VERY COLD DUST ASSOCIATED WITH MOLECULAR GAS

We report the detection of very cold dust in a small and isolated dust cloud. Observations at 60, 90, 135, and 200 mu m show a constant surf ace brightness ratio I-135/I-200 and a flattening of 1(90)/1(200) towa rds the cloud centre. The dust temperature derived from the far-infrar ed colours can be confined to the range of 12-15 K assuming a lambda(- 2) dust emissivity. The 60 mu m emission comes mainly from outer dust layers surrounding the core. We infer that a fraction of the power in the 90 mu m band comes from the warmer grain component also causing I- 60. This fraction is approximately equal to the total power in the 60 mu m band. The cloud is also detected in (CO)-C-12, (CO)-C-13, (CO)-C- 18, HCO+ and CS. The detections indicate that the dust emission is ass ociated with a molecular cloud core where n(H-2) greater than or equal to 3 10(4) cm(-3). Using the column density derived from the molecula r observations we find an extinction cross section per H-atom of 4.1-9 .5 cm(2)/H-atom.