Astronomy and Astrophysics, volume 399, 1073-1082 (2003/3-1)
Dust properties of the dark cloud IC 5146. Submillimeter and NIR imaging.
KRAMER C., RICHER J., MOOKERJEA B., ALVES J. and LADA C.
Abstract (from CDS):
We present the results of a submillimeter dust continuum study of a molecular ridge in IC 5146 carried out at 850µm and 450µm with SCUBA on the James Clerk Maxwell Telescope (JCMT). The mapped region is ∼14'x2.5' in size (∼2pcx0.3pc) 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 ∼10mag, rising up to 35mag in the cores. A map of dust temperatures, constructed from the continuum flux ratios, shows significant temperature gradients: we find temperatures of up to ∼20K in the outskirts and between the cores, and down to ∼10K in the cores themselves. The cores themselves are almost isothermal, although their average temperatures vary between 10K and 18K. We used the extinction data to derive in addition a map of the dust emissivity parametrized by κ'=κ850/κV. The average value of κ' agrees well with the canonical value of Mathis (1990ARA&A..28...37M). We find that κ' increases by a factor of ∼4 from ∼1.3x10–5 to ∼5x10–5 when the dust temperature decreases from ∼20K to ∼12K. 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 (1994A&A...291..943O) 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 850µm dust opacity. This interpretation is furthermore supported by the previous detection of gas-phase depletion of CO in one of the IC5146 cores (Kramer et al., 1999A&A...342..257K). Observations of dust fluxes at short wavelengths are however needed to verify this result.