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Appendix A: Spectroscopic line parameters

The frequencies, upper energy levels, upper level degeneracies, and Einstein coefficients of the observed transitions were taken from the JPL spectroscopic database (Pickett et al. 1998) and are summed up here in Table A.1.

Appendix B: Column density determination

The column densities were determined within the LTE approximation, using (B.1)where ν is the frequency of the transition, c the velocity of light, h and k the Planck and Boltzman constants, respectively, g_up the upper level degeneracy, A_ul the spontaneous emission Einstein coefficient, T_ex the excitation temperature, Q(T_ex) the partition function at T_ex, E_up the upper level energy, and J_ν(T) is the radiation temperature that is defined as (B.2)Equation (B.1) assumes that the lines are optically thin. We note that since the temperatures are very low, J_ν(T_bg) is not negligible with respect to J_ν(T_ex).

© ESO, 2012