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

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_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_b = 1.40 ± 0.06 R_⊕, R_c = 1.34 ± 0.08 R_⊕), while the outer planet is a warm sub-Neptune (R_d = 2.6 ± 0.1 R_⊕). We estimate the stellar age to be 360_(-140)^(+490) 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.