EDP Sciences
Free Access
Issue
A&A
Volume 406, Number 3, August II 2003
Page(s) 915 - 935
Section Formation, structure and evolution of stars
DOI https://doi.org/10.1051/0004-6361:20030726


A&A 406, 915-935 (2003)
DOI: 10.1051/0004-6361:20030726

A multiwavelength study of the S 106 region

II. Characteristics of the photon dominated region
N. Schneider1, 2, 3, R. Simon1, 4, C. Kramer1, K. Kraemer4, J. Stutzki1 and B. Mookerjea1

1  I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
2  IRAM and Observatoire de Grenoble, BP 53, 38406 Saint Martin d'Hères, France
3  Observatoire de Bordeaux, BP 89, 33270 Floirac, France
4  Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

(Received 11 October 2002 / Accepted 6 May 2003 )

Abstract
The O star S 106 IR powers a bright, spatially extended $10'\times 3'$ ( $1.75\times 0.5$ pc at a distance of 600 pc) photon dominated region (PDR) traced by our observations of FIR fine structure lines and submm molecular transitions. The [C II] 158  $\mu$m, [C I] 609 and 370  $\mu$m, CO 7 $\to$6, and CO 4 $\to$3 measurements probe the large scale (1.2 pc) PDR emission, whereas [O I] 63  $\mu$m, CN  $N=3{\to}2$, and CS  $J=7{\to}6$ observations are focused on the immediate (~ 1' (0.2 pc)) environment of S 106 IR. A hot ( T>200 K) and dense ( $n>3 \times10^5$ cm -3) gas component (emission peaks of [C II] 158  $\mu$m, CO 7 $\to$6, and CO 4 $\to$3) is found at S 106 IR. Cooler gas associated with the bulk emission of the molecular cloud is characterized by two emission peaks (one close (20 '' east) to S 106 IR and one 120 '' to the west) seen in the [C I] and low- J ( $J_{\rm up}<4$) CO emission lines. In the immediate environment of the star, the molecular and [C I] lines show high-velocity emission due to the interaction of the cloud with the stellar wind of S 106 IR. The intensities of the FIR lines measured with the KAO are compared to those observed with the ISO LWS towards two positions, S 106 IR and 120 '' west. We discuss intensities and line ratios of the observed species along a cut through the molecular cloud/H II region interface centered on S 106 IR. The excitation conditions ( $T_{\rm ex}$, opacities, column densities) are derived from an LTE analysis. We find that the temperature at the position of S 106 IR obtained from the [C I] excitation is high ( >500 K), resulting in substantial population of the energetically higher $\rm ^{3}P_2$ state; the analysis of the mid- and high- J CO excitation confirms the higher temperature at S 106 IR. At this position, the [O I] 63  $\mu$m line is the most important cooling line, followed by other atomic FIR lines ([O III] 52  $\mu$m, [C II] 158  $\mu$m) and high- J CO lines, which are more efficient coolants compared to [C I] 2 $\to$1 and 1 $\to$0. We compare the observed line ratios to plane-parallel PDR model predictions and obtain consistent results for UV fluxes spanning a range from 10 2 to 10 3.5 G 0 and densities around 10 5 cm -3 only at positions away from S 106 IR. Towards S 106 IR, we estimate a density of at least  $3\times10^5$ at temperatures between 200 and 500 K from non-LTE modelling of the CO 16 $\to$15/14 $\to$13 ratio and the CO 7 $\to$6 intensity. Our new observations support the picture drawn in the first part of this serie of papers that high-density ( n>105 cm -3) clumps with a hot PDR surface are embedded in low- to medium density gas ( $n\le10^4$ cm -3).


Key words: ISM: atoms -- ISM: clouds -- ISM: individual objects: S 106 -- ISM: structure -- radio lines: ISM

Offprint request: N. Schneider, schneider@obs.u-bordeaux1.fr

SIMBAD Objects



© ESO 2003

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.