Cold spots in the chamaeleon dark clouds

S. Hotzel ¹, D. Lemke ¹, L. V. Toth ^1,2, M. Stickel ¹, O. Krause ¹, & ISOPHOT CISS Consortium: MPIA, ESA, AIP, ICSTM, IPAC

¹ Max-Planck-Institut für Astronomie, Koenigstuhl 17, D-69117 Heidelberg, Germany

² Eotvos University, Dept. of Astronomy, Ludovika ter 2, H-1183, Budapest, Hungary

The ISOPHOT Serendipity Survey is a far-infrared (FIR) survey at 170  using the slewing time of the ISO telescope. Altogether ca. 15% of the sky is covered with an angular resolution of 1.5 arcminutes. The pointing accuracy is about 1 arcminute, and the dynamical range is 1 MJy/sr to 400 MJy/sr (cf. Stickel et al., this conference). The classes of objects detected by the Serendipity Survey are: (almost) unresolved FIR sources - mostly galaxies, cold spots in the Milky Way (sizes between 2 and 30 arcminutes), and Galactic cirrus.

One of the first target fields for the investigation of cold cloud cores with the ISOPHOT Serendipity Survey has been the molecular cloud complex in Chamaeleon, which is an active low mass star forming region, being studied before in the optical, NIR and FIR continuum, and by millimeter line spectroscopic measurements. The aim is to find cold dust associated with known molecular clouds, and to give detailed physical description of these cold spots. This report discusses 6 of the coldest spots found.

The targets to search for 170 um excess emission were selected from the CO survey of Vilas-Boas et al. (1994, ApJ 433, p. 94) and from the C¹⁸O mapping of Haikala et al. (1998, in: Star Formation with ISO, ed. by Yun & Liseau, p. 147). In order to estimate dust temperatures, 100 um IRAS/ISSA maps have been used in addition to the ISOPHOT Serendipity Survey data. After extracting simulated slews from the ISSA maps and smoothing the ISOPHOT Serendipity data to the IRAS 100 um resolution of 4.4 arcminutes, the two datasets have the same format and have been used in direct comparison.

The I(170 um)/I(100 ) intensity ratio is found to be about 2.5 outside the CO cores and often higher than 4 inside the cores. For deriving the latter number, the processing routine takes the FIR background for each spot individually into account. Assuming the FIR spectral energy distribution to be , the dust temperatures are calculated from the brightness ratio above. It shows that several spots in Chamaeleon have dust temperatures of 13 K and below. Finally, the derived physical parameters of the dust are compared to the parameters of the gas as derived by the molecular line radio measurements, in order to be able to assess the physical conditions in these clumps as astrophysical objects in the Chamaeleon dark clouds.