Wednesday, January 22, 2014

Kepler-51 System Observation Gives Appearance of ExoPlanet Eclipses

Very Low-Density Planets around Kepler-51 Revealed with Transit Timing Variations and an Anomaly Similar to a Planet-Planet Eclipse Event

Authors:

Masuda et al

Abstract:


We present an analysis of the transit timing variations (TTVs) in the multi-transiting planetary system around Kepler-51 (KOI-620). This system consists of two confirmed transiting planets, Kepler-51b (Pb=45.2days) and Kepler-51c (Pc=85.3days), and one transiting planet candidate KOI-620.02 (P02=130.2days), which lie close to a 1:2:3 resonance chain. Our analysis shows that their TTVs are consistently explained by the three-planet model, and constrains their masses as Mb=2.1+1.50.8M (Kepler-51b), Mc=4.0±0.4M (Kepler-51c), and M02=7.6±1.1M (KOI-620.02), thus confirming KOI-620.02 as a planet in this system. The masses inferred from the TTVs are rather small compared with the planetary radii based on the stellar density and planet-to-star radius ratios determined from the transit light curves. Combining these estimates, we find that all the three planets in this system have among the lowest densities yet determined, ρp0.05gcm3. With this feature, the Kepler-51 system serves as another example of low-density compact multi-transiting planetary systems. We also identify a curious feature in the archived Kepler light curve during the double transit of Kepler-51b and KOI-620.02, which could be explained by their overlapping on the stellar disk (a planet-planet eclipse). If this is really the case, the sky-plane inclination of KOI-620.02's orbit relative to that of Kepler-51b is given by ΔΩ=25.3+6.26.8deg, implying significant misalignment of their orbital planes. This interpretation, however, seems unlikely because such a event that is consistent with all of the observations is found to be exceedingly rare.

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