THE MILLIMETER WAVELENGTH EMISSIVITY IN IC5146

We have observed a core in the northern streamer of the IC5146 cloud u sing the MPIfR 19-channel Bolometer system on the IRAM 30m telescope a t a wavelength of 1.2 mm. We smoothed our observations to the same ang ular resolution (30'') as a new map of the NIR extinction of this clou d (Lada, Alves, and Lada 1998) and in this way obtained direct measure ments of the ratio of millimeter emissivity to dust extinction. Our re sults are compatible with a ratio of the visual extinction coefficient kappa(V) to the 1.2 mm grain absorption coefficient kappa(1.2) of (4 +/- 2) X 10(4). This is in good agreement with the theoretical predict ions for bare interstellar grains (Draine & Lee 1984; Mathis 1990). Wi thin the errors our measurements are also consistent with recent model s of grains with ice mantles whose size distribution has been modified due to coagulation but whose millimeter emissivities are not a strong function of grain size (Ossenkopf & Henning 1994). We find that the r atio of millimeter grain emissivity to visual extinction varies roughl y inversely with the visual extinction over our map and interpret this as implying a gradient in dust temperature from roughly 8 K in the co re interior (A(V) > 20 mag) to 20 K in regions of low (5 mag) extincti on. One consequence of our result is that the 1.2 mm intensity, by its elf, is not a good tracer of mass in this cloud.