This test builds a carbon-oxygen white dwarf starting from a specified pre main-sequence mass. It does this by running through a series of inlists for different stages of evolution. By default, the first two steps (pre main-sequence and main-sequence through core helium burning) are skipped so that the test will run in a reasonable amount of time, and the test produces a 0.6 \({\rm M}_\odot\) white dwarf from a roughly 3 \({\rm M}_\odot\) progenitor.

Starting from the beginning to produce a white dwarf descended from a progenitor of different mass or metallicity can be accomplished by setting the environment variable MESA_RUN_OPTIONAL=t and editing the values assigned to initial_mass or initial_z in inlist_common.

Larger values for initial_mass can be used to produce more massive carbon-oxygen white dwarfs, but note that this test is not designed to produce a realistic initial-to-final-mass relation (IFMR). Instead, this test is designed to robustly produce usable white dwarf models as soon as evolution has yielded the desired core structure, and so this procedure truncates the AGB evolution just before reaching the thermally-pulsing AGB (TP-AGB) stage, which can be difficult and/or resource-intensive to model. Skipping the TP-AGB stage means that the procedure in this test case will generally require a somewhat larger progenitor mass to produce a given white dwarf mass than what would be expected from a realistic IFMR.

The five steps in this procedure are:

1. inlist_zams (optional)

This step starts from the pre main-sequence to produce a ZAMS model with the initial mass and metallicity specified in inlist_common.

2. inlist_to_end_he_core_burn (optional)

This step evolves from ZAMS through the end of core helium burning.

3. inlist_co_core

This step evolves to near the end of shell helium burning, producing the final C/O core profile in the interior. This step terminates when the He layer mass falls below 0.04 \({\rm M}_\odot\), avoiding the TP-AGB phase that would begin when the He layer becomes smaller. After the AGB envelope is removed in the next step, residual burning in the He layer will reduce its final mass to around 0.01 \({\rm M}_\odot\).

4. inlist_remove_env

This step removes the AGB envelope using the star_relax_to_star_cut method in src/run_star_extras.f90. The location of the cut is specified using x_ctrl(1) to leave \(10^{-3}\) \({\rm M}_\odot\) of the hydrogen envelope. After the relaxation ends, residual burning will reduce the final hydrogen envelope mass to around \(10^{-4}\) \({\rm M}_\odot\) (for the default 0.6 \({\rm M}_\odot\) white dwarf).

5. inlist_settle

This step turns on diffusion in the young proto-WD model to allow the model to settle into a stratified envelope structure with a pure hydrogen atmosphere. This final step ends when the white dwarf has cooled down to reach a luminosity of 1 \({\rm L}_\odot\).