On the evolutionary status of λ Bootis stars using HIPPARCOS data.

Abstract

We have used the Hipparcos data to derive absolute magnitudes and thus the evolutionary status for the group of λ Bootis stars. The origin for this small group of nonmagnetic, chemically peculiar stars, still remains a matter of debate. Using new evolutionary tracks, we are able to provide an age determination to distinguish between the two proposed theories - the diffusion/mass-loss and the accretion theory. Our results establish the member of this group as objects which are very close to the Main Sequence. This is also supported by Pre-Main Sequence evolutionary tracks as well as by observational results. We therefore contradict prior conclusions that most of these stars are in the middle of their Main Sequence lifetime. The new results strongly support the predictions of the accretion theory.