A super-Earth orbiting near the inner edge of the habitable zone around the M4.5 dwarf Ross 508
Henning, Thomas; Nakagawa, Takao; Currie, Thayne; Kwon, Jungmi; Tamura, Motohide; Uyama, Taichi; Wisniewski, John; Izumiura, Hideyuki; Hirano, Teruyuki; Sato, Bun'ei; Beichman, Charles A.; Kudo, Tomoyuki; Fukui, Akihiko; Kuzuhara, Masayuki; Narita, Norio; Konishi, Mihoko; Takarada, Takuya; Omiya, Masashi; Harakawa, Hiroki; Kambe, Eiji; Brandt, Timothy D.; Kokubo, Eiichiro; Kusakabe, Nobuhiko; Janson, Markus; McElwain, Michael W.; Serabyn, Eugene; Livingston, John; Aoki, Wako; Kawahara, Hajime; Wang, Ji; Hori, Yasunori; Nishikawa, Jun; Ishikawa, Hiroyuki Tako; Kotani, Takayuki; Kurokawa, Takashi; Ogihara, Masahiro; Ueda, Akitoshi; Kasagi, Yui; Kodama, Takanori; Hodapp, Klaus; Krishnamurthy, Vigneshwaran; Serizawa, Takuma; Jacobson, Shane; Vievard, Sébastien; Ishizuka, Masato; Matsumoto, Yuji; Mitsui, Koyu; Nugroho, Stevanus K.; Takahashi, Aoi
United States, Japan, China, Germany, Sweden, Spain
Abstract
We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on a 10.77 d orbit around the M4.5 dwarf Ross 508 (Jmag = 9.1). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of $3.92^{+0.60}_{-0.58}\:\mbox{m}\:{\mbox{s}^{-1}}$, corresponding to a planet with a minimum mass $m \sin i = 4.00^{+0.53}_{-0.55}\, M_{\oplus }$. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semi-major axis of $0.05366^{+0.00056}_{-0.00049}\:$au. This gives an orbit-averaged insolation of ≈1.4 times the Earth's value, placing Ross 508 b near the inner edge of its star's habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role in finding a low-mass planet around cool M dwarfs like Ross 508.