The TESS-Keck Survey. XIII. An Eccentric Hot Neptune with a Similar-Mass Outer Companion around TOI-1272

Mason G. MacDougall, Erik A. Petigura, Tara Fetherolf, Corey Beard, Jack Lubin, Isabel Angelo, Natalie M. Batalha, Aida Behmard, Sarah Blunt, Casey Brinkman, Ashley Chontos, Ian J. M. Crossfield, Fei Dai, Paul A. Dalba, Courtney Dressing, Benjamin Fulton, Steven Giacalone, Michelle L. Hill, Andrew W. Howard, Daniel Huber, Howard Isaacson, Stephen R. Kane, Molly Kosiarek, Andrew Mayo, Teo Mocnik, Joseph M. Akana Murphy, Daria Pidhorodetska, Alex Polanski, Malena Rice, Paul Robertson, Lee J. Rosenthal, Arpita Roy, Ryan A. Rubenzahl, Nicholas Scarsdale, Emma V. Turtelboom, Dakotah Tyler, Judah Van Zandt, Lauren M. Weiss, Emma Esparza-Borges, Akihiko Fukui, Keisuke Isogai, Kiyoe Kawauchi, Mayuko Mori, Felipe Murgas, Norio Narita, Taku Nishiumi, Enric Palle, Hannu Parviainen, Noriharu Watanabe, Jon M. Jenkins, David W. Latham, George R. Ricker, S. Seager, Roland K. Vanderspek, Joshua N. Winn, Allyson Bieryla, Douglas A. Caldwell, Diana Dragomir, M. M. Fausnaugh, Ismael Mireles, David R. Rodriguez

Submitted on 28 June 2022


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 d and Rp,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 measurements from the HIRES instrument at the Keck Observatory, we measured the mass of TOI-1272b to be Mp,b=25±2 M. We also confirmed a high eccentricity of eb=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-d orbit with a similar mass of Mp,c sini=27±3 M and ec0.35. 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 fenv11% 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.


Comment: Accepted at The Astronomical Journal; 17 pages, 11 figures

Subject: Astrophysics - Earth and Planetary Astrophysics