High-contrast Imaging of Intermediate-mass Giants with Long-term Radial Velocity Trends
Henning, Thomas; Terada, Hiroshi; Usuda, Tomonori; Currie, Thayne; Kwon, Jungmi; Pyo, Tae-Soo; Tamura, Motohide; Takami, Michihiro; Hayashi, Masahiko; Uyama, Taichi; Wisniewski, John; Izumiura, Hideyuki; Sato, Bun'ei; Yoshida, Michitoshi; Hashimoto, Jun; Kudo, Tomoyuki; Abe, Lyu; Brandner, Wolfgang; Kuzuhara, Masayuki; Narita, Norio; Grady, Carol A.; Yamada, Toru; Omiya, Masashi; Harakawa, Hiroki; Kambe, Eiji; Ando, Hiroyasu; Brandt, Timothy D.; Itoh, Yoichi; Kokubo, Eiichiro; Mayama, Satoshi; Kusakabe, Nobuhiko; Hayashi, Saeko S.; Carson, Joseph C.; Feldt, Markus; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Serabyn, Eugene; Suto, Hiroshi; Suzuki, Ryuji; Takato, Naruhisa; Thalmann, Christian; Turner, Edwin L.; Watanabe, Makoto; Takami, Hideki; Ida, Shigeru; Hełminiak, Krzysztof G.; Ryu, Tsuguru; Takeda, Yoichi; Suenaga, Takuya; Takahashi, Yasuhiro H.; Mede, Kyle; Egner, Sebastian
Japan, United States, France, Germany, Sweden, Taiwan, Switzerland
Abstract
A radial velocity (RV) survey for intermediate-mass giants has been in operation 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 of six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to γ Hya B ({0.61}-0.14+0.12{M}⊙ ), HD 5608 B (0.10+/- 0.01{M}⊙ ), and HD 109272 B (0.28+/- 0.06{M}⊙ ). For the remaining targets (ι Dra, 18 Del, and HD 14067), we exclude companions more massive than 30-60 M Jup at projected separations of 1″-7″. 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 ι Dra b, HD 5608 b, and HD 14067 b.