Astero-oscillometry is presented as a new method for deriving stellar parameters on the basis of a physical modeling of line profile variability (lpv) caused by nonradial pulsation (nrp). First applications to rapidly rotating B-type stars show that the method is able to yield reasonable stellar parameters. The radii are systematically smaller compared to those derived by conventional methods. This could be attributed to possible effects of rapid rotation on stellar evolution. Since the method requires only one or a few pulsation modes to be excited, it is ideally suited to investigating early-type stars.

Highlights are presented from a theoretical study of the photometric characteristics of slowly pulsating B stars. One outstanding result is the discovery, for l ≥ 2 modes, of cancellation between the flux variations originating from surface temperature perturbations, and those arising from radius perturbations. In addition to reducing greatly the variability generated by such modes, the cancellation introduces significant phase differences between the flux changes in each passband. On the grounds that similarly-large phase differences are not seen in observational data, it is suggested that the light variations of slowly pulsating B stars might be due primarily to l = 1 modes.

We derive mean stellar parameters for 14 SPB stars observed during the IUE satellite mission, using an algorithmic procedure fitting theoretical flux distributions (Kurucz, 1996) to the IUE low-resolution spectra. We focus our attention on the metallicity parameter [m/H]. We found the mean value of [m/H] = -0.27 ± 0.22.

We present the results of 1.5 years of Spectroscopic monitoring of 10 bright northern SPB candidates discovered from the Hipparcos mission. All stars have line-profile variations and are periodic, with periods corresponding to high-order g-modes. We therefore confirm them to be new SPBs.

HD 147394 is a Slowly Pulsating B star for which we found three periods in the moments of the Si II 4128-4130 lines: f1 = 0.8008 c/d, f2 = 0.7813 c/d and f3 = 0.6710 c/d. A mode identification is perform ed by using the moment method.

The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.

New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.

No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1.

Observations carried out for 5 years on o And show that 65 to 85% of its light variations can be described by a double wave: A sin (2πt/P1 + ϕ1) + B sin (2πt/P2 + ϕ2) + C with P1 ≈ 1.6 d = 2P2. When determined independently, P1 and P2 are always found in a 2:1 ratio (within 1%), while they can vary together by as much as 4%. The peak to peak amplitudes of this double-wave fit lay between 40 and 140 mmag (and can even be reduced to less than 10 mmag - our 1987 observations). The rest of the light variations do not show any permanent period or behavior, although a ∼ 2.3 d. (i.e. ≈ 3P1/2) period is frequently detected. Sometimes a marginal ∼ 6 d. period or time constant has been detected.

In spite of the quality of our photometric data, the precision on the periods and amplitudes obtained over a few nights is never increased by longer observations: our phase diagrams show significant irregular displacements around the average double-wave analytical solution if we include longer data strings (Fig. 1). This phenomenon was already apparent in our 1992 study (Sareyan et al., 1998): the star shows real irregular behaviour superimposed onto its double-wave “mean” light curve; these changes may show up as a progressive, or sometimes abrupt, modification of the shape of the double-wave light curve (Fig. 1).

Recently, the line profile variability (lpv) of two low-v sin i Be stars, μ Cen and ω (28) CMa was successfully modelled as nonradial pulsation (nrp) of rapidly rotating stars seen pole-on. In this work, it is shown that the lpv of low-v sin i early-type Be stars in general closely resembles these two cases, and is therefore explainable by the same mechanism. The lpv of intermediate to high-v sin i Be stars can be explained by the same model if the inclination angle of the model alone is increased. Consequently, early-type Be stars form a distinct, fairly homogeneous class of non-radial low-order g-mode pulsators.

The geometric deformation, as well as the non-uniform surface gravity and temperature distributions induced by the fast rotation, are taken into account to determine the fundamental parameters of 10 Be stars seen nearly equator-on. The stars occur in the first half of the main sequence evolutionary span, which suggests that their fast rotation is related to initial formation conditions, rather than to evolutionary effects.

ω Ori is a rapidly rotating B2IIIe star with known spectral variability. We applied a frequency analysis to the MuSiCoS (MUlti Site Continuous Spectroscopy) campaign 1998-dataset to search for line-profile variations (Ipv). Variability was found in all studied spectral lines and interpreted as due to non-radial pulsations (NRP).

In spite of considerable progress in the investigation of rapid line-profile variations (lpv) of Be stars, at least two models still compete in the literature: the rotational modulation, assuming mostly corotating circumstellar structures (Balona, 2000), and nonradial pulsations (Maintz et al. and Rivinius et al., these proceedings). Attempts to explain the lpv of Be stars were often connected with the proto-typical star 28 (ω) CMa (HR 2749 = HD 56139, B2IV-Ve, v sin i = 80 km/s). Štefl et al. (1998) described variability in three line-profile components: in the narrow component of the line core, in the line core itself and in the wings. The Balmer emission of 28 CMa is variable and has always been observed to be at least moderate, mostly strong.

HR 4074 (HD 89890, B3 III, v sin i = 70 km/s) has a different history of its emission activity. From a single spectrogram taken in 1893, Pickering (1898) reported an emission in Hβ. Subsequent observations never confirmed this. If it was not mis-identified by Pickering, HR 4074 would be in the probably longest B-star phase known of any Be star. HR 4074 is very probably not an SPB star - the spectral type is too early, the rotational velocity too high and light variations too low for this classification. Baade (1984) detected rapid lpv with a period P ≈ 2.25 d. Our time series analysis of radial velocity (RV) variations, measured as line modes, and that of full profiles give P = (2.3179 ± 0.0008) d.

Omicron Andromedae is a multiple system composed of at least four components. The main component “A” is a variable Be star (B5II-III). The variations of this star are multiform: the circumstellar emission and absorption can vary drastically and can even disappear and reappear later, whereas changes in magnitude are also observed (see e.g. Sareyan et al., 1998). Rapid Spectroscopic and photometric variations are observed as well. As explained below, the rapid Spectroscopic variations of the Hα line observed in 1992 during a phase of moderate emission are very special (Briot et al., 2001). Then the emission of о And increased, so another program of observations of the Hα line was performed to investigate its rapid variations during different emission phases. We present here some preliminary results.

We review the current status of our monitoring project on Be stars. Line profile variations in Helλ667.8 nm were detected in the Be star η Cen, by means of high resolution and S/N Spectroscopic observations. They were interpreted in terms of nonradial pulsations (NRP). The fundamental parameters of η Cen obtained from BCD spectrophotometric data and interpreted using models of rapidly rotating stars, have been used to estimate the stellar rotational frequency.

An analysis of the UBV photometric measurements obtained at Hvar Observatory and Hp HIPPARCOS photometry has been performed in order to disclose the suspected rapid periodic variations of the Be star ϕ Per. The reliability of the derived 0.5 day period is examined and the difficulties of detecting the period due to the complex character of the light variations on the longer time-scales are outlined. Possible explanations of these rapid variations are briefly discussed.

Major improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and λ Boötis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.

We report monoperiodic variability for the four B-type stars HD 131120, HD 105382, HD 138769 and HD 55522, which we explain by rotational modulation rather than by pulsation. Consequently these variables are removed from the list of candidate Slowly Pulsating B stars.

This work is a continuation of the Montréal stellar evolutionary model development (Richard et al., 2001 and references therein) where the effects of atomic diffusion are taken into account for 28 elements (see Turcotte, these proceedings), along with an approximate treatment of turbulent transport (Richer et al., 2000).

We used the CEFF equation of state and the Bahcall nuclear energy generation routine. The Rosseland opacity is computed at each time step, from the OPAL monochromatic opacities for 21 elements (to which we added locally computed spectrum tables for Li, Be, and B) for each mesh point in the model for the current local chemical composition. Convection and semi-convection are taken into account in every species’ diffusion velocity and in the determination of the thermal gradient (Richard et al., 2001). The models also take into account gravitational settling, thermal diffusion, radiative accelerations and turbulent transport. The radiative accelerations are from Richer et al. (1998). The turbulent transport is modeled as a diffusion process (Richer et al., 2000) with diffusion coefficient: DT = ωD(He)0 (ρ/ρ0)n where D(He)0 is the Ηe atomic diffusion coefficient at density ρ0.

The current status of the research concerning rapidly oscillating Ap stars is reviewed, paying particular attention to the interplay between recent developments in the theoretical and observational aspects of these stars.

We identify Spectroscopic differences between roAp stars and Ap stars with no observational evidence for pulsation, but with otherwise similar Teff and log g values. These differences concern the abundance pattern, Hydrogen line profile anomalies, evidence for stratification, and effects of pulsation on spectral lines.

We report results of Spectroscopic monitoring of the roAp stars γ Equ, α Cir and HR 3831 with the ESO 3.6-meter telescope. Series of very high-resolution and high S/N spectra allowed to resolve changes of line profiles due to the pulsations. We found that pulsational behaviour of all three roAp stars is dominated by the variations of the doubly ionized rare-earth lines. Detailed analysis of the pulsational changes of Nd III and Pr III spectral features allowed us to identify the pulsational mode of γ Equ and to study rotational modulation of the pulsational pattern in the spectra of α Cir and HR 3831.