[Mesa-users] Extreme helium stars

[Josiah Schwab]

Hi Abdel,

> The best path would probably be to evolve the two pre-merger stars
> individually in MESA (or even in binary) and then note their composition,
> and then use stellar engineering to create the post merger star based on
> the information you get from the pre merger stars and what you can deduce
> they should look like post merger. In my experience this is a pretty
> difficult undertaking, but it may be you can piece it together with some
> astro-knowledge and the help of the mailing list.

Amber's suggestion is likely the way to go.

There's no existing MESA magic that's going to let you evolve 2 WDs and
make an EHe out of them in one easy step.  A 1D stellar evolution code
is necessarily not quite the right tool to study the merger and its
immediate aftermath.

You may be interested in working through Ken Shen's 2015 MESA summer
school lecture which covers the topic of modeling double white dwarf
mergers in MESA

  http://cococubed.asu.edu/mesa_market/education.html

There are not necessarily easy answers here.  This is an active topic of
research.

Your initial message suggests to me that you're not familiar with the
literature on this topic.  I recommend investing some time and
understanding how others have tackled this problem.  There's significant
work using MESA from the LSU group and from Simon Jeffery's group.

For example, see

  Menon, A. et al. (2013)
  Reproducing the Observed Abundances in RCB and HdC Stars with Post-double-degenerate Merger Models\mdashconstraints on merger and post-merger simulations and physics processes
  http://adsabs.harvard.edu/abs/2013ApJ...772...59M

  Zhang, X. et al. (2014)
  Post-merger evolution of carbon-oxygen + helium white dwarf binaries and the origin of R Coronae Borealis and extreme helium stars
  http://adsabs.harvard.edu/abs/2014MNRAS.445..660Z


There's also my own work on white dwarf mergers at the higher mass end

  Schwab, J. et al. (2016)
  The evolution and fate of super-Chandrasekhar mass white dwarf merger remnants
  http://adsabs.harvard.edu/abs/2016MNRAS.463.3461S

and I've made RCB-like mergers with a similar approach, though they remain unpublished.


Josiah