We present ISOPHOT observations of eight interstellar regions in the 60-200 μm wavelength range. The regions belong to mostly quiescent high-latitude clouds and have optical extinction peaks from A_V~1-6 mag. From the 150- and 200-μm emission, we derived colour temperatures for the classical big grain component which show a clear trend of decreasing temperature with increasing 200-μm emission. The 200-μm emission per unit A_V, however, does not drop at lower temperatures. This fact can be interpreted in terms of an increased far-infrared (FIR) emissivity of the big grains. We developed a two-component model including warm dust with the temperature of the diffuse interstellar medium (ISM) of T= 17.5 K, and cold dust with T= 13.5 K and FIR emissivity increased by a factor of >4. A mixture of the two components can reproduce the observed colour variations and the ratios I₂₀₀/A_V and τ₂₀₀/A_V. The relative abundance of small grains with respect to the big grains shows significant variations from region to region at low column densities. However, in lines of sight of higher column density, our data indicate the disappearance of small grains, perhaps a signature of adsorption/coagulation of dust. The larger size and porous structure could also explain the increased FIR emissivity. Our results from eight independent regions suggest that these grains might be ubiquitous in the galactic ISM.

Related paper:

Title: The far-infrared signature of dust in high-latitude regions

Authors: del Burgo, C.; Laureijs, R. J.; Ábrahám, P.; Kiss, Cs.

Journal: Monthly Notices of the Royal Astronomical Society, Volume 346, Issue 2, pp. 403-414.

We examined the dust emissivity at far-infrared wavelengths, and proposed a method to reproduce ISOPHOT temperatures combining ISOPHOT and IRAS far-infrared data. Analysing a sample of 13 clouds we compared the temperature values obtained using our method to those determined from ISOPHOT data and verified the accuracy of our method. This method allows one to extend the sample of clouds appropriate for investigation of dust emissivity properties. We applied our method for 8 clouds, for which ISOPHOT data are available olny at one wavelength, to determine dust colour temperature, and the dust emissivity was also computed for 3 of these clouds.

Related paper:

Title: Determination of dust temperature and emissivity from IRAS and ISO observations

Authors: Z.T. Kiss, Cs. Kiss, P. Ábrahám and L.V. Tóth

Journal: PADEU Vol. 14, p.

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