Comparison of the HL Tau Band 6–7 (ALMA Partnership 2015) and the HL Tau Band 9 radial profiles of the brightness temperature. We plot the Band 6–7 ALMA image with the lowest resolution (33 mas, yellow), the Band 9 image with 22 mas (black), and the Band 9 image with 13 mas (green). The substructures are shallower in the radial brightness temperature for Band 9 than in the Band 6–7 image, and the emission from the Band 9 image extends up to 140 au. In the inset, we show the first 20 au of the HL Tau disk. We plot the brightness temperatures of the three images, and assuming that T_disk = T_B because of the optically thick regime, we display the position (in temperature) of the water snowline.