A representative sample of Be stars - II. K band spectroscopy

We present K band (2.05 mu m - 2.22 mu m) spectra of 66 isolated Be stars of spectral types O9-B9 and luminosity classes III, IV & V. We find that objects with Hf I features either in emission or absorption are B3 of earlier. Objects with Mg II emission but no He I are B2 to B4, while objects with Br gamma emission but no evidence of HeI or MgII are B5 or later. NaI emission in the spectra of 4 objects appears to indicate that regions of the circumstellar envelopes of these stars must be shielded from direct stellar radiation. Systematic trends in the line strength and profile of Br gamma are seen from early to late spectral types which can be understood in terms of differences in thf disc temperature and density. 30 per-cent of the stars do not currently show evidence for line emission. Compared to the emission line stars these objects have a significantly lower mean rotational velocity and a distribution of spectral types that is significantly earlier. This can be explained either as the original misidentification of these objects as Bt stars (i.e. they never had line emission), or as evidence that stars with lower rotational velocities may be more prone to changes between the Be and B phases.