Submillimetre line and continuum observations of the S255 molecular cloud

The S255 molecular cloud has been observed using both continuum and spectral line techniques at several submillimetre and millimetre wavelengths. From photometry at 350, 760 and 1070 μm, the dust is estimated to have a central temperature of 44K and an emissivity which varies as λ-1. Spectral mapping of the source has been carried out in the CO J = 2-1, CO J = 3-2 and HCN J = 4-3 molecular lines, and central spectra obtained in the transitions HCO+ J = 4-3 and H13CO+ J = 4-3. Many features of the line observations can be modelled. Mapping at 350 μm has revealed an elongated central structure, also suggested by the HCN mapping, in which two clumps are separated by 1 arcmin along a north-south line. The intensity ratios between the pairs of transitions CO J = 3-2, CO J = 2-1 and HCO+ J = 4-3, H13CO+ J = 4-3, suggest that fragmentation has occurred in the cloud. An optically thin, high-velocity component is detected in the CO J = 3-2 line, for which a density of n(H2+He) ~ 4 - 7×104cm-3 and a size of ~0.7 arcmin are deduced. This component is hotter than the ambient cloud material and may originate from a high-velocity molecular outflow. Additional evidence for this hypothesis is provided by our detection towrds S255-IRS1 of emission in the 2.12-μm V=1-) S(1) line of shocked molecular hydrogen, at a surface brightness of ~10-11W com-2sr-1