A stellar prominence eruption associated with a white-light flare on an M dwarf observed simultaneously by LAMOST and TESS

Stellar coronal mass ejections (CMEs) are regarded as major drivers of space weather in exoplanetary systems. Their large-scale expulsions of magnetised plasma may erode planetary atmospheres and influence the long-term evolution of close-in exoplanets. Nevertheless, confirmed detections of stellar CMEs and prominence eruptions remain extremely rare compared to the frequent occurrence of stellar flares. We investigated Doppler-shift signatures of stellar prominence eruptions associated with flares by combining simultaneous observations from LAMOST medium-resolution time-domain spectroscopy and TESS photometry. We analysed temporal Hα line profiles obtained with LAMOST's medium-resolution spectrograph. Blue-wing enhancements were identified through double-Gaussian fitting, and the integrated Hα blue-wing emission was used to estimate the mass and kinetic energy of the erupting prominence. In parallel, flares were identified in the TESS light curves, from which bolometric flare energies were derived. The temporal relationship between the Hα blue-wing signatures and the TESS flares was then examined and compared with solar eruptive events and existing theoretical models. In the active M-type dwarf LAMOST J063150.73+412942.2, we detect a white-light flare associated with a stellar prominence eruption. The flare has a bolometric energy of 2.94 $ and a maximum projected blueshift of -242 km,s^-1. We estimate a lower-limit prominence mass of 1.74 erg; the erupting prominence exhibits pronounced Hα blue-wing enhancements with a line-of-sight projected bulk velocity of -84 km,s -1 g and a corresponding kinetic energy of 6.14 erg. From the TESS photometry, we identify 79 flares with energies spanning 8.19 erg whose frequency distribution follows a power law with a slope of $α=-1.52. The flare associated with the prominence eruption lies towards the lower-energy end of this distribution and corresponds to a relatively frequent event. The comparable magnitudes of the flare radiative energy and the prominence kinetic energy indicate a near equipartition between these two components in an active M dwarf, resembling solar eruptive events. These results provide an observational constraint on magnetic reconnection and mass-ejection processes in low-mass stars and have potential implications for the space-weather environments of close-in exoplanets.