A large-area search for low-mass objects in Upper Scorpius. I. The photometric campaign and new brown dwarfs

We present a wide-field photometric survey covering similar to 200 deg(2) toward the Upper Scorpius OB association. Data taken in the R and I bands with the Quest-2 camera on the Palomar 48 inch (1.2m) telescope were combined with the Two Micron All Sky Survey JHK(S) survey and used to select candidate pre-main-sequence stars. Follow-up spectroscopy with the Palomar 200 inch (5.1 m) telescope of 62 candidate late-type members identified 43 stars that have surface gravity signatures consistent with association membership. From the optical/near-infrared photometry and derived spectral types we construct an H-R diagram for the new members and find 30 likely new brown dwarfs, nearly doubling the known substellar population of the Upper Scorpius OB association. Continuation of our spectroscopic campaign should reveal hundreds of new stellar and substellar members.