The TESS-Keck Survey I: A Warm Sub-Saturn-Mass Planet and a Caution about Stray Light in TESS Cameras

Creators: Dalba, Paul A.; Gupta, Arvind F.; Rodriguez, Joseph E.; Dragomir, Diana; Huang, Chelsea X.; Kane, Stephen R.; Quinn, Samuel N.; Bieryla, Allyson; Esquerdo, Gilbert A.; Fulton, Benjamin J.; Scarsdale, Nicholas; Batalha, Natalie M.; Crossfield, Ian J. M.; Dressing, Courtney D.; Howard, Andrew W.; Huber, Daniel; Isaacson, Howard; Petigura, Erik A.; Robertson, Paul; Roy, Arpita; Weiss, Lauren M.; Knudstrup, Emil; Andersen, Mads F.; Grundahl, Frank; Yao, Xinyu; Pepper, Joshua; Villanueva, Steven, Jr.; Ciardi, David R.; Cloutier, Ryan; Jacobs, Thomas Lee; Kristiansen, Martti H.; LaCourse, Daryll M.; Lendl, Monika; Osborn, Hugh P.; Palle, Enric; Stassun, Keivan G.; Stevens, Daniel J.; Ricker, George R.; Vanderspek, Roland; Latham, David W.; Seager, S.; Winn, Joshua N.; Jenkins, Jon M.; Caldwell, Douglas A.; Daylan, Tansu; Fong, William; Goeke, Robert F.; Rose, Mark E.; Rowden, Pamela; Schlieder, Joshua E.; Smith, Jeffrey C.; Vanderburg, Andrew; Behmard, Aida; Rosenthal, Lee J.; Rubenzahl, Ryan A.

Abstract

We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD 332231—an F8 dwarf star with a V-band magnitude of 8.56—was observed by TESS in Sectors 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder, Keck I, and SONG telescopes. The orbital period we infer from radial velocity (RV) observations leads to the discovery of another transit in Sector 14 that was masked by PDC due to scattered light contamination. A joint analysis of the transit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size (0.867^(+0.027)_(−0.025) R_J), sub-Saturn-mass (0.244±0.021M_J) exoplanet on a 18.71 day circular orbit. The low surface gravity of HD 332231 b and the relatively low stellar flux it receives make it a compelling target for transmission spectroscopy. Also, the stellar obliquity is likely measurable via the Rossiter–McLaughlin effect, an exciting prospect given the 0.14 au orbital separation of HD 332231 b. The spectroscopic observations do not provide substantial evidence for any additional planets in the HD 332231 system, but continued RV monitoring is needed to further characterize this system. We also predict that the frequency and duration of masked data in the PDC light curves for TESS Sectors 14–16 could hide transits of some exoplanets with orbital periods between 10.5 and 17.5 days.

Additional Information

© 2020 The American Astronomical Society. Received 2020 January 16; revised 2020 March 20; accepted 2020 March 27; published 2020 April 29. The authors thank the anonymous referee for a helpful review of this work. P.D. gratefully acknowledges support from a National Science Foundation (NSF) Astronomy & Astrophysics Postdoctoral Fellowship under award AST-1903811. 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 by the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379) awarded through the TESS Guest Investigator Program. I.J.M.C. acknowledges support from the NSF through grant AST-1824644. 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). R.C. is supported by a grant from the National Aeronautics and Space Administration in support of the TESS science mission. The contribution by ML was carried out within the framework of the National Centre for Competence in Research "PlanetS" supported by the Swiss National Science Foundation (SNSF). M.L. also acknowledges support from the Austrian Research Promotion Agency (FFG) under project 859724 "GRAPPA." T.D. acknowledges support from MIT's Kavli Institute as a Kavli postdoctoral fellow. D.D. acknowledges support from NASA through Caltech/JPL grant RSA-1006130 and through the TESS Guest Investigator Program Grant 80NSSC19K1727. D.J.S. is supported as an Eberly Research Fellow by the Eberly College of Science at the Pennsylvania State University. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. H.P.O. acknowledges funding from NCCR-PlanetS for the CHESS postdoctoral fellowship. The authors wish to thank Bradford Holden for assistance in scheduling some of the observations presented in this paper. T.J., M.H.K., and D.L. gratefully acknowledge Allan R. Schmitt and Troy Winarski for making their light-curve software LcTools and AKO-TPF freely available. 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 research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. 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. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Observations in this paper made use of the NN-EXPLORE Exoplanet and Stellar Speckle Imager (NESSI). NESSI was funded by the NASA Exoplanet Exploration Program and the NASA Ames Research Center. NESSI was built at the Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. This paper includes observations made with the Hertzsprung SONG telescope operated on the Spanish Observatorio del Teide on the island of Tenerife by the Aarhus and Copenhagen Universities and by the Instituto de Astrofísica de Canarias. Research at the Lick Observatory is partially supported by a generous gift from Google. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Finally, the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Automated Planet Finder (Levy) - , FLWO:1.5 m (TRES) - , Keck:I (HIRES) - , SONG - , TESS - , WIYN (NESSI). - Software: emcee (Foreman-Mackey et al. 2013), EXOFASTv2 (Eastman 2017), Lightkurve (Lightkurve Collaboration et al. 2018), RadVel (Fulton et al. 2018), SpecMatch (Fulton et al. 2015a; Petigura et al. 2017).

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