Program: GS-2023A-Q-116

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 becomes optically thin and thus the emission arises from regions close to the former stellar core. The physical interpretation of the spectrum is relatively straightforward 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 are required for spectroscopy. The proposed observations will greatly contribute to our knowledge of massive-star evolution and fate.