[mesa-users] crazy C shell burning

[Tuguldur Sukhbold]

forgot to attach the inlist. I am using 4798:

&star_job

      mesa_dir = ''

      create_pre_main_sequence_model = .true.

      set_rate_c12ag = 'Buchmann'
      num_special_rate_factors = 1
      reaction_for_special_factor(:) = 'r_c12_ag_o16'
      special_rate_factor(1) = 1.2

      eos_file_prefix = 'mesa'
      kappa_file_prefix = 'gs98'
      
/

&controls

      initial_mass = 15
      initial_Z = 0.02
      initial_Y = 0.25

      mixing_length_alpha = 2

      RGB_wind_scheme = 'Nieuwenhuijzen'
      AGB_wind_scheme = '' 
      RGB_to_AGB_wind_switch = 1d-4
      Nieuwenhuijzen_wind_eta = 1.0d0

      photostep = 50
      profile_interval = 25
      history_interval = 1
      terminal_interval = 20
      write_header_frequency = 5

      log_center_temp_limit = 9.07918

/

Tuguldur






> On Apr 16, 2013, at 10:24 PM, Tuguldur Sukhbold <sukhbold at ucolick.org> wrote:
> 
>> Dear MESA users,
>> 
>> many of us are now well aware that due to lack of NSE treatment you're likely to get into trouble during Si burning. But in my 2+ year experience with MESA I have seen many times this weird behavior well before Si ignition, during the C burning. The attached plot shows the central T and rho evolution during C burning for two identical 15Msun models with different alpha_mlt. You see the alpha_mlt=2 case goes smoothly, but the alpha_mlt=1 case is doing some crazy stuff. I could wait for thousands of time steps and it would be just doing its weird loops back and forth, and never manage to ignite Ne.
>> 
>> With older MESA versions I noticed sometimes even very slight changes in the composition could result into this problem during C burning. If I remember correctly, during the last summer school Josh Shiode also reported similar results when he played with the time step and zoning (?) parameters.
>> 
>> I was wondering if anybody had looked into details of why this happens? how to avoid? previously I used to almost 'randomly' play with certain parameters until I find that sweet spot to make it through C burning. But now I am trying to make a detailed comparison with another code, so i need to be a bit careful.
>> 
>> thanks,
>> Tuguldur
>> 
>> ***just to clarify, in this plot the alpha_mlt=1 case only shows data since the ignition of C in the core. While the other case shows data from previous evolution.
>> 
>> <Screen Shot 2013-04-16 at 9.51.50 PM.png>
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