3 Results and general spectral morphology

The spectral range employed ( 2.05 - 2.22 $\mu$m) was chosen due to the large number of transitions of differing species present. Expected transitions within the range include Br$\gamma$ at 2.166 $\mu$m and He I transitions at 2.058 $\mu$m, 2.112/2.113 $\mu$m and 2.161 $\mu$m. Various metallic transitions expected include Fe II 2.089 $\mu$m, Mg II 2.138/ 2.144 $\mu$m and Na I 2.206/ 2.209 $\mu$m. Several transitions of higher excitation species such as He II, C IV and N III are also present in the observed range. However we do not expect to see these given the relatively low temperature expected for the circumstellar envelope of Be stars (e.g. McGregor et al. 1988; Morris et al. 1996).

We present the spectra in Figs. 7-12. Since one of the aims of this work was to derive a K band spectral classification scheme, we have chosen to display the spectra based on their morphology rather than optical spectral classification. We define 5 groups for the spectra, based on the presence and strength of the Br$\gamma$, Mg II and He I features; we list the selection criteria below.

$\bf Group 1$: Br$\gamma$ in emission and He I features present.
$\bf Group 2$: Br $\gamma$ in absorption and He I features present.
$\bf Group 3$: Br$\gamma$ & Mg II in emission, no evidence for He I features.
$\bf Group 4$: Br$\gamma$ in absorption, no evidence for He I or Mg II features.
$\bf Group 5$: Br$\gamma$ in emission, no evidence for He I or Mg II features.

In Fig. 1 we plot the membership of each group by spectral type, and find that this provides a good indication of the broad optical spectral classification of a given star (the small number of non main sequence objects precludes comment on luminosity class). The presence of He I features in either emission or absorption indicates a spectral type of B3 or earlier. The small number of stars that show Mg II in emission, but no evidence of He I features are found to be slightly later (B2-B4), while those stars with Br$\gamma$ in emission, but which show no evidence of He I or Mg II features are found to be of spectral type B5 or later. Note we chose not to classify stars on the basis of line profiles so that the scheme is applicable to stars for which only low resolution spectra are available.

We summarise the various emission features observed as a function of spectral type in Table 3 (only those stars with classifications given in Paper I are listed). In Tables 4 to 8 we present the measured equivalent widths (EW) of the emission and absorption line features present in each object. These were measured relative to a continuum defined using the interactive routine ABLINE in FIGARO.