Herschel PACS and SPIRE observations of TW Hydrae association brown dwarf disks

Abstract

We present Herschel SPIRE observations of the TW Hydrae association (TWA) brown dwarf disks SSSPM J1102-3431 (SS1102) and 2MASSW J1207334-393254 (2M1207). Both disks are undetected in the SPIRE 200-500 μm bands. We analyzed the archival PACS data and found no detection of either source in the 160 μm band. On the basis of radiative transfer modeling, we estimate an upper limit to the disk mass for both sources of 0.1 MJup. The lack of detection in the SPIRE bands could be due to a paucity of millimeter-sized dust grains in the 2M1207 and SS1102 disks. We also report a non-detection for the brown dwarf 2MASS J1139511-315921 (2M1139) in the PACS 70 and 160 μm bands. We argue for the presence of a warm debris disk around 2M1139, based on an excess emission observed at 24 μm. The mid-infrared colors for 2M1139 are similar to the transition disks in the Taurus and Ophuichus regions. A comparison of the brown dwarf disk masses over a ~1-10 Myr age interval suggests that there is a decline in the disk mass with the age of the system.