Balloon-borne imaging of the Cygnus-X region at 260 μm wavelength

Abstract

We report on 260 μm far-infrared observations of the galactic Cygnus-X region which contains many active star-forming clouds. Successful measurements with a 60 cm Cassegrain-type telescope on a stratospheric balloon gondola designed at ETH Zurich in collaboration with the Geneva Observatory have been made on the dust emission of the molecular cloud complexes DR21-W75 and S 106 as well as on Jupiter on the occasion of a flight in 12/13 May 1992. These measurements supplement the 80 μm and 130 μm wavelength data obtained by a previous flight in 26/27 September 1990. Observations were performed during 6 h on the occasion of this flight on 12/13 May 1992 with a 380,000m 3 stratospheric balloon at a height of 39km at the balloon station of CNES, Aire-sur-1'Adour, France. These measurements are the first ever performed at the wavelength of 260 μm in the Cygnus-X region. On this occasion we used a liquid helium-cooled mesh-bandpass filter of 25% bandwidth and a helium-cooled bolometer with a noise equivalent power (NEP) of about 1.1 × l0 −14WHz − 1 2 . The pointing accuracy of the telescope was ±17 arcsec with a stability of typically 3 arcsec rms. The chopping frequency of the secondary mirror was 8 Hz and the chopper throw ± 5 arcmin with respect to the optical axis of the telescope. For the flight of May 1992 we have, compared to the flight of September 1990, increased the size of the chopper throw, improved its symmetry and the stability of the chopper motion. In view of improvements of the performance for future flights we also report on a careful investigation of the entire telescope and photometer system. On the basis of the new data at 260 μ, as well as on those measured during the flight of 1990, the color temperatures of the dust in the sources mentioned above have been calculated. Furthermore, peak-flux densities, and total flux densities have been determined. With the aid of the color temperatures the optical depths of the various molecular cloud cores have also been evaluated. These results, together with the so-called “Chicago assumptions”, were used to derive the emissivity of the dust grains, the optical depth of dust cores and grain densities in dust. We have further determined the H 2 column densities, the average H 2 space density and the mass of the cloud cores. By taking into account our own data and all flux densities published so far, we have collated the spectral emissions in the far-infrared for the various sources mentioned above and decomposed into contributions from hot, warm and cold dust. Individual spectra pertaining to these components are represented by modified Planck-functions of the form λ - β B λ ( T) with β = 2 for λ > 40 μm.