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

2020; Oxford University Press; Volume: 494; Issue: 1 Linguagem: Inglês

10.1093/mnras/staa138

1365-2966

Nora L. Eisner, Oscar Barragán, S. Aigrain, Chris Lintott, G. E. Miller, N. Zicher, Tabetha S. Boyajian, César Briceño, Edward M. Bryant, Jessie L. Christiansen, Adina D. Feinstein, Lauren Melissa Flor Torres, M. Fridlund, D. Gandolfi, James Gilbert, Natalia Guerrero, Jon M. Jenkins, K. Jones, Martti H. Kristiansen, Andrew Vanderburg, Nicholas M. Law, Á. R. López-Sánchez, Andrew W. Mann, Emily Safron, Megan E. Schwamb, Keivan G. Stassun, H. P. Osborn, J. Wang, Andrew Zic, Carl Ziegler, F Barnet, S J Bean, D M Bundy, Z. Chetnik, J L Dawson, J. Garstone, Andrés Stenner, Marc Huten, S. Larish, L D Melanson, Terence N. Mitchell, C. J. Moore, K Peltsch, David J. Rogers, C. Schuster, D. Steve Smith, Dean Joseph Simister, Christopher Tanner, Ivan A. Terentev, A. Tsymbal,

Gamma-ray bursts and supernovae

We report on the discovery and validation of TOI 813b (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 $2 M_{Jup}$ (99 % confidence) on the mass of the companion, and to statistically validate its planetary nature. Detailed modelling of the transits yields a period of $83.8911_{ - 0.0031 } ^ { + 0.0027 }$ days, a planet radius of $6.71 \pm 0.38$ $R_{\oplus}$, and a semi major 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 under-explored region of parameter space. We estimate that TOI-813b induces a reflex motion in its host star with a semi-amplitude of $\sim6$ ms$^{-1}$, making this system a promising target to measure the mass of a relatively long-period transiting planet.