DOPPLER TOMOGRAPHY OF ACCRETION DISKS IN ALGOL BINARIES

Doppler tomography of H alpha spectra of four Algol-type binaries TT H ya, SW Cyg, U CrB, and U Sge has revealed quasi-stable accretion disks around the mass gaining star in each system. In the tomograms, these accretion structures are nearly symmetric distributions of gas between the stellar surface and the Roche lobe around the mass gainer. The di sk is most stable in TT Hya and SW Cyg, which have orbital periods gre ater than 4.5 days. However, the morphology of the accretion structure s in the shorter period systems, U CrB and U Sge, can change from a di sklike distribution to a streamlike distribution. During a streamlike epoch of these systems, the gas stream in the Doppler tomogram closely follows the predicted free fall path from the inner Lagrangian point toward the mass gainer. However, during the disklike stage, the intens ity of the disk is comparable to that of the gas stream. These tomogra ms display the first maps of accretion disks in the Algol-type class o f interacting binaries.