Re: mesa-users] Brunt-vaisala frequency and gradB

[Bill P. <pa...@ki...>]

Hi Joshua,

On Jul 29, 2010, at 7:33 PM, Joshua Shiode wrote:

> Hi all,
> 
> First off, this is an awesome suite of tools for evolving stars, and thanks to everyone involved!

And thank you for the kind words -- it is great to have that kind of feedback.  ; - )

> I've just recently started using MESA to evolve massive stars for pulsation analysis with ADIPLS.

> I'd like to use the value of the Brunt computed within MESA, but I've found that the gradB term acts very strangely.
> I notice the following in my trials:
> 
> With eval_gradB = .true., I find that the code actually sets gradB=0 everywhere. I believe I tracked this down to the fact that alpha_semiconvection and thermo_haline_coeff = 0, their defaults. However... with eval_gradB = .false. (alpha_semi... and thermo_... still at their defaults), the value of the Brunt *does* include a contribution from gradB, which is orders of magnitude too large (only a few in some cases, as many as 40 in others). All other mixing parameters are at their default values. I've been trying to understand the origin of this problem myself, but have had little success so far (I'm very much a novice with fortran.)
> 
> I am currently evolving an 80 solar mass star at solar metallicity, but I have done this for lower mass stars (10, 25, 30..) and seen the same results.
> 
> Even more perplexing.. when I watch the evolution with pgstar, the convective and radiative zones look fine, but the output values in the log files (brunt_n2, gradB, and sign_brunt_n2) reflect the odd behavior documented above... 

So how do you calculate the gradB term from the model info?   
Unfortunately, the mesa/eos doesn't know about partials wrt mu, so we can't rely on that.

> 
> Unrelated to all this, I was also wondering if there are any routines in the mesa suite that could be used to re-grid an output profile for pulsation calculations.

Stellar evolution codes seem to have problems importing models for other sources, and I'm afraid mesa/star is no exception.
So the best use of itfor this will be to create models with the mesh tuned for the needs of pulsation calculations.
I'd be happy to help with that if you are interested -- just let me know where you want to get enhanced resolution.

For the Brunt/gradB issue, it would be a great help if you could take a saved model from mesa/star and calculate gradB independently.
Then I can use that to debug or reimplement the relevant routines in star.

Thanks,
Bill