conspire to give you the desired
> change in h1 & he4 mass.
>
> This would involve directly manipulating s% xa(:,:) -- the array that
> stores the abundances.  So long as the changes needed are small (that is
> say, the amount of h1 lost in a timestep is very small compared to the
> total h1 in the outer convective zone) I bet one would be able to get
> away with that.
>
> In summary, I think this is doable, but not trivial, and I'm not aware
> of it being done in MESA before.  (But I may be wrong on both counts!)
>
> Josiah
>
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