[Mesa-users] How do I change the initial_z value of a star module

[Pablo Marchant]

Hi James, unfortunately its not very easy for us to support such old mesa
versions, what I say below applies to the latest mesa version (10398), but
might still work for  5118.

First of all, it seems you are trying to change the metallicity of an
evolved saved model. I really would not recommend this, you should
consistently model the same star with the corresponding metallicity from
the beginning, using create_pre_main_sequence_model=.true. and initial_Z,
initial_Y to create your initial models.

When using relax_Z, are you also setting change_Z to true? I think that
would produce two different calls, one to the routines that change Z in one
go, and then the relaxation ones. So things would still fail. You should
have relax_Z = .true. and change_Z = .false..

Also, when using the relax routines, you can reduce the amount of per-step
change in Z using the option relax_dlnZ (see
star/defaults/controls.defaults, its not in star_job, or also here
http://mesa.sourceforge.net/controls_defaults.html#miscellaneous_controls).
I can't verify if this option is available in your old MESA version.

On Sun, Apr 8, 2018 at 7:56 AM, James via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear all,
>
>
> I'm using mesa-r5118 on Ubuntu (16.04  LTS) with mesasdk (version
> 20141023) and have encountered an issue with trying to change the initial_z
> value of my star.  I'm currently using MESA for a final year project at
> University and am using the inlist_flash inlist of the "Hydrogen Burning on
> Accreting White Dwarfs: Stability, Recurrent Novae, and the Post-Nova
> Supersoft Phase" paper from http://cococubed.asu.edu/mesa_
> market/inlists.html (5th from bottom). I'm trying to expand upon this by
> changing the metallicity of the star, and seeing how the metallicity will
> change the evolution of the star. However, when I try to change the
> metallicity it fails to converge.  I've currently added the following
> commands to the following namelists.
>
>
> &star_job
> change_initial_Z = .TRUE.
> change_z = .true.
> new_Z = 0.005
>
> &controls
> initial_z = 0.005
>
> When I run MESA I get the following lines of output before the program
> stops:
>
>  All this and more are saved in the LOGS directory during the run.
>                                          set_tau_factor
> 3.0000000000000000D+01
> load saved model /home/james/MESA/nova/HB_on_
> WD_bw/steady_burning_models/1.00Msun_Tc_3e7_init.mod
>
>  set_net cno_extras_o18_to_mg26_plus_fe56.net
>  set_initial_age   0.0000000000000000
>  set_initial_dt   1.0000000000000000E-003
>  set_initial_model_number           0
>  change to cno_extras_o18_to_mg26_plus_fe56.net
>  number of species =          24
>  change_v_flag = T
>                                                change_Z
> 5.0000000000000001D-03
>                                                   new z
> 5.0000000000010635D-03
>                                        change_initial_Z
> 5.0000000000000001D-03
>                                                   new z
> 5.0000000000001927D-03
>  net name cno_extras_o18_to_mg26_plus_fe56.net
>  v_flag = T
>                                              tau_factor
> 3.0000000000000000D+01
>                          which_atm_option: grey_and_kap
>                       use small_mtx_decsol bcyclic_dble
> 24         100
>  kappa_file_prefix gn93
>  kappa_lowT_prefix lowT_fa05_gs98
>    eos_file_prefix mesa
>                                         OMP_NUM_THREADS           4
>
>
> MESA runs for about 27 iterations then stops with the following
> information:
>
>                                                      dt
> 6.1216685478627150D-13
>                                      min_timestep_limit
> 9.9999999999999998D-13
>
>  stopping because of convergence problems dt < min_timestep_limit
>
>
> terminated evolution: convergence problems
>
> termination code: min_timestep_limit
>
> I've tried using relax_Z = .true. but that doesn't seem to change anything
> as I get the same error. I tried using the command relax_initial_z but that
> doesn't exist within this version. Is there a way to change the initial_Z
> value of the module I'm using? Also, could I ask why the initial_Z is
> limited to 0 to 0.04?
>

If you upgrade to the latest MESA version this will not be an issue.


Cheers


>
> Many Thanks for the help,
> James
>
>
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
>


-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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