TESS Hunt for Young and Maturing Exoplanets (THYME). V. A Sub-Neptune Transiting a Young Star in a Newly Discovered 250 Myr Association
Vanderburg, Andrew; Latham, David W.; Quinn, Samuel N.; Stassun, Keivan G.; Zhou, George; Howell, Steve B.; Collins, Karen A.; Wohler, Bill; Ricker, George R.; Vanderspek, Roland; Winn, Joshua N.; Jenkins, Jon M.; Hawkins, Keith; Seager, S.; Rizzuto, Aaron C.; Kraus, Adam L.; Mann, Andrew W.; Twicken, Joseph D.; Boyd, Patricia T.; Bouma, Luke G.; Schwarz, Richard P.; Glidden, Ana; Essack, Zahra; McLean, Brian; Newton, Elisabeth R.; Tofflemire, Benjamin M.; Wood, Mackenna L.; Osborn, Hugh; Nelson, Tyler; Fűrész, Gábor
United States, Sweden, Switzerland
Abstract
The detection and characterization of young planetary systems offer a direct path to study the processes that shape planet evolution. We report on the discovery of a sub-Neptune-sized planet orbiting the young star HD 110082 (TOI-1098). Transit events we initially detected during TESS Cycle 1 are validated with time-series photometry from Spitzer. High-contrast imaging and high-resolution, optical spectra are also obtained to characterize the stellar host and confirm the planetary nature of the transits. The host star is a late-F dwarf (M⋆ = 1.2M⊙) with a low-mass, M dwarf binary companion (M⋆ = 0.26M⊙) separated by nearly one arcminute (∼6200 au). Based on its rapid rotation and Lithium absorption, HD 110082 is young, but is not a member of any known group of young stars (despite proximity to the Octans association). To measure the age of the system, we search for coeval, phase-space neighbors and compile a sample of candidate siblings to compare with the empirical sequences of young clusters and to apply quantitative age-dating techniques. In doing so, we find that HD 110082 resides in a new young stellar association we designate MELANGE-1, with an age of ${250}_{-70}^{+50}$ Myr. Jointly modeling the TESS and Spitzer light curves, we measure a planetary orbital period of 10.1827 days and radius of Rp = 3.2 ± 0.1R⊕. HD 110082 b's radius falls in the largest 12% of field-age systems with similar host-star mass and orbital period. This finding supports previous studies indicating that young planets have larger radii than their field-age counterparts.