The origin of the 10 megagauss Zeeman features in the AM Herculis system EF Eridani

This paper examines in detail the circularly polarized absorption feature present in the spectrum of EF Eri around 6300 A, reported by Schmidt et al. (1986) and interpreted in terms of magnetically strongly shifted sigma(-) absorption of H-alpha by circumstellar matter close to the surface of the white dwarf. The discovery of the corresponding circularly polarized sigma(+) component is reported, which strongly argues in favor of the above interpretation and confirms a magnetic field value around 10 MG. From an analysis of polarization spectra at different phases, values are obtained for the radial velocities of the absorbing cold circumstellar material and at detailed information on the geometry of the system. In particular, a double change of sign in the circular polarization in both the continuum and the 6300 A feature during one period suggests the presence of two accreting spots with opposite field polarity on the same hemisphere. 13 refs.