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

TL;DR

This paper reports the discovery and detailed characterization of a hot Jupiter orbiting K2-34, including its mass, orbit alignment, and a potential stellar companion, using combined photometry, radial velocity, and high-contrast imaging.

Contribution

It presents the first detailed characterization of K2-34b, including mass, orbit alignment, and potential stellar companion, using combined observational techniques.

Findings

K2-34b has a mass of 1.773±0.086 M_J.

The system has a well-aligned spin-orbit angle (~0°).

A faint stellar companion candidate was detected near K2-34.

Abstract

We report on the detection and early characterization of a hot Jupiter in a 3-day orbit around K2-34 (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 companion star. Our intensive RV measurements show that K2-34b has a mass of $1.773\pm0.086M_J$, confirming its status as a planet. We also detect the Rossiter-McLaughlin effect for K2-34b and show that the system has a good spin-orbit alignment ($\lambda=-1_{-9}^{+10}$ degrees). High-contrast images obtained by the HiCIAO camera on the Subaru 8.2-m telescope reveal a faint companion candidate ($\Delta m_H=6.19\pm 0.11$ mag) at a separation of $0\farcs36$. Follow-up observations are needed to confirm that the companion candidate is physically associated with K2-34. K2-34b 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.