Poster Abstracts

Name/Affiliation:  Koraljka Muzic (European Southern Observatory (ESO), Chile)

Title:  Where Do Brown Dwarfs Come From? Insights From The SONYC Survey

The origin of the objects populating the substellar tail of the Initial Mass Function (IMF) is one of the major unsolved questions in star formation. A fundamental prerequisite to test the various competing theories is to establish a census of brown dwarfs (BDs) in nearby young star forming regions. Such a census allows us to probe the shape of the IMF, and yields large and homogeneous samples required to study disks, multiplicity, and accretion in the substellar regime. This is the goal of our SONYC (Substellar Objects in Nearby Young Clusters) survey program. SONYC is based on deep imaging, combined with proper motions, and followed up with extensive spectroscopic campaigns that have resulted in more than 700 spectra of candidate objects in NGC1333, Rho-Ophiuchi, Chamaeleon-I, Upper-Sco, and Lupus-3. We have identified and characterized more than 60 new young BDs, including a handful with masses close to, or below the Deuterium-burning limit. Through SONYC and similar surveys, the substellar IMF is now well characterized down to 5-10 Mjup, with the ratio of stars to BDs ranging between 2 and 5. Furthermore, our results suggest that free-floating objects with planetary masses are only a small fraction of al lBDs. We also see tentative evidence for regional differences in the efficiency of BD formation. For the first time we are now starting to explore the substellar IMF in an environment with very high stellar density and many OB stars, based on an imaging study of the young massive cluster RCW38. The comparison with the low-mass star forming regions within 500 pc provides an excellent test for variations of the IMF in the substellar regime caused by environment. In this contribution, I will give an overview of SONYC's findings, present new results in RCW38, and outline the impact on our understanding of star formation.