EC11575-1845 - A NEW CLOSE BINARY WITH A LARGE REFLECTION EFFECT DISCOVERED BY THE EDINBURGH-CAPE SURVEY

EC11575 - 1845 is a non-eclipsing binary consisting of an sdO primary and a late M-type secondary showing a large reflection effect. UBVRI p hotometry reveals an orbital period of 7.86 h, with the amplitude of t he reflection effect increasing with wavelength as expected. The spect roscopic behaviour reveals absorption lines from the primary and varia ble intensity emission-line features from the heated face of the secon dary. The radial velocity variations of both components restrict the m ass ratio to M(2)/M(1) = 0.29-0.32. A self-consistent model can be der ived for the system using Napier's algorithm, which constrains the mas ses and radii of the components, the orbital inclination and the effec tive temperature of the primary. From evolutionary considerations it i s shown that EC11575 - 1845 belongs to a small class of progenitors of cataclysmic variable stars which on a time-scale of 10(8)-10(10) yr, may develop cataclysmic activity.