C¹⁷O (top panels) and C¹⁸O (bottom panels) spectra at the PDR position ($\delta x\approx {15}_{\cdot }^{\mathrm{\prime }\mathrm{\prime }}1,\delta y\approx 1_{\cdot }^{\mathrm{\prime }\mathrm{\prime }}2$) and dense core position ($\delta x\approx {44}_{\cdot }^{\mathrm{\prime }\mathrm{\prime }}7,\delta y\approx {16}_{\cdot }^{\mathrm{\prime }\mathrm{\prime }}5$), as observed in the Horsehead WHISPER survey. The best-fit models are overlaid in red. The best-fit excitation conditions and associated uncertainties, shown in the middle of each panel, correspond to the 16th, 50th, and 84th percentiles of the posterior distributions.