The Environments of Type Ib/c Supernovae

Up to about 1985, supernovae (SNe) generally were placed into the two Minkowski classes, type I and type II, defined by the absence or presence, respectively, of hydrogen in their optical spectra. Around that time it was acknowledged that several type I SNe were systematically peculiar, both spectroscopically and photometrically (Elias et al. 1985; Wheeler & Levreault 1985; Uomoto & Kirshner 1985; Branch 1986; Filippenko 1986), by missing the characteristic Si II spectral feature near 6150 å, having distinct infrared light curves, being optically redder and subluminous, and showing radio emission (Sramek et al. 1984). These SNe were designated as type Ib (Elias et al. 1985; Branch 1986) to distinguish them from the classical type Ia. Harkness et al. (1987) identified He I lines in spectra of the SN Ib 1984L, but some subsequent examples showed no He in their spectra and were further subclassified as Type Ic (Wheeler & Harkness 1990). The two subtypes, however, are nearly indistinguishable at late times. In this Symposium the entire class has been referred to as type Ib/c SNe. A recent bright example is SN 1994I in M51 (Filippenko et al. 1994).