TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star. Issue 3 (28th December 2020)

• Record Type: Journal Article
• Authors: Addison, Brett C; Wright, Duncan J; Nicholson, Belinda A; Cale, Bryson; Mocnik, Teo; Huber, Daniel; Plavchan, Peter; Wittenmyer, Robert A; Vanderburg, Andrew; Chaplin, William J; Chontos, Ashley; Clark, Jake T; Eastman, Jason D; Ziegler, Carl; Brahm, Rafael; Carter, Bradley D; Clerte, Mathieu; Espinoza, Néstor; Horner, Jonathan; Bentley, John; Jordán, Andrés; Kane, Stephen R; Kielkopf, John F; Laychock, Emilie; Mengel, Matthew W; Okumura, Jack; Stassun, Keivan G; Bedding, Timothy R; Bowler, Brendan P; Burnelis, Andrius; Blanco-Cuaresma, Sergi; Collins, Michaela; Crossfield, Ian; Davis, Allen B; Evensberget, Dag; Heitzmann, Alexis; Howell, Steve B; Law, Nicholas; Mann, Andrew W; Marsden, Stephen C; Matson, Rachel A; O'Connor, James H; Shporer, Avi; Stevens, Catherine; Tinney, C G; Tylor, Christopher; Wang, Songhu; Zhang, Hui; Henning, Thomas; Kossakowski, Diana; Ricker, George; Sarkis, Paula; Schlecker, Martin; Torres, Pascal; Vanderspek, Roland; Latham, David W; Seager, Sara; Winn, Joshua N; Jenkins, Jon M; Mireles, Ismael; Rowden, Pam; Pepper, Joshua; Daylan, Tansu; Schlieder, Joshua E; Collins, Karen A; Collins, Kevin I; Tan, Thiam-Guan; Ball, Warrick H; Basu, Sarbani; Buzasi, Derek L; Campante, Tiago L; Corsaro, Enrico; González-Cuesta, L; Davies, Guy R; de Almeida, Leandro; do Nascimento, Jose-Dias; García, Rafael A; Guo, Zhao; Handberg, Rasmus; Hekker, Saskia; Hey, Daniel R; Kallinger, Thomas; Kawaler, Steven D; Kayhan, Cenk; S. Kuszlewicz, James; Lund, Mikkel N; Lyttle, Alexander; Mathur, Savita; Miglio, Andrea; Mosser, Benoit; Nielsen, Martin B; Serenelli, Aldo M; Aguirre, Victor Silva; Themeßl, Nathalie;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 502:Issue 3(2021)
• Page Start: 3704
• Page End: 3722
• Publication Date: 2020-12-28
• Subjects: asteroseismology -- techniques: photometric -- techniques: radial velocities -- techniques: spectroscopic -- planetary systems -- stars: individual (TIC 200723869/TOI-257); Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3960
• Languages: English
• ISSNs: 0035-8711

Abstract

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 $\rm {R_{sun}}$, T eff = 6075 ± 90 $\rm {K}$, and v sin 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.