We present medium-resolution (R ~ 600) mid-infrared (8-13.3μm) spectra of γ Cas and a coadded spectrum of nine Be stars. A large number of lines have been observed and identified in these spectra, including 39 hydrogen recombination lines in the spectrum of γ Cas. In the majority of our spectra, all of the observed lines are attributable to hydrogen recombination. Two additional sources, β Lyr and MWC 349, show [Ne II] emission and β Lyr also displays [He I] emission. We tabulate the effective line strength and line widths for the observed lines, and briefly discuss the physical implications of the observed line series. We also use a simple model of free-free emission to characterize the disks around these sources.

Because of their spectral peculiarities, stellar parameters of objects undergoing the Be phenomenon cannot be determined in the same way as for normal B stars. In particular, the use of the first lines of the Hydrogen series is hampered by the presence of emission components. On the other end, the recently generalized use of CCD detectors, well adapted to the deep red spectral region, provides a large amount of quantitative and well calibrated flux measurements with spectral resolutions around 0.1 nm. We propose to use the shape of the continuum and line flux distribution in the range of the higher Paschen lines of Hydrogen to determine first the effective temperature and superficial gravity of Be stars where, in most cases, the photospheric spectrum is not disturbed by line or continuum emission.

A sample of Be stars with large far-infrared excesses detected by IRAS is selected and their high-resolution IRAS images are examined. The far-infrared emission from most of them is marginally extended and is associated with the optical sources. Modeling of the stars’ spectral energy distributions allows us to rule out the infrared cirrus nature of the excesses. We suggest that the excesses are more likely due to circumstellar dust, possibly formed early in the evolution of the star.

In an earlier work (Cruzado, Di Rocco & Ringuelet, 1998), we showed that the dielectronic recombination of Mg II atoms contributes strongly to the infrared flux. In the present paper we aim at investigating whether the approximations made before could have biased our conclusions.

We are interested in the atomic processes taking place in the envelopes of early type stars; the first part of our project consists of an investigation of the dielectronic recombination (DR) of metals. In earlier papers, we have studied the DR of Mg II and its contribution to the IR continuum; now, we are interested in accomplishing similar results analysing the Fe II atom.

We selected a group of 11 B-type emission-line stars with large IR excesses, which show a steep flux decrease towards longer wavelengths. Analysis of their observational characteristics has been carried out on the basis of the data collected from literature, results of our recent photometric and high-resolution spectroscopic observations. Possible nature and evolutionary state of the group objects are discussed.

We present the results of optical and near–IR spectroscopy of the massive young star associated with the extended reflection nebula Gy 2-18 (HHL31). The optical spectrum between 4000-5000 Å suggests a B0-B2 classification for this object. In addition the Hα line profile indicate the presence of a consistent stellar wind with a velocity of the order of 1200 km/s. The near-IR spectrum is dominated by the presence of the hydrogen recombination emission lines (Pfund and Bracket series). The measured line intensities of these lines are in agreement with the presence of a strong stellar wind in Gy2-18.

We study the continuum flux excess at λ4471 by comparing the observed He I λ4471 line profiles with non-LTE model line profiles. Assuming that emission of the Hγ line is formed nearly in the same regions of the circumstellar envelope as those where the visible continuum flux excess rises, we estimate the continuum opacity needed to account for the veiling of the He I λ4471 line. The flux excess so derived is then studied as a function of the stellar aspect angle in an attempt to determine the degree of incidence of the envelope geometry near the central star on the continuum flux of Be stars.

Observed visible energy distributions of Be stars were studied with analytic flux distributions produced by flattened circumstellar envelopes. The theoretical representation of emitted fluxes also allows for density distribution effects in the region where the visible continuum emission/absorption is raised. Two main conclusions were reached: (a) regions responsible for spectrophotometric ”shell” phases have, on average, steeper density distributions than those producing the spectrophotometric ”Be” phases; (b) the mean temperatures of the studied circumstellar envelope regions shows a linear relation with their mean ”inverse” extent R*/R.

The long-term visible spectrophotometric variations depicted by the following parameters: V the apparent visual magnitude; Φrb the gradient of the observed Paschen energy distribution and D the total Balmer discontinuity (BD) of 49 Be stars in different spectrophotometric phases (SPh-E: spectrophotometric phase where the second component of the BD is in emission; SPh-A: spectrophotometric phase where the second component of the BD is in absorption) were translated into CE physical parameters. These parameters are: R/R* the mean extent of the CE zone that produces the visible energy distribution; Tenv its mean temperature; τ the continuum opacity at λ0.56μm. The results obtained show that the triplet of parameters (V, Φrb, D) do not depend on the (R/R*, Tenv, τ) set of parameters in the same way if Be stars are in a SPh-E or in a SPh-A phase. Independently of the spectrophotometric phase, Tenv always decreases as a linear function of (R/R*)−1. In SPh-E it is (R/R*,)−1 ≤ 0.7, and in SPh-A it is (R/R*)−1 ≥ 0.7. All SPh behaviours can be summarized by the relation ∂Tenv/∂(R*/R) = ∂Tenv/∂τ × ∂τ/∂(R*/R) ≥ 0, which describes different spectrophotometric behaviours in both SPh-E and SPh-A phases.

Correlations between long-term spectrophotometric and optical spectroscopic variations are investigated in some Be stars. Using spectrophotometric variations as a function of time and a compilation of spectroscopic measurements, we investigated temporal variations of emission and shell line parameters. In some cases time lags between spectroscopic and spectrophotmetric variations could be estimated. We could not find precise relations between the spectroscopic and spectrophotometric behaviours, but a number of tendencies could be derived which give information on physical parameters of circumstellar envelopes in Be stars.

Shell lines have high diagnostic potential for the kinematical conditions in Be disks. We present here results from our long-term spectroscopic monitoring campaign of Fe II shell lines. We demonstrate that most of them are likely to arise in Keplerian disks being hydrostatically supported. There is furthermore one class of shell lines (dubbed NOACs) which does not fit into this simple scheme.

Applying the SAC (self absorption curve) method to χ Oph (HD 148184) we conclude that Fell emission lines are optically thick. We estimate the excitation temperature of the permitted Fe II line formation region and the dimensions of this region. We conclude that this region may possibly have a non-uniform density structure.

We constrain the rotation law in Be star circumstellar disks. We show that Keplerian rotation is a valid approximation.

We have computed the Balmer-line profiles for the one-armed oscillation model and found that the model can naturally account for the cyclic Balmer progression phenomenon observed in the V/R variable shell stars.

We present our recent photometric and spectroscopic observations of the bright classical Be star π Aquarii and analyse those available in literature. This star currently shows only weak signs of circumstellar emission and a low optical brightness. Physical parameters of the underlying star are determined from data obtained during quiescence, while those of its circumstellar disk are estimated during the active period.

The recent cycle of the V/R ratio and RV variations in ζ Tau has been found similar to that reported by Delplace (1970). As a rule, in both cycles, singly-ionized metallic shell lines display discrete components when the descending branch of RV curve of Balmer lines crosses the stellar RV value; a narrow sharp feature is mainly superimposed on a broad and bluer one, both being slowly varying over some months; very weak additional components are suspected on stronger Fe II lines. On another hand, in the ascending branch of RV curve (RV ≥ RVstar), secondary shell components varying in intensity are conspicuous on V and R emissions of the first Balmer lines.

The parameters of the Hα line profile of the Be star o And were determined from observations carried out during the period 1985 - 1998. At this time the line has undergone significant changes – from a pure absorption photospheric profile with no sign of an envelope in 1985 to the transition into the shell phase with a very narrow and deep absorption component in 1989. During 1991 - 1998 the Hα emission remained at the level achieved in 1989. The line profile showed short-term changes. The envelope development in the time interval 1985 - 1998 does not confirm the previously found period of 8.5 years.

V923 Aquilae (HD 183656) is a Be star which shows emission in Hα, cyclic V/R variations and variations in the near infrared region. This star displays a shell spectrum recognized by Harper(1937) and Bidelman (1950) who both remarked the presence of shell H lines, strong Fe II lines and variable radial velocity. Koubský et al. (1989) proposed V923 Aquilae to be a spectroscopy binary with an orbital period of 214.756 days and a semi-amplitude of 6.2 km/s. Iliev et al. (1994) found a correlation between the changes of the Balmer progression and the asymmetries of the Balmer lines with the orbital phase, considering the period calculated by Koubský.

The Be shell star EW Lac was observed in September 1993 during a multi-site campaign. Results from visual spectroscopy and polarimetry are summarized here. He I 6678 profiles have been compared to previous observations held in 1989 and show an additional complex and highly variable circumstellar component which can due to material expelled from the star just prior to these observations. Two groups of frequencies are found again in 1993 observations compared with 1989 ones. In the frame of nrp, they could be associated to low degree g-modes.