MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models

Abstract: This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ($5 \leq \rm \log(Age)\;[yr] \leq 10.3$), masses ($0.1 \leq M/M_{\odot} \leq 300$), and metallicities ($-2.0 \leq \rm [Z/H] \leq 0.5$). The models are self-consistently and continuously evolved from the pre-main sequence to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the pre-main sequence to the end of core helium burning for $-4.0 \leq \rm [Z/H] < -2.0$. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/.

• The paper presents comprehensive solar-scaled stellar evolution models using MESA, covering a wide range of masses, ages, and metallicities.
• It employs advanced methods like the OPAL equation of state and ATLAS12 boundary conditions to ensure accurate modeling across key stellar phases.
• The models reliably reproduce solar observations and improve computational efficiency, aiding diverse studies from stellar evolution to galactic archaeology.

Analysis of MESA Isochrones and Stellar Tracks (MIST). I: Solar-scaled Models

The "MESA Isochrones and Stellar Tracks (MIST). I: Solar-scaled models" paper presents a substantial advancement in the modeling of stellar evolution, leveraging the capabilities of the Modules for Experiments in Stellar Astrophysics (MESA). The authors, Choi et al., provide a detailed description of generating a comprehensive set of stellar evolutionary tracks and isochrones under a broad range of initial conditions. The models encompass a wide array of ages, masses, and metallicities, presenting a significant resource for researchers in stellar astrophysics and related fields.

Key Methodological Approaches

The work extensively utilizes MESA, an advanced 1D stellar evolution code, to develop isochrones and evolutionary tracks. The models are initiated from the pre-main sequence (PMS) phase and traced through various stages depending on the initial mass, reaching the end of hydrogen burning, the white dwarf cooling sequence, or carbon burning stages. This extensive coverage allows for examining evolutionary scenarios across a significant portion of the Hertzsprung–Russell (HR) diagram. Importantly, the authors prioritize consistency by employing the OPAL equation of state and opacity tables combined with the use of photospheric boundary conditions from the ATLAS12 code. This approach ensures enhancements in model accuracy, particularly in high and low-temperature regimes.

Numerical Results and Comparisons

The MIST models present a substantial improvement in computation, enabling parallel processing thanks to MESA's architecture. By calibrating against the solar model, the authors achieve models that can reproduce solar observations, albeit with known limitations in helium surface abundance due to differences in reference solar models (e.g. AGS2009 vs. GS1998). They provide convergence tests to validate the numerical accuracy across various resolutions, highlighting reliability in resultant models, especially for low-mass stars.

Notably, the authors address the implications of mass loss rates using the Reimers and Bloecker prescriptions for low-mass stars and the "Dutch" scheme for hotter, more massive stars, delineating substantial effects on MSTO morphology and advanced evolutionary phases like the AGB and WR stages. This careful treatment emphasizes the model's adaptability and precision, grounding its predictions in empirical data such as the IFMR and AGB luminosity functions. Comparison to other major databases such as PARSEC and Geneva reveals a broad alignment, providing confidence in the models' applicability.

Broader Implications

The MIST project stands to impact diverse astrophysical inquiries, ranging from stellar population synthesis to galactic archaeology. The rich parameter space covered by these models broadens the investigatory scope for understanding the physical underpinnings of stellar phenomena and addressing longstanding questions in cosmic evolution. The robust treatment of multiple variables (e.g., convection, rotation, mixing processes) adds depth to these models, ensuring their utility in generating insight into the dynamic processes shaping stellar interiors.

Future Directions

Recognizing the current models' constraints, including the lack of binary systems and 2D/3D dynamics, the authors outline future expansions. These include incorporating α-enhanced models and exploring variable mixing length parameters to better represent real-world phenomena. Efforts to reconcile discrepancies in observed-simulated CMDs through improved bolometric corrections offer a pathway to enhancing model fidelity further.

In sum, the MIST solar-scaled models provide a powerful and flexible tool for stellar and galactic researchers, setting a solid foundation for probing the underlying mechanics of stellar evolution and contributing to a greater understanding of our universe's history. The interdisciplinary potential for these models is substantial, promising significant insights spanning stellar to extragalactic scales.