1. Introduction
2. Observations
2.1. GTC OSIRIS Instrument Setup
2.2. Observing Log
2.3. Reduction
3. Analysis
3.1. Transit Light Curve Fits
3.2. Noise Estimation
4. Discussion
4.1. Atmospheric Signatures of Potassium
4.2. Limits on Stellar Activity
4.3. Transit Timing Studies
5. Conclusions