Distribution of the physical and chemical properties of C¹⁸O in Oph N l. (a) Excitation temperature map derived from the CO peak main beam temperature. The color bar represents the excitation temperature in units of K, while the contour represents an excitation temperature of 7.5 K. (b) Peak C¹⁸O (J = 1 −0) opacity map. (c) C¹⁸O column density map at an angular resolution of 3′ (d) C¹⁸O fractional abundance map. The contours represent the C¹⁸O fractional abundances of 5 × 10^-8 and 1 × 10^-7. The two dashed circles represent the observed CO depletion holes. In each panel, the beam size is shown in the lower right corner, the two Planck cold clumps (G008.67+22.14 and G008.52+21.84) are indicated by the two blue open circles.