Rotational temperature diagram for IK Tau, assuming an emitting region of 75 mas (20 AU in radius). The red line and red shaded region indicate the fit to the data and 1σ errors on the fit parameters. The green fit is based only on the N = 4−3and9−8 transitions. The purple line represents an abundance of 2.6 × 10^-8 in combination with a likely representative rotational temperature of 1000 K (Gobrecht et al. 2016). The blue line represents the T_rot and N_col values found by Kamiński et al. (2013) for AlO around VY CMa.