Chemical compositions of giants in the Hyades and Sirius superclusters

Abstract

An abundance analysis for 20 elements from Na to Eu is reported for 34 K giants from the Hyades supercluster and for 22 K giants from the Sirius supercluster. Observed giants were identified as highly probable members of their respective superclusters by Famaey et al. Three giants each from the Hyades and Praesepe open clusters were similarly observed and analysed. Each supercluster shows a range in metallicity: −0.20 ≤ [Fe/H] ≤ +0.25 for the Hyades supercluster and −0.22 ≤ [Fe/H] ≤ +0.15 for the Sirius supercluster with the metal-rich tail of the metallicity distribution of the Hyades supercluster extending beyond that of the Sirius supercluster and spanning the metallicity of the Hyades and Praesepe cluster giants. Relative elemental abundances [El/Fe] across the supercluster giants are representative of the Galactic thin disc as determined from giants in open clusters analysed in a similar way to our approach. Judged by metallicity and age, very few and likely none of the giants in these superclusters originated in an open cluster: the pairings include the Hyades supercluster with the Hyades – Praesepe open clusters and the Sirius supercluster with the U Ma open cluster. Literature on main-sequence stars attributed to the two superclusters and the possible relation to the associated open cluster is reviewed. It is suggested that the Hyades supercluster’s main-sequence population contains few stars from the two associated open clusters. As suggested by some previous investigations, the Sirius supercluster, when tightly defined kinematically, appears to be well populated by stars shed by the U Ma open cluster.