[Mesa-users] Si burning on TRho plot

[Francis Timmes]

the approximate, visual indicator to plot is rather simple.

for silicon burning

eps_nuc ~ 1.8e28 * T9**1.5 * X(28Si) * exp(-142.0/T9) * 124.0 * (T9/3.5)**5  erg/g/s

independent of the density.

assuming pure silicon and setting eps_nuc = 1 to be commensurate with 
the other lines in the TRho plot, a root find shows the curve to plot 
is a horizontal line at at T9 ~ 2.1.

as josiah notes though, neutrino losses dominate the cooling.
based on balanced power arguments, we expect silicon to burn 
at T9 ~ 3.5 for rho ~ 1e7 g/cc.

fxt





> On Oct 4, 2018, at 4:45 PM, Josiah Schwab <jwschwab at ucsc.edu> wrote:
> 
> Hi Nicholas,
> 
>> i believe the burning lines in the Trho plot show when
>> the energy generation rate is 1 erg/g/s for a pure composition.
>> the data is in $MESA_DIR/data/star_data/plot_info .
>> 
>> they were constructed by running a network on a sparse grid
>> of temperatures and densities and finding the 1 erg/g/s contour.
>> their purpose is to provide approximate, visual indicators.
>> 
>> as you note, this was not was not done for silicon burning.
>> one could create a $MESA_DIR/data/star_data/plot_info/silicon_burn.data
>> from analytical approximations to silicon burning, and then with a
>> tweak or two of the relevant pgstar routines, have the si burn contour shown.
> 
> Yes, as Frank says, these are just constant eps_nuc lines to guide the
> eye.  Importantly, as you move to later burning stages thermal neutrino
> losses become more important, so these are not really ignition lines.
> 
> You can easily add your own line to the plot using the pgstar option
> 
>  TRho_Profile_fname=''
> 
> You give it the name of a data file with the line you want to draw.
> There is an example of doing something like that in the custom_rates
> test_suite case.
> 
> Hope that helps,
> Josiah
> 
> P.S.  PGSTAR plots also have the idea of a "decorator", which is a
> user-supplied routine in run_star_extras that can draw whatever you want
> in the plot.  Unfortunately, that functionality is broken in r10398 fot
> the TRho_Profile profile plot.  (It's a trivial fix that has already
> been made.)  If you really want to go that route, I attached the patch.
> 
> 
> From 5c761be0dfaf0734d23bf97b532749efa25c2e1e Mon Sep 17 00:00:00 2001
> From: jschwab <jschwab at 72b9428e-be27-0410-b682-8dde6657b448>
> Date: Fri, 6 Jul 2018 22:36:18 +0000
> Subject: [PATCH] Fix pgstar decorator for TRho_Profile
> 
> git-svn-id: svn+ssh://svn.code.sf.net/p/mesa/code/trunk@10866 72b9428e-be27-0410-b682-8dde6657b448
> ---
> star/defaults/pgstar.defaults    | 2 +-
> star/private/pgstar_ctrls_io.f90 | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/star/defaults/pgstar.defaults b/star/defaults/pgstar.defaults
> index b246ee468..057643408 100644
> --- a/star/defaults/pgstar.defaults
> +++ b/star/defaults/pgstar.defaults
> @@ -245,7 +245,7 @@
> 
>          ! Enables calling a subroutine to add extra information to a plot
>          ! see `$MESA_DIR/star/other/pgstar_decorator.f90`
> -         TRho_use_decorator = .false.
> +         TRho_Profile_use_decorator = .false.
> 
> 
>          ! axis limits
> diff --git a/star/private/pgstar_ctrls_io.f90 b/star/private/pgstar_ctrls_io.f90
> index ce434d1c3..4180392e4 100644
> --- a/star/private/pgstar_ctrls_io.f90
> +++ b/star/private/pgstar_ctrls_io.f90
> @@ -1654,7 +1654,7 @@
>             profile_mass_point_str, &
>             profile_mass_point_str_clr, &
>             profile_mass_point_str_scale, &
> -            TRho_use_decorator, &
> +            TRho_Profile_use_decorator, &
> 
>             Dynamo_win_flag, &
>             Dynamo_file_flag, &
> -- 
> 2.19.0
>