THE NATURE OF THE ENIGMATIC 10 MINUTE ACCRETING BINARY SYSTEM ES CET

We propose to obtain Xray/UV observations of the 10.3 minute accreting binarysystem ES Cet. It is the brightest out of three recently identifiedultracompact accreting binaries with orbital periods of 510 minutes. Thesesystems provide crucial insights into the physics of compact white dwarfbinaries that are the dominant gravitational wave sources in our galaxy, and theprogenitor population of Type Ia supernovae. The XMMNewton lightcurves andspectra will be correlated with the strong optical variability, and compared tothe two other ultracompacts and longer period AM CVn binaries. These Xraymeasurements will be crucial for establishing the nature of this enigmaticsystem, in particular the various accretion geometries that have been proposed. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]