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Irradiation of the Secondary Star in Cataclysmic Variable Stars

Stephen Davey

出版	University of Sussex, 1994
URL	http://books.google.com.hk/books?id=OS76HAAACAAJ&hl=&source=gbs_api

註釋

With the continual improvement in CCD detectors, particularly in the red and far red parts of the spectrum, there have been more and more observations of the secondary star in cataclysmic variables. However, it soon became apparent that radial velocity determinations using, for example, the Na I doublet might need to be corrected to allow for the effects of irradiation by the white dwarf and accretion disc. In general, the effect of irradiation is to ionize some of the sodium atoms and push the centre of light of the secondary star, determined by the Na I doublet, back from the centre of mass. This over-estimates the orbital velocity of the secondary star. The radial velocity measurements of the secondary star and Na I doublet line profile variations for a number of cataclysmic variable systems are analysed and used to map surface features. It is found that for many of the systems in which irradiation is distorting the derived radial velocity curves, the surface distribution of the Na I doublet is far more asymmetrical than would be predicted from simple models. In order to explain some of these results the hydrodynamics of the upper atmosphere of the secondary star is investigated using a finite difference scheme and also Smoothed Particle Hydrodynamics. Atmospheric motions driven by the heating of the front face of the star are studied, with Coriolis forces and the varying surface gravity and geometry included. The numerical simulations suggest that the irradiation will induce large scale gas motions of around lkm s - 1 , leading to global weather systems, and can go some way towards explaining the observed asymmetries.