On the dispersion in direction of interstellar polarization

The spatial distribution of polarization angle is summarized for 15 dark clouds that lack prominent star formation, for four star clusters embedded in dark clouds, for one evolved cluster with little associated extinction, and for six dark cloud complexes. Most clouds have either one well-defined mean direction over their spatial extent or two or three spatial zones having noticeably different mean directions. Nearly all regions have a single local maximum in their number distribution of polarization angle. Clouds with embedded clusters have a more complex distribution of polarization direction than do clouds without clusters. It is proposed that the enhanced dispersion of polarization angle in clusters may be more closely associated with young stars and/or with dense gas, than simply with the number of stars in the cluster. The greatest dispersion in direction among clouds without clusters, 0.7 radians, occurs in L1689 in Ophiuchus.