Comparison of the OH molecular abundances from this work to abundances measured in Wiesemeyer et al. (2016). Data, symbols and systematic uncertainties as in Fig. 8. Measurements from Table 4 of Wiesemeyer et al. (2016) are overplotted as purple diamonds. Filled diamonds use HF as proxy for the H₂ column density. Empty diamonds use CH. If both HF and CH measurements are available, OH measurements are drawn twice. Black diagonal lines indicate sensitivity limits of X_OH for typical 4σ limits on optical depth in the OH main lines and assuming a line width of 2.5 km s −1 (the detection limits of τ = 0.025, 0.05 and 0.1 are acchieved for continuum sources stronger than F_cont = 2.10, 1.05 and 0.53 Jy beam−1, respectively).