POLARIZATION OF THE WHITE-LIGHT CORONA AND ITS LARGE-SCALE STRUCTURE IN THE PERIOD OF SOLAR-CYCLE MAXIMUM

Distributions of brightness and polarization, p, were obtained for the February 16, 1980 solar corona. Isophotes have a circular shape, typi cal for the period of the solar cycle maximum. A variety of structural features are distinctly seen in the distribution of p. The polarizati on reaches 55 %, and the p values are comparatively high, not only in the well-defined streamers, but in the overlapping faint rays and smal l streamers, as well. A theoretical interpretation of the observed hig h degrees of polarization, taking into account the data on coronal bri ghtness, is very difficult. This cannot be done within the scope of sp herically symmetric models of the corona; the assumption of a high con centration of coronal matter into the plane of the sky is needed. With the most extreme densities in coronal structures, it is not, however, possible to exceed the observed value p = 55%. Taking into account th e accuracy of the polarization measurements, there are no reasons to r eject the Thomson scattering as a basic mechanism to explain the origi n of the white-light corona.