Variations of the theoretical contrast across the grids GRID_1RHO (upper row), GRID_2RHO (middle row), and GRID_4RHO (lower row). The results for the Hα line are presented in the lefthand column plots, for CaII H line in the righthand column plots. In each panel there are curves calculated for the line center (solid lines with squares), and for the line wings Hα–0.7 and CaII H −2.35 Å (dotted lines with stars). The horizontal lines visible in each plot represent the observed contrast for EB_1 at the moment of its maximum brightness derived from DOT filtergrams obtained in the Hα (plots in the left column) and in the CaII H line (plots in the right column). Solid lines correspond to the contrast observed in lines centers, and dotted lines denote the contrast observed in line wings.