[Mesa-users] Mesa-users Digest, Vol 96, Issue 10

Sun Jul 27 01:26:00 UTC 2025

Hi Sunny, Rich, Ebraheem,

Yep, the issue was indeed the he3! Upon removing it, I no longer have any
unexpected hydrogen burning, which is nice. More precisely, just setting
initial_he3=0 doesn't work because the relaxation of center_M and center_R
fails (possibly because the code tries to relax M first). However, using
replace_element to turn all he3 into he4 in a subsequent inlist does the
job.

@Ebraheem: This may be helpful in future projects, but, for the first
inlist, the goal was to relax the model to a thermal equilibrium, so these
options end up not being necessary. That being said, for other
applications, it would be nice to know if there is some option that
disables heat transport (i.e., force evolution to be adiabatic).

Best wishes,
Nicholas

On Sat, Jul 26, 2025 at 5:00 AM <mesa-users-request at lists.mesastar.org>
wrote:

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> Today's Topics:
>
>    1. Hydrogen burning with no hydrogen? (Nicholas Rui)
>    2. Re: Hydrogen burning with no hydrogen? (Sunny Wong)
>    3. Re: Hydrogen burning with no hydrogen? (Richard Townsend)
>    4. Re: Hydrogen burning with no hydrogen? (Farag, Ebraheem)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 25 Jul 2025 14:51:16 -0700
> From: Nicholas Rui <nrui.mailing.list at gmail.com>
> To: mesa-users at lists.mesastar.org
> Cc: "nicholas.z.rui at gmail.com" <nicholas.z.rui at gmail.com>
> Subject: [Mesa-users] Hydrogen burning with no hydrogen?
> Message-ID:
>         <CAAPjU6EQ2kjPhyHY5F86heZbXtYo0W64A+FQB1M=
> 9rFWZjE2Lg at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi everyone,
>
> I've been experimenting a bit with ways to artificially construct stellar
> merger remnants in MESA. However, I have noticed a strange issue in some
> models where a significant amount of hydrogen burning can happen even if
> there is no hydrogen (down to ~machine precision?).
>
> I have attached two zip files with two illustrative runs. I am using
> version r24.08.1.
>
> >> run 1: pure helium envelope (directory: "1_helium_envelope")
>
> I initialize a pre-main-sequence model made entirely of helium (no H). I
> then relax the initial mass and radius to some nonzero values (in this
> case, to "match" an oxygen-neon WD model). To get the model into thermal
> equilibrium, I have used dxdt_nuc_factor = 0 (preventing abundances from
> changing due to burning) while evolving for a long time. In addition to the
> inlist, I have also attached a pgstar plot.
>
> Bizarrely, even though the model should be 100% helium by construction, the
> envelope is actually supported by hydrogen burning (there is no helium
> burning). Because dxdt_nuc_factor=0, I don't think this can be because
> protons are being produced by some nuclear reaction somehow.
>
> I also suspected that maybe the machine-precision levels of hydrogen (X ~
> 1e-99) are able to burn significantly at high temperatures due to the
> strong temperature dependence, but that sounds difficult to believe and I
> don't know how to check it for sure. I couldn't find any option to disable
> energy release due to burning at sufficiently low mass fractions either, so
> I'm not sure how to practically deal with this.
>
> >> run 2: RG+HeWD "merger remnant" (directory: "2_rg_hewd_merger")
>
> I am attempting to create a model qualitatively similar to the "Model C2"
> red giant--He WD merger in Zhang & Jeffery 2013. In this model, a cooled He
> WD "subducts" to the center of the "warm" helium core of a red giant, and
> the resulting thing quickly ignites helium.
>
> However, I had some trouble accreting helium onto the WD model using
> mass_change, as was done in the original paper. I also wasn't sure if
> relax_mass would do the desired thing of adding warm degenerate helium onto
> the surface of the WD without modifying the pre-existing entropy
> profile---I could only find a description in the documentation for what
> this does when relax_mass is used to decrease the mass of the star
> (although if it does, I think this would be acceptable for my purposes).
> The difficulty with using mass_change in newer versions for applications
> has been discussed on this list in the past:
> https://lists.mesastar.org/pipermail/mesa-users/2015-November/005915.html
>
> Instead, I did a very roundabout procedure of generating a "warm"
> degenerate non-burning shell of helium by creating a pre-MS helium star,
> disabling burning, and relaxing M_center and R_center. I then manually in
> python "stitched" the He WD model to this helium shell. I added a hydrogen
> envelope in the same way. The resulting star is "rung down" in the
> hydrodynamical mode without burning until the velocities are small.
>
> I then try to turn hydro mode off and burning back on. The MESA run somehow
> loads the initial model and starts, although the timestep becomes very
> small and eventually crashes (even with convergence_ignore_equL_residuals
> enabled). "Full physics" is on in this case (I don't set
> dxdt_nuc_factor=0). Given the pathological way I made this model, I'm not
> really surprised it doesn't run for long.
>
> However, again, the pgstar snapshot shows that, in addition to the expected
> amount of hydrogen shell burning, there is also a significant amount of
> both pp- and cno-burning in the helium core itself, with reaction rates
> exceeding even that of triple alpha. The core has solar metallicity but
> negligible hydrogen, which I confirmed by plotting the hydrogen fraction
> (plot included). I don't know what's going on.
>
> So... does anyone have any idea what's going on?
>
> Best wishes,
> Nicholas Rui
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> ------------------------------
>
> Message: 2
> Date: Fri, 25 Jul 2025 16:42:38 -0700
> From: Sunny Wong <twong31 at physics.ucsb.edu>
> To: mesa-users at lists.mesastar.org
> Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?
> Message-ID:
>         <
> CAKD5RjyV5eO6jb8yy4FygZhOa34GfN62nM7kSfO1-VPAyu0V1Q at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Nicholas,
>
> Here's my guess for what happened (and others please
> correct me):
>
> If you didn't change the initial_he3
> <https://docs.mesastar.org/en/24.08.1/reference/controls.html#initial-he3>
> flag in controls, MESA will
> assume that he4/he3 has the same value as the Sun. Then,
> once the temperature reaches ~10^7 K, part of the pp chain
> starts: He3 + He3 -> He4 + 2 H1 .
>
> Once some He burning has happened, some C12 is produced.
> Since there is some H1 lying around, you can then start the
> CNO cycle.
> (Fun MESA problem: even if you start with a zero metallicity
> H-rich star, it will eventually do CNO cycle on the main sequence
> via this way, because there's a tiny amount of He burning that
> produces C12. )
>
> In short, you can set
> initial_he3 = 0d0
> on top of what you already have (initial_y = 1d0)
> and I believe this would solve the H burning issue.
>
> As an aside, I notice that you set initial_z = 0d0.
> You might want to set Zbase
> <https://docs.mesastar.org/en/24.08.1/reference/controls.html#initial-he3>
> = 0d0 in your &kap section as well.
>
> Cheers,
> Sunny
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> ------------------------------
>
> Message: 3
> Date: Fri, 25 Jul 2025 23:47:18 +0000
> From: Richard Townsend <townsend at astro.wisc.edu>
> To: Sunny Wong <twong31 at physics.ucsb.edu>
> Cc: MESA Users List <mesa-users at lists.mesastar.org>
> Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?
> Message-ID: <514BFA8F-EB15-42BF-84FF-5D868A8429AD at wisc.edu>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Sunny ?
>
> This is a good analysis, but I think because Nicholas has dxdt_nuc_factor
> = 0, no H will be produced.
>
> However, the energy generation from 3He + 3He (and 3He + 4He) will still
> generate energy, and this energy will be counted as ?hydrogen burning?
> since it is part of the pp chains.
>
> Either way, your fix of setting initial_he3 should work fine.
>
> cheers,
>
> Rich
>
> > On Jul 25, 2025, at 6:42?PM, Sunny Wong via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> >
> > Hi Nicholas,
> >
> > Here's my guess for what happened (and others please
> > correct me):
> >
> > If you didn't change the initial_he3 flag in controls, MESA will
> > assume that he4/he3 has the same value as the Sun. Then,
> > once the temperature reaches ~10^7 K, part of the pp chain
> > starts: He3 + He3 -> He4 + 2 H1 .
> >
> > Once some He burning has happened, some C12 is produced.
> > Since there is some H1 lying around, you can then start the
> > CNO cycle.
> > (Fun MESA problem: even if you start with a zero metallicity
> > H-rich star, it will eventually do CNO cycle on the main sequence
> > via this way, because there's a tiny amount of He burning that
> > produces C12. )
> >
> > In short, you can set
> > initial_he3 = 0d0
> > on top of what you already have (initial_y = 1d0)
> > and I believe this would solve the H burning issue.
> >
> > As an aside, I notice that you set initial_z = 0d0.
> > You might want to set Zbase = 0d0 in your &kap section as well.
> >
> > Cheers,
> > Sunny
> >
> >
> >
> >
> >
> > _______________________________________________
> > mesa-users at lists.mesastar.org
> >
> https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!Mak6IKo!PN0oj-s-f7zUmtxNIYBmNmh-OGeO4hb56R1WgDi8_YBDqWbZn-xHKvxTOmR7Gutr3QWzgzUKYEbVFWxTDeHYwKxBSDJii5U$
> >
>
> --
> Rich Townsend ? Professor of Astronomy
> Astronomy Department ? University of Wisconsin-Madison
> Phone: 608-262-1752 ? E-mail: rhtownsend at wisc.edu
>
>
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Sat, 26 Jul 2025 00:01:33 +0000
> From: "Farag, Ebraheem" <ebraheem.farag at yale.edu>
> To: Sunny Wong <twong31 at physics.ucsb.edu>, Richard Townsend
>         <townsend at astro.wisc.edu>
> Cc: MESA Users List <mesa-users at lists.mesastar.org>
> Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?
> Message-ID:
>         <
> SN7PR08MB8566A5655EBC97FD5EA370D4FD59A at SN7PR08MB8566.namprd08.prod.outlook.com
> >
>
> Content-Type: text/plain; charset="utf-8"
>
> As an aside,
>
> For no changes at all: burning/neutrinos/mixing set:
>
>    eps_nuc_factor = 0 ! No energy from burning
>    non_nuc_neu_factor = 0 ! No thermal neutrino losses
>    dxdt_nuc_factor = 0 ! No composition changes
>    mix_factor = 0 ! No mixing
>
> Instead of just dxdt_nuc_factor = 0.
>
> -EbF
> ________________________________
> From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of
> Richard Townsend via Mesa-users <mesa-users at lists.mesastar.org>
> Sent: Friday, July 25, 2025 7:47 PM
> To: Sunny Wong <twong31 at physics.ucsb.edu>
> Cc: MESA Users List <mesa-users at lists.mesastar.org>
> Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?
>
> Hi Sunny ?
>
> This is a good analysis, but I think because Nicholas has dxdt_nuc_factor
> = 0, no H will be produced.
>
> However, the energy generation from 3He + 3He (and 3He + 4He) will still
> generate energy, and this energy will be counted as ?hydrogen burning?
> since it is part of the pp chains.
>
> Either way, your fix of setting initial_he3 should work fine.
>
> cheers,
>
> Rich
>
> > On Jul 25, 2025, at 6:42?PM, Sunny Wong via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> >
> > Hi Nicholas,
> >
> > Here's my guess for what happened (and others please
> > correct me):
> >
> > If you didn't change the initial_he3 flag in controls, MESA will
> > assume that he4/he3 has the same value as the Sun. Then,
> > once the temperature reaches ~10^7 K, part of the pp chain
> > starts: He3 + He3 -> He4 + 2 H1 .
> >
> > Once some He burning has happened, some C12 is produced.
> > Since there is some H1 lying around, you can then start the
> > CNO cycle.
> > (Fun MESA problem: even if you start with a zero metallicity
> > H-rich star, it will eventually do CNO cycle on the main sequence
> > via this way, because there's a tiny amount of He burning that
> > produces C12. )
> >
> > In short, you can set
> > initial_he3 = 0d0
> > on top of what you already have (initial_y = 1d0)
> > and I believe this would solve the H burning issue.
> >
> > As an aside, I notice that you set initial_z = 0d0.
> > You might want to set Zbase = 0d0 in your &kap section as well.
> >
> > Cheers,
> > Sunny
> >
> >
> >
> >
> >
> > _______________________________________________
> > mesa-users at lists.mesastar.org
> >
> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2F%2Flists.mesastar.org%2Fmailman%2Flistinfo%2Fmesa-users__%3B!!Mak6IKo!PN0oj-s-f7zUmtxNIYBmNmh-OGeO4hb56R1WgDi8_YBDqWbZn-xHKvxTOmR7Gutr3QWzgzUKYEbVFWxTDeHYwKxBSDJii5U%24&data=05%7C02%7CEbraheem.Farag%40yale.edu%7C13c973efc6bb4953713108ddcbd5bde4%7Cdd8cbebb21394df8b4114e3e87abeb5c%7C0%7C0%7C638890841067920487%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=5deDSFdWVVxdTedgrTHrVNwT2XYBtdP%2FisVhAVFStMY%3D&reserved=0
> <
> https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!Mak6IKo!PN0oj-s-f7zUmtxNIYBmNmh-OGeO4hb56R1WgDi8_YBDqWbZn-xHKvxTOmR7Gutr3QWzgzUKYEbVFWxTDeHYwKxBSDJii5U$
> >
> >
>
> --
> Rich Townsend ? Professor of Astronomy
> Astronomy Department ? University of Wisconsin-Madison
> Phone: 608-262-1752 ? E-mail: rhtownsend at wisc.edu
>
>
>
>
>
> _______________________________________________
> mesa-users at lists.mesastar.org
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> End of Mesa-users Digest, Vol 96, Issue 10
> ******************************************
>
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