  Time-resolved H-alpha spectra of magnetically-active interacting binaries
have been used to create 3D Doppler tomograms by means of the Radioastronomical
Approach. This is the first 3D reconstruction of Beta Per, with RS Vul for
comparison. These 3D tomograms have revealed evidence of the mass transfer
process (gas stream, circumprimary emission, localized region, absorption
zone), as well as loop prominences and coronal mass ejections (CMEs) in Beta
Per and RS Vul that could not be discovered from 2D tomograms alone. The gas
stream in both binaries may have been deflected beyond the central plane by the
mass loser's magnetic field. The stream was more elongated along the predicted
trajectory in RS Vul than in Beta Per, but not as pronounced as in U CrB
(stream-state). The loop prominence reached maximum Vz velocities of +/- 155
km/s compared to +/- 120 km/s in Beta Per, while the CME reached a maximum Vz
velocity of +150 km/s in RS Vul and +100 km/s in Beta Per. The 3D tomograms
show that the gas flows are not symmetric relative to the central plane and are
not confined to that plane; a result confirmed by recent 15GHz VLBI radio
images of Beta Per. Both the 3D H-alpha tomography and the VLBI radio images
support an earlier prediction of the superhump phenomenon in Beta Per: that the
gas between the stars is threaded with a magnetic field even though the hot B8V
mass gaining star is not known to have a magnetic field.
