We report recent ground-based photometry of the transiting super-Earthexoplanet GJ1214b at several wavelengths, including the infrared near 1.25microns (J-band). We observed a J-band transit with the FLAMINGOS infraredimager and the 2.1-meter telescope on Kitt Peak, and we observed severaloptical transits using a 0.5-meter telescope on Kitt Peak and the 0.36-meterUniversidad de Monterrey Observatory telescope. Our high-precision J-bandobservations exploit the brightness of the M-dwarf host star at this infraredwavelength as compared to the optical, as well as being significantly lessaffected by stellar activity and limb darkening. We fit the J-band transit toobtain an independent determination of the planetary and stellar radii. Ourradius for the planet (2.61^+0.30_-0.11 Earth radii) is in excellent agreementwith the discovery value reported by Charbonneau et al. based on optical data.We demonstrate that the planetary radius is insensitive to degeneracies in thefitting process. We use all of our observations to improve the transitephemeris, finding P=1.5804043 +/- 0.0000005 days, and T0=2454964.94390 +/-0.00006 BJD.
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