A Search for L/T Transition Dwarfs With Pan-STARRS1 and WISE: Discovery of Seven Nearby Objects Including Two Candidate Spectroscopic Variables

TL;DR

This study uses combined optical and mid-infrared surveys to identify nearby L/T transition brown dwarfs, discovering seven objects and revealing variability and binary candidates, advancing understanding of these faint, complex objects.

Contribution

First wide-field search combining Pan-STARRS1 and WISE data to find L/T transition brown dwarfs within 25 pc, discovering seven new objects and candidate variables.

Findings

Identified seven nearby L/T transition brown dwarfs.

Detected spectroscopic and photometric variability in some objects.

Found candidate unresolved binary systems.

Abstract

We present initial results from a wide-field (30,000 deg^2) search for L/T transition brown dwarfs within 25 pc using the Pan-STARRS1 and WISE surveys. Previous large-area searches have been incomplete for L/T transition dwarfs, because these objects are faint in optical bands and have near-infrared colors that are difficult to distinguish from background stars. To overcome these obstacles, we have cross-matched the Pan-STARRS1 (optical) and WISE (mid-IR) catalogs to produce a unique multi-wavelength database for finding ultracool dwarfs. As part of our initial discoveries, we have identified seven brown dwarfs in the L/T transition within 9-15 pc of the Sun. The L9.5 dwarf PSO J140.2308+45.6487 and the T1.5 dwarf PSO J307.6784+07.8263 (both independently discovered by Mace et al. 2013) show possible spectroscopic variability at the Y- and J-bands. Two more objects in our sample show evidence of photometric J-band variability, and two others are candidate unresolved binaries based on their spectra. We expect our full search to yield a well-defined, volume-limited sample of L/T transition dwarfs that will include many new targets for study of this complex regime. PSO J307.6784+07.8263 in particular may be an excellent candidate for in-depth study of variability, given its brightness (J = 14.2 mag) and proximity (11 pc).