[mesa-users] Accretion: max_star_mass_for_gain and eps_grav

[Dean Townsley]

Hi Philip,

Just to confirm Josiah's comments...

You have found pretty much the right culprit.  This appears to be a hole 
in the logic treating the max_star_mass_for_gain parameter in 
mesa/star/private/adjust_mass.f90.

The following changes seem to make your inlist_A work as expected for 
me.  Hopefully the syntax of diff is obvious enough for you to make 
these changes easily.  Just add the lines with the + to your 
adjust_mass.f90 file near the line numbers following the @@, 113 and 130 
in this case.

Dean



--- star/private/adjust_mass.f90     (revision 7624)
+++ star/private/adjust_mass.f90     (working copy)
@@ -113,6 +113,8 @@
              .or. (delta_m < 0 .and. s% star_mass <= s% 
min_star_mass_for_loss) &
              .or. (delta_m > 0 .and. s% max_star_mass_for_gain > 0 &
                    .and. s% star_mass >= s% max_star_mass_for_gain)) then
+            delta_m = 0
+            s% mstar_dot = 0
              call save_for_d_dt(s)
              if (dbg) write(*,*) 'do_adjust_mass return 2'
              return
@@ -130,9 +132,11 @@
                 .and. new_mstar > Msun*s% max_star_mass_for_gain) then
              new_mstar = Msun*s% max_star_mass_for_gain
              delta_m = new_mstar - old_mstar
+            s% mstar_dot = delta_m/dt
           else if (delta_m < 0 .and. new_mstar < Msun*s% 
min_star_mass_for_loss) then
              new_mstar = Msun*s% min_star_mass_for_loss
              delta_m = new_mstar - old_mstar
+            s% mstar_dot = delta_m/dt
           end if

           frac = old_xmstar/new_xmstar


On 08/14/2015 04:02 PM, Josiah Schwab wrote:
> Hello Philip,
>
>> I want to use MESA 7624 to model accretion which stops when a chosen
>> mass is exceeded. I find strange behaviour when the
>> max_star_mass_for_gain parameter is used to achieve this. The strange
>> behaviour seems to be because the eps_grav calculation still thinks
>> the star is accreting even after the maximum mass is exceeded.
> Thank you for this excellent report.  It looks like you uncovered a bug
> in the `max_star_mass_for_gain' and `min_star_mass_for_loss' controls.
> You may be the first person to use these :)
>
> This will be fixed in the next release.  I will follow up with you
> off-list about the specific fix that gets applied.
>
> Until then, if you want to be able to change the accretion rate while
> the run is going, you can do the same thing using run_star_extras.f.
>
> Add the following lines to "extras_finish_step"
>
>      ! turn off mass loss when the star grows larger than ? (in Msun)
>      if (s% star_mass > s% x_ctrl(1)) s% mass_change = 0
>
> Then, you can specify the meas
>
> &controls
>
>    x_ctrl(1) = 0.6
>
> /
>
> Best,
> Josiah
>
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