[mesa-users] pre-MS central T

[Bill Paxton]

Hi Tug,

Sorry for the slow response --- the last week was totally consumed by the MESA summer school (it was great!!!).

I think the only way to satisfy your curiosity is for you to plunge into the details of the build_pre_ms_model routine.
It lives in mesa/private/pre_ms_model.f.   You can have many hours of entertainment watching it at work.
Of course the real fun starts when build_pre_ms_model hands off a model to the regular star evolution.
That's where the failure to converge demon emerges.

If you come up with a good scheme for making this more robust, we'll all be grateful. ;p

cheers,
bill




On Aug 12, 2013, at 12:09 AM, Tuguldur Sukhbold wrote:

> Dear MESA users,
> 
> I have one question just out of curiosity. In the past whenever I experience convergence problems trying to create a preMS model, I have been changing the starting central temperature, and it has been working 'great'. Today I noticed that in one particular model (attached inlist) it works when I change the default central T only by 10kelvins. 
> 
> Why such a small change (0.003%) affects convergence? People often attribute this kind of effects to the fact that we're solving highly non-linear set of eqn.s and small changes often propagate to create large effects in the end etc… but here were looking at rather simple case of just initial convergence.
> 
> My other question is, why MESA doesn't tweak this (and other similar parameters) automatically when it fails to find convergence?
> 
> thanks,
> Tuguldur
> 
> 
> 
> &star_job
> 
>      mesa_dir = ''
>      create_pre_main_sequence_model = .true.
> 
>      change_net = .true. ! switch nuclear reaction network
>      new_net_name = 'o18_and_ne22.net'
> 
>      eos_file_prefix = 'mesa'
>      kappa_file_prefix = 'gs98'
> 
>      set_rate_c12ag = 'Buchmann'
>      num_special_rate_factors = 1
>      reaction_for_special_factor(1) = 'r_c12_ag_o16'
>      special_rate_factor(1) = 1.2
> 
>      set_rate_1212 = 'CF88' 
>      num_special_rate_factors = 2
>      reaction_for_special_factor(2) = 'r1212_to_ne20'
>      special_rate_factor(2) = 1.0
> 
> !      pre_ms_T_c = 3.0001e5
> 
>      pgstar_flag = .false.
> /
> 
> &controls
> 
>      initial_mass = 16.0d0
>      initial_Z = 0.02
>      initial_Y = 0.25
> 
>      photostep = 100
>      profile_interval = 50
>      history_interval = 1
>      terminal_interval = 10
>      write_header_frequency = 10
> 
>      RGB_wind_scheme = 'Nieuwenhuijzen'
>      AGB_wind_scheme = '' 
>      RGB_to_AGB_wind_switch = 1d-4
>      Nieuwenhuijzen_wind_eta = 1.0d0
> 
>      xa_central_lower_limit_species(1) = 'h1'
>      xa_central_lower_limit(1) = 0.72
> 
>      rate_factor_for_fe56ec_to_cr56 = 1d-4
>      min_timestep_limit = 1d-12 ! (seconds)
> 
>      xa_scale = 1d-5
>      newton_itermin = 2
> 
>      mixing_length_alpha = 1.0
>      use_Ledoux_criterion = .true.
>      alpha_semiconvection = 0.1
> 
>      overshoot_f_above_burn_h = 0.01
>      overshoot_f_above_burn_he = 0.01
>      overshoot_f_above_nonburn = 0.01
>      overshoot_f_below_nonburn = 0.01
>      overshoot_f_above_burn_z = 0.01
>      min_overshoot_q = 1d-3 
> 
>      screening_mode = 'extended'
> /
> 
> &pgstar
> 
> /
> 
> 
> 
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