2003A&A...399L..43B

We have observed the dark cloud Barnard 68 with SCUBA at 850 µm and with SIMBA at 1.2 mm. The submillimetre and millimetre dust emission correlate well with the extinction map of Alves et al. (2001Natur.409..159A). The A_V/850µm correlation is clearly not linear and suggests lower temperatures for the dust in the inner core of the cloud. Assuming a model for the temperature gradient, we derive the cloud-averaged dust emissivities (normalised to the V-band extinction efficiency) at 850µm and 1.2mm. We find κ_850µm/κ_V=4.0±1.0x10^–5 and κ_1.2 mm_/κV_=9.0±3.0x10^–6. These values are compared with other determinations in this wavelength regime and with expectations for models of diffuse dust and grain growth in dense clouds.