Issue 
A&A
Volume 520, SeptemberOctober 2010



Article Number  A20  
Number of page(s)  20  
Section  Interstellar and circumstellar matter  
DOI  https://doi.org/10.1051/00046361/201014283  
Published online  23 September 2010 
Online Material
Appendix A: Gaussian decomposition and calculation of column densities
Table A.1: HCO^{+} (01) absorption line analysis results.
Table A.2: HNC (01) absorption line analysis products.
Table A.3: HCN (01) absorption line analysis products.
Table A.4: CN (01) absorption line analysis products.
Tables A.1A.4 contains the
results of the Gaussian
decompostion procedure that we have applied to the spectra. The column
densities, given in the last columns, are derived assuming a single
excitation temperature
for all the levels of a given molecule as
where , , and are the rest frequency, the upper and lower level degeneracies and the Einstein's coefficients of the observed transition, is the partition funtion, and c is the speed of light. We also remind that for a Gaussian profile of peak opacity and FWHM , the opacity integral is . For an excitation temperature of 2.73 K, Eq. (A.1) becomes
(A.2) 
(A.3) 
(A.4) 
and
(A.5) 
using the HCO^{+} J=01, HNC J=01, HCN J,F=0,11,2, and CN J,F1,F=0,1/2,3/21,1/2,3/2 transitions respectively.
Appendix B: Impact of the abscissa uncertainty on the multiGaussian decomposition procedure
In a spectrum, the possible velocity substructures are systematically
erased due to the finite velocity resolution
.
This could be
modelled as an uncertainty on the velocity position of each point.
Unfortunately the errors on the abscissa are rarely included in
nonlinear fitting
procedures because the system is considerably heavier to solve and
because it
often prevents convergence. To evaluate the resulting uncertainties on
the fit
parameters, namely the central opacity, the velocity centroid, and the FWHM,
we apply the fitting procedure on 3000 synthetic spectra of FWHM
varying
between 0.3 and 3.4 km s^{1} sampled with
the finite
spectral resolution of the observations
km s^{1}. A noise is added to
the xcoordinates of all the spectral points. The
rms of all
the measured linewidths
is found to scale as
(B.1) 
and decreases from 0.04 to 0.01 km s^{1} as the true linewidth increases from 0.3 to 3.4 km s^{1}. These uncertainties are smaller than (or comparable to) those inferred from the fitting procedure and the resulting errors on the column densities are at most 12%. In comparison the resulting errors on central opacities and velocity centroids are negligible.
Appendix C: Cyanides chemical network
Table C.1: Rates k of the main reactions of the cyanide chemistry.
Figures C.1
and C.2
show the main production and destruction pathways of the hydrogenation
chains of carbon, nitrogen, and
cyano, resulting from the PDR (
cm^{3},
A_{V} = 0.4)
and
TDR (
cm^{3},
A_{V} = 0.4,
a
= 10^{11} s^{1})
models
respectively. These figures are simplified: for each species, only the
reactions which altogether contribute at least to 70 percent of the
total destruction and formation rate are displayed. There is one major
difference between these networks: in a UVdominated chemical model,
the cyanide chemistry is initiated by:
(C.1) 
(C.2) 
and
(C.3) 
while in a chemistry driven by turbulent dissipation, the hydrogenation chain of cyano is triggered by the ionneutral reactions:
(C.4) 
(C.5) 
and
(C.6) 
Since the pathways displayed in Figs. C.1 and C.2 depend on the chemical rates, and since the nitrogen and cyanide chemistry are still poorly known, we list the chemical rates we have adopted in our models for several reactions in Table C.1.
Figure C.1: Chemical network of a UVdominated chemistry: = 50 cm^{3} and A_{V} = 0.4. This figure is simplified: for each species, only the reactions which altogether contribute at least to 70 percent of the total destruction and formation rate are displayed. The red arrow show the endoenergetic reactions with the energy involved. 

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Figure C.2: Same as Fig. C.1 for a turbulencedominated chemistry: = 50 cm^{3}, A_{V} = 0.4 and a = 10^{11} s^{1}. For the sake of simplicity, the main destruction route of N (N + CH_{2}^{+} HCN^{+} + H) and the main formation pathway of N^{+} (photodissociation of NO^{+}) are not displayed here: those two species are therefore highlighted. 

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