A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone Around the M4.5 Dwarf Ross 508

• Published in: Publications of the Astronomical Society of Japan 2022-08, Vol.74 (4), p.904-922
• Main Authors: Harakawa, Hiroki, Hirano, Teruyuki, Kotani, Takayuki, Kawahara, Hajime, Fukui, Akihiko, Hori, Yasunori, Ogihara, Masahiro, Brandt, Timothy D, Currie, Thayne, Aoki, Wako, Beichman, Charles A, Henning, Thomas, Hodapp, Klaus, Ishizuka, Masato, Izumiura, Hideyuki, Janson, Markus, Kambe, Eiji, Kodama, Takanori, Kokubo, Eiichiro, Konishi, Mihoko, Krishnamurthy, Vigneshwaran, Kudo, Tomoyuki, Kurokawa, Takashi, Kwon, Jungmi, McElwain, Michael W, Serabyn, Eugene
• Format: Article
• Language: English
• Subjects: infrared: planetary systems; Lunar and Planetary Science and Exploration; planets and satellites: terrestrial planets; techniques: radial velocities
• ISSN: 0004-6264; 2053-051X; 2053-051X
• DOI: 10.1093/pasj/psac044

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 ms−1, corresponding to a planet with a minimum mass m sin i = 4.00 +0.53 −0.55 M⊕. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators orMEarth 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.