Substellar Objects in Nearby Young Clusters (SONYC). II. The brown dwarf population of ρ Ophiuchi

Abstract

SONYC-Substellar Objects in Nearby Young Clusters-is a survey program to investigate the frequency and properties of brown dwarfs (BDs) down to masses below the deuterium-burning limit in nearby star-forming regions. In this second paper, we present results on the ∼1 Myr old cluster ρ Ophiuchi, combining our own deep optical-and near-infrared imaging using Subaru with photometry from the Two Micron All Sky Survey and the Spitzer Space Telescope. Of the candidates selected from iJKs photometry, we have confirmed three-including a new BD with a mass close to the deuterium limit-as likely cluster members through low-resolution infrared spectroscopy. We also identify 27 substellar candidates with mid-infrared excess consistent with disk emission, of which 16 are new and 11 are previously spectroscopically confirmed BDs. The high and variable extinction makes it difficult to obtain the complete substellar population in this region. However, current data suggest that its ratio of low-mass stars to BDs is similar to those reported for several other clusters, though higher than what was found for NGC 1333 in Scholz et al. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.