[Mesa-users] mesh grid controls for radial comparison in two separately evolved solar models.

[Clarke, Josh]

Hello MESA users,

I have come across a bit of a conundrum. I am currently trying to replicate a test that a collaborator of mine used with their own code.
I am modifying the temperature gradients in overshooting regions, comparing it’s inclusion in a solar-like star of 1Msun to a model of the same star with no modification.
Both stars are evolved from a zero age main-sequence model. The aim is to compare the profiles of these two models once they terminate at a set age, modifying the mixing_length_alpha of the modified model so that it reaches solar structure at the terminal age.

The difficulty is that the changes in the structural parameters I expect to see are very small. In order for the linear interpolation to be accurate I have been advised to get the compared mesh points to have a relative radial difference of 1x10-5 Rsun. My concern is that since MESA is lagrangian in nature I will be unable to achieve this degree of relative accuracy. I was wondering if any of you smart people know anyway to control the mesh so that this kind of radial comparison is possible? Or if it’s just realistically unfeasible? Please feel free to correct me if I have made any horrendous assumptions.

My main models have been run with mesh_delta_coeff = 1d-1 but I’ve also run models with 5d-1 and 1d0 to decrease simulation run time. mesh_min_dlnR = 1d-14.
All other mesh grid controls are default. I am using Gold tolerances with:
gold_tol_residual_norm1 = 1d-11
gold_tol_max_residual1 = 1d-9
gold_iter_for_resid_tol2 = 10
gold_tol_residual_norm2 = 1d-10
gold_tol_max_residual2 = 1d-8
gold_iter_for_resid_tol3 = 15
gold_tol_residual_norm3 = 1d-6
gold_tol_max_residual3 = 1d-4

For my 1d-1 mesh_delta_coeff model the average radial shift of a cell in the modified model compared to its nearest cell in the base model is 5.361718481731894e-05 rsun, while the relative radial shift is 2.2747013522397857e-04 rsun.

I am using MacOS Catalina 0.15.7 (19H524) , MESA Star version 12115, and Mesa SDK x86_64-osx-macos-19.11.2.

Cheers,
Josh

Joshua Clarke
PhD Student
Department of Physics & Astronomy, University of Exeter,
Stocker Road, Exeter, EX4 4QL, UK






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