[Mesa-users] Resolving TP-AGB

Thu Mar 26 11:51:00 UTC 2026

Dear Mesa users,

I’m trying to evolve stars with mass varying between 1-5 Msun from ZAMS to white dwarf cooling track with version r25.12.1. However, I encounter numerical difficulties during the late TP-AGB phase for a 5Msun model with Z=0.012 (remaining mass ~1.25 Msun). The first thermal pulses go smoothly, but the late evolution struggles and the timestep becomes small and goes into a loop of increase/decrease between -3 < log dt <  -2.5. The limiting factor for dt is labelled as max increase until a retry and loops like this. I tried to lower max_timestep_factor to 1.01 but it does not solve the issue. I observe a lot of retries during that part of evolution until crash due to min_timestep_limit.  

I am fairly new to mesa and not very experienced with debugging. Here are typical examples of error messages I get:

avg resid  0.223E-06     max resid dv_dt     1  0.35367E-03 mix type xx000 avg corr  0.474E-03      max corr lnd   451 -0.21100E-01 mix type 00000  avg+max corr+resid -- give up

hydro_mtx: logT too small       26764         407           3    6.7237179921904777D-01    5.3757388036508846D+00

hydro_mtx: logRho too large       26738         421           5    5.6268674362592407D+01   -7.8503397605837941D+00

I tried to include okay_to_reduce_gradT_excess = .true. which I found used in some inlists online, but with this parameter activated the star shows non-physical behavior (log L > 10^5-6 with few small timesteps) so I keep it to false.

Please find below the enlists I use which are based on make_co_wd test_suite which I modified to include element diffusion during MS and thermal pulses to remove the enveloppe instead of remove_env routine. Thanks a lot!

Best regards,

Théo

Common inlist for shared parameters
&star_job
      show_log_description_at_start = .false.

      change_net = .true.      
      new_net_name = 'co_burn_extras.net'

      ! age start at ZAMS
      set_initial_age = .false.
      set_initial_model_number = .false.

      num_special_rate_factors = 2
      reaction_for_special_factor(1) = 'r_c12_ag_o16'
      special_rate_factor(1) = 1
      filename_of_special_rate(1) = 'c12ag_deboer_sigma_0p0_2000_Tgrid.dat'

      reaction_for_special_factor(2) = 'r_he4_he4_he4_to_c12'
      special_rate_factor(2) = 1
      filename_of_special_rate(2) = 'r_he4_he4_he4_to_c12_cf88.txt'

/ ! end of star_job namelist

&eos

/ ! end of eos namelist

&kap
      Zbase = 1.2d-02

      kap_file_prefix = 'gs98'
      use_Type2_opacities = .true.

/ ! end of kap namelist

&controls

initial_mass = 5.00d+00

! winds
      cool_wind_full_on_T = 9.99d9
      hot_wind_full_on_T = 1d10
      cool_wind_RGB_scheme = 'Reimers'
      cool_wind_AGB_scheme = 'Blocker'
      RGB_to_AGB_wind_switch = 1d-4
      Reimers_scaling_factor = 0.1d0  
      Blocker_scaling_factor = 0.2d0

! when to stop
      max_age = 1.4d+10

! mesh
      max_allowed_nz = 20000 ! preventing 'fail to adjust mesh'

! diffusion
      diffusion_v_max = 1d-5
      do_element_diffusion = .false. ! Activated during MS and settling only
      diffusion_use_full_net = .true.

      ! Solver controls.
      diffusion_use_cgs_solver = .true.
      diffusion_use_isolve = .true.
      diffusion_rtol_for_isolve = 1d-4
      diffusion_atol_for_isolve = 1d-5
      diffusion_min_X_hard_limit = -1d-4
      diffusion_maxsteps_for_isolve = 1000
      diffusion_isolve_solver = 'ros2_solver'

      ! Timestep controls to prevent steps that are difficult for diffusion.
      diffusion_steps_limit = 20
      diffusion_steps_hard_limit = 150
      diffusion_iters_limit = 50
      diffusion_iters_hard_limit = 100      

! convection
      mlt_option = 'Henyey'
      mixing_length_alpha = 1.8
      use_Ledoux_criterion = .true.
      thermohaline_coeff = 1d2

! timesteps
      max_years_for_timestep = 1d7
      time_delta_coeff = 1.0d0
      use_gold2_tolerances = .true.

      varcontrol_target = 1d-3
      dX_nuc_drop_limit = 1d-2
      delta_HR_limit = 0.1

! Atm
      atm_option = 'T_tau'
      atm_T_tau_relation = 'Eddington'
      atm_T_tau_opacity = 'iterated'
      atm_T_tau_max_iters = 100

! Overshoot
      overshoot_scheme(1) = 'exponential'
      overshoot_zone_type(1) = 'any'
      overshoot_zone_loc(1) = 'any'
      overshoot_bdy_loc(1) = 'any'
      overshoot_f(1) = 0.014
      overshoot_f0(1) = 0.004

/ ! end of controls namelist

AGB inlist

&star_job

      load_saved_model = .true.
      load_model_filename = 'end_he_core_burn.mod'
      save_model_when_terminate = .true.
      save_model_filename = 'end_AGB.mod'
      required_termination_code_string = ''
      set_initial_model_number = .true.
      initial_model_number = 0
      pgstar_flag = .true.

/ ! end of star_job namelist

&eos

/ ! end of eos namelist

&kap

/ ! end of kap namelist

&controls
      log_directory = 'LOGS_AGB'

! energy conservation
      energy_eqn_option = 'eps_grav'
      use_time_centered_eps_grav = .true.

! when to stop
      envelope_mass_limit = 1e-3

! winds
      max_wind = 1d-2

! solver
      retry_hold = 0
      neg_mass_fraction_hold = 3

! mesh
      mesh_delta_coeff = 1.0

! convection & dragging
      num_cells_for_smooth_gradL_composition_term = 0
      drag_coefficient = 1d0
      min_q_for_drag = 0.98d0
      alpha_semiconvection = 0.1

! timesteps

      varcontrol_target = 1d-4
      delta_lgL_He_limit = 0.005
      lgL_He_burn_min = 2.0
      dX_nuc_drop_limit = 1d-3
      delta_HR_limit = 0.1
      max_timestep_factor = 1.01d0

      delta_lgTeff_limit = 0.005
      delta_lgTeff_hard_limit = 0.01
      delta_lgL_limit = 0.02 
      delta_lgL_hard_limit = 0.05

! output
      num_trace_history_values = 2
      trace_history_value_name(1) = 'rel_E_err'
      trace_history_value_name(2) = 'log_rel_run_E_err'

      !report_solver_progress = .true. ! set true to see info about solver iterations
      !report_ierr = .true. ! if true, produce terminal output when have some internal error
      !stop_for_bad_nums = .true.

/ ! end of controls namelist

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