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

Sun Jan 29 18:42:05 UTC 2023

Hi Pablo,

Thank you! I looked at the rates for each of the CNO atoms, and indeed the issue is that the C and O is being turned into N and building up. Plotting the rate of these shows that -(ΔC+ΔO) = ΔN. Thank you for pointing this out!

Cheers,
- Ben

On Jan 28, 2023, at 2:23 PM, Pablo Marchant <pamarca at gmail.com> wrote:

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<mailto: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<http://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

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

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