Re: [mesa-users] very thin shell burning

[Frank T. <fx...@ma...>]

hi stan,

nice to see mesa being used in your grad class.

fxt


On Mar 30, 2011, at 8:44 AM, 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
>>> 
>>> 
>>> 
>> -- 
>> 
>> 
>> ------------------------------------------------------------------------------
>> Enable your software for Intel(R) Active Management Technology to  
>> meet the
>> growing manageability and security demands of your customers.  
>> Businesses
>> are taking advantage of Intel(R) vPro (TM) technology - will your  
>> software
>> be a part of the solution? Download the Intel(R) Manageability Checker
>> today! http://p.sf.net/sfu/intel-dev2devmar
>> _______________________________________________
>> mesa-users mailing list
>> mes...@li...
>> https://lists.sourceforge.net/lists/listinfo/mesa-users
>> 
>> !DSPAM:212,4d93368d111132383122390!
>> 
> 
> 
> ------------------------------------------------------------------------------
> Create and publish websites with WebMatrix
> Use the most popular FREE web apps or write code yourself; 
> WebMatrix provides all the features you need to develop and 
> publish your website. http://p.sf.net/sfu/ms-webmatrix-sf
> _______________________________________________
> mesa-users mailing list
> mes...@li...
> https://lists.sourceforge.net/lists/listinfo/mesa-users