Inferring the efficiency of convective-envelope overshooting in Red Giant Branch stars

Abstract

The understanding of mixing processes in stars is crucial for improving our knowledge of the chemical abundances in stellar photospheres and of their variation with evolutionary phase. This is fundamental for many astrophysical issues on all scales, ranging from stellar evolution to the chemical composition, formation and evolution of stellar clusters and galaxies. Among these processes, convective-envelope overshooting is in dire need of a systematic calibration and comparison with predictions from multi-dimensional hydrodynamical simulations. The Red Giant Branch bump (RGBb) is an ideal calibrator of overshooting processes, since its luminosity depends on the maximum depth reached by the convective envelope after the first dredge-up. Indeed, a more efficient overshooting produces a discontinuity in the Hydrogen mass fraction profile deeper in the stellar interior and consequently a less luminous RGBb. In this work, we calibrated the overshooting efficiency by comparing the RGBb location predicted by stellar models with observations of stellar clusters with HST and Gaia photometry, as well as solar-like oscillating giants in the Kepler field. We explored the metallicity range between -2.02 dex and +0.35 dex and found overshooting efficiencies ranging from $0.009_{-0.016}^{+0.015}$ to $0.062_{-0.015}^{+0.017}$. In particular, we found that the overshooting efficiency decreases linearly with [M/H], with a slope of $(-0.010\pm 0.006)$ dex${}^{-1}$. We suggest a possible explanation for this trend, linking it to the efficiency of turbulent entrainment at different metallicities.

14 pages, 15 figures; 1 appendix page, 2 appendix figures; Accepted for publication in A&A

References in corpus (25)

• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• Gaia Data Release 3: Summary of the content and survey properties
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Improving PARSEC models for very low mass stars
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• Basic physical parameters of a selected sample of evolved stars
• Gaia EDR3 view on Galactic globular clusters
• Improving the open cluster census. II. An all-sky cluster catalogue with Gaia DR3
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• Exploiting the Gaia EDR3 photometry to derive stellar temperatures
• On the primordial scenario for abundance variations within globular clusters. The isochrone test
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• Lithium depletion in solar-like stars: effect of overshooting based on realistic multi-dimensional simulations
• NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation? Cluster mass and age in the multiple population context
• Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf Spheroidal galaxy?
• APOGEE [C/N] Abundances Across the Galaxy: Migration and Infall from Red Giant Ages
• Spectroscopy and photometry of the least-massive Type-II globular clusters: NGC1261 AND NGC6934
• Two-dimensional simulations of solar-like models with artificially enhanced luminosity -- I. Impact on convective penetration
• 3D hydrodynamics simulations of internal gravity waves in red giant branch stars
• Mixed Mode Asteroseismology of Red Giant Stars Through the Luminosity Bump
• A search for solar-like oscillations in K giants in the globular cluster M4
• Constraints on the properties of macroscopic transport in the Sun from combined lithium and beryllium depletion
• Local heating due to convective overshooting and the solar modelling problem
• Core overshoot constrained by the absence of a solar convective core and some solar-like stars