Research Note

Chemical composition of A and F dwarfs members of the Pleiades open cluster ^*,**

¹ Groupe de Recherche en Astronomie et Astrophysique du Languedoc, UMR 5024, Université Montpellier II, Place Eugène Bataillon, 34095 Montpellier, France e-mail: gebran@graal.univ-montp2.fr
² Laboratoire Universitaire d'Astrophysique de Nice, UMR 6525, Université de Nice–Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 2, France e-mail: Richard.Monier@unice.fr

Received: 18 December 2007
Accepted: 17 February 2008

Abstract

Aims. We derive the abundances of 18 chemical elements for 16 A-dwarf, both normal and chemically-peculiar, and 5 F-dwarf members of the Pleiades open cluster to place constraints on evolutionary models.

Methods. Abundances and rotational and microturbulent velocities were derived by fitting synthetic spectra to high-resolution (R ~ 42 000 and R ~ 75 000) observations of high signal-to-noise ratio (S/N).

Results. The abundances exhibit correlation with neither the effective temperature nor the projected rotational velocity. Interestingly, A stars exhibit larger star-to-star variations in C, Sc, Ti, V, Cr, Mn, Sr, Y, Zr and Ba, than F stars. F stars have solar abundances of almost all elements. In A stars, the abundances of Si, Ti and Cr are correlated with that of Fe, and the [X/Fe] ratios are solar for these three elements. The derived abundances are compared with the predictions of evolutionary models for the age of Pleiades (100 Myr). For F stars, small predicted underabundances of light elements and overabundances of Cr, Fe and Ni are confirmed by our findings. For A stars, the predicted overabundances in iron-peak elements are confirmed for a few stars only.

Conclusions. The large scatter in the abundances of A stars, discovered previously in the Hyades, Coma Berenices, UMa group, and in field stars, appears to be a characteristic property of dwarf A stars. Hydrodynamical processes competing with radiative diffusion in the radiative zone of A dwarfs, could account for the scatter in abundances that we determine.