Herschel PACS and SPIRE Observations of TWA brown dwarf discs

TL;DR

This study uses Herschel observations to investigate brown dwarf discs in the TWA, finding non-detections in far-infrared bands and suggesting low dust mass and grain size, with implications for disc evolution.

Contribution

First Herschel SPIRE and PACS observations of TWA brown dwarf discs, providing upper limits on disc mass and insights into dust grain properties and disc evolution.

Findings

No detection in SPIRE 200-500μm bands.

Estimated disc mass upper limit of 0.1 M_Jup.

Evidence for a warm debris disc around 2M1139.

Abstract

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