Chemical abundances of A and F-type stars: the Hyades open cluster

Abundances of 11 chemical elements have been determined for 29 F and 19 A dwarfs (“normal” and chemically peculiar with apparent rotational velocities ranging from 11 to 237 km.s−1) members of the Hyades cluster using Takeda’s (1995) iterative procedure well suited for fast rotators. High quality spectra of high to moderate resolution have been synthesized to derive the apparent rotational velocities, microturbulent velocities and abundances of C, O, Na, Mg, Si, Ca, Sc, Fe, Ni, Y and Ba. For the F stars, the found abundances are compared to the predictions of Turcotte et al.’s (1998) evolutionary models for the age of the Hyades. We fail to find the expected underabundances for light elements nor the overabundances for the ironpeak elements for stars having effective temperatures greater than 6500 K. This suggests that diffusion alone cannot account for the derived abundances: other transport processes which counteract diffusion are probably at play. For the A stars, abundances of Na, Mg, Si, Ca, Fe, Ni and Ba are anticorrelated (correlated for O) with the apparent equatorial velocities for ve sin i higher than ∼ 100 km.s−1. Below this value, we find no correlation in agreement with the predictions of Charbonneau & Michaud (1991) except possibly for the abundance of Ni which might be anticorrelated with ve sin i. The fastest rotators (ve sin i ≥ 150 km.s−1) are strongly depletted in Mg, Si, Ca, Fe, Ni and Ba (between −0.3 dex and −0.94 dex) while their O abundance is normal.