The large-scale disk fraction of brown dwarfs in the Taurus cloud as measured with Spitzer^*

¹ Laboratoire d'astrophysique de Grenoble, Université Joseph Fourier, CNRS, BP 53, 38041 Grenoble, France e-mail: Jean-Louis.Monin@obs.ujf-grenoble.fr
² Science Center, Mail Code 220-6 Pasadena, CA 91125, USA
³ University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴ Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena, California 91109, USA
⁵ Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
⁶ Caltech, Pasadena, CA 91125, USA
⁷ University of Maryland, 1000 Hilltop Circle Baltimore, MD 21250, USA
⁸ Cal State University at Los Angeles, 5151 State University Drive Los Angeles, CA 90032-8601, USA
⁹ Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland

Received: 16 April 2009
Accepted: 25 January 2010

Abstract

Aims. The brown dwarf (BD) formation process has not yet been completely understood. To shed more light on the differences and similarities between star and BD formation processes, we study and compare the disk fraction among both kinds of objects over a large angular region in the Taurus cloud. In addition, we examine the spatial distribution of stars and BD relative to the underlying molecular gas.

Methods. In this paper, we present new and updated photometry data from the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope on 43 BDs in the Taurus cloud, and recalculate of the BD disk fraction in this region. We also useed recently available CO mm data to study the spatial distribution of stars and BDs relative to the cloud's molecular gas.

Results. We find that the disk fraction among BDs in the Taurus cloud is 41 ± 12%, a value statistically consistent with the one among TTS (58 ± 9%). We find that BDs in transition from a state where they have a disk to a diskless state are rare, and we study one isolated example of a transitional disk with an inner radius of ≈0.1 AU (CFHT BD Tau 12, found via its relatively small mid-IR excess compared to most members of Taurus that have disks. We find that BDs are statistically found in regions of similar molecular gas surface density to those associated with stars. Furthermore, we find that the gas column density distribution is almost identical for stellar and substellar objects with and without disks.