We present the first paper in a series detailing the results of 13CO observations of a ∼1 deg2 region of the giant molecular cloud (GMC) complex associated with the H ii region RCW 106. The 13CO observations are also the first stage of a multimolecular line study of the same region. These observations were amongst the first made using the new on‐the‐fly mapping capability of the Australia Telescope National Facility Mopra Telescope. In the configuration used, the instrument provided a full width at half‐maximum (FWHM) beam size of 33 arcsec and a velocity resolution of 0.17 km s−1. The gas emission takes the form of a string of knots, oriented along an axis that extends from the north‐west (NW) to the south‐east (SE) of the field of the observations, and which is surrounded by a more extended, diffuse emission. We analyse the 2D integrated 13CO emission using the clumpfind algorithm and identify 61 clumps. We compare the gas data in the GMC with the dust data provided by 21‐μm Midcourse Space Experiment (MSX) and 1.2‐mm Swedish European Southern Observatory Submillimetre Telescope (SEST) images that we both regridded to the cell spacing of the Mopra data and smoothed to the same resolution. The 13CO emission is more diffuse and extended than the dust emission revealed at the latter two wavebands, which both have a much higher contrast between the peaks and the extended emission. From comparison of their centre positions, we find that only ∼50 per cent of the 13CO clump fits to the data are associated with any dust clumps. Using the clump fits, the total local thermodynamic equilibrium gas mass above the 3σ level measured from the molecular data is 2.7 × 105 M⊙, whereas that measured from the smoothed 1.2‐mm SEST dust data is 2.2 × 105 M⊙.
We present MERLIN maps of the 22-GHz H 2 O masers around four low-mass late-type stars (IK Tau, U Ori, RT Vir and U Her), made with an angular resolution of ∼15 milliarcsec and a velocity resolution of 0.1 km s −1 . The H 2 O masers are found in thick expanding shells with inner radii ∼6 to 16 au and outer radii four times larger. The expansion velocity increases radially through the H 2 O maser regions, with logarithmic velocity gradients of 0.5-0.9. IK Tau and RT Vir have well-filled H 2 O maser shells with a spatial offset between the near and far sides of the shell, which suggests that the masers are distributed in oblate spheroids inclined to the line of sight. U Ori and U Her have elongated poorly filled shells with indications that the masers at the inner edge have been compressed by shocks; these stars also show OH maser flares. MERLIN resolves individual maser clouds, which have diameters of 2-4 au and filling factors of only ∼0.01 with respect to the whole H 2 O maser shells. The circumstellar envelope velocity structure gives additional evidence the maser clouds are densitybounded. Masing clouds can be identified over a similar time-scale to their sound crossing time (∼2 yr) but not longer. The sizes and observed lifetimes of these clouds are an order of magnitude smaller than for those around red supergiants, similar to the ratio of low-mass:high-mass stellar masses and sizes. This suggests that cloud size is determined by stellar properties, not local physical phenomena in the wind.
We present multimolecular line maps obtained with the Mopra telescope towards the southern giant molecular cloud (GMC) complex G333, associated with the H ii region RCW 106. We have characterized the GMC by decomposing the 3D data cubes with gaussclumps, and investigated spatial correlations among different molecules with principal component analysis (PCA). We find no correlation between clump size and linewidth, but a strong correlation between emission luminosity and linewidth. PCA classifies molecules into high‐ and low‐density tracers, and reveals that HCO+ and N2H+ are anticorrelated.
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