A small number of Wolf-Rayet colliding-wind binaries studied at extremely high angular resolution show elegant dust plumes with an intuitive geometry: that of an Archimedian spiral. A great deal of fundamental information on the binary and the winds is encoded, ultimately teaching us about dust formation and wind-wind collision zones in these fascinating systems. New results are presented summarizing a concerted campaign encompassing a number of systems studied with various techniques over the last five years.

Massive stars in binary systems can generate X-ray emission in the region between the two stars where stellar winds collide. Colliding wind X-ray emission acts as an in-situ probe of important wind parameters like mass-loss rates, chemical abundances, wind velocities, and possibly magnetic field strengths. Variations in observed colliding-wind X-ray emission can be produced by the changing line-of-sight to the colliding wind region as the stars move in orbit and/or the changing emission measure of the shocked gas in the wind collision zone produced if the separations between the two stars change. X-ray variability depends on the wind and orbital parameters and so can in principal allow the direct measurement of mass functions even for low inclination systems and provide a connection between the stellar and wind parameters. X-ray emission from colliding wind systems can thus be used to refine our understanding of the evolutionary state of massive stars and to help test evolutionary models. We discuss recent advances in defining the X-ray spectral and temporal signatures of colliding wind X-ray emission using ROSAT, ASCA, RXTE, Chandra and XMM-Newton data.

The pinwheel nebulae observed in some WC-binaries essentially mirror a transport phenomenon. We show the importance of the central wind collision zone in setting the ‘initial conditions’ for this transport. In order to understand some of the newly observed features, we postulate that standard theory of colliding flows must be extended by considering radiative breaking, heat-conduction, and the clumped character of the winds. We suggest that clumped winds can be modeled by highly compressible turbulence and outline some consequences for the physics of the wind collision zone. With regard to dust production we argue that the system center is the only location where dust nucleation can happen.

We have analyzed eight single WC4-7 stars in M 33, spanning a variety of galactocentric distances, using optical CFHT-MOS spectroscopy. Provisional stellar parameters are determined using the code of Hillier & Miller (1998), which are compared here to Galactic and LMC counterparts.

In the colliding wind region of early-type binaries, electrons can be accelerated up to relativistic energies, as demonstrated by the detection of non-thermal radio emission from several WR+OB systems. The particle acceleration region is exposed to strong photon fields, and inverse-Compton cooling of the electrons could result in a substantial high-energy non-thermal flux. We present here preliminary results of a study of the binaries WR 140, WR 146, and WR 147 in the light of recent radio and γ-ray observations. We show that under reasonable assumptions WR 140 can produce the γ-ray flux from the GRO-egret source 3EG J 2022+4317. WR 146 and WR 147 are below the detection threshold.

The aim is to determine the role and influence of the hypothesis concerning both dynamics and radiative transfer in models of winds and mass loss of evolved stars, when the radiative force on dust grains plays a major role in the structuration of the circumstellar envelope of the star. The flow is described successively using two models coupling the grains-gas dynamics in a self-consistent way with radiative transfer for two different approaches of the dynamics: the Momentum Coupling Hypothesis and the Full Problem. Complete radiative transfer including multiple scattering, absorption and thermal emission is taken into account. The medium is not necessarily optically thin. In all cases, numerical iterations couple dynamics with transfer. This study emphasizes the importance of the drift velocity between the grains and the gas and the inertia of dust together with hydrodynamics and transfer coupling.

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Because of this, they form a very heterogeneous group. This group contains objects with different evolutionary stages. Lamers et al. (1998) have suggested a new designation with five sub-groups, which indicate the evolutionary stage. They are: supergiants, pre-main sequence or Herbig Ae/Be, compact planetary nebulae, symbiotic and unclassified. The unclassified group has many objects that need a better study to resolve their evolutionary status. Forbidden lines can be a useful tool to solve this problem. They can give informations about chemical composition, ionization and density of the circunstellar medium and probably the evolutionary phase of these objects. We analize spectra of some galactic objects, obtained with the feros and b&c spectrographs at the 1.52m telescope in ESO (La Silla-Chile), with a special focus on the forbidden lines. We have studied the spectra of five B[e] stars of uncertain evolutionary stage. We find that one of them is a pre-WN star, the other four are supergiant B[e] stars.

We have investigated the properties of main-sequence O-type stars in the SMC. Mass-loss rates, luminosities and Teff are much smaller for these stars than for Galactic ones, resulting in a steeper wind-momentum relation.

We have carried out the wind analysis of six A-type supergiants in NGC 300. The derived Wind Momentum-Luminosity Relationship is compared with that of Galactic and M 31 blue supergiants and with theoretical models.

We present the results of photometric searches for LBV candidates (LBVc) made in some Local Group galaxies. We found eight candidates in a southern region of M 33 with characteristics similar to Var B and Var C. In IC 10, a galaxy without any LBV or LBVc reported before, we found one candidate.

We present non-LTE abundances of carbon, nitrogen, oxygen, magnesium, aluminum, silicon and sulfur, derived for a sample of 70 O9-B2 main sequence stars of the Galactic disk and analyze the distribution of the chemical abundances in terms of radial gradients within 4.4-12.9 kpc from the center of the Galaxy. The derived gradients are flatter than those presented by the most recent studies about the radial gradients of stellar abundances.

We show that the stellar masses implied by our predictions of the wind properties of massive stars are in agreement with masses derived from evolution theory and from direct measurements using spectroscopic binaries, contrary to previous attempts to derive masses from wind theory.

We present a theoretical study of hot star wind emissivity in the presence of hypothetical large scale wind structures. Contrary to previous investigations that have focused on the resulting P-Cygni profile variability, we investigate the impact on observable optical and near-infrared emission lines. Our working hypothesis assumes, that such extended wind over-densities are formed via a rotationaly modulated stellar mass loss rate, that gives rise to the so-called co-rotating interaction regions (CIR). Within this context, we find that the variability of emission lines traces an un-equivocal S-shape in the frequency-time space, i.e., a spiraling pattern with positive and negative accelerations towards the line-of-sight over one stellar rotation period. Further, we demonstrate how lines forming at different heights can then be used to provide dynamical and geometrical constraints on the wind structures. Complementary to this spectroscopic approach, we also present theoretical expectations for forthcoming VLT-amber observations of a perturbed hot star outflow presenting such CIRs. The spectrally dispersed visibility and fringe phase output by the Differential Interferometry (DI) method show clearly-defined signatures of the presence of these CIRs. Extrapolating the adequacy of DI beyond the detection of CIRs, we speculate that this method provides very fruitful information on putative large scale structures in hot star environments.

We present theoretical calculations of emission-line-profile variability (LPV), based on radiation hydrodynamics simulations of the infamous radiative instability of hot star winds. We demonstrate that spherically symmetric wind structures (shells) cannot account for the observed profile variability at line center. Hence, we resort to a model that breaks-up the wind volume into a number of independent star-centered cones. The essential approximation made here is that each of these cones can be described by a structure calculated with a one-dimensional (1d) radiation hydrodynamics model. Such pseudo-3d ‘patch’-method leads to a satisfactory reproduction of the fundamental characteristics of LPV observed in O-type and Wolf-Rayet star optical spectra: the low-level fluctuations in the profile centre region, a migration of variable sub-peaks from line center to edge, that mimics the underlying wind acceleration. Our method highlights the correlation between the velocity scale of profile sub-peaks at line center and the lateral extent of wind structures, while at line edge it reflects the intrinsic radial velocity dispersion of emitting clumps. However, our model fails to reproduce the increase in this characteristic velocity scale from line center to edge, which we believe is a shortcoming of our purely 1d hydrodynamics approach.

We present preliminary calculations of the spatial distribution of the radio emission from a WR+OB colliding wind system, based on high-resolution hydrodynamical simulations and solutions to the radiative transfer equation. We account for both thermal and non-thermal radio emission, under the assumption of equipartition between magnetic and relativistic particle energy densities, and that the latter is a simple fraction of the thermal particle energy density. These calculations provide the foundation for modeling high resolution radio images and light curves of colliding-wind systems like WR 140, WR 146 and WR 147.

Massive stars which are fast rotators can give rise to asymmetric winds. These winds may result in the formation of aspherical wind-blown nebulae. In this work the theory of radiatively-driven winds from massive stars is used to model the formation of bipolar nebulae around LBV stars.

We present new spectroscopic observations of WC9 stars. As predicted by Williams & van der Hucht (2000), O ii lines are weak in the dust-free star WR88, which also shows a high ionization. Spectral variability is detected in WR 106 and WR 121. These findings are briefly discussed in terms of the conditions for dust formation in Wolf-Rayet winds.

We present results from optical and ultraviolet analysis of nine LMC/SMC supergiants. Temperatures, mass-loss rates and CNO abundances are obtained using the non-LTE, line-blanketed model atmosphere code of Hillier & Miller (1998). In general, the derived temperatures are significantly lower than those determined from unblanketed, plane-parallel models.

Massive binary star systems are not uncommon, and neither the supersonic collision of their winds. In the present work we study these shocks and the further consequences on wind structure. The post-shock gas is a warm and high-density environment, which allows dust to form and grow. We show that this growth is fast, of just a few hours. An application to η Car shows that, probably, the decline of X-rays fluxes observed in its light curve is the consequence of its high absorption in periodic dust formation events, at periastron passage.

We have undertaken a large and extensive spectroscopic survey of WNE stars both in the SMC and LMC with various 2m and 4m telescopes, reaching a total of 78 nights, spread over three years, and obtaining over 1500 long-slit spectra of medium resolution. The first goal is a systematic search for binaries via periodic radial-velocity variations. We enlarged our dataset with photometric data from the ogle and macho databases, and with archival X-ray data from the ROSAT and Chandra satellites.