Kepler-411: a four-planet system with an active host star^★

¹ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, PR China
e-mail: sunleilei@ynao.ac.cn, wangxb@ynao.ac.cn
² Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, PR China
³ University of Chinese Academy of Sciences, Beijing 100049, PR China
⁴ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: pioannidis@hs.unihamburg.de
⁵ Department of Mathematical Sciences, Xian Jiaotong-Liverpool University (XJTLU), 111 Renai Road, Suzhou Dushu Lake Science and Education Innovation District, Suzhou Industrial Park, Suzhou 215123, PR China

Received: 19 September 2018
Accepted: 13 December 2018

Abstract

We present a detailed characterization of the Kepler-411 system (KOI 1781). This system was previously known to host two transiting planets: one with a period of 3 days (R = 2.4 R_⊕; Kepler-411b) and one with a period of 7.8 days (R = 4.4 R_⊕; Kepler-411c), as well as a transiting planetary candidate with a 58-day period (R = 3.3 R_⊕; KOI 1781.03) from Kepler photometry. Here, we combine Kepler photometry data and new transit timing variation (TTV) measurements from all the Kepler quarters with previous adaptive-optics imaging results, and dynamical simulations, in order to constrain the properties of the Kepler-411 system. From our analysis, we obtain masses of 25.6 ± 2.6 M_⊕ for Kepler-411b and 26.4 ± 5.9 M_⊕ for Kepler-411c, and we confirm the planetary nature of KOI 1781.03 with a mass of 15.2 ± 5.1 M_⊕, hence the name Kepler-411d. Furthermore, by assuming near-coplanarity of the system (mutual inclination below 30°), we discover a nontransiting planet, Kepler-411e, with a mass of 10.8 ± 1.1 M_⊕ on a 31.5-day orbit, which has a strong dynamical interaction with Kepler-411d. With densities of 1.71 ± 0.39 g cm⁻³ and 2.32 ± 0.83 g cm⁻³, both Kepler-411c and Kepler-411d belong to the group of planets with a massive core and a significant fraction of volatiles. Although Kepler-411b has a sub-Neptune size, it belongs to the group of rocky planets.