This award will support collaborative research in astronomy between Dr. Steven Howell, Planetary Science Institute, Tucson, Arizona and Dr. Keith Mason, Mullard Space Science Laboratory, University College London. The objective of the proposed project is to investigate a previously unstudied group of cataclysmic variable stars which may be members of the Galactic halo. The standard picture of a cataclysmic variable (CV) is a close binary system consisting of a late type main sequence star which transfers mass to a white dwarf companion. The material that leaves the secondary forms a disk around the primary star. The intersection of this stream and the disk gives rise to a "hot spot", which can provide a large fraction of the system light. If the white dwarf has a sufficiently strong magnetic field, the transferred material will be disturbed and even the formation of the disk can be retarded. The only direct method of finding the true location of these cataclysmic variables is through distance determination. The investigators are analyzing spectroscopic data, using software which they developed jointly at the Mullard Space Science Laboratory, to model and deconvolve the contributions to the data from the various systems components. This procedure will allow them to derive a distance for these stars. If these binary systems are really located in the Galactic halo, they should have very different properties from their well studied counterparts located in the disk. The results of this study will make an important contribution to understanding the true nature of cataclysmic variables and how these populations differ, as well as to understanding the structure and evolution of our Galaxy in general. The project will benefit from the complementary expertise of the two investigators in the area of theoretical interpretations of binary stars.
