A Novel Approach to Constrain Rotational Mixing and Convective-core Overshoot in Stars Using the Initial–Final Mass Relation

Abstract

The semi-empirical initial–final mass relation (IFMR) connects spectroscopically analyzed white dwarfs (WDs) in star clusters to the initial masses of the stars that formed them. Most current stellar evolution models, however, predict that stars will evolve to WDs ∼0.1 M ⊙ less massive than that found in the IFMR. We first look at how varying theoretical mass-loss rates, third dredge-up efficiencies, and convective-core overshoot may help explain the differences between models and observations. These parameters play an important role at the lowest masses ( M initial  < 3  M ⊙ ). At higher masses, only convective-core overshoot meaningfully affects WD mass, but alone it likely cannot explain neither the observed WD masses nor why the IFMR scatter is larger than observational errors predict. These higher masses, however, are also where rotational mixing in main sequence stars begins to create more massive cores, and hence more massive WDs. This rotational mixing also extends a star's lifetime, making faster-rotating progenitors appear like less massive stars in their semi-empirical age analysis. Applying the observed range of young B-dwarf rotations to the MIST or SYCLIST rotational models demonstrates a marked improvement in reproducing both the observed IFMR data and its scatter. The incorporation of both rotation and efficient convective-core overshoot significantly improves the match with observations. This Letter shows that the IFMR provides a valuable observational constraint on how rotation and convective-core overshoot affect the core evolution of a star.