[mesa-users] BV frequency, gradients and mlt problems - bugs?

[Jakub Ostrowski]

Hi again,

I really meant "gradT = grada", but I wasn't specific enough, sorry for that. I was thinking about this tiny convective region or generally any convective region in a center of star.

I haven't thought about inefficiency of convection in the outermost zone, thank you for clarifying it! I'm definitely going to read more about superadiabatic convection and check the entropy behavior.

Thank you for your help and attached plots.

Cheers,
Jakub



On 2 sty 2013, at 21:08, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

> Hi Jakub,
> 
> First, concerning the gradients:
> 
> On Jan 2, 2013, at 9:58 AM, Jakub Ostrowski wrote:
> 
>> And here comes the problem: in the outer convective zone related to the Z-bump it seems to work properly (as you can see in the figure) but in the outermost zone related to He opacity bump it looks like the gradT = grada just like in the core.
> 
> Is that a typo?  do you really mean "gradT = grada" or do you mean "gradT = gradr"?   
> 
> in the core gradT = gradr because it is a radiative region (except for a tiny convective region right at the center).
> in the envelope around logT = 4.6 or so, gradT = gradr because it is extremely inefficient convection ("superadiabtic").
> all perfectly fine as far as I can tell.   (well, it is fine to the extent that MLT is okay in such situations, which of course it isn't!)
> 
> to double check, plot entropy as well --- in normal situations it is flat in convective regions and increases outward in radiative ones.
> however when you get superadiabtic gradients, entropy actually decreases outward, and that's exactly what you see
> in both of the envelope "bumps".
> <entropy.pdf><Convection.pdf>
> 
> For a lovely discussion of superadiabatic convection in radiation dominated regions, 
> see section 7.2 in the new mesa instrument paper.  ;-)
> it should be out on astro-ph tomorrow or the next day.
> 
> 
> I'll take a look at your N^2 issues next and get back to you when I understand what's happening.
> 
> Cheers,
> Bill
> 
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