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

Ph. Stee; J. Bittar

doi:doi:10.1051/0004-6361:20000458

Free access

Issue		A&A Volume 367, Number 2, February IV 2001


Page(s)		532 - 548
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20000458

A&A 367, 532-548 (2001)
DOI: 10.1051/0004-6361:20000458

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

Ph. Stee¹ and J. Bittar²

¹ Observatoire de la Côte d'Azur, Département Fresnel UMR 6528, Caussols, 06460 St. Vallier de Thiey, France
² Observatoire Midi-Pyrénées, CNRS UMR 5572, 14 Av. Edouard Belin, 31400 Toulouse, France

(Received 5 October 2000 / Accepted 14 November 2000 )

Abstract
We report theoretical HI visible and near-IR line profiles, i.e. H $\alpha$ (6562 Å), H $\beta$ (4861 Å) and Br $\gamma$ (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 $\gamma$ 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 $\rho$ = 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 $\alpha$ and in the infrared. We found that for a density $\rho$ = 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 ( $\sim$ 10^-11 g cm^-3). On the other hand, we found that around $\rho$ = 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.

Key words: stars: circumstellar matter; emission line; Be -- infrared: stars -- winds: models -- techniques: interferometric

Offprint request: Ph. Stee, Philippe.Stee@obs-azur.fr

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