Coronal Green-Line Emission During a Solar Prominence Eruption: Spectroscopic Evidence of Its Correspondence with the EUV Late Phase

We report spectroscopic observations during a prominence eruption on 9 October 2025 from the Sun's west limb, associated with an M2.0 flare that commenced at 12:11 UT. The event was captured in sit-and-stare mode by the Visible Emission Line Coronagraph (VELC) onboard Aditya-L1, providing continuous observations of the Fe XIV 5303 Åcoronal greenline. The spatially averaged green-line emission exhibits a clear correspondence with the EUV late-phase (ELP) emission observed in multiple SDO/AIA channels. In particular, an enhanced 5303 Åemission peak at 15:24 UT coincides with secondary peaks in the AIA 211, 171, 193, and 335 Åpassbands, occurring about173 minutes after the X-ray peak. The 5303 Åline-width information provides important constraints on the mechanism responsible for the ELP. The line-width decreases progressively by about 28% toward the ELP peak, broadly consistent with the cooling of post-flare coronal loops. This behavior suggests that the ELP is predominantly associated with plasma cooling, with relatively weak additional energy input from magnetic reconnection, which does not produce a significant enhancement in line-widths. The estimated non-thermal velocity decreases from about 36 km s-1 during the impulsive phase to about 21 km s-1 during the gradual phase, indicating a reduction in turbulent plasma motions. And doppler velocities evolve from predominantly positive values during the eruptive rise phase to negative values during the later gradual phase, implying upward and subsequent downward plasma motions. To our knowledge, this study provides the first space-based spectroscopic evidence linking coronal green-line emission with the ELP and its origin during a solar flare.