[Mesa-users] Question regarding do_tidal_sync

[Warrick Ball]

Hi Ealeal,

> Where in the code\which equation it effects?

I don't use the `binary` module myself but this is a chance to demonstrate how you can try to answer this question yourself.

If you what to know where something is implemented in the code, a good first step is to search for a relevant control.  E.g., if I search for `do_tidal_sync` in my r15140 installation, I find

     $ cd $MESA_DIR
     $ grep do_tidal_sync binary/*/*.f90
     binary/private/binary_ctrls_io.f90:         do_tidal_sync, &
     binary/private/binary_ctrls_io.f90:         b% do_tidal_sync = do_tidal_sync
     binary/private/binary_ctrls_io.f90:         do_tidal_sync = b% do_tidal_sync
     binary/private/binary_tides.f90:         if (.not. b% do_tidal_sync) return

Sometimes it isn't completely obvious how a control gets transferred into the code but in this case it's straightforward.  The match in `binary_tides.f90` is presumably the relevant one.

If you open that file and search for `do_tidal_sync`, you'll find a subroutine called `sync_spin_orbit_torque`.  If `do_tidal_sync` is `.true.`, it sets up some parameters and then calls `sync_spin_to_orbit`.  I'm not going to delve into what that last subroutine does myself but from a glance it appears to apply a torque that synchronizes the rotation and orbital periods.  The binary controls `sync_type_1/2` and `sync_mode_1/2` further control what torque is calculated and where it's applied to the star.

Cheers,
Warrick


___________

Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552

On Tue, 26 Oct 2021, mesa-users at lists.mesastar.org wrote:

> Dear Prof. Marchant
> Thank you for your reply, I apologize but I did not understand, can you point me to the change caused by setting:
> 
> do_tidal_sync = .true.
> 
> Where in the code\which equation it effects?
> 
> As you mentioned do_jdot_ls is at default (true).
> 
> Thanks,
> 
> Ealeal
> 
>  
> 
> The inlist_project we used is:
> 
> &binary_job
> 
>    inlist_names(1) = 'inlist1'
> 
>    inlist_names(2) = 'inlist2'
> 
>    evolve_both_stars = .false.
> 
> / ! end of binary_job namelist
> 
> &binary_controls
> 
>    m1 = 1.32d0  !  Msun
> 
>    m2 = 0.00063d0 ! companion mass in Msun  Try: 0.001
> 
>    initial_period_in_days = 3.66! Also tried 4, 3.5...
> 
>    initial_eccentricity =0 ! try 0,0.05,0.1
> 
>    fr = 0.05 ! default is 0.01
> 
> do_tidal_sync = .true.
> 
> !do_tidal_circ = .false. ! only apply if e>0
> 
> / ! end of binary_controls namelist
> 
>  
> 
> The inlist1 contains rotation:
> 
> &star_job
> 
>       mesa_dir = '../../..'
> 
>       show_log_description_at_start = .false.
> 
>       save_model_when_terminate = .true.
> 
>       save_model_filename = 'final.mod'
> 
>       new_rotation_flag = .true.
> 
>       change_rotation_flag = .true.
> 
>       new_surface_rotation_v = 25.18 ! solar (km sec^1)
> 
>       set_surface_rotation_v = .true.
> 
>       set_initial_surface_rotation_v = .true
> 
>       change_initial_Z = .true. ! also tried with solar metallicity
> 
>       new_Z = 0.03  ! also tried with solar metallicity
> 
>  ! end of star_job namelist
> 
> &controls
> 
>       All regular things  as test suite, instabilities are set:
> 
> D_DSI_factor = 0
> 
> D_SH_factor = 1
> 
> D_SSI_factor = 1
> 
> D_ES_factor = 1
> 
> D_GSF_factor = 1
> 
> D_ST_factor = 1
> 
> / ! end of controls namelist
> 
> &pgstar
> 
>    / ! end of pgstar namelist
> 
> 
> 
> Thank you,
> Ealeal
> 
> On Tuesday, October 26, 2021, 09:55:51 AM GMT+3, Pablo Marchant <pamarca at gmail.com> wrote:
> 
> 
> Hi Bear,
> 
> Without more information it is unclear if the difference on the fifth digit you mention is incorrect. What kind of system are you modeling precisely (always better to share inlists and other input files)? What were you expecting from the model and
> why? Does the star evolve towards synchronicity?
> 
> there are two controls taking care of activating tides in MESA:
> 
> - do_tidal_sync, this is by defalt set to false. It determines whether there is a torque term applied to each star.
> - do_jdot_ls, which defaults to true. This determines if there is a sink term in the equation for the evolution of orbital angular momentum which accounts for the torque imparted on the stars.
> 
> One important thing is that these controls assume you have rotation included in your stellar models. do_jdot_ls only accounts for the torque applied through the star, and do_tidal_sync can only apply a torque if there is rotation included in the
> star. But you should beware of how tidal strength is actually computed (see various options in the documentation). I'd suggest you take a closer look at these as well.
> 
> Cheers
> 
> On Tue, Oct 26, 2021 at 8:08 AM Bear Ealeal via Mesa-users <mesa-users at lists.mesastar.org> wrote:
>
>       Dear MESA users,
>
>       I am trying to run MESA binary+point mass, where the star is a MS and the point mass is a planet.
>
>       I turned on do_tidal_sync = .true.
>
>       I did it for both MESA 10398 and MESA 15140.
> I am not sure what "do_tidal_sync"  does, if it is true or false, tidal occurs and I see that the  binary separation decreases.
> 
> In the defaults it says:
> 
> ! If true, apply tidal torque to the star
> 
>       do_tidal_sync = .false.
> But true or false, I get the same results up to the 5 digit...
> 
> Do  you know what it does and on which parameter it effects?
> 
> Thank you very much for you help,
> 
> Ealeal
> 
> 
> 
> 
> _______________________________________________
> mesa-users at lists.mesastar.org
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> 
> 
> 
> --
> Pablo Marchant Campos
> M.Sc on Astrophysics, Universidad Católica de ChilePhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
> 
>