Comparison between the observed C¹⁸O (1–0) integrated intensity as a function of the offset from the core center (blue dots with error bars) and the predictions our fiducial model for different chemical ages (solid, dotted and dashed lines) in L1498 (left panel) and L1517B (right panel). Observations have been radially (or ellipsoidally) averaged, and the error bars show the 1σ standard deviation in each “bin”.