Degeneracy plots of LVG II (right) and LVG III (left). Each square represents a model with specific density (x-axis) and temperature (y-axis) for the best fitting N(CO)/δv. The color scale represents the χ² value of that model fit to the CO data. Since we use a modified Pearson’s χ², the actual values of the gray scale are not meaningful, only their relative differences. The large black asterisk represents the best fitting model (minimum χ²).