[Mesa-users] Luminosity evolution during core he-burning of a solar-mass model

[Warrick Ball]

Hi everyone,

I think I've exhausted myself of ideas trying to barrel down on this issue 
so it's time to share.  Some colleagues here came across some unusual 
luminosity evolution during low-mass core He-burning in r11554.  The 
attached plot shows the luminosity during core helium burning for a 
solar-mass model for a simple model (see below) in r10398, r11554, and 
r11554 with a few changes to restore r10398 defaults.

I believe the initial downward jump in Y_c (to ~= 0.94) marks when the 
first off-center burning region reaches (and mixes with) the centre.  The 
luminosities in the two versions is qualitatively similar until Y_c ~= 
0.84, at which r11554 becomes somewhat brighter.  At Y_c ~= 0.75, the 
luminosity drops back towards about where I'd expect it to be by 
comparison with the r10398 track.

I created the tracks for both revisions with this minimal inlist:

```
&star_job
/ ! end of star_job namelist

&controls
     history_interval = 1
     initial_mass = 1d0 ! in Msun units
     xa_central_lower_limit_species(1) = 'he4'
     xa_central_lower_limit(1) = 1d-3
/ ! end of controls namelist
```

To cut a long story short, I ended up doing a bisection search through 
MESA revisions and identified that the issue around somewhere between 
r10589 and r10593.  Intermediate revisions don't all finish compiling. 
Drawing on this result (and annoyed myself for not noticing it when I 
diff'ed the default controls between r10398 and r11554), I tried 
re-running my inlist with `use_eosELM = .false.`, which failed to get 
through the core He-flash.  So I tried again with `use_gold_tolerances = 
.false.` too, which worked and recovers roughly the same evolution as in 
r10398, as can also be seen in the plot.

In summary, the core He-burning evolution of my solar mass model in r11554 
looks qualitatively different from r10398 unless I set `use_eosELM = 
.false.` and `use_gold_tolerances = .false.`.

I'm not yet sure where to point my finger in the code.  I still need to 
determine what the code does when it isn't using ELM and compare structure 
models from the two sets of tracks.  But I have other things I need to do 
for the next few days so thought I'd put this up here in case anyone has 
any bright ideas.

Cheers,
Warrick



------------
Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552
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