Upper left: 1D modeling of the intensity of C¹⁸O(5−4) (red solid line) and of the ratio o-HO/CO(9 − 8) (black line) in the velocity interval Δv_c. The intensities are calculated as a function of the kinetic temperature and the local density, assuming different abundances of o-H₂O and beam filling factors. The uncertainties (30% in the absolute intensity and a factor of 2 for the line ratios) are represented with dotted lines. Upper right: the corresponding results for ¹²CO(9 − 8) (red solid line) and o-H₂O/¹²CO in the velocity interval Δv_r. Bottom: results for the o-NH₃ observations in the velocity interval Δv_c. No solutions are found for a lower beam filling factor.