A Study of the Blue Stragglers in the Open Cluster NGC 7789

Image-tube spectrograms and Str5mgren 4-color and H photometry were obtained for twelve possible blue-straggler members of the open cluster NGC 7789. Membership was established for eight of these twelve blue-straggler candidates. From the data obtained, it was possible to test three competing hypotheses for the origin of these stars. Estimates of masses based on a match of our photometry with model atmospheres show that blue stragglers have masses appropriate to their location in the colormagnitude diagram. Furthermore, of four blue-straggler members studied carefully for radial-velocity variations, all four exhibited definite changes in velocity. These observations suggest strongly that blue stragglers are members of binary systems in which mass exchange has taken place.