The field Am and ρ Puppis-like stars: Lithium and heavier elements

Abstract

With observations at the Canada-France-Hawaii telescope, photospheric abundances of two evolved field Am stars, τ UMa and HR 178, have been determined for Li, Al, Si, S, Fe, Ni, and Eu by model abundance analysis. Thanks to these new determined abundances and the HIPPARCOS mission, making it possible to better estimate the evolutionary stage of field stars, one can consider the influence of evolution on the abundances of Am stars. No abundance trend for Al, Si, S, and Fe is found during Main Sequence evolution, up to its very last phases. The abundance of Li is, generally, cosmic. Large Li deficiencies may be observed in the very last phases (the ``hook'' region of the H-R diagram) and, too, on the red side of the Am phenomenon region where the ρ Puppis-like stars lie.

Based on observations collected at the Canada-France-Hawaii telescope (Hawaii).