Astronomy and Astrophysics, volume 466, 969-976 (2007/5-2)
ISO far-infrared observations of the high-latitude cloud L 1642. II. Correlated variations of far-infrared emissivity and temperature of ``classical large'' dust particles.
LEHTINEN K., JUVELA M., MATTILA K., LEMKE D. and RUSSEIL D.
Abstract (from CDS):
Our aim is to compare the infrared properties of big, ``classical'' dust grains with visual extinction in the cloud L1642
. In particular, we study the differences in grain emissivity between diffuse and dense regions in the cloud. The far-infrared properties of dust are based on large-scale 100µm and 200µm maps. Extinction through the cloud was derived by using the star count method in the B- and I-bands, and colour excess method in the J, H, and K_ s_ bands. Radiative transfer calculations were used to study the effects of increasing absorption cross-section on the far-infrared emission and dust temperature. Dust emissivity, measured by the ratio of far-infrared optical depth to visual extinction, τ(far-IR)/AV
, increases with decreasing dust temperature in L1642
. There is about a two-fold increase in emissivity over the dust temperature range of 19K-14K. Radiative transfer calculations show that, in order to explain the observed decrease of dust temperature towards the centre of L1642
, an increase of absorption cross-section of dust at far-IR is necessary. This temperature decrease cannot be explained solely by the attenuation of interstellar radiation field. Increased absorption cross-section also manifests itself as an increased emissivity. We find that, due to temperature effects, the apparent value of optical depth τapp
(far-IR), derived from 100µm and 200µm intensities, is always lower than the true optical depth.
ISM: individual objects: Lynds 1642 - ISM: clouds - ISM: dust, extinction - infrared: ISM
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