[mesa-users] Calculating oscillation modes of higher degree

[Ehsan Moravveji]

Hi Wiebke,
Your concern is very relevant, and deserves full developer’s attention, the way it is going on. I am very glad that Bill and Rich (after his successful Turkey hunting expedition) are on it. :-D

Let me pass some ideas to you for your personal tests:

> - increasing the mesh up to mesh_delta_coeff = 0.1
Indeed that is one way to go. However, this dramatically slows you down. Instead, keep mesh_delta_coeff to a reasonable value, say 0.50, and only “locally” increase your mesh resolution, around e.g. convective boundaries. MESA is extremely rich in controling such.
Then, make your tests again, and see if your eigenfunctions are still shaky.
> - smaller time steps, down to max_years_for_timestep = 1d7
I suspect if this is relevant.
> - turning diffusion on/off
I suspect if this is relevant.
> - starting with a pre-MS model instead of loading a ZAMS model
I suspect if this is relevant.
> - different convection/overshooting settings

Make sure you adequately resolve these zones (see above). 

Additionally, these tests cross my mind:
1. How does increasing the mesh in your GYRE inlist influence eigenfunctions?
2. Have you played around with 
          tol_correction_norm = 3d-5
          tol_max_correction = 3d-3
    and the whole list of options in your controls inlist? They shall help you enforce HSE.
3. Explore the effect of setting change_lnPgas_flag off and on, and notice the difference. I bet you will see stuff going on.
4. Start with non-rotating models first, and get them working before going to rotating models.
5. Explore your input model around where you wiggly eigenfunctions first. What happens around r/R~0.017? mu-gradient zone? H-shell?
    You may need to iron-out wiggles from your brunt profile too. That incredibly helps the numerics.

Good luck with your tests, and keep us informed how you resolve the issue.

Best regards,
Ehsan 



On Nov 25, 2014, at 8:31 PM, Wiebke Herzberg <wiebke at kis.uni-freiburg.de> wrote:

> Hi everyone,
> 
> I am having trouble calculating oscillation modes of higher degree (l >= 8) for subgiant models created with MESA.
> 
> I first tried this some months ago using GYRE for the mode calculation, but for higher l values I noticed inconsistencies in the radial mode order n and the corresponding eigenfunctions appeared strangely shifted. I went ahead and reported the problem on the GYRE forums (http://www.astro.wisc.edu/~townsend/gyre-forums/viewtopic.php?f=3&t=88). Rich suggested, that this problem was likely caused by the model not being in complete hydrostatic equilibrium as assumed by the pulsation codes and his advice was to try and increase the grid points of the model.
> 
> When I recently picked up this work again, I tried all kinds of (more or less basic) things, such as:
> 
> - increasing the mesh up to mesh_delta_coeff = 0.1
> - smaller time steps, down to max_years_for_timestep = 1d7
> - turning diffusion on/off
> - starting with a pre-MS model instead of loading a ZAMS model
> - different convection/overshooting settings
> 
> but nothing seemed to help. Of course, I am not an experienced modeler, so maybe I just did not try the "right" thing, since I could not really localize the problem?
> 
> I also used the minilab provided by Pieter Degroote (http://www.ster.kuleuven.be/~pieterd/mesa/run_star_extras.html) to have a look at the hydrostatic equilibrium in my models. And while there are some deviations from the equilibrium at the surface, the bottom of the convection zone and the core of the model, they are generally small, of the order of 1e-9 in the core region up to 1e-6 at the surface.
> 
> Additionally, I tried adipls for the mode calculation and encountered the same (I assume?) problem there, although it showed itself differently. For modes with l>=8 inconsistencies in the radial mode order n appeared and when looking at the corresponding eigenfunctions they showed a small region close to the core where the function was no longer smooth, but looked noisy/jumpy. A plot showing this behavior for three example eigenfunctions is attached. (Note: This problem only occurred for the p-dominated mixed modes whose eigenfunctions have small amplitudes in the core region.)
> 
> Has anyone experienced the same difficulties? Is it indeed a problem with the hydrostatic equilibrium that hampers the mode calculation? And if so, is there a remedy or maybe a workaround for it? I would be interested in calculating modes up to about l=20 for my MESA models. Any comments or suggestions are greatly appreciated.
> 
> Wiebke
> 
> 
> PS: I also attached the inlist I used recently, just in case.
> 
> -- 
> Wiebke Herzberg               Kiepenheuer-Institut für Sonnenphysik
> Phone: +49 761 3198-232       Schöneckstraße 6
> Fax:   +49 761 3198-211       79104 Freiburg, Germany
> wiebke at kis.uni-freiburg.de    http://www.kis.uni-freiburg.de/
> <eigfun.pdf><inlist_subgiant.txt>------------------------------------------------------------------------------
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