Astronomy and Astrophysics, volume 337, 539-557 (1998/9-2)
A multi-wavelength study of the Sharpless 151 region.
BRAND J. and WOUTERLOOT J.G.A.
Abstract (from CDS):
Result. are presented of an extensive, multi-wavelength study of the area around the evolved HII region Sh 2-151. We discuss the excitation of the HII region, and analyze its interaction with molecular clouds in the vicinity, the clouds themselves, and their embedded objects. We present KOSMA 3-m 12CO(2-1) and (3-2) observations of a 26'x46' region around Sh 2-151. These observations reveal five clouds, with a total mass of 2.9x104M☉. A small (2'x4') region to the SW of Sh 2-151 was mapped in several CO and CS transitions with the IRAM 30-m telescope. The latter region contains 1.8x103M☉ of molecular mass, and hosts an IRAS- and H2O maser source (WB89-234). Tracers of higher (column-) densities, such as C18O and CS, show the existence of two clumps (N(H2)≃1-2x1022cm–2) connected by a ridge of warm (Tkin∼36K) narrow-line (Δv(12CO)<1km/s) gas. The southern clump contains the IRAS/maser source, exhibits a molecular outflow (M≃5M☉, τdyn≃2x105yr), and is therefore probably a region of active star formation. In the northern clump the line profiles have an intermediate width (1-3km/s; partly due to the presence of two emission components) and are non-gaussian (shoulders, wings) at several positions. IRAS (HIRES) observations show there is also FIR emission associated with the northern clump. NIR (J, H, K, H2) observations show the presence of several red star-like objects and diffuse emission in both clumps; some of the diffuse emission is stronger and more extended in K and H2, and may be due to dust emission around embedded objects. HIRES data reveal that IRAS 23004+5642 (WB 89-234) nearly coincides with the H2O maser and the outflow, and not with the strong, narrow-line CO-emitting gas detected towards the point source catalog position. The linewidth of this relatively low-density warm gas, the heating source of which is as yet unknown, indicates the absence of dynamical interaction with both Sh 2-151 and the embedded IR sources. From the HIRES 60µm and 100µm data we derive dust temperatures of 30-40K, the highest values occurring near the maser, and a dust mass of ∼30M☉; assuming a gas-to-dust ratio of 100, this implies we detect ∼10% of the dust. Evidence from the available (literature) data leads to the conclusion that the exciting star(s) of Sh 2-151 has (have) not yet been identified. We suspect that one or more early type (<B0) stars may be hidden behind the molecular cloud associated with WB 89-234. The ionized gas mass of Sh 2-151 is ∼700M☉. Star formation in the Sh 2-151 area may occur in the whole region of strong FIR emission (as seen in the HIRES maps: ∼0.5 degrees, or 50pc, in length); north of Sh 2-151, activity is seen near the edge of a large (20pc diameter) molecular cloud.
ISM: clouds - ISM: molecules - radio lines: ISM - ISM: individual objects: Sh 2-151
Table 3: [BW98] Cloud A (Nos A-D). Table 5: [BW98] Ridge N (Nos 1-2), [BW98] > (Nos N, S).
H2O maser = EQ 2300+5641
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