A Spectroscopic Study of the Region of the Double Cluster in Perseus.

Spectral classes and spectroscopic absolute magnitudes have been derived from low-dispersion spec- trograms for 153 early-type stars in the vicinity of the double cluster in Perseus. The material is complete to apparent magnitude 7.5 over a large region (100 X 15°) about the double cluster and symmetrical with respect to the galactic circle; it is complete, also, to magnitude 8.5 over an area of 60 diameter symmetrical about the double cluster. A few stars have been taken which make the material complete to apparent magnitude 9.5 in a small region near the center of each cluster. True distance moduli have been found for all stars later than 08 by using the photoelectric colors measured by Stebbins, Huff er, and Whitford. The results indicate that (1) there is a pronounced cluster- ing of early-type supergiants in the direction of, and at the distance of, the h and x Persei cluster, and (2) the diameter of this cluster of supergiants is considerably larger than that usually ascribed to the double cluster and may be estimated as about 5°. The variation in selective and total interstellar absorption across the field studied is discussed, and a reproduction shows the effect on star density caused by the considerable absorption suffered by these stars. On the bases of spectroscopic absolute magnitude, radial velocity, and interstellar line intensity, a considerable number of the stars investigated are attributed to the h and x Persei cluster, and the most probable distance of the cluster is found to be 1920 parsecs. There is an appreciable difference between the distance as found from spectroscopic absolute magnitudes and that obtained from the galactic-rota- tion ei~ect on the radial velocity of the cluster members. This discrepancy in distance, however, repre- sents a discrepancy in distance modulus of only about 0.6 mag., which may be due to an error in the abso- lute magnitudes ascribed to these supergiants. The cluster may, of course, have a small peculiar velocity. Many of the stars between apparent magnitudes 8.5 and 9.5 show the diffuse lines characteristic of rapidly rotating stars, and a number of the fainter stars show emission. It is shown that highly luminous stars of other types, such as the irregular M-type variables, appear in the same region about the double cluster. The Russell-Hertzsprung diagram for early-type stars attributed to the cluster is plotted, using the data of this investigation and that of Trumpler

Перевод пока недоступен