Planet Hunters TESS I: TOI 813, a subgiant hosting a transiting Saturn-sized planet on an 84-day orbit

May 2020 • 2020MNRAS.494..750E

Authors • Eisner, N. L. • Barragán, O. • Aigrain, S. • Lintott, C. • Miller, G. • Zicher, N. • Boyajian, T. S. • Briceño, C. • Bryant, E. M. • Christiansen, J. L. • Feinstein, A. D. • Flor-Torres, L. M. • Fridlund, M. • Gandolfi, D. • Gilbert, J. • Guerrero, N. • Jenkins, J. M. • Jones, K. • Kristiansen, M. H. • Vanderburg, A. • Law, N. • López-Sánchez, A. R. • Mann, A. W. • Safron, E. J. • Schwamb, M. E. • Stassun, K. G. • Osborn, H. P. • Wang, J. • Zic, A. • Ziegler, C. • Barnet, F. • Bean, S. J. • Bundy, D. M. • Chetnik, Z. • Dawson, J. L. • Garstone, J. • Stenner, A. G. • Huten, M. • Larish, S. • Melanson, L. D. • Mitchell, T. • Moore, C. • Peltsch, K. • Rogers, D. J. • Schuster, C. • Smith, D. S. • Simister, D. J. • Tanner, C. • Terentev, I. • Tsymbal, A.

Abstract • We report on the discovery and validation of TOI 813 b (TIC 55525572 b), a transiting exoplanet identified by citizen scientists in data from NASA's Transiting Exoplanet Survey Satellite (TESS) and the first planet discovered by the Planet Hunters TESS project. The host star is a bright (V = 10.3 mag) subgiant (R_\star - 1.94 R_⊙, M_\star = 1.32 M_⊙). It was observed almost continuously by TESS during its first year of operations, during which time four individual transit events were detected. The candidate passed all the standard light curve-based vetting checks, and ground-based follow-up spectroscopy and speckle imaging enabled us to place an upper limit of 2 M_Jup (99 per cent confidence) on the mass of the companion, and to statistically validate its planetary nature. Detailed modelling of the transits yields a period of 83.8911_-0.0031^+0.0027 d, a planet radius of 6.71 ± 0.38 R_⊕ and a semimajor axis of 0.423_-0.037^+0.031 AU. The planet's orbital period combined with the evolved nature of the host star places this object in a relatively underexplored region of parameter space. We estimate that TOI 813 b induces a reflex motion in its host star with a semi-amplitude of ∼6 m s^-1, making this a promising system to measure the mass of a relatively long-period transiting planet.

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• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2020MNRAS.494..750E
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• PREPRINT http://arxiv.org/abs/1909.09094
• DATA http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?type=REFERENCE&bibcode=2020MNRAS.494..750E
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• DATA https://irsa.ipac.caltech.edu/bibdata/2020/E/2020MNRAS.494..750E.html
• ELECTR https://doi.org/10.1093%2Fmnras%2Fstaa138