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

[Evan Bauer]

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 <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 <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/ <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 <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 <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 <mailto:mesa-users-bounces at lists.mesastar.org>> on behalf of KAYLA MARTIN via Mesa-users <mesa-users at lists.mesastar.org <mailto:mesa-users at lists.mesastar.org>>
> Sent: Thursday, August 1, 2024 9:48:50 AM
> To: mesa-users at lists.mesastar.org <mailto: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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20240801/4bc4d9ae/attachment.htm>