An Investigation of the Linear Polarization in Emission Features of Active Regions

A study has been made of linear polarization in `moustaches' using the Hα and Hβ lines. A Wollaston prism and an achromatic λ/2-plate were employed in the study. In the course of the observations, the major axis of the plate was placed at 0° and 22°.5 with respect to the horizontal axis of the installation. The Stokes parameters J, Q, and U were recorded, thus enabling the degree of polarization and the field azimuth to be determined. During the first three minutes of the existence of the moustaches, the two lines revealed a linear polarization of about 7% located at the center of the lines. No polarization was found during the later stage of the moustaches' lifetimes. Whenever the linear polarization is present, there is a tendency for the polarization to decrease rapidly, in accompaniment of a turning of the azimuth. Several mechanisms for interpreting the polarization observed in the moustaches are examined. Some suggestions are made in support of the excitation of hydrogen atoms in the moustaches initiated by a high-energy electron flux or vertical heat conduction.