Abstract
ABSTRACT Using a recently completed proper-motion membership study of NGC 7789 and photographic magnitudes and colors, 29 blue stragglers are identified. The two-dimensional distribution of these stars on the plane of the sky is shown to be intermediate between the massive giant stars and that of stars extending approximately 2 magnitudes below the cluster turnoff point. These data suggest that the blue stragglers have masses appropriate to their observed main-sequence positions. Based on a model suggested by Strom and Strom (1970) of the binary origin of blue stragglers, the predicted number of cluster blue stragglers and the number observed are found to be in good agreement. However, this agreement rests on the untested assumption of the similarity of the Hyades and NGC 7789 binary frequency. Five blue stragglers are also identified which are estimated to have masses above the limiting binary value of MBS ≲ 2 MTO. This result, if substantiated, casts severe doubt on the validity of the binary mass-exchange hypothesis of blue stragglers.
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