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 ($0.61^{+0.12}_{-0.14} M_odot$), HD 5608 B ($0.10 pm 0.01 M_odot$), and HD 109272 B ($0.28 pm 0.06 M_odot$). 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.
Download