A Compact Multi-planet System with a Significantly Misaligned Ultra Short Period Planet
Kristiansen, Martti H.; Omohundro, Mark; Vanderburg, Andrew; Bieryla, Allyson; Latham, David W.; Quinn, Samuel N.; Berlind, Perry; Calkins, Michael L.; Esquerdo, Gilbert A.; Stassun, Keivan G.; Schlieder, Joshua E.; Adams, Fred C.; Ciardi, David R.; Rodriguez, Joseph E.; Eastman, Jason D.; Dressing, Courtney D.; Khain, Tali; Becker, Juliette C.; Rappaport, Saul; Hadden, Sam; Mayo, Andrew; Schwengeler, Hans Martin; Terentev, Ivan
United States, Denmark
Abstract
We report the discovery of a compact multi-planet system orbiting the relatively nearby (78 pc) and bright (K = 8.9) K-star, K2-266 (EPIC 248435473). We identify up to six possible planets orbiting K2-266 with estimated periods of P b = 0.66, P .02 = 6.1, P c = 7.8, P d = 14.7, P e = 19.5, and P .06 = 56.7 days, and radii of R P = 3.3 R ⊕, 0.646 R ⊕, 0.705 R ⊕, 2.93 R ⊕, 2.73 R ⊕, and 0.90 R ⊕, respectively. We are able to confirm the planetary nature of two of these planets (d and e) by analyzing their transit timing variations ({m}d={8.9}-3.8+5.7 {M}\oplus and {m}e={14.3}-5.0+6.4 {M}\oplus ), confidently validate the planetary nature of two other planets (b and c), and classify the last two as planetary candidates (K2-266.02 and .06). From a simultaneous fit of all six possible planets, we find that K2-266 b’s orbit has an inclination of 75.°32 while the other five planets have inclinations of 87°-90°. This observed mutual misalignment may indicate that K2-266 b formed differently from the other planets in the system. The brightness of the host star and the relatively large size of the sub-Neptune sized planets d and e make them well-suited for atmospheric characterization efforts with facilities like the Hubble Space Telescope and upcoming James Webb Space Telescope. We also identify an 8.5 day transiting planet candidate orbiting EPIC 248435395, a co-moving companion to K2-266.