(CO)-C-13 AND (CO)-O-18 OBSERVATIONS OF S140 - DELINEATION OF THE OUTFLOW STRUCTURE, A STUDY OF FRACTIONATION EFFECTS AND COMPARISON WITH CI OBSERVATIONS

The outflow and photon-dominated region (PDR) associated with the S140 complex have been observed at high resolution (similar to 14 arcsec) in the (CO)-C-13 and (CO)-O-18 J = 3-->2 lines. The (CO)-O-18 map conf irms earlier (CO)-O-17 J = 3-->2 line observations (Minchin et al. 199 4) that show an 'are' of emission observed to the south of the peak, a nd also reveals a similar (and more prominent) are feature to the east , a region not covered by the (CO)-O-17 map. This is a particularly fi ne example of the classic 'tuning fork' morphology, where emission at the ambient cloud velocity is tracing the outflow cavity wall of the b lueshifted lobe. The N((CO)-C-13)/N((CO)-O-18) ratio has been plotted against extinction and fits the power law relation N((CO)-C-13)/N((CO) -O-18) = 21A(v)(-0.35). The highest values, as expected, occur for obs erved positions towards the PDR, with N((CO)-C-13)/N((CO)-O-18) exceed ing the terrestrial value (5.5) for A(v) less than or equal to 40 magn itudes. In the outermost parts of the cloud (A(v) less than or equal t o 10 magnitudes) the N((CO)-C-13)/N((CO)-O-18) ratio is largest, up to 20. The increased fractionation may be due to higher photoionization of the optically thinner isotope, (CO)-O-18. There is a close correlat ion between N(CI)/N(CO) and visual extinction over a wide extinction r ange (A(v)=3-100 mags.). The best fit power law is N(CI)/N(CO)=4.2A(v) -(0.9). For positions toward the outflow (A(v) similar to 50-100) N(CI )/N(CO)similar to 0.1 (0.07-0.12). N(CI)/N(CO) increases with decreasi ng extinction to similar to 1 for A(v) less than or equal to 5 mags., corresponding to positions near the edge of the cloud. A detailed comp arison of antenna temperatures and linewidths for the (CO)-C-13, (CO)- O-18 and CI lines is presented. The (CO)-C-13 and (CO)-O-18 antenna te mperatures and linewidths are closely correlated, and imply the emissi on, for both isotopes, emanates from gas that is in LTE and is well mi xed. The CI emission from the PDR implies that here the atomic carbon is in LTE, but occupies a different volume of gas than the isotopic CO . Towards the outflow the CI linewidths are systematically broadened r elative to those for the isotopic CO lines. This is interpreted as evi dence that atomic carbon is produced by the effect of shocks on the ch emical and physical processes at the interface between a stellar wind and the outflow cavity wall.