Supernovae 1983i and 1983v - Evidence for abundance variations in type Ib supernovae

Spectra are presented of SN 1983i 5 days after discovery and of SN 1983v 13 days after discovery. The similarity of these two spectra argues that they are of similar origin and phase. Theoretical atmosphere calculations provide evidence for a connection to the type Ib supernovae 1983n and 1984l, with SN 1983i and 1983v having a similar structure but less helium and more carbon and oxygen. Available photometry suggests that the spectra correspond to a phase about 20 days after maximum light. These spectra are consistent with an interpretation of type Ib supernovae arising in the bare cores of moderately massive stars, with individual events showing a range in He/O mass ratio from approximately 10 to less than 1.