We report on combined spectroscopic and photometric observations of EW Lac during its outburst of 1983. At this time the star’s Hα and Hβ lines showed strong doubled-peaked emission profiles which were variable with time. UBV photometry exhibited a long-term and frequent erratic short-term variations. The amplitude of U, B and V variations reached about 0.3 magnitude on October 15, 1983. Both Hβ emission and the structure of the shell absorption lines of the star also displayed anomalous behavior in 1983. It is evident that this star was in a strong active phase at that time.

The spectral change of Pleione in the present Be phase (1988-1999) is briefly described. The Hα emission reached its maximum in 1995-1999. The V/R values of Hγ and metallic lines changed from V/R < 1 in 1995 to V/R > 1 in 1998-1999. The broad component of Mg II λ4481 line further weakened in Be phase.

The long-term variation in 1968-1999 is shown for several observational quantities. These quantities which reflect various levels from the photosphere up to the outer envelope did not change in a parallel way. The basic unsolved problems are pointed out.

We analyze a series of spectroscopic observations of the Hβ and Fe II λ4924Å lines of the Be-shell star Pleione (HD23862), which entered a new Be phase since 1988. Their evolution show that the Hβ-emitting envelope expands regularly from 1987 to 1996 (r/r*=8.6 to 25.0), then diminishes slightly in 1997-98 (r/r*=20.0). The Fe II-emitting envelope expands regularly between 1987 and 1998 (r/r*=6.7 to 13.4), but remains always inside the Hβ-one. The evolution of the emitting envelope of Pleione is similar to the one observed between 1954 and 1972, and this one should decrease regularly in the next years, if the former scenario is repeated.

This is a preliminary report on spectral variability of Pleione during the present Be phase. The spectral activity of the star confirms the observed photometrical trend.

HDE 245770 = V725 Tau, the optical counterpart of A0535+26, presented in the last three years a period of uncommon optical faintness and of exceptionally low spectral activity. Photometric data obtained in 1997 and 1998 show a fading in all color, followed in 1999 by a nearly constant phase in which the star attained the lowest level of the last 23 years. In 1998 the emission lines became much fainter than in 1997, changing slowly from emission to absorption. In November 1998 only Hα was still showing a weak emission with an absorption core; this behaviour suggests the occurrence of a shell phase.

The Be binary star CX Dra has been observed with the IUE satellite over a period of 14 years. More than 60 SWP high resolution spectra were obtained. After processing the quotient flux spectra of the Al III and Si IV lines show very complicated behaviour. The most important features are the violet shifted components in these lines which show very negative velocities (up to −800 km/s) in a particular phase interval.

We present phase resolved spectra of the Be binary ϕ Per. It is shown that orbital phase variations of the He I line profiles are due to a sector emission region in the circumprimary disk facing the secondary. The increasing asymmetry of Fe II emission lines indicates a density inhomogeneity in the circumprimary disk that developed after 1996.

The binarity of 59 Cygni was confirmed and orbital parameters from the radial velocity curve of the primary derived. The observed emission variability resembles the one of ɸ Per in quite some detail, suggesting a similar nature of the companion: a hot, compact star.

UBVRI photoelectric monitoring of the Be star X Per, a transient X-ray binary, during the last four years, along with some optical spectra are presented and briefly discussed in the context of the long term behaviour of the system.

We present optical photometry and high resolution optical spectra of the Be star X Persei/HD 24534, the counterpart to the X-ray pulsar 4U0352+30, obtained over the past ~10 years. These spectra show a variety of behaviour, ending with the onset of a strong V/R cycle. Observations of the He 16678 line suggest several episodes of discrete disc forming. This data forms part of a major long-term multiwavelength monitoring programme (UBVRIJHKL photometry plus optical and UV spectroscopy).

We present the results of high-resolution (0.24Å/pix) monitoring of the variability of Hα and He I 6678 lines in the spectrum of X Per in 1996-99 at Tartu Observatory. The main characteristics of the line variability distinguishable in our data are:

1) the intensity of emission peaks in both lines varies with a cycle-length ≈450 days, and displays a phase-lag between curves of two lines considered,

2) in a cycle, both violet or red emission peaks emerge at high Doppler velocities but attain their maxima and disappear gradually at much lower velocities,

3) despite of the considerable variability of equivalent width (EW) of both lines, the “relative emission measure” (EW(Hα)/EW(HeI)) behaves more constantly.

We have successfully determined the kinetic temperature of the electron gas as a function of position in the circumstellar envelopes of Be stars. Our method yields a self-consistent solution of the equation for energy conservation, thus eliminating the necessity to assume arbitrarily a temperature for the gas. Our technique has been applied to Be stars of differing spectral classes, and we have also used several models for the distribution of the circumstellar material. The observed shape and relative line strength of the Hα line for several Be stars were matched successfully with these models. Recently we have begun to investigate the role of the diffuse radiation field in the Lyman continuum using the on-the-spot approximation. As a preliminary step to including metallic line cooling by the circumstellar gas, we have determined iron ionization fractions throughout the disks of both an early-type and a late-type Be star.

We describe a technique for estimating average temperatures of Be star disks from analysis of ultraviolet spectropolarimetry. The technique utilizes the fact that the spectrum of the scattered starlight is sensitive to the circumstellar opacity, and hence temperature, since the signature of the disk material is imprinted on the scattered light spectrum. Analysis of the polarization spectrum thus allows us to disentangle the relative contributions of the star and disk, and thereby obtain an estimate of the average disk opacity as a function of wavelength. Using an LTE line-blanketed model (containing about 106 spectral lines) for the opacity, we determine a theoretical opacity as a function of temperature. By comparing this to the opacity deduced from the spectropolarimetry, we can estimate the average disk temperature. For classical Be stars, the relative strengths of the Fe II and Fe III multiplets at around 2400Å and 1900Å, respectively, are a sensitive temperature diagnostic, so that the temperature estimate can be made within ±1000K. We demonstrate our technique with analysis of UV spectropolarimetry (from WUPPE) of the classical Be star ζ Tau, for which we infer an isothermal disk temperature of14000K.

Through the analysis of line profiles of atoms in different ionization stages, we study the source function behavior of those elements that allow us to outline temperature structures in moving extended atmospheres. The radiative transfer equation is solved in the comoving frame and NLTE for multilevel atoms.

An investigation of the formation and evolution of Be stars show that these stars could have dipolar fossil magnetic fields. This magnetic field should constrain the circumstellar magnetic disk and influence its dynamical features. For studying these effects we refine the alphamodel of accretion disks of Shakura and Sunyaev by incorporating into this model the evolution of large-scale magnetic fields. In the frame of our model we can investigate the rotational history of the star with the disk and the ionization and thermal properties of disks. We show in particular that in the magnetopause region a current sheet can form that can generate X-ray radiation.

It is assumed that the dynamics of Be star discs is dominated by the effects of viscous stresses. By examining angular momentum transport in discs, we show that many, if not all observed Be star discs should be accretion discs unless (i) the disc is acted upon by another agent (e.g. magnetic fields or the stellar radiation field), or (ii) the disc cools significantly as it flows outwards.

In rapidly rotating stars with a purely radially driven stellar wind, conservation of wind angular momentum can lead to formation of an equatorial Wind Compressed Disk (WCD). However, for a line-driven stellar wind, recent 2D hydrodynamical simulations based on a localized, Sobolev treatment of the line-force indicate that nonradial components of the line-force can effectively inhibit formation of such a WCD. This presentation will describe current efforts to extend such 2D simulations to a nonlocal, smooth-source-function treatment of the line-force that can incorporate the intrinsically strong instability of line-driving to formation of small-scale, clumped structure. Key questions are how such small-scale clumped structure affects the nonradial line-force components that arise from large-scale velocity-gradient asymmetries, and in particular whether such nonradial forces can still inhibit WCD formation in a clumped flow. The results have important implications for the viability of the WCD mechanism as a paradigm for disk formation in Be stars.

We present results of 2.5-D radiation hydrodynamical simulations of winds from rapidly rotating stars. For the first time, we consider the dependence of the line statistics on local density and radiation temperature implying a spatial variation of the force-multiplier parameters k, α and δ which control the dynamics of the flow.

We apply our models to the problem of disk formation in B[e]-star winds.

Using the wind-compressed disk model to determine the density and velocity of a rapidly rotating wind, we calculate the 2-D ionization structure and corresponding line profiles. We find that previous estimates of the mass-loss rate based on spherically symmetric models may be a factor of 5–10 too small.

The theory of radiative-line driven wind including stellar rotation is re-examined. After a suitable change of variables, new analytical equations for the mass loss rate and position of the critical point are derived. A non-linear equation for the position of the critical point is obtained, in order to solve it, a β-field is used, and in addition to the standard CAK critical point two other critical points as function of star’s rotational speed (Vϕ) are founded. When the stellar rotation velocity is approximate or greater than 0.8 × Vbreak–up, the CAK critical point is located far away in the wind (r > 4R*) and there we have again only one critical point. Numerical solutions from this new critical point are obtained, they have very low terminal velocities (approx. 400 km/sec). The applicability of this new solution in the frame of Be stars are discussed.