Total hydrogen column density (purple) derived from the ¹³CO J = 6−5 to J = 2−1 line ratio, the integrated C¹⁸O J =2−1 line intensity, and the optical depth for LkCal5 (left) and HD 169142 (right). The dotted line indicates the rotational temperature and column density inside the dust cavity if the emission were optically thin. The purple downward triangles in the left panel indicate the upper limit on column density due to the upper limit on the integrated C¹⁸O J =2−1 intensity in the dust cavity. The green bars with downward triangles in the right panel indicate the Scupper limit on the hydrogen column density derived from the non-detection of ¹²CO J = 2−1 in this region and assuming a temperature of 100 Κ and 300 K, respectively.