Stellar relaxation

When mapping 1D profile from MESA to a 3D code such as Phantom, a relaxation procedure is required to ensure that the particles are in hydrostatic equilibrium.

In phantom this is achieved by a process called relax-o-matic (Lau et al., 2022 - please see its appendix C for full details of how it works).

To run relax-o-matic after setting up a star, just follow the instructions during setup (from phantomsetup) and type yes when prompted “Relax star automatically during setup?”;

Then, modify the .setup file and fill in the relaxation options, which are pretty self-explanatory:

relax_star        =           T    ! relax star automatically during setup
tol_ekin          =   1.000E-07    ! tolerance on ekin/epot to stop relaxation
tol_dens          =       1.000    ! % error in density to stop relaxation
maxits            =        1000    ! maximum number of relaxation iterations
write_rho_to_file =           F    ! write density profile to file

Run the phantomsetup again to start the auto relaxation process. You are now good to go!

If interruptted during the relaxation, run phantomsetup again and it will pick up from where it left off automatically.

If in doubt, you can always run the star in isolation for a few years to see if relaxation procedure worked.