## 4. AnalysisTable 2 gives intensities and column densities for each line at the head of the jet from slit 2. To calculate the intensities, the emission lines were fitted with single Gaussians, with uncertainties from a least squares fit. The line column densities can be calculated from (Gredel 1994): where is the specific intensity of the line, is the Einstein A coefficient of the transition, is the wavelength of the transition, and is the population of the upper level.
A reliable estimate of the excitation temperature for molecules undergoing rotational and vibrational transitions can be obtained from the rotation diagram. This method can be applied if the lines are optically thin and the level populations are characterised by a single rotation temperature. The total column density can then be calculated (Gredel 1994), using coefficients taken from Irwin (1987) for the partition function of : where is the population of the upper level, is the statistical weight for the transition, is the total column density, Z is the partition function, is the energy of the upper level and is the rotation temperature. The rotation diagram for the jet head is shown in Fig. 4. The error
bars are from the uncertainties in the line integrated intensities. A
straight line fit to the rotation diagram at the head of the jet,
gives a rotational temperature of 2200 K from the gradient, and a
total column density of 1.10
cm
Similar calculations have been carried out for several positions along the length of the jet. Due to the drop in intensity along the length of the jet, it is the 1-0 lines which dominate these calculations, although all detected lines are included. Table 4 gives the total column densities and temperatures found from slit 2, along the length of the jet. The intensity from each line was summed across a number of rows, corresponding to the size of the peaks and troughs. Nearer to the source, the line intensities become weaker and the temperatures and column densities become correspondingly more uncertain. These results are shown graphically in Fig. 5, which also shows the confidence limits on the derived parameters. This figure shows that there is probably a difference in temperature between the peaks and the troughs. The jet head, while having a similar temperature to the peaks, has a much higher column density.
© European Southern Observatory (ESO) 1999 Online publication: July 26, 1999 |