Issue 
A&A
Volume 531, July 2011



Article Number  L16  
Number of page(s)  5  
Section  Letters  
DOI  https://doi.org/10.1051/00046361/201116893  
Published online  04 July 2011 
Online material
Appendix A: Gaussian fitting
Gaussian fit results to the OH line components using the velocity range [− 100, 30] and first order baselines.
Appendix B: Line width comparison
The comparison of OH and H_{2}O column densities in the outflow is based on the assumption that the emission arises from the same gas. Figure B.1 illustrates the similar widths of the broad components of OH (Δ3 ≈ 27 km s^{1}), CO (Δ3 ≈ 29 km s^{1}), and H_{2}O (Δ3 ≈ 26 km s^{1}). The broad component of OH is a blend of three hyperfine components with individual widths of Δ3 ≈ 22 km s^{1}, derived from the best fit slab model (Sect. 3.1).
Fig. B.1
Comparison of the broad component of OH (black), H_{2}O 2_{02} − 1_{11} (red), and CO(10 − 9) (blue) observed with HIFI. The black dashed line indicates the source velocity (3_{lsr} = −38.4 km s^{1}). 

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Appendix C: Slab modeling details
The modeling of the OH line spectrum (cf. Sect. 3.1) is carried out with the slab model code presented in Appendix B of Bruderer et al. (2010). Both OH line components (narrow/envelope and broad/outflow) are represented by a slab in front of a continuum source. The continuum temperature T_{cont} is derived from the observed singlesideband continuum value and the source is assumed to be fully covered by both slabs. No geometry is included, except that the outflow slab is placed
in front of the envelope slab. Each slab has four free parameters per line: the OH column density N_{OH}, the excitation temperature T_{ex}, the line width Δ3, and the position (in velocity space) of the line center 3_{lsr}, but the excitation temperature is assumed to be the same for all hyperfine transitions. The normalized level populations of the upper (x_{u}) and lower level (x_{l}) are therefore determined by the Boltzmann distribution at T_{ex}, (C.1)with the statistical weights g_{u} and g_{l} of the upper and lower level, respectively, Boltzmann’s constant k_{B}, Planck’s constant h, and the frequency ν_{0} of the transition. The radiation temperature is derived from the solution of the radiative transfer equation, using the RayleighJeans approximation, as (C.2)with c being the speed of light, B_{ν0} the Planck function, τ^{env} the optical depth of the envelope layer, and τ^{ofl} the optical depth of the outflow layer. The line optical depth of every slab is the sum of the contributions of all M hyperfine components and can be calculated from (C.3)where A_{ul} is the Einstein coefficient and the normalized line profile function of the transition, assumed to be a Gaussian of width Δ3 centered at 3_{lsr}. This approach takes line overlap into account.
Fig. C.1
1σ and 2σ contours for the fit of the narrow (envelope) component with slab models. The best fit is indicated by the red dot. 

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© ESO, 2011
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