Determining the physical parameters of AM CVn binaries

AM CVn binaries are a group of stars in which a white dwarf accretes from ahydrogen deficient companion in a very short period binary (P_orb565 mins). Wecan study accretion flows of almost pure helium. They are predicted to bestrongest known sources for the gravitational wave observatory LISA. We aim toextend our survey of these objects using XMM which has shown that a largefraction of their accretion luminosity is emitted in the UV and Xray bands. Inparticular, we will determine the mass transfer rate, the element abundance fromtheir Xray spectra and characterise the Xray and UV variability for 4 systems.Together with our existing dataset of these systems it will give us importantclues for our understanding of their evolutionary history and their energy balance. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]