The chemical composition of nearby young associations: s-process element
  abundances in AB Doradus, Carina-Near, and Ursa Major
  Recently, several studies have shown that young, open clusters are
characterised by a considerable over-abundance in their barium content. In
particular, D'Orazi et al. (2009) reported that in some younger clusters
[Ba/Fe] can reach values as high as ~0.6 dex. The work also identified the
presence of an anti-correlation between [Ba/Fe] and cluster age. For clusters
in the age range ~4.5 Gyr-500 Myr, this is best explained by assuming a higher
contribution from low-mass asymptotic giant branch stars to the Galactic
chemical enrichment. The purpose of this work is to investigate the ubiquity of
the barium over-abundance in young stellar clusters. We analysed
high-resolution spectroscopic data, focusing on the s-process elemental
abundance for three nearby young associations, i.e. AB Doradus, Carina-Near,
and Ursa Major. The clusters have been chosen such that their age spread would
complement the D'Orazi et al. (2009) study. We find that while the s-process
elements Y, Zr, La, and Ce exhibit solar ratios in all three associations, Ba
is over-abundant by ~0.2 dex. Current theoretical models can not reproduce this
abundance pattern, thus we investigate whether this unusually large Ba content
might be related to chromospheric effects. Although no correlation between
[Ba/Fe] and several activity indicators seems to be present, we conclude that
different effects could be at work which may (directly or indirectly) be
related to the presence of hot stellar chromospheres.
