Averaged [¹²CII] and [¹³CII] emission originating from the ridge of the Orion bar. The blue spectrum shows the [¹² CII] line, and the orange spectrum shows the velocity-corrected [¹³CII] emission averaged over the three hyperfine components and multiplied by 67, the carbon isotopic ratio in Orion (Langer & Penzias 1990). The black data points with error bars show the determined optical depth for each velocity channel, which is above unity around the peak of the line [¹² CII]. The inner panel shows the three [¹³CII] hyperfine transitions lines detected alongside the [¹²CII] line.