Examining the Rotation of the Planet-hosting M Dwarf GJ 3942

Abstract Based on radial velocities, EXORAP photometry, and activity indicators, the HArps-n red Dwarf Exoplanet Survey (HADES) team reported a 16.3 days rotation period for the M dwarf GJ 3942. However, an estimate of the magnitude-squared coherence between the HADES RV and H α time series has significant peaks at frequencies 1/16 day −1 and 1/32 day −1 . We turn to TESS photometry to test the hypothesis that the true rotation period is 32 days with 16 days harmonic. Although the average TESS periodogram has peaks at harmonics of 1/16 day −1 , the harmonic sequence is not fully resolved according to the Rayleigh criterion. The TESS observations suggest a 1/16 day −1 rotation frequency and a 1/32 day −1 subharmonic, though resolution makes the TESS rotation detection ambiguous.