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We present three transits of GJ 1214b, observed as part of the Apache PointObservatory Survey of Transit Lightcurves of Exoplanets (APOSTLE). We usedAPOSTLE r-band lightcurves in conjunction with previously gathered data of GJ1214b to re-derive system parameters. By using parameters such as transitduration and ingress/egress length we are able to reduce the degeneraciesbetween parameters in the fitted transit model, which is a preferred conditionfor Markov Chain Monte Carlo techniques typically used to quantifyuncertainties in measured parameters. The joint analysis of thismulti-wavelength dataset confirms earlier estimates of system parametersincluding planetary orbital period, the planet-to-star radius ratio and stellardensity. We fit the photometric spectralenergy distribution of GJ 1214 toderive stellar luminosity, which we then use to derive its absolute mass andradius. From these derived stellar properties and previously published radialvelocity data we were able to refine estimates of the absolute parameters forthe planet GJ 1214b. Transit times derived from our study show no evidence forstrong transit timing variations. Some lightcurves we present show featuresthat we believe are due to stellar activity. During the first night we observeda rise in the out-of-eclipse flux of GJ 1214 with a characteristic fast-riseexponential decay shape commonly associated with stellar flares. On the secondnight we observed a minor brightening during transit, which we believe mighthave been caused by the planet obscuring a star-spot on the stellar disk.

APOSTLE Observations of GJ 1214b: System Parameters and Evidence for Stellar Activity