The TESS-Keck Survey. III. A Stellar Obliquity Measurement of TOI-1726 c
Kristiansen, Martti H.; Batalha, Natalie M.; Latham, David W.; Quinn, Samuel N.; Kane, Stephen R.; Huber, Daniel; Howard, Andrew W.; Petigura, Erik A.; Behmard, Aida; Chontos, Ashley; Crossfield, Ian J. M.; Dalba, Paul A.; Kosiarek, Molly; Rubenzahl, Ryan A.; Weiss, Lauren M.; Ricker, George R.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Caldwell, Douglas A.; Günther, Maximilian N.; Dai, Fei; Albrecht, Simon; Mann, Andrew W.; Daylan, Tansu; Giacalone, Steven; Charbonneau, David; Fulton, Benjamin; Rose, Mark E.; Smith, Jeffrey C.; Robertson, Paul; Roy, Arpita; Isaacson, Howard; Beard, Corey; Lubin, Jack; Akana Murphy, Joseph M.; Dressing, Courtney; Scarsdale, Nicholas; Van Zandt, Judah; Rosenthal, Lee; Hill, Michelle; Mocnik, Teo; Hirsch, Lea; Mayo, Andrew; Morgan, Edward
United States, Denmark, Australia, Spain
Abstract
We report the measurement of a spectroscopic transit of TOI-1726c, one of two planets transiting a G-type star with V = 6.9 in the Ursa Major Moving Group (∼400 Myr). With a precise age constraint from cluster membership, TOI-1726 provides a great opportunity to test various obliquity excitation scenarios that operate on different timescales. By modeling the Rossiter-McLaughlin (RM) effect, we derived a sky-projected obliquity of $-{1}_{-32}^{{+35}^\circ} $ . This result rules out a polar/retrograde orbit and is consistent with an aligned orbit for planet c. Considering the previously reported, similarly prograde RM measurement of planet b and the transiting nature of both planets, TOI-1726 tentatively conforms to the overall picture that compact multitransiting planetary systems tend to have coplanar, likely aligned orbits. TOI-1726 is also a great atmospheric target for understanding differential atmospheric loss of sub-Neptune planets (planet b 2.2 R⊕ and c 2.7 R⊕ both likely underwent photoevaporation). The coplanar geometry points to a dynamically cold history of the system that simplifies any future modeling of atmospheric escape.