For 26 stars with effective temperatures known from directly measured angular diameters and total absolute fluxes (Code et al., 1976), HIPPARCOS parallaxes (ESA, 1997) can be used to derive empirical luminosities and radii. The empirical effective temperatures and luminosities allow a comparison of the position of these stars in the fundamental H-R diagram with evolutionary tracks. Note that no calibration, photometric or any other, is involved in the process. As noted by Jerzykiewicz & Molenda-Żakowicz (2000), the comparison shows an overall coincidence with the phases of slow nuclear burning of the solar composition evolutionary tracks, computed with OPAL opacities and moderate amount of overshooting from the convective core.

Several of the stars fall in the theoretical β Cep, SPB or δ Sct instability domains. Unfortunately, none of them is known to be an SPB variable, while the two that have been classified as δ Sct stars lack convincing evidence of variability. For the four β Cep stars that occur in the sample, the empirical radii are used to identify the radial order of pulsation.

With the advent of surveys generating multi-epoch photometry and their discoveries of large numbers of variable stars, the classification of the obtained time series has to be automated. We have developed a classification algorithm for the periodic variable stars using a Bayesian classifier on a Fourier decomposition of the light curve. This algorithm is applied to ASAS (AII Sky Automated Survey, Pojmanski, 2000). In ASAS 85% of the variables are red giants. A remarkable relation between their period and amplitude is found for a large fraction of those stars.

The analysis of the OGLE-I data using the standard profile-fitting software yielded a large set of new variable stars. However, due to the severe crowding of the images many variables may have been missed. Therefore, we decided to reanalyze these data by means of the image subtraction method. Our main goal was the detection of new variables. In addition, we intend to extend the time-base of the observations for the variables found in the course of the OGLE-II project (Udalski et al. 1997). We present the preliminary results of our study.

In this work, we present preliminary results based on an LMC Bar sample (AGAPEROS) of ⷍ 400 variable stars combined with near-Infared photometry (DENIS). About 50% of our objects are semiregular Variables (SRVs) while 20% are regular Variables with a period range from 30d up to 600d. A second period is present in ∼ 40% of the SRVs. We find a large fraction of regular variables with P < 100d which could be SRVs undergoing a phase of periodic variability. The Period-Colour relation (log P versus I – J), unstudied so far on the LMC, differs from the one found in the Galactic bulge: an effect of metallicity?

The GEOS, Groupe Européen d’Observation Stellaires, is composed of observers living in France, Italy, Spain, Belgium and Switzerland. The main purpose is to give amateur astronomers the opportunity of carrying out scientific analyses in specific fields. Further details can be found at the web site http://www.upv.es/geos/

In the past years, GEOS has approached the analysis of visual estimates of variable stars (Ralincourt et al., 1987) in an original manner, obtaining accurate light curves on red semiregulars. Moreover, the collaboration with teams of professional researchers allowed the group to obtain interesting results on the double-mode Cepheid EW Set (Figer et al., 1991), on the Be star OT Gem (Arellano Ferro et al., 1998) and on the eclipsing binary V753 Cyg (Beltraminelli et al., 2000). More recently, several GEOS members have started collecting a large sample of times of maximum brightness of RR Lyr stars in order to build-up a database as extensive as possible. Such a database is decribed below together with the results of a campaign on RR Lyr itself.

Fourier coefficients are a valuable tool in the study of a wide variety of pulsating stars. They can be used to derive various physical parameters, including mass, luminosity, metallicity and effective temperature and are frequently used to discriminate between different pulsation modes. With the increase in large-scale surveys and the availability of data on the Internet, the number of Fourier coefficients available for study has expanded greatly and it is difficult to find all current data for individual stars or a subset of stars. To assist others in obtaining and making use of Fourier coefficients, an archive of published values of Fourier coefficients has been set up. Users can search for data on individual stars or for a range of parameters. Several Java programs are used to display the data in a variety of ways. The archive is located at the Web site http://www.earth.uni.edu/fourier/.

Stellar interferometry represents a qualitative jump toward stellar surface imaging. We propose a method that tunes and filters out high degree non-radial pulsation (NRP) modes from the Fourier plane associated to the stellar brightness distribution. The proposed method can be applied to continuum flux, slow stellar rotation and high degree multi mode NRP stars.

We present the imaging potential of a tomographic technique which combines time-resolved spectroscopy and long baseline interferometry, providing information that cannot be obtained otherwise with each of these techniques separately.

We discuss the properties of pulsations in rotating stars, which include frequency shifts, the effects on the stability of p- and g-modes, and the properties of low-frequency modes whose frequencies are comparable to or less than the rotation frequency.

After showing that the anelastic approximation is better than the subseismic one to filter out acoustic waves when studying low-frequency stellar oscillations, we compute gravito-inertial modes of a typical γ Doradus star using this approximation. We show that eigenmodes can be regular or singular, according to the possible focusing towards attractors of the underlying characteristics. Consequences on the oscillations spectrum are then discussed.

We present the current understanding of the dynamical aspects of the oscillations of rapidly rotating stars.

Two-dimensional hydrodynamic simulations were calculated for ZAMS models with Z=0.02, and masses of 3, 5, 8, 12, and 20 M⊙. For each mass five models were calculated - one nonrotating and four with progressively higher rotation rates. The rotating models were categorized by the ratio of the polar to the equatorial radius, with values of 0.985, 0.92, 0.84, and 0.72. The simulations were performed with the fully two-dimensional implicit code ROTORC (actually what is known as 2.5 dimensions, with azimuthal symmetry, but with a conservation law for the rotational velocity in the azimuthal direction).

All models showed considerable core overshooting. To first order, the value is about 0.5 Hp, but with a fairly large variation of about 0.2 Hp. It is not clear why the variation is so large, but comparison with other turbulence models shows that overshooting/is one of the more sensitive features of the model (Deupree, 1998). However, there are some trends that may be significant. For the two highest masses there was apparently no dependence on the rotation rate, but the three smaller masses showed a linear decrease in the extent of overshooting with increasing rotation. There is a hint that the 20 M⊙ model has slightly larger overshooting than models of the other masses. With the random variations, it is difficult to assign a level of significance to these trends.

The observational characteristics of the p-modes of β Cep stars are compared to those of the g-modes of slowly pulsating B stars (SPBs). For the β Cep stars, previous reviews based on photometric surveys are updated with recent results from our high-resolution spectroscopic surveys. For the slowly pulsating B stars, it is the first time a broad observational overview can be given.

It is known that early-B type main-sequence stars can be unstable against pulsations induced by the κ mechanism. Traditionally, radial and low-degree non-radial β Cephei-like pulsations have been detected photometrically; nowadays radial, low-degree and intermediate-degree pulsations can be detected spectroscopically through line-profile variations (LPVs). Whereas most of the brightest early-B type stars have been photometrically monitored for variability (72 of the 541 O9.5-B3 III-V stars in the BSC are classified as β Cephei stars), a systematic LPV survey to look for pulsational behaviour was lacking. Here we present some preliminary results of the southern part of our Spectroscopic survey of early-B type stars. We have made a high spectral resolution survey of the Si III λ 4552, 4567, 4574 Å triplet in early-B type stars in order to look for LPVs due to non-radial pulsation (NRP). Our sample consists of 82 southern O9.5-B3 stars with spectral classes III-V, taken from the BSC; 27% of all O9.5-B2.5 III-V stars in the BSC were sampled. This sample is not fully representative for all nearby early-B stars, because we concentrated on stars with high rotational velocities, because many of the stars are members of the Sco-Cen associations, and because we focused on the β Cephei stars in the BSC. As much as 40% of the β Cephei stars in the BSC with v sin г ≥ 25 km s-1 were sampled. The observations were carried out with the ESO CAT telescope at resolution R∼65000. Our targets were observed during 6 runs in September 1995 – June 1998. Some stars were observed many times, but most targets were observed only once or twice.

High spectral and time resolution observations show that the monoperiodic β Cephei star BW Vul presents differences in both line profiles and velocities from one cycle to another, which may be due to the consequence of the passage of two strong shock waves.

With updated microphysics such as opacity, we revise the result of asteroseismic investigations for β Cephei and show the tolerable range of the physical parameters of the star.

We have searched for magnetic signatures in the B2IV star V 2052 Oph, a β Cep star with stellar wind behavior typical for an oblique magnetic rotator, as β Cep itself. From UV spectroscopy we determined an accurate rotational period and v sin i and present the magnetic measurements as a function of rotational phase. The (small) class of magnetic pulsating early B stars are of great asteroseismological interest.

We present a new method of mode identification based on the line profile variations. We calculate time series of Si III 455.26 nm for models of β Cep stars with a mass of 10 M⊙. The Spectroscopic observables are amplitude ratio and phase difference for various oscillation parameters derived from the line profile changes. Based on the computed values we plot diagrams to search for the best discriminators of modes.

In most Spectroscopic diagrams the unstable modes are grouped in well-defined regions with different m-values, and a few of them give also separation with respect to l-values. Moreover, on the basis of almost all of the diagrams we can distinguish the prograde modes from the retrograde ones, and the zonal modes from those with m ≠ 0.

In this paper we discuss also the influence of the inclination angle, the amplitude of the radius variation and the equatorial velocity on the diagnostic values of the Spectroscopic diagrams.

In a series of papers, Telting & Schrijvers (1997) have demonstrated the correlation between the phase shift across a line, ∆Ψ0 and the l-value of a mode. In addition, they found that the phase shift of the harmonic (i.e., at frequency 2ω) was an indicator of m. In this poster, we present a heuristic derivation of these results under a set of idealized assumptions. Within this framework, exact analytical formulae for the Ilrn(x) were calculated, which are available upon request.

We present simulations of line-profile variations of Silicon lines in slowly-rotating non-radially pulsating β Cephei stars and SPB stars. Our goal is to examine how sensitive Si lines are to the non-adiabatic temperature variations at the surface of the star. We find that for realistic amplitudes of the velocity field, and for realistic amplitudes and phase differences for the non-adiabatic temperature and gravity variations, the Silicon lines variations are very little affected.