TESS-Keck Survey. IX. Masses of Three Sub-Neptunes Orbiting HD 191939 and the Discovery of a Warm Jovian plus a Distant Substellar Companion

Creators: Lubin, Jack; Van Zandt, Judah; Holcomb, Rae; Weiss, Lauren M.; Petigura, Erik A.; Robertson, Paul; Murphy, Joseph M. Akana; Scarsdale, Nicholas; Batygin, Konstantin; Polanski, Alex S.; Batalha, Natalie M.; Crossfield, Ian J. M.; Dressing, Courtney; Fulton, Benjamin; Howard, Andrew W.; Huber, Daniel; Isaacson, Howard; Kane, Stephen R.; Roy, Arpita; Beard, Corey; Blunt, Sarah; Chontos, Ashley; Dai, Fei; Dalba, Paul A.; Kaz, Gary; Giacalone, Steven; Hill, Michelle L.; Mayo, Andrew; Močnik, Teo; Kosiarek, Molly R.; Rice, Malena; Rubenzahl, Ryan A.; Latham, David W.; Seager, S.; Winn, Joshua N.

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Abstract

Exoplanet systems with multiple transiting planets are natural laboratories for testing planetary astrophysics. One such system is HD 191939 (TOI 1339), a bright (V = 9) and Sun-like (G9V) star, which TESS found to host three transiting planets (b, c, and d). The planets have periods of 9, 29, and 38 days each with similar sizes from 3 to 3.4 R_⊕. To further characterize the system, we measured the radial velocity (RV) of HD 191939 over 415 days with Keck/HIRES and APF/Levy. We find that M_b = 10.4 ± 0.9 M_⊕ and M_c = 7.2 ± 1.4 M_⊕, which are low compared to most known planets of comparable radii. The RVs yield only an upper limit on M_d (<5.8 M_⊕ at 2σ). The RVs further reveal a fourth planet (e) with a minimum mass of 0.34 ± 0.01 M_(Jup) and an orbital period of 101.4 ± 0.4 days. Despite its nontransiting geometry, secular interactions between planet e and the inner transiting planets indicate that planet e is coplanar with the transiting planets (Δi < 10°). We identify a second high-mass planet (f) with 95% confidence intervals on mass between 2 and 11 M_(Jup) and period between 1700 and 7200 days, based on a joint analysis of RVs and astrometry from Gaia and Hipparcos. As a bright star hosting multiple planets with well-measured masses, HD 191939 presents many options for comparative planetary astronomy, including characterization 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 2021 April 21; revised 2021 November 17; accepted 2021 November 24; published 2022 January 31. We thank the anonymous referee for their insightful and thorough comments. We are grateful to Tim Brandt for his insight and contributions to the methods of Section 5. 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 the TESS-Keck Survey with observing time at Keck Observatory and on the Automated Planet Finder. 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 the opportunity to conduct observations from this mountain. We thank Ken and Gloria Levy, who supported the construction of the Levy Spectrometer on the Automated Planet Finder. 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 the NASA Explorer Program. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). E.A.P. acknowledges the support of the Alfred P. Sloan Foundation. L.M.W. is supported by the Beatrice Watson Parrent Fellowship and NASA ADAP grant 80NSSC19K0597. A.C. acknowledges support from the National Science Foundation through the Graduate Research Fellowship Program (DGE 1842402). D.H. acknowledges support from the Alfred P. Sloan Foundation, the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379), and the National Science Foundation (AST-1717000). I.J.M.C. acknowledges support from the NSF through grant AST-1824644. P.D. acknowledges support from a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1903811. A.B. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. R.A.R. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. C.D.D. acknowledges the support of the Hellman Family Faculty Fund, the Alfred P. Sloan Foundation, the David & Lucile Packard Foundation, and the National Aeronautics and Space Administration via the TESS Guest Investigator Program (80NSSC18K1583). J.M.A.M. is supported by the NSF Graduate Research Fellowship, grant No. DGE-1842400. J.M.A.M. also 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 the NSF Graduate Research Fellowship, grant No. DGE 1339067. Facilities:Automated Planet Finder (Levy), Keck I (HIRES), TESS. Software: Astropy (Astropy Collaboration et al. 2013), corner.py (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), isoclassify (Huber et al. 2017), Jupyter (Kluyver et al. 2016), KeckSpec (Rice & Brewer 2020) matplotlib (Hunter 2007), numpy (Van Der Walt et al. 2011), pandas (McKinney 2010), Python Limb Darkening Toolkit (Parviainen & Aigrain 2015) RadVel (Fulton et al. 2018), Smint (Piaulet et al. 2021) SpecMatch-Syn (Petigura et al. 2017) Transit Least Squares (Hippke & Heller 2019) exoplanet (Foreman-Mackey et al. 2020a) and its dependencies (Agol et al. 2020; Astropy Collaboration et al. 2018; Espinoza 2018; Luger et al. 2019; Salvatier et al. 2016; Theano Development Team 2016).

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