Photometric Variability at the L/T Dwarf Boundary

We have monitored the photometric variability of nine field L and T browndwarfs for 10 nights during the course of one month with the Palomar 60 inchTelescope Near-Infrared Camera. Results of statistical analyses indicate thatat least three of the nine targets show significant evidence for variability,and three more are possibly variable. Fractional deviations from the medianflux vary from 5% to 25%. Two of the variable targets, 2MASS 0030-14 (L7) andSDSS 0151+12 (T1), have marginally significant peaks in their periodograms. Thephased light curves show evidence for periodic behavior on timescales of 1.5hours and 3.0 hours respectively. No significant correlations betweenvariability amplitude and spectral type or (J-K_s) color are found. While it isclear that variability exists in objects near the L/T dwarf boundary, we findno evidence that variability near the L/T boundary is more likely than it isfor early L dwarfs.Comment: 29 pages including 11 figures, 4 tables; accepted for publication in A