Interstellar extinction in the direction of the open cluster IC 348 and the Per OB2 association The relationship between interstellar extinction and distance in thedirection of dark clouds in the areas around the open cluster IC 348 andthe association Per OB2 is determined using the results of photoelectricphotometry of 189 stars in the Vilnius photometric system. Two absorbinglayers are found. The nearest layer, covering the whole area around IC348, shows the mean extinction A(V) of about 0.7 mag. It begins at thedistance of 160 pc and probably is an extension of the Taurus darkclouds to the northwest. The second absorbing layer has the form of achain of dark condensations named L1468, L1470, and L1471 and is at 260pc distance. This layer has a higher density, its mean extinction beingabout 2.0 mag. The cluster IC 348 is at about the same distance and isphysically related to the dark cloud L1470. The distance of the Per OB2association is found to be 340 pc and the mean extinction of its membersis 0.95 mag. A model of the spatial distribution of the Perseus andTaurus dark clouds based on photometric distance determinations in thisand previous papers is proposed. Six stars in the IC 348 area aresuspected to have emission in the H-alpha line.
Helium abundance in the atmospheres of B stars in open clusters The model-atmosphere method is applied to 6-m telescope spectrograms of46 B stars in the Per OB2 and Sco-Cen associations and in the alpha Percluster and the Pleiades to determine effective temperatures, surfacegravities, and helium abundances log epsilon(He). To within the erorrs,each cluster has the same mean epsilon(He).
