A deep 70 micrometer study of cold circumstellar disks in rho Oph: down below the brown dwarf limit

Most stars form in clusters, and the nearest example of an embedded young cluster is the one in the L1688 cloud of the rho Ophiuchi region. It is one of the best explored starforming region, an intermediate exemplar between the sparse regions of Taurus and the rich, massive cluster of Orion. With the aim of detecting brown dwarfs (BDs) with masses down to a few Jupiter masses, our group conducted a major preparatory observational project in L1688, where we have spectroscopically confirmed 28 new brown dwarfs. The new discoveries increased the known population of BDs by a factor of 3 and provided the so far most complete census of the (sub)stellar population of the rho Oph cluster. Here we propose a comprehensive study of the cold circumstellar disks of the premain sequence population, with particular emphasis on the very low mass objects and BDs. Utilizing the unprecedented farinfrared sensitivity and spatial resolution of Herschel, we will obtain deep 70 and 160 micrometer maps of a 1.6 deg^2 area centred on the L1688 cloud, covering also the location of the 28 new brown dwarfs. We intend to (1) study the most complete population of brown dwarf disks in rho Oph; (2) analyse disk properties and evolution across the stellar mass range; and (3) characterize the protostar population and its luminosity function. Our programme provides the opportunity to characterize the complete, homogeneous population of disks around both young BDs and lowmass stars in the benchmark protocluster of rho Oph. The produced deep 70 micrometer map of the region will also have a very high legacy value, since flux densities for sources to be discovered (e.g. new confirmed BDs) can be extracted in the future. The total Herschel observing time for the proposed programme is 12.8 h. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]