[mesa-users] Scratchy surface metallicity profile with diffusion in 1.3Msun star

[Warrick Ball]

Hi,

I've just been debugging some asteroseismic runs, and I've found that I'm 
getting some scratchy surface metallicities in hotter stars.  Attached is 
a plot of [Fe/H] vs age for a 1.3 Msun star (inlist attached), from 
revision 7184.  As you can see, it gets quite scratchy around 2 Gyr.

I've taken a look at the abundance and diffusion velocity profiles, and it 
appears that the outermost meshpoint swaps between higher and lower 
values, as seen in the history plot, even though the underlying abundance 
(i.e. the abundance just below the surface) is more stable.

I know diffusion is a bit iffy in hotter stars, like this one, which peaks 
around 6400K.  But I wouldn't mind seeing the metals drained from the 
surface completely as much as I'm perturbed by this kind of behaviour. 
This star has a thin convective shell by mass (~0.002 Msun at core H 
exhaustion), and the diffusion velocities reach a few times 10^-7 cm/s in 
the outermost layers by the end.

I'm gradually going through all the parameters in the diffusion controls, 
but any pro tips would be appreciated.  I'm mainly hoping to smooth out 
the outermost meshpoints so that the fluctuations are suppressed and the 
surface abundance matches the underlying layers.

Cheers,
Warrick


------------
Warrick Ball
Postdoc, Institut für Astrophysik Göttingen
wball at astro.physik.uni-goettingen.de
+49 (0) 551 39 5069
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&star_job

      read_extra_star_job_inlist1 = .true.
      extra_star_job_inlist1_name = 'inlist_diff'

/ ! end of star_job namelist



&controls

      read_extra_controls_inlist1 = .true.
      extra_controls_inlist1_name = 'inlist_diff'

/ ! end of controls namelist



&pgstar

      read_extra_pgstar_inlist1 = .true.
      extra_pgstar_inlist1_name = 'inlist_diff'

/ ! end of pgstar namelist
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&star_job
      show_log_description_at_start = .false. 
      mesa_dir = '' ! empty string defaults to environment variable MESA_DIR

      astero_just_call_my_extras_check_model = .true.

      change_lnPgas_flag = .true. ! see discussion on forum
      new_lnPgas_flag = .true.    ! more accurate

      eos_file_prefix = 'mesa'
      kappa_file_prefix = 'gs98'

      kappa_blend_logT_upper_bdy = 4.50 ! 4.10 ! <= 0 means use default
      kappa_blend_logT_lower_bdy = 3.75 ! 4.00 ! <= 0 means use default

      pgstar_flag = .false. ! .true.

      load_saved_model = .true.
      saved_model_name = 'pms.mod'

  ! relax PMS model to new parameters
      relax_mass_scale = .true.
      new_mass = 1.30 ! in Msun units

      relax_Y = .true.
      new_Y = .259

      relax_Z = .true.
      new_Z = 0.019
/ !end of star_job

&controls
  ! when to stop
      max_years_for_timestep = 50d6
      max_age = 15d9 ! we don't expect stars older than the Universe, right?
      photosphere_r_upper_limit = 25d0 ! must be more than pre-ms!

  ! starting specifications and global/fixed parameters
      cubic_interpolation_in_Z = .true.
      use_Type2_opacities = .false.

      ! use_Henyey_MLT = .true. ! .false.
      MLT_option = 'Henyey' ! options are ML1, ML2, Mihalas, Henyey (default)

      which_atm_option = 'Eddington_grey' ! 'simple_photosphere' or 'Krishna_Swamy' (needs different alpha_MLT)

      mesh_delta_coeff = 0.25 ! 1.0 ! = 1/4 of default

      varcontrol_target = 1d-4 ! 1d-4 ! = 1/4 of default

      !do_element_diffusion = .true. ! determines whether or not we do diffusion

      terminal_interval = 50 ! save some space
      write_header_frequency = 10

  ! output to files and terminal
      photostep = -1

      write_profiles_flag = .true. ! .false. ! .true. not needed, save space
      profile_interval = 10 ! -1

      do_history_file = .true.
      history_interval = 1

      xa_central_lower_limit_species(1) = 'h1'
      xa_central_lower_limit(1) = 1d-4

  ! model parameters
      initial_mass = 1.30 ! in Msun units
      initial_Z = 0.019
      initial_Y = .259
      mixing_length_alpha = 1.8

      do_element_diffusion = .true.
      ! diffusion_v_max = 1d99
     
/ ! end of controls

&pgstar
/ ! end of pgstar namelist
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&astero_search_controls

      do_redistribute_mesh = .true.
         ! note: number of zones for redistribute is set in the redistrb.c input file
      

/ ! end astero_search_controls
   


&astero_pgstar_controls

/ ! end astero_pgstar_controls