Re: [mesa-users] very thin shell burning

[Falk H. <fh...@uv...>]

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
>
>
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--
Falk Herwig
Dept of Physics & Astronomy, U of Victoria
fh...@uv..., tel: +1 (250) 721-7743