A combined study of thermohaline mixing and envelope overshooting with PARSEC: Calibration to NGC 6397 and M4

Abstract

Thermohaline mixing is one of the main processes in low-mass red giant stars that affect the transport of chemicals and, thus, the surface abundances along the evolution. The interplay of thermohaline mixing with other processes, such as the downward overshooting from the convective envelope, should be carefully investigated. This study aims to understand the combined effects of thermohaline mixing and envelope overshooting. After implementing the thermohaline mixing process in the \textsc{parsec} stellar evolutionary code, we compute tracks and isochrones (with \textsc{trilegal} code) and compare them with observational data. To constrain the efficiencies of both processes, we perform a detailed modelling that is suitable for globular clusters NGC 6397 and M4. Our results indicate that an envelope overshooting efficiency parameter, ${\Lambda }_{\mathrm{e}}=0.6$, and a thermohaline efficiency parameter, ${\alpha }_{\mathrm{th}}=50$, are necessary to reproduce the RGB bump magnitudes and lithium abundances observed in these clusters. We find that both envelope overshooting and thermohaline mixing have a significant impact on the variation of ${}^7$Li abundances. Additionally, we also explore the effects of adopting solar-scaled or $\alpha$-enhanced mixtures on our models. The ${}^{12}$C and the ${}^{12}$C/${}^{13}$C ratio are also effective indicators to probe extra mixing in RGB stars. Although, their usefulness is currently limited by the lack of precise and accurate C-isotopes abundances.

14 pages, 14 figures

References in corpus (33)

• Improving PARSEC models for very low mass stars
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• The White Dwarf Cooling Sequence of NGC6397
• PARSEC V2.0: Stellar tracks and isochrones of low and intermediate mass stars with rotation
• Standard big bang nucleosynthesis and primordial CNO Abundances after Planck
• YBC, a stellar bolometric corrections database with variable extinction coefficients: an application to PARSEC isochrones
• Mass loss on the red giant branch: the value and metallicity dependence of Reimers' η in globular clusters
• Mixing by overshooting and rotation in intermediate mass stars
• Carbon star formation as seen through the non-monotonic initial-final mass relation
• 3D NLTE spectral line formation of lithium in late-type stars
• Rubidium and lead abundances in giant stars of the globular clusters M4 and M5
• Inhibition of thermohaline mixing by a magnetic field in Ap star descendants: Implications for the Galactic evolution of 3He
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• Lithium depletion and angular momentum transport in solar-type stars
• Multiple stellar populations in NGC 1866. New clues from Cepheids and Colour-Magnitude Diagram
• Light element abundances in carbon-enhanced metal-poor stars
• Integrated Mass Loss of Evolved Stars in M4 using Asteroseismology
• Evolutionary tracks, ejecta, and ionizing photons from intermediate-mass to very massive stars with PARSEC
• Asteroseismology of the multiple stellar populations in the Globular Cluster M4
• Sodium abundances of AGB and RGB stars in Galactic globular clusters II. Analysis and results of NGC 104, NGC 6121 and NGC 6809
• A phenomenological modification of thermohaline mixing in globular cluster red giants
• Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio
• HST observations of the globular cluster NGC 6402 (M14) and its peculiar multiple populations
• Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)
• The Impact of the Third Dredge-up and Mass Loss in Shaping the Initial-Final Mass Relation of White Dwarfs
• Lithium in the lower red giant branch of 5 Galactic globular clusters
• He-enriched STAREVOL models for globular cluster multiple populations. Self-consistent isochrones from ZAMS to the TP-AGB phase

Cited by in corpus (4)

• Explaining the ${}^{12}\text{C}{/}^{13}\text{C}$ ratio in the Galactic halo: the contribution from shell mergers in primordial massive stars
• PARSEC V2.0: Rotating tracks and isochrones for seven addtional metallicities in the range Z=0.0001-0.03
• Lithium evolution in the Galactic thin disc from Main-Sequence and early Red-Giant-Branch stars
• Gaia-Sausage-Enceladus: Lithium evolution from early red-giant-branch and main-sequence stars