[mesa-users] New eps_grav Test

[Broxton Miles]

Hey everyone,

So we (Dean Townsley and I) wanted to run a few tests using the eps_grav
scheme to get a feel for how the new routine and its new time step
constraints work, and how they may affect calculations of values of certain
values like effective temperature. This is of particular importance to us
because we are attempting to us MESA to model the Teff of cataclysmic
variable stars.

If you're new to the list, we found in the previous release version (v
5456) we found that with different time step sizes you could wind up at
fairly different final Teffs for the same scenario. For this test, I ran
MESA using the same scenario as before: a .6 solar mass white dwarf
(cooling.mod from /star/test_suite/wd_cool_0.6M) accreting 10^-10 solar
masses per year using the inlist from the WD2 test suite case. This is run
for about 2.6 million years which the about where an outburst begins.

For the particulars of the new routine, I picked three values for
factor_for_test_CpT_absMdot_div_L: 1, 5, and 10, and for each of those I
chose three values for CpT_absMdot_div_L_limit = .75, .50, and .25. The
results of these 9 runs are attached in 3 figures, one for each factor
choice. These figures each have two plots: the top is Teff vs Star Age and
the bottom is log dt vs Star Age. Also, you will notice that there is a
line labeled as "No Constraint", this means that I have set the factor to 1
and the limit to -1, turning off that time control and allowing the other
controls that are set in the wd2 inlist to control the size of the time
step.

The results are pretty interesting, in all three cases there is a bit of
spread between the Teffs starting at about 1.5x10^6 years, but they all
converge at the end of the run. So, this looks much better. The time step
size differs by order of magnitudes with smaller limits, which isn't
really surprising. The question I have is why does the time step size seem
to bounce around? I may be missing something pretty simple, but it's not
really clear to me why that should be happening.

Anyhow, I hope this has been informative, and any insights, comments, or
questions is more than welcome.

Thanks for your time,
Broxton
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