a) Three-color integrated intensity ¹²CO (1–0) image of the surveyed region (red: integrated between 45 and 58 km s^-1; green: integrated between 19 and 35 km s^-1; blue: integrated between 10 and 19 km s^-1). b) ¹²CO (1–0) integrated intensity map (background) overlaid with a ¹³CO (1–0) integrated intensity map (contours). The two integrated velocity ranges extend from 10 to 19 km s^-1. The grayscale colors correspond to a linear stretch of ¹²CO (1–0) integrated intensities in units of K km s^-1. The contours represent ¹³CO (1–0) integrated intensities that start at 1.5 K km s^-1 and increase by 2.5 km s^-1. c) Same as Fig. 3b, but integrated velocity ranges extend from 19 to 35 km s^-1. The contours start at 2.0 K km s^-1 , and each contour is twice the previous one. The purple solid line marks the highest H₂ column density line of the filament S287-main along its long axis. d) Same as Fig. 3b, but integrated velocity ranges reach from 45 to 58 km s^-1. The contours start at 1.8 K km s^-1 and increase by 1.8 K km s^-1. The subregions of the three clouds are marked and labeled in the respective panels.