A refined spectral classification of 09.7 lab (p-var) has been derived for the supergiant star associated with the X-ray source Cyg X-1. The blue-violet absorption-line spectrum is entirely normal; however, a peculiar, variable emission line is present at He ii x4686. Two spectrograms of the star are illustrated. Subject headings: stars, individual - X-ray sources
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N. R. Walborn (1973) studied this question.