Kepler-447b: a hot-Jupiter with an extremely grazing transit
Lilo-Box et al
We present the radial velocity confirmation of the extrasolar planet Kepler-447b, initially detected as a candidate by the Kepler mission. In this work, we analyze its transit signal and the radial velocity data obtained with the Calar Alto Fiber-fed Echelle spectrograph (CAFE). By simultaneously modeling both datasets, we obtain the orbital and physical properties of the system. According to our results, Kepler-447b is a Jupiter-mass planet (Mp=1.37+0.48−0.46MJup), with an estimated radius of Rp=1.65+0.59−0.56RJup (uncertainties provided in this work are 3σ unless specified). This translates into a sub-Jupiter density. The planet revolves every ∼7.8 days around a G8V star with detected activity in the Kepler light curve. Kepler-447b transits its host with a large impact parameter (b=1.076+0.112−0.086), being one of the few planetary grazing transits confirmed so far and the first in the Kepler large crop of exoplanets. We estimate that only around 20% of the projected planet disk occults the stellar disk. The relatively large uncertainties in the planet radius are due to the large impact parameter and short duration of the transit. Within the transit time interval, we find the presence of large (somehow modulated) outliers during the transit. We propose and analyze different scenarios that could explain these brighter data points, including instrumental effects, additional perturbing bodies, stellar pulsations, rotation of a non-spherical planet, and spot-crossing events. However, short-cadence photometric data (at the 1 minute level) is still needed to unveil the nature of this observational effect.