Optical studies of the X-ray transient XTE J2123-058; 1, Photometry

We present optical photometry of the X-ray transient XTE J2123-058, obtainedin July-October 1998. The light curves are strongly modulated on the 5.95hrsorbital period, and exhibit dramatic changes in amplitude and form during thedecline. We used synthetic models which include the effect of partial eclipsesand X-ray heating effects, to estimate the system parameters, and we constrainthe binary inclination to be i=73+-4 degrees. The model is successful inreproducing the light curves at different stages of the decay by requiring theaccretion disc to become smaller and thinner by 30as the system fades by 1.7mags in the optical. From Aug 26 the system reaches quiescence with a meanmagnitude of R=21.7+-0.1 and our data are consistent with the opticalvariability being dominated by the companion's ellipsoidal modulation