[Mesa-users] Alpha-enhanced low-Z models

[Balázs Kertész]

Hi all,

I'm trying to evolve low metallicity (Z_o/10), low mass (around 0.8 M_o),
alpha enhanced (A/Fe=+0.2) stars to the HB. I found an older thread (
https://lists.mesastar.org/pipermail/mesa-users/2024-August/015292.html)
describing a possible approach, which I implemented in the attached inlist
in the kap section.

Without the enhancement, the model evolves as expected, but after including
it, the MS temperature jumps from around 6000K to 10000K, which doesn't
seem reasonable. I attached a HRD plot comparing the two cases, the dotted
lines are the estimated edges of the instability strip for this
metallicity. Has anyone encountered this issue before, or are there any
alternatives?

Thanks in advance!

Best regards,
Balázs

&star_job

    create_pre_main_sequence_model = .true.

    save_model_when_terminate = .true.
    save_model_filename = '0.8M_Re_0.33_at_TACHeB_net_kap_uj.mod'
    pgstar_flag = .true.

    pause_before_terminate = .true.


  history_columns_file = 'my_history_columns.list'

  change_initial_net = .true.
  new_net_name = 'pp_and_cno_extras.net'

/ ! end of star_job namelist




&eos

/ ! end of eos namelist


&kap

  use_Type2_opacities = .true.
  Zbase = 0.0014

  kap_file_prefix = 'gs98_aFe_p2'

  user_num_kap_Xs = 10
  user_kap_Xs = 0.0d0, 0.1d0, 0.2d0, 0.35d0, 0.5d0, 0.7d0, 0.8d0, 0.9d0,
0.95d0, 1.0d0

  user_num_kap_Zs = 13
  user_kap_Zs = 0.000d0, 0.0001d0, 0.0003d0, 0.001d0, 0.002d0, 0.004d0,
0.01d0, 0.02d0, 0.03d0, 0.04d0, 0.06d0, 0.08d0, 0.100d0

/ ! end of kap namelist


&controls

  ! starting specifications
    initial_mass = 0.8 ! in Msun units
    initial_z = 0.0014

  ! when to stop

     HB_limit = 0.01

  ! wind

    hot_wind_scheme = 'Reimers'
    cool_wind_RGB_scheme = 'Reimers'
    Reimers_scaling_factor = 0.33

  ! atmosphere

  ! rotation

  ! element diffusion

  ! mlt

  ! mixing

  ! timesteps

  time_delta_coeff = 1

  ! mesh

  mesh_delta_coeff = 1

  ! solver
     ! options for energy conservation (see MESA V, Section 3)
     energy_eqn_option = 'dedt'
     use_gold_tolerances = .true.

     convergence_ignore_equL_residuals = .true.

  ! output

   log_directory = '0.8M_Re_0.33_at_TACHeB_net_kap_uj'
   photo_interval = 1000
   photo_digits = 5
   profile_interval = 750
   history_interval = 1
   terminal_interval = 50


/ ! end of controls namelist

[image: problem.png]
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