Characterizing K2 planet discoveries: a super-Earth transiting the bright K dwarf HIP 116454

Abstract

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 [plus or minus] 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H] = −0.16 [plus or minus] 0.08 and has a radius R[subscript star] = 0.716 [plus or minus] 0.024 R[subscript circled dot] and mass M[subscript star] = 0.775 [plus or minus] 0.027 M[subscript circled dot]. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of R[subscript p] = 2.53 [plus or minus] 0.18 R[subscript circled plus]. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 [plus or minus] 1.33 M[subscript circled plus] planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.