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

Journal article

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 (USDR_\star=1.94\,R_\odotUSD, USDM_\star=1.32\,M_\odotUSD). 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 USD2 M_{Jup}USD (99 % confidence) on the mass of the companion, and to statistically validate its planetary nature. Detailed modelling of the transits yields a period of USD83.8911_{ - 0.0031 } ^ { + 0.0027 }USD days, a planet radius of USD6.71 \pm 0.38$ $R_{\oplus}$, and a semi major axis of $0.423_{ - 0.037 } ^ { + 0.031 }USD 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 USD\sim6USD msUSD^{-1}USD, making this system a promising target to measure the mass of a relatively long-period transiting planet.

Authors: Eisner, NL; Barragán, O; Aigrain, S; Lintott, C; Miller, G

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 494
• Issue: 1
• Pages: 750-763
• Publication date: 2020-01-23
• Acceptance date: 2020-01-06
• DOI: 10.1093/mnras/staa138
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: detection; astro-ph.EP; stars: fundamental parameters; FFR; planets and satellites; methods:statistical; stars:individual (TIC-55525572, TOI 813)