APOSTLE transits of XO-2 system

We present measurements that confirm previous estimates of system parameters like the normalized semi-major axis (a/R_*_), stellar density ({rho}_*_), impact parameter (b), and orbital inclination (i_orb_). Our errors on system parameters like a/R_*_ and {rho}_*_ have improved by ~40% compared to previous best ground-based measurements.

Our study of the transit times show no evidence for transit timing variations (TTVs) and we are able to rule out co-planar companions with masses >=0.20M_{Earth}_ in low order mean motion resonance with XO-2b. We also explored the stability of the XO-2 system given various orbital configurations of a hypothetical planet near the 2:1 mean motion resonance. We find that a wide range of orbits (including Earth-mass perturbers) are both dynamically stable and produce observable TTVs.