Three small planets transiting the bright young field star K2-233

11 Apr 2018  ·  David Trevor J., Crossfield Ian J. M., Benneke Björn, Petigura Erik A., Gonzales Erica J., Schlieder Joshua E., Yu Liang, Isaacson Howard T., Howard Andrew W., Ciardi David R., Mamajek Eric E., Hillenbrand Lynne A., Cody Ann Marie, Riedel Adric, Schwengeler Hans Martin, Tanner Christopher, Ende Martin ·

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 $\pm$ 0.06 R$_\oplus$, $R_c$ = 1.34 $\pm$ 0.08 R$_\oplus$), while the outer planet is a warm sub-Neptune ($R_d$ = 2.6 $\pm$ 0.1 R$_\oplus$). We estimate the stellar age to be 360$^{+490}_{-140}$ 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.

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Earth and Planetary Astrophysics