MAGNETISM IN THE POLAR BL HYDRI

We report on phase-resolved low-resolution spectrophotometry of the ma gnetic cataclysmic binary BL Hyi in low, intermediate, and high states of accretion. The cyclotron spectrum of the main accreting pole is re d and displays no resolvable cyclotron lines, which is indicative of a low field strength in the accretion spot. This supposition is confirm ed by the detection of halo Zeeman absorption in a field of only 12 Me gaGauss (MG), one of the lowest values measured among the polars. The effective photospheric field of the white dwarf measured during a low state, B-eff similar or equal to 22 MG is higher than in the accretion region which is usually assumed to lie in the vicinity of one of the magnetic poles. Thus deviations from a centered dipole field seem to b e present. Numerical synthetization of white dwarf photospheric spectr a shows that many of the observed features can be explained by a dipol e-/quadrupole combination, with both constituents having approximately the same strength.