A Neptune-sized exoplanet consistent with a pure rock composition

摘要: We report the discovery of BD+ 20594b, a Neptune-sized exoplanet consistent with a pure rock composition, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission. The host star is a bright (V= 11.04, Ks= 9.37), slightly metal poor ([Fe/H]=− 0.15±0.05 dex) solar analogue located at 152.1+ 9.7− 7.4 pc from Earth, for which we find a radius of R∗= 0.928+ 0.055− 0.040R⊙ and a mass of M∗= 0.961+ 0.032− 0.029M⊙. A joint analysis of the K2 photometry and HARPS radial velocities reveal that the planet is in a≈ 42 day orbit around its host star, has a radius of 2.23+ 0.14− 0.11R⊕, and a mass of