Volume 531, July 2011
|Number of page(s)||5|
|Published online||04 July 2011|
Gaussian fit results to the OH line components using the velocity range [− 100, 30] and first order baselines.
The comparison of OH and H2O 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 H2O (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).
Comparison of the broad component of OH (black), H2O 202 − 111 (red), and CO(10 − 9) (blue) observed with HIFI. The black dashed line indicates the source velocity (3lsr = −38.4 km s-1).
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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 Tcont is derived from the observed single-sideband 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 NOH, the excitation temperature Tex, the line width Δ3, and the position (in velocity space) of the line center 3lsr, but the excitation temperature is assumed to be the same for all hyperfine transitions. The normalized level populations of the upper (xu) and lower level (xl) are therefore determined by the Boltzmann distribution at Tex, (C.1)with the statistical weights gu and gl of the upper and lower level, respectively, Boltzmann’s constant kB, Planck’s constant h, and the frequency ν0 of the transition. The radiation temperature is derived from the solution of the radiative transfer equation, using the Rayleigh-Jeans approximation, as (C.2)with c being the speed of light, Bν0 the Planck function, τenv the optical depth of the envelope layer, and τofl 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 Aul is the Einstein coefficient and the normalized line profile function of the transition, assumed to be a Gaussian of width Δ3 centered at 3lsr. This approach takes line overlap into account.
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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