Stellar Mixing and the Primordial Lithium Abundance

TL;DR

This study compares lithium abundances in halo stars with theoretical models including rotational mixing, finding that observed data supports some depletion consistent with primordial lithium predictions, challenging models with no depletion.

Contribution

It provides an analysis of lithium abundance data in halo stars in relation to rotational mixing models, highlighting the importance of observational measurement differences and chemical evolution effects.

Findings

Data supports lithium depletion consistent with rotational mixing models.

Differences in equivalent width measurements affect conclusions on lithium dispersion.

Observed lithium abundances align with Big Bang predictions when depletion is considered.

Abstract

We compare the properties of recent samples of the lithium abundances in halo stars to one another and to the predictions of theoretical models including rotational mixing, and we examine the data for trends with metal abundance. We find from a KS test that in the absence of any correction for chemical evolution, the Ryan, Norris, & Beers (1999} sample is fully consistent with mild rotational mixing induced depletion and, therefore, with an initial lithium abundance higher than the observed value. Tests for outliers depend sensitively on the threshold for defining their presence, but we find a 10$--$45% probability that the RNB sample is drawn from the rotationally mixed models with a 0.2 dex median depletion (with lower probabilities corresponding to higher depletion factors). When chemical evolution trends (Li/H versus Fe/H) are treated in the linear plane we find that the dispersion in the RNB sample is not explained by chemical evolution; the inferred bounds on lithium depletion from rotational mixing are similar to those derived from models without chemical evolution. We find that differences in the equivalent width measurements are primarily responsible for different observational conclusions concerning the lithium dispersion in halo stars. The standard Big Bang Nucleosynthesis predicted lithium abundance which corresponds to the deuterium abundance inferred from observations of high-redshift, low-metallicity QSO absorbers requires halo star lithium depletion in an amount consistent with that from our models of rotational mixing, but inconsistent with no depletion.