A Search for Substellar Companions to the Two Nearest Brown Dwarf Systems

TL;DR

This study searched for substellar companions around the two nearest brown dwarf systems using multi-epoch mid-infrared and near-infrared adaptive optics imaging, finding no new companions and setting mass detection limits.

Contribution

First comprehensive search for companions to the closest brown dwarf systems using combined Spitzer and VLT observations, establishing new detection limits.

Findings

No new companions detected in either system.

Sensitivity to companions with masses >=1 Jupiter mass at wide separations.

Adaptive optics imaging sensitive to companions >=7 Jupiter masses at smaller separations.

Abstract

WISE J104915.57-531906.1 A+B and WISE J085510.83-071442.5 were recently discovered as the third and fourth closest known systems to the Sun, respectively (2.0 and 2.3 pc). The former consists of a L8+T0.5 binary and the latter is a probable Y dwarf and is the coldest known brown dwarf (~250 K). We present a search for common proper motion companions to these brown dwarfs using multi-epoch mid-infrared images from the Spitzer Space Telescope. We have also obtained near-infrared adaptive optics images of WISE J104915.57-531906.1 A+B with the Very Large Telescope to search for companions at smaller separations than reached by Spitzer. No new companions are detected in either system. At projected separations of 25-420" (50-840 AU) for WISE J104915.57-531906.1 A+B and 4-420" (9-970 AU) for WISE J085510.83-071442.5, the Spitzer images are sensitive to companions with M_4.5<21.6 and 21.9, respectively, which correspond to masses of >=1 M_Jup for ages of >=1 Gyr and temperatures of >=150 K. The detection limit in the adaptive optics images of WISE J104915.57-531906.1 A+B is dH~10 at 3-15" (6-30 AU), or >=7 M_Jup for >=1 Gyr.