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

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 ( $v _{\rm e}$ sin $i$ $\lesssim$ 50 km s $^{-1}$ , 7000 K $\lesssim$ $T_{\rm eff}$ $\lesssim$ 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 $T_{\rm eff}$ , which means that Na becomes enriched similarly to Fe in accordance with the degree of Am peculiarity. Regarding lithium, $A$ (Li) mostly ranges between $\sim$ 3 and $\sim$ 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 $T_{\rm eff}$ at $T_{\rm eff}$ $\lesssim$ 8000 K, though several stars exceptionally show distinctly larger depletion. The abundances of potassium also revealed an apparent $T_{\rm eff}$ -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 $\sim$ 5.0 ( $T_{\rm eff}$ $\sim$ 8500 K) to $\sim$ 4.6 ( $T_{\rm eff}$ $\sim$ 7500 K), while those for early-A stars remain near-solar around $\sim$ 5.0–5.2. These observational facts may serve as important constraints for any theory aiming to explain chemical anomalies of A-type stars.