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_e sin i ≲ 50 km s^-1, 7000 K &lesssim T_eff &lessim 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_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 ∼ 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 T_eff at T_eff &lesssim 8000 K, though several stars exceptionally show distinctly larger depletion. The abundances of potassium also revealed an apparent T_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 ∼ 5.0 (T_eff ∼ 8500 K) to ∼ 4.6 (T_eff ∼ 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.