Planet Hunters TESS I: TOI 813, a subgiant hosting a transiting Saturn-sized planet on an 84-day orbit. Issue 1 (23rd January 2020)

• Record Type: Journal Article
• 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;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 494:Issue 1(2020)
• Page Start: 750
• Page End: 763
• Publication Date: 2020-01-23
• Subjects: methods: statistical -- planets and satellites: detection -- stars: fundamental parameters -- stars: individual (TIC-55525572 -- TOI 813); Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa138
• Languages: English
• ISSNs: 0035-8711

Abstract

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 ($R_\star =1.94\, R_\odot$, $M_\star =1.32\, M_\odot$ ). 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 $2\, M_{\rm Jup}$ (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.