[Mesa-users] Suppressing CNO reactions

[Aaron Dotter]

Hi Rich,

It depends on which net you're using.  Some nets have conglomerate rates.
For a given net you can print out which reactions are actually being used
with show_net_reactions_info and then turn your
reaction_for_special_factor()'s to those reactions.

Aaron

On Mon, Mar 11, 2019 at 1:40 PM RICHARD H D TOWNSEND <
townsend at astro.wisc.edu> wrote:

>
> > On Mar 11, 2019, at 12:36 PM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
> >
> > i’m not sure that max_abar_for_burning will do what Rich wants.
> >
> > here are the lines from mesa/star/private/net.f90 where it is used:
> >
> >          if ((s% eps_nuc_factor == 0d0 .and. s% dxdt_nuc_factor == 0d0)
> .or. &
> >               s% abar(k) > s% max_abar_for_burning) then
> >             return
> >          end if
> >
> > it is checking the abar for the cell to decide whether or not to do
> nuclear burning for that particular cell.
> >
> > so it won’t turn off one kind of burning while leaving another kind.
> >
> > the special rate factors should do the job however.
> >
> > assuming you are using basic.net, open that file
> (mesa/data/net_data/nets/basic.net)
> >
> > in the “add_reactions” section, you’ll find these lines:
> >
> >          ! cno cycles
> >
> >          rc12_to_n14         ! c12(p g)n13(e+nu)c13(p g)n14
> >          rn14_to_c12         ! n14(p g)o15(e+nu)n15(p a)c12
> >          rn14_to_o16         ! n14(p g)o15(e+nu)n15(p g)o16
> >          ro16_to_n14         ! o16(p g)f17(e+nu)o17(p a)n14
> >
> > those are the ones you want to disable, so set their
> special_rate_factors to 0 in your inlist
> >
> > num_special_rate_factors = 4
> > reaction_for_special_factor(1) = ‘rc12_to_n14'
> > special_rate_factor(1) = 0d0
> > reaction_for_special_factor(2) = ‘rn14_to_c12'
> > special_rate_factor(2) = 0d0
> > reaction_for_special_factor(3) = 'rn14_to_o16'
> > special_rate_factor(3) = 0d0
> > reaction_for_special_factor(4) = ‘ro16_to_n14'
> > special_rate_factor(4) = 0d0
> >
> > i haven’t tested this myself, so please let us know if it actually works.
> >
>
> Thanks for the info -- but I confess I'm a little confused, as I had been
> changing the rates thus:
>
>    num_special_rate_factors = 7
>    reaction_for_special_factor(1) = 'r_c12_pg_n13'
>    reaction_for_special_factor(2) = 'r_c13_pg_n14'
>    reaction_for_special_factor(3) = 'r_n14_pg_o15'
>    reaction_for_special_factor(4) = 'r_n15_pa_c12'
>    reaction_for_special_factor(5) = 'r_n15_pg_o16'
>    reaction_for_special_factor(6) = 'r_o16_pg_f17'
>    reaction_for_special_factor(7) = 'r_o17_pg_f18'
>    special_rate_factor(1) = 0.
>    special_rate_factor(2) = 0.
>    special_rate_factor(3) = 0.
>    special_rate_factor(4) = 0.
>    special_rate_factor(5) = 0.
>    special_rate_factor(6) = 0.
>    special_rate_factor(7) = 0.
>
> I found the reaction names in data/rates/reactions.list. But it seems
> there's a different set of names I should be looking at. Can you explain?
>
> cheers,
>
> Rich
>
> > cheers,
> > bill
> >
> >
> >
> >
> >> On Mar 11, 2019, at 10:20 AM, Aaron Dotter via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> >>
> >>
> >> Hi Rich,
> >>
> >> In &star_job you can set these:
> >>
> >>          !### num_special_rate_factors
> >>          !### reaction_for_special_factor
> >>          !### special_rate_factor
> >>          ! For using other special rate factors.
> >>          ! `num_special_rate_factors` must be <=
> `max_num_special_rate_factors`.
> >>
> >>       num_special_rate_factors = 0
> >>       reaction_for_special_factor(:) = ''
> >>       special_rate_factor(:) = 1
> >>
> >> or in &controls you can set this:
> >>
> >>          !### max_abar_for_burning
> >>
> >>          ! if abar > this, suppress all burning
> >>          ! e.g., if want an "inert" core heavy elements, set this to 55
> >>          ! or, if want to turn off the net, set this to -1
> >>
> >>       max_abar_for_burning = 199
> >>
> >> Either one should give you the desired effect.
> >>
> >> Aaron
> >>
> >>
> >>
> >> On Mon, Mar 11, 2019 at 1:17 PM RICHARD H D TOWNSEND via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> >> Hi folks --
> >>
> >> A question that I'm sure I've asked before, but I can't seem to find it
> in the archives: what's a straightforward approach to suppressing CNO
> reactions in a MESA run? I'd like to do this to demonstrate to my class
> what would happen to the luminosity of massive ZAMS stars if they were
> 'forced' to use the PP chain.
> >>
> >> cheers,
> >>
> >> Rich
> >>
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> >>
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> >
>
>
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