New Evidence of Magnetic Interactions between Stars from Three-dimensional Doppler Tomography of Algol Binaries: β PER and RS VUL

Time-resolved Hα spectra of magnetically active interacting binaries have been used to create three-dimensional (3D) Doppler tomograms by means of the Radioastronomical Approach. This is the first 3D reconstruction of β 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 β Per and RS Vul that could not be discovered from two-dimensional tomograms alone. The gas stream in both binaries may have been deflected beyond the central plane by the donor star's magnetic field. The stream was more elongated along the predicted trajectory in RS Vul than in β Per, but not as pronounced as in U CrB (stream state). The loop prominence reached maximum Vz velocities of ±155 km s–1 in RS Vul compared to ±120 km s–1 in β Per, while the CME reached a maximum Vz velocity of +150 km s–1 in RS Vul and +100 km s–1 in β 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 15 GHz VLBI radio images of β Per. Both the 3D Hα tomography and the VLBI radio images support an earlier prediction of the superhump phenomenon in β 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.