Exploring persistent Doppler signals in rapidly-rotating M dwarfs

The recent detection of a candidate exoplanet at the stellar rotation period of the young M dwarf AD Leo places a new emphasis on understanding the persistence and chromaticity of starspot signals for the lowest-mass stars.  We have obtained highly precise multi-wavelength Doppler spectroscopy of four rapidly-rotating M dwarfs using the near-infrared Habitable-zone Planet Finder on McDonald Observatory's 10m Hobby-Eberly Telescope, and the optical HIRES spectrometer on the 10 Keck I Telescope.  Our Doppler observations are complemented by photometry from Kepler, TESS, and the Las Cumbres Observatory (LCO) network of telescopes.  For all four targets, we recover strong RV signals at the stellar rotation period.  Some of these signals remain coherent for hundreds of stellar rotations, which bears important implications for detecting exoplanets around similar objects.  We will discuss the persistence, chromaticity, and relation to photometry of each.