Constraining Exoplanetary Physical and Orbital Parameters with TAR-Fit

Photodynamical modeling of star systems using available Kepler transit photometry and radial velocity observations has provided unique constraints on physical parameters of stars, providing insight into stellar structure and formation models (Carter et al. 2011). The inclusion of forthcoming astrometric measurements from the ongoing ESA Gaia mission will help improve the accuracy and precision of these models by constraining the orbital motion of stars around the system barycenter in the plane of the sky. Here I use the self-developed Transit, Astrometry, and RV Fitter (TAR-Fit) photodynamical model to update the parameters of the KOI-126 system, first reported in Carter et al. (2011). KOI-126 is a triply-eclipsing stellar system composed of a low-mass binary in orbit around a solar-type star. I use a Bulirsch-Stoer numerical integrator written in C to compute the dynamics of the system in a heliocentric frame, and run a Markov Chain Monte Carlo fitting process calculating the chi-square value for the simulated transits, astrometry, and RV data produced by the integrator compared to observational data. The best-fit model parameters I calculated for the dataset from Carter et al. (2011) were consistent with their parameters, but not consistent with the full photometric dataset, and required slight tweaks in the orbital angles of the system in order to fit all the transits. The evolution of the parameters for KOI-126 throughout the 7 years of Kepler and radial velocity observations provides strong constraints on the best-fit parameter values.