[mesa-users] Approx21

Robert Farmer rjfarmer at asu.edu
Mon Oct 17 00:59:36 EDT 2016


Hi

>In simulations up to Fe core collapse, the primary central isotope which
remains at the end is cr56 which in my reading conflicts with research.

The cr56 in approx nets is not "real" cr56, it is there to set the final ye
value. If you look in the net folder there are many approx21_* nets, each
ones picks a different set of final isotopes (but all use the same fudge
factored reaction rate) so you can set your desired final ye.

>. There are some reactions which contain isotopes such as Fe53 and Fe55
which are not in the isotope list. This will not work for data files

If you can assume you species is in equilibrium (for instance fe54 <> fe55
<> fe56) then with a bit of maths you can remove the explicit dependence on
the amount of fe55 by creating a compound rate based on each of the
components in the equilibrium chain. If you are making your own net then
you'll have to add them in yourself, the approx nets have many hard coded
assumptions.

net/rpivate/net_approx21_procs.inc approx21_special_reactions subroutine for
all the details

>3. The isotope Na23 is missing. In intermediate stars, research shows the
main ingredients of the degenerate cores are o16, Ne20, Na23 and Mg24.

The approx nets are only meant to track the energy generation, by following
alpha chain reactions. Whether the composition is correct is
irrelevant(-ish) we only want the energy "right", either you need to make
your own net with isotopes you think are important (or are needed as
intermediate steps) or post process the model to add in missing reactions
afterwards (if you can assume they make negligible contributions to the
energy budget)

I find approx21_cr60_plus_co56.net
<https://sourceforge.net/p/mesa/code/HEAD/tree/trunk/data/net_data/nets/approx21_cr60_plus_co56.net>
gets to CC well (though choice of inlist settings is crucial for getting
there efficiently, especially during si burning). For other nets i'd look
at the mesa_* nets with at least 80 isotopes to start to get things going
the "right" way composition wise.

Rob

On Sun, Oct 16, 2016 at 9:23 PM, Ian Foley <ifoley2008 at gmail.com> wrote:

> Hi,
>
> Love to get some more insight into this net. It's no longer produced by a
> data file, but by code. It enables a simple net with broad brush treatment
> allowing simple simulations up to core collapse.
>
> But
> 1. In simulations up to Fe core collapse, the primary central isotope
> which remains at the end is cr56 which in my reading conflicts with
> research.
>
> 2. There are some reactions which contain isotopes such as Fe53 and Fe55
> which are not in the isotope list. This will not work for data files
>
> 3. The isotope Na23 is missing. In intermediate stars, research shows the
> main ingredients of the degenerate cores are o16, Ne20, Na23 and Mg24.
>
> So I've been looking for ways to create a simple net which does not have a
> big performance hit, but gives results closer to research.
>
> I also wanted to find a net which can simulate up to core collapse leading
> to electron capture supernovas. Are there any in mesa which can do this?
>
> Kind regards
> Ian
>
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