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Published June 2019 | Version Accepted Version + Published
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A Hot Saturn Orbiting An Oscillating Late Subgiant Discovered by TESS

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Abstract

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 μHz 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⊙), mass (M★ = 1.212 ± 0.074 M⊙), 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⊕) with an orbital period of ~14.3 days, irradiance of F = 343 ± 24 F⊕, and moderate mass (M_p = 60.5 ± 5.7 M⊕) and density (ρ_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⊕) 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 ~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.

Additional Information

© 2019 The American Astronomical Society. Received 2019 January 6; revised 2019 March 23; accepted 2019 March 26; published 2019 May 30. 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 Científica 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 Skłodowska-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 NAS5-26555. 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 Lendület 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 Astrofísica 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). Software: Astropy (Astropy Collaboration et al. 2018), Matplotlib (Hunter 2007), DIAMONDS (Corsaro & De Ridder 2014), isoclassify (Huber et al. 2017), EXOFASTv2 (Eastman 2017), ktransit (Barclay 2018).

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Published - Huber_2019_AJ_157_245.pdf

Accepted Version - 1901.01643.pdf

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Additional details

Identifiers

Eprint ID
92462
Resolver ID
CaltechAUTHORS:20190124-122617088

Related works

Describes
https://arxiv.org/abs/1901.01643 (URL)

Funding

NASA
80NSSC18K1585
NSF
AST-1717000
NSF Graduate Research Fellowship
Science and Technology Facilities Council (STFC)
United Kingdom Space Agency (UKSA)
European Social Fund
Lithuanian Science Council
09.3.3-LMTK-712-01-0103
Danish National Research Foundation
DNRF106
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)
1171208
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)
BASAL AFB-170002
Ministerio de Economía, Fomento y Turismo
IC 120009
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)
3180246
Millennium Institute of Astrophysics (MAS)
Ministerio de Economía, Industria y Competitividad (MINECO)
ESP2017-82674-R
Agència de Gestió d'Ajuts Universitaris i de Recerca
SGR2017-1131
Centre National d'Études Spatiales (CNES)
European Research Council (ERC)
338251
European Research Council (ERC)
647383
Fundação para a Ciência e a Tecnologia (FCT)
UID/FIS/04434/2013
Fondo Europeo de Desarrollo Regional (FEDER)
POCI-01-0145-FEDER-007672
Fondo Europeo de Desarrollo Regional (FEDER)
PTDC/FIS-AST/30389/2017
Fondo Europeo de Desarrollo Regional (FEDER)
POCI-01-0145-FEDER-030389
Marie Curie Fellowship
792848
Marie Curie Fellowship
664931
Danish Council for Independent Research
7027-00096B
Australian Research Council
DP150100250
NASA
NNX16AI09G
NSF
AST-1514676
European Research Council (ERC)
772293
Ramón y Cajal Programme
RYC-2015-17697
Carlsberg Foundation
CF17-0760
HBCSE-NIUS
NASA Hubble Fellowship
HST-HF2-51399.001
NASA Hubble Fellowship
HST-HF2-51424.001
NASA
NAS5-26555
National Research, Development, and Innovation Office (Hungary)
NKFIH K-115709
Hungarian Academy of Sciences
LP2018-7/2018

Dates

Created
2019-01-25
Created from EPrint's datestamp field
Updated
2021-11-16
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Caltech groups
Infrared Processing and Analysis Center (IPAC), Astronomy Department