On the evolutionary status of lambda Bootis stars using Hipparcos data

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Using the Hipparcos data, absolute magnitudes and thus the evolutionary status for the group of lambda Bootis stars were derived. The origin of this small group of non-magnetic, chemically peculiar stars, still remains a matter of debate. Using new evolutionary tracks, an age determination could be provided to distinguish between the two competing theories - the diffusion/mass-loss and the accretion. The results establish the members of this group as objects which are very close to the Main Sequence. This is supported by Pre-Main Sequence evolutionary tracks as well as by observational results. This contradicts 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.