Using the Gemini infrared camera on the 3?m Shane telescope at Lick Observatory, we have searched for broadband J and K' photometric variability for a sample of 15 L- and T-type brown dwarfs, including 7 suspected spectral binaries. Four of the dwarfs—2MASS?J0939–2448, 2MASS?J1416+1348A, 2MASS?J1711+2232, and 2MASS?J2139+0220—exhibit statistically significant variations over timescales ranging from ~0.5?hr to 6?days. Our detection of variability in 2MASS?J2139+0220 confirms that reported by Radigan et?al., and periodogram and phase dispersion minimization analysis also confirms a variability period of approximately 7.6 ± 0.2?hr. Remarkably, two of the four variables are known or candidate binary systems, including 2MASS?J2139+0220, for which we find only marginal evidence of radial velocity variation over the course of a year. This result suggests that some spectral binary candidates may appear as such due to the blending of cloudy and non-cloudy regions in a single "patchy" atmosphere. Our results are consistent with an overall variability fraction of 35% ± 5%, with no clear evidence of greater variability among brown dwarfs at the L dwarf/T dwarf transition.
展开▼
