Color Dependence of the Transit Detectability of Young Active M Dwarfs

Abstract

We investigate the planetary transit detectability in the presence of stellar rotational activity from light curves of young M dwarfs, and estimate the improvements in detection at near-infrared (NIR) wavelengths. By making maps of the transit signal detection efficiency over the orbital period and planetary radius with light curves of the members of four clusters observed by the K2 mission—Hyades, Praesepe, Pleiades, and Upper Scorpius—we evaluate the detectability of the rotation period and the modulation of the semi-amplitude. We find that the detection efficiency decreases remarkably, to about 20%, for rapid rotators with P rot ≤ 1 day, and that the lack of planets in Pleiades is likely due to the high fraction of rapidly rotating M dwarfs. We also evaluate the improvements in planet detection with NIR photometry via tests that use mock light curves, assuming that the signal amplitude of the stellar rotation decreases at NIR wavelengths. Our results suggest that NIR photometric monitoring will double the relative detection efficiency for transiting planetary candidates with P rot ≤ 1 day, and find planets around M dwarfs with approximately 100 Myr that are missing from previous transit surveys from space.