1999A&A...352..167M

Phase-resolved spectroscopic observations of BL Hyi obtained during the high mass transfer state are presented. The Hα, HeI5875 and HeI6678 emission line profiles are analyzed with the Doppler tomography technique. It is shown that these emissions arise from a single region in the accretion stream. No emission from the secondary star, either in the Hα or in the HeI line, could be identified. The accretion column could not be detected on the tomographic reconstructions of the system. An orbital ephemeris based on the radial velocities of the NaID emission line is derived, assuming a chromospheric origin in the secondary star. The spectroscopic observations provide a consistent picture of the accretion geometry in the system. Most of the optical emission line flux was found to be formed in a reservoir of low angular momentum gas filling a substantial fraction of the Roche lobe. Combining our results with literature data it was possible to constrain the absolute longitude of the magnetic axis in this classical polar.