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

[Alexey Zinger]

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>
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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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