Investigation of effect of temperature variation between 15 and 20 K. The panels show the projected best χ² values in the ζ versus t plane for the P2 position for the XR (left), UR (middle) and R (right) search methods, but with a further constraint of T = 16 K, for Case 1 (fitting to abundances of CO, HCO⁺ and N₂H⁺). The location of the minimum χ² is marked with a white cross in each panel.