As in Fig. 2, but for IRAS 20353. For this source no SiO 2  →  1 was detected, and the H¹³CO⁺ 4  →  3/1  →  0 integrated intensity ratio map did not contain a sufficient number of valid pixels, therefore these maps are not shown. For maps b) to d) (showing the integrated intensities of only H¹³CO⁺ 1  →  0, HN¹³C 1  →  0 and H¹³CO⁺ 4  →  3), the values of σ (and contour step) in K km s^-1 are: b) 0.034 (0.074), c) 0.067 (0.067), and d) 0.021 (0.014). Here the first contour level of H¹³CO⁺ 4  →  3 (map d)) is 3σ, as opposed to 5σ used in all the previous maps.