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

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.

On Stellar Evolution in a Neutrino Hertzsprung–Russell Diagram

“…These masses are chosen to delineate features in a forthcoming neutrino HR diagram. We use MESA revision r12115 to construct our stellar models (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015(Paxton et al , 2018(Paxton et al , 2019. Each star is modeled as a single, non-rotating, mass losing, solar metallicity object.…”

“…Relatively large nuclear networks are required to fully capture the energy generation rate, and thus the neutrino luminosity from β-processes, in neutron-rich compositions. The current defaults for nuclear reaction rates are described in Appendix A.2 of Paxton et al (2019). Rates are taken from a combination of NACRE (Angulo et al 1999) and the Joint Institute for Nuclear Astrophysics REACLIB library (default version, dated 2017-10-20) (Cyburt et al 2010).…”

“…The models approximate convection using the recipes described in Paxton et al (2019Paxton et al ( , 2018. The adopted values of the mixing-length parameter, α and overshooting parameter f ov , as well as the initial hydrogen fraction X, helium fraction Y, and metallicity Z and are determined from our calibrated Solar model.…”

Moving and reactive boundary conditions in moving-mesh hydrodynamics

“…We summarize the simulation setup here, but refer the reader to PC19 for a more detailed discussion. We first use MESA (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015(Paxton et al , 2018(Paxton et al , 2019 to evolve a 2 M star with metallicity Z = 0.02 from the pre-main sequence to the red giant phase. We stop when the stellar radius reaches 52 R with a helium core of mass M c = 0.36 M .…”

“…This moving-mesh solver is known as MANGA, which is described in detail by Chang et al (2017, hereinafter CWQ17). In Prust & Chang (2019, hereinafter PC19), we incorporated individual time-steps into MANGA as well as the equations of state implemented in the open source stellar evolution code MESA (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015(Paxton et al , 2018(Paxton et al , 2019. We used these tools to simulate common envelope evolution (CEE) in binary star systems.…”