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

November 2021 • 2021AJ....162..215S

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.

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 (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 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 < 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.


IPAC Authors


Jessie Christiansen

Associate Scientist


David Ciardi

Senior Scientist


Benjamin Fulton

Assistant Scientist