Matter accretion in metal-poor stars down to extremely metal-poor stars and the lithium problem

Abstract

The formation and evolution of light elements in the Universe act as important cosmological constraints. It has long been assumed that the oldest stars of the Galaxy display the primordial Li abundance in their outer layers, although studies of stellar physics have proven that this abundance must have decreased with time. The primordial Li abundance deduced from the observations of the cosmic background is larger than the maximum observed in these stars. Recent observations have given evidence of a large Li abundance dispersion in very metal-poor stars. Many of these stars are carbon-rich, the carbon-enhanced metal-poor (CEMP) stars. We address the general question of the observed abundances in metal-poor stars and we focus our study on the case of CEMP-s stars. We study how the accretion of the wind of stellar companions, especially asymptotic giant branch stars, modifies the element abundances of metal-poor stars and, in particular Li, taking into account the stellar structure and the hydrodynamic processes that take place after accretion. We compare the results with the observations of Li and heavier elements in these old stars on the main sequence. We use the Montréal/Montpellier stellar evolution code, which includes atomic diffusion and thermohaline convection, to compute the internal structure of the proto-CEMP-s stars and their evolution, from [Fe/H]=-2.31 down to [Fe/H]=-5.45. We study a number of cases that vary according to the masses of the stars, their ages, metallicities, and the distances to their respective companions. We show that the observations of Li dispersion that is associated (or not) with carbon enrichment are well accounted for in terms of accretion on to the metal-poor stars of the winds of stellar companions, with accreted masses smaller than those considered in previous studies. The derived primordial value is in accordance with the cosmological results.

14 pages, 8 figures, accepted for publication in A&A

References in corpus (22)

• Binary interaction dominates the evolution of massive stars
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• A probable stellar solution to the cosmological lithium discrepancy
• First stars VII. Lithium in extremely metal poor dwarfs
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• The Hamburg/ESO R-process Enhanced Star survey (HERES) III. HE 0338-3945 and the formation of the r+s stars
• Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics
• Thermohaline mixing and gravitational settling in carbon-enhanced metal-poor stars
• CS22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star
• Primordial nucleosynthesis
• Lithium abundances in CEMP stars
• Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. I. Detailed analysis of 15 binary stars with known orbital periods
• Inhibition of thermohaline mixing by a magnetic field in Ap star descendants: Implications for the Galactic evolution of 3He
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• Light element abundances in carbon-enhanced metal-poor stars
• Enhanced mixing in magnetized fingering convection, and implications for RGB stars
• AGB dust and gas ejecta in extremely metal-poor environments
• Microscopic diffusion of partly ionized metals in the Sun and metal-poor stars
• Fingering convection induced by atomic diffusion in stars: 3D numerical computations and applications to stellar models
• The interaction between shear and fingering (thermohaline) convection
• Chemical abundances of giant stars in the Crater stellar system
• Rotational mixing in carbon-enhanced metal-poor stars with s-process enrichment

Cited by in corpus (9)

• Probing Physics Beyond the Standard Model: Limits from BBN and the CMB Independently and Combined
• Stellar winds and metal enrichment from fast-rotating Population III stars
• Long-Term Lithium Abundance Signatures following Planetary Engulfment
• Primordial nucleosynthesis with varying fundamental constants: Solutions to the Lithium problem and the Deuterium discrepancy
• Discovery of a thin lithium plateau among metal-poor red giant branch stars
• Constraints on the properties of macroscopic transport in the Sun from combined lithium and beryllium depletion
• The cosmological lithium problem
• A catalogue of asteroseismically calibrated ages for APOGEE DR17. The predictions of a CatBoost machine learning model based on the [Mg/Ce] chemical clock and other stellar parameters
• New nickel opacities and their impact on stellar models