POWRE: Direct Impact Accretion in Interacting Binary Star Systems

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

AST-0074586 Richards Direct impact accretion in stars occurs in the class of interacting binary star systems known as the Algol-type binary stars. These systems contain a type B-A main sequence star and a cool type F-K giant star or subgiant companion that fills its Roche lobe. In the short-period Algol stars, the gas flow from the cool component makes contact with the surface of the companion in a direct impact. This impact does not occur in the long-period Algols because they are wider and the radius of the mass gainer is relatively small when compared to the separation of the stars in the binary. The accretion structures produced by the direct impact range from a hot spot on the surface of the star to nearly stable accretion disks called accretion annuli. Data using Doppler tomogram observations of these binaries show evidence of Hydrogen-alpha accretion along the predicted gravitational path of the mass transfer stream. Such distinct images are unique among the entire class of interacting binaries because the Algols are in the slow phase of mass transfer and hence provide an opportunity to capture the process of mass transfer in action. Some short-period Algols have stable accretion structures while others are quite variable and they change within an orbital cycle from a stream-like distribution to one which resembles a classical accretion disk. Dr. Richards has studied these accretion structures by means of Hydrogen-alpha (H-alpha) wavelength and ultraviolet spectroscopy observations, Doppler tomography, and hydrodynamic simulations. Recently, Dr. Richards completed a major study of the H-alpha spectroscopic morphologies of 18 Algol-type star systems. Dr. Richards will take academic leave from the University of Virginia to go to the Institute of Advanced Studies for a sabbatical visit. Dr. Richards will be able to work on enhancing the results from the previous research, during the sabbatical period, by using data from similar studies of ultraviolet spectra and the comparison of Doppler tomograms generated at both optical and ultraviolet wavelengths. This project is funded by the Division of Astronomical Sciences and the Office of Multidisciplinary Activities in the Mathematical and Physical Sciences Directorate. ***