The TESS-Keck Survey. XIII. An Eccentric Hot Neptune with a Similar-mass Outer Companion around TOI-1272
Batalha, Natalie M.; Bieryla, Allyson; Latham, David W.; Rice, Malena; Kane, Stephen R.; Huber, Daniel; Rosenthal, Lee J.; 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.; Fetherolf, Tara; Ricker, George R.; Winn, Joshua N.; Jenkins, Jon M.; Caldwell, Douglas A.; Seager, S.; Mireles, Ismael; Dai, Fei; Fukui, Akihiko; Narita, Norio; Palle, Enric; Dragomir, Diana; Vanderspek, Roland K.; Angelo, Isabel; Giacalone, Steven; Fausnaugh, M. M.; Murgas, Felipe; Fulton, Benjamin; Robertson, Paul; Roy, Arpita; Blunt, Sarah; Isaacson, Howard; Močnik, Teo; Beard, Corey; Lubin, Jack; Akana Murphy, Joseph M.; Dressing, Courtney; Hill, Michelle L.; Kawauchi, Kiyoe; MacDougall, Mason G.; Scarsdale, Nicholas; Tyler, Dakotah; Van Zandt, Judah; Parviainen, Hannu; Esparza-Borges, Emma; Isogai, Keisuke; Brinkman, Casey; Mori, Mayuko; Watanabe, Noriharu; Nishiumi, Taku; Pidhorodetska, Daria; Turtelboom, Emma V.; Rodriguez, David R.; Mayo, Andrew; Polanski, Alex
United States, Australia, Spain, Japan
Abstract
We report the discovery of an eccentric hot Neptune and a non-transiting outer planet around TOI-1272. We identified the eccentricity of the inner planet, with an orbital period of 3.3 days and R p,b = 4.1 ± 0.2 R ⊕, based on a mismatch between the observed transit duration and the expected duration for a circular orbit. Using ground-based radial velocity (RV) measurements from the HIRES instrument at the Keck Observatory, we measured the mass of TOI-1272b to be M p,b = 25 ± 2 M ⊕. We also confirmed a high eccentricity of e b = 0.34 ± 0.06, placing TOI-1272b among the most eccentric well-characterized sub-Jovians. We used these RV measurements to also identify a non-transiting outer companion on an 8.7 day orbit with a similar mass of M p,c sin i = 27 ± 3 M ⊕ and e c ≲ 0.35. Dynamically stable planet-planet interactions have likely allowed TOI-1272b to avoid tidal eccentricity decay despite the short circularization timescale expected for a close-in eccentric Neptune. TOI-1272b also maintains an envelope mass fraction of f env ≈ 11% despite its high equilibrium temperature, implying that it may currently be undergoing photoevaporation. This planet joins a small population of short-period Neptune-like planets within the "Hot Neptune Desert" with a poorly understood formation pathway.