Program: GN-2021B-Q-210

We propose GMOS-S and GMOS-N observations of core-collapse supernovae (SNe) at late phases (200-400 days after explosion). At such late times the SN spectrum becomes dominated by broad emission lines from forbidden transitions, i.e. a nebular spectrum. The SN ejecta become optically thin and thus the emission arises from regions close to the former stellar core. The physical interpretation of the spectrum is relatively straight-forward and it serves to constrain crucial properties, such as progenitor mass, chemical composition, and explosion mechanism. Due to the faintness of SNe at late phases, the use of 8-m class telescopes such as Gemini is required for spectroscopy. The proposed observations will greatly contribute to our knowledge of massive-star evolution and fate.