We present the results of a submillimeter dust continuum study of a molecular ridge in IC 5146 carried out at 850 \mu m and 450 \mu m with SCUBA on the James Clerk Maxell Telescope ( JCMT ) .
The mapped region is \sim 14 ^ { \prime } \times 2 \aas@@fstack { \prime } 5 in size ( \sim 2 pc \times 0.3 pc ) and consists of at least four dense cores which are likely to be prestellar in nature .
To study the dust properties of the ridge and its embedded cores , we combined the dust emission data with dust extinction data obtained by Lada et al .
( 1999 ) from the NIR colors of background giant stars .
The ridge shows dust extinctions above \sim 10 mag , rising up to 35 mag in the cores .

A map of dust temperatures , constructed from the continuum flux ratios , shows significant temperature gradients : we find temperatures of up to \sim 20 K in the outskirts and between the cores , and down to \sim 10 K in the cores themselves .
The cores themselves are almost isothermal , although their average temperatures vary between 10 K and 18 K. We used the extinction data to derive in addition a map of the dust emissivity parametrized by \kappa ^ { \prime } = \kappa _ { 850 } / \kappa _ { V } .
The average value of \kappa ^ { \prime } agrees well with the canonical value of Mathis ( 1990 ) .
We find that \kappa ^ { \prime } increases by a factor of \sim 4 from \sim 1.3 10 ^ { -5 } to \sim 5 10 ^ { -5 } when the dust temperature decreases from \sim 20 K to \sim 12 K. A Monte Carlo simulation shows that this change is significant with regard to the estimated calibration uncertainties .
This is consistent with models of dust evolution in prestellar cores by Ossenkopf & Henning ( 1994 ) which predict that grain coagulation and the formation of ices on grain surfaces in the cold , dense cloud interiors lead to a significant increase of the 850 \mu m dust opacity .
This interpretation is furthermore supported by the previous detection of gas-phase depletion of CO in one of the IC 5146 cores ( Kramer et al .
1999 ) .
Observations of dust fluxes at short wavelengths are however needed to verify this result .