RECENT TRANSITS OF THE SUPER-EARTH EXOPLANET GJ 1214b

We report recent ground-based photometry of the transiting super-Earth exoplanet GJ 1214b at several wavelengths, including the infrared near 1.25 mu m (J band). We observed a J-band transit with the FLAMINGOS infrared imager and the 2.1 m telescope on Kitt Peak, and we observed several optical transits using a 0.5 m telescope on Kitt Peak and the 0.36 m Universidad de Monterrey Observatory telescope. Our high-precision J-band observations exploit the brightness of the M dwarf host star at this infrared wavelength as compared with the optical and are significantly less affected by stellar activity and limb darkening. We fit the J-band transit to obtain an independent determination of the planetary and stellar radii. Our radius for the planet (2.61(-0.11)(+0.30)R(circle plus)) is in excellent agreement with the discovery value reported by Charbonneau et al. based on optical data. We demonstrate that the planetary radius is insensitive to degeneracies in the fitting process. We use all of our observations to improve the transit ephemeris, finding P = 1.5804043 +/- 0.0000005 days and T(0) = 2454964.94390 +/- 0.00006 BJD.