Recent observations of the young supernova remnant Cas A (Fesen et al., 1987) suggest an exploding Wolf-Rayet (WR) star of WNL type as a progenitor of this object. The majority of the WR stars seems to originate from massive O-stars of M > 40 M⊙. According to current investigations (Schild and Maeder, 1984; Langer, 1987; cf. also: Langer, this volume) WNL stars rank among the most massive WR stars. Hence, it is possible to assume that the stellar progenitor of Cas A was indeed a very massive star.As shown by Langer and El Eid (1986), (see also Woosley, 1986) a population I star of initially 100 M⊙ may loose enough mass during its evolution up to core He exhaustion to become a WN star of ∼ 45 M⊙, which then mainly consists of oxygen (more than 80%) synthesized during He burning.
G7.7–3.7: A Young Supernova Remnant Probably Associated with the Guest Star in 386 CE (SN 386)
