Linear polarization measurements at H β of early-type emission line stars

Linear polarization measurements across the Hβ emission lines of the stars γ Cas, zeta Tau and 48 Per are presented. For the first two stars there is a marked reduction of the polarization at the centre of the line and for γ Cas, this varies from night to night. During the Hβ observations of zeta Tau, a change of polarization over tens of minutes was indicated in a monitor channel tuned to the continuum on the blue side of Hβ. For the fainter star, 48 Per, the uncertainties of the polarimetry were increased in relation to γ Cas and zeta Tau by a factor of about two and at this precision, no differential effects across the line were recorded. Observations of α Cyg are also given to demonstrate the reliability of the polarimeter. (author)