The discovery of new embedded sources in the centrally condensed core of the Rho Ophiuchi dark cloud - The formation of a bound cluster

Abstract

New and extensive millimeter-wave and near-infrared observations of the central regions of the ρ Oph cloud are presented. C18O observations have revealed a 1×2 pc ridge which forms the centrally condensed core of the ρ Oph cloud. Extremely large gas and dust column densities prevail in this core with Av = 50-106 mag. A cloud mass of 550 M_sun; is obtained for the area mapped. A completely sampled 2 μm survey to a limiting magnitude of K = +12.0 mag was conducted in a 105 arcmin2 box centered on the region of highest extinction. This survey and subsequent J, H, K, L photometry have resulted in the discovery of a population of 20 objects embedded in the dense, central region of the cloud. These new data and published results enable the authors to discuss the nature of the embedded stellar population and to calculate a star formation efficiency of 34% - 47% for the central core of the cloud. It is suggested that the formation of a bound cluster of predominantly low-luminosity stars with a total mass between 135 and 240 M_sun; is imminent in the ρ Oph cloud.