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Description
For the very short period subdwarf B eclipsing binary HW Vir, we present new CCD photometry made from 2000 through 2008. In order to obtain consistency of the binary parameters, our new light curves, showing sharp eclipses and a striking reflection effect, were analyzed simultaneously with previously published radial velocity data. The secondary star parameters of M_2_=0.14M_{sun}_, R_2_=0.18R_{sun}_, and T_2_=3084K are consistent with those of an M6-7 main-sequence star. A credibility issue regarding bolometric corrections is emphasized. More than 250 times of minimum light, including our 41 timings and spanning more than 24yr, were used for a period study. From a detailed analysis of the O-C diagram, it emerged that the orbital period of HW Vir has varied as a combination of a downward-opening parabola and two sinusoidal variations, with cycle lengths of P_3_=15.8yr and P_4_=9.1yr and semiamplitudes of K_3_=77s and K_4_=23s, respectively. The continuous period decrease with a rate of -8.28x10^-9^d/yr may be produced by angular momentum loss due to magnetic stellar wind braking but not by gravitational radiation.
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