[Mesa-users] Regarding some clarifications

Fri May 5 11:15:43 UTC 2023

Hello Nathali,

Neat project!

>"My question is, if there is more than one evolutionary track that
intersects the star's error box, how do we know the best suitable track for
that star? "

This is a great question! I'm not sure I can provide a great answer,
Desmond seems to know more on this topic, and someone else in the
mesa-users might also have better advice on this topic. If the only
information you have is logTeff and LogL, one approach could be to choose
the model that spends the most evolutionary time within the error box of
your target, or use some other chi2 type metric to evaluate which model is
'best', as Desmond helpfully suggested.

>Secondly, I would like to clarify some other questions regarding the code
which I used. How can we select when to use 'kap_file_prefix' or
'use_type2_opaities'? Should we use 'kap_file_prefix' for stars that are
rich in hydrogen and 'use_type2_opacities' for stars that have heavy metals?

First: see kap_module_controls
<https://docs.mesastar.org/en/release-r22.11.1/kap/defaults.html#kap-module-controls>
 and
In your case, the 'kap_file_prefix' settings should be set at the
beginning of the run and not changed.
For example, if I am evolving a star with the proposed photospheric
asplund et al. 2009 chemical composition (e.g. Y = 0.2703, z=0.0142) I
would set something like the following in my inlists:

&star_job
   initial_zfracs = 6 ! sets the composition of each element to the z
fractions from asplund et al. 2009 (AGSS09), mesa default is '3' for GS98
   !new_Z = 1.42d-2 , I used the controls but what you have is fine.
/ ! end of star_job namelist

&kap
  *   ! Type 1 Atomic opacity tables*
     ! this is for OPAL opacities with a heavy element mixture from AGSS09
      kap_file_prefix = 'a09'   ! mesa default is 'gs98' computed with OPAL
opacities

  *   ! Type 2 Atomic opacity tables*
     ! This is for OPAL opacities with a heavy element mixture from AGSS09,
with varying C and O (for Helium burning and on when c12 and he4 vary.)
     ! These are only used if 'use_Type2_opacities = .true', see
kap-type2-full-on-dz
<https://docs.mesastar.org/en/release-r22.11.1/kap/defaults.html#kap-type2-full-on-dz>
to
see when they are slowly turned on.
      kap_CO_prefix   = 'a09_co'   ! mesa default is 'gs98_co', these are
computed with OPAL opacities
      use_Type2_opacities = .true.
    ! Zbase is the base metallicity for the type 2 opacity tables.
    ! This provides the reference metallicity necessary to calculate
element variations.
    ! Physically, this usually corresponds to the initial metallicity of
the star.
      Zbase = 1.42d-2

    *! Type 1 molecular opacity tables*
    ! These are the low temperature molecular opacities computed by
Alexander and Ferguson 2005 for logT <3.88 (mesa default).
    ! this should be identical to your kap and kap_CO, although there are
other options that exist which need not conform to this rule, see
kap-lowt-prefix
<https://docs.mesastar.org/en/release-r22.11.1/kap/defaults.html#kap-lowt-prefix>
      kap_lowT_prefix = 'lowT_fa05_a09p'

/ ! end of kap namelist

&controls
   initial_z = 1.42d-2 ! photospheric abundance reccomend by asplund et al.
2009 (AGSS09)
   initial_y    = 0.2703d0 ! from asplund et al. 2009 (AGSS09)
/ ! end of controls namelist
---------

> If I use both of these two conditions at the same time will MESA select
one condition among them?
Yes, kind of, Mesa will interpolate between both tables depending on ----->
kap-type2-full-on-dz
<https://docs.mesastar.org/en/release-r22.11.1/kap/defaults.html#kap-type2-full-on-dz>
.
Click to see when and how they are turned on.

>And if anyone sees any mistake in my code, please let me know. I would
like to learn and correct my mistakes.

You are not necessarily creating a pre-ms model but loading from a
pre_computed MESA late_pre_ms model. To create a pre-ms model, add
'create_pre_main_sequence_model
= .true.' to your &starjob. You might want to turn off the mixing controls
while your pre-ms model is relaxing (if it causes numerical difficulties).
You can comment them out and save a pre-ms model then load it in, use a
seperate inlist, or turn them on later your other controls in the
run_star_extras (might be a good exercise). What you have now seems fine
though for your case.

The remainder of your inlist including the kap section looks fine to me :)

-EbF

On Fri, May 5, 2023 at 3:39 AM Desmond Helmut Grossmann via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear Natalia,
>
> I am working on a quite similar project and in the beginning of it had the
> same questions.
>
> For the evaluation of the best model, you should use some figure of merit.
> As a first order approach, a Chi-Squared (combined) evaluation comparing
> the values of your model grid to the observed values can be helpful, as a
> more advanced option a Mahalanobis- distance approach ( as in
> https://arxiv.org/pdf/1806.06869.pdf
> <https://urldefense.com/v3/__https://arxiv.org/pdf/1806.06869.pdf__;!!IKRxdwAv5BmarQ!fthpSHOcJs3oCW_sjKo0rL6-Xu-OX_xuKWGR_qK9id_1HEefADpLKUI7xCl4krh6DSp1jQoq2v6z-jvWWkfx871h$>)
> could be advisable. The observational errors itself is a bit more tricky,
> but in general can also be incorporated in these methods, as demonstrated
> for the (Asteroseismic) frequency error in the reference provided. If you
> are interested in discussing this in more detail, just let me know.
>
>
> Regarding the second question, I hope for advice of more advanced people
> on this list.
>
> Best
>
> Desmond
>
>
>
>
> Am 05.05.2023 um 11:45 schrieb Nathali Perera via Mesa-users <
> mesa-users at lists.mesastar.org>:
>
> Hello everyone,
> I'm a beginner to MESA and I'm working with this software for my final
> year research project. I'm currently modeling detached binary star systems
> which have almost similar masses like 1.875 and 1.856 solar mass. Since the
> binary star system is detached and not assumed to be mass transferring,
> these two stars were modeled as single evolutionary stars. Then I tried to
> change their mass (starting from 1.75 to 1.9 with a step size of 0.05),
> chemical composition (changes 0.01, 0.014, 0.018), mixing length (change as
> 1.8 and 0.2), and overshooting (0.005, 0.01,0.015)to see the effect for
> their evolutionary tracks. My question is, if there is more than one
> evolutionary track that intersects the star's error box, how do we know the
> best suitable track for that star?
>
> Secondly, I would like to clarify some other questions regarding the code
> which I used. How can we select when to use 'kap_file_prefix' or
> 'use_type2_opaities'? Should we use 'kap_file_prefix' for stars that are
> rich in hydrogen and 'use_type2_opacities' for stars that have heavy
> metals? If I use both of these two conditions at the same time will MESA
> select one condition among them?
>
> And if anyone sees any mistake in my code, please let me know. I would
> like to learn and correct my mistakes.
>
> And I'm using mesa release r22.11.1.I have attached a figure that I
> obtained from my work and in that figure, I have marked the binary star
> system with error bars and several evolutionary tracks.
>
> Thank You
> Nathali Perera
> <inlist.txt><Figure.jpg>_______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
> <https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!IKRxdwAv5BmarQ!fthpSHOcJs3oCW_sjKo0rL6-Xu-OX_xuKWGR_qK9id_1HEefADpLKUI7xCl4krh6DSp1jQoq2v6z-jvWWvj_tVxT$>
>
>
> _______________________________________________
> mesa-users at lists.mesastar.org
>
> https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!IKRxdwAv5BmarQ!fthpSHOcJs3oCW_sjKo0rL6-Xu-OX_xuKWGR_qK9id_1HEefADpLKUI7xCl4krh6DSp1jQoq2v6z-jvWWvj_tVxT$
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20230505/a1413e8c/attachment.htm>