¹³CO spectral maps in black overlaid with the model envelope spectra in red shown on the left panels. Right panels: color maps of the UV heated gas distribution are shown. These are obtained by subtracting the model envelope emission from the observed spectra on a pixel-by-pixel basis. The sources are B335 (top) and L483 mm (bottom). The axes show the offsets (Δα, Δδ) in arcsec. The color scale is in units of K km s^-1.