2000A&A...364..769T

ISOPHOT Serendipity Survey (ISOSS) observations at 170µm reveal cold dust clouds in the nearby star forming region Chamaeleon. The distribution of the ISOSS/IRAS based T(I₁₇₀/I₁₀₀) colour temperature have been studied in a nearby low-mass star forming region. T(I₁₇₀/I₁₀₀) separates the obscured and intercloud regions as seen from a comparison to optical extinction data. The interstellar medium in Chamaeleon-Musca appears to be cold with dust colour temperatures of ≃16.3K for intercloud regions, and ≤14.5K for obscured clouds. The cold clouds account for 3% of the area. ISOSS found 9 very cold cores with colour temperatures as low as T_dust1mm~<12.5K in an 11°x8° sized region. All C¹⁸O cores of the Chamaeleon main clouds which were crossed by ISOSS slews were also detected. Of these 11 (73%) are cold with T_dust≤15K, 6 (40%) are associated with very cold cores. The very cold cores have high gas column densities, N(H₂)>10²¹cm^–2, and 7 out of 9 have low gas kinetic temperatures as indicated by T_ex(C¹⁸O)≃8K. The physical parameters of the very cold cores agree with the results of radiative transfer calculations of a spherical model cloud heated from outside by one third of the the solar neighbourhood ISRF intensity. A check of the photometric calibration of ISOSS against ISOPHOT AOT PHT22 maps and DIRBE interpolated 170µm values showed an agreement of ±10% and ±20%, respectively. We expect to discover in total more than 100 very cold cores in the Galaxy by ISOSS.