[Mesa-users] he_core_mass definition

Warrick Ball W.H.Ball at bham.ac.uk
Thu Apr 11 03:39:08 EDT 2019

Hi G\F6khan,

Did you search the MESA Users' archive before asking this question?  I 
searched for "core mass definition", for which the 7th hit is a reply by 
Josiah [1], which is still relevant:

> By default, the core boundaries are determined by the point at which the 
> "previous" isotope decreases below some abundance threshold and the 
> where the "new" isotope is above some abundance threshold.

> For example, the boundary of the helium core is defined to be the point 
> (moving inwards) where the h1 mass fraction falls below 0.01 
> (he_core_boundary_h1_fraction) and the he4 mass fraction is greater than 
> 0.1 (min_boundary_fraction).  Then the he_core_mass is the mass interior 
> to this boundary location, etc.

He links to the relevant part of the documentation, too [2].

The reason you see the sudden rise is because until the very end of the 
main sequence, no part of the star is sufficiently depleted of hydrogen to 
satisfy the defaults' definition of a core.

If you want to define the core differently, you can modify the controls or 
implement something in `run_star_extras.f`.


[1] https://lists.mesastar.org/pipermail/mesa-users/2016-September/007066.html
[2] http://mesa.sourceforge.net/controls_defaults.html#definition_of_core_boundaries

Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552

On Thu, 11 Apr 2019, gokhanyucel at akdeniz.edu.tr wrote:

> Dear MESA users,
> I have a weird problem/question about "he_core_mass" definition. What is the exact definition of this term?
> This is why I'm asking. I have been trying to see how much helium core is being created by hydrogen burning in single stars until TAMS, and binary stars until mass transfer. When I check my output files, I see that "he_core_mass" is 0 for a long time then it goes up from 0 to some small number, such as 0.24, then mass transfer begins. Since most of stars starts to burn their hydrogen to helium after immediately they enter the ZAMS, so this "he_core_mass" should be more than 0 in a very short time after the evolution star. So, what is this he_core_mass?
> I attached a file that shows the change of "helium_core_mass" against time for a single star.
> Regards,
> G\F6khan

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