Lithium depletion and angular momentum transport in F-type and G-type stars in Galactic open clusters

Abstract

Context. Open clusters provide unambiguous clues to understand the evolution of 7Li at the surface of low-mass stars and its possible correlation with stellar rotation, which is a challenge for both stellar hydrodynamics and Galactic chemical evolution. Aims. We aim to quantify the efficiency of the transport processes for both angular momentum and chemicals that are required to explain simultaneously the observed behaviour of surface 7Li (and 9Be) and rotation as well as the internal rotation profiles inferred from helio- and asteroseismology in F- and G-type main sequence stars. Methods. We apply the model for the transport of angular momentum and chemicals that we tailored in a previous work for solar-type stars to an extended range of initial masses and metallicities corresponding to F- an G-type stars in a sample of 20 Galactic open clusters. We evaluate its ability to explain the 7Li, 9Be, and rotation periods observations. This model includes atomic diffusion, rotation-induced processes (for which we tested different prescriptions for shear turbulence), penetrative convection with a rotational dependence, parametric viscosity and turbulence, and magnetic braking. Results. Over the entire range of masses, metallicities, and ages explored, we reproduce the evolution of the surface rotation rates and predict, for the first time, the observed anti-correlation between the surface rotation rate and 7Li depletion as a consequence of the penetrative convection prescription. The 7Li behaviour and its evolution with time is well reproduced for G-type stars. However, the ability of the model to reproduce the so-called 7Li dip centred around ∼6600 K strongly depends on the adopted prescriptions for shear turbulence. It also requires a stellar mass dependence for the parametric viscosity adopted for the transport of angular momentum, similar to the behaviour predicted for the generation and luminosity of internal gravity waves generated by stellar convective envelopes. Finally, the model predicts internal rotation profiles in good agreement with asteroseismic constraints in main sequence stars. Conclusions. We provide an efficient way to model G-type stars of different ages and metallicities successfully. However, the 7Li and 9Be dip constraints urgently call for further hydrodynamical studies to better model turbulence in stars, and for the exploration of physical processes such as tachocline mixing for the transport of chemicals and internal gravity waves for the transport of angular momentum. Finally, additional data for the internal rotation and for 9Be in main sequence low-mass stars are definitively needed.

Metallicity and age effects on lithium depletion in solar analogues

“…More metallic stars with larger conv ectiv e masses (larger markers) present lower Li content. This depletion according to metallicity is qualitatively in line with the works of Castro et al ( 2008 ) and Dumont et al ( 2021b ).…”

“…Qualitatively, our strong anticorrelation with age is in line with non-standard models of Li depletion (Charbonnel & Talon 2005 ;Nascimento et al 2009 ;Xiong & Deng 2009 ;Denissenkov 2010 ;Andr ássy & Spruit 2015 ), as those models are constructed to reproduce the low Li observed in the solar photosphere. The strong anticorrelation with metallicity observed in our sample is also within the predictions of non-standard models, due to the deepening of the convection zone (Castro et al 2008 ;Dumont et al 2021b ). Ho we ver, there is a lack of detailed predictions of Li depletion both with age and metallicity, preventing more detailed comparisons with our results.…”

Follow-up of Young Stars Identified with BANYAN Σ: New Low-mass Members of Nearby Moving Groups

“…Nondetections are not displayed; some error bars are too small to be visible. (Dumont et al 2021), the lithium dip has been observed in M35, the Hyades, open clusters a few billion years old, and even field stars (Steinhauer & Deliyannis 2004). However, it has not been found in the Pleiades (Soderblom et al 1993).…”

Origin of the elements

“…Presently predicted Li abundances are a factor of 3 beyond the Spite plateau. Certainly stellar effects, depleting Li, have to be considered (Dumont et al 2021) and there exist clear indications that this is the case (Korn 2020;Fields and Olive 2022), but physics beyond the standard model might also be required on the theory side, for details see the white paper by Grohs et al (2019).…”