We present new physical and orbital parameters of an early-type double-lined eclipsing binary system ALS 1135. The UBVIC light curves and radial velocity curves were modeled simultaneously by means of the Wilson-Devinney code. As a result, we obtained inclination and size of the orbit, as well as masses, radii and effective temperatures of the components.

Rapidly rotating stars are readily produced in binary systems. An accreting star in a binary system can be spun up by mass accretion and quickly approach the break-up limit. Mergers between two stars in a binary are expected to result in massive, fast rotating stars. These rapid rotators may appear as Be or Oe stars or at low metallicity they may be progenitors of long gamma-ray bursts.

Given the high frequency of massive stars in close binaries it seems likely that a large fraction of rapidly rotating stars result from binary interaction. It is not straightforward to distinguish a a fast rotator that was born as a rapidly rotating single star from a fast rotator that resulted from some kind of binary interaction. Rapidly rotating stars resulting from binary interaction will often appear to be single because the companion tends to be a low mass, low luminosity star in a wide orbit. Alternatively, they became single stars after a merger or disruption of the binary system during the supernova explosion of the primary.

The absence of evidence for a companion does not guarantee that the system did not experience binary interaction in the past. If binary interaction is one of the main causes of high stellar rotation rates, the binary fraction is expected to be smaller among fast rotators. How this prediction depend on uncertainties in the physics of the binary interactions requires further investigation.

We present a preliminary analysis of our six-year observation campaign of the B[e] stellar system V2028 Cyg (MWC 623). The time variability of spectral features is described.

Recently, Reese et al. (2008), Lignières & Georgeot (2008) and Lignières & Georgeot (2009) showed that the frequencies of low-degree acoustic modes in rapidly rotating stars, also known as “island modes”, follow an asymptotic formula, the coefficients of which can be deduced from ray dynamics. We investigate how this asymptotic behaviour is affected by μ gradients by comparing pulsation spectra from models with and without such a discontinuity.

Binary/multiple status can affect stars at all stages of their lifetimes: evolution onto the main sequence, properties on the main sequence, and subsequent evolution. 5 M⊙ stars have provided a wealth of information about the binary properties fairly massive stars. The combination of cool evolved primaries and hot secondaries in Cepheids (geriatric B stars) have yielded detailed information about the distribution of mass ratios. and have also provided a surprisingly high fraction of triple systems. Ground-based radial velocity orbits combined with satellite data from Hubble, FUSE, IUE, and Chandra are needed to provide full information about the systems, including the masses. As a recent example, X-ray observations can identify low mass companions which are young enough to be physical companions. Typically binary status and properties (separation, eccentricity, mass ratio) determine whether any stage of evolution takes an exotic form.

We report the first dynamic mass for an O-type supergiant, the interferometrically resolved SB2 system ζ Ori A (O9.5Ib+B0/1). The separation of the system excludes any previous mass-transfer, ensuring that the derived masses can be compared to single star evolutionary tracks.

BI 108 is a luminous variable star in the Large Magellanic Cloud classified B1 II. The variability consists of two resonant periods (3:2), of which only one is orbital, however. We discuss possible mechanisms responsible for the second period and its resonant locking.

FN CMa is visually double with a separation of ~0.6 arcsec. Sixty high-cadence VLT/UVES spectra permit the A and B components to be disentangled, as the relative contribution of each star to the total light entering the spectrograph fluctuates between exposures due to changes in seeing. Component A exhibits rapid line-profile variations, leading us to attribute the photometric variability seen by HIPPARCOS (with a derived P = 0.08866 d) to this component. From a total of 122 archival and new echelle spectra it is shown that component A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of 0.6 may result in tidal modulation of the pulsation(s) of component Aa.

Nonradial pulsations (NRPs) are a possible formation mechanism for the equatorial disks surrounding Be stars. The open cluster NGC 3766 has a high fraction of transient Be stars, Be stars that have been observed with both emission due to a circumstellar disk and a non-emitting B-type spectrum. Because of the large fraction of transient Be stars, this cluster is a prime location for studying the formation mechanisms of Be star disks. We observed NGC 3766 for more than 25 nights over three years to generate Strömgren uvby light curves of the Be population. We present the results of a period search to investigate the presence of NRPs.

First we investigate the spectral and photometric properties (colours, magnitudes) of a sample of faint Be stars observed in the first exoplanet fields of CoRoT (IR1, LRA1 and LRC1). We determine the fundamental parameters by fitting ESO-FLAMES/GIRAFFE spectra with synthetic models taking account for non-LTE effects. After that we correct these parameters from fast rotation effects. We also study the location of each star in the (logL vs logT) HR diagram. Second we start to analyse the CoRoT light curves to investigate further the possible correlation between the pulsating properties and the fundamental parameters of the stars.

As part of a long term observational project, we are investigating the macroturbulent broadening in O and B supergiants (Sgs) and its possible connection with spectroscopic variability phenomena and stellar oscillations. We present the first results of our project, namely firm observational evidence for a strong correlation between the extra broadening and photospheric line-profile variations in a sample of 13 Sgs with spectral types ranging from O9.5 to B8.

We report on two SMC objects with remarkable light curves and spectra. Both are in fact A I + B III binaries that exhibit interacting winds. We show a sketch of the geometry.

Massive stars are inherently extreme objects, in terms of radiation, mass loss, rotation, and sometimes also magnetic fields. Concentrating on a (personally biased) subset of processes related to pulsations, rapid rotation and its interplay with mass-loss, and the bi-stability mechanism, we will discuss how active (and normal) OB stars can serve as appropriate laboratories to provide further clues.

Understanding phenomena of activity in stars, like pulsations or magnetism, benefits from systematic comparisons of some key physical parameters of active with those of “normal” stars. Here we concentrate on a careful derivation of fundamental parameters of a well selected sample of 27 “normal” B stars in nearby OB associations and in the field. A quantitative spectral analysis methodology based on hybrid non-LTE techniques is applied to high-resolution and high-S/N spectra. Results derived from the pure spectroscopic analysis are compared to other data/indicators of stellar parameters in order to prove the reliability of the method. Very good agreement is obtained among all of them. Besides the fundamental parameters, the chemical composition of the stars is also determined at high precision, turning out to be highly homogeneous. A comparative study of the present results with those of well known active massive stars will help to improve our understanding of the driving mechanisms of activity.

I review recent progress on understanding eruptions of unstable massive stars, with particular attention to the diversity of observed behavior in extragalatic optical transient sources that are generally associated with giant eruptions of luminous blue variables (LBVs). These eruptions are thought to represent key mass loss episodes in the lives of massive stars. I discuss the possibility of dormant LBVs and implications for the duration of the greater LBV phase and its role in stellar evolution. These eruptive variables show a wide range of peak luminosity, decay time, expansion speeds, and progenitor luminosity, and in some cases they have been observed to suffer multiple eruptions. This broadens our view of massive star eruptions compared to prototypical sources like Eta Carinae, and provides important clues for the nature of the outbursts. I will also review and discuss some implications about the possible physical mechanisms involved, although the cause of the eruptions is not yet understood.

γ-ray binaries are systems that emit most of their radiative power above 1 MeV. They are associated with O or Be stars in orbit with a compact object, possibly a young pulsar. Much like colliding wind binaries, the pulsar generates a relativistic wind that interacts with the stellar wind. The result is non-thermal emission from radio to very high energy γ-rays. The wind, radiation and magnetic field of the massive star play a major role in the dynamics and radiative output of the system. They are particularly important to understand the high energy physics at work. Inversely, γ-ray binaries offer novel probes of stellar winds and insights into the fate of O/B binaries.

Perhpas the most extreme examples of “Active OB stars" are the subset of high-mass X-ray binaries – consisting of an OB star plus compact companion – that have recently been observed by Fermi and ground-based Cerenkov telescopes like HESS to be sources of very high energy (VHE; up to 30 TeV!) γ-rays. This paper focuses on the prominent γ-ray source, LS5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical (e ≈ 0.24) orbit with its companion, assumed here to be a black-hole or unmagnetized neutron star. Using 3-D SPH simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of γ-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of γ-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the γ-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE γ-ray emission in massive-star binaries.

Guillaume Dubus: As far as I can tell your model is exactly the same as standard models for high-mass x-ray binaries, the on difference is that you have a mechanism for generating γ rays. My question is, we know that there are dozens of other systems that are just LS 5039, so why are they not emitting γ rays?

Some late-type O stars display anomalously weak winds, possibly due to decoupling of the main driving ions from the bulk plasma. This issue and the uncertainty about the nature of wind clumping are a challenge to line-driven wind theory and need resolving in order to fully understand hot stars. We describe the results from the computation of ion fractions for the various elements in O star winds using non-LTE code CMFGEN, including parameterisation of microclumping and X-rays.

Double mode pulsations of the B4 component in the system of CI Cam were detected. The photometric 19.4 day orbital period of CI Cam was confirmed with the plates of the Sonneberg collection for a long period of time before the unique 1998 outburst. The amplitude of the periodic component of 0.08 mag before the outburst was larger than that of 0.03 mag after the outburst.