[Mesa-users] Mesastar Question: Setting Initial CO Abudance Enhancements

Fri Aug 2 06:18:49 UTC 2024

Lynn, Frank, Evan

Thank you very much for your responses!

Currently I am just trying to specify individual metal abundances in the
model, so Lynn's initial answer is very helpful for that! That being said,
I was initially trying to simply set an alpha-enhancement in the model
([alpha/Fe]=+0.2), though did not think this was possible so deferred to
specifying individual elements instead (we care mostly about C and O in our
current project), so Evan's answer was very helpful. Frank, I will need to
set specific isotopes so thank you for sending through how one might go
about doing that.

I do have some follow up questions if you wouldn't mind helping me
further...

Regarding Lynn's response:

   - If I do not have the individual metal fractions for ALL elements in
   the current net (i.e., the ones I do have only add to 0.9026), what will
   happen to the remaining fraction?
   - Is there an equivalent option to
   accretion_dump_missing_metals_into_heaviest = .true. (which I assume is for
   accretion only) for initialising a model?

Regarding Frank's response:

   - From what I understand, the options you send go in the star_job
   section of the inlist. Where does one put the example.dat file in mesa?
   - Additionally, if I have not used a custom net (i.e., I have only
   specified gs98 and gs98_co composition) where would I find the information
   on the isotope species included in the net? So far I can only find
   composition tables but they don't seem to list the isotope names (i.e.,
   they are just numbers).

Regarding Evan's response:

   - I have had a look at the tables available in data/kap_data and the
   closest one to my case is 'gs98_aFe_p2_z0.004_x0.7.data' (however I need
   initial values of Z=0.008, Y=0.26, X=0.732). How would I go about creating
   a similar .data table (i.e., one with  [alpha/Fe]=0.2) for my required z
   and x initial composition values instead?
   - If I set my required initial X, Y, Z values in the controls section of
   the inlist (with initial_z, initial_y), will this change the z and x values
   of the  gs98_aFe_p2_z0.004_x0.7.data table (despite the table being
   constructed with z=0.004 and x=0.7) while still preserving [alpha/Fe]=0.2?
   - Additionally, I don't think I am quite understanding what the values
   listed for user_kap_Xs and user_kap_Zs are. Could you elaborate on what
   they correspond to?

Thank you all once again for your help!

On Fri, Aug 2, 2024 at 8:00 AM Evan Bauer <evan.bauer.astro at gmail.com>
wrote:

> Thanks Lynn! I'll just chime in to note that MESA happens to ship with
> some "alpha-enhanced" opacity tables for gs98 mixtures included with the
> opacity data. While not exactly the same as [O/Fe]=+0.2, I think you could
> use the following kap inlist options to get something that's at least
> qualitatively similar as a starting point:
>
>   kap_file_prefix = 'gs98_aFe_p2' ! aFe_p2 means [alpha/Fe]=+0.2
>
>   user_num_kap_Xs = 10
>   user_kap_Xs = 0.0d0, 0.1d0, 0.2d0, 0.35d0, 0.5d0, 0.7d0, 0.8d0, 0.9d0,
> 0.95d0, 1.0d0
>
>   user_num_kap_Zs = 13
>   user_kap_Zs = 0.000d0, 0.0001d0, 0.0003d0, 0.001d0, 0.002d0, 0.004d0,
> 0.01d0, 0.02d0, 0.03d0, 0.04d0, 0.06d0, 0.08d0, 0.100d0
>
> Cheers,
> Evan
>
> On Aug 1, 2024, at 10:48 AM, Buchele, Lynn via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
> Dear Kayla (sending this again as I forgot to cc the mailing list) ,
> I can give an initial answer to your questions, although others on the
> list may have more details to add. For setting the composition, I'm
> guessing that your composition changes are at the level of elements, not
> isotopes.
> In this case (and assuming you create your model with either
> create_pre_main_sequence_model or create_initial_model), you can set
> set_uniform_initial_composition = .true. and
> initial_zfracs = 0 in star jobs and set the element abundances using
> z_fraction_* in the controls section (
> https://docs.mesastar.org/en/release-r24.03.1/reference/controls.html#accretion-dump-missing-metals-into-heaviest
>  this points to a section about accretion but the z_fraction_* controls
> are also used in generating an initial model). For this, you need to set
> all the elements and have them sum to one.
>
> If you want to make changes to the abundance of isotopes (rather than
> elements) you can use set_uniform_initial_xa_from_file, see
> https://docs.mesastar.org/en/release-r24.03.1/reference/star_job.html#set-uniform-initial-xa-from-file
> .
>
> As for custom opacity tables, you are correct that AESOPUS only provides
> low temperature opacity tables. It looks like the webpage for generating
> custom OPAL tables is down, but you might be able to use OP tables which
> you can generate here: http://op-opacity.obspm.fr/opacity/
> The caveat is that these only generate type 1 tables, which won't account
> for changes in the C/O ratio. If you're only dealing with hydrogen burning,
> this shouldn't be a problem. You can look at when MESA (by default) starts
> using type 2 tables here:
> https://docs.mesastar.org/en/release-r24.03.1/kap/defaults.html#use-type2-opacities
>
> If you do need type 2 tables, perhaps someone else on the mailing list has
> a suggestion for how to generate them.
> I think the preprocessor instructions given in the README should work (you
> can use the inlist_OP_* as a template since your custom files should be in
> the same format). The inlists discussed here are inlists for the opacity
> preprocessor, not the star kap insists, so they will have different options
> available. Otherwise, you can provide information about the structure of
> the tables in the kap inlist using the controls described here:
> https://docs.mesastar.org/en/release-r24.03.1/kap/defaults.html#custom-tables
> .
> For the lowT AESOPUS tables, you only need to use the inlist parameter
> AESOPUS_filename.
>
> Hopefully this helps!
>
>
> Best,
> Lynn
>
> ------------------------------
> *From:* Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of
> KAYLA MARTIN via Mesa-users <mesa-users at lists.mesastar.org>
> *Sent:* Thursday, August 1, 2024 9:48:50 AM
> *To:* mesa-users at lists.mesastar.org
> *Subject:* [Mesa-users] Mesastar Question: Setting Initial CO Abudance
> Enhancements
>
>
> This email originates from an external sender. Please verify the sender's
> identity carefully before opening any attachments or links!
>
> Hi,
>
> This is my first post on the mesa user list.
>
> I am creating a model with X=0.732, Y=0.26, and Z=0.008, with the chemical
> composition mixture of Grevesse & Sauval (1998). In this model, I need to
> set [O/Fe]=+0.2 (equivalent to [O/H]=-0.1 or X(O)=0.0042), though I cannot
> see a clear way to implement this in my model.
>
> I have attempted to create an opacity table using the AESOPUS tool
> <http://stev.oapd.inaf.it/cgi-bin/aesopus>, though it seems this only
> applies at 'low temperatures' (the tool won't let me set higher than
> Teff=log3.7)? Further, the implementation of the tables generated from this
> tool are unclear -- the related instructions in mesa have outdated
> information (last updates ~2013), and contains variables that no longer
> exist in more recent mesa versions (e.g.,
> $MESA_DIR/kap/preprocessor/README_creating_OPAL_type2_tables notes inlist
> variables such as Zfrac_O).
>
> Any guidance on how to correctly specify the initial oxygen abundance in
> my model with a gs98 reference solar composition will be very helpful.
>
> Thanks!
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
>
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