Investigating Brown Dwarf Variability at 3.4 & 4.6 Microns with AllWISE Multi-Epoch Photometry

Abstract

Multi-epoch photometry from AllWISE provides the opportunity to investigate variability at 3.4 and 4.6 microns for most known brown dwarfs. WISE observed the same patch of sky repeatedly and within a day's time, roughly 12 observations were obtained on a given patch of sky; then, another 12 were obtained roughly six months later when that patch of sky was again in view. For most of the sky, AllWISE contains two separate epochs of about a dozen observations each, although ~30% of the sky has three such epochs available in AllWISE. With the AllWISE multi-epoch photometry of ~1500 known M, L, T, and Y dwarfs, I computed the Stetson J Index and quantified variability as a function of spectral type. I found that the average single-exposure photometric uncertainty in AllWISE (~0.2 magnitudes) is too large to robustly identify flux variability smaller than ~20%. However, multi-epoch photometry from AllWISE remains a useful resource in cases where flux variability is known to be present with large amplitudes, or for bright nearby objects with lower photometric uncertainties.

Proceedings of the 18th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Eds G. van Belle & H. Harris, 16 pages, 8 figures