The Transit Light Curve Project. XIII. Sixteen Transits of the Super-Earth GJ 1214b

TL;DR

This study presents detailed optical photometry of 16 transits of the super-Earth GJ 1214b, refining its parameters, analyzing starspot effects, and searching for additional planets through transit timing variations.

Contribution

It provides new transit data, refines system parameters, and investigates starspot effects and potential additional planets around GJ 1214b.

Findings

Transit times are periodic within 15 seconds.

Starspots cause detectable crossing events and variability.

Planet density estimates depend on stellar radius assumptions.

Abstract

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 star spots. 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 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 approximately equal to 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 15s, ruling out the existence of any other super-Earths with periods within a factor-of-two of the known planet.