Elemental abundances in the Blanco 1 open cluster

Abstract

High resolution spectroscopy is used to determine the detailed chemical abundances of a group of eight F- and G-type stars in the young open cluster Blanco 1. An average [Fe/H] of +0.04 +/- 0.02 (internal error) +/- 0.04 (external error) is found, considerably lower than a previous spectroscopic estimate for this cluster. The difference is due mainly to our adoption of significantly cooler temperatures which are consistent with both photometric and spectroscopic constraints. Blanco~1 exhibits sub-solar [Ni/Fe] (-0.18 +/- 0.01 +/- 0.01), [Si/Fe] (-0.09$ +/- 0.02 +/- 0.03), [Mg/Fe] (-0.14 +/- 0.02 +/- 0.03) and [Ca/Fe] (-0.09 +/- 0.03 +/- 0.03); ratios which are not observed among nearby field stars. The material from which Blanco 1 formed may not have been well mixed with interstellar matter in the galactic disc, which tallies with its current location about 240pc below the galactic plane. A simultaneous deficit of Ni and alpha elements with respect to Fe is hard to reconcile with most published models of yields from supernovae of types Ia and II. The revised abundances for Blanco 1 indicate that overall radiative opacities in its stars, and hence convective zone properties at a given mass, are similar to those in the Pleiades at approximately the same age. This can explain a previous observation that the Li depletion patterns of G- and K-type stars in the two clusters are indistinguishable. The lower overall metallicity of Blanco 1 now make it less attractive as a target for discovering transiting, short period exoplanets.