[Mesa-users] make_co_wd test case in r15140

[Evan Bauer]

Hi Kevin,

Thanks for calling attention to this. I don’t think you’re doing anything wrong per se. I’ve noticed that massive C/O WDs have gotten harder to produce with make_co_wd in recent MESA versions as well, and I can confirm that I run into similar convergence problems when starting with an initial mass of 5.7.

I think the problem is that the solver is struggling to converge for the outer layers during some parts of the very luminous post-AGB evolution. I was able to get around this by adding this control in inlist_remove_env and inlist_settle:
	Pextra_factor = 4

That’s somewhat inspired by the test case wd_nova_burst, which also has a massive WD evolving through a similar luminous post-nova phase. This control might make some parts of the evolution slightly unrealistic, but if your goal is just to produce a fresh C/O WD model to work with, this should get your model where you want it to end up.

Perhaps we can add this as a default in future MESA releases so that massive C/O WDs aren’t so hard to produce consistently.

By the way, I think the RAM constraint that you were seeing comes from all of the EOS table caching that occurs during the relaxation phase if you haven’t run models through that range of composition space before on your MESA installation. I noticed that I had quite large RAM usage when I first ran the model and had many EOS tables to cache, but the next time I ran the model my RAM usage was much more reasonable.

Cheers,
Evan

> On Jan 10, 2022, at 12:58 PM, Kevin Rorke via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Hi everyone
> 
> I've been trying to run the make_co_wd test case in r15140 with a 5.7 Msun (or thereabouts) starting mass for some time now. Previously the run failed during the inlist_remove_env step because of memory constraints - it seems to require about 16GB of RAM. But even with that amount of memory, the run eventually fails for any starting mass in that region.
> 
> The only value I've changed is the initial_mass value in inlist_common. And the environment variables are set to create a new zams model each time. Can anyone suggest what I might be doing wrong?
> 
> Cheers
> 
> Kevin
> 
>  Exceeded max_iters iterations in eval_T_tau_uniform
>  retry: error in PT_eqns_surf    1887
>                                                      dt 5.6302130558697700D-21
>                                      min_timestep_limit 9.9999999999999995D-21
> 
>  stopping because of problems dt < min_timestep_limit
> 
> 
> terminated evolution: cannot find acceptable model
> 
> termination code: min_timestep_limit
> DATE: 2022-01-10
> TIME: 19:24:41
> 
> ******************************************************************
> failed to create co_wd.mod when running inlist_remove_env_header
> ******************************************************************
> 
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