Near-IR and visible interferometry of Be stars: Constraints from wind models

We report theoretical HI visible and near-IR line profiles, i.e. H alpha (6562 Angstrom), H beta (4861 Angstrom) and Br gamma (21 656 Angstrom), 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 gamma 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 alpha 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 p = 5 10(-13) gcm(-3) 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 alpha and in the infrared. We found that for a density p = 5 10(-12) gcm(-3), 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 (similar to 10(-11) gcm(-3)). On the other hand, we found that around p = 5 10(-13) g cm(-3), it is possible to have a large envelope contribution in the Br gamma line and a similar or even smaller emission in the Balmer lines. Even if Br gamma 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 gamma line increases when the envelope becomes more and more disk-like, contrary to the H alpha and H beta lines.