TESS-Keck Survey. V. Twin Sub-Neptunes Transiting the Nearby G Star HD 63935

Full list of authors: Scarsdale, Nicholas; Murphy, Joseph M. Akana; Batalha, Natalie M.; Crossfield, Ian J. M.; Dressing, Courtney D.; Fulton, Benjamin; Howard, Andrew W.; Huber, Daniel; Isaacson, Howard; Kane, Stephen R.; Petigura, Erik A.; Robertson, Paul; Roy, Arpita; Weiss, Lauren M.; Beard, Corey; Behmard, Aida; Chontos, Ashley; Christiansen, Jessie L.; Ciardi, David R.; Claytor, Zachary R.; Collins, Karen A.; Collins, Kevin I.; Dai, Fei; Dalba, Paul A.; Dragomir, Diana; Fetherolf, Tara; Fukui, Akihiko; Giacalone, Steven; Gonzales, Erica J.; Hill, Michelle L.; Hirsch, Lea A.; Jensen, Eric L. N.; Kosiarek, Molly R.; de Leon, Jerome P.; Lubin, Jack; Lund, Michael B.; Luque, Rafael; Mayo, Andrew W.; Močnik, Teo; Mori, Mayuko; Narita, Norio; Nowak, Grzegorz; Pallé, Enric; Rabus, Markus; Rosenthal, Lee J.; Rubenzahl, Ryan A.; Schlieder, Joshua E.; Shporer, Avi; Stassun, Keivan G.; Twicken, Joe; Wang, Gavin; Yahalomi, Daniel A.; Jenkins, Jon; Latham, David W.; Ricker, George R.; Seager, S.; Vanderspek, Roland; Winn, Joshua N.
We present the discovery of two nearly identically sized sub-Neptune transiting planets orbiting HD 63935, a bright (V = 8.6 mag), Sun-like (Teff = 5560 K) star at 49 pc. TESS identified the first planet, HD 63935 b (TOI- 509.01), in Sectors 7 and 34. We identified the second signal (HD 63935 c) in Keck High Resolution Echelle Spectrometer and Lick Automated Planet Finder radial velocity data as part of our follow-up campaign. It was subsequently confirmed with TESS photometry in Sector 34 as TOI-509.02. Our analysis of the photometric and radial velocity data yielded a robust detection of both planets with periods of 9.0600 ± 0.007 and 21.40 ± 0.0019 days, radii of 2.99 ± 0.14 and 2.90 ± 0.13 R?, and masses of 10.8 ± 1.8 and 11.1 ± 2.4 M?. We calculated densities for planets b and c consistent with a few percent of the planet mass in hydrogen/helium envelopes. We also describe our survey's efforts to choose the best targets for James Webb Space Telescope atmospheric followup. These efforts suggest that HD 63935 b has the most clearly visible atmosphere of its class. It is the best target for transmission spectroscopy (ranked by the transmission spectroscopy metric, a proxy for atmospheric observability) in the so far uncharacterized parameter space comprising sub-Neptune-sized (2.6 R? < Rp < 4 R?), moderately irradiated (100 F? < Fp < 1000 F?) planets around G stars. Planet c is also a viable target for transmission spectroscopy, and given the indistinguishable masses and radii of the two planets, the system serves as a natural laboratory for examining the processes that shape the evolution of sub-Neptune planets. © 2021 Institute of Physics Publishing. All rights reserved.
We thank NASA for funding associated with our Key Strategic Mission Support project. We thank the University of California and Google for supporting Lick Observatory and the UCO staff for their dedicated work scheduling and operating the telescopes of Lick Observatory. This paper is based on data collected by the TESS mission. 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 SPOC. 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 Program through the NASA Advanced Supercomputing 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 MAST. This research has made use of the NASA Exoplanet Archive and Exoplanet Follow-up Observation Program website, which are operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Based on observations made with the Italian TNG operated on the island of La Palma by Fundacion Galileo Galilei of Istituto Nazionale di Astrofisica at the Spanish Observatorio del Roque de los Muchachos of Instituto de Astrofisica de Canarias under programs CAT19A_162 and CAT19A_96. This work has made use of data from the European Space Agency mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data 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 partly supported by JSPS KAKENHI grant Nos. JP17H04574 and JP18H05439, JST PRESTO grant No. JPMJPR1775, and a Grant-in-aid for JSPS Fellows, No. JP20J21872.
With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.