Spectrophotometry and period analysis of the sdB eclipsing binary HW Virginis

New CCD observations of the pre-cataclysmic binary HW Virginis are presente d and discussed. The R-filtered CCD photometry was supplemented with medium -band (Cousins VRI) spectrophotometry based on low-resolution objective-pri sm spectra. The period variation is reanalysed by means of the standard O-C technique. The new data support the conclusions of Kilkenny et al. (2000) on the strong and continuous period change. The long-term period variation can be described approximately with two Linear branches in the O-C diagram corresponding to a sudden period jump between two constant periods around J D 2448500 (1991). Additional smooth small-scale changes in the period disto rt the linearity. The present data do not support the hypothetical light-ti me effect of Cakirli & Devlen (1999). The eclipse depths in V, R, and I do not show colour dependence, which sugg ests negligible continuum variations due to the cool secondary component in the far-red region (up to 8800 Angstrom). The magnitude of the reflection effect was used to estimate the mean effective temperature of the illuminat ed hemisphere of the secondary. The result is 13300+/-200 K or 11000+/-200 K, depending on the primary temperature (35000 K or 26000 K). An albedo nea r unity is implied for the cool component.