Modules for Experiments in Stellar Astrophysics (MESA) (1009.1622v1)

Abstract: 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 (http://mesa.sourceforge.net/).

• The paper presents a modular, open-source suite that enables comprehensive simulations of stellar structure and evolution.
• It details advanced numerical methods like adaptive mesh refinement and robust time-stepping algorithms to accurately model diverse stellar phenomena.
• Its validation against established codes and observed astrophysical phenomena underscores MESA’s potential for wide-ranging applications in modern stellar research.

Overview of "Modules for Experiments in Stellar Astrophysics ($MESA$)"

The paper presents the development and capabilities of Modules for Experiments in Stellar Astrophysics (MESA), an open-source, comprehensive software suite for stellar astrophysics and evolution simulations. Authored by Bill Paxton and colleagues, the paper lays out the motivation, design, numerical methods, and scientific implications of MESA. The software is designed to simulate a wide range of stellar phenomena, leveraging modern computing techniques to enhance astrophysical research.

Design and Implementation

MESA is conceived as a modular framework, facilitating targeted advances in computational stellar modeling. Each module corresponds to a specific physical or numerical aspect of stellar modeling—such as equations of state (EOS), nuclear reaction networks, and opacity calculations. These modules are individually testable and designed for independent development, enabling significant flexibility and usability across various research domains. A notable feature is the thread-safe design, optimizing parallel computations on modern processors.

Numerical and Physical Modules

MESA integrates several advanced computational techniques: adaptive mesh refinement, sophisticated time-stepping algorithms, and parallel computation via OpenMP. The suite includes microphysical modules providing up-to-date models for equations of state, opacities, and nuclear reaction networks. For instance, the $eos$ module combines OPAL and SCVH tables with the HELM and PC equations of state for a comprehensive thermodynamic treatment. Similarly, the $kap$ module synthesizes data from multiple sources to deliver accurate opacity tables essential for stellar interior modeling.

Stellar Evolution Capabilities

The core of MESA, $MESA star$, models one-dimensional stellar structure and evolution by solving fully coupled sets of stellar structure and composition equations. Its capabilities span from simulating substellar objects and very low-mass stars to modeling the life cycles of massive stars including up to the pre-supernova phase. Key features include simulations of hydrogen and helium burning stars, as well as dynamic phases like the helium core flash in low-mass stars.

Validation and Verification

MESA has been meticulously validated against existing stellar evolution codes and benchmarked with observed astrophysical phenomena. The software's results exhibit close agreement with well-established codes such as BaSTI/FRANEC, DSEP, and GARSTEC in main-sequence and advanced evolutionary phases. It has demonstrated strengths particularly in handling complex phenomena like convective boundaries in massive stars and helium shell flashes in asymptotic giant branch stars.

Scientific Implications and Future Directions

The development of MESA underscores the importance of community-driven, open-source software in advancing stellar astrophysics. It provides a robust platform to test theoretical predictions, interpret observational data, and explore stellar behaviors in diverse environments. The modular nature of MESA ensures continuous evolution and adaptation, allowing researchers to implement cutting-edge physics and apply it to a broad spectrum of astrophysical problems.

Looking forward, MESA is expected to incorporate enhancements such as more nuanced treatments of convective processes and integration with hydrodynamic simulations, further expanding the boundaries of computational astrophysics. Its open-source nature encourages collaborative development contributing to a more comprehensive understanding of stellar phenomena.

In summary, MESA equips researchers with a powerful, flexible tool to address contemporary challenges in stellar astrophysics, facilitating new discoveries and improving our grasp of stellar dynamics, from brown dwarfs to supermassive stars.