[Mesa-users] ZAMS models: a bug or feature?

[Natasha Ivanova]

Thank you Evan and Warrick!

On Mon, Jul 24, 2023 at 5:59 AM Evan Bauer <evan.bauer.astro at gmail.com>
wrote:

> Hi Natasha,
>
> Thanks again for the bug report. We've added it to the known bugs page in
> the documentation for r23.05.1, and provided a patched file there as a
> workaround:
> https://docs.mesastar.org/en/release-r23.05.1/known_bugs.html#zams-model-central-composition
>
> Hopefully the steps for the workaround are simple enough that you can
> continue including models based on ZAMS files in your course materials. Let
> us know if you have any feedback!
>
> I've also attached a plot of the central compositions for the model grid
> in the patched ZAMS file. You can see some more discussion on the pull
> request that Bill Wolf opened to work on a more complete solution:
> https://github.com/MESAHub/mesa/pull/566.
>
> Cheers,
> Evan
>
>
> On Jul 18, 2023, at 11:23 PM, Warrick Ball via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
> Hi Natasha,
>
> I just had a look at the ZAMS models, which you can find in
>
>    $MESA_DIR/data/star_data/zams_models/zams_z2m2_y28.data
>
> and I think you've found a genuine bug.  There are models with masses
> 1.000, 1.259 and 1.584 and the 1.259 Msun model has a central H abundance
> of 0.574.
>
> For anyone looking to confirm, each new model has a line with "M/Msun" and
> the mass, so a quick way to see the issue is to find those lines and look 2
> lines before for the last line of the previous model e.g.
>
>    $ grep -B 2 M/Msun
> $MESA_DIR/data/star_data/zams_models/zams_z2m2_y28.data | less -S
>
> All the other models have X₀ > 0.69 so should be okay.  The inlists to
> generate the ZAMS models are in
>
>    mesa/mesahub/data/star_data/zams_models/create_z2m2_y28
>
> so we'll check if those work ASAP to create appropriate ZAMS models and,
> if not, fix them.
>
> We'll investigate this right away.  Note that ZAMS models either side of
> 1.000 and 1.584 Msun should be okay (but we'll definitely check!).
>
> Cheers,
> Warrick
>
>
> ___________
>
> Warrick Ball
> Senior Research Software Engineer
> University of Birmingham
> W.H.Ball at bham.ac.uk
>
> On Tue, 18 Jul 2023, Natasha Ivanova via Mesa-users wrote:
>
> CAUTION: This email originated from outside the organisation. Do not click
> links or open attachments unless you recognise the sender and know the
> content is safe.
> Hello all,
> By chance, I have found that the use of pre-calculated models
> (create_pre_main_sequence_model = .false.) in MESA version 23.05.1 leads to
> a huge discrepancy with the use of the models that are obtained as pre-MS
> (create_pre_main_sequence_model =
> .true.).
> A simple inlist to reproduce is attached.
> Specifically, the problem seems to be in that the stored low mass ZAMS
> model(s) have a significantly depleted central hydrogen -- see the table
> below, where I provided ages at the end of the MS, obtained with and
> without pre-MS calculations (and so
> MS starts with X=0.7), and also the H content in the center with which the
> calculations start in the stored zams model (ZAMS X_0).
> The minimum central H content seems to be for 1.25 Msun - it is as small
> at the zero age as 0.578248. This also leads to a more massive star having
> a longer MS lifetime.
> For me, it seems that the trend in deleted central H concentration is due
> to only one stellar model with a very low central H, and the rest of the
> models are interpolated; I also believe that that specific stored model is
> wrong. So my question is, is
> that a bug (an erroneous stored model) or a feature, and if that is the
> physical feature, then why?
> My question is motivated by the fact that I used to use the ZAMS models
> when teaching my stellar astro class, in the first introductional
> computational lab (and then later on). But if one can no longer believe in
> pre-calculated ZAMS models, I need to
> update my lab(s) - unless of course I am missing something and that is,
> for some reason, how it should be.
> M/Msun Age with preMS Age from "ZAMS"      ZAMS X_0
> 1.0 8.7599E+09     8.7154E+09          0.699498
> 1.1 5.6064E+09     5.0309E+09      0.666448
> 1.2   4.2840E+09     3.4859E+09        0.614212
> 1.23 3.9819E+09 3.1354E+09      0.587010
> 1.25 3.7561E+09 2.9156E+09      0.578248
> 1.27 3.6174E+09 2.7330E+09      0.583083
> 1.28 3.4796E+09 2.6863E+09      0.596698
> 1.29 3.4140E+09 2.6717E+09      0.605975
> 1.3 3.3239E+09 2.6728E+09      0.613373
> 1.4 2.6296E+09 2.2952E+09      0.650336
> 1.5 2.1518E+09 1.9827E+09      0.672308
> Best,
> Natasha
>
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