TOI-257b (HD 19916b): A Warm sub-Saturn Orbiting an Evolved F-type Star

Addison, Brett C. ORCID: and Wright, Duncan J. and Nicholson, Belinda A. and Cale, Bryson and Mocnik, Teo and Huber, Daniel and Plavchan, Peter and Wittenmyer, Robert A. and Vanderburg, Andrew and Chaplin, William J. and Chontos, Ashley and Clark, Jake T. and Eastman, Jason D. and Ziegler, Carl and Brahm, Rafael and Carter, Bradley D. ORCID: and Clerte, Mathieu and Espinoza, Nestor and Horner, Jonathan and Bentley, John and Jordan, Andres and Kane, Stephen R. and Kielkopf, John F. and Laychock, Emilie and Mengel, Matthew W. and Okumura, Jack and Stassun, Keivan G. and Bedding, Timothy R. and Bowler, Brendan P. and Burnelis, Andrius and Blanco-Cuaresma, Sergi and Collins, Michaela and Crossfield, Ian and Davis, Allen B. and Evensberget, Dag and Heitzmann, Alexis and Howell, Steve B. and Law, Nicholas and Mann, Andrew W. and Marsden, Stephen C. and Matson, Rachel A. and O'Connor, James and Shporer, Avi and Stevens, Catherine and Tinney, C. G. and Tylor, Christopher and Wang, Songhu and Zhang, Hui and Henning, Thomas and Kossakowski, Diana and Ricker, George and Sarkis, Paula and Schlecker, Martin and Torres, Pascal and Vanderspek, Roland and Latham, David W. and Seager, Sara and Winn, Joshua N. and Jenkins, Jon M. and Mireles, Ismael and Rowden, Pam and Pepper, Joshua and Daylan, Tansu and Schlieder, Joshua E. and Collins, Karen A. and Collins, Kevin I. and Tan, Thiam-Guan and Ball, Warrick H. and Basu, Sarbani and Buzasi, Derek L. and Campante, Tiago L. and Corsaro, Enrico and Gonzalez-Cuesta, Lucia and Davies, Guy R. and de Almeida, Leandro and do Nascimento, Jose-Dias, Jr. and Garcia, Rafael A. and Guo, Zhao and Handberg, Rasmus and Hekker, Saskia and Hey, Daniel R. and Kallinger, Thomas and Kawaler, Steven D. and Kayhan, Cenk and Kuszlewicz, James S. and Lund, Mikkel N. and Lyttle, Alexander and Mathur, Savita and Miglio, Andrea and Mosser, Benoit and Nielsen, Martin B. and Serenelli, Aldo M. and Aguirre, Victor Silva and Themeßl, Nathalie (2020) TOI-257b (HD 19916b): A Warm sub-Saturn Orbiting an Evolved F-type Star. Monthly Notices of the Royal Astronomical Society. pp. 1-20. ISSN 0035-8711


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 M<SUB>P</SUB> = 0.138 ± 0.023 $\rm {M_J}$ (43.9 ± 7.3 M<SUB>⊕</SUB>), a radius of R<SUB>P</SUB> = 0.639 ± 0.013 $\rm {R_J}$ (7.16 ± 0.15 R<SUB>⊕</SUB>), 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<SUB>*</SUB> = 1.390 ± 0.046 $\rm {M_{sun}}$ , R<SUB>*</SUB> = 1.888 ± 0.033 $\rm {R_{sun}}$ , T<SUB>eff</SUB> = 6075 ± 90 $\rm {K}$ , and vsin i = 11.3 ± 0.5 km s<SUP>-1</SUP>. 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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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Date Deposited: 02 Feb 2021 06:44
Last Modified: 11 Feb 2021 03:20
Uncontrolled Keywords: planetary systems; techniques: radial velocities; techniques; photometric; techniques: spectroscopic; asteroseismology; stars:; individual (TIC 200723869/TOI-257); Astrophysics - Earth and Planetary; Astrophysics; Astrophysics - Solar and Stellar Astrophysics
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
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