Three Small Planets Transiting the Bright Young Field Star K2-233

Abstract

We report the detection of three small transiting planets around the young K3 dwarf K2-233 (2MASS J15215519-2013539) from observations during Campaign 15 of the K2 mission. The star is relatively nearby (d = 69 pc) and bright (V = 10.7 mag, K[subscript s] = 8.4 mag), making the planetary system an attractive target for radial velocity follow-up and atmospheric characterization with the James Webb Space Telescope. The inner two planets are hot super-Earths (R[subscript b] = 1.40 ± 0.06 R[subscript ⊕], R[subscript c] = 1.34 ± 0.08 R[subscript ⊕]), while the outer planet is a warm sub-Neptune (R[subscript d] = 2.6 ± 0.1 ). We estimate the stellar age to be Myr based on rotation, activity, and kinematic indicators. The K2-233 system is particularly interesting given recent evidence for inflated radii in planets around similarly aged stars, a trend potentially related to photo-evaporation, core cooling, or both mechanisms.