Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...436..569n&link_type=abstract
Astronomy and Astrophysics, Volume 436, Issue 2, June III 2005, pp.569-584
Astronomy and Astrophysics
Astrophysics
6
Stars: Formation, Ism: Individual Objects: Sh 2-106, Instrumentation: Interferometers, Hii Regions, Astrochemistry
Scientific paper
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 (~16 km s-1). Integral field spectroscopy with BEAR, an imaging Fourier Transform Spectrometer (FTS), on a field of ~40´´in diameter, in the H2 1-0 S(1), 2-1 S(1), Brγ, He I and [Fe III] lines. From the data several maps were obtained: intensity, velocity and linewidth in the Brγ and the H2 1-0 S(1) line, 1-0 S(1)/2-1 S(1) line ratio, and continuum emission at 2.1 μm. 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 H2 was found to be clumpy while the velocity is almost uniformely at vLSR ≃ 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 H2 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 × 105 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 H II region probed by Brγ 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 H II region. Emission lines of He I and [Fe III] 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 H II 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 ≃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 H2 marks the transition of the H II region to the molecular cloud. From the data, there are locally no signs of ongoing star formation.
Joblin Ch.
Maillard Jean Pierre
Noel Benjamin
Paumard Thibaut
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