LIGHT VARIATIONS OF THE DWARF NOVA DX-ANDROMEDAE DURING 10 CONSECUTIVE ORBITAL CYCLES

A total of 360 R-band and 76 I-band photometric observations of the lo ng period dwarf nova DX And is presented. All the data were obtained o n five consecutive nights with a CCD camera on the 0.9-m James Gregory Telescope at the University Observatory, St Andrews, and provide the first detailed description of the light variations of DX And on orbita l time-scales. It is shown that the light variations over the 10.6-h o rbital period may be explained primarily by an ellipsoidal variation o f amplitude 0.13 mag caused by synchronous rotation of the Roche-lobe- filling companion star, the dereddened (R-I) colour index of which cor responds to a spectral type of K0-1V. Additional variability, with a r ange of amplitude up to 0.05 mag, is also present at least in the R ba nd and might itself exhibit the orbital period. This additional Variab ility may be due to star-spot activity on the rapidly rotating and hen ce magnetically active K-type companion star, or to a variable contrib ution from a non-uniform accretion disc. Analysis of the light variati ons with the synthesis code LIGHT2 suggests an orbital inclination in the range 45 degrees-53 degrees, with a formal solution of 48 degrees/-1 degrees for an adopted mass ratio of 0.9. Hence the overall model for the system proposed by Drew, Jones & Woods is well supported by th ese data, including the need for the companion to be oversized for its mass.