The Structure of the Super-Star Clusters in NGC 1569 from Hubble Space Telescope WFPC2 Images

Abstract

We present high-resolution observations of the super-star clusters in the nearby irregular galaxy NGC 1569, obtained with the WFPC2 on board the Hubble Space Telescope. Our analysis shows that the brightest of these clusters, NGC 1569A, results from the superposition of two clusters with an angular separation of ~0.2". Recent ground-based spectroscopy revealed that both red supergiant and Wolf-Rayet stars are associated with NGC 1569A. According to current evolutionary models, this finding requires the coexistence of two noncoeval stellar populations within the same cluster. Our discovery that NGC 1569A is double simplifies the interpretation, since red supergiants and Wolf-Rayet stars may belong to different clusters. We derive for the three clusters half-light radii of ~1.6-1.8 pc, smaller than indicated by previous HST observations. The size, mass, and luminosity of the brightest of these superclusters confirm that these objects could be young globulars, reinforcing previous conclusions.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA for NASA under contract NAS5-26555.