Scattering polarization due to light source anisotropy - I. Large spherical envelope

Expressions are developed for the flux and polarization of radiation scatte red by a spherically symmetric envelope for a central point stellar light s ource that radiates anisotropically. These are obtained in terms of the com ponents of the spherical harmonics of the flux anisotropy from the source. Such anisotropy can arise from stellar spots, or from distortion of the sta r through rotation, pulsation, or magnetic effects. Explicit expressions fo r the Stokes parameters are obtained in the case of an ellipsoidal star of uniform surface brightness. It is thus shown that even when the scattering envelope is spherical, observationally significant polarization can arise f rom stars with physically realistic degrees of distortion. The time depende nce of the polarization is computed for models of ellipsoidal stars in the cases of pure rotation, pure pulsation, and both rotation and pulsation.