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

Abstract

Abstract 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_{\rm eff}$ range of $ \sim$ 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: $ \langle$ [C$ /$ H]$ \rangle$$ =$$ +$ 0.15 ($ \sigma$$ =$ 0.08), $ \langle$ [O$ /$ H]$ \rangle$$ =$$ +$ 0.22 ($ \sigma$$ =$ 0.14), and $ \langle$ [Fe$ /$ H]$ \rangle$$ =$$ +$ 0.11 ($ \sigma$$ =$ 0.08), suggesting that the primordial abundances are almost retained for these elements. Strictly, however, they show a slightly increasing trend with a decrease in $ T_{\rm eff}$ (typically on the order of $ \sim$ 10$ ^{-4}$ dex K$ ^{-1}$ ); while this might be due to an improper choice of atmospheric parameters, we found it difficult to give a quantitatively reasonable explanation. Regarding Li, we confirmed the well-known $ T_{\rm eff}$-dependent trend in the Li abundance reported so far (a conspicuous Li-trough at 6300 K $ ≲$$ T_{\rm eff}$$ ≲$ 6700 K and a progressive decrease toward a lower $ T_{\rm eff}$ at $ T_{\rm eff}$$ ≲$ 6000 K), which means that the surface Li of Hyades stars is essentially controlled only by $ T_{\rm eff}$ ; other parameters, such as the rotational velocity, are almost irrelevant.