A Compact Multi-Planet System With A Significantly Misaligned Ultra Short Period Planet

Abstract

We report the discovery of a compact multi-planet system orbiting the relatively nearby (78pc) and bright ($K=8.9$) K-star, K2-266 (EPIC248435473). 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${}_{\oplus }$, 0.646 R${}_{\oplus }$, 0.705 R${}_{\oplus }$, 2.93 R${}_{\oplus }$, 2.73 R${}_{\oplus }$, and 0.90 R${}_{\oplus }$, respectively. We are able to confirm the planetary nature of two of these planets (d & e) from 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 & c), and classify the last two as planetary candidates (K2-266.02 & .06). From a simultaneous fit of all 6 possible planets, we find that K2-266 b's orbit has an inclination of 75.32${}^{\circ }$ while the other five planets have inclinations of 87-90${}^{\circ }$. 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 EPIC248435395, a co-moving companion to K2-266.

18 pages, 12 figures, 7 tables, Accepted for Publication in the Astronomical Journal