We confirm the planetary nature of Kepler-539 b ( aka Kepler object of interest K00372.01 ) , a giant transiting exoplanet orbiting a solar-analogue G2 V star .
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 M _ { \mathrm { p } } = 0.97 \pm 0.29 M _ { \mathrm { Jup } } and a radius of R _ { \mathrm { p } } = 0.747 \pm 0.018 R _ { \mathrm { Jup } } , making a complete circular revolution around its parent star in 125.6 days .
The semi-major axis of the orbit is roughly 0.5 au , implying that the planet is at \approx 0.45 au 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 _ { \mathrm { Jup } } , revolving on a very eccentric orbit ( 0.4 < e \leq 0.6 ) with a period larger than 1000 days .
The high eccentricity of planet c is the probable cause of the TTV modulation of planet b .
The analysis of the CAFE spectra revealed a relatively high photospheric lithium content , A ( \mathrm { Li } ) = 2.48 \pm 0.12 dex , which , together with both a gyrochronological and isochronal analysis , suggests that the parent star is relatively young .