TOI-1696: A Nearby M4 Dwarf with a 3R_⊕ Planet in the Neptunian Desert

Creators: Mori, Mayuko; Livingston, John H.; de Leon, Jerome P.; Narita, Norio; Hirano, Teruyuki; Fukui, Akihiko; Collins, Karen A.; Fujita, Naho; Hori, Yasunori; Ishikawa, Hiroyuki Tako; Kawauchi, Kiyoe; Stassun, Keivan G.; Watanabe, Noriharu; Giacalone, Steven; Gore, Rebecca; Schroeder, Ashley; Dressing, Courtney D.; Bieryla, Allyson; Jensen, Eric L. N.; Massey, Bob; Shporer, Avi; Kuzuhara, Masayuki; Charbonneau, David; Ciardi, David R.; Doty, John P.; Esparza-Borges, Emma; Harakawa, Hiroki; Hodapp, Klaus; Ikoma, Masahiro; Ikuta, Kai; Isogai, Keisuke; Jenkins, Jon M.; Kagetani, Taiki; Kimura, Tadahiro; Kodama, Takanori; Kotani, Takayuki; Krishnamurthy, Vigneshwaran; Kudo, Tomoyuki; Kurita, Seiya; Kurokawa, Takashi; Kusakabe, Nobuhiko; Latham, David W.; McLean, Brian; Murgas, Felipe; Nishikawa, Jun; Nishiumi, Taku; Omiya, Masashi; Osborn, Hugh P.; Palle, Enric; Parviainen, Hannu; Ricker, George R.; Seager, Sara; Serizawa, Takuma; Teng, Huan-Yu; Terada, Yuka; Twicken, Joseph D.; Ueda, Akitoshi; Vanderspek, Roland; Vievard, Sébastien; Winn, Joshua N.; Zou, Yujie; Tamura, Motohide

Abstract

We present the discovery and validation of a temperate sub-Neptune around the nearby mid-M dwarf TIC 470381900 (TOI-1696), with a radius of 3.09 ± 0.11 R_⊕ and an orbital period of 2.5 days, using a combination of Transiting Exoplanets Survey Satellite (TESS) and follow-up observations using ground-based telescopes. Joint analysis of multiband photometry from TESS, Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT), MuSCAT3, Sinistro, and KeplerCam confirmed the transit signal to be achromatic as well as refined the orbital ephemeris. High-resolution imaging with Gemini/'Alopeke and high-resolution spectroscopy with the Subaru InfraRed Doppler (IRD) confirmed that there are no stellar companions or background sources to the star. The spectroscopic observations with IRD and Infrared Telescope Facility SpeX were used to determine the stellar parameters, and it was found that the host star is an M4 dwarf with an effective temperature of T_(eff) = 3185 ± 76 K and a metallicity of [Fe/H] = 0.336 ± 0.060 dex. The radial velocities measured from IRD set a 2σ upper limit on the planetary mass to be 48.8 M_⊕. The large radius ratio (Rₚ/R_⋆ ∼ 0.1) and the relatively bright near-infrared magnitude (J = 12.2 mag) make this planet an attractive target for further follow-up observations. TOI-1696 b is one of the planets belonging to the Neptunian desert with the highest transmission spectroscopy metric discovered to date, making it an interesting candidate for atmospheric characterizations with JWST.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 March 3; revised 2022 April 21; accepted 2022 April 28; published 2022 May 31. Funding for the TESS mission is provided by NASA's Science Mission Directorate. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). This work makes use of observations from the Las Cumbres Observatory global telescope network. Some of the observations in the paper are based on observations made with the MuSCAT3 instrument, developed by the Astrobiology Center and under financial supports by JSPS KAKENHI (JP18H05439) and JST PRESTO (JPMJPR1775), at Faulkes Telescope North on Maui, HI, operated by the Las Cumbres Observatory. This research is in part based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and at the Gemini North telescope, located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawaii. Our data reductions benefited from PyRAF and PyFITS, which are the products of the Space Telescope Science Institute, which is operated by AURA for NASA. This research made use of Astropy, 53 a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018). Some of the observations in the paper made use of the High-Resolution Imaging instrument(s) Alopeke. Alopeke was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Alopeke (and/or Zorro) was mounted on the Gemini North (and/or South) telescope of the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Some of the observations in this paper made use of the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR19D0030 with the National Aeronautics and Space Administration. The IRTF observations were collected under the program 2020B115 (PI: S. Giacalone). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the GaiaData Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work is supported by Grant-in-Aid for JSPS Fellows, grant No. JP20J21872, JSPS KAKENHI grant Nos. JP20K14518, JP19K14783, JP21H00035, JP18H05439, JP18H05439, JP20K14521, JP17H04574, JP21K20376, JP21K13975, JP18H05442, JP15H02063, JP22000005, and JP21K20388, SATELLITE Research from Astrobiology Center (grant No. AB031010, AB022006, and AB031014), and JST CREST grant No. JPMJCR1761. E.E.-B. acknowledges financial support from the European Union and the State Agency of Investigation of the Spanish Ministry of Science and Innovation (MICINN) under grant PRE2020-093107 of the Pre-Doc Program for the Training of Doctors (FPI-SO) through FSE funds. Software: AstroImageJ (Collins et al. 2017), LCOGT BANZAI pipeline (McCully et al. 2018), PyMC3 (Salvatier et al. 2016), exoplanet (Foreman-Mackey et al. 2019), starry (Luger et al. 2019), celerite2 (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), PyTransit (Parviainen 2015), Vespa (Morton 2015a), Isochrones(Morton 2015b), Triceratops (Giacalone & Dressing 2021), and astropy (Astropy Collaboration et al. 2013, 2018).

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