28 Cygni was observed during two seasons spectroscopically. The radial velocities of more than 15 spectral lines were measured and searched for periodic variability. Two closely spaced periods were found. A two-dimensional analysis of the line profile variability yielded the same periods and provided the power and phase distribution across the line profiles. An outburst covered by our data coincides with the time of constructive interference of both periods. 28 Cyg is the second case for which outbursts seem to be triggered by multi-mode beating.

The Be star 28 CMa was one of the first periodic Be stars to be discovered and shows very large line profile variations with a period of 1.37 d. Recently, it has been shown that the line profile and light variations can be modeled by a patch of gas suspended above the photosphere. We present echelle observations of the Hβ and Hϒ line and several helium and metal absorption lines. We show that the radial velocity variations of these lines are unchanged since they were first observed two decades ago. We also examined several emission lines of Fe II and show that they do not partake of the periodic variation. We attribute the periodic variations of the lines formed close to the photosphere to a co-rotating cloud, whereas the Fe II emission lines are formed in the circumstellar disk outside the co-rotating radius.

Spectra of the Be star 28 CMa obtained with the HEROS echelle spectrograph in 1996 and 1997 were used to check the presence of transient periods in commonly measured scalar parameters of absorption and emission lines. Transient periods can be convincingly detected in modes of higher absorption and single peak emission lines of the Balmer series as well as in the V/R ratio of Fell lines. Consequences for the frequency analyses of datasets containing radial velocities derived from different ions are discussed. The significant differences in amplitudes of radial velocities of different ions and in individual seasons were confirmed and a mean ephemeris derived.

Adopting non-radial pulsation (nrp) the line profile variability lpv of several absorption lines of different ions was modeled for ω (28) CMa. The parameters suggested by Baade (1982) to characterise the pulsation could be confirmed. The pulsation period in the inertial frame was found to be negative, i.e. an actually retrograde mode appears prograde due to the rapid stellar rotation. The line profiles could be reproduced in detail including structures like spikes and ramps. They were identified as velocity effect due to the latitudinal component of the nrp velocity field υϑ in combination with low inclination i. In spite of small photometric variations (Štefl et al. 1999) the lpv of the absorption lines can be explained by nrp entirely.

ζ Ophiuchi and η Centauri are hot, rapidly rotating, southern Be stars showing multi-mode nonradial pulsations (nrp). We use high resolution, high signal-to-noise ratio spectroscopic observations of these objects to test the Telting and Schrijvers’ method (TS) of mode degree l and azimuthal order | m | estimation. In this method, these quantum numbers are calculated from the blue-to-red phase difference of the corresponding main frequency and its first harmonic, respectively. The phase differences were obtained withe the help of the Clean and Cleanest algorithms. Quantum numbers calculated with TS are compatible with those obtained with the Fourier Doppler method within the estimated errors. In the absence of other tools, the TS method can thus be used to estimate l and | m | with reasonably accuracy.

We report attempts to model the observed line-profile variations (lpv) of λ Eri during a productive spectroscopic and photometric campaign in 1994 November. We find that none of the nonradial pulsation spheroidal modes with m = −1 — −3 could explain the lpv associated with the dominant 16.9 hr period since the horizontal velocity components and the temperature variations dominate the lpv for such modes. In contrast, certain tesseral toroidal modes can reproduce the observed lpv well both for the main 16.9 hr period and the 6.45 hr period.

66 Oph has shown recurrent short-lived outbursts nicely detected from ground-based and space (Hipparcos) photometry.

Spectroscopic observations of He I 6678 and Hα lines were performed in June 1997 and June 1998. Search for short-term periodicities was done in He I 6678 line profiles as in equivalent width EW, radial velocity of the line centroid, and V and R components. At least two frequencies were present: ν = 4.0 c/d and ν = 2.2 c/d. The phase distribution of these frequencies over the line profile corresponds in the nrp frame to g-modes with ℓ ~ 3 − 4 and ℓ = 2 respectively.

The pole-on Be star υ Cyg (HD 202904) displayed with Hipparcos photometry a strong long-lived outburst between 1989 and 1993. High S/N spectroscopic observations were obtained in August-September 1998. The photospheric λ6678 line is strongly perturbed by variable outer V and R emission components and is itself highly variable.

All the studied quantities (profiles, EW, radial velocity of the line centroid, V and R emission components, V/R ratio) are dominated by ν = 1.5 c/d frequency. The first harmonic (ν = 3.0 c/d) is also detected in the central part of the profile. In the nrp frame, this pair of frequencies corresponds to a low degree sectorial g-mode l = |m| = 2. Moreover mid-term variations are superimposed to short ones.

In addition to the common applications (temperature, magnetic field, abundance distributions) the Doppler Imaging technique can also be applied to non-radial stellar pulsations (NRP). Due to their rapid rotation, the Be stars are ideal candidates for Doppler Imaging. However, for the stars for which the periodic temporal line profile variability is produced by multiple mode NRP, the classical Doppler image in not an appropriate representation. When the corotating frequencies of existing pulsation modes are non-zero, the reference frame in which the resulting NRP is quasi-stationary cannot be defined. The technique can be applied “mode-by-mode”, which is illustrated in time-wavelength and Fourier frequency domain, using the time-resolved sequence of high resolution, high signal-to-noise ratio spectra of the Be star ζ Oph.

We apply the surface imaging technique to high-resolution spectra of the rapidly rotating β Cep-type star ω1 Sco. Assuming only temperature fluctuations due to pulsations, we obtain a map of the surface corotating with the dominant pulsation mode. Prom the map we identify the dominant mode and find traces of a second pulsation mode. We conclude that the traditional surface imaging technique can be successfully used for mapping stellar non-radial pulsations.

We present an analysis of line profile variability of the Be star α Eri (Achernar). Spectra of He I λ667.8nm were collected at Brazilian Laboratório Nacional de Astrofísica (LNA) during 10 observing runs covering 27 nights in 6 years. The presence of a 1.26 days period reported previously is confirmed and we report also the detection of other periods (0.73 and 0.53 days) and a possible 12.5 days modulation. A transient high-velocity absorption component with RV = −500 km/s, higher than −υsini (−220 km/s) has appeared at the end of 1993, near the presumed maximum of the Hα emission phase.

In this work we have adopted the non radial pulsation (NRP) model in order to explain the rapid spectroscopic time variations observed in the Be star ζ Ophiuchi. Time series analysis were performed with CLEAN and Sequential CLEANEST techniques. We have also applied a different version of the Local CLEANEST that is optimized for multiperiodic signals observed in monosite campaigns. The frequencies of 7.19 and 11.89 cycles/day have been identified. These frequencies were found in previous papers about the star.

The analysis of high S/N spectra and photometric data of 60 Cyg shows that: (1) Pronounced long-term variations in spectra are accompanied with light variations. (2) The medium-term variations of RV could indicate that 60 Cyg is a spectroscopic binary. (3) Two independent structures dominate the rapid variability of both spectrum and light of the star.

We have examined whether the kappa-mechanism at the ”Z” opacity bump can excite overstable nonradial pulsation (NRP) modes such as those responsible for the line-profile variations (lpv) observed for ϵ Persei (Gies et al. 1999).

From the lpv modeling with realistic stellar parameters and the state-of-the-art codes, we confirmed that the observed lpv can generally be explained by the modes with l values suggested by Gies et al. (1999). We have also found that some tesseral modes, which have smaller m than those of sectoral modes, can reproduce the observed lpv well for the periods of 3.51hr/3.84 hr and 4.06hr/4.54 hr. Our linear non-adiabatic nonradial pulsation analysis applied to massive (13M⊙––14M⊙) stars shows that the periods of higher |m| values in the co-rotating frame are too long to be excited by the Z-bump kappa-mechanism while the smaller |m| values give marginal consistency.

The phenomenon of trans-photospheric wave leakage in stars undergoing non-radial pulsation is investigated, with an emphasis on its significance for Be stars. It is demonstrated that a symmetry breaking in line-profile variability may be used as a diagnostic for such wave leakage in these stars.

This review focuses on aperiodic line profile activity in several Be stars, ignoring attributes of pulsations probably occurring in any of the stars studied. Herein, I discuss spectroscopic evidence of heating (and cooling) of regions of Be star atmospheres, of line profile transients called dimples and high velocity absorptions. These features will be interpreted in terms of mass ejections (not necessarily permanent). Some of these events are violent and spasmodic, some are ordered and quasisteady, and some are associated with downflows. I close with new evidence for time-varying, corotating clouds suspended over a few Be stars.

A wide range of stellar analogs of solar X-ray flares has been observed. During the maximum of the solar activity cycle, one or two Mclass flares peaking at Lx ~ 1026 erg s−1 in the GOES 1−8 Å passband take place on average every day on the Sun. Such run-of-the-mill events have been measured by ASCA on our nearest neighbor, Proxima Centauri, a dM5.5e flare star (Haisch, Antunes & Schmitt 1995). At the other extreme, RS CVn systems and T Tauri stars have been observed to flare with peak luminosities of Lx ~ ×1032 ergs s−1 (Haisch & Schmitt 1996 and references therein). Current wisdom has it that this wide range of flares spanning at least six order of magnitude (and another factor of 10–100 if one counts even lower level solar flares) on the young T Tauri stars, main sequence G, K and M stars, and in evolved RS CVn subgiants and giants can all be understood as versions of solar flares originating ultimately in a convectively-driven magnetic dynamo. There is evidence pointing to two distinct types of dynamo perhaps even in the Sun (Durney, Young and Roxburgh 1993): the α − ω dynamo generated in a rather thin boundary layer near — in some interpretations just below — the interface between a star’s radiative core and convective envelope; and a turbulent distributed dynamo operative more or less throughout a convection zone. But what is one to make of the evidence for flares on Be stars (Smith, Robinson and Corbet 1998) where there is no subsurface convection to drive a dynamo? (Convective envelopes are thought to begin among the late-A spectral type stars, and steadily deepen for cooler stars.) This paper does not attempt to provide an answer, but it does attempt to outline the characteristics and requirements of magnetically-powered flaring.

The results of observations aimed at detecting magnetic fields in the Be star λ Eri are reported. The observational data are analyzed both through application of an approximate analytical method and through computation of a number of simple numerical models in view of deriving constraints on the magnetic fields. General conclusions are drawn about future prospects for magnetic field detections in Be stars.

New circular spectropolarimetric observations of the B1 IIIe star β Cep (υsini = 25 km s−1) show a sinusoidally varying weak longitudinal magnetic field (~ 200 G peak-to-peak). The period corresponds to the 12 day period in the stellar wind variations observed in ultraviolet spectral lines. Maximum field occurs at maximum emission in the UV wind lines. This gives compelling evidence for a magnetic-rotator model for this star, with an unambiguous rotation period of 12 days.

The similarity between the Hα emission phases in β Cep and in Be stars suggests that the origin of the Be phenomenon does not have to be rapid rotation: we propose that in β Cep the velocity to bring material in (Keplerian) orbit is provided by the high corotation velocity at the Alfvén radius (~10 R*), whereas in Be stars this is done by the rapid rotation of the surface. In both cases the cause of the emission phases has still to be found. Weak temporary magnetic fields remain the strongest candidate.

A full paper, with results including additional measurements in June and July 1999, will appear in A & A.

An alternative explanation to the light variations of some Be stars observed during their Be ⇌ Be-shell phase changes is proposed in terms of orbiting or passing clouds. Discrete ejections of matter and/or the presence of orbiting clouds suggest that the circumstellar envelopes of these Be stars may be clumpy.