[mesa-users] central hydrogen sudden increase

[Ehsan Moravveji]

Hi Andres,
What happens if you suppress the drop in center H1 by the following switches?
They will make your run longer, since they limit the time step, but take
care of gradual drop in center H1. You may need to give them a try. You
can find these in /star/public/star_defaults.dek

            ! limit on magnitude of decrease in any cell hydrogen
abundance during a single timestep
            ! dH here is abs(xa(h1,k) - xa_old(h1,k)) for any cell k
            ! considers all cells except where have convective mixing
            dH_limit_min_H = 1d99
               ! dH limits only apply where xa(h1,k) >= this limit
            dH_limit = 1d99
               ! if max dH is greater than this, reduce the next timestep
by dH_limit/max_dH
            dH_hard_limit = 1d99
               ! if max dH is greater than this, retry with smaller timestep
            dH_decreases_only = .true. ! if true, then only consider
decreases in abundance

            ! limit on magnitude of relative decrease in any cell hydrogen
abundance
            ! dH_div_H here is abs(xa(h1,k) - xa_old(h1,k))/xa(h1,k)
            ! considers all cells except where have convective mixing
            dH_div_H_limit_min_H = 1d-3
               ! dH_div_H limits only apply where xa(h1,k) >= this limit
            dH_div_H_limit = 0.5d0
               ! if max dH_div_H is greater than this, reduce the next
timestep by dH_limit/max_dH
            dH_div_H_hard_limit = 1d99
               ! if max dH_div_H is greater than this, retry with smaller
timestep
            ! dH_decreases_only applies to dH_div_H also


Best.
Ehsan.



> Hi all,
>
> I noticed that the fraction of central hydrogen during the main sequence
> in
> very standard runs of massive stars sometimes shows a couple sudden jumps,
> which then considerably lengthens the duration of the star's central
> hydrogen, as compared to a stellar model with just one more or one less
> solar mass.
>
> I repeated the run, saving a model before the sudden jump and restarting
> from it, and still keep getting the same results.
>
> As an example, I attach a plot comparing the evolution of a 77 and 78
> solar
> mass models where you can see a jump in the central hydrogen fraction
> around 1.6 Myr for both models and one around 3Myr that only appears in
> the
> 77 solar mass model. I notice that the jump that only shows in the 77
> solar
> mass model makes its main sequence last significantly longer. I could not
> find the reason behind any of these two jumps.
>
> My question is if you guys would have some insight as to what is causing
> this jump.
> I also attach the inlist file for the 77 solar mass model (which shows two
> jumps).
>
> Regards,
> a.
>
> &star_job
>
>       mesa_data_dir = '/home/andres/Arbeit/mesa/data'
>
>       create_pre_main_sequence_model = .false.
>
>       change_net = .true. ! switch nuclear reaction network
>       new_net_name = 'o18_and_ne22.net'
>
> / !end of star_job
>
> &controls
>      ! starting specifications
>          initial_mass = 77 ! in Msun units
>          initial_Z = 0.02
>          initial_Y = -1
>
>      ! mass gain or loss
>          RGB_wind_scheme = 'Reimers'
>          Reimers_wind_eta = 0.4
>
>      ! when to stop
>          xa_central_lower_limit_species(1) = 'h1'
>          xa_central_lower_limit(1) = 1d-10
>             ! stop when the center abundance by mass of h1 drops below
> this
> limit.
>
> /
>
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