High-Contrast Imaging of Intermediate-Mass Giants with Long-Term Radial Velocity Trends

Abstract

A radial velocity (RV) survey for intermediate-mass giants has been operated for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct imaging observations can help clarify what objects generate these RV trends. We present the results of high-contrast imaging observations or six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to $\gamma$ Hya B ($0.61_{-0.14}^{+0.12}{M}_{\odot }$), HD 5608 B ($0.10\pm 0.01M_{\odot }$), and HD 109272 B ($0.28\pm 0.06M_{\odot }$). For the remaining targets($\iota$ Dra, 18 Del, and HD 14067) we exclude companions more massive than 30-60 $M_{\mathrm{Jup}}$ at projected separations of 1arcsec-7arcsec. We examine whether these directly imaged companions or unidentified long-period companions can account for the RV trends observed around the six giants. We find that the Kozai mechanism can explain the high eccentricity of the inner planets $\iota$ Dra b, HD 5608 b, and HD 14067 b.

33 pases, 9 figures, accepted to ApJ

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• SAFARI I: A SPHERE discovery of a super metal-rich M dwarf companion to the star HD 86006