[Mesa-users] Post-AGB evolution

[Glenn-Michael Oomen]

Hi Natalie,

Post-AGB evolution is very difficult and slow for the higher-mass CO cores (>= 0.65 Msun). This is due to similar instabilities that plague the evolved TP-AGB models. When the envelope mass becomes low, convection becomes inefficient due to the low density. At the same time, the opacity is high at the bottom of the still convective envelope (especially around the iron peak at ~10^5 K). This leads to convergence errors and very small timesteps. This phenomenon is discussed in e.g. Lau et al. (2012), in appendix C of Miller Bertolami (2016), or in Sect. 2.2.3 of my PhD thesis (https://fys.kuleuven.be/ster/pub/phd-glenn-michael-oomen/phdthesis-glennmichaeloomen.pdf).

You can work around this problem by artificially boosting the convective energy transport, which in MESA is called MLT++ described in Paxton et al. (2013). The massive star community experience similar problems in their models and also use this sometimes to avoid convergence issues. However, by boosting the energy transport, you also change the radius and Teff of the star.

I hope this helps!

Cheers,
Glenn

From: Yuan Qi Ni via Mesa-users<mailto:mesa-users at lists.mesastar.org>
Sent: Monday, 26 April 2021 17:33
To: mesa-users<mailto:mesa-users at lists.mesastar.org>; Natalie Rees<mailto:n.rees at surrey.ac.uk>
Subject: Re: [Mesa-users] Post-AGB evolution

Hi Natalie,

Are you doing this using test_suite/make_co_wd?
Or something else?

-Chris

From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of Natalie Rees via Mesa-users <mesa-users at lists.mesastar.org>
Sent: Monday, April 26, 2021 9:06 AM
To: mesa-users <mesa-users at lists.mesastar.org>
Subject: [Mesa-users] Post-AGB evolution

EXTERNAL EMAIL:
Dear MESA Users,

I have been evolving AGB stars to the end of the TP-AGB stage and am now trying to evolve them off the AGB and to the white dwarf cooling track. Unfortunately, I am finding the post-AGB evolution to be very slow (it is taking about 140,000 models to go from logTeff = 3.56 to 3.63). So, I am trying to figure out what is limiting the timestep as there is very little change in the structure variables. The terminal output for dt_limit often says "max increase", but this is not listed in the table for dt_limit in controls.defaults. Does anyone know what this means and/or have any tips for faster post-AGB evolution?

Thanks,
Natalie Rees

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