The Stellar Content of H and Chi Persei-Cluster and Association.

Supergiants, 0 stars, giants, subgiants, and their fainter neighbors (used to obtain reddenings) have been measured photoelectrically in UB V in the general association (approximately 5 x 7 ) the nucleus of which is formed by the clusters proper, h and Persei. Photoelectric observations were made of 336 stars. In addition, within the nuclei, photographic interpolation has been obtained on an additional 608 stars, complete down to V = 17 photoelectric and a.bout V = 18 photographic. The results appear to signify a non-unique age and do not show significant correlation with spatial position. In particular, three pronounced ma4nia are found in the past rate of star formation; this is suggested by the fine structure in the color-magnitude (C-M) diagram for stars above the vertical main sequence and a fainter "main-sequenc breakoff" at M = -4. Another sequence of stars seems to be in gravitational contraction with the inain-sequence stars extending, nevertheless, to the observational limit. Hayashi's and Cameron's theoretical evolutionary track for helium burning agrees with observations of one of the early supergiant sequences; and the predicted gap between helium exhaustion and the onset of carbon-neon burning corresponds to the observed Hertzsprung gap. The expected neutrino losses in the M supergiant stage should produce a ratio of late-to-early supergiants so much smaller than that which is observed that it is difficult to imagine that the dilemma will be vitiated by later investigations where greater attention is payed to completeness (over the 5 X 7 region). Such an investigation is, nevertheless, presently under way. Contraction and nuclear time scales for the different features are compatible. The differences in apparent evolutionary tracks between the Galaxy, the Large Magellanic Cloud (LMC), and the Small Magellanic Cloud (SMC) are reconfirmed. The two-color diagram of the 0 stars is of a black-body character, and that of the early supergiants exhibits the previously found ultraviolet excess. In contrast to other studies the M supergiants are found to be shifted redward and show a steep two-color relation. Spectral type versus (B - V) o is monotonic for all stars.