Ratios of integrated intensities of ¹²CO /¹³CO in binary post-AGB stars in light grey. We also show line-peak ratios in dark grey (J = 2−1 at top; J = 1−0 at Bottom). Sources are ordered by outflow dominance and enumerated as follows: a – HR 4049, b – DY Ori, 1 – AC Her, 2 – Red Rectangle, 3 – 89 Her, 4 – HD 52961, 5 – IRAS 19157-0257, 6 – IRAS 18123+0511, 7 – IRAS 19125+0343, 8 – AI CMi, 9 – IRAS 20056+1834, and 10 – RSct. Sources a and b are not included in this mm-wave survey. Sources 1, 2, a, and b are disk-dominated binary post-AGB stars, sources 6 to 10 are outflow-dominated, and sources 3, 4, and 5 are intermediate cases.