To study the physical cause of the variations and the distorsions in the light curve of BH Vir, the archival photoelectric observations in BV by Koch (1967) were also analyzed by us based on the spot model. Zhai et al. (1990) have published an average solution for the observations of 1963-1964 and 1977, but they did not consider any activity regions on the secondary star. They gained results of the spotted regions at two epochs being all close to the equator. Their theoretical light curves, around the primary eclipse, could not fit the observations well (see Fig. 5), and the systematic deviations in the O-C residuals are greater than 0.050 mag (V) and 0.030 mag (B).
Koch (1967) found that there were night-by-night light curve changes. He suggested that there might be a brighter exterior hemisphere of the cooler component responsible for the depth changes in the primary eclipse. The primary eclipse of the light curve in 1963-1964 is found approximately deeper than those in other epochs. We can use the photometric elements given by former authors (Koch 1967; Zhai et al. 1990; Zeilik et al. 1990) to estimate that the primary component is covered by approximately from 94.8% to 78.8% of its hemisphere by the secondary star at the primary eclipse. Hoffmann (1982) and Scaltriti et al. (1985) have emphasized that both components of BH Vir are intrinsically variable and have nonuniform brightness distributions over their surfaces. We considered that the observed distortion, that of the primary eclipse in 1963-1964 being deeper than those in other epochs, could be caused by a cool region on the secondary component, so several groups of cool spots placed on the surface of both components were tried. We used q, i, T1, , , L1 as the adjustable parameters and used Wilson-Devinney program to obtain final solution. The results of the spotted solution are included in Tables 2 and 3. The fit of the theoretical light curves of our solution to the observations is fairly good and the systematic deviations in O-C are less than 0.019 mag (V) and 0.009 mag (B) as show in Figs. 6 and 7.
|Figure 6: Light curves of BH Vir in 1963.64. Open circles represent the observations. Solid lines are theoretical light curves calculated from the parameters in Tables 2 and 3|
From the positions and relative size of the spots on both components for the data of 1963-1964 and 1991, the following conclusions can be drawn:
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