Lithium, Sodium, and Potassium Abundances in Sharp-Lined A-Type Stars

TL;DR

This study investigates the abundances of lithium, sodium, and potassium in sharp-lined A-type stars, revealing correlations with metallicity and temperature that inform theories of chemical peculiarities.

Contribution

It provides the first detailed non-LTE abundance analysis of alkali elements in a sample of sharp-lined A-type stars, highlighting their relation to Am peculiarities and stellar parameters.

Findings

Na abundance scales with Fe abundance regardless of Teff.

Li abundance mostly near solar, with some depletion at lower Teff.

K abundance shows Teff-dependent trend, decreasing in late-A stars.

Abstract

The abundances of alkali elements (Li, Na, and K) were determined from the Li I 6708, Na I 5682/5688, and K I 7699 lines by taking into account the non-LTE effect for 24 sharp-lined A-type stars v sin i < 50 km/s, 7000 K < Teff <10000 K, many showing Am peculiarities to different degrees), based on high-dispersion and high-S/N spectral data secured at BOAO (Korea) and OAO (Japan). We found a significant trend that A(Na) tightly scales with A(Fe) irrespective of Teff, which means that Na becomes enriched similarly to Fe in accordance with the degree of Am peculiarity. Regarding lithium, A(Li) mostly ranges between ~3 and ~3.5 (i.e., almost the same as or slightly less than the solar system abundance of 3.3) with a weak decreasing tendency with a lowering of Teff at Teff < 8000 K, though several stars exceptionally show distinctly larger depletion. The abundances of potassium also revealed an apparent Teff-dependence in the sense that A(K) in late-A stars tends to be mildly subsolar (possibly with a weak anti-correlation with A(Fe)) systematically decreasing from ~5.0 (Teff ~ 8500 K) to ~4.6 (Teff ~ 7500 K), while those for early-A stars remain near-solar around ~5.0-5.2. These observational facts may serve as important constraints for any theory aiming to explain chemical anomalies of A-type stars.