Characterizing the Exoplanet Population Around Mid-to-Late M Dwarfs

Abstract

Around Sun-like stars and early M dwarfs alike, super-Earths and sub-Neptunes form a bimodal distribution separated by a dearth of planets between 1.6 and 1.9 Earth radii known as the radius valley. Modeling these planet populations and the radius valley have refined planet formation models but full understanding of the planet formation process requires a complete picture of the planet population extending to the lowest mass stars. As of yet, transiting exoplanet surveys have been largely insensitive to planets around mid-to-late M dwarfs. Fortunately, NASA’s Transiting Exoplanet Survey Satellite (TESS) has opened a window into the exoplanet population around mid-to-late M dwarfs. I have led a systematic search for small transiting planets around 9,131 mid-to-late M dwarfs observed by TESS to characterize the planet population. I will present my pipeline to process TESS light curves and to detect and vet signals from transiting planets. Over the set of targets, this survey recovers a population of 73 manually vetted transiting planet signals. Using injection-recovery tests, I characterize the sensitivity of my pipeline to transiting planets around stars in the sample as a function period, instellation and radius. Using the recovered planet population combined with my survey completeness, I measure an occurrence rate of 1.326(+0.210/−0.208) planets per star, with radii < 6.5R⊕ and orbital periods within 30 days dominated by a population of sub- and super-Earths with very few sub-Neptunes compared to more massive M dwarfs. This result is in agreement with previous work in this regime, while surveying a factor of 25 more stars, and aligns with theoretical predictions of the planet population. Along with our occurrence rate calculation, we provide strong evidence that the radius valley disappears in this stellar mass regime.