[Mesa-users] Low m high z stars - run in v10398 but not in v12778

[Francis Timmes]

mostly this has to do with the eos at high metallicities.
the attached inlist runs a 0.3 msun model with 0.01 < Z < 0.1
from the pre-main sequence to the main-sequence in ~200 timesteps.

fxt




> On Oct 2, 2020, at 10:33 AM, Samuel Baltz via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Hello,
> 
> when I attempt to run pre-main sequence stars with initial_mass from about 0.1 up to 0.5 solar masses, and varying initial_z from about 0.01 to 0.15, I get the error "stopping because of problems dt < min_timestep_limit
> 
> terminated evolution: cannot find acceptable model
> 
> termination code: min_timestep_limit". This typically happens well before the star reaches the main sequence. The strange thing is that this happens in v12778, but I have no trouble running stars with identical settings all the way through the main sequence in v10398.
> 
> Here are 3 troubleshooting steps I've tried. First, I replicated the v12778 error on two different machines with independent installations, using many different inlists from the test suite. Second, previous mesa-users posts have suggested that the which_atm_option (and the multiple controls it was replaced with before v12778) might cause version-specific errors related to metallicity, since some atm tables assume solar metallicity. The controls.defaults file on my v10398 machine set which_atm_option to "simple_photosphere" and that runs fine, so I used Rich Townsend's atm user guide from September 2019 to enforce the equivalent settings on my v12778 machine (assuming that hasn't changed since v12115, but I couldn't find anything about that in the v12778 release notes). However, I still got the error, and trying many different atm_option and atm_off_table_option values did not help either. Third, when I wasn't able to find a setting that would make the star run longer, I tried copying over the controls.defaults from my v10398 machine and updating the settings that were deprecated to their equivalents in v12778; even running the same inlist with the same settings (or their equivalents) didn't get rid of the error. Finally I should note that lowering the min_timestep_limit can squeeze a few more iterations out of the model but doesn't actually help it get to the main sequence (and I believe many posts here have said that just changing the timestep limit is rarely a solution to anything).
> 
> I've attached 2 files: my inlist from v12778 (some of the options that I've tried varying are left as comments in the file, and nearly exactly the same inlist works in v10398), and a csv that shows the number of iterations before hitting the error for stars of 0.3 mass and varying metallicities. I also included a few reference values from my v10398 machine to show how much longer those runs are.
> 
> Thanks very much for any suggestions that anyone might have.
>  
> Samuel
> <n_iterations.csv><inlist_vlm>




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