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Context.Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of iron-peak elements in the envelope of the star. In the Milky Way,p-modes are observed in stars that are hotter than or equal to the B3 spectral type, while g-modes are observed at the B2 spectral type and cooler.Aims.We observed a B0IVe star, HD 51452,with the high-precision, high-cadence photometric CoRoT satellite and high-resolution, ground-based HARPS and SOPHIE spectrographs to study its pulsations in great detail. We also used the lower resolution spectra available in the BeSS atabase. Methods.We analyzed the CoRoT and spectroscopic data with several methods: Clean -NG, Freq Find, and a sliding window method.We also analyzed spectral quantities, such as the violet over red (V/R) emission variations, to obtain information about the variation in the circumstellar environment. We calculated a stellar structure model with the ESTER code to test the various interpretation of the results.Results.We detect 189 frequencies of variations in the CoRoT light curve in the range between 0 and 4.5 c d−1. The main frequencies are also recovered in the spectroscopic data. In particular we find that HD 51452 undergoes gravito-inertial modes that are not in the domain of those excited by the κ-mechanism. We propose that these are stochastic modes excited in the convective zones and that at least some of them are a multiplet of r-modes (i.e. subinertial modes mainly driven by the Coriolis acceleration). Stochastically excited gravito-inertial modes had never been observed in any star, and theory predicted that their very low amplitudes would be undetectable even with CoRoT. We suggest that the amplitudes are enhanced in HD 51452 because of the very rapid stellar rotation.In addition, we find that the amplitude variations of these modes are related to the occurrence of minor outbursts.Conclusions.Thanks to CoRoT data, we have detected a new kind of pulsations in HD 51452, which are stochastically excited gravito-inertial modes, probably due to its very rapid rotation. These modes are probably also present in other rapidly rotating hot Be stars.

Context. Be stars undergo outbursts producing a circumstellar disk from the ejected material. The beating of non-radial pulsations has been put forward as a possible mechanism of ejection. Aims. We analyze the pulsational behavior of the early B0.5IVe star HD 49330 observed during the first CoRoT long run towards the Galactical anticenter (LRA1). This Be star is located close to the lower edge of the β Cephei instability strip in the HR diagram and showed a 0.03 mag outburst during the CoRoT observations. It is thus an ideal case for testing the aforementioned hypothesis. Methods. We analyze the CoRoT light curve of HD 49330 usin g Fourier methods and non-lin ear least square fitting. Results. In this star, we find pulsation modes typical of β Cep stars (p modes) and SPB stars (g modes) with amplitude variations along the run directly correlated with the outburst. These results provide new clues about the origin of the Be phenomenon as well as strong constraints on the seismic modelling of Be stars.

Context. We present spectroscopic ground-based observations of the early Be star HD 49330 obtained simultaneously with the CoRoT-LRA1 run just before the burst observed in the CoRoT data. Aims. Ground-based spectroscopic observations of the early Be star HD 49330 obtained during the precursor phase and just before the start of an outburst allow us to disantangle stellar and circumstellar contributions and identify modes of stellar pulsations in this rapidly rotating star. Methods. Time series analysis (TSA) is performed on photospheric line profiles of He i and Si iii by means of the least squares method. Results. We find two main frequencies f1 = 11.86 c d^−1 and f2 = 16.89 c d^−1 which can be associated with high order p-mode pulsations. We also detect a frequency f3 = 1.51 c d^−1 which can be associated with a low order g-mode. Moreover we show that the stellar line profile variability changed over the spectroscopic run. These results are in agreement with the results of the CoRoT data analysis, as shown in Huat et al. (2009). Conclusions. Our study of mid- and short-term spect roscopic variability allows the identification of p- and g- modes in HD 49330. It also allows us to display changes in the line profile variability before the start of an outburst. This brings new constraints for the seimic modelling of this star.

Context. HD 181231 is a B5IVe star, which has been observed with the CoRoT satellite during ∼5 consecutive months and simultaneously from the ground in spectroscopy and spectropolarimetry. Aims. By analysing these data, we aim to detect and characterize as many pulsation frequencies as possible, to search for the presence of beating effects possibly at the origin of the Be phenomenon. Our results will also pr ovide a basis for seismic modelling. Methods. The fundamental parameters of the star are determined from spectral fitting and from the study of the circumstellar emission. The CoRoT photometric data and ground-based spectroscopy are analysed using several Fourier Techniques: CLEAN-NG,PASPER,and TISAFT, as well as a time-frequency technique. A search for a magnetic field is performed by applying the LSD technique to the spectropolarimetric data. Results. We find that HD 181231 is a B5IVe star seen with an inclination of ∼45 degrees. No magnetic field is detected in its photo-sphere. We detect at least 10 independent significant frequencies of variations among the 54 detected frequencies, interpreted in termsof non-radial pulsation modes and rotation. Two longer-term variations are also detected: one at ∼14 days resulting from a beating effect between the two main frequencies of short-term variations, the other at ∼116 days due either to a beating of frequencies or to a zonal pulsation mode. Conclusions. Our analysis of the CoRoT light curve and ground-based spectroscopic data of HD 181231 has led to the determination of the fundamental and pulsational parameters of the star, including beating effects. This will allow a precise seismic modelling of this star.

Context.The origin of the short-term variability in Be stars remains a matter of controversy. Pulsations and rotational modulation are the components of the favored hypothesis.Aims.We present our analysis of CoRoT data of the B8IIIe star HD 175869 observed during the first short run in the center direction (SRC1).Methods.We review both the instrumental effects visible in the CoRoT light curve and the analysis methods used by the CoRoT Be team. We applied these methods to the CoRoT light curve of the star HD 175869. A search for line-profile variations in the spectroscopic data was also performed. We also searched for a magnetic field, by applying the LSD technique to spectropolarimetric data.Results.The light curve exhibits low-amplitude variations of the order of 300 μ mag with a double wave shape. A frequency within the range determined for the rotational frequency and 6 of its harmonics are detected. The main frequency and its first harmonic exhibit amplitude variations of a few days. Other significant frequencies of low-amplitude from 25 to a few μmag are also found. The analysis of line profiles from ground-based spectrosc opic data does not detect an y variation. In addition, no Zeeman signature was found.Conclusions.Inhomogeneities caused by stellar activity in or just above the photosphere are proposed to produce the photometric variability detected by CoRoT in the Be star HD 175869. The hypothesis that non-radial pulsations are the origin of these variations cannot be excluded.

Astron. & Astrophys., 411, p. 565 (2003); International audience

VizieR On-line Data Catalog: J/A+A, 409, p. 275 (2003); International audience

Astron. & Astrophys., 409, pp. 275-286 (2003); International audience

An analysis of a rich series of spectroscopic and photometric observations of the Be star 4 Her led to the following conclusions: 4 Her is another example of a long-term Be variable with a type of correlation between the brightness and emission strength, similar to 88 Her (V744 Her) and BU Tau (Pleione). It is argued that the formation of a new Be envelope of 4 Her starts with the creation of a slightly cooler pseudophotosphere at the equatorial regions of the star (seen under some intermediate inclination angle) which only gradually grows into an optically thin extended envelope. Radial-velocity measurements of the centre of the Halpha emission and of the photospheric lines confirm the binary nature of the star. The first reliable orbital elements are presented. The 46-d orbit is nearly circular and has a semiamplitude of 5-8 .() {kms() -1}. An LTE model atmosphere analysis of the photospheric spectrum of the primary leads to {T_{eff}}=12500K, log g = 4.0, and {v\sin i}=300{kms^-1}. No direct evidence of the low-mass secondary was found and the possibility that the secondary fills its Roche lobe can be safely excluded. The central quasi-emission bumps (CQEB) visible as "doubling" of some shell lines appear during the phase of the formation of a new shell. They are strongest during the light minimum and become fainter as the Halpha emission strengthens. An unusual blue-shifted absorption component of the Halpha line, never reported before, re-appears strictly periodically in the V peak of the Halpha emission at a limited range of velocities and orbital phases. It is argued that the observational facts about 4 Her are probably best reconciled by a model which assumes that the secondary is a hot and rotationally unstable object which looses mass towards the primary via a gas stream. However, some important findings remain unexplained. This research is based on spectra from the \Ond\ and Haute Provence Observatories and on photometry from Hvar, \Ond, Mt. Kobau, Toronto, APT Phoenix-10, and AAVSO observers.