[Mesa-users] Total number of carbon atoms changing during main sequence

[Pablo Marchant]

Hi Ben,

have you checked if the total number of CNO atoms is conserved? Even though
the CNO atoms are just catalysts, the CNO cycle swaps their relative
ratios, in particular turning carbon into nitrogen and (usually much more
slowly) oxygen into nitrogen.

Cheers

On Sat, Jan 28, 2023 at 10:44 PM Roulston, Benjamin via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Hello,
>
> I’m hoping that I am missing something easy and that you all might be able
> to tell me where I am going wrong.
>
> I am trying to model the formation of *dwarf* carbon stars (on the main
> sequence). I’m using “accrete_given_mass_fractions” to add mass at a
> specific abundance ratio (mainly controlling for the C/O ratio). This works
> great and I indeed see the surface and total C/O change as I add mass
> (including mixing down further into the interior).
>
> However, once the accretion is finished, during further evolution the *total
> number of C *(and O, but to a less extent) *atoms decreases.* As my
> models are all on the main sequence (I stop them when core H is depleted) I
> do not expect there to be any loss of C or O atoms during this evolution.
> Especially since I’m only considering stars with M<1Msun. I have winds
> turned off currently.
>
> I’ve checked that I am calculating this correctly, using the built in
> “total_mass_c12” etc history columns, and using my own “run_star_extras”
> routine to calculate the numbers as a profile and history column. I’m
> tracking all stable isotopes (C12, C13, O16, O17, O18).
>
> This effect seems larger than perhaps any numeric error one might expect
> from such large numbers, and it seems to visibly change the C/O as the star
> evolves through the main sequence.
>
> I’ve checked a “plain” MESA build. Using no extras, and just tracking via
> the “total_mass_XNN” columns I find this loss of C and O atoms as well. The
> rate seems to change with mass, and I’ve checked this for 0.3, 0.5, 0.8,
> and 0.9Msun models, and all show the loss.
>
> Am I totally wrong here in expecting the total number of C and O atoms to
> remain constant during main sequence evolution? Even if these stars were
> massive (which they are not) and could have appreciable CNO cycle going on,
> I wouldn’t expect a loss then either (as they’re just catalysts). Anyone
> have insight into what might be happening?
>
> Thank you for any help someone might be able to provide!
>
> I’ve included my inlists and my extras file. I use “inlist_make_preMS” to
> make a model that is at ZAMS for a given mass. “inlist_evolve_Gyr” evolves
> a model to 1Gyr. “inlist_accrete_Crich” is then that inlist that accretes
> the C rich material to make my dwarf carbon star. This also continues the
> evolution until H core depletion.
>
>
> I am using MESA 22.10.1 and also using the SDK
> (mesasdk-aarch64-macos-22.10.1). MESA builds and runs fine.
>
> *uname -a=*Darwin dhcp-195-210.caltech.edu 22.2.0 Darwin Kernel Version 22.2.0: Fri Nov 11 02:03:51 PST 2022; root:xnu-8792.61.2~4/RELEASE_ARM64_T6000 arm64
>
> *gfortran -v=*Using built-in specs.
> COLLECT_GCC=/Users/benjaminroulston/Dropbox/Research/MESA/MESA_SDKs/mesasdk-aarch64-macos-22.10.1/bin/gfortran.exec
> COLLECT_LTO_WRAPPER=/Users/benjaminroulston/Dropbox/Research/MESA/MESA_SDKs/mesasdk-aarch64-macos-22.10.1/bin/../libexec/gcc/aarch64-apple-darwin20/12.2.0/lto-wrapper
> Target: aarch64-apple-darwin20
> Configured with: /opt/sdk2-tmp/build/gcc/configure CC=clang CXX=clang++ --build=aarch64-apple-darwin20 --host=aarch64-apple-darwin20 --target=aarch64-apple-darwin20 --prefix=/opt/sdk2-tmp/mesasdk --with-gmp=/opt/sdk2-tmp/mesasdk --with-mpfr=/opt/sdk2-tmp/mesasdk --with-mpc=/opt/sdk2-tmp/mesasdk --enable-languages=c,c++,fortran --disable-multilib --disable-nls --disable-libsanitizer --with-sysroot=/opt/sdk2-tmp/mesasdk/sysroot --without-build-config
> Thread model: posix
> Supported LTO compression algorithms: zlib
> gcc version 12.2.0 (GCC)
>
> *echo $MESASDK_ROOT=*/Users/benjaminroulston/Dropbox/Research/MESA/MESA_SDKs/mesasdk-aarch64-macos-22.10.1
>
> *echo $PATH=*/Users/benjaminroulston/Dropbox/Research/MESA/MESA_SDKs/mesasdk-aarch64-macos-22.10.1/bin:/Users/benjaminroulston/Dropbox/Research/Coding/PYTHON3_ENVS/Research/bin:/Users/benjaminroulston/Dropbox/Research/Coding/miniconda3/condabin:/opt/homebrew/bin/python3:/opt/homebrew/opt/tcl-tk/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin
>
> *echo $MESA_DIR=*/Users/benjaminroulston/Dropbox/Research/MESA/MESA/mesa-r22.11.1
>
>
> Cheers,
> - Ben
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>

-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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