Kepler-539 CAFE radial velocity measurements

The mass of Kepler-539 b was accurately derived thanks to a series of precise radial velocity measurements obtained with the CAFE spectrograph mounted on the CAHA 2.2-m telescope. A simultaneous fit of the radial-velocity data and Kepler photometry revealed that Kepler-539 b is a dense Jupiter-like planet with a mass of Mp=0.97M_Jup_ and a radius of Rp=0.747R_Jup_, making a complete circular revolution around its parent star in 125.6-days.

The semi-major axis of the orbit is roughly 0.5au, implying that the planet is at 0.45au from the habitable zone. By analysing the mid-transit times of the 12 transit events of Kepler-539 b recorded by the Kepler spacecraft, we found a clear modulated transit time variation (TTV), which is attributable to the presence of a planet c in a wider orbit. The few timings available do not allow us to precisely estimate the properties of Kepler-539 c and our analysis suggests that it has a mass between 1.2 and 3.6 M_Jup_, revolving on a very eccentric orbit (0.4<e<0.6) with a period larger than 1000-days.