[mesa-users] Convergence issues when simulating massive eruptions by modifying .mod file

Alexey Zinger zinger.alexey at gmail.com
Thu Apr 18 13:48:50 EDT 2013


Hi David,

There is a suspicion that this event might be intrinsically
higher-dimensional and thus couldn't be accurately simulated in MESA. TYCHO
says it can also do higher dimensions, so that may be the way to go in the
long shot.

Alexey



On 4/18/2013 12:23, David Arnett wrote:

MESA is mostly hydrostatic; exceptions are convection (assumed to be steady
state) and mass loss (winds assumed to be steady state). Your goal is to do
an eruption. This is not steady state but hydrodynamic (hyperbolic in the
language of differential equations).
This means that neglected (time dependent) terms are not small, and MESA
loses its solution.

I have done a version of this problem (125 Msun) by using a symplectic
radiation hydrodynamic module in TYCHO. The original hydrostatic model was
simply continued using the hydrodynamic module. It gave a "supernova
imposter", ejecting 10 Msun and brightening, sort of LBV like. The Fe bump
in opacity caused radiative acceleration which did the eruption. Bill and I
have discussed adding such a module to MESA; it is on the "to do" list.

I think Bill's suggestion is a good intermediate step.

-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona

Facts are stubborn, but statistics are more pliable.  Mark Twain
Facts do not cease to exist because they are ignored.  Aldous Huxley


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On Thu, Apr 18, 2013 at 12:32 PM, Alexey Zinger <zinger.alexey at gmail.com>wrote:

> Hi Falk,
>
> I'm trying to model mass ejections experienced by supernova impostors such
> as Eta Carinae. One of the hypothesis for the underlying physics is the
> 'geyser' type of event, when all the removed mass is ejected as a whole. So
> this wast the motivation for the 'instantaneous' eruption. But I think I'd
> choose a gradual solution that works over an instantaneous one that doesn't
> :).
>
> Thanks for all the help, guys!
>
> Alexey
>
>
> On Thu, Apr 18, 2013 at 12:17 PM, Falk Herwig <fherwig at uvic.ca> wrote:
>
>> Alexey,
>> of course it depends on what kind of physics situation you have in mind.
>> But simply loosing a lot of mass through the mass loss procedure is maybe
>> an option. Jean-Claude Passy has used this to explore "The Response of
>> Giant Stars to Dynamical-timescale Mass Loss"  (
>> http://adsabs.harvard.edu/abs/2012ApJ...760…90P) and in this
>> calculations he increased the mass loss up to ~1Msun/yr for a star a red
>> giant of ~0.9Msun. These are dynamic mass loss rates in the sense that they
>> represent the expected mass ejection of a common envelope phase in terms of
>> total mass to be ejected and time scale (see
>> http://adsabs.harvard.edu/abs/2012ApJ...744…52P).
>> Falk.
>>
>> On 2013-04-18, at 7:29 AM, Alexey Zinger wrote:
>>
>> Hi MESA community,
>>
>> I am simulating rapid massive eruptions (>1 M_sun) from massive stars
>> (~100 M_sun). I do this by artificially modifying the saved model file and
>> restarting the evolution with loading that file.
>>
>> The easiest (crudest) way to do this is to simply truncate the model by
>> removing a specified number of the outer zones. Of course, this new model
>> is very unnatural and does not converge when plugged into MESA, unless the
>> amount of mass removed is minuscule. A slightly better approximation is to
>> create a smooth gradient of parameters (temperature, etc) in the outer
>> layers, rather than a sharp drop. This works a little better, but still
>> does not allow a substantial amount of mass to be removed. Finally, the
>> approach I use now is to put the outer layers in hydrostatic equilibrium
>> (to facilitate convergence) with the constant specific entropy in that
>> region (to simulate the star adjustment to a sharp temperature gradient).
>> This allows for instantaneous removal of over a half-solar mass, but there
>> are still convergence problems when trying to go to higher masses.
>>
>> The non-convergence message MESA throws are different depending on the
>> mass removed - I think I've seen almost all of them (varcontrol,
>> neg_mass_fraction, etc). I've tried increasing the number of zones in the
>> .mod file by changing mesh_delta_coeff, decreasing the initial time steps,
>> and modifying various additional settings to make MESA less finicky about
>> its convergence requirements, but with little success. I have also tried to
>> trace the problem in the source code, but have quickly bogged down in it
>> (the fact that the non-convergence reason is different every time does not
>> help at all).
>>
>> Astrophysicists that I've talked to say that this new model is not
>> unphysical, so, in principle, it should converge.
>> So my question is: is there a relatively painless way to figure out the
>> reason for non-convergence (without going through all the source code)? If
>> I know a physical reason for this behavior, I can adjust my model
>> accordingly to make it play nice with MESA.
>>
>>
>> Inlists plus some graphs are in attach. I'm using version 4298 of MESA.
>>
>>
>> Alexey
>> <inlist_after_eruption><inlist_before_eruption><inlist_common><SvsM.png>
>> <TvsM.png><TvsR.png>
>> ------------------------------------------------------------------------------
>>
>> Precog is a next-generation analytics platform capable of advanced
>> analytics on semi-structured data. The platform includes APIs for building
>> apps and a phenomenal toolset for data science. Developers can use
>> our toolset for easy data analysis & visualization. Get a free account!
>>
>> http://www2.precog.com/precogplatform/slashdotnewsletter_______________________________________________
>> mesa-users mailing list
>> mesa-users at lists.sourceforge.net
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>>
>>
>>  --
>> Falk Herwig
>> Dept of Physics & Astronomy, U of Victoria
>> fherwig at uvic.ca, tel: +1 (250) 721-7743
>>
>>
>>
>>
>
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