Phase changes from Be to Be-shell and/or B normal, and conversely, presently remain unpredictable in Be stars (except in some binaries where the transition to a shell phase seems to be associated with the orbital period). Because of their unpredictable character, these phenomena have been monitored in very few cases and are still very poorly understood. However, the existence of phase transitions have strong modelling implications. Under the disk model, the inclination of the star's rotation axis determines the type of spectrum, Be or Be-shell, that a given Be star may exhibit. It is obvious that this picture is contradicted by phase transitions (Doazan 1982).

In this paper we report results concerning the photospheric Balmer discontinuity of Pleione. They show that after the Be → Be-shell phase transitions, the stellar photosphere keeps its characteristics unchanged.

48 Lib (B3IV, vsin i=395 km/s) is a well known Be shell star. Cuypers et al. (1989) found a period of 0.4017 d, the single wave light curve being asymmetric. Rapid variations in the radial velocity of metallic shell lines have been found by Ringuelet-Kaswalder (1963) with a period of 0.115 d.

From line and continuun data of the ultraviolet and visible spectrum of 48 Lib, the fundamental parameters of the circumstellar envelope are derived.

We have found that the range in wavelength of the line-profile variations (lpv) in the Be star λ Eridani increases by some 20% during its emission phases. This growth is associated with a possible increase in the equatorial velocity of the star during emission. We discuss the significance of this in connection with other features of the lpv and our earlier discovery of a weak correlation between the amplitude of the lpv and Be outbursts in ζ Ophiuchi.

4 Her (HD 142926, HR 5938; V=5m.75, v.sini=300 km s-1) is a well known and rather frequently observed Be and shell star. It was recognized as a Be star by Heard (1939) and Mohler (1940). The estimates of its spectral type by different authors vary between B7 IV-V and B9e. Hubert (1971) reported remarkable spectral changes of 4 Her which occurred between 1953 and 1970. Harmanec et al. (1973) discovered periodic radial-velocity variations of the hydrogen shell lines with a period 46.023 days and suggested the object is a single-line spectroscopic binary. The system elements were later refined by Heard et al. (1975) to P=46.194 days, K=12 km s-1 and e=0.3. In a subsequent paper, Harmanec et al. (1976) studied the variations of emission and absorption components of the hydrogen lines and concluded that 4 Her is an interacting binary and that the observed eccentricity of the orbit is spurious, caused by the effects of circumstellar matter.

ζ Tau is a well-known V/R-variable shell star. It is a single-lined spectroscopic binary with an orbital period of 133 days (Harmanec 1984, and Jarad 1987). Delplace (1970) found that the long-term radial velocity variations of the Balmer shell absorption lines are cyclic in 1960–67. Subsequently, similar behaviour has been observed and studied by several authors (Delplace and Chambon 1976, Hubert-Delplace et al 1983, Harmanec 1984, and Guo and Cao 1987). Mon et al (1992) showed that the cyclic variation had terminated and the star seems to have entered a new quiet phase around 1982.

V923 Aql is a well known Be star with strong shell spectrum. It was included in the list of shell stars of Merrill and Burwell (1949). A detailed study of the radial velocity variations in the spectrum of the star based on wide collection of spectral observations was presented in the work of Koubsky et al. (1988). In this work an orbital period of 214.756 days was suggested for the binary system consisting of a B5–7 primary and low mass (0.5 Msol).

We present a quantitative study of the variability in ultraviolet resonance lines of Nv, Siiv and Civ of the Be star γ Cas, following up on the work of Henrichs et al. (1983). For this purpose we used 133 IUE spectra obtained over a period of eleven years. Variability occurs in the form of discrete absorption components (DACs), which are formed in the fast-outflowing radiatively driven part of the stellar wind. We constructed a template spectrum from spectra containing no or minor extra absorption due to DACs and modelled the isolated DACs in the obtained quotient spectra. Besides the frequently observed narrow components (vt typically ≤ 250 km/s) at high velocity, we found several broad components occurring at low and intermediate wind velocities.

We confirm the finding of Doazan et al. (1987) who reported that the number of observed DACs is associated with the cyclic V/R variability of the Balmer-emission lines. This V/R variability most probably originates in the slowly outflowing high-density equatorial disc-like wind of the star (see e.g. Telting et al. 1993 for the case of γ Cas). We show that when V/R≪1 the central optical depth of DACs is significantly lower than when V/R≪1. In our interpretation this is due to a correlation between the column density associated with the DACs and the phase of the V/R cycle.

We find that the Hβ observations of Doazan et al. are consistent with a model in which the cyclic V/R variability is due to a global, one-armed oscillation moving through an equatorial disc (Okazaki 1991, Papaloizou et al. 1992, Savonije and Heemskerk 1993). We suggest that the higher column density of DACs in phases of V/R≪1 is the result of the higher density in the region of their origin, namely close to or in the part of the equatorial disc which is rotating towards the observer.

We consider the formation of the Balmer emission lines and the decrement Hα/Hβ/Hγ, by solving the non-LTE problems in elementary regions of the envelope divided by equal line-of-sight velocities. These envelope-elements are characterized by different optical depths in the Balmer lines and by different dilution factors for the incident stellar radiation. It is shown that the decrements sensitively depend on these parameters of the envelope-elements. We show that the observed spectral-type dependence and large scatter of the decrements among Be stars can be explained in terms of the variation of these physical parameters.

One-armed (i.e., m = 1) density waves are the only global waves in nearly Keplerian disks (Kato 1983). Their frequencies are much smaller than the angular frequency of disk rotation. Based on this theory, Okazaki (1991) proposed that the long-term V/R variations of Be stars are phenomena caused by the global m = 1 oscillations in the equatorial disks. Hummel and Hanuschik (1993) showed that line profiles of disks with m = 1 perturbation patterns are in agreement with the observed V/R variability.

Based on 3D radiative line transfer calculations we present Hα emission line profiles of Be star circumstellar envelopes undergoing one-armed global disk oscillations. The results are in agreement with the observed line profile variability.

Since 1982, we are performing a long-term spectroscopic observing programme of emission-lines in Be stars (Hanuschik 1987, Hanuschik et al. 1988, Dachs et al. 1992, Sutorius 1992, Dietle 1993). We are using ESO's 1.4m CAT, at resolution R ≥ 50 000 and S/N = 100–1000. Spectral lines chosen are the optically thick Hα, Hβ lines and the optically thin Fe ii λ5317 line. The latter line is an extremely sharp tracer (Δvth = 2 km s−1) for the kinematics in the disks. We believe that our atlas shows the full range of intrinsic structure of these emission lines.

The present report gives the results on the Hα line profile investigation of two the most well-known A0e Herbig stars of the so-called P Cyg -subgroup: AB Aur and HD 163296. 35 high-resolution CCD spectra (R ~ 50 000) of HD 163296 (ESO, CAT+CES, July 1991 and 1992) and 43 CCD spectra (R ~ 30 000) of AB Aur (Crimean Observatory, 2.6-meter telescope, January 1993) were obtained. A striking profile variability is discovered in both objects on the timescale from one our to a few days. The most dominant part of rapid variations (τ ~ hours) is the monotonous flux drift of different profile components. Positional shift of sharp spectral bumps, found in HD 163296 is probably connected with local inhomogeneities moving in the envelope. Shape variability of the absorption P Cyg -component of the Hα -line in AB Aur is suspected to be periodic with P = 35 or 70 hours. A model for a circumstellar envelope is proposed to explain the observed variability in this type of objects. It supposes the existence of an active non-stable region near the star, formed by equatorially concentrated stellar wind and an outer cool shell.

Significant profile variability of Hα on the timescale of months is investigated on the basis of high-dispersion CCD spectra of the B3e Herbig star HD 200775. Variations in position and shape of the central absorption component are considered to indicate complex structure of circumstellar environment, containing infalling streams and inhomogeneous stellar wind.

Herbig Ae/Be (HAEBE) stars are young objects with strong infrared excesses, variable brightness, intrinsic polarization and complex spectral line profiles. Almost all of these features are due to the presence of circumstellar (CS) shells. We consider the group of HAEBE stars with non-periodic Algol-like minima (UX Ori, WW Vul, etc.). They have irregular brightness drops by 2–3 mag in the visual, accompanied by an increase of linear polarization.

Quasi-simultaneous optical and IR photometric (BVRIJHK-bands) and optical polarimetric (RI-bands) observations were made at the 1m telescope of the Assy Observatory, Institute of Astrophysics of Kazakhstan between October 1985 and August 1992. We used the photopolarimeter of the Pulkovo Observatory described by Bergner et al. (1988). Most of our measurements were done with an aperture of 26″. We obtained 26 polarimetric measurements of MWC 349, mainly in the R band. Our data show significant variations in the polarization which has not been reported previously. The amplitude of the polarization parameters is: ΔP = 8% and ΔP.A. = 15°. During 12–13.09.90 five polarimetric observations have been obtained and ΔP = 3% on a time scale of 7 hours was detected. We found strong photometric variability in all photometric bands. There is however no correlation between brightness and polarization in any photometric band.

We present a new study of MWC 314 = BD +14°3887 – a poorly investigated object with strong emission lines and IR excesses. Merrill (1927) payed attention to it because of the presence of hydrogen and Fe II emissions in its spectrum. Swensson (1942) also detected interstellar lines H and K CaII and 4430 Å band, Balmer emissions from Hα to H8, NaI 5890 and 5896 Å emissions and estimated its spectral type as gG2-3 or dG4-5 from the SED in continuum, and B2 from the excitation degree. Photospheric lines and spectral features of late-type stars were not observed. Allen (1973) noted that the object's SED corresponds to that of a late-type star but it might be a symbiotic system or a reddened normal star. The IRAS fluxes were obtained only at 12 and 25 μm. The object is unknown as a radio source. From this we can conclude that this system consists of, at least, a hot star surrounded by a gaseous envelope.

We review observations that are relevant for the determination of the structure and geometry of the circumstellar envelopes of Be stars. Evidence is summarized suggesting that Be stars have rotating discs. Infrared and radio continuum and line measurements and their interpretation are discussed.

FeII emission lines are present in a variety of astrophysical objects and, in particular, in Be stars, where in some situations they can also be seen in absorption. Selvelli & Araujo (1984) studied a sample of classical Be stars that have FeII emission lines in the optical region. The analysis of IUE spectra of those stars revealed that, for the majority of the objects, neither absorption nor emission FeII features were present in the UV. The conclusion was that their data could not support excitation of FeII by continuum fluorescence. On the other hand, FeIII of circumstellar origin is often seen in absorption in the UV spectra of Be stars (Snow & Stalio 1987 and references therein). This could be an indication that the optical FeII emission lines are originated from recombination and cascade. However, Selvelli & Araujo (1984) argued that, since the multiplet UV 191 of FeII does not appear in emission, that mechanism is probably not relevant. In the present work we report new spectroscopic observations in the near infrared of a sample of 60 Be stars, including the prominent FeII 999.7 nm emission line. This line is also present in the spectra of superluminous B stars for which mass loss rates have recently been estimated (Lopes, Damineli-Neto & Freitas Pacheco 1992). We derived mass loss rates from the infrared line luminosities, in agreement with those derived by other methods. We also found a new evidence of the Be envelope flattening through the FeII/Paδ line ratio.