Abstract. We report here the first observations of a rapidly rotating Be star, α Eridani, using Earth-rotation synthesis on the Very Large Telescope (VLT) Interferometer. Our measures correspond to a 2a/2b = 1.56 ± 0.05 apparent oblate star, 2a and 2b being the equivalent uniform disc angular diameters in the equatorial and polar direction. Considering the presence of a circumstellar envelope (CSE) we argue that our measurement corresponds to a truly distorted star since α Eridani exhibited negligible Hα emission during the interferometric observations. In this framework we conclude that the commonly adopted Roche approximation (uniform rotation and centrally condensed mass) should not apply to α Eridani. This result opens new perspectives to basic astrophysical problems, such as rotationally enhanced mass loss and internal angular momentum distribution. In addition to its intimate relation with magnetism and pulsation, rapid rotation thus provides a key to the Be phenomenon: one of the outstanding non-resolved problems in stellar physics.

Abstract. V 2052 Oph is a β Cep star with v sin i ∼ 60 km s −1 . The behavior of its stellar wind was studied in the ultraviolet wavelength region with the IUE satellite. It revealed periodic variations in the equivalent widths (EW) of the resonance lines of wind-sensitive ions with a period of 3.638833 d, which is identified as the rotational period. These variations are typical of magnetic stars. Therefore time-resolved circular spectropolarimetric observations were obtained with the Musicoséchelle spectropolarimeter at the 2-m Télescope Bernard Lyot (TBL) to search for a magnetic field in the star. Stokes V patterns were observed, the inclination and magnetic angles were derived and a value was determined for the polar magnetic field (250 ± 190 G) using an oblique rotator dipole model. The spectroscopic information was used to search for periodicity in line-profile variations (lpv), radial velocity and minimum intensity curves. Multiperiodicity was found, corresponding to radial ( f 1 = 7.15 c d −1 ) and non-radial ( f 2 = 6.82 c d −1 , l = 3 or 4) pulsation modes. The rotation period is also detected in rotationally modulated observables because of the magnetic poles passing through the observer's line of sight. We determined the stellar parameters of the star, which was found to be chemically peculiar, in particular He-enriched. This makes V 2052 Oph the first magnetic He-strong early B star with known pulsational properties.Key words. stars: magnetic fields -stars: winds, outflows -stars: chemically peculiar -stars: early-type -stars: oscillations IntroductionThe B2 IV-V star V 2052 Oph (HD 163472, HR 6684, V = 5.85) is classified as a β Cep variable. It has one of the shortest periods and lowest luminosity of its type. The period of 3h 21min in its light variability discovered by Jerzykiewicz (1972) has also been detected in radial velocity variations (Pike 1974). The periodic variability in the light curve is also reported with high accuracy in the Hipparcos catalogue (Perryman et al. 1997). Morton & Hansen (1974) deduced temperature variations up to 900 K from near-UV light variations. Since then, the pulsation period of V 2052 Oph has been well Send offprint requests to: C. Neiner, e-mail: cneiner@rssd.esa.intBased on observations obtained with the MuSiCoS spectropolarimeter at the Observatoire du Pic du Midi, France, and by the International Ultraviolet Explorer, collected at NASA Goddard Space Flight Center and Villafranca Satellite Tracking Station of the European Space Agency, retrieved from the INES database. Table 7 is only available in electronic form at http://www.edpsciences.org studied. Cugier et al. (1994) and Heynderickx et al. (1994) found that it corresponds to a l = 0 single radial mode. Rountree & Sonneborn (1991) classified the star from the photospheric lines in the UV spectrum as B2 IVw, where the w-designation signifies anomalous wind lines. They also noted that the single spectrum they considered looked very similar to that of ζ Cas, a star being known for its variable C  wind li...

Abstract. ω Ori is a B2IIIe star for which rotational modulation and non-radial pulsations (NRP) have been recently investigated from two independent observational campaigns in 1998 and 1999. Putting the data of these 2 campaigns together, and adding data obtained in 2001, we search for multiperiodicity in the line profile variations and evidence for outbursts. From new spectropolarimetric data obtained at the Télescope Bernard Lyot (TBL, Pic du Midi, France) in 2001 we also measure the Stokes V parameter in the polarised light. We find evidence for the presence of a weak magnetic field in ω Ori sinusoidally varying with a period of 1.29 d. The equivalent widths (EW) of the wind sensitive UV resonance lines also show a variation with the same period, which we identify as the rotational period of the star. We propose an oblique rotator model and derive B pol = 530 ± 230 G to explain the observations. Moreover, we carry out an abundance analysis and find the star to be Nenriched, a property which is shared with other magnetic stars. We propose ω Ori as the first known classical Be star hosting a magnetic field.