A super-Earth orbiting near the inner edge of the habitable zone around the M4.5 dwarf Ross 508

Creators: Harakawa, Hiroki; Takarada, Takuya; Kasagi, Yui; Hirano, Teruyuki; Kotani, Takayuki; Kuzuhara, Masayuki; Omiya, Masashi; Kawahara, Hajime; Fukui, Akihiko; Hori, Yasunori; Ishikawa, Hiroyuki Tako; Ogihara, Masahiro; Livingston, John; Brandt, Timothy D.; Currie, Thayne; Aoki, Wako; Beichman, Charles A.; Henning, Thomas; Hodapp, Klaus; Ishizuka, Masato; Izumiura, Hideyuki; Jacobson, Shane; Janson, Markus; Kambe, Eiji; Kodama, Takanori; Kokubo, Eiichiro; Konishi, Mihoko; Krishnamurthy, Vigneshwaran; Kudo, Tomoyuki; Kurokawa, Takashi; Kusakabe, Nobuhiko; Kwon, Jungmi; Matsumoto, Yuji; McElwain, Michael W.; Mitsui, Koyu; Nakagawa, Takao; Narita, Norio; Nishikawa, Jun; Nugroho, Stevanus K.; Serabyn, Eugene; Serizawa, Takuma; Takahashi, Aoi; Ueda, Akitoshi; Uyama, Taichi; Vievard, Sébastien; Wang, Ji; Wisniewski, John; Tamura, Motohide; Sato, Bun'ei

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 (J_(mag) = 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) m s⁻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 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.

Additional Information

© The Author(s) 2022. Published by Oxford University Press on behalf of the Astronomical Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 06 March 2022. Accepted: 23 May 2022. Published: 30 June 2022. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical, and natural significance in Hawaii. M.T. is supported by Japan Society for the Promotion of Science (JSPS) KAKENHI grant Nos. 18H05442, 15H02063, and 22000005. YH was partly supported by a Grant-in-Aid for Scientific Research on Innovative Areas (JSPS KAKENHI Grant Number 18H05439). This work is partly supported by JSPS KAKENHI Grant Numbers JP18H05439 and JP21K20388, Japan Science and Technology Agency (JST), Core Research for Evolutional Science and Technology (CREST) Grant Number JPMJCR1761, the Astrobiology Center of National Institutes of Natural Sciences (NINS) (Grant Number AB031010). This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France (Wenger et al. 2000). This research made use of Astropy,3 a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018). This research has made use of the NASA Exoplanet Archive 〈https://exoplanetarchive.ipac.caltech.edu〉, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research has made use of data obtained from or tools provided by the portal exoplanet.eu of The Extrasolar Planets Encyclopaedia. The corner (Foreman-Mackey 2016) Python module has been helpful to create the figures in this paper.

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