The K2-ESPRINT Project IV: A Hot Jupiter in a Prograde Orbit with a Possible Stellar Companion

Teruyuki Hirano, Grzegorz Nowak, Masayuki Kuzuhara, Enric Palle, Fei Dai, Liang Yu, Vincent Van Eylen, Yoichi Takeda, Timothy D. Brandt, Norio Narita, Sergio Velasco, Jorge Prieto Arranz, Roberto Sanchis-Ojeda, Joshua N. Winn, Tomoyuki Kudo, Nobuhiko Kusakabe, Akihiko Fukui, Bun'ei Sato, Simon Albrecht, Ignasi Ribas, Tsuguru Ryu, Motohide Tamura

Published 2016-02-01Version 1

We report on the detection and early characterization of a hot Jupiter in a 3-day orbit around EPIC 212110888, a metal-rich F-type star located in the K2 Cycle 5 field. Our follow-up campaign involves precise radial velocity (RV) measurements and high-contrast imaging using multiple facilities. The absence of a bright nearby source in our high-contrast data suggests that the transit-like signals are not due to light variations from such a contaminant star. Our intensive RV measurements show that EPIC 212110888b has a mass of $1.726\pm0.085M_J$, confirming its status as a planet. We also detect the Rossiter-McLaughlin effect for EPIC 212110888b and show that the system has a good spin-orbit alignment ($\lambda=4_{-10}^{+11}$ degrees). High-contrast images obtained by the HiCIAO camera on the Subaru 8.2-m telescope reveal a faint companion candidate ($\Delta m_H=6.19\pm 0.11$) at a separation of $\sim 0\farcs36$. Follow-up observations are needed to confirm that the companion candidate is physically associated with EPIC 212110888. EPIC 212110888b appears to be an example of a typical ``hot Jupiter,' albeit one which can be precisely characterized using a combination of K2 photometry and ground-based follow-up.