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TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star

Brett C. Addison Duncan J. Wright Belinda A. Nicholson Bryson Cale Teo Mocnik Daniel Huber Peter Plavchan Robert A. Wittenmyer Andrew Vanderburg William J. Chaplin Ashley Chontos Jake T. Clark Jason D. Eastman Carl Ziegler Rafael Brahm Bradley D. Carter Mathieu Clerte Néstor Espinoza Jonathan Horner John Bentley Andrés Jordán Stephen R. Kane John F. Kielkopf Emilie Laychock Matthew W. Mengel Jack Okumura Keivan G. Stassun Timothy R. Bedding Brendan P. Bowler Andrius Burnelis Sergi Blanco-Cuaresma Michaela Collins Ian Crossfield Allen B. Davis Dag Evensberget Alexis Heitzmann Steve B. Howell Nicholas Law Andrew W. Mann Stephen C. Marsden Rachel A. Matson James H. O'Connor Avi Shporer Catherine Stevens C. G. Tinney Christopher Tylor Songhu Wang Hui Zhang Thomas Henning Diana Kossakowski George Ricker Paula Sarkis Martin Schlecker Pascal Torres Roland Vanderspek David W. Latham Sara Seager Joshua N. Winn Jon M. Jenkins Ismael Mireles Pam Rowden Joshua Pepper Tansu Daylan Joshua E. Schlieder Karen A. Collins Kevin I. Collins Thiam-Guan Tan Warrick H. Ball Sarbani Basu Derek L. Buzasi Tiago L. Campante Enrico Corsaro L. González-Cuesta Guy R. Davies Leandro de Almeida Jose-Dias Do Nascimento Rafael A. García Zhao Guo Rasmus Handberg Saskia Hekker Daniel R. Hey Thomas Kallinger Steven D. Kawaler Cenk Kayhan James S. Kuszlewicz Mikkel N. Lund Alexander Lyttle Savita Mathur Andrea Miglio Benoit Mosser 1 Martin B. Nielsen Aldo M. Serenelli Victor Silva Aguirre Nathalie Themeßl 
Abstract : We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the MINERVA-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 $\rm {M_J}$ (43.9 ± 7.3 $\, M_{\rm \oplus}$ ), a radius of RP = 0.639 ± 0.013 $\rm {R_J}$ (7.16 ± 0.15 $\, \mathrm{ R}_{\rm \oplus}$ ), bulk density of $0.65^{+0.12}_{-0.11}$ (cgs), and period $18.38818^{+0.00085}_{-0.00084}$ $\rm {days}$ . TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 $\rm {M_{sun}}$ , R* = 1.888 ± 0.033 $\rm {R_{sun}}$ , Teff = 6075 ± 90 $\rm {K}$ , and vsin i = 11.3 ± 0.5 km s-1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.
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Submitted on : Tuesday, July 5, 2022 - 8:24:19 AM
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Brett C. Addison, Duncan J. Wright, Belinda A. Nicholson, Bryson Cale, Teo Mocnik, et al.. TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star. Monthly Notices of the Royal Astronomical Society, 2021, 502, pp.3704-3722. ⟨10.1093/mnras/staa3960⟩. ⟨insu-03713781⟩

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