The Nearby Poor Cluster Collinder 399

Collinder 399, a loose cluster of bri ht stars around 4 and 5 Vulpeculae, is studied with new and old data. Photoe ectric UBV magnitudes of 29 stars were obtained, as well as hotographic UBV magnitudes of 250 stars, and objective prism spectral classiication of 42 stars. Existing radial velocity and proper motion measures and spectral classifications were collected. We conclude Collinder 399 is a cluster but contains only six main-sequence early-A stars (+194000, + 194004, + 194009, 5 Vul, and + ) and one red giant (+ ). The cluster is only slightly reddened, with = 006. A fit to the zero-a e main sequence (ZAMS) yielded a tii'e distance modulus of about 5'-'5; this p aces Collinder 399 as near as the Pleiades. For this distance there is a complete absence of even possible members between A2 and F5, and the possible members later than F5 are no more numerous than in an outl ing control region of equal area; thus it appears that the main sequence actua ly ends at about Mv = +2!!'. The five nearby bright B stars once considered members of Collinder 399 are shown to lie in the background. Collinder 399 is about 2 X 10 years old, between M 11 and the Hyades in age. It is thus consistent that, in Mv, the giant + lies between the giant branch of M 11 and that of the Hyades.