A hot Saturn on an eccentric orbit around the giant star EPIC228754001
Jones et al
Although the majority of radial velocity detected planets have been found orbiting solar-type stars, a fraction of them have been discovered around giant stars. These planetary systems have revealed different orbital properties when compared to solar-type stars companions. In particular, radial velocity surveys have shown that there is a lack of giant planets in close-in orbits around giant stars, in contrast to the known population of hot-Jupiters orbiting solar-type stars. The reason of this distinctive feature in the semimajor-axis distribution has been theorized to be the result of the stellar evolution and/or due to the effect of a different formation/evolution scenario for planets around intermediate-mass stars. However, in the past few years, a handful of transiting short-period planets (P≲ 10 days) have been found around giant stars, thanks to the high precision photometric data obtained initially by the Kepler mission, and later by its two-wheels extension K2. These new discoveries, have allowed us for the first time to study the orbital properties and physical parameters of these intriguing and elusive sub-stellar companions. In this paper we report on an independent discovery of a transiting planet in field 10 of the K2 mission, also reported recently by Grunblatt et al. (2017). The main orbital parameters of EPIC\,228754001\,b, obtained with all the available data for the system, are the following: P = 9.1708 ± 0.0025 d, e = 0.290 ± 0.049, Mp = 0.495 ± 0.007 Mjup \,and Rp = 1.089 ± 0.006 Rjup. This is the fifth known planet orbiting any giant star with a less than 0.1, and the most eccentric one among them, making EPIC\,228754001\,b a very interesting object.