DISCOVERY OF A COLD EXTENDED CONDENSATION IN THE ORION-A COMPLEX

The central region of the Orion A cloud complex has been observed in t he submillimeter range, using the French balloon-borne 2 m telescope P RONAOS-SPM during its first flight, in 1994 September. An area coverin g 50' x 10' and including the M42 Nebula has been mapped in four submi llimeter photometric bands: lambda 180-240, 240-340, 340-560, and 560- 1050 mu m, with high sensitivity (less than or equal to 2 MJy sr(-1)) and an angular resolution from 2' to 3.'5. Four brightness enhancement s are visible and have been identified with the following sources: (1) the brightest peak corresponding to the central core of the nebula, i n the BN/KL source direction; (2) an extended emission region around 5 ' x 8', to the southeast of BN/KL, correlated with 100 mu m IRAS and ( CO)-C-13 emission (this has been identified as a gas-density enhanceme nt associated with a shock region); (3) the edge of an ionized part of the cloud, correlated with the 100 mu m emission; and (4) a very cold and extended condensation, discovered at 16' northwest of BN/KL. The emission spectra obtained for these sources show a variation of the du st emissivity spectral index within a large range, from 1 +/- 0.1 to 2 .2 +/- 0.2. The cold condensation discovered (T = 12.5 +/- 3 K) has a very low brightness emission, undetected on the 100 mu m IRAS map. It extends over approximately 0.7 pc(FWHM), with a total mass of 11 M-. a nd a total luminosity of 2.4 L-..