Optical depth maps of C¹⁸O (1–0) (a) and C¹⁸O (2–1) (b) overlaid with contours of signal-to-noise ratio (τ∕σ_τ) of 2 and 3 indicated by the red and black lines, respectively. The beam size is shown in the lower right corner of each panel. In all panels, the (0, 0) offset corresponds to α_J2000 = 18^h28^m50.^s4, δ_J2000 = 00°49′58.′′72, the three green pluses show the positions of the three embedded YSOs, emb10, emb16, and Ser-emb 28 (Enoch et al. 2009), and the white crosses mark the positions of the seven dust cores (Enoch et al. 2007).