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

Creators: Scarsdale, Nicholas; Murphy, Joseph M. Akana; Batalha, Natalie M.; Crossfield, Ian J. M.; Dressing, Courtney D.; Fulton, Benjamin J.; 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.

Abstract

We present the discovery of two nearly identically sized sub-Neptune transiting planets orbiting HD 63935, a bright (V = 8.6 mag), Sun-like (T_(eff) = 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 follow-up. 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_⊕ < R_p < 4 R_⊕), moderately irradiated (100 F_⊕ < F_p < 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.

Additional Information

© 2021. The American Astronomical Society. Received 2021 May 24; revised 2021 July 21; accepted 2021 July 27; published 2021 October 26. We thank the anonymous referee for helpful feedback that improved the quality of this work. We thank the time assignment committees of the University of California, the California Institute of Technology, NASA, and the University of Hawai'i for supporting TKS with observing time at Keck Observatory and on APF. We thank NASA for funding associated with our Key Strategic Mission Support project. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff for support of HIRES and remote observing. We recognize and acknowledge the cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are deeply grateful to have had the opportunity to conduct observations from this mountain. We thank Ken and Gloria Levy, who supported the construction of the Levy Spectrometer on APF. 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 Fundación 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. This work makes use of observations from the LCOGT Network. D.D. acknowledges support from the TESS Guest Investigator Program grant 80NSSC19K1727 and the NASA Exoplanet Research Program grant 18-2XRP18_2-0136. J.M.A.M. is supported by the National Science Foundation (NSF) Graduate Research Fellowship Program under grant No. DGE-1842400. J.M.A.M. acknowledges the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant No. 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. M.R.K. is supported by an NSF Graduate Research Fellowship, grant No. DGE 1339067. P.A.D. acknowledges support from an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1903811. Facilities: APF (Levy), HARPS-N (TNG), HIRES (Keck I), LCOGT, NIRC2 (Keck II), PHARO (Palomar), TESS. Software: AstroImageJ (Collins et al. 2017), Astropy (Robitaille et al. 2013), batman (Kreidberg 2015), emcee (Foreman-Mackey et al. 2013), exoplanet and its dependencies (Foreman-Mackey et al. 2021; Agol et al. 2020; Kumar et al. 2019; Luger et al. 2019; Salvatier et al. 2016; Theano Development Team 2016), isoclassify (Huber et al. 2017), juliet (Espinoza et al. 2019), Jupyter (Kluyver et al. 2016), kiauhoku (Claytor et al. 2020), matplotlib (Hunter 2007), numpy (Harris et al. 2020), pandas (McKinney 2010), Radvel (Fulton et al. 2018), smint (Piaulet et al. 2021), SpecMatch-Syn (Petigura et al. 2017), Transit Least Squares (Hippke & Heller 2019).

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