M dwarf variability could mimic microlensing signals in Roman survey

Regular M dwarfs are the most common type of star in our Galaxy, with the stellar mass function peaking around 0.23M☉ (T* = 3200 K, M4V). Given Roman’s deep sensitivity, these stars will dominate both the sources and the lenses of exoplanet microlensing events observed in Roman’s Galactic Bulge Time Domain Survey (GBTDS).

M dwarfs are highly magnetically active, producing photometric variability from both stellar rotation and flares. Stars cooler than M4 retain rapid rotation and high levels of magnetic activity for several Gyr, and both rotation and flare signatures can persist even for the older, more slowly rotating subset.

The proposal demonstrates that intrinsic M dwarf variability can masquerade as or hinder the detection of microlensing events. Although flares are typically asymmetric and stronger at bluer wavelengths, their shapes can closely resemble microlensing signals, creating a need to train detection algorithms to separate true planetary events from stellar activity.

m dwarfs, microlensing, roman survey, galactic bulge, gbtds, stellar variability, magnetic activity, stellar flares, stellar rotation, exoplanet detection