Sketch of three putative compression fronts in dashed blue (Arc 1), dashed yellow (Arc 2), and dashed green (Arc 3), corresponding to density enhancements, overlaid on the Herschel high-resolution column density map of L1688 (grayscale). All three compression arc-like structures point roughly toward the direction of the O9V star σ Sco (cf. Fig. 1), and are possibly skewed by the influence of the bubble around the star ρ Ophiuchi. The yellow cross marks the rough center of the three arcs and the red star indicates the center of mass of L1688.