[mesa-users] approx13

[Ken Shen]

Hi Bill, Frank, David, et al.,

I very much appreciate the input and suggestions!  It seems like the main
advice is to start from one of the approx nets included with MESA and
remove reactions as necessary without touching isotopes.  So I've taken
approx_base.net, left the isotopes intact, and taken out the relevant
reactions.  The results from this net seem to be the same as my original
attempt (which did not have 3He and 14N).

But my main question is why I need to include 5 isotopes that shouldn't
matter.  I guess I can envision a scenario where including 1H or protons in
the abundance list somehow affects the equilibrium calculation of the
(a,p)(p,g) reactions (although as far as I can see in the code, that
calculation doesn't ever make an actual reference to the presence of those
isotopes in the isotope list).  But I'm really confused as to why including
neutrons should matter the most, since almost none of the reactions, direct
or auxiliary, include neutrons.

I've also found that neglecting or including neutrons in the list affects
all reaction rates in the network by the same multiplicative factor,
regardless of the actual composition.  And that factor gets larger as the
temperature gets higher.  (E.g., the rates are 9600 times too low at T =
3e9, and 1e9 times too low at T = 5e9.)

So it all makes me a little worried that this net will yield wrong results
somewhere I haven't checked.  Ideally, I'd like to figure out exactly how
neglecting those isotopes screws things up...



On Thu, May 15, 2014 at 9:50 AM, Francis Timmes <fxt44 at mac.com> wrote:

> its easier to zero rates in aprox20 to effectively reduce it to aprox13
> than trying to detangle the various built-in equilibrium assumptions.
>
> fxt
>
>
>
>
> On May 15, 2014, at 8:59 AM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
>
> >
> > On May 14, 2014, at 4:00 PM, Ken Shen wrote:
> >
> >> > you might start with a copy of approx20 and remove reactions to get
> to something very close to approx13.
> >>
> >> That's essentially what I did to produce the .net file I attached
> before (although I started with approx_base.net).
> >
> > "essentially" means "not" in this case.  you didn't just remove
> reactions. you removed isotopes.
> >
> > you might try it my way!  ;D
> >
> > -b
> >
> >
> >
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