Molecules in an infrared cirrus cloud

One of the clouds that form the Polar Loop was observed in the 1(sub 10)-1(sub 11) 4.8 GHz transition of formaldehyde and in J equal to 1-0 transitions of CO-12 and CO-13 at 115 and 110 GHz resp. The cloud consists of several filaments. From the correlation of IRAS 60 and 100 microns intensities a color temperature of the dust of 21 K and a maximum optical depth of 3 x 10(exp -4) were derived. At one local maximum of the 100 micron intensity, the hyperfine structure of formaldehyde could be resolved. Since the infrared optical depth is small, the 100 micron intensity can be used as a measure of dust column density.