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 BentleyStephen R. Kane, John F. Kielkopf, Emilie Laychock, Matthew W. Mengel, Jack Okumura, Keivan G. Stassun, Timothy R. Bedding, Brendan P. Bowler, Andrius Burnelis, Michaela Collins, Ian Crossfield, Allen B. Davis, Dag Evensberget, Alexis Heitzmann, Steve B. Howell, Nicholas Law, Andrew W. Mann, Stephen Marsden, James O'Connor, Avi Shporer, Catherine Stevens, C. G. Tinney, Christopher Tylor, Songhu Wang, Hui Zhang, Thomas Henning, Diana Kossakowski, George Ricker, Paula Sarkis, 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, Lucía González-Cuesta, Guy R. Davies, Rafael ~A. ~Garcí a, 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, Martin B. Nielsen, Aldo M. Serenelli, Victor Silva Aguirre, Nathalie Themessl

Research output: Contribution to journalArticlepeer-review

182 Downloads (Pure)


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 MJ (43.9 ± 7.3 M⊕⁠), a radius of RP = 0.639 ± 0.013 RJ (7.16 ± 0.15 R⊕⁠), bulk density of 0.65+0.12−0.11 (cgs), and period 18.38818+0.00085−0.00084 days⁠. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 Msun⁠, R* = 1.888 ± 0.033 Rsun⁠, Teff = 6075 ± 90 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.
Original languageEnglish
Pages (from-to)3704–3722
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date28 Dec 2020
Publication statusE-pub ahead of print - 28 Dec 2020

Bibliographical note

21 pages, 20 figures, 5 tables, submitted to MNRAS. Feedback welcome!


  • asteroseismology
  • techniques: photometric
  • techniques: radial velocities
  • techniques : spectroscopic
  • planetary systems
  • stars: individual (TIC 200723869/TOI-257)


Dive into the research topics of 'TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star'. Together they form a unique fingerprint.

Cite this