[mesa-users] Sound-speed discontinuity in solar-like main sequence model

Richard Townsend townsend at astro.wisc.edu
Wed Dec 2 10:31:32 EST 2015

Hi Earl —

It looks like there’s a problem where the (Eddington) atmosphere connects to the stellar envelope.

I’ve encountered this myself, and had meant to look into it further, but then other stuff got in the way. My recollection is that this issue arises for *some* but not all choices of atmosphere model. As a temporary workaround, you could try other atmosphere choices; I think the default ‘simple_photosphere’ works OK.

It’s not yet clear to me whether there is a fundamental issue with the atmosphere-envelope boundary (which impacts the overall structure calculation), or whether it’s just a problem in the pulsation output code. My understanding is that it’s only when you write a pulsation model file (in your case, in FGONG format) that the atmosphere data get added on; I don’t believe the usual MESA profile files contain the atmosphere data.



> On Dec 2, 2015, at 4:22 PM, Bellinger, Earl <bellinger at mps.mpg.de> wrote:
> Well that went poorly. Let's try this again in plain text.
> Hello everyone,
> I'm a new Ph.D. student at the Max-Planck-Institut für Sonnensystemforschung in Göttingen, Germany, and this is my first post on this mailing list. So, hello!
> I am using MESA r7623 to generate models of solar-like stars on the main sequence. I use an Eddington atmosphere, enable atomic diffusion, and disable rotation. All of my model tracks are varied by mixing length, initial helium, initial metallicity, and mass. I start each track on the PMS and begin collecting profiles once it hits the ZAMS. I also changed pre_ms_T_c from 3e5 to 9e5 to get the models on the PMS to converge. Other than those things, my inlist is basically the same as the 1M-pms-to-wd in the test suite.
> In some (around 3%) of my model tracks, I notice a sound-speed discontinuity that is present in all the models in the track. I haven't noticed anything in the output logs that indicate anything being amiss.
> I have (I hope) attached a plot of one such model with M=1.290625, Y=0.259375, Z=0.002055, alpha_MLT=1.8125 at an age of t=2.2E-005 (just after hitting ZAMS). The discontinuity in this model happens very near the boundary of the star at a radius of 99.235% of the total radius. I have also attached the inlist for this track as well as the output log and the profile file corresponding to the plot.
> I am wondering the source of this discontinuity, and whether it is possible to eliminate it?
> Thanks in advance for any assistance.
> Best regards,
> Earl Bellinger
> Stellar Ages & Galactic Evolution Group
> Max-Planck-Institut für Sonnensystemforschung <discontinuity.png>------------------------------------------------------------------------------
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