[Mesa-users] numerical noise in Brunt-Vaisala -- eos issue

[Alina Istrate]

Hi Josiah,

Thank you so much for the quick (and very kind) answer!

By just using the PC eos, I am happy to report that it did remove the noisy
peak and now I have a beautiful Brunt -Vaisala plot.  I am sure that the
same fix would solve the problem for the more massive CO WD case.

 Thanks again and looking forward to the new MESA release!

Best regards,
Alina



On Wed, Jul 15, 2020 at 4:21 PM Josiah Schwab <jwschwab at ucsc.edu> wrote:

> Hi Alina,
>
> First, thank you for the excellent message. This is a great example of
> what a useful problem report looks like!
>
> Does anyone have a suggestion on how to get rid of this type of noise ?
>>
>
> As you suspected, I think you're hitting an eos discontinuity,
> specifically, the Z-switch between HELM and PC.  By default, that occurs at
> PC_min_Z = 0.999d0, which matches the location of the jump in your
> eos_sample.
>
> Evan was also displeased by these sudden switches between HELM and PC as a
> function of composition in WD interiors and led a successful campaign to
> eliminate PC_min_Z in future MESA versions.
>
> For now, I'd suggest putting that switch at Z = 0, so that MESA
> always uses PC.
>
> Please try
>
>     set_eos_PC_parameters = .true.
>     PC_min_Z = 0d0
>     mass_fraction_limit_for_PC = 0d0 ! default of 1d-3 can also cause
> small discontinuities
>
> in your star_job inlist and see if that helps.
>
> Let us know how it goes.
>
> Josiah
>


-- 
*--------------------------------------------------------------------*
Dr. Alina Istrate
Institute for Mathematics, Astrophysics & Particle Physics
Department of Astrophysics
Radboud University
P.O. Box 9010, MC 62
NL-6500 GL Nijmegen, The Netherlands
r: HG02.738
a.istrate at astro.ru.nl
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