Differences in chemical composition among main sequence stars within a given cluster are probably due to differences in their masses and other effects such as radiative diffusion, magnetic field, rotation, mixing mechanisms, mass loss, accretion and
multiplicity. The early type main-sequence members of open clusters of different ages allow to study the competition between radiative diffusion and mixing mechanisms. We have analysed low and high resolution spectra covering the spectral range 4500 - 5840 Angs. of late B, A, and F type members of the open Cluster M6 (age about 100 Myr). The spectra were obtained using the FLAMES/GIRAFFE spectrograph mounted at UT2, the 8 meter class VLT telescope. The effective temperatures, surface gravities and microturbulent velocities of the stars were derived using both photometric and spectral methods. We have also performed a chemical abundance analysis using synthetic spectra. The abundances of the elements were determined for C, O, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Y, Ba. The star-to-star variations in elemental abundances among the members of the open cluster M6 were discussed.
Context. The study of rotational velocity distributions for normal stars requires an accurate spectral characterization of the objects in order to avoid polluting the results with undetected binary or peculiar stars. This piece of information is a ke
y issue in the understanding of the link between rotation and the presence of chemical peculiarities. Aims. A sample of 47 low v sin i A0-A1 stars (v sin i < 65km/s), initially selected as main-sequence normal stars, are investigated with high-resolution and high signal-to-noise spectroscopic data. The aim is to detect spectroscopic binaries and chemically peculiar stars, and eventually establish a list of confirmed normal stars. Methods. A detailed abundance analysis and spectral synthesis is performed to derive abundances for 14 chemical species. A hierarchical classification, taking measurement errors into account, is applied to the abundance space and splits the sample into two different groups, identified as the chemically peculiar stars and the normal stars. Results. We show that about one third of the sample is actually composed of spectroscopic binaries (12 double-lined and five single-lined spectroscopic binaries). The hierarchical classification breaks down the remaining sample into 13 chemically peculiar stars (or uncertain) and 17 normal stars.
