VY Canis Majoris. III. Polarization and Structure of the Nebulosity.

Direct photographs of VY CMa taken in the 6500 A region through a Polaroid analyzer confirm 120- inch (305 cm) visual observations in showing that the small (approximately 8" X 12") nebula surrounding the star is radially plane-polarized in amounts up to 70 percent. The semistellar nuclei C, D, F, and F in the nebula that were discovered and measured by micrometric observers show the same heavy radial polarization as their nebular background, and hence must be structure in the nebulosity, not faint stars. The close component B could be neither seen nor photographed in 1971 January. The time variation in amount and direction of polarization that has been observed for the integrated radiation of VY CMa plus nebula can be explained by the known variability of the brightness of the star, or of portions of the nebula. The rotation of the plane of polarization with wavelength can be explained by a wavelength variation of the relative brightness of the star and various parts of the nebula.