A STUDY OF THE ASYMMETRIC WIND OF P CYGNI

In this paper we present results of the first optical linear spectropolarimetric measurements of the hypergiant P Cygni. Our data indicate that both the intrinsic polarization and the position angle vary with time. Prior to removing the interstellar polarization vector, we find that the polarization varies by 0.642% while the position angle takes on values between 27.0-degrees and 39.8-degrees. The wavelength dependence of the polarization curve also changes with time indicating that the intrinsic polarization curve is not always constant with wavelength. After determining a model for interstellar polarization, we find that the amplitude of the intrinsic polarization of P Cyg varies from 0.04% to 0.48% with a change of 0.12% on successive nights. This large variation in polarization on such a short timescale probably indicates that the scattering material lies close to the star. In addition, there appears to be no strong preferential direction of the scattering angle since values of the position angle range from 5-degrees to 149-degrees. These data rule out the idea that P Cyg is surrounded by a spherically symmetric wind or an axisymmetric shell. Several possible geometries to describe the circumstellar material of this hypergiant are presented in the paper. Although electron scattering is the dominant polarizing mechanism, changes in the absorptive opacity may produce a color dependence to the polarization. Assuming that the material is confined to plumes or blobs, lower limits on the column density of electrons in the plume range from 3 x 10(22) cm-2 to 4 x 10(23) cm-2. We also find that H-alpha, H-beta, H-gamma, and He I (5876 angstrom) are not intrinsically polarized.