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Noel, B and Joblin, C and Maillard, JP and Paumard, T;
Astronomy & Astrophysics
New results on the massive star-forming region S106 by BEAR spectro-imagery
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As a typical example of interaction of a massive star with its parent cloud, the close environment of S106 IR in the star-forming region S106 was observed at high spectral resolution (similar to 16 km s(-1)). Integral field spectroscopy with BEAR, an imaging Fourier Transform Spectrometer (FTS), on a field of similar to 40(eta) in diameter, in the H-2 1-0 S (1), 2-1 S (1), Br gamma, HeI and [FeIII] lines. From the data several maps were obtained: intensity, velocity and linewidth in the Br gamma and the H-2 1-0 S (1) line, 1-0 S (1)/2-1 S (1) line ratio, and continuum emission at 2.1 mu m. From the latter, about twenty low-mass stars were detected with photometry in this band, and an estimate of their mass was made leading to the conclusion that S106 is a site of formation of mainly sub-solar mass stars. The intensity structure of the excited molecular gas H-2 was found to be clumpy while the velocity is almost uniformely at v(LSR) similar or equal to 1.5 km s(-1) except to the south where the velocity reaches up to 15 km s(-1) in a zone limited by the long edge of a rectangular hole in the emission. The H-2 line ratio map with values from 1 to 9 implies that UV-absorption and shocks are participating in the excitation process. A PDR model with a temperature of 3700 K for S106 IR was used to retrieve the H2 gas density and temperature. The density was found to vary between 1 and 3.5 x 10(5) cm(-3) with corresponding temperatures between 660 and 1240 K. The study of the linewidth distribution indicates for most of the gas a supersonic turbulence with a mean contribution to the observed profiles of >=6 km s(-1). Turbulence is likely to be responsible for the observed clumpy structure of the excited gas. Point-like spots with a linewidth as high as 30 km s(-1) in one position are detected, which may be vortices in the molecular gas. The HII region probed by Br gamma shows a broad range of velocity, from -45 to +80 km s(-1), organized in velocity structures that correspond to two pairs of large, bipolar outflows originating from the massive source, not directed along the axis of the HII region. Emission lines of HeI and [FeIII]are detected in a bright area to the southwest of S106 IR, with point-like structures suggesting photoevaporating clumps. From the velocity data, a 3-D model of the environment of S106 IR is proposed. S106 is an example of an evolved HII region seen face-on. The central source located at the edge of its parent molecular cloud has carved an expanding cylinder of turbulent, atomic gas of similar or equal to 0.1 pc in radius. This massive object was formed by an accretion disk process. The disk is still present and the bipolar outflows are remnants of the massive star activity. A time scale of 1400 yr is estimated for the most recent event. A thin and quiescent clumpy layer of warm H-2 marks the transition of the HII region to the molecular cloud. From the data, there are locally no signs of ongoing star formation.
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