All lines of H₂¹³CO with the best fit LTE model overplotted. Synthetic spectra in red indicate optical depth beginning to play a significant role i.e., τ > 0.6. Numbers in top right corner with red boxes indicate lines used to fit the column density. The number in parenthesis is the estimated optical depth. The line in panels 9 and 11, at 355.04 and 355.20 GHz could be blended with significantly weaker H₂C¹⁷O lines (see panels 5 and 8 in Fig. B.1).