Table 1: Line parameters.
Line Freq. $E_{\rm {u}}/k$ $n_{\rm {crit}}^a$
  [GHz] [K] [105 cm-3]
HCN(1-0), F=1-1 88.630 4 32
HCN(1-0), F=2-1 88.632 4 32
HCN(1-0), F=0-1 88.634 4 32
CH3CN(54-44) 91.959 128 7
CH3CN(53-43) 91.971 78 7
CH3CN(52-42) 91.980 42 7
CH3CN(51-41) 91.985 20 6
CH3CN(50-40) 91.987 13 6
For all observed lines the columns list (left to right) the species/quantum numbers, frequencies, upper level energy states $E_{\rm {u}}/k$ (k is the Boltzmann constant) and critical densities $n_{\rm {crit}}$.
a The critical densities $n_{\rm {crit}}=A/\gamma$ are calculated at 60 K (Einstein coefficient A and collisional rate $\gamma$). For HCN, A and $\gamma$ are taken from LAMBDA (Schöier et al. 2005). For CH3CN, A is calculated from $A=0.3\lambda_{100}^{-3}\mu ^2$ ( $\lambda_{100}$ in units of 100 $\mu$m and $\mu=3.9$ debye), and the corresponding $\gamma$-values are from Pei & Zeng (1995b,a). For a line optical depth $\tau >1$, $n_{\rm {crit}}$ has to be multiplied by $1/\tau$ (Tielens 2005).

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