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Paper: Images of Active Mass Transfer in Direct Impact Close Binary Systems
Volume: 293, 3D Stellar Evolution
Page: 120
Authors: Richards, M. T.
Abstract: This work summarizes our current knowledge of mass transfer in the short-period Algol-type binaries. In these systems, the gas stream flows directly into the photosphere of the mass gaining star because it does not have enough room to avoid impact with the star. Observational evidence of active mass transfer in these systems has been found from time-resolved optical and ultraviolet spectra collected at positions around the orbit of the binary. Doppler tomography of these spectra has demonstrated that the Algols are quite complex systems. They contain a range of circumstellar structures that include a gas stream, accretion annulus, accretion disk, stream-star impact region, and sometimes a source of chromospheric emission associated with the cool, mass-losing companion. Some systems alternate between stream-like and disk-like states, and provide direct evidence of active mass transfer within these systems. There are now Doppler tomograms of 12 Algol-type binaries with orbital periods ranging from 1.20 days to 6.95 days. These include tomograms obtained at H alpha, H beta, He I (lambda 6678 A), Si II (lambda 6371 A) and Si IV (lambda 1394 A).
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