Precise Radial Velocity Measurements for Kepler Giants Hosting Planetary Candidates: Kepler-91 and KOI-1894

Bun'ei Sato; Teruyuki Hirano; Masashi Omiya; Hiroki Harakawa; Atsushi Kobayashi; Ryo Hasegawa; Takuya Takarada; Kiyoe Kawauchi; Kento Masuda

doi:10.1088/0004-637x/802/1/57

arXiv · 1501.05415

Precise Radial Velocity Measurements for Kepler Giants Hosting Planetary Candidates: Kepler-91 and KOI-1894

Bun'ei Sato·Teruyuki Hirano·Masashi Omiya·Hiroki Harakawa·Atsushi Kobayashi·Ryo Hasegawa·Takuya Takarada·Kiyoe Kawauchi·Kento Masuda

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Abstract

We present results of radial-velocity follow-up observations for the two Kepler evolved stars Kepler-91 (KOI-2133) and KOI-1894, which had been announced as candidates to host transiting giant planets, with the Subaru 8.2m telescope and the High Dispersion Spectrograph (HDS). By global modeling of the high-precision radial-velocity data taken with Subaru/HDS and photometric ones taken by Kepler mission taking account of orbital brightness modulations (ellipsoidal variations, reflected/emitted light, etc.) of the host stars, we independently confirmed that Kepler-91 hosts a transiting planet with a mass of 0.66 M_Jup (Kepler-91b), and newly detected an offset of ~20 m s$^{-1}$ between the radial velocities taken at ~1-yr interval, suggesting the existence of additional companion in the system. As for KOI-1894, we detected possible phased variations in the radial velocities and light curves with 2--3 sigma confidence level which could be explained as a reflex motion and ellipsoidal variation of the star caused by the transiting sub-saturn-mass (~0.18 M_Jup) planet.

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Bun'ei Sato, Teruyuki Hirano, Masashi Omiya, Hiroki Harakawa, Atsushi Kobayashi, Ryo Hasegawa, Takuya Takarada, Kiyoe Kawauchi, Kento Masuda. 2015-01-22. Precise Radial Velocity Measurements for Kepler Giants Hosting Planetary Candidates: Kepler-91 and KOI-1894. https://doi.org/10.1088/0004-637x%2F802%2F1%2F57

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