[Mesa-users] Cooling of WD with C/O atmosphere

[Montgomery, Michael H]

Hi Everyone,

I gave some undergrads a project to calculate the cooling (and element diffusion) of a white dwarf that has Carbon and Oxygen throughout its interior, all the way to the surface.

I mixed in a little Helium so that we could watch it diffuse up to the surface. At least that was what was supposed to happen.

Without diffusion turned on this model goes from 150,000 K to 20,000 in about 25 seconds. But when I turn on diffusion, the diffusion of helium upward seems to interact with some narrow carbon convection zones, and this slows things down immensely.

I thought that this might be due to the convective mixing interacting with the diffusive mixing, so I set “mix_factor = 0.0” which I think turns off all chemical mixing due to convection. The resulting profiles are smoother, but still quite slow. Evolving down to 38,000 K took about 10 hours, which is 1000 times slower than the non-diffusive situation.

So to sum up, I feel I must be doing something wrong but I don’t know what it is.

I updated to version 15140 of MESA to see if that would help, but the results are the same.

I’m attaching my inlist and input model (both for MESA version 15140) in case anyone can spot what I’m doing wrong.

Thanks!

Mike




_____________________________________

Michael Houston Montgomery
Research Scientist
Deputy Director of CAPP
Research Educator, FRI Program
Department of Astronomy
University of Texas
mikemon at astro.as.utexas.edu
www.as.utexas.edu/~mikemon/<http://www.as.utexas.edu/~mikemon/>
_____________________________________

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