[Mesa-users] Difference between s% mass_change and s% mstar_dot

[Bhattacharjee, Soumyadeep]

Hello MESA users,

I am Soumyadeep, a graduate student at Caltech. I am trying a simple thing for now: accrete mass on a ZAMS star (eventually I have to put some conditions, so I am editing the run_star_extras.f90 file). I found that two parameters can potentially do it: s% mass_change and s% mstar_dot. In the parameter space where both work, I am getting the same output from both. However, s% mass_change is breaking if I increase the accretion to just a moderately high value (like 1e-5 Msun/year). This means, the timestep is becoming too small, and I am getting the following output:

“169 50  coeff 1.0000 avg resid  0.343E-07      max resid equL   744  0.10841E-03 mix type 11111 avg corr  0.411E-09      max corr lnd   744  0.14721E-06 mix type 11111  avg+max resid -- give up"

Whereas, s% mstar_dot seems to be working fine. I also see that if I set s% mass_change, it also sets s% mstar_dot, but not the other way around. I was wondering what is the main difference between the two parameters, and why they are behaving differently, and which is the right way to do it. I am new to MESA, so any help would be really appreciated.

Here are the MESA information:

1) MESA version: mesa-r24.03.1
2) I am suing MESA SDK: Version: aarch64-macos-25.3.1
3) Machine: MacBook Pro, Apple Silicon, OS: macOS Tahoe
4) Error message: attached and described above
5) Build log: attached

Command outputs:

1) uname -a: Darwin Mac.lan 25.0.0 Darwin Kernel Version 25.0.0: Wed Sep 17 21:35:32 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T6020 arm64

2) gfortran -v:

Using built-in specs.

COLLECT_GCC=/Applications/mesasdk/bin/gfortran.exec

COLLECT_LTO_WRAPPER=/Applications/mesasdk/bin/../libexec/gcc/aarch64-apple-darwin20/13.3.0/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 --with-sysroot=/opt/sdk2-tmp/mesasdk/sysroot

Thread model: posix

Supported LTO compression algorithms: zlib

gcc version 13.3.0 (GCC)


3) echo $MESASDK_ROOT

/Applications/mesasdk


4) echo $PATH

/Applications/mesasdk/bin:/Applications/Anaconda/anaconda3/bin:/Applications/Anaconda/anaconda3/condabin:/opt/homebrew/bin:/opt/homebrew/sbin:/opt/local/bin:/opt/local/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/X11/bin:/Library/Apple/usr/bin:/Users/soumyadeep/mesa-r24.03.1/scripts/shmesa


5) echo $MESA_DIR

/Users/soumyadeep/mesa-r24.03.1


With regards,
Soumyadeep Bhattacharjee

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