J. Cernicharo 1 S.J. Leeks 2 M.J. Sempere 1 T. Lim 3 S. Perez 1 P. Cox 4 J.P. Baluteau 5 E. Caux 6
1 Consejo Superior de Investigaciones Cientificas. Instituto de Estructura de la Materia. Dpto Fisica Molecular. C/Serrano 121. 28006 Madrid. Spain
2 Queen Mary & Westfield College, London, E1 4NS, U.K.
3 ISO Science Operations Centre, Space Science Department of ESA, Villafranca, P. O. Box 50727, 28080, Madrid, Spain
4 IAS. Paris. France
5 LAS. Obs. Marseille. France
6 CESR. Toulouse. France
We present LWS-grating and LWS-FP data of the Orion molecular cloud.
Five full LWS-grating rasters, centred on IRc2 and giving a total of
23 positions, have been obtained. The grating spectrum of the central
position was consequently observed five times over two orbits.
For each position of each raster, 6 scans between 43 and 197 
m were
obtained. The data were reprocessed to remove non-linear effects using
special procedures (see contribution by S.J. Leeks et al). All the features
present in the final averaged grating spectrum of the central position were
detected in each individual scan. Although Orion-IRc2 is practically a
point-like source for the LWS beam, residual fringes due to the extended
Orion molecular cloud have been observed and removed using special data
processing algorithms.
A North-South raster with five positions was also obtained in some
lines of water vapour and OH. Finally, around 100 lines of water
vapour (including many lines from H218O and H217O) were
observed with the LWS-FP spectrometer in the direction of
Orion-IRc2. Taking into account the extra data provided by the
LWS-FP, we have covered a range of about 100 m with a good
signal to noise ratio (typically 12 scans per line).
The Orion-IRc2 far-infrared spectrum is dominated by the lines of CO, H2O, OH, the isotopes of water vapour, NH3, some lines of HCO+ and HCN, and probably by a large number of b-type transitions of the slightly asymmetrical molecules as HCO, HOCO+, ...
In this contribution we analyse the role of these molecules, their spatial extent, particularly for the case of H2O and OH, and their abundances. The role of b-type transitions from relatively heavy molecules in the far-infrared spectrum of warm molecular clouds will be also discussed.
Details on the CO emission at large scale in the Orion molecular cloud are given in the contribution by M.J. Sempere et al.