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

(Received 5 October 2000 / Accepted 14 November 2000 )

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