We discuss the determination of fundamental parameters of "normal" hot, massive OB-type stars, namelytemperatures, luminosities, masses, gravities and surface abundances. We also present methods used to derive properties of stellar winds - mass-loss rates and wind velocities from early-type stars.

We discuss the impact of the inclusionof both mass loss and rotation in massive star models at different metallicities.Rotation much improves the agreement between theory and observation. In particular rotational mixing allows to produce variations of the surface abundances already during the Main-Sequence phase. The changes of the surface abundances are more important when, for a given initial velocity, the initial mass increases, and/or the initial metallicity decreases. Alsothe observed high number of red supergiants at low metallicity can be accounted for by rotating stellar models, as well asthe observed variation of the number ratioof Wolf-Rayet to O-type stars as a function of the metallicity and the variation with themetallicity of the number ratio of type Ibc to type IIsupernovae. In all these questionsnon-rotating models give unsatisfactory fits. Rotating models can also give interestinginsights on questions as the origin of the Be stars, themechanisms responsible for thehuge mass loss rates undergone by the Luminous Blue Variables, the sources of primary nitrogen at low metallicity, the rotation rateof pulsars and the progenitors of the collapsars.

Contrary to what is assumed in building standard stellar models, all stars undergo some mild mixing in their radiation zones. This mixingis due mainly to a slow thermally driven meridional circulation, andshear turbulence presumably contributes to it.It is the rotation of the star which isresponsible for these motions, and therefore the transport of angular momentum must be described in time and space when modeling stellar evolution. This rotational mixing plays an important role in the evolution of massive stars; in particular it determines the late, pre-supernova phases. We review the present state of the problem and discuss briefly the open questions.

Despite their important luminosity, massive stars keep unveiledmost of their formation mainly because they are deeply embedded withintheir native cloud. This difficulty is accentuated by their small numberand by their larger distances compared to low mass stars.This explains why models for the various stages oftheir formation are still in their infancy.We briefly present here the initial conditions andthe most common models for the formation of massive stars. Also, we focus onto a family of self-similar modelsthat allow accretion and outflows around massive protostars.Finally, we try to sketch the temporal evolution of massive star formation.

A brief account is given of the advanced evolutionary stagesof massive stars, from central C-burning up to the final supernova explosion.We describe the role of neutrino losses, the phases of C, Ne, O and Si burning,the Fe core collapse, current ideas on the supernova explosion, as well as theexplosive nucleosynthesis resulting from the passage of the shock wave.

We discuss the various post-main sequence phases of massive stars,focusing on Wolf-Rayet stars, Luminous Blue Variables, plus connectionswith other early-type and late-type supergiants. End states for massive stars are also investigated, emphasising connections between Supernovae originating fromcore-collapse massive stars and Gamma Ray Bursts.

In the present review we summarize direct and indirect evidence that the massive close binary frequency is very large. Wethen discuss the binary evolutionary processes and we present a general massive close binary evolutionary scheme. Finally,we highlight the importance of massive close binaries for population number synthesis and the chemical evolution ofgalaxies.

I review driving mechanisms for stellar winds, using first the example of the coronal, pressure-driven solar wind, but then focussing mainly on radiation-pressure driven winds from hot, luminous stars.For the latter, I review the central role of line-opacity as a coupling between matter and radiation, emphasizing how the Doppler shift of an accelerating wind outflow exposes the strong line opacity toa substantial continuum flux, and thus allows the line force to sustain the outward acceleration against gravity.Through the CAK formalism that assumes a power-law distribution of line-opacity, I derive the mass loss rate and wind velocity law, and discuss how these are altered by various refinements like a finite-disk correction, ionization variations in opacity, and a non-zero sound speed.I also discuss how multiline scattering in Wolf-Rayet (WR) winds can allow them to exceed the single scattering limit, for which the wind and radiative momenta are equal. Through a time-dependent perturbation analysis, I show how the line-driving leads to a fast, inward "Abbott-wave" mode for long wavelength perturbations, and a strong Line-Deshadowing-Instability at short wavelengths, summarizing also 1D and 2D numerical simulations of the nonlinear evolution of this instability.I next discuss how rapid stellar rotation alters the latitudinal variation of mass loss and flow speed, and how this depends on treatment of gravity darkening, nonradial line forces, and "bi-stability" shifts in ionization.Finally, I conclude with a discussion of the large mass loss epochs of Luminous Blue Variable (LBV) stars, and how these might be modeled via super-Eddington, continuum driving moderated by the "porosity" associated with extensive spatial structure.

Hot luminous stars are characterized by their fast, dense and persistent outflows.Here, we analyze the unambiguous spectroscopic signatures of the presence of these winds. We then present various observational elements that suggest that hot star winds are not smoothly expanding outflows.The unstable nature of line-driving could be at the origin of these propertiesof radiatively-driven outflows and we investigate here its ability to explainthe Line Profile Variability (LPV) observed in hot star spectra. Such variabilityfeatures profile sub-peaks migrating away from line center, and with characteristic velocity scales increasing from50 to 100-200 km s-1 (from center to edge). Based on radiation-hydrodynamics simulations, we compute the average and temporal evolution of the emissivity of a hot star wind, and compare with LPV datasets of Wolf-Rayet (WR) spectra.The inferred inadequacy of the spherically-symmetric assumption suggests a globally asymmetrical wind structure, which we model by mapping the 3D wind volume with closely-packed star-centered cones. We find that the cone-angle α, which represents the lateral extent of wind structures, controls the sub-peak width at line center. Given the absence of an explicit lateral velocity in our simulations, the best match to observations suggest an upper limit of ca. 1-3 deg to these structures. At line edge, syntheticsub-peaks are narrower than observed by a factor 2-3, suggesting the lack of radial velocity dispersion of computed wind structures, a likely artifact of our 1D simulations.Additionally, assuming that sub-peak lifetimes in LPV time-series represents the crossing-time of the Line Emission Region (LER), we determine the wind acceleration in the LER. Contrary to previous findings, we find no firm evidence for very extended acceleration of WR winds, which would require usingspectral diagnostics with LER located distinctly below v∞.Although the best candidates, WR objects and their optically thick outflows constitute a big challenge for constraining observationally the velocity law of radiatively-driven winds.

In this review, we focus on the winds of standard massive starsof spectral types O and B. We introduce the fundamental parametersthat are used to characterize the stellar winds and we describethe various techniques available nowadays to derive the windproperties. The latter are reviewed and interpreted in theframework of the standard theory of line-driven winds.

In this contribution, I review recent results from observational investigations of early-type binaries of spectral types O and Wolf-Rayet. These studies aim at an accurate determination of fundamental parameters such as masses and radii of the most massive stars. In addition, multi-wavelength analyses of wind collisions in massive binaries provide constraints on the properties of stellar winds of massive stars and shock physics of cosmic plasmas.

In the present paper we review some basic facts regarding the similarities and differences between Galactic planetary nebulae (PN) and Galactic Wolf-Rayet (WR) nebulae within the scope of stellar mass-loss history and its subsequent impact on the nebular dynamics and morphology. The case of planetary nebulae with [WR] nucleus, which allows one to perform a more direct comparison with WR nebulae, is emphasized.In particular, we reviewselected studies on the PN NGC 40 and on the WR nebula M 1-67.We describe the apparently ubiquitous turbulent-like phenomena originating in WR/[WR] stellar atmospheres and the surrounding nebulae, and discuss the possible impact of turbulence on ejected nebula studies. The properties of turbulence observed in ejectednebulae (apparently supersonic) are at odds with the ones related toKolmogorov's subsonic, incompressibleturbulence. The large compressibility of the nebular gases and the possiblemultiplicity of turbulence energy sources are likely the main explanationsfor that difference. The Universal Multifractal approach ofLovejoy & Schertzer is presented and constitutes a physically realistic and natural way of modeling andquantifyingnebular turbulence data with only three independent parameters, includingthe key C1 intermittence parameter.

Spectroscopy can be used as a tool to study stellar winds and mass-loss. Thecombination of spectroscopic data at several wavelengths, in particularUltra-Violet (UV), visible and Infra-Red (IR), provides a complete picture ofthe stellar environment. In this paper, Be stars are taken as an example forwhich multiwavelength spectroscopy provides essential information on thestellar wind and mass-loss.

This paper proposes a brief tutorial on the high angularresolution techniques and especially for the case of optical longbaseline interferometry. Through a review of published results inthe field of circumstellar environments, we will show the greatpotential of interferometry in this field. We will conclude thispaper by a description of the ESO-VLTI interferometer and show thenew capabilities of MIDI and AMBER focal instruments for thestellar physic and especially for the study of circumstellarenvironments.

Astronomy and astrophysics can today produce a lot of discoveries and syntheses, driven by the convergence of sophisticated technology (advanced detectors and instrumentation, and supercomputers) with new observation platforms (VLT, Keck) and a revitalised satellite program. These advances will decisively affect many of the fundamental studies of origins, dynamics, and emission for all scales of astrophysical phenomena. Traditionally astrophysical research has been divided into observations and theoretical modelling or a combination of both. But scientists have discovered that existing models did not explain their observations of the great supernova of 1987. Since is born a closed collaboration between astrophysicists and plasma scientists leading to perform laboratory experiments motivated by the astrophysics. Start many collaborations is essential in order to progress in this new field and together astro/plasma physicists and laser bench scientists are pushing the frontiers of recreating the Universe's most exotic phenomena. The goal is to create in the laboratory a sample plasma similar to what would be found in the astronomical body, then to study its properties (radiation or thermodynamical state).