Hello Nicholas,
> 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).
See https://docs.mesastar.org/en/latest/reference/controls.html#mlt-gradt-fraction
Perhaps setting mlt_gradT_fraction = 1d0 will do the job of making gradT = grada everywhere, an adiabatic star (as far as convection is concerned)? Otherwise, you can explore the other hooks for other_gradr_factor and other_adjust_mlt_gradt_fraction.
I'm less sure on how to disable thermal diffusion except to initialize an isothermal ball with a fixed temperature exterior boundary condition and a zero surface luminosity, so energy cannot escape.
Perhaps you'll figure out the best way and let us know!
-EbF
________________________________
From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of Nicholas Rui via Mesa-users <mesa-users at lists.mesastar.org>
Sent: Saturday, July 26, 2025 9:26 PM
To: mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
Cc: nicholas.z.rui at gmail.com <nicholas.z.rui at gmail.com>
Subject: Re: [Mesa-users] Mesa-users Digest, Vol 96, Issue 10
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<mailto: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<mailto:nrui.mailing.list at gmail.com>>
To: mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>
Cc: "nicholas.z.rui at gmail.com<mailto:nicholas.z.rui at gmail.com>" <nicholas.z.rui at gmail.com<mailto:nicholas.z.rui at gmail.com>>
Subject: [Mesa-users] Hydrogen burning with no hydrogen?
Message-ID:
<CAAPjU6EQ2kjPhyHY5F86heZbXtYo0W64A+FQB1M=9rFWZjE2Lg at mail.gmail.com<mailto: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<mailto:twong31 at physics.ucsb.edu>>
To: mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>
Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?
Message-ID:
<CAKD5RjyV5eO6jb8yy4FygZhOa34GfN62nM7kSfO1-VPAyu0V1Q at mail.gmail.com<mailto:CAKD5RjyV5eO6jb8yy4FygZhOa34GfN62nM7kSfO1-VPAyu0V1Q at mail.gmail.com>>
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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<mailto:townsend at astro.wisc.edu>>
To: Sunny Wong <twong31 at physics.ucsb.edu<mailto:twong31 at physics.ucsb.edu>>
Cc: MESA Users List <mesa-users at lists.mesastar.org<mailto: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<mailto: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<mailto: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<mailto: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<mailto:rhtownsend at wisc.edu>
------------------------------
Message: 4
Date: Sat, 26 Jul 2025 00:01:33 +0000
From: "Farag, Ebraheem" <ebraheem.farag at yale.edu<mailto:ebraheem.farag at yale.edu>>
To: Sunny Wong <twong31 at physics.ucsb.edu<mailto:twong31 at physics.ucsb.edu>>, Richard Townsend
<townsend at astro.wisc.edu<mailto:townsend at astro.wisc.edu>>
Cc: MESA Users List <mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>>
Subject: Re: [Mesa-users] Hydrogen burning with no hydrogen?
Message-ID:
<SN7PR08MB8566A5655EBC97FD5EA370D4FD59A at SN7PR08MB8566.namprd08.prod.outlook.com<mailto: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<mailto:mesa-users-bounces at lists.mesastar.org>> on behalf of Richard Townsend via Mesa-users <mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>>
Sent: Friday, July 25, 2025 7:47 PM
To: Sunny Wong <twong31 at physics.ucsb.edu<mailto:twong31 at physics.ucsb.edu>>
Cc: MESA Users List <mesa-users at lists.mesastar.org<mailto: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<mailto: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<mailto: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$><https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!Mak6IKo!PN0oj-s-f7zUmtxNIYBmNmh-OGeO4hb56R1WgDi8_YBDqWbZn-xHKvxTOmR7Gutr3QWzgzUKYEbVFWxTDeHYwKxBSDJii5U$>
>
--
Rich Townsend ? Professor of Astronomy
Astronomy Department ? University of Wisconsin-Madison
Phone: 608-262-1752 ? E-mail: rhtownsend at wisc.edu<mailto:rhtownsend at wisc.edu>
_______________________________________________
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