Light chemical elements in stars: mysteries and unsolved problems

TL;DR

This review discusses the synthesis, primordial abundances, and observational discrepancies of light elements in stars, highlighting unresolved issues in stellar evolution and Big Bang nucleosynthesis.

Contribution

It provides a comprehensive overview of the current understanding and highlights unresolved problems related to light element abundances in stars and the early universe.

Findings

Good agreement between SMBB and observed hydrogen and helium isotopes.

Discrepancy of ~0.5 dex for lithium abundances in old stars.

Abundances depend on initial stellar rotation velocities.

Abstract

The first eight elements of the periodic table are discussed: H, He, Li, Be, B, C, N, and O. They are referred to as key elements, given their important role in stellar evolution. It is noteworthy that all of them were initially synthesized in the Big Bang. The primordial abundances of these elements calculated using the Standard Model of the Big Bang (SMBB) are presented in this review. The good agreement between the SMBB and observations of the primordial abundances of the isotopes of hydrogen and helium, D, 3He, and 4He, is noted, but there is a difference of ~0.5 dex for lithium (the isotope 7Li) between the SMBB and observations of old stars in the galactic halo that has not yet been explained. The abundances of light elements in stellar atmospheres depends on the initial rotation velocity, so the typical rotation velocities of young Main Sequence (MS) stars are examined. Since the data on the adundances of light elements in stars are very extensive, the main emphasis in this review is on several unsolved problems.