[Mesa-users] Convergence issues with massive stars

Thu Aug 5 20:43:10 UTC 2021

Hi everyone,

I've run some more tests and I think I have figured out what the problem
is, I just don't know how to fix it (if indeed it can be fixed).

I realized that models using the default EOS also undergo the fall to a
very small time-step (dt=-4.99). This happens around logT = 8.5 and after
core helium depletion. During this phase the star is contracting and the
temperature is increasing, which increases the rate of carbon burning and
the time step rises.

When I switch my modified EOS on, the same thing happens i.e. the star
contracts but the temperature never rises anywhere near as rapidly. I think
I have traced this back to my EOS mods. In particular, if I look at [image:
\Gamma_3], it is much lower than the MESA default during this phase (it
falls below 4/3), which explains the very slow temperature rise during the
contraction.

Therefore, I think that this effect is physical in the sense that it is an
expected result of my EOS mods, and that it's caused by the contraction not
raising the temperature sufficiently quickly.

I would like to test this hypothesis. Can someone tell me if there are any
controls I can change to speed up this process, either by speeding up the
gravitational contraction or evolving through C-burning at low-T faster (or
any other suggestions you may have).

Cheers,

Jeremy

On Wed, Aug 4, 2021 at 7:19 AM Jeremy Sakstein <sakstein at hawaii.edu> wrote:

> Hi Frank,
>
> I went through the files in $MESA_DIR/eos/private and compared with what I
> did in run_star_extras and I think my mods indeed use the consistency
> conditions you mentioned.
>
> Essentially, what I am doing is adding a new boson to the EOS by
> performing Bose-Einstein integrals and fitting the results as a function of
> density and temperature.
>
> My mods then add this to the EOS by first calling eosDT_get() and then
> updating the entries in res(:) and the partial derivatives. For quantities
> like pressure, entropy, C_V and derivatives at constant T or rho, these are
> just additive. For other quantities, there are some rescalings to account
> for the fact that the old pressure used in logarithmic derivatives needs to
> have the boson added to it, and for others, I use thermodynamic relations
> to compute them from scratch from the newly updated variables described
> above.
>
> Looking ta e.g. eos/private/eoselm_eval.f90, it looks like I am using the
> same relations as the default EOS to calculate these changes, so the
> consistency relations should be satisfied.
>
> The version I sent that won't converge corresponds to a boson with some
> specific mass. For other masses, the models converge as I would expect, and
> even for this mass higher and lower mass models converge as well.
>
> This is why I suspect it may be something that I can solve by changing one
> of the controls but I'm happy to look at my EOS mods again too if you see a
> problem with what I have done.
>
> Cheers,
>
> Jeremy
>
> On Fri, Jul 30, 2021 at 10:38 AM Jeremy Sakstein <sakstein at hawaii.edu>
> wrote:
> >
> > Hi Frank,
> >
> > I just sent my inlists and run_star_extras so that might answer some of
> your questions.
> >
> > "i have no idea what eos modifications you've made, but if you've
> modified the eos
> > over any appreciable region in (rho,T) space, then its not helm, but a
> helm with
> > modifications on top, yes?"
> >
> > This is correct. I am calling eosdt_get and then updating the entries in
> res(:) to include contributions from a new particle so it is HELM+DM. I
> think the quantities e.g. gradad are computed using the relations you
> mentioned below.
> >
> > For your second point, I am updating all of the partials as well as the
> EOS variables so I think everything should be consistent. In fact, in an
> earlier version I got failures until I updated the partials to high
> precision.
> >
> > Cheers,
> >
> > Jeremy
> >
> > On Fri, Jul 30, 2021 at 9:46 AM Francis Timmes <fxt44 at mac.com> wrote:
> >>
> >>
> >>
> >> > On Jul 30, 2021, at 12:22 PM, Jeremy Sakstein <sakstein at hawaii.edu>
> wrote:
> >> >
> >> > Thanks Frank,
> >> >
> >> > For (b), I am starting from helium cores, so as far as I can tell I
> am always in the regime of the HELM EOS. I can get this to converge for
> lower mass models (M<28 or so) and higher mass (M>40) no problem but it is
> just this small range that gives the convergence issue.
> >>
> >> i have no idea what eos modifications you've made, but if you've
> modified the eos
> >> over any appreciable region in (rho,T) space, then its not helm, but a
> helm with
> >> modifications on top, yes?
> >>
> >>
> >> > For (a), I am using fitting functions that have all quantities to 8
> decimal places and tested that what MESA is spitting out matches what I put
> in, but I am not sure how high a precision I need. Is there some benchmark
> I should be shooting for?
> >>
> >> apologies for not being clear. starting from a helmholtz free energy F,
> >> the pressure, entropy, and energy are related to the partial
> derivatives of F.
> >> in addition, the partials of P, S, and E - which are related to things
> like
> >> grad_ad, specific heats, and so on - have to obey consistency relations.
> >> finally, the derivatives of grad_ad, c_v and so on should also have
> continuous
> >> and smooth behaviors. so its not necessarily the precision of a given
> quantity,
> >> although that helps, but how the entire thermodynamic framework hangs
> together numerically.
> >> for example, if an eos modification changes P but not its derivatives
> or S or E and their
> >> derivatives, then troubles usually ensue.
> >>
> >> again, i'm only raising the possibility that the behavior your seeing is
> >> related to the eos modifications made. that the model runs without the
> >> eos modification seems to be hint though.
> >>
> >> fxt
> >>
> >>
> >>
> >>
> >>
> >> >
> >> > Cheers,
> >> >
> >> > Jeremy
> >> >
> >> > On Fri, Jul 30, 2021 at 8:53 AM Francis Timmes <fxt44 at mac.com> wrote:
> >> > a comment from the cheap seats. changing the eos is fraught
> >> > with danger due to (a) the myriad of thermodynamic relationships
> >> > that must be satisfied numerically to high precision and
> >> > (b) the mesa eos in 15140 and previous versions being a composite
> >> > patchwork of different eos's with different treatments for how
> >> > and where they merge with a neighboring eos. its possible that
> >> > your modified eos is running into difficulties with (a) or (b)
> >> > at the elevated temperatures associated with a ~30 msun zams model.
> >> >
> >> > fxt
> >> >
> >> >
> >> >
> >> >
> >> > > On Jul 30, 2021, at 10:20 AM, Jeremy Sakstein <sakstein at hawaii.edu>
> wrote:
> >> > >
> >> > > Thanks Rob!
> >> > >
> >> > > I am already using  so I turned off conv_vel to test that.
> >> > >
> >> > > This did speed up the runs but only in the sense that it hit the
> phase where the time-step goes to -4.49 faster, so I don't think it
> addressed the underlying issue.
> >> > >
> >> > > I am attaching some terminal output in case you have any more
> suggestions.
> >> > >
> >> > > In the meantime, I am going to make a minimal working example that
> encounters this problem so I can send my inlists and run_star_extras.
> >> > >
> >> > > Cheers,
> >> > >
> >> > > Jeremy
> >> > >
> >> > > On Thu, Jul 29, 2021 at 4:06 AM Rob Farmer <
> robert.j.farmer37 at gmail.com> wrote:
> >> > > Hi,
> >> > > I've found lowering the starting core temperature helps low-Z
> models:
> >> > >
> >> > > pre_ms_T_c =2.8e5
> >> > >
> >> > > You may also want to turn off conv_vel until after core helium
> burning.
> >> > >
> >> > > Rob
> >> > >
> >> > >
> >> > > On Mon, 26 Jul 2021 at 19:21, Jeremy Sakstein <sakstein at hawaii.edu>
> wrote:
> >> > > Hi everyone,
> >> > >
> >> > > I'm trying to evolve Z= He cores from ZAHB to core collapse. I've
> updated the EOS to include a new particle that softens the EOS and
> everything runs fine for lower mass objects but for stars with ZAHB mass
> 30M I'm running into convergence issues.
> >> > >
> >> > > The time-step falls to -4.49 and stays there indefinitely.
> >> > >
> >> > > I've tried to vary parameters like the overshooting controls (both
> location and f and f0 parameters) and turning on MLT++ but to no avail. The
> same thing happens every time.
> >> > >
> >> > > I'm attaching some
> >> > > Kippenhahn plots. "no_DM" (x-axis goes to model number 15,000) is
> the default case with no modifications and DM (model number goes to 50,000)
> includes my mods.
> >> > >
> >> > > I was hoping someone would be able to suggest other controls for me
> to vary to try to get through to CC.
> >> > >
> >> > > Happy to send more info if this is not sufficient.
> >> > >
> >> > > Cheers,
> >> > >
> >> > > Jeremy
> >> > >
> >> > > <DM_2.png>
> >> > >
> >> > > <DM.png><noDM_2.png><noDM.png>
> >> > >
> >> > >
> >> > > --
> >> > > 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
> >> > > _______________________________________________
> >> > > mesa-users at lists.mesastar.org
> >> > > https://lists.mesastar.org/mailman/listinfo/mesa-users
> >> > >
> >> > >
> >> > >
> >> > > --
> >> > > 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
> >> > > <DM_100_CV2.out>_______________________________________________
> >> > > mesa-users at lists.mesastar.org
> >> > > https://lists.mesastar.org/mailman/listinfo/mesa-users
> >> > >
> >> >
> >> >
> >> >
> >> > --
> >> > 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
> >>
> >
> >
> > --
> > 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
>
>
>
> --
> 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
>

-- 
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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