Color Dependence of the Transit Detectability for Young Active M-dwarfs

TL;DR

This study examines how stellar activity affects the ability to detect planetary transits around young M-dwarfs, showing that near-infrared observations can significantly improve detection rates, especially for rapidly rotating stars.

Contribution

It provides the first detailed analysis of color-dependent transit detectability for young active M-dwarfs and demonstrates the potential of NIR photometry to enhance detection efficiency.

Findings

Detection efficiency drops to ~20% for rapid rotators with P_{rot} <= 1 d.

High fraction of rapid rotators in Pleiades explains the lack of detected planets.

NIR photometry can double detection efficiency for fast rotators.

Abstract

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