All Tables

Table 1: Observed transitions.
Table 2: Source list and detection summary.
Table 3: Sources observed during the first observing run only. Columns 6-9 give the peak of each line or the rms level of the spectrum, both in K.
Table 4: Main physical parameters of our sources found in literature: dust temperature ( $T_{\rm d}$ ), H₂ column and volume densities ( $N_{\rm H_2}$ and $n_{\rm H_2}$ , respectively) and gas kinetic temperature ( $T_{\rm kin}$ ). The references are shown between brackets.
Table 5: N₂H⁺ line parameters.
Table 6: N₂D⁺ line parameters.
Table 7: Deconvolved source angular diameters (in arcseconds) derived from each tracer assuming a Gaussian source.
Table 8: Source properties derived from (sub-)mm continuum emission: deconvolved angular diameter ( $\theta _{\rm cont}$ ), integrated 850 $\mu$ m continuum flux ( $F_{\nu }$ , for IRAS 18517+0437 we give the integrated 1.2 mm continuum flux), linear size (D), gas+dust mass ( $M_{\rm cont}$ ), visual extinction ( $A_{\rm v}$ ) and H₂ column and volume densities ( $N_{\rm H_2}$ and $n_{\rm H_2}$ ), derived from $M_{\rm cont}$ and $A_{\rm v}$ .
Table 9: N₂H⁺ and N₂D⁺ total column densities ( $N({\rm N_2H^+})$ and $N({\rm N_2D^+})$ ), deuterium fractionation ( $D_{\rm frac}$ ), and N₂H⁺ chemical abundance relative to H₂( $X_{\rm N_2H^+}$ ). $X_{\rm N_2H^+}$ has been calculated from the molecular hydrogen column density given in Col. 8 of Table 8.
Table 10: H₂ volume densities and N₂H⁺ and N₂D⁺ column densities, derived in the LVG approximation.
Table 11: Parameters used to determine the CO depletion factor: source Galactocentric distance ( $D_{\rm GC}$ ), "expected'' C¹⁷O abundance ( $X_{\rm C^{17}O}^{\rm E}$ ), integrated intensity of C¹⁷O at the dust peak position ( $I({\rm C^{17}O}))$ ), beam filling factor ( $\eta _{\nu }$ ), C¹⁷O total column density ( $N({\rm C^{17}O})$ ), observed C¹⁷O abundance ( $X_{\rm C^{17}O}^{\rm O}$ ) and CO depletion factor ( $f_{\rm D}$ ).