[Mesa-users] Extreme helium stars

[amber lauer]

On Thu, Feb 15, 2018 at 11:17 AM, Josiah Schwab <jwschwab at ucsc.edu> wrote:

> 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
>
>   https://urldefense.proofpoint.com/v2/url?u=http-3A__
> cococubed.asu.edu_mesa-5Fmarket_education.html&d=DwIBAg&c=
> imBPVzF25OnBgGmVOlcsiEgHoG1i6YHLR0Sj_gZ4adc&r=IZ3U2LUL6yhDK-
> Uf8F_eU9W85o61MM43boq-nVwHt38&m=f-MZW-MKwdO4fU88X9rpgjDDxerUJS1fEXXa
> 1fWu8-s&s=VOdCe2THElCE2wnZ4kYutyUTyLmqCdS5LNEuhEUXLUI&e=
>
> 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
>   https://urldefense.proofpoint.com/v2/url?u=http-3A__adsabs.
> harvard.edu_abs_2013ApJ...772...59M&d=DwIBAg&c=
> imBPVzF25OnBgGmVOlcsiEgHoG1i6YHLR0Sj_gZ4adc&r=IZ3U2LUL6yhDK-
> Uf8F_eU9W85o61MM43boq-nVwHt38&m=f-MZW-MKwdO4fU88X9rpgjDDxerUJS1fEXXa
> 1fWu8-s&s=vbIT-PSEfqDkrtC369Gg9DrT4QGFNhUmB2vXaA0iDYo&e=
>
> ​Menon simply uses composition relaxation to ​design a white dwarf with a
custom abundance file. This is a useful start but probably much more of the
physics is missing from this model. Also, despite the rules her inlists as
well as Zhangs below are not available on the marketplace.



>   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
>   https://urldefense.proofpoint.com/v2/url?u=http-3A__adsabs.
> harvard.edu_abs_2014MNRAS.445..660Z&d=DwIBAg&c=
> imBPVzF25OnBgGmVOlcsiEgHoG1i6YHLR0Sj_gZ4adc&r=IZ3U2LUL6yhDK-
> Uf8F_eU9W85o61MM43boq-nVwHt38&m=f-MZW-MKwdO4fU88X9rpgjDDxerUJS1fEXXa
> 1fWu8-s&s=geBJzDwJXIFFBgqGWnX5QqBZH2qyaeT6mB65MgI3W0M&e=
>
>
​One thing that's important to note in Zhang et al is that they were able
to mimic a merger in MESA using high accretion rates, but that was an older
version and likely only possible because the physics was not as well
designed as it is today. ​



> 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
>   https://urldefense.proofpoint.com/v2/url?u=http-3A__adsabs.
> harvard.edu_abs_2016MNRAS.463.3461S&d=DwIBAg&c=
> imBPVzF25OnBgGmVOlcsiEgHoG1i6YHLR0Sj_gZ4adc&r=IZ3U2LUL6yhDK-
> Uf8F_eU9W85o61MM43boq-nVwHt38&m=f-MZW-MKwdO4fU88X9rpgjDDxerUJS1fEXXa
> 1fWu8-s&s=-VCg3Qt36wUvrnO3Ducm9I-avgTOrxRLJbp-qL3Svy0&e=
>
> and I've made RCB-like mergers with a similar approach, though they remain
> unpublished.
>
> ​I knew it!​


>
> Josiah
>



-- 
Amber Lauer
Postdoctoral Researcher
Triangle University Nuclear Lab
Duke University
amber.lauer at tunl.duke.edu <amber.lauer at duke.edu>
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