A 1.9 EARTH RADIUS ROCKY PLANET AND THE DISCOVERY OF A NON-TRANSITING PLANET IN THE KEPLER-20 SYSTEM

作者：Buchhave Lars A; Dressing Courtney D; Dumusque Xavier; Rice Ken; Vanderburg Andrew; Mortier Annelies; Lopez Morales Mercedes; Lopez Eric; Lundkvist Mia S; Kjeldsen Hans; Affer Laura; Bonomo Aldo S; Charbonneau David; Cameron Andrew Collier; Cosentino Rosario; Figueira Pedro; Fiorenzano Aldo F M; Harutyunyan Avet; Haywood Raphaelle D; Johnson John Asher; Latham David W; Lovis Christophe; Malavolta Luca; Mayor Michel; Micela Giusi; Molinari Emilio

来源：Astronomical Journal, 2016, 152(6): 160.

DOI：10.3847/0004-6256/152/6/160

• planetary systems
• planets and satellites: composition
• stars: individual
• techniques: radial velocities

Kepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own solar system. A transition from rocky to gaseous planets with a planetary transition radius of similar to 1.6 R-circle plus has recently been proposed by several articles in the literature. Kepler-20b (R-p similar to 1.9 R-circle plus) has a size beyond this transition radius; however, previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of three of the planets in the Kepler-20 system that are facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (M-star = 0.948 +/- 0.051M and R-star =. 0.964 +/- 0.018 R). Kepler-20b is a 1.868(-0.034)(+0.066) R-circle plus planetiat 3.7 day period with a mass of 9.70(-1.44)(+1.41) M-circle plus, resulting in a mean density of 8.2(-1.3)(+1.5) g cm(-3), indicating a rocky composition with an iron-tosilicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of 19.96(-3.61)(+3.08) M-circle plus and an orbital period of similar to 34 days in the gap between Kepler-20f (P similar to 11 days) and Kepler-20d (P similar to 78 days).

• 出版日期2016-12