We have analysed the spectra of 66 isolated Be stars and found emission from H I, He I, Mg II, Fe II and Na I to be present in subsets of the spectra. We find the presence of He I and Mg II features to be a good diagnostic of early spectral type. The possible presence of Na I emission in the spectrum of 4 stars 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
are seen from early to late spectral types;
this can be understood in terms of differences in the disc temperature
and density (and the increasing strength of the photospheric feature
in the later stars). Correlations between the
FWHM of Br
and He I 2.058 
m and the stellar
rotational velocity were found. No correlations were found between stellar
rotational velocity and the EW of either of these transitions.
No significant difference between
the projected rotational velocities of the stars (expressed as a
function of the stellar breakup velocity) and the emission
characteristics (defined by the strength of Br
emission and the
presence of Mg II) of the emission line stars was found. However, stars
which appear to have undergone a phase transition from emission ("e'') to
non emission ("non-e'') stars
were found to have a smaller mean rotational velocity than the Be
stars in the sample. In addition these objects have a distribution
of spectral types that is significantly earlier than the
emission line objects. 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 low rotational
velocities may be more prone to changes between the Be and B phases.
Acknowledgements
We wish to thank the UK PATT panel for the allocation of observing time for this programme. In addition we thank the support astronomers and staff of UKIRT for their invaluable assistance at the telescope, and Ignacio Negueruela for his valuable input. UKIRT is operated by the Joint Astronomy Centre, Hawaii for the UK PPARC. Data reduction and analysis for this paper was carried out using the Liverpool JMU and Sussex University Starlink Nodes. JSC wishes to acknowledge a PPARC research award.
Copyright The European Southern Observatory (ESO)