[mesa-users] Core hydrogen mass fraction increases in early evolution of 1.5 Msun star

[Bill Wolf]

I shared Conny's suspicion and just ran it with pgstar. There is indeed some convection going on at that point, so I would guess that it's just the introduction of fresh hydrogen to the core.

Bill

On Jan 14, 2013, at 9:40 AM, Conny Aerts <conny at ster.kuleuven.be> wrote:

> 
> Hi Rich,
> 
> without having computed MESA models in this regime, I would tell my 
> students that this is due to the increase of the convective core during 
> the early MS for such a mass, such that fresh hydrogen fuel enters the 
> core and is instantaneously mixed. This increase in convective core is 
> due to the relative increase of importance of the H burning by CN cycle 
> versus  pp chains (different dependencies of opacity: pp only on X and 
> CN on X and Z with X decreasing).  In fact, this is about the mass where 
> this effect is largest (the convective core starts shrinking as you move 
> above 1.6 solar masses birth mass). This is beautifully illustrated in 
> Fig.3.6 of the book "Asteroseismology"...;-)
> 
> Hope this is a valid explanation,
> Conny
> 
> 
> On 01/14/2013 06:21 PM, Richard Townsend wrote:
>> Hi folks --
>> 
>> I'm running a vanilla MESA (4740) calculation for a 1.5 Msun star, from MS to He flash. Surprisingly (to me), the core hydrogen mass fraction *rises* slightly during the early evolution (~timestep 170). Can anyone explain why this might be so? I attach the inlist.
>> 
>> cheers,
>> 
>> Rich
>> 
>> 
>> 
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________________________
William Wolf
wmwolf at physics.ucsb.edu

UCSB Department of Physics

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