A representative sample of Be stars II. K band spectroscopy

Abstract. We present K band (2.05 m − 2.22 m) spec-tra of 66 isolated Be stars of spectral types O9-B9 and luminosity classes III, IV & V. We nd that objects with He i features either in emission or absorption are B3 or earlier. Objects with Mg ii emission but no He i are B2 to B4, while objects with Brγ emission but no evidence of He i or Mg ii are B5 or later. Na i emission in the spec-tra 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 prole of Brγ are seen from early to late spectral types which can be understood in terms of dif-ferences in the disc temperature and density. 30 per-cent of the stars do not currently show evidence for line emis-sion. Compared to the emission line stars these objects have a signicantly lower mean rotational velocity and a distribution of spectral types that is signicantly earlier. This can be explained either as the original misidentica-tion of these objects as Be 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