2 Observations

The system HW Vir was observed on two nights, namely 26/27 and 27/28 May 1997. The observations were obtained with the 40 cm Cassegrain reflector of the TUBITAK Turkish National Observatory. The observatory is at an altitude of 2500 m and had seen the first light on January 1997. An SSP5A type photometer was attached to the telescope. The Johnson's wide - band U, B, V and R filters were used. Each measurement is a mean of the two 10 seconds integrations. In this study we measured the sky background before and after the measurements of the comparison and variable, but not during the eclipse. The main comparison star was BD $-~8^\circ$ 3411. The differential observations, variable minus comparison, were corrected for atmospheric extinction. The extinction coefficients were obtained for each night using the observations of the main comparison star. The times were also reduced to the Sun's center.The orbital phases were calculated using the light elements given by Gürol & Selam (1994) as,

$${\rm Min~I = JD~Hel.~2448~294.88647 + 0\hbox{$.\!\!^{\rm d}$}~11671953}~E.$$

The differential magnitudes for each band were plotted against the orbital phase and are shown in Fig. 1.

  

Figure 1: U, B, V and R light curves of HW Vir. Filled circles represent the magnitudes obtained on May 26, and open circles for May 27, 1997

The observations obtained on two nights agree well in B, V and R bands; but there are some differences in U filter. These differences in U band arise mainly from the fact that the photometer we used is more sensitive to the longer wavelengths.