Re: [mesa-users] very thin shell burning

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Herwig, Stan,

Yes, I work with Chris Fryer from time to time. I haven't done serious
astronomy in a long time (I've focused my career on time-dependent
thermal radiation transport for about 20 years) but would really like to
get back in the game.

I rolled my own star code a year or two ago, rolled my own Pop3
opacities for it, and found that the convective helium-burning core
expanded into the hydrogen-burning shell with spectacular consequences.
Apparently it's not just my code. Chris pointed me at Mesa last fall and
I pretty much abandoned my own code. (Reinventing the wheel is a
worthwhile learning exercise only to a point, and I'd reached it.) I've
put together a C++ interface for Mesa since (mostly as a learning
exercise for me, partly as an exercise in breaking down programming
language barriers generally) and have been having great fun -- but am
still looking for a viable research angle.

FWIW.

--KGB

On Wed, 2011-03-30 at 08:44 -0700, Stan Woosley wrote:
> Kent, Falk, et al.,
> 
> I am on this list because I am attempting to use Mesa in my
> graduate class, but I have worried a lot about these same issues
> and am currently writing a paper on Pop III pulsational pair SN in the
> 80 - 150 Msun range. I use the Kepler code for this.
> 
> Falk is right about the dredge up of carbon in these massive low
> Z stars. It is almost explosive once the first contact is made and the
> radius of the star goes  above 2 x 10**14 cm. It hangs by a thread
> and my guess is the envelope gets lost - somehow.  BUT
> 
> The carbon is converted to nitrogen in the envelope and C << O
> so it is not clear that grains will form AND
> 
> If the He core is uncovered one switches to a different sort
> of mass loss, which Vink has said (for WR stars) depends on the Fe  
> abundance,
> not the CO abundance. So it could be small.
> 
> Also, in most cases this very violent mixing only occurs when
> rotational mixing is included and the extent is very sensitive to
> an unknown convective undershoot parameter.
> 
> Another issue here is that the usual opacity tables don't work
> when you have large CNO mass fractions and no Fe.
> 
> Another is that the mass loss propto sqrt(Z) is generally for stars that
> have Fe and again, these have none.
> 
> Best wishes,
> 
>     Stan Woosley
> 
> 
> 
> On Mar 30, 2011, at 6:56 AM, Kent Budge wrote:
> 
> > This is exactly the kind of thing that has piqued my interest. It  
> > looks
> > like it might be a fruitful topic for research for me.
> >
> > On Tue, 2011-03-29 at 23:25 -0700, Falk Herwig wrote:
> >> On 8-Mar-11, at 9:55 AM, Kent Budge wrote:
> >>
> >>> So I'm running some Population III calculations at the lower end of
> >>> the
> >>> mass range, and the very thin shell burning on the giant branch is
> >>> taking *forever*.
> >>>
> >>> What's the latest thinking about mass loss in Population III? I know
> >>> it's thought to be rather low, but just how rather low?
> >>
> >> I think that really depends on the type of stars. There is common
> >> scaling out there in which Mdot ~ sqrt(Z) but that applies only to
> >> mass loss processes that are driven by radiation pressure on lines,
> >> and if there is no self-enrichment of the surface. For AGB stars both
> >> assumptions are wrong, since AGB stars will bring lots of C, O and
> >> other metals to the surface. I am not an expert on dust formation,  
> >> but
> >> I think it is not clear that in particular in the C-rich phase for
> >> advance AGB stars, even at Pop III you could not have effective dust
> >> formation, which would activate the characteristic dust-driven wind
> >> mechanism of AGB stars. Observations seem to indicate at least that  
> >> in
> >> the MCs Mdot is not smaller than in the Galaxy.
> >>
> >>>
> >>> What is the state of the art in modeling very thin shell burning?
> >>> Brute
> >>> force seems, well, like brute force. Are there methods out there  
> >>> that
> >>> treat it as a front propagation problem?
> >>>
> >>
> >> In Pop III AGB stars or even very low metallicity AGb stars you will
> >> encounter convective-overshoot induced H-flame propagation into the
> >> core when the convective envelope gets in touch with the hot CO core.
> >> This is not the regular H-shell in AGB stars, but rather a hot  
> >> dregde-
> >> up after thermal pulses. That is a situation where a flame model  
> >> would
> >> be needed, but I believe we have not much right now to base this on.
> >> Note that this is a flame across a fuel-mix boundary.
> >>
> >> BEst, Falk.
> >>
> >>> Interested in any information anyone has.
> >>>
> >>> -- Kent G. Budge
> >>> CCS-2, LANL
> >>>
> >>>
> >>> ------------------------------------------------------------------------------
> >>> What You Don't Know About Data Connectivity CAN Hurt You
> >>> This paper provides an overview of data connectivity, details
> >>> its effect on application quality, and explores various alternative
> >>> solutions. http://p.sf.net/sfu/progress-d2d
> >>> _______________________________________________
> >>> mesa-users mailing list
> >>> mes...@li...
> >>> https://lists.sourceforge.net/lists/listinfo/mesa-users
> >>
> >> --
> >> Falk Herwig
> >> Dept of Physics & Astronomy, U of Victoria
> >> fh...@uv..., tel: +1 (250) 721-7743
> >>
> >>
> >>
> > -- 
> >
> >
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-- 