# Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation

## TL;DR

This paper details updates to MESA, enhancing its capabilities in modeling stellar pulsations, rotation, convective boundaries, and energy conservation, with improved numerical accuracy and computational performance for stellar evolution simulations.

## Contribution

The paper introduces new modules and improvements in MESA, including pulsation modeling, energy conservation, rotation treatment, convective boundary tracking, and software infrastructure enhancements.

## Key findings

- Energy conservation during He flash improved to better than 0.001%.
- Enhanced modeling of rotating stars with gravity darkening effects.
- Improved computational efficiency and new physics modules implemented.

## Abstract

We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (MESA). RSP is a new functionality in MESAstar that models the non-linear radial stellar pulsations that characterize RR Lyrae, Cepheids, and other classes of variable stars. We significantly enhance numerical energy conservation capabilities, including during mass changes. For example, this enables calculations through the He flash that conserve energy to better than 0.001 %. To improve the modeling of rotating stars in MESA, we introduce a new approach to modifying the pressure and temperature equations of stellar structure, and a formulation of the projection effects of gravity darkening. A new scheme for tracking convective boundaries yields reliable values of the convective-core mass, and allows the natural emergence of adiabatic semiconvection regions during both core hydrogen- and helium-burning phases. We quantify the parallel performance of MESA on current generation multicore architectures and demonstrate improvements in the computational efficiency of radiative levitation. We report updates to the equation of state and nuclear reaction physics modules. We briefly discuss the current treatment of fallback in core-collapse supernova models and the thermodynamic evolution of supernova explosions. We close by discussing the new MESA Testhub software infrastructure to enhance source-code development.