Comparison between the observations and the predictions from the radiative transfer model for the ¹²CO J = 7 → 6 to J = 4 → 3 (black-solid contours) and ¹³CO to ¹²CO J = 4 → 3 (gray-dashed contours) line ratios for kinetic temperatures of 80, 120, and 160 K. The plots assume a fractional abundance of ¹²CO/¹³CO of 35. The observed ¹²CO J = 7 → 6 to J = 4 → 3 ratio of 0.52 is shown as a blue line with boxes while the ¹³CO to ¹²CO J = 4 → 3 ratio of 0.15 is shown as a red line with circles.