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Abstract. We present an atlas of Hγ, He i λ 4471 and Mg ii λ 4481 line profiles obtained in a 10 year observation period of 116 Be stars, which enabled many of them to be observed at quite different emission epochs. From the best fit of the observed He i λ 4471 line profiles with non-LTE, uniform (T eff , log g) and full limb-darkened model line profiles, we determined the V sin i of the program stars. To account, to some degree, for the line formation peculiarities related to the rapid rotation-induced non-uniform distributions of temperature and gravity on the stellar surface, the fit was achieved by considering (T eff , log g) as free parameters. This method produced V sin i estimations that correlate with the rotational velocities determined by Slettebak (1982) within a dispersion σ ≤ 30 km s −1 and without any systematic deviation. They can be considered as given in the new Slettebak's et al. (1975) system. Only 13 program stars have discrepant V sin i values. In some objects, this discrepancy could be attributed to binary effects. Using the newly determined V sin i parameters, we found that the ratio of true rotational velocities V /Vc of the program Be stars has a very low dispersion around the mean value. Assuming then that all the stars are rigid rotators with the same ratio V (ω)/Vc, we looked for the value of ω that better represents the distribution of V sin i/Vc for randomly oriented rotational axes. We obtained ω = 0.795. This value enabled us to determine the probable inclination angle of the stellar rotation axis of the program stars. In the observed line profiles of Hγ, He i λ 4471, Mg ii λ 4481 and Fe ii λ 4351 we measured several parameters related to the absorption and/or emission components, such as: equivalent width, residual emission and/or absorption intensity, FWHM, emission peak separations, etc. The parameters related to the Hγ line emission profiles were used to investigate the structure of the nearby environment of the central star. From the characteristics of the correlations between these quantities and the inferred inclination angle, we concluded that in most of cases the Hγ line emission forming regions may not be strongly flattened. Using a simple representation of the radiation flux emitted by the star+envelope system, we derived first order estimates of physical parameters characterizing the Hγ line emission formation region. Thus, we obtained that the total extent of the Hγ region is R f 2.5 ± 1.0 R * and that the density distribution in these layers can be mimicked with a power law ρ ∼ R −α , where α = 2.5−0.6 . The same approach enabled us to estimate the optical depth of the Hγ line emission formation region. From its dependence with the aspect angle, we concluded that these regions are caracterized by a modest flattening and that the ρ(equator)/ρ(pole) density contrast of the circumstellar envelope near the star should be two orders of magnitude lower than predicted by models based on a priori disc-shaped circumstellar envelopes. We found that the separation between the e...

Abstract.A sample of 97 galactic field Be stars were studied by taking into account the effects induced by the fast rotation on their fundamental parameters. All program stars were observed in the BCD spectrophotometric system in order to minimize the perturbations produced by the circumstellar environment on the spectral photospheric signatures. This is one of the first attempts at determining stellar masses and ages by simultaneously using model atmospheres and evolutionary tracks, both calculated for rotating objects. The stellar ages (τ) normalized to the respective inferred time that each rotating star can spend in the main sequence phase (τ MS ) reveal a mass-dependent trend. This trend shows that: a) there are Be stars spread over the whole interval 0 < ∼ τ/τ MS < ∼ 1 of the main sequence evolutionary phase; b) the distribution of points in the (τ/τ MS , M/M ) diagram indicates that in massive stars (M > ∼ 12 M ) the Be phenomenon is present at smaller τ/τ MS age ratios than for less massive stars (M < ∼ 12 M ). This distribution can be due to: i) higher mass-loss rates in massive objets, which can act to reduce the surface fast rotation; ii) circulation time scales to transport angular momentum from the core to the surface, which are longer the lower the stellar mass.

Context. Effective temperatures of early-type supergiants are important to test stellar atmosphere-and internal structure-models of massive and intermediate mass objects at different evolutionary phases. However, these T eff values are more or less discrepant depending on the method used to determine them. Aims. We aim to obtain a new calibration of the T eff parameter for early-type supergiants as a function of observational quantities that are: a) highly sensitive to the ionization balance in the photosphere and its gas pressure; b) independent of the interstellar extinction; c) as much as possible model-independent. Methods. The observational quantities that best address our aims are the (λ 1 , D) parameters of the BCD spectrophotometric system. They describe the energy distribution around the Balmer discontinuity, which is highly sensitive to T eff and log g. We perform a calibration of the (λ 1 , D) parameters into T eff using effective temperatures derived with the bolometric-flux method for 217 program stars, whose individual uncertainties are on average |ΔT eff |/T f eff = 0.05. Results. We obtain a new and homogeneous calibration of the BCD (λ 1 , D) parameters for OB supergiants and revisit the current calibration of the (λ 1 , D) zone occupied by dwarfs and giants. The final comparison of calculated with obtained T eff values in the (λ 1 , D) calibration show that the latter have total uncertainties, which on average are T eff /T f eff ±0.05 for all spectral types and luminosity classes. Conclusions. The effective temperatures of OB supergiants derived in this work agree on average within some 2000 K with other determinations found in the literature, except those issued from wind-free non-LTE plane-parallel models of stellar atmospheres, which produce effective temperatures that can be overestimated by up to more than 5000 K near T eff = 25 000 K. Since the stellar spectra needed to obtain the (λ 1 , D) parameters are of low resolution, a calibration based on the BCD system is useful to study stars and stellar systems like open clusters, associations or stars in galaxies observed with multi-object spectrographs and/or spectro-imaging devices.