Stellar winds

Tasks W.1

1. Setting up your run:
   • We want to save our run in a separate folder again: change: log_directory = 'LOGS_winds'
   • Remove the Tayler Spruit dynamo that we added in the previous exercise, i.e. comment out or remove D_ST_factor = 1.0 and am_nu_ST_factor = 1.0.
   • Add some wind prescriptions to our model, by including the following in the controls section of our inlist_rotating_star:

     	
     ! wind
     	cool_wind_full_on_T = 1d4 ! cool wind scheme takes effect below this temperature
     	cool_wind_RGB_scheme = 'Dutch'
     	cool_wind_AGB_scheme = 'Dutch'
     	Dutch_scaling_factor = 0.8d0 ! scaling for the Dutch wind scheme (default = 0, so no mass loss)
     
     	hot_wind_full_on_T = 1.01d4 ! hot wind scheme takes effect above this temperature
     	hot_wind_scheme = 'Vink'
     	Vink_scaling_factor = 3d0 
     	
     

     where the top 4 lines set the wind schemes for cool stars (that is winds on the red giant branch and asymptotic giant branch), and the bottom 3 lines are for hot stars (i.e., main sequence, Hertzsprung-gap and Wolf-Rayet stars).
   • Run your model with ./rn !
2. Plot the 'star_age' versus the log of the wind mass loss rate 'log_abs_mdot'. When is the star losing more mass, earlier or later in its evolution?
3. Plot the j-profile, this time only at only at core-He exhaustion..
   • Surface effects: Does the wind carry away high or low specific-angular momentum?
     How will this affect the surface rotation? Check your expectation by printing out the surface rotation rate at the end of the simulation (e.g., histdata.surf_avg_v_rot[-1]).
   • What is happening to the core?
     Focus on the core-envelope boundary, is the core-envelope boundary at higher or lower mass? Now focus on the height of the specific angular momentum at that core-envelope boundary, is it higher or lower when winds are included?

Solution W.1:

1. At this point, your inlist_rotating_star should look like this.
2. The notebook with the solution to the plots can be found here.
   
   The mass loss rates increases towards the end of the stars evolution.
3. Your j-profiles should look like this:
   
   • The wind carries away the outer layers of the star, which has high specific angular momentum. This means that we should expect windy stars to spin down. If we print the last surf_avg_v_rot from the history file for the model without and with winds, we indeed see that the model with winds has lower surface rotation.
   • When winds are included, the core-envelope boundary is at a lower mass. The height of the specific angular momentum at the core-envelope boundary moves down, but only a little. This shows that the angular momentum is not carried outward (when we don't include magnetic fields).

Tasks W.2

1. Open the file $MESA_DIR/star/other/other_wind.f90. From there, copy the subroutine "null_other_wind" to your run_star_extras.f90 file located at ~/rotating_star_proj/src/run_star_extras.f90
   This routine will set your stellar wind mass loss to a constant rate specified by w (in units of Msun/year).
2. Rename this routine to "other_wind_routine" for clarity. Don't forget to rename both the beginning (declaration) and the end statement of the subroutine!
3. Choose a constant mass loss rate between $5\cdot10^{-8}\,\mathrm{M_{\odot}/yr}$ and $8\cdot10^{-7}\,\mathrm{M_{\odot}/yr}$ which you would like to apply to the star, by writing your name next to the chosen rate in this google spreadsheet. In your run_star_extras.f90, change w=0 to your chosen rate.
   

   Note! Runs with higher values of w tend to take longer to run

4. We need to tell MESA to actually use the wind routine we just created. Add a pointer your other_wind_routine in the subroutine 'extras_controls' by adding the line s% other_wind => other_wind_routine
5. Finally, activate the 'other_wind_routine' in your simulation by replacing the previously added winds (e.g., by commenting them out), with a pointer to the new 'other_wind_routine'.
   Do this by adding use_other_wind = .true. as a line to the &controls section of inlist_rotating_star
   If you want to save this in a separate folder again (recommended), change: log_directory = 'LOGS_other_winds'
6. Don’t forget to recompile the simulations by using the command ./clean ; ./mk from the terminal in your rotating star directory, before you ./rn!
7. Write down the stellar mass (star_mass, Radius, and total angular momentum (log_total_angular_momentum) at the end of the simulation in the google spreadsheet. next to your name. When everyone has filled out their values: what happens to the stars radius when the star has a higher mass loss rate?

Solution W.2:

• Your inlist_rotating_star will now look like this, and your run_star_extras.f90 will look like this.
• We will compare the results in the google spreadsheet with the whole group after everyone has filled in their values!

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