[Mesa-users] Nuclear binding energy released

[Josiah Schwab]

Hi Shiv,

> I want to compute the nuclear binding energy released by burning in my
> mesa (mesa-r7624) simulations. Could anyone suggest what would be the
> parameter I need to look for in history columns list to compute the
> nuclear BE by burning?

Do you want the rate at a given timestep, the total over a timestep, or
the total over your whole simulation?

> I have looked into the history columns list and came across the
> parameter 'cumulative nuclear heating'. I am entirely not sure if this
> the right parameter I need to look into and/or what this parameter
> does. Could anyone also guide me where should I look for the job
> description of a parameter from the history columns list?

If it isn't described in sufficient detail in history_columns.list,
you'll have to go hunting through the source.  History columns get their
start in star/private/history.f90

With some digging, you'll find that total nuclear heating is the sum of
eps_nuc integrated over the star over a timestep, i.e.,

  s% dot_product(s% dm(1:nz), s% eps_nuc(1:nz)) * s% dt

and then that cumulative_nuclear_heating is the cumulative sum of the
single step totals.

Now, neither of those quantities are probably actually what you want,
because the MESA definition of eps_nuc in r7624 has the reaction
neutrinos subtracted off (plus some electron energy terms).


I think the easiest thing is to calculate this yourself in
run_star_extras.  Here's snippet to get you started.


    use chem_def
    integer :: i, k, ci

    real(dp) :: eps_nuc_mc2

    eps_nuc_mc2 = 0
    do k=1, s% nz
       do i=1, s% species
          ci = s% chem_id(i)
          ! dxdt_nuc = chem_isos% Z_plus_N(ci)*dydt_nuc
          eps_nuc_mc2 = eps_nuc_mc2 - chem_isos% mass_excess(ci)*s% dxdt_nuc(i,k)/chem_isos% Z_plus_N(ci)
       end do
    end do

which will get you the rate of change of rest mass due to nuclear
reactions.  Time-integrate as desired.


Josiah