[Mesa-users] Pre-Correction Frequencies

Erica Sawczynec ericasaw at hawaii.edu
Wed Dec 23 16:15:26 EST 2020 

Hi Warrick and Dennis,
	Thanks so much for all of your help! I was convinced I was just plotting something wrong so it’s great to know there was something else at hand. I’ve made the changes Warrick suggested and I am going to rerun my model and make sure the correction changes reasonably. I should note that I ran a variety of different physics variations for this star and all of them that used the Ball & Gizon correction had uncorrected frequencies that looked like this, interesting to me that all of these variations suffered from the same pitfall. 
Thanks again!
Erica

> On Dec 23, 2020, at 10:36 AM, Warrick Ball <W.H.Ball at bham.ac.uk> wrote:
> 
> Hi Erica,
> 
> In my case, my `delta_nu` cuts meant that MESA was missing the best-fitting model, for which the cubic surface correction has the "correct" (i.e. Sun-like) sign.  There are multiple ways to expand the range of `delta_nu` so that MESA will start computing mode frequencies earlier but a simple way is to increase `chi2_delta_nu_limit`.  I'm pretty sure you've encountered the same problem.
> 
> As a reminder, MESA uses the "asymptotic" large separation to decide when it's worth starting to calculate mode frequencies.  This differs from the large separations derived from the mode frequencies. e.g. for Model S, the "asymptotic" large separation is about 140 uHz, the uncorrected large separation of the radial modes is about 136 uHz, and the observed value is about 135 uHz.
> 
> Cheers,
> Warrick
> 
> 
> ____________
> 
> Warrick Ball
> Postdoc, School of Physics and Astronomy
> University of Birmingham, Edgbaston, Birmingham B15 2TT
> W.H.Ball at bham.ac.uk
> +44 (0)121 414 4552
> 
> 
> On Wed, 23 Dec 2020, mesa-users at lists.mesastar.org wrote:
> 
>>> Finally, I noticed that your inlist has
>>> 
>>>    sigmas_coeff_for_delta_nu_limit = 10
>>> 
>>> which should terminate the run if ?? increases past the observed value
>>> plus 10?.  You might have meant
>>> 
>>>    sigmas_coeff_for_delta_nu_limit = -10
>>> 
>>> so that it terminates when ?? *decreases* past the observed value *minus*
>>> 10?.
>> 
>> In case this is unclear because the unicode Greek characters appear to have been messed up, "??" is $\Delta\nu$ and "?" is $\sigma$.
>> 
>> W
>> 
>> 
>> ____________
>> 
>> Warrick Ball
>> Postdoc, School of Physics and Astronomy
>> University of Birmingham, Edgbaston, Birmingham B15 2TT
>> W.H.Ball at bham.ac.uk
>> +44 (0)121 414 4552
>> 
>> 
>> On Wed, 23 Dec 2020, mesa-users at lists.mesastar.org wrote:
>> 
>>> Hi Erica,
>>> 
>>> Dennis is right: the coefficients of the cubic correction aren't
>>> constrained to have the same sign as the surface correction we'd need for
>>> the Sun, nor to be especially small or anything, so nothing prevents this
>>> from happening.
>>> 
>>> From your output, it looks like you're using r12778 or earlier.  If you'd
>>> like to constrain the coefficient, you can edit the subroutines
>>> `get_cubic_...` in `star/astero/src/astero_support.f`. e.g. replace
>>> 
>>>    a3 = Xty/XtX
>>> 
>>> with something like
>>> 
>>>     a3 = Xty/XtX
>>>     if (a3 > 0) a3 = 0
>>> 
>>> Coincidentally I've just run into the same issue so will be looking more
>>> closely at why this happens, when I previously haven't found it to be an
>>> issue.
>>> 
>>> Finally, I noticed that your inlist has
>>> 
>>>    sigmas_coeff_for_delta_nu_limit = 10
>>> 
>>> which should terminate the run if ?? increases past the observed value
>>> plus 10?.  You might have meant
>>> 
>>>    sigmas_coeff_for_delta_nu_limit = -10
>>> 
>>> so that it terminates when ?? *decreases* past the observed value *minus*
>>> 10?.
>>> 
>>> Cheers,
>>> Warrick
>>> 
>>> ____________
>>> 
>>> Warrick Ball
>>> Postdoc, School of Physics and Astronomy
>>> University of Birmingham, Edgbaston, Birmingham B15 2TT
>>> W.H.Ball at bham.ac.uk
>>> +44 (0)121 414 4552
>>> 
>>> On Wed, 23 Dec 2020, mesa-users at lists.mesastar.org wrote:
>>> 
>>>>  Hi Erica,
>>>> 
>>>>  w/o having looked at your attachments (except the plots) my guess is
>>>>  that
>>>>  you found too different models in the two cases (Kjeldsen vs Ball).? The
>>>>  (pre-corrected) model found using Ball is clearly further from the
>>>>  'best'
>>>>  model (its density is further from the observed) but the correction
>>>>  takes
>>>>  care of that.
>>>> 
>>>>  However, if by 'look a little strange' you mean that the correction goes
>>>>  in the 'wrong direction', then it might be because you are not limiting
>>>>  the fitting coefficients.
>>>>  I recall seeing similar issues when using the Kjeldsen correction (in a
>>>>  MESA simplex fit) for some stars.
>>>> 
>>>>  But perhaps Warrick can chip in as well.
>>>> 
>>>>  Best
>>>>  Dennis/
>>>> 
>>>>  On 23/12/2020 15:08, Erica Sawczynec wrote:
>>>>>   Hi all!
>>>>>   ??????? I have a few questions about the frequency output in the
>>>>>   simplex_results.data file. I am trying to make an echelle diagram that
>>>>>   shows the frequencies before and after correction from the best fit
>>>>>   MESA
>>>>>   model. When I use the Kjeldsen correction I am able to plot l0_freq_#
>>>>>   and
>>>>>   get the results I expect, frequencies that lean slightly to the right
>>>>>   of
>>>>>   the input frequencies, but when I use the Ball & Gizon correction the
>>>>>   uncorrected frequencies look a little strange. I?ve attached an image
>>>>>   below that demonstrates what I mean.
>>>>> 
>>>>>   So I just wanted to be sure anything labeled l(0,1,2)_freq_# is mean
>>>>>   to
>>>>>   be
>>>>>   the original output model frequency before correction and
>>>>>   l(0,1,2)_freq_corr_# is meant to be the frequency after using either
>>>>>   the
>>>>>   Kjeldsen or Ball & Gizon correction. If that is true, I was wondering
>>>>>   why
>>>>>   the Ball & Gizon pre-corrected frequencies look like that? If not,
>>>>>   what
>>>>>   is
>>>>>   the proper column I should be using to plot the uncorrected model
>>>>>   frequencies?
>>>>> 
>>>>>   I?ve also attached my inlist and simplex_results.data file below, let
>>>>>   me
>>>>>   know if there is anything else I can provide that would be useful!
>>>>>   Thanks,
>>>>>   Erica
>>>>> 
>>>>>   _______________________________________________
>>>>>   mesa-users at lists.mesastar.org
>>>>>   https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>>>   <https://lists.mesastar.org/mailman/listinfo/mesa-users>
>>>> 
>>>>  --
>>>>  DENNIS STELLO | Associate Professor
>>>>  School of Physics | Faculty of Science
>>>> 
>>>>  UNIVERSITY OF NEW SOUTH WALES
>>>>  Rm136, K15 | University of New South Wales | NSW | 2052
>>>>  T +61 2 9065 1334  | F +61 2 9385 6060
>>>>  E d.stello at unsw.edu.au  | W http://www.physics.usyd.edu.au/~stello/
>>>> 
>>>> 
>>> _______________________________________________
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