Here are some things to test if you found yourself done early, or are looking for some extra challenge.
For massive stars, mass loss through winds is also a considerable factor for their evolution, and very massive stars’ lives can be completely dictated by it. Since we will discuss mass loss in much greater detail for today’s Lab 3, we will relegate it to a bonus exercise (See Section 1.6.1) for the time being. This does mean that our stars here will be evolved without any mass loss. That is fine for the purposes of this lab’s exploration of stellar engineering!
Here we use a set of near-default options for our massive stars, however you may wish to use a different mass loss scheme, your own custom scheme, or none at all! The possibilities for this will be further explored in Minilab 3 .
We will implement one of the default, and widely used, mass loss schemes found within MESA - the Dutch mass loss. This is a collection of recipes (which are all coincidentally Dutch authors) for massive stars, and will automatically switch between appropriate recipes depending on temperature, surface hydrogen conditions, and inlist control options. As before, the full documentation for these options can be found here.
As with overshooting above, we are interested in setting the following controls:
Cool scheme: Which recipe should MESA use when in the “cool” temperatures?
Hot scheme: Which recipe should MESA use when in the “hot” temperatures?
Cool and Hot Temperatures: What are the temperatures for the cool and hot winds mentioned above? Note that these are two separate temperature criteria, and between this two values, MESA will interpolate between both hot and cold schemes, weighted depending on where in temperature space the model is at that time.
Task B1. Enable mass loss through winds
Enter controls for winds using the Dutch scheme, with the cool wind temperature at log(Teff) = 8, 000 K, and the hot wind temperature at log(Teff) = 12, 000 K. The Dutch wind should use the de Jager recipe at low T.
Questions
What recipe (from those available in Dutch) will the model use when it starts?
Answers
Vink
Partial Solutions
! Modify inlist_to_end_core_he_burn
! These lines go somewhere within &controls.
cool_wind_full_on_T = 0.8d4
hot_wind_full_on_T = 1.2d4
cool_wind_RGB_scheme = 'Dutch'
cool_wind_AGB_scheme = 'Dutch'
hot_wind_scheme = 'Dutch'
Dutch_wind_lowT_scheme = 'de Jager'
Dutch_scaling_factor = 1
20 M from TAMS to End He with Dutch Winds
Duration ~ 5 Mins, 8 THREADS
The alternative to superad_reduction is MLT++, which is an explicit method of artificially boosting energy transport near the surface. In this section, we will take the 20M⊙ test model from before and this time use MLT++ to evolve until the end of core Helium burning to see the differences in the model.
NOTE: Firstly, it is VERY important that we turn off superad_reduction first. Otherwise we will be twice boosting the energy transport! To this effect, you may simply set use_superad_reduction = .false.. Now we want to add in MLT++. The documentation for which can be found here . The controls for MLT++ go in the same namelist as superad_reduction.
Task B2. MLT++ model
Set up and run a 20M⊙ model from TAMS to the end of core helium burning using MLT++ instead of superad_reduction.
Questions
If we are to compare to our original 20M⊙ model, what options must we re-enable in our inlists?
Hints
We disabled these in 6.1 and 6.2
Answer
Mass loss and stopping conditions
Partial Solutions
! Modify inlist_mass_Z_wind_rotation
! These lines go somewhere within &controls.
okay_to_reduce_gradT_excess = .true.
gradT_excess_f1 = 1d-4
gradT_excess_f2 = 1d-3
20 M from TAMS to End He with MLT++
Duration ~ 5 Mins, 8 THREADS
Questions
What differences do you notice between MLT++ and superad_reduction in the HRD?
What are the numerical differences between MLT++ and superad_reduction?