Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source, robust, efficient, thread-safe libraries for a wide range of applications in computational stellar astrophysics. A one-dimensional stellar evolution module, MESAstar, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very low mass to massive stars, including advanced evolutionary phases. MESAstar solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. State-of-the-art modules provide equation of state, opacity, nuclear reaction rates, element diffusion data, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own explicitly defined public interface to facilitate independent development. Several detailed examples indicate the extensive verification and testing that is continuously performed and demonstrate the wide range of capabilities that MESA possesses. These examples include evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets to very old ages; the complete evolutionary track of a 1 M ☉ star from the pre-main sequence (PMS) to a cooling white dwarf; the solar sound speed profile; the evolution of intermediate-mass stars through the He-core burning phase and thermal pulses on the He-shell burning asymptotic giant branch phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; the complete evolutionary tracks of massive stars from the PMS to the onset of core collapse; mass transfer from stars undergoing Roche lobe overflow; and the evolution of helium accretion onto a neutron star. MESA can be downloaded from the project Web site (http://mesa.sourceforge.net/).

https://iopscience.iop.org/article/10.1088/0067-0049/192/1/3/pdf

Modules for Experiments in Stellar Astrophysics (MESA)

Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source libraries for a wide range of applications in computational stellar astrophysics. A newly designed 1-D stellar evolution module, MESA star, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very-low mass to massive stars, including advanced evolutionary phases. MESA star solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. Independently usable modules provide equation of state, opacity, nuclear reaction rates, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own public interface. Examples include comparisons to other codes and show evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets; the complete evolution of a 1 Msun star from the pre-main sequence to a cooling white dwarf; the Solar sound speed profile; the evolution of intermediate mass stars through the thermal pulses on the He-shell burning AGB phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; evolutionary tracks of massive stars from the pre-main sequence to the onset of core collapse; stars undergoing Roche lobe overflow; and accretion onto a neutron star. Instructions for downloading and installing MESA can be found on the project web site (this http URL).

▪ Abstract We present a review of nucleosynthesis in AGB stars outlining the development of theoretical models and their relationship to observations. We focus on the new high resolution codes with...

/pdf/nucleosynthesis-in-asymptotic-giant-branch-stars-relevance-1594it3sxd.pdf

Nucleosynthesis in asymptotic giant branch stars: Relevance for galactic enrichment and solar system formation

▪ Abstract The metallicity of stars in the Galaxy ranges from [Fe/H] = −4 to +0.5 dex, and the solar iron abundance is e(Fe) = 7.51 ± 0.01 dex. The average values of [Fe/H] in the solar neighborhood, the halo, and Galactic bulge are −0.2, −1.6, and −0.2 dex respectively. Detailed abundance analysis reveals that the Galactic disk, halo, and bulge exhibit unique abundance patterns of O, Mg, Si, Ca, and Ti and neutron-capture elements. These signatures show that environment plays an important role in chemical evolution and that supernovae come in many flavors with a range of element yields. The 300-fold dispersion in heavy element abundances of the most metal-poor stars suggests incomplete mixing of ejecta from individual supernova, with vastly different yields, in clouds of ∼106 M. The composition of Orion association stars indicates that star-forming regions are significantly self-enriched on time scales of 80 million years. The rapid self-enrichment and inhomogeneous chemical evolution models are required...

/pdf/abundance-ratios-and-galactic-chemical-evolution-215ebkykwj.pdf

Abundance ratios and galactic chemical evolution

In this paper we follow the Galactic enrichment of three easily observed light n-capture elements: Sr, Y, and Zr. Input stellar yields have been first separated into their respective main and weak s-process components and r-process component. The s-process yields from asymptotic giant branch (AGB) stars of low to intermediate mass are computed, exploring a wide range of efficiencies of the major neutron source, 13 C, and covering both disk and halo metallicities. AGB stars have been shown to reproduce the mains-component in the solar system, i.e., the s-process isotopic distribution of allheavy isotopes with atomic mass number A > 90, with a minor contribution to the light s-process isotopes up to A � 90. The concurrent weak s-process, which accounts for the major fraction of the light s-process isotopes in the solar system and occurs in massive stars by the operation of the 22 Ne neutron source, is discussed in detail. Neither the main s -n or the weaks-components are shown to contribute significantly to the neutron-capture element abundances observed in unevolved halo stars. Knowing the s-process distribution at the epoch of the solar system formation, we first employed the r-process residuals method to infer the isotopic distribution of the r-process. We assumed a primary r-process production in the Galaxy from moderately massive Type II supernovae that best reproduces the observational Galactic trend of metallicity versus Eu, an almost pure r-process element. We present a detailed analysis of a large published database of spectroscopic observations of Sr, Y, Zr, Ba, and Eu for Galactic stars at various metallicities, showing that the observed trends versus metallicity can be understood in light of a multiplicity of stellar neutron-capture components. Spectroscopic observations of the Sr, Y, and Zr to Ba and Eu abundance ratios versus metallicity provide useful diagnostics of the types of neutron-capture processes forming Sr, Y, and Zr. In particular, the observed [Sr, Y, Zr/Ba, Eu] ratio is clearly not flat at low metallicities, as we would expect if Ba, Eu and Sr, Y, Zr all had the same r-process nucleosynthetic origin. We discuss our chemical evolution predictions, taking into account the interplay between different processes to produce Sr-Y-Zr. Making use of the very r-process‐rich and very metal-poor stars like CS 22892� 052 and CS 31082� 001, we find hints and discuss the possibility of a primary process in low-metallicity massive stars, different from the ‘‘classical s-process’’ and from the ‘‘classical r-process’’ that we tentatively define LEPP (lighter element primary process). This allows us to revise the estimates of the r-process contributions to the solar Sr, Y, and Zr abundances, as well as of the contribution to the s-only isotopes 86 Sr, 87 Sr, and 96 Mo. Subject headings: Galaxy: abundances — Galaxy: evolution — nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: AGB and post-AGB

/pdf/galactic-evolution-of-sr-y-and-zr-a-multiplicity-of-shmddyl67n.pdf

GALACTIC EVOLUTION OF Sr, Y, AND Zr: A MULTIPLICITY OF NUCLEOSYNTHETIC PROCESSES

Thermal pulses: p-capture, alpha -capture, s-process nucleosynthesis; and convective mixing in a star of intermediate mass.

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Thermal pulses: p-capture, alpha -capture, s-process nucleosynthesis; and convective mixing in a star of intermediate mass.