[Mesa-users] Hydrogen burning with no hydrogen?

[Sunny Wong]

Hi Nicholas,

Here's my guess for what happened (and others please
correct me):

If you didn't change the initial_he3
<https://docs.mesastar.org/en/24.08.1/reference/controls.html#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
<https://docs.mesastar.org/en/24.08.1/reference/controls.html#initial-he3>
= 0d0 in your &kap section as well.

Cheers,
Sunny
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20250725/0d60fd2c/attachment.htm>