A transiting super-Earth close to the inner edge of the habitable zone of an M0 dwarf star

Abstract

We present a super-Earth orbiting close to the inner edge of the habitable zone of the cool dwarf star K2-286 (EPIC 249889081), detected with data from the K2 mission in its $15^{th}$ campaign. The planet has radius of $2.1\pm 0.2$ R${}_{\oplus }$, near the 1.5 - 2.0 R${}_{\oplus }$ gap in the radii distribution. The equilibrium temperature is $347_{-11}^{+21}$ K, cooler than most of the small planets with well measured masses, and the orbital period is $27.359\pm 0.005$ days. K2-286, located at a distance of $76.3\pm 0.3$ pc, is an M0V star with estimated effective temperature of $3926\pm 100$ K, less active than other M dwarf stars hosting exoplanets. The expected radial velocity semi-amplitude induced by the planet on the star is $1.9_{-1.2}^{+1.3}$ m$\cdot$s${}^{-1}$, and the amplitude of signals in transit transmission spectroscopy is estimated at $5.0\pm 3.0$ ppm. Follow-up observations for mass measurements and transit spectroscopy should be desirable for this relatively bright target ($m_V=12.76,m_{Ks}=9.32$) hosting a transiting super-Earth within the inner edge of the habitable zone.

Accepted for publication in MNRAS