Quantifying the Effect of Short-timescale Stellar Activity Upon Transit Detection in M Dwarfs

Abstract M dwarf stars comprise 70%–80% of the galaxy's stars and host most of its rocky planets. They also differ from Sunlike stars in that they are “active” for billions of years or more: rotating quickly, flaring often, and emitting large amounts of UV and X-ray light. The effects of stellar activity upon both photometry and spectroscopy make their exoplanets more difficult to detect. While activity signals such as flaring and stellar rotation can be more readily modeled or removed from photometry, the contribution of unresolved stellar activity to transit sensitivity is harder to quantify. We investigate the difference in the detectability of planetary transits around a sample of M dwarfs observed by NASA's Transiting Exoplanet Survey Satellite (TESS) Mission, characterized by a common stellar radius, effective temperature, and TESS magnitude. Our sample is classified as either “active” or “inactive” based upon the presence of H α in emission. After removing more readily identifiable signatures of activity: stellar rotation and large flares, we perform an injection-and-recovery analysis of transits for each star. We extract detection sensitivity as a function of planetary radius and orbital period for each star. Then, we produce averaged sensitivity maps for the “active” stars and the “inactive” stars, for the sake of comparison. We quantify the extent to which signal-to-noise ratio is degraded for transit detection, when comparing an active star to an inactive star of the same temperature and apparent brightness. We aim for these sensitivity maps to be useful to the exoplanet community in future M dwarf occurrence-rate studies.