1998A&A...338.1073B

In the second of a series of papers on the A stars in open clusters, the Praesepe cluster is investigated; in the first paper, it was the Pleiades. Ten A Praesepe stars were observed with the Canada-France-Hawaii telescope at high spectral resolution and high signal-to-noise ratios. Photospheric abundances of the sample, which has turned out to be composed exclusively with Am stars, have been determined for Li, Al, Si, S, Fe, Ni, and Eu from model atmosphere abundance analysis. The A stars of Praesepe are well advanced in the Main Sequence evolution: several of the observed stars are in the turn-off (and one is a blue straggler). The Li abundance in Am stars is the same as in non-evolved Praesepe F stars on the hot side of the Li dip, and Fe is twice its original value as given by Praesepe F stars. The abundances of the studied elements were found remarkably uniform in the cluster over a large range of T_eff, i.e., for various structure envelopes and evolution. Surface abundances of Li and Fe remain unchanged in Am stars at both ages of the Pleiades and Praesepe clusters. The Li results for the Am stars challenge predictions from evolutionary model envelopes in the framework of a diffusion-dominant description.