A Hot Saturn Orbiting an Oscillating Late Subgiant Discovered by TESS

Abstract

WOS: 000469975500005 ; We present the discovery of HD 221416 b, the first transiting planet identified by the Transiting Exoplanet Survey Satellite (TESS) for which asteroseismology of the host star is possible. HD 221416 b (HIP 116158, TOI-197) is a bright (V = 8.2 mag), spectroscopically classified subgiant that oscillates with an average frequency of about 430 mu Hz and displays a clear signature of mixed modes. The oscillation amplitude confirms that the redder TESS bandpass compared to Kepler has a small effect on the oscillations, supporting the expected yield of thousands of solar-like oscillators with TESS 2 minute cadence observations. Asteroseismic modeling yields a robust determination of the host star radius (R-* = 2.943 +/- 0.064 R-circle dot), mass (M-* = 1.212 +/- 0.074 M-circle dot), and age (4.9 +/- 1.1 Gyr), and demonstrates that it has just started ascending the red-giant branch. Combining asteroseismology with transit modeling and radial-velocity observations, we show that the planet is a "hot Saturn" (R-p = 9.17 +/- 0.33 R-circle plus) with an orbital period of similar to 14.3 days, irradiance of F = 343 +/- 24 F-circle plus, and moderate mass (M-p = 60.5 +/- 5.7 M-circle plus) and density (rho(p) = 0.431 +/- 0.062 g cm(-3)). The properties of HD 221416 b show that the host-star metallicity-planet mass correlation found in sub-Saturns (4-8 R-circle plus) does not extend to larger radii, indicating that planets in the transition between sub-Saturns and Jupiters follow a relatively narrow range of densities. With a density measured to similar to 15%, HD 221416 b is one of the best characterized Saturn-size planets to date, augmenting the small number of known transiting planets around evolved stars and demonstrating the power of TESS to characterize exoplanets and their host stars using asteroseismology. ; National Aeronautics and Space Administration through the TESS Guest Investigator Program [80NSSC18K1585]; National Science FoundationNational Science Foundation (NSF) [AST-1717000]; Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC); UK Space Agency; European Social Fund via the Lithuanian Science Council [09.3.3-LMT-K-712-01-0103]; Danish National Research FoundationDanmarks Grundforskningsfond [DNRF106]; FONDECYT projectComision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)CONICYT FONDECYT [1171208]; CONICYT projectComision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) [BASAL AFB-170002]; Ministry for the Economy, Development, and Tourism's Programa Iniciativa Cientifica Milenio [IC 120009]; FONDECYTComision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)CONICYT FONDECYT [3180246]; Millennium Institute of Astrophysics (MAS); MINECOSpanish Ministry of Economy & Competitiveness [ESP2017-82674-R]; AGAURAgencia de Gestio D'Ajuts Universitaris de Recerca Agaur (AGUAR) [SGR2017-1131]; PLATO grant from the CNES; European Research Council under the European Community's Seventh Framework Programme (FP72007-2013) ERC grant [338251]; European Research Council through the SPIRE grant [647383]; FCT (Portugal); FEDER through COMPETE2020 [UID/FIS/04434/2013, POCI-01-0145-FEDER-007672, PTDC/FIS-AST/30389/2017, POCI-01-0145-FEDER-030389]; European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grantEuropean Union (EU) [792848]; European UnionEuropean Union (EU) [664931]; Independent Research Fund Denmark [7027-00096B]; Australian Research CouncilAustralian Research Council; NASANational Aeronautics & Space Administration (NASA) [NNX16AI09G, AS5-26555]; NSFNational Science Foundation (NSF) [AST-1514676]; Australian Research CouncilAustralian Research Council [DP150100250]; ERCEuropean Research Council (ERC) [772293]; Ramon y Cajal fellowshipMinistry of Education and Science, Spain [RYC-2015-17697]; Carlsberg FoundationCarlsberg Foundation [CF17-0760]; HBCSE-NIUS programme; NASA through Hubble Fellowship grants - Space Telescope Science Institute [HST-HF2-51399.001, HST-HF2-51424.001]; Premiale 2015 MITiC; NKFIH [K-115709]; Lendulet Program of the Hungarian Academy of Sciences [LP2018-7/2018]; NASA's Science Mission directorate ; 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 Hawai'ian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We thank Andrei Tokovinin for helpful information on the Speckle observations obtained with SOAR. D.H. acknowledges support by the National Aeronautics and Space Administration through the TESS Guest Investigator Program (80NSSC18K1585) and by the National Science Foundation (AST-1717000). A.C. acknowledges support by the National Science Foundation under the Graduate Research Fellowship Program. W.J.C., W.H.B., A.M., O.J.H., and G.R.D. acknowledge support from the Science and Technology Facilities Council and UK Space Agency. H.K. and F.G. acknowledge support from the European Social Fund via the Lithuanian Science Council grant No. 09.3.3-LMT-K-712-01-0103. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (grant DNRF106). A.J. acknowledges support from FONDECYT project 1171208, CONICYT project BASAL AFB-170002, and by the Ministry for the Economy, Development, and Tourism's Programa Iniciativa Cientifica Milenio through grant IC 120009, awarded to the Millennium Institute of Astrophysics (MAS). R.B. acknowledges support from FONDECYT Post-doctoral Fellowship Project 3180246, and from the Millennium Institute of Astrophysics (MAS). A.M.S. is supported by grants ESP2017-82674-R (MINECO) and SGR2017-1131 (AGAUR). R.A.G. and L.B. acknowledge the support of the PLATO grant from the CNES. The research leading to the presented results has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP72007-2013) ERC grant agreement No. 338251 (StellarAges). S.M. acknowledges support from the European Research Council through the SPIRE grant 647383. This work was also supported by FCT (Portugal) through national funds and by FEDER through COMPETE2020 by these grants: UID/FIS/04434/2013 and POCI-01-0145-FEDER-007672, PTDC/FIS-AST/30389/2017, and POCI-01-0145-FEDER-030389. T.L.C. acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 792848 (PULSATION). E.C. is funded by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 664931. V.S.A. acknowledges support from the Independent Research Fund Denmark (Research grant 7027-00096B). D.S. acknowledges support from the Australian Research Council. S.B. acknowledges NASA grant NNX16AI09G and NSF grant AST-1514676. T.R.W. acknowledges support from the Australian Research Council through grant DP150100250. A.M. acknowledges support from the ERC Consolidator Grant funding scheme (project ASTEROCHRONOMETRY, G.A. n. 772293). S.M. acknowledges support from the Ramon y Cajal fellowship number RYC-2015-17697. M.S.L. is supported by the Carlsberg Foundation (grant agreement No. CF17-0760). A.M. and P.R. acknowledge support from the HBCSE-NIUS programme. J.K.T. and J.T. acknowledge that support for this work was provided by NASA through Hubble Fellowship grants HST-HF2-51399.001 and HST-HF2-51424.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract AS5-26555. T.S.R. acknowledges financial support from Premiale 2015 MITiC (PI B. Garilli).; This project has been supported by the NKFIH K-115709 grant and the Lendulet Program of the Hungarian Academy of Sciences, project No. LP2018-7/2018.; Based on 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 Astrofisica de Canarias. Funding for the TESS mission is provided by NASA's Science Mission directorate. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. 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. This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST).