The nebular phase spectra of SN1993J

From June 19 to August 27, using the 2.16m telescope in the Beijing Astronomical Observatory, we obtained some low resolution spectra of SN1993J. The forbidden emission lines O I], Ca II] were very strong and dominated the spectra. However, the H and He lines were very weak. Many fine structures appeared in the H and O I] lines. We found that the supernova had entered the nebular phase and strong instability and chemical mixing had occurred in the ejecta.