The structure of the Orion bar

We have obtained NIR spectral line maps of a limited region around the Orio n Bar ionization front using the red and blue grisms of SOFI on the ESO NTT telescope. The wavelength range covered was from 0.95 to 2.3 mum. In addit ion to many well studied features, we detected two lines at 1.07 and 1.17 m um due to recombination to CI which have excitations above 60000 cm(-1). We also observe several features at around 1 micron of atomic nitrogen (at st ill higher excitations) which we believe are caused by fluorescence of UV l ines at approximately 955 Angstrom in gas within the ionization front. We g ive a brief analysis of this process showing that one can infer the relativ e UV intensities incident upon the ionization front on the basis of the NIR spectra. Analogously, the spatial distribution of the fluorescent OI 1.317 mum line allows one to infer the geometry of the ionization front. We cons ider various geometries and conclude that the Orion Bar is most likely to b e a cylinder or filament in the plane of the sky. Maps in the 9840 Angstrom CI line were also obtained and compared with the corresponding intensity d istribution in C91 alpha from Wyrowski et al. (1997). These are emitted fro m the same general area but show differences in detail which are likely par tly to be due to patchy extinction. The CI NIR line correlates well with mo lecular hydrogen emission away from the high density high radiation held la yers of the Bar. The measured CI line ratios tin particular the ratio of th e 0.984 and 1.07 mum lines) suggest higher temperatures in the C+ layer tha n allowed from the measured radio line width. The explanation for this disc repancy is not clear but it points up the need for observations in the NIR with higher spectral resolution and in the radio with higher spatial resolu tion.