The TESS-Keck Survey. VIII. Confirmation of a Transiting Giant Planet on an Eccentric 261 Day Orbit with the Automated Planet Finder Telescope

Paul A. Dalba*, Stephen R. Kane, Diana Dragomir, Steven Villanueva, Karen A. Collins, Thomas Lee Jacobs, Daryll M. Lacourse, Robert Gagliano, Martti H. Kristiansen, Mark Omohundro, Hans M. Schwengeler, Ivan A. Terentev, Andrew Vanderburg, Benjamin Fulton, Howard Isaacson, Judah Van Zandt, Andrew W. Howard, Daniel P. Thorngren, Steve B. Howell, Natalie M. BatalhaAshley Chontos, Ian J.M. Crossfield, Courtney D. Dressing, Daniel Huber, Erik A. Petigura, Paul Robertson, Arpita Roy, Lauren M. Weiss, Aida Behmard, Corey Beard, Casey L. Brinkman, Steven Giacalone, Michelle L. Hill, Jack Lubin, Andrew W. Mayo, Teo Močnik, Joseph M. Akana Murphy, Alex S. Polanski, Malena Rice, Lee J. Rosenthal, Ryan A. Rubenzahl, Nicholas Scarsdale, Emma V. Turtelboom, Dakotah Tyler, Paul Benni, Pat Boyce, Thomas M. Esposito, E. Girardin, Didier Laloum, Pablo Lewin, Christopher R. Mann, Franck Marchis, Richard P. Schwarz, Gregor Srdoc, Jana Steuer, Thirupathi Sivarani, Athira Unni, Nora L. Eisner, Tara Fetherolf, Zhexing Li, Xinyu Yao, Joshua Pepper, George R. Ricker, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn, Jon M. Jenkins, Christopher J. Burke, Jason D. Eastman, Michael B. Lund, David R. Rodriguez, Pamela Rowden, Eric B. Ting, Jesus Noel Villaseor

*Corresponding author for this work

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    We report the discovery of TOI-2180 b, a 2.8 MJ giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.
    Original languageEnglish
    Article number61
    JournalAstronomical Journal
    Issue number2
    Number of pages17
    Publication statusPublished - 2022


    • Amateur astronomy
    • Extrasolar gaseous giant planets
    • Transit photometry
    • Radial velocity
    • Planetary interior


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