SOPHIE velocimetry of Kepler transit candidates. XIX. The transiting temperate giant planet KOI-3680b

TL;DR

This paper reports the discovery and detailed characterization of KOI-3680b, a long-period transiting giant exoplanet with a highly eccentric orbit, expanding our understanding of such planets beyond close-in systems.

Contribution

It provides the first detailed characterization of KOI-3680b, a long-period transiting giant planet, using combined Kepler photometry and two-year radial velocity follow-up.

Findings

KOI-3680b has a 141-day orbital period.

It has a mass of approximately 1.93 Jupiter masses.

It exhibits a high orbital eccentricity of 0.50.

Abstract

Whereas thousands of transiting giant exoplanets are known today, only a few are well characterized with long orbital periods. Here we present KOI-3680b, a new planet in this category. First identified by the Kepler team as a promising candidate from the photometry of the Kepler spacecraft, we establish here its planetary nature from the radial velocity follow-up secured over two years with the SOPHIE spectrograph at Observatoire de Haute-Provence, France. The combined analysis of the whole dataset allows us to fully characterize this new planetary system. KOI-3680b has an orbital period of 141.2417 +/- 0.0001 days, a mass of 1.93 +/- 0.20 M_Jup, and a radius of 0.99 +/- 0.07 R_Jup. It exhibits a highly eccentric orbit (e = 0.50 +/- 0.03) around an early G dwarf. KOI-3680b is the transiting giant planet with the longest period characterized so far around a single star; it offers opportunities to extend studies which were mainly devoted to exoplanets close to their host stars, and to compare both exoplanet populations.