Astron. Astrophys. 315, L317-L320 (1996)
Very cold dust associated with molecular gas*
R.J. Laureijs1, L. Haikala2, M. Burgdorf1, F.O. Clark3, T. Liljeström2, K. Mattila2, and T. Prusti1
1 ISO Science Operations Centre, Astrophysics Division of ESA,
Villafranca, Apdo 50727, E-28080 Madrid, Spain
Received 15 July 1996 / Accepted 3 September 1996
Abstract. We report the detection of very cold dust in a small and isolated dust cloud. Observations at 60, 90, 135, and 200 m show a constant surface brightness ratio and a flattening of towards the cloud centre. The dust temperature derived from the far-infrared colours can be confined to the range of 12-15 K assuming a dust emissivity. The 60 m emission comes mainly from outer dust layers surrounding the core. We infer that a fraction of the power in the 90 m band comes from the warmer grain component also causing . This fraction is approximately equal to the total power in the 60 m band.
The cloud is also detected in 12CO, 13CO, 18CO, and CS. The detections indicate that the dust emission is associated with a molecular cloud core where . Using the column density derived from the molecular observations we find an extinction cross section per H-atom of 4.1-9.5 .
Key words: interstellar medium: dust, extinction - interstellar medium: clouds - interstellar medium: molecules
* Based on observations made with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA
Last change: December 16, 1996