The TESS-Keck Survey. VI. Two Eccentric Sub-Neptunes Orbiting HIP-97166

December 2021 • 2021AJ....162..265M

Authors • MacDougall, Mason G. • Petigura, Erik A. • Angelo, Isabel • Lubin, Jack • Batalha, Natalie M. • Beard, Corey • Behmard, Aida • Blunt, Sarah • Brinkman, Casey • Chontos, Ashley • Crossfield, Ian J. M. • Dai, Fei • Dalba, Paul A. • Dressing, Courtney • Fulton, Benjamin • Giacalone, Steven • Hill, Michelle L. • Howard, Andrew W. • Huber, Daniel • Isaacson, Howard • Kane, Stephen R. • Mayo, Andrew • Močnik, Teo • Akana Murphy, Joseph M. • Polanski, Alex • Rice, Malena • Robertson, Paul • Rosenthal, Lee J. • Roy, Arpita • Rubenzahl, Ryan A. • Scarsdale, Nicholas • Turtelboom, Emma • Zandt, Judah Van • Weiss, Lauren M. • Matthews, Elisabeth • Jenkins, Jon M. • Latham, David W. • Ricker, George R. • Seager, S. • Vanderspek, Roland K. • Winn, Joshua N. • Brasseur, C. E. • Doty, John • Fausnaugh, Michael • Guerrero, Natalia • Henze, Chris • Lund, Michael B. • Shporer, Avi

Abstract • We report the discovery of HIP-97166b (TOI-1255b), a transiting sub-Neptune on a 10.3 day orbit around a K0 dwarf 68 pc from Earth. This planet was identified in a systematic search of TESS Objects of Interest for planets with eccentric orbits, based on a mismatch between the observed transit duration and the expected duration for a circular orbit. We confirmed the planetary nature of HIP-97166b with ground-based radial-velocity measurements and measured a mass of M b = 20 ± 2 M along with a radius of R b = 2.7 ± 0.1 R from photometry. We detected an additional nontransiting planetary companion with M c sini = 10 ± 2 M on a 16.8 day orbit. While the short transit duration of the inner planet initially suggested a high eccentricity, a joint RV-photometry analysis revealed a high impact parameter b = 0.84 ± 0.03 and a moderate eccentricity. Modeling the dynamics with the condition that the system remain stable over >105 orbits yielded eccentricity constraints e b = 0.16 ± 0.03 and e c < 0.25. The eccentricity we find for planet b is above average for the small population of sub-Neptunes with well-measured eccentricities. We explored the plausible formation pathways of this system, proposing an early instability and merger event to explain the high density of the inner planet at 5.3 ± 0.9 g cc-1 as well as its moderate eccentricity and proximity to a 5:3 mean-motion resonance.


IPAC Authors


Benjamin Fulton

Assistant Scientist