3 Line identification

Based upon this material we have made line identifications in the traditional way, paying attention to both wavelengths and intensities within the multiplets. The identifications were made with the help of the tables of Moore (1959); for Fe II we also used Johansson's (1978) compilation and for [Ni II] Nussbaumer & Storey (1982). In addition we have used the Meinel et al. (1969) catalogue for lines which we could not identify. (See notes to Table 2). Some contamination with Hg I from city lights was unavoidable and is signaled in Fig. 1, which reproduces part of the spectrum.

Part of the material is reproduced in Fig. 1, where also some line identifications are provided. The region $\lambda$ 7123 to 7400 has been corrected by atmospheric absorption, which permitted to see a number of lines given in Table 2, but being hardly visible in Fig. 1. The correction by atmospheric extinction was done in the conventional way by dividing the spectrum of the star by that of comparison stars observed at similar airmasses.

In our spectra are present 197 emission lines and 4 absorption lines. We have not included in the latter count lines in which both emission and absorption features figure, like the He I lines. 18 emission lines could not be identified. The iron lines represent 40% of all identified emission lines.

Of the pure absorption lines we could identify only one, namely $\lambda$ 6613, with an interstellar feature (Herbig 1975). The weakness of the interstellar features contrasts strongly with the extinction of 8$\hbox{$.\!\!^{\rm m}$}$0 derived from photometry.

In the remainder of the paper, when we speak of lines,we refer always to emission lines, except if stated otherwise.

  

Figure 1: The different parts are given from top to bottom and from left to right. The first wavelength range is 4133 - 4930 Å. The spectrum is under exposed, specially for $\lambda < 4470$ Å. CL = city lights. The second range is 4923 - 5755 Å, the third is 7124 - 7942 Å and the fourth, 8073 - 8909 Å. The atmospheric absorption of the Z band of H2O has been corrected, but the star used was observed several hours after MWC 297. There result absorption residuals in the region $\lambda < 8180$ Å