Temperature derived from the line ratio analysis. The rotational temperature (red) is derived from the ¹³CO J = 6−5 to J = 2−1 line ratio, including optical depth constraints (solid lines), for LkCal5 (left) and HD 169142 (right). The dotted lines in corresponding colors indicate the rotational temperature inside the dust cavity if the emission were optically thin. For comparison, the brightness temperature of the optically thick ¹²CO J = 2−1 transition (green) is shown. We note the difference in the vertical temperature axes. In the case of LkCal5, the dotted blue line shows the rotational temperature assuming optically thin emission for the (combined) high resolution observations. The downward triangles indicate the upper limit on the rotational temperature due to the upper limit on the integrated C¹⁸O J = 2−1 intensity in the dust cavity. The intensity outside the MRS of the observations is shown in a lighter shade of the corresponding colors.