The Mv-spectral type calibration of the O and Wolf-Rayet (W-R) stars is reexamined. The actual numbers and distributions of stars and their W-R descendants in a volume-limited sample of stars within 2.5 kpc of the sun are compared. Evolutionary computations, with and without a simplified overshooting criterion for massive stars, are discussed in view of the observations in this sample. The following conclusions are reached: (1) Wolf-Rayet stars are descendant from stars with initial masses greater than 40 solar masses; and (2) with conventional models and assuming continuous star formation, the observed number ratio of W-R to Q stars is at least a factor of 3 larger than theoretically expected. This discrepancy can be lessened by taking account of the following: (1) the number and distribution of very luminous early-B supergiants suggests that they are also core hydrogen burning objects, so that these predecessors to W-R stars must be counted among the O star statistics; (2) overshooting during the W-R core helium burning phase might be important, thus lengthening the lifetime of this phase; (3) star formation in the Galaxy, at least for the most massive stars, might occur in relatively short-lived bursts.
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Conti et al. (1983) studied this question.