Accretion Regions in Direct-Impact Algol Binaries
Session 61 -- Novae and Stellar Accretion
Oral presentation, Tuesday, 10, 1995, 10:00am - 11:30am

## [61.04D] Accretion Regions in Direct-Impact Algol Binaries

Geary E. Albright, Mercedes T. Richards (University of Virginia)

The short-period Algols (P $<$ 6 days) are semi-detached systems where the gas stream from Roche-lobe overflow strikes the mass gaining star directly. Some of the material survives the impact with the photosphere and is feed into a structure known as a `transient accretion disk'. We have obtained full-orbit observations of 10 different Algol-type systems with different periods, mass ratios, stellar temperatures and radii. The two-dimensional distribution of the accretion structures can be determine from this database of over 1700 H$\alpha$ spectra. The types of accretion structures observed depend most sensitively on the angle of incidence of the gas stream and the mass transfer rate. The accretion regions observed include transient disks, the gas stream, a circumprimary bulge created by penetration of the gas stream into the mass gainer, chromospheric emission from the active secondary star, and nearly Keplerian accretion disks similar to those seen in the cataclysmic variables. The transitional stages from transient to nearly Keplerian disks have been investigated with this data set. Doppler tomograms calculated for each system confirm the presence of these accretion structures. In addition, the relationship between the high temperature UV absorbing regions and the Balmer-line emitting/absorbing regions was investigated by obtaing simultaneous IUE and H$\alpha$ spectroscopy for the systems U Sge and CX Dra.