Dust around H II regions. II. W 49A.

Sub-mm continuum maps, and IRAS calibrated raw data maps, on which a new destriping technique has been used, are presented of W49A, showing extensive emission from cool dust in the region. The dust emission is fitted by a greybody function with a temperature of 50 K and sub-mm spectral index beta = 1.8 + or - 0.2, consistent with previous work. The cloud is shown to be optically thin at wavelengths longer than 150 microns, so the sub-mm fluxes can be used to estimate the total dust mass, which is found to be 2400 solar masses. The total FIR luminosity of the cloud is found to be 27 million solar luminosities, making W49A one of the most luminous star-forming regions in the Galaxy. The morphology of the cloud is diagnosed as consisting of an association of H II regions surrounded by a dust cloud composed of grains at two characteristic temperatures.