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

Author(s): Brett C. Addison, Duncan Wright, Belinda A. Nicholson, Bryson Cale, Teo Mocnik, Thomas Kallinger
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 M_P = 0.138 ± 0.023 M_J (43.9 ± 7.3 M_⊕), a radius of R_P = 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 M_sun, R_* = 1.888 ± 0.033 R_sun, T_eff = 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.
Organisation(s): Department of Astrophysics
External organisation(s): University of Southern Queensland, University of Oxford, George Mason University, University of California, Riverside
Journal: Monthly Notices of the Royal Astronomical Society
Volume: 502
Pages: 3704-3722
No. of pages: 19
ISSN: 0035-8711
DOI: https://doi.org/10.1093/mnras/staa3960
Publication date: 04-2021
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/9fb83484-7085-4e68-aae5-b9da3e2e897a

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