THE TRANSIT LIGHT CURVE PROJECT. XIII. SIXTEEN TRANSITS OF THE SUPER-EARTH GJ 1214b

We present optical photometry of 16 transits of the super-Earth GJ 1214b, allowing us to refine the system parameters and search for additional planets via transit timing. Starspot-crossing events are detected in two light curves, and the star is found to be variable by a few percent. Hence, in our analysis, special attention is given to systematic errors that result from starspots. The planet-to-star radius ratio is 0.11610 ± 0.00048, subject to a possible upward bias by a few percent due to the unknown spot coverage. Even assuming this bias to be negligible, the mean density of the planet can be either 3.03 ± 0.50 g cm−3 or 1.89 ± 0.33 g cm−3, depending on whether the stellar radius is estimated from evolutionary models, or from an empirical mass–luminosity relation combined with the light curve parameters. One possible resolution is that the orbit is eccentric (e ≈ 0.14), which would favor the higher density, and hence a much thinner atmosphere for the planet. The transit times were found to be periodic within about 15 s, ruling out the existence of any other super-Earths with periods within a factor of two of the known planet.