[Mesa-users] Hydrogen burning with no hydrogen?

[Farag, Ebraheem]

As an aside,

For no changes at all: burning/neutrinos/mixing set:

   eps_nuc_factor = 0 ! No energy from burning
   non_nuc_neu_factor = 0 ! No thermal neutrino losses
   dxdt_nuc_factor = 0 ! No composition changes
   mix_factor = 0 ! No mixing

Instead of just dxdt_nuc_factor = 0.

-EbF
________________________________
From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of Richard Townsend via Mesa-users <mesa-users at lists.mesastar.org>
Sent: Friday, July 25, 2025 7:47 PM
To: Sunny Wong <twong31 at physics.ucsb.edu>
Cc: MESA Users List <mesa-users at lists.mesastar.org>
Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?

Hi Sunny —

This is a good analysis, but I think because Nicholas has dxdt_nuc_factor = 0, no H will be produced.

However, the energy generation from 3He + 3He (and 3He + 4He) will still generate energy, and this energy will be counted as “hydrogen burning” since it is part of the pp chains.

Either way, your fix of setting initial_he3 should work fine.

cheers,

Rich

> On Jul 25, 2025, at 6:42 PM, Sunny Wong via Mesa-users <mesa-users at lists.mesastar.org> wrote:
>
> Hi Nicholas,
>
> Here's my guess for what happened (and others please
> correct me):
>
> If you didn't change the initial_he3 flag in controls, MESA will
> assume that he4/he3 has the same value as the Sun. Then,
> once the temperature reaches ~10^7 K, part of the pp chain
> starts: He3 + He3 -> He4 + 2 H1 .
>
> Once some He burning has happened, some C12 is produced.
> Since there is some H1 lying around, you can then start the
> CNO cycle.
> (Fun MESA problem: even if you start with a zero metallicity
> H-rich star, it will eventually do CNO cycle on the main sequence
> via this way, because there's a tiny amount of He burning that
> produces C12. )
>
> In short, you can set
> initial_he3 = 0d0
> on top of what you already have (initial_y = 1d0)
> and I believe this would solve the H burning issue.
>
> As an aside, I notice that you set initial_z = 0d0.
> You might want to set Zbase = 0d0 in your &kap section as well.
>
> Cheers,
> Sunny
>
>
>
>
>
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>

--
Rich Townsend • Professor of Astronomy
Astronomy Department • University of Wisconsin-Madison
Phone: 608-262-1752 • E-mail: rhtownsend at wisc.edu





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