Transit Timing Variation of Near-resonant Koi Pairs: Confirmation of 12 Multiple Planet Systems

We extract Transit Timing Variation (TTV) signals for pairs of transiting planet candidates that are near first-order Mean Motion Resonances (MMR), using publicly available Kepler lightcurves (Q0-Q9). We are able to solidly confirm the planetary nature of 12 new pairs because their TTV signals exhibit sinusoidal variations at the expected timescale and with reasonable phases. Applying the analytical TTV expressions to these systems, we determine planet masses for three pairs of them (KOI 148, 500, 1589), based on the fact that they have nearly zero TTV phase shifts and therefore likely zero free eccentricities. For the remaining nine systems (KOI 152, 248, 829, 869, 877, 880, 898, 1270, and 1336) that show non-zero TTV phase shifts, we are able to obtain their mass upper limits, mass ratios and thus density ratios. Combining another 11 previously confirmed Kepler near-MMR pairs, we find that the whole sample is generally consistent with the fiducial mass-radius relation, m ∝ R, and most of them are like twins with similar sizes and densities, although a few distinct exceptions, such as KOI 148, 869 and Kepler 36. In addition, there seems to be a marginal pattern, i.e., for slightly more pairs, the inner one has a smaller radius but larger density than that of the outer one. Finally, we discuss the uncertainties and implications of our findings. Subject headings: planetary systems−planets and satellites: detection and dynamical evolution