[mesa-users] Calibration of Kjeldsen-Bedding-JCD surface effect power law

stello at physics.usyd.edu.au stello at physics.usyd.edu.au
Mon Nov 11 05:47:34 EST 2013


Hi Warrick,

Thank you for sharing this.  The exercise you have embarked on is one  
I have wanted to do for some time but not got around to do, so would  
be happy to help where possible.

The 4.25, I think, is just a value Bill found long ago when he did the  
first attempt to fit HD49..... Whether he matched it to a solar model  
or just found that it gave a good fit for HD49... I am not 100% sure  
off (Bill can chip in if he remembers himself...probably not ;0) ).   
Where it comes from is however not very important.

Your approach is a sensible one to take [using MESA to find a solar  
model at find 'b' by comparing it to, say, BiSON].  However, one  
should note that just because b=<your fit result for the Sun> works  
for the Sun, does not mean it is the most appropriate b-value for  
another star....not to mention using a power law to correct the freqs.
What I am trying to say is: there is a limit to which one should seek  
to obtain the 'right' b-parameter.

That said, which solar calibration should you use? MESA now has a  
second option for doing a solar calibration, which is in 'astero'.   
[dont have access to my MESA stuff so can give you details].  But you  
could try use both options in MESA to make your own solar calibrations  
and see how much that in the end changes your b-parameter.

Keep playing!

Cheers
Dennis/



Quoting Warrick Ball <wball at astro.physik.uni-goettingen.de>:

> Fellow MESAlians*,
>
> I'm trying to recover the calibration of the Kjeldsen-Bedding-JCD  
> surface-effect law [1] in the astero_search routines.
>
> In mesa/star/astero/defaults/astero_search_controls.defaults, one finds
>
>    ! surface corrections (see K08 -- ApJ 683, pg 175)
>       correction_factor = 0
>          ! use this fraction of the correction; set to 0 to skip  
> doing corrections.
>       correction_b = 4.90d0
>
> So the surface power law is b=4.90.  This is the canonical value in  
> the paper, based on the calibrations in their models.  It is often  
> used elsewhere.
>
> In  
> mesa/star/test_suite/example_astero/inlist_astero_search_controls,  
> there is, instead,
>
>    ! surface corrections (see K08 -- ApJ 683, pg 175)
>       correction_factor = 1
>          ! use this fraction of the correction; set to 0 to skip  
> doing corrections.
>       l0_n_obs(:) = -1 ! the observed radial orders (ignored if < 0)
>          ! the observed radial orders are used in calculating  
> surface corrections
>          ! if <= 0, use default calculation for radial orders
>       correction_b = 4.25d0
>
> So b=4.25.  Hmmm...
>
> For any given evolutionary code, what one should probably do is use  
> that code to calibrate a solar model, compute the oscillation  
> frequencies and fit a power law to the differences with, e.g. the  
> BiSON frequencies [2]. So I ran  
> mesa/star/test_suite/example_solar_model, saved the final model as  
> an FGONG file (attached) and handed that to GYRE, with the JCD  
> boundary condition, for l=0,1,2,3 in the range 500 to 4500 uHz.  I  
> then calculated the difference between the MESA model and the BiSON  
> frequencies.  A plot is attached.
>
> I then tried fitting the parameters myself.  First, I did a fit  
> (with scipy.optimize.leastsq) with all the observed frequencies, in  
> which case I got b=4.53.  I then did a fit just with the radial  
> modes, in which case I got b=4.68.
>
> What value should one use?  Where did b=4.25 in example_astero come from?
>
> Now, I realise that this probably isn't a settled issue.  But in the  
> absence of a definitively correct answer, I'll settle for a  
> well-justified one! :p  As a first note, I know that changing the  
> range of frequencies over which one fits modifies the power law.   
> Second, the calibrated model seems to show a small offset of about  
> 0.5 uHz even at the lowest frequencies.  Should I add one or two  
> frequencies to the calibration to try to fix this, then fit again?   
> Or is the model in example_solar_model outdated, and I should run  
> the calibration in solar_calibration myself before fitting?  And  
> should one fit only to the frequencies in the target of the  
> astero_search? e.g. HD 49835?
>
> All input is obviously welcome, and I'm happy to work on this  
> problem and report to the community how I progress.
>
> Cheers,
> Warrick
>
> * Is this the correct word?  Is there an official stance? :p
>
> [1] http://adsabs.harvard.edu/abs/2008ApJ...683L.175K
> [2] http://adsabs.harvard.edu/abs/2009MNRAS.396L.100B
>
>
> ------------
> Warrick Ball
> Postdoc, Institut für Astrophysik Göttingen
> wball at astro.physik.uni-goettingen.de
> +49 (0) 551 39 5069



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