[mesa-users] create_pre_ms_model sometimes slow with T(tau) atmosphere relations

[Warrick Ball]

Hi all,

This issue isn't a dealbreaker for me, but I figured it's probably worth 
bringing up in case someone else knows a solution.  Attached is an inlist 
for a typical work directory (r7624), which uses the create_pre_ms_model 
option in &star_job to create a pre-main-sequence stellar model with 
central temperature around 8.5e5 K.

If I run with the default atmosphere (i.e. by commenting out 
which_atm_option), everything runs just fine.  However, if I try with

which_atm_option = 'Eddington_grey'

MESA seems to have a hard time converging the first model.

  create pre-main-sequence model
                                                 species           8
  abundances
                                                      h1    7.0000000000000007D-01
                                                     he3    2.9797635251138625D-05
                                                     he4    2.7997020236474895D-01
                                                     c12    3.4416106108120410D-03
                                                     n14    1.0081585468366043D-03
                                                     o16    9.3604466091399760D-03
                                                    ne20    2.0994599496976492D-03
                                                    mg24    4.0903242835137509D-03


                                         relax_num_steps

hydro_newton_step returned ierr       retry cnt, step, log10(dt/yr), retry_factor     1     1       -5.602060        0.500000
hydro_newton_step returned ierr       retry cnt, step, log10(dt/yr), retry_factor     2     1       -5.903090        0.500000
  have reached retry limit so now backup
hydro_newton_step returned ierr       retry cnt, step, log10(dt/yr), retry_factor     1     1       -8.204120        0.500000
hydro_newton_step returned ierr       retry cnt, step, log10(dt/yr), retry_factor     2     1       -8.505150        0.500000
  first model is slow to converge: num tries          70
  first model is slow to converge: num tries          80
  first model is slow to converge: num tries          90
  first model is slow to converge: num tries         100
  first model is slow to converge: num tries         110
  first model is slow to converge: num tries         120
  first model is slow to converge: num tries         130
  first model is slow to converge: num tries         140
  first model is slow to converge: num tries         150
  first model is slow to converge: num tries         160
  first model is slow to converge: num tries         170
  first model is slow to converge: num tries         180
  have reached retry limit so now backup
  first model is slow to converge: num tries         190
<snip>
  first model is slow to converge: num tries         350

after which it gets going as usual.  Things are similarly slow if 
which_atm_option is set to the other T(tau) relations: 'solar_Hopf_grey' 
or 'Krishna_Swamy'.  In my experience, this is more of a problem at masses 
between about 1.4 and 1.9 solar.  I haven't experimented much at higher 
masses.

So, why would the T(tau) relations cause such problems?

I've tried to track down where exactly the problem comes in, but I didn't 
really get anywhere.  The error message is generated in 
star/private/hydro_mtx.f90, but that's not terribly useful.  I think 
that's just where the matrix for the relaxation iterations is set up.  So 
I'm currently trying to follow my way through all the function calls to 
see where the atmosphere is called and what effect that has.  I'm trying 
to work backwards from calls to the atmosphere T(tau) relations and 
forwards from the pre-main-sequence model routines, but the two threads 
haven't connected yet...

Anyway, has anyone else come across this problem and, if so, worked around 
it?  Or is there somewhere obvious I should look to try to fix things?

Cheers,
Warrick



------------
Warrick Ball
Postdoc, Institut für Astrophysik Göttingen
wball at astro.physik.uni-goettingen.de
+49 (0) 551 39 5069
-------------- next part --------------
! inlist to evolve a 15 solar mass star

! For the sake of future readers of this file (yourself included),
! ONLY include the controls you are actually using.  DO NOT include
! all of the other controls that simply have their default values.

&star_job

  ! begin with a pre-main sequence model
    create_pre_main_sequence_model = .true.
    pre_ms_T_c = 8.5d5 ! slow with 8.5d5

  ! save a model at the end of the run
    save_model_when_terminate = .false.
    save_model_filename = '15M_at_TAMS.mod'

  ! display on-screen plots
    pgstar_flag = .true.

/ !end of star_job namelist


&controls

  ! starting specifications
    initial_mass = 1.65 ! in Msun units ! slow with 1.65
    which_atm_option = 'Eddington_grey' ! slow with any T(tau), esp. Eddington_grey

    initial_Y = 0.28 ! slow with 0.28
    initial_Z = 0.02 ! slow with 0.02

  ! stop when the star nears ZAMS (Lnuc/L > 0.99)
    Lnuc_div_L_zams_limit = 0.99d0
    stop_near_zams = .true.

  ! stop when the center mass fraction of h1 drops below this limit
    xa_central_lower_limit_species(1) = 'h1'
    xa_central_lower_limit(1) = 1d-3

/ ! end of controls namelist