[Mesa-users] Brunt-Vaisala frequency is noisy

[Francis Timmes]

you've found that, physically, BV should be spikey at some level in certain locations.
the spikes are saying something physical about the types of oscillations and the 
oscillation frequencies that can be present. one doesn't want the spikes to disappear! 

as rich townsend mentioned in his reply, the main ways to play with how spikey/smooth BBV is 
http://mesa.sourceforge.net/controls_defaults.html#num_cells_for_smooth_brunt_B
http://mesa.sourceforge.net/controls_defaults.html#threshold_for_smooth_brunt_B

fxt




> On Dec 10, 2018, at 4:04 PM, Pedro Nuno David Gomes <pedro.david.gomes at ist.utl.pt> wrote:
> 
> A 2018-12-05 19:45, Francis Timmes escreveu:
>>> I don't understand why this is happening.
>> consider plotting the composition, noting the locations where there are
>> sharp abundance gradients, and compare those locations to where the BV spikes.
>> do the same for thermodynamic variables such as the density and temperature.
>> what do you surmise?
>> fxt
>>> On Dec 5, 2018, at 10:22 AM, Pedro Nuno David Gomes via Mesa-users <mesa-users at lists.mesastar.org> wrote:
>>> Dear MESA users,
>>> I'm trying to evolve a 1.5 solar mass star to a point in the red giant branch. For this model, among other quantities, I need the Brunt-Vaisala (which from here on I shall call BV) frequency in the main sequence, subgiant and red giant phases.
>>> The BV determined by MESA is shown to be extremely noisy, and I don't understand why. I'm sending attached the BV^2 plots for these 3 phases, as well as the inlist I am using. I am using release 10398.
>>> I don't understand why this is happening, so I would be greatly appreciated if someone could help me solving this problem.
>>> Thank you very much for your attention,
>>> Pedro<BV2_MS.png><BV2_redgiant.png><BV2_subgiant.png><inlist_project_1.5M>_______________________________________________
>>> mesa-users at lists.mesastar.org
>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
> 
> I followed your advice, and plotted the quantities you mentioned, plus dlnRho_dlnR, for a star with a mass of 1.6 solar masses at the end of the subgiant branch.
> 
> The temperature profile seems normal, but lnRho varies sharply at r = 0.10 (in units of solar radius). Consequently, dlnRho_dlnR also has a sharp variation at this point. I'm assuming this density variation is caused by a sharp variation of the helium abundance?... , also in the images.
> 
> If this is the cause is there anyway to solve it?
> 
> 
> 
> <brunt_N2-vs-radius.png><dlnRho_dlnR-vs-radius.png><dlnRho_dlnR-vs-radius2.png><grada_sub_gradT-vs-radius.png><he4-vs-radius.png><logRho-vs-radius.png><temperature-vs-radius.png>