Undersampled J = 1–0 ¹²CO (left panels) and ¹³CO (right panels) maps of molecular clouds in the field of Simeis 57, whose center is denoted by a cross. The emission at +5 km s⁻¹ is shown in the leftmost two panels (averaged over a 5 km s⁻¹ velocity interval), and the central two panels show the emission at −10 km s⁻¹ (averaged over a 4 km s⁻¹ interval). In the ¹²CO panels, the regions with improved sampling are indicated by a solid-line boundary. The rightmost two panels show the position–velocity map along the dashed line in the ¹³CO map. Position offsets are relative to α = 20^h16^m16.7^s, δ = + 43°47′54″ (J = 2000).