Modules for Experiments in Stellar Astrophysics (${\mathtt{M}}{\mathtt{E}}{\mathtt{S}}{\mathtt{A}}$): Convective Boundaries, Element Diffusion, and Massive Star Explosions

Abstract

We update the capabilities of the software instrument Modules for Experiments in Stellar Astrophysics (MESA) and enhance its ease of use and availability. Our new approach to locating convective boundaries is consistent with the physics of convection, and yields reliable values of the convective core mass during both hydrogen and helium burning phases. Stars with M < 8 M become white dwarfs and cool to the point where the electrons are degenerate and the ions are strongly coupled, a realm now available to study with MESA due to improved treatments of element diffusion, latent heat release, and blending of equations of state. Studies of the final fates of massive stars are extended in MESA by our addition of an approximate Riemann solver that captures shocks and conserves energy to high accuracy during dynamic epochs. We also introduce a 1D capability for modeling the effects of Rayleigh-Taylor instabilities that, in combination with the coupling to a public version of the STELLA radiation transfer instrument, creates new avenues for exploring Type II supernovae properties. These capabilities are exhibited with exploratory models of pair-instability supernova, pulsational pair-instability supernova, and the formation of stellar mass black holes. The applicability of MESA is now widened by the capability of importing multi-dimensional hydrodynamic models into MESA. We close by introducing software modules for handling floating point exceptions and stellar model optimization, and four new software tools − MESA-Web, MESA-Docker, pyMESA, and mesastar.org − to enhance MESA's education and research impact.

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.…”

“…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.…”

“…We iterate on differences between the final model at t = 4.568 Gyr (Bouvier & Wadhwa 2010) and the solar radius, R = 6.9566 × 10 10 cm, solar luminosity, L γ, = 3.828 × 10 33 erg s −1 (Prša et al 2016), and surface heavy element abundance Z/X. We use the builtin MESA simplex module to iteratively vary the mixinglength parameter, α, and the initial composition X, Y, and Z, including the effects of element diffusion (Thoul et al 1994;Paxton et al 2018). This calibration is performed for two estimates of the heavy element abundance at the surface of the Sun, Z/X = 0.0181 (Asplund et al 2009) and Z/X = 0.0229 (Grevesse & Sauval 1998).…”

Sensitivity of the lower edge of the pair-instability black hole mass gap to the treatment of time-dependent convection

“…Our first grid of models, which we refer to as the "classic MLT" grid, is computed using MESA release 10108. For this grid, the convective velocity v c is obtained from MLT under the steady-state assumption, similarly to Paxton et al (2018) and Leung et al (2019), although the latter authors turn off convection during hydrodynamical phases of evolution. For this grid we employ MLT++, which is an enhancement of the convective flux in superadiabatic radiation-pressure dominated regions prone to developing density inversions (Paxton et al 2013;Jiang et al 2018) and a semiconvection efficiency of 0.01.…”

The expansion of stripped-envelope stars: Consequences for supernovae and gravitational-wave progenitors

“…For our calculation of the interacting binary stars, we use the open-source 1D stellar evolution code MESA (version 10398, Paxton et al 2011Paxton et al , 2013Paxton et al , 2015Paxton et al , 2018Paxton et al , 2019. The models are computed at solar metallicity (initial metal fraction of Z ≡ 0.0142, based on values from Asplund et al (2009) and subsolar metallicity (Z = 0.001, representative of nearby lowmetallicity environments such as the Small Magellanic Cloud, Z SMC Z /5).…”