Validation of TOI-1221 b: A Warm Sub-Neptune Exhibiting Transit Timing Variations around a Sun-like Star

Christopher Mann, David Lafreniére, Diana Dragomir, Samuel N. Quinn, Thiam Guan Tan, Karen A. Collins, Steve B. Howell, Carl Ziegler, Andrew W. Mann, Keivan G. Stassun, Martti H. Kristiansen, Hugh Osborn, Tabetha Boyajian, Nora Eisner, Coel Hellier, George R. Ricker, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. WinnJon M. Jenkins, Jesus Noel Villaseñor, Brian McLean, Pamela Rowden, Guillermo Torres, Douglas A. Caldwell, Kevin I. Collins, Richard P. Schwarz

Research output: Contribution to journalArticlepeer-review


We present a validation of a long-period ( 91.68278-0.00041+0.00032 days) transiting sub-Neptune planet, TOI-1221 b (TIC 349095149.01), around a Sun-like (m V = 10.5) star. This is one of the few known exoplanets with a period >50 days, and belongs to the even smaller subset of which have bright enough hosts for detailed spectroscopic follow-up. We combine Transiting Exoplanet Survey Satellite light curves and ground-based time-series photometry from the Perth Exoplanet Survey Telescope (0.3 m) and Las Cumbres Observatory global telescope network (1.0 m) to analyze the transit signals and rule out nearby stars as potential false-positive sources. High-contrast imaging from the Southern Astrophysical Research Telescope and Gemini/Zorro rule out nearby stellar contaminants. Reconnaissance spectroscopy from CHIRON sets a planetary scale upper mass limit on the transiting object (1.1 and 3.5 M Jup at 1σ and 3σ, respectively) and shows no sign of a spectroscopic binary companion. We determine a planetary radius of Rp=2.91-0.12+0.13R⊕, placing it in the sub-Neptune regime. With a stellar insolation of S=6.06-0.77+0.85S⊕, we calculate a moderate equilibrium temperature of T eq = 440 K, assuming no albedo and perfect heat redistribution. We find a false-positive probability from the TRICERATOPS tool of FPP = 0.0014 ± 0.0003 as well as other qualitative and quantitative evidence to support the statistical validation of TOI-1221 b. We find significant evidence (>5σ) of oscillatory transit timing variations, likely indicative of an additional nontransiting planet.

Original languageEnglish (US)
Article number217
JournalAstronomical Journal
Issue number5
StatePublished - May 1 2023

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Validation of TOI-1221 b: A Warm Sub-Neptune Exhibiting Transit Timing Variations around a Sun-like Star'. Together they form a unique fingerprint.

Cite this