UBVR photometry of pre-catacylismic binaries: HW Virginis

New UBVR light curves of the eclipsing binary HTN Vir have been obtained. A ll the published times of primary and secondary eclipses have been collecte d. By adding the new times of the eclipses obtained by us; the general beha vior of the O-C changes has been revealed. The updated O-C change seems to show a cyclic character. This behavior may be the result of whether rotatio n of the apsis connecting the star's centers or revolution of the couple ar ound a third body. The former has been excluded due to the fact that the O- C values of primary and secondary eclipses show similar variation, i.e., no t 180 degrees out of phase. Therefore the O-C changes have been analysed un der the assumption of the light-time effect. The period of revolution aroun d the third body was found to be 19 years. The time span following the disc overy of eclipsing nature of the system covers 69 percent of the period pre dicted. The B, V and R light curves have been analysed by the WD code and t he physical parameters of the components were obtained. The hotter, primary component is an sdB star with a temperature of about 36 000 K, and the coo ler one is a late-type main sequence star with a temperature of 3300 K. The physical parameters derived for the secondary component are in accordance with the parameters of the theoretical models. This analysis indicates that the low mass, cooler secondary does not fill its critical Roche lobe. Ther efore, mass accretion from the cool main sequence star to the hot sdB prima ry is not yet expected.