[mesa-users] Helium Core definition.

[Bill Paxton]

Hi Grant,

You might propose a precise new scheme for mesa to use for core size computations.
Then folks can focus on a refining a specific definition that can go into the next release.
I'd like to have the users decide this one rather than have me try to figure out what to do!

Thanks,
Bill


On Feb 21, 2014, at 3:49 AM, Grant Newsham wrote:

> Hi Josiah,
> 
> It's not that such and such a definition is useful or not - but it is a fact the He core mass never in my experience means anything but where hydrogen is exhausted. Whether it is databases of stellar evolution tracks/isochrones or growth of the core up the RGB studies or HB morphology and 2nd parameter investigations - He core means no hydrogen not some idea of when He reaches about 49% and is just greater in mass fraction than H. In fact I can't think of an instance where such a definition is used.
> 
> As it stands, someone experienced in this field using Mesa for the first time or glancing at Mesa results would conclude something is wrong with the code.
> 
> Regards,
> 
> Grant
> 
> 
> On Fri, Feb 21, 2014 at 2:27 AM, Josiah Schwab <jwschwab at berkeley.edu> wrote:
> 
> Aaron Dotter <aaron.dotter at gmail.com> writes:
> 
> > They seem to disappear around revision 5000.  I have *_boundary_mass in
> > 4930 but not in 5329.  My preference would be to have *_boundary_mass
> > available in the history files as they are very useful for isochrone
> > construction, in my heavily biased opinion.  ;-)
> 
> There was some student confusion at the 2013 MESA Summer school about
> he4_boundary_mass representing c12_core_mass, which was the impetus for
> this change I believe.
> 
> It was announced in the release notes for r5456.  Quoth Bill:
> 
>     I've finally fixed my counter-intuitive naming of the mass locations
>     where there are changes in dominant abundances.  Unlike everyone
>     else, I was naming these according to what was more abundant above
>     the transition instead of below.  Now that's reversed, so what was
>     called "h1_boundary_mass" is now called "he_core_mass", what was
>     "he4_boundary_mass" is now "c_core_mass", etc.  The criterion for
>     the locations is simply what has the maximum mass fraction -- e.g.,
>     he_core_mass is the outermost location where the mass fraction of
>     he4 is larger than for anything else, the c_core_mass is outermost
>     where mass fraction of c12 is larger than any other, etc.
> 
> Personally, I have found both definitions useful at times.
> 
> Josiah
> 
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