Lithium, Carbon, and Oxygen Abundances of Hyades F-G Type Stars

In an attempt to carry out a systematic study on the behavior of the photospheric abundances of Li, C, and O (along with Fe) for Hyades main-sequence stars in the T-eff range of similar to 5000-7000 K, we conducted an extensive spectrum-synthesis analysis applied to four spectral regions (comprising lines of Fe-group elements, Li I 6708 line, C I 7111-7119 lines, and O I 6156-8 lines), based on the high-dispersion spectra of 68 selected F-G type stars belonging to this cluster. The abundances of C and O turned out to be fairly uniform in a marginally supersolar level, such as like the case of Fe: <[C/H]> = +0.15 (sigma = 0.08), <[O/H]> = +0.22 (sigma = 0.14), and <[Fe/H])> = +0.11 (sigma = 0.08), suggesting that the primordial abundances are almost retained for these elements. Strictly, however, they show a slightly increasing trend with a decrease in T-eff (typically on the order of similar to 10(-4) dex K-1); while this might be due to an improper choice of atmospheric parameters, we found it difficult to give a quantitatively reasonable explanation. Regarding Li, we confirmed the well-known T-eff-dependent trend in the Li abundance reported so far (a conspicuous Li-trough at 6300 K less than or similar to T-eff less than or similar to 6700 K and a progressive decrease toward a lower T-eff at T-eff less than or similar to 6000K), which means that the surface Li of Hyades stars is essentially controlled only by T-eff; other parameters, such as the rotational velocity, are almost irrelevant.