Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...284..559o&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 284, no. 2, p. 559-572
Astronomy and Astrophysics
Astrophysics
26
Astronomical Maps, Astronomical Models, Carbon Monoxide, Massive Stars, Molecular Clouds, Radio Spectra, Star Formation, Submillimeter Waves, Astronomical Photometry, H Ii Regions, Nebulae
Scientific paper
We present high signal-to-noise, high angular resolution, submillimeter continuum and C(18)O (J = 2 - 1) maps of the core of the W 3 molecular cloud. Continuum maps at 450 and 800 micrometers reflect the distribution of the dust, but maps at 1100, 1300 and 2000 micrometers are contaminated by free-free radiation from the H II radio sources: W 3(A), (b), (C) and (D). We adopt a suitable model for this emission which we then subtract from the continuum maps to reveal the true distribution of the dust. The continuum emission of the embedded infrared sources is distinguished from that of the molecular cloud, enabling us to model the quiescent cloud and the sources separately. An isothermal fit to the data gives an average dust emissivity beta-index of approximately 1 for the quiescent cloud, indicating that the grains are composed of amorphous carbon or silicate. No large-scale variation in beta-index is found, with a maximum value of beta = 1.4 at the position of IRS5. We compare the morphology and physical properties as determined by the line and continuum maps. A strikingly difference is found around IRS4, which we attribute to temperature and optical depth effects. The submillimeter source IRS4 south is found to be cooler than the other sources and optically thick at 450 micrometers. The maps are split into 3 regions for which we calculate the mass independently from C(18)O and 800 micrometers data. Derived masses agree closely for an assumed average temperature of 35 K and we derive a total mass for the core of 1700 solar mass. We emphasize that the common assumption of a uniform temperature across a region such as W 3 is frequently invalid and can lead to an overestimate of the mass. The relative merits of line and continuum observations as mass tracers are discussed. C(18)O is a better tracer of mass, whilst continuum emission better identifies embedded sources.
Griffin Matt J.
Oldham P. G.
Richardson K. J.
Sandell Goeran
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