[Mesa-users] Question about neon burning rates

[Frank Timmes]

hi jeremy,

nomenclature. one approach is to say the term "neon burning" means the net sequence 2(ne20) -> 16o + mg24 + gamma. another approach is to say the term "neon burning" means any reaction that changes the abundance of a neon isotope. mesa adopts the latter appraoach, which can be seen in $MESADIR/data/rates_data/reactions.list . 

by convention (p,g) reactions are the forward direction and (g,p) reactions are the reverse direction. hence, the redirect of ne20gp to f19(p,g)ne20 where the forward and reverse rates are calculated.
 
the expected temperature range of operation of these two "neon burning" approaches are different, the former operating at ~1.5e9 k and the latter operating at ~5e8 k. i don't know what models are being considered, but f19(p,g)ne20 is usually of interest as a leakage channel out of the cno cycles to the ne-na cycles, finding applications in agb stars, f19 yields, metal-poor stars, stellar neutrino emission, and others. the "neon burning" ne20gp goes for the ride in these scenarios.

does this help?

fxt




> On Dec 4, 2023, at 11:12 PM, Jeremy Sakstein via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Hi everyone,
> 
> I am interested in tracking neon burning, and have arrived at a bit of a puzzle.
> 
> I am seeing significant neon burning via the 'burn_ne' profile variable at temperatures of order logT=8.6-8.8 i.e., lower than I would expect neon burning to be significant. I am working with version 12778.
> 
> When I look at rates/private/ratelib.f90, I can see that the ne20gp reaction redirects me to f19(p,g)ne20. When I look up this rate, it appears that it is important at the temperatures I am working with, so could be responsible for the neon burning I am seeing. My current hypothesis is that I am seeing the inverse reaction happening.
> 
> Does anyone have any insight into this?
> 
> Also, can someone tell me why the rne20gp redirects me to f19(p,g)ne20?
> 
> Cheers,
> 
> Jeremy 
> 
> -- 
> Jeremy Sakstein (He/Him/His)
> Assistant Professor of Theoretical Physics
> Department of Physics & Astronomy
> University of Hawaiʻi at Mānoa
> Watanabe Hall
> 2505 Correa Road
> Honolulu, HI, 96822, USA
> http://www.jeremysakstein.com
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