2001A&A...367..532S

We report theoretical HI visible and near-IR line profiles, i.e. H α (6562Å), H β (4861Å) and Br γ (21656Å), and intensity maps for a large set of parameters (density, temperature, envelope geometry, inclination angle), representative of early to late Be spectral types. We have computed the size of the emitting region in the Br γ line and its nearby continuum which both originate from a very extended region, i.e. at least 40 stellar radii which is twice the size of the H α emitting region. We predict the relative fluxes from the central star, the envelope contribution in the given lines and in the continuum for a wide range of parameters characterizing the disk models. For a density ρ=5x10^–13g/cm³ at the base of the stellar photosphere, we obtain the largest probability of HI IR lines in emission, which is a factor of 100 lower than typical values found for Be stars. We have also studied the effect of changing the spectral type on our results and we obtain a clear correlation between the luminosity in H α and in the infrared. We found that for a density ρ=5x10^–12g/cm³, the probability of detecting HI IR lines in emission must be stronger for late-B spectral type stars. If no IR lines are detected for late types, it may indicate that the density in the disc is very high ( ∼10^–11g/cm³). On the other hand, we found that around ρ=5x10^–13g/cm³, it is possible to have a large envelope contribution in the Br γ line and a similar or even smaller emission in the Balmer lines. Even if Br γ is formed in an extended region, it is possible to obtain a FWHM and a V/R that agree well with observed profiles. Finally, it seems that the contribution in the Br γ line increases when the envelope becomes more and more ``disk-like'', contrary to the H α and H β lines.