Comparison between the observations and the predictions from the radiative transfer model for the ¹²CO J = 1 → 0 and J = 4 → 3 line ratios (black-solid contour) and the ¹³CO to ¹²CO J = 1 → 0 line ratio (gray-dashed contour) for T_kin = 160 K. The observed ¹³CO to ¹²CO J = 1 → 0 ratio of 0.08 is shown as a blue line with boxes while the ¹²CO J = 1 → 0 to J = 4 → 3 ratio of 0.22 is shown as a red line with circles.