[mesa-users] [MESA]: Question Astrophysical Factor

[Josiah Schwab]

Hello Gonçalo,

> I found this email on the MESA community website and I decided to try
> it as a last resource.

We definitely encourage users to email the list.  You first stop should
be http://mesa.sourceforge.net/index.html but if you don't have a local
MESA expert, mesa-users is probably next.

> The thing I need to do now in my project is to change the
> Astrophysical Factor (S-Factor) from the pp nuclear reaction to try to
> find out what changes does it have in the star and if these can be
> measured using seismology. The problem is I've been been searching
> online for some weeks and I can't find out how to change this
> factor. I've tried several things, the closest to what I wanted, I
> think, was to change the value on the file
> $MESA_DIR/rates/private/ratelib.f90 , but after that change the code
> no longer compiles...

How to you want to change it?  If you want to change the rate by a
constant multiplicative factor, you can use the controls

http://mesa.sourceforge.net/star_job_defaults.html#num_special_rate_factors

to re-scale the rates.

You'll need to know the name of the rate you want to change so that you
can set reaction_for_special_factor.  This will depend on the network
that you're using.

You can see the reactions in your network by looking at the net file in
$MESA_DIR/data/net_data/nets, or you have MESA print them at startup
with the control

http://mesa.sourceforge.net/star_job_defaults.html#list_net_reactions

Note that in something like basic.net there's not just a pp reaction.
There's a compound reaction p(p,e+nu)h2(p,g)he3, i.e. one that assumes
the 2nd step in the PP-I chain happens instantaneously after the first.

Hope that helps,
Josiah