[Mesa-users] neutron definition and a neutron rich wd atms

[Francis Timmes]

hi ana,

please post a minimal working example.

fxt



> On Jan 16, 2024, at 6:38 AM, Ana Antonini via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Dear MESA users,
> I'm working on massive WD models with version r22.11.1, using an inlist to go from pre-zams to the start/middle of the wd cooling curve and a modified version of the wd_diffusion test_suite to further cool the models until Log_L < -3.
> 
> The models use the sagb_NeNa_MgAl.net net, they start with Z=0.02 and initial masses between 6-7.3 Msol. 
> And well, the reason I'm writing is that for initial masses 6-7.1Msol my models end with a significant amount of neutrons in the atmosphere, and for the 7.15 and 7.2Msol initial mass models all the hydrogen is gone and replaced by neutrons. (7.25 and 7.3Msol models are still running and I hope they might provide some insight into this, since the whole H envelope was lost before they entered the wd cooling curve). 
> 
> Further investigating the problem led to the discovery that H + neut = 1 in the atmosphere in all the explored profiles, and that the neutron fraction grows with mass and as the models cool. 
> My advisors suggested it might just be a definition problem that is making MESA "log" as neutrons what is in fact hydrogen. Especially because turning off nuclear reactions during the cooling curve still results in the same pattern. 
> 
> So here are my questions:
> How are neutrons defined in MESA? 
> Is it possible that high-energy protons are being mistaken for neutrons?  
> And if so, is there a simple way to fix this?
> Even if they're not quite as simple, any suggestions would be appreciated!!
> 
> Kind Regards,
> Ana Antonini
>  
> 
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