Compositions of halo clusters and the formation of the galactic halo

Abstract

A method of abundance determination based on reddening-independent properties of low-resolution spectral scans is described and applied to 177 red giants in 19 globular clusters, most of which are at galactocentric distances in excess of 8 kpc. The general properties of the halo-cluster system inferred from the abundance results are examined. It is found that the distribution over abundance of the halo globular clusters is independent of galactocentric distance for distances exceeding 8 kpc and that the clusters exhibit differences in the morphology of their color-magnitude diagrams that are uncorrelated with metal abundance. The characteristics of the system of halo clusters are compared with implications of some simple conceptual schemes for the formation of the Galaxy. It is suggested that the halo clusters originated within transient protogalactic fragments that gradually lost gas while undergoing chemical evolution and continued to fall into the Galaxy after the collapse of its central regions had been completed.