A representative sample of Be stars III: H band spectroscopy

We present H band (1.53 μm-1.69 μm) spectra of 57 isolated Be stars of spectral types O9-B9 and luminosity classes III, IV & V. The H I Brackett (n-4) series is seen in emission from Br-11-18, and Fe II emission is also apparent for a subset of those stars with H I emission. No emission from species with a higher excitation temperature, such as He II or C III is seen, and no forbidden line emission is present. A subset of 12 stars show no evidence for emission from any species; these stars appear indistinguishable from normal B stars of a comparable spectral type. In general the line ratios constructed from the transitions in the range Br-11-18 do not fit case B recombination theory particularly well. Strong correlations between the line ratios with Br-γ and spectral type are found. These results most likely represent systematic variations in the temperature and ionization of the circumstellar disc with spectral type. Weak correlations between the line widths and projected rotational velocity of the stars are observed; however no systematic trend for increasing line width through the Brackett series is observed