Previous
abstract 
Next abstract
We present new R-band polarimetry of 132 members of the Cygnus OB2 association. From these data we have determined the angular coherence length of the polarization position angle and tested two models for interstellar polarization toward a region where the galactic magnetic field is expected to be primarily along the line of sight. Statistically, the degree of polarization and its dispersion are in good agreement with a model which describes the polarization in terms of preferential extinction in small dark clouds threaded by a two-component magnetic field. One component is constant in direction, while the second is random in orientation and is characterized by the amplitude of Alfv\`en waves in the interstellar medium. The polarization position angle in our sample decorrelates on a size scale of~${\approx}0.4$~degrees, compared to 0.2 degrees for the extinction. This constrains the variations in dust and magnetic field geometries to sizes less than 12 pc. It is difficult to explain our polarization data in terms of previously proposed models for this region which invoked two parallel slabs of obscuring material with different magnetic field orientations.
We compare the polarization position angles of stars in the vicinity of Cygnus X-3 to the position angle of the elliptical radio scattering reported by Molnar et~al. (1989). The measured position angle of the elliptical scattering is approximately orthogonal to the mean position angle of the interstellar polarization. We speculate that a region of enhanced turbulence in or near the energetic Cygnus OB2 association may be responsible for the observed scattering.
