A representative sample of Be stars

II. K band spectroscopy

¹ Astronomy Centre, CPES, University of Sussex, Brighton, BN1 9QH, UK
² Astrophysics Research Institute, Liverpool John Moores University, Liverpool, L41 1LD, UK

Send offprint request to: J.S. Clark

Received: 16 February 1999
Accepted: 29 September 1999

Abstract

We present K band (2.05 μm - 2.22 μm) spectra of 66 isolated Be stars of spectral types O9-B9 and luminosity classes III, IV & V. We find 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 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 Brγ are seen from early to late spectral types which can be understood in terms of differences in the 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 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.