BALLOON-BORNE FAR-INFRARED IMAGING OF THE CYGNUS-X REGION

We report on far-infrared observations of the galactic Cygnus-X region. Measurements have been performed with a 60cm diameter far-infrared balloon-borne telescope developed at ETH Zurich in collaboration with the Geneva Observatory. The Cassegrain-type telescope is equipped with secondary-mirror chopping and an attached photometer including a liquid helium cooled silicon bolometer with an NEP of 1.3 x 10(-14) W/Hz1/2 and three mesh bandpass filters. The latter are centered at the wavelengths 80 mum, 130 mum and 310 mum with bandwidths of only +/-3 mum, +/-3 mum and +/-15 mum, respectively. These bandwidths are the smallest used in astrophysical photometers ever flown. The pointing accuracy of the stabilized telescope is +/-17 arcsec with a stability of typically 3 arcsec RMS. Observations have been performed during 5 hours on the occasion of a flight with a 380'000 m3 stratospheric balloon at a height of 39 km at Aire/Adour, France, on September 26/27, 1990. Successful measurements have been made on the dust emission of the molecular cloud complexes DR21/W75N and S106 at 80 mum and 130 mum wavelength as well as on Mars at all wavelengths mentioned above. Because of the considerably smaller bandwidths of our filters our measured contour maps axe of higher quality than those performed by the Infrared Astronomical Satellite (IRAS) in spite of the fact that the 60cm IRAS telescope was operated at a temperature of 3K in comparison to 250 K of our telescope. On the basis of the 80 mum and 130 mum data dust colour temperatures of 36+/-2K for DR21, 34+/-4K for W75N and 45+/-6K for S106 have been calculated. Furthermore, peak intensities and total luminosities for the various sources have been determined and compared with the results of other authors.