We present the results of a high-resolution Chandra X-ray image of the Wolf-Rayet binary system WR 147, which consists of a WN8 star and an early-type companion located 0″.6 to its north. The image provides the first direct evidence for spatially extended X-ray emission in an early-type binary system, and shows that the emission peaks north of the WN8 star and close to the position of the radio bow shock. Simulated X-ray images of the wind-wind collision have a fwhm consistent with the data, but cannot account for the full spatial extension, unless emission from the stars is also included.

We present preliminary results concerning the O4If+ star HD 15570. Of-type supergiants are believed to represent an evolved evolutionary stage of very high mass stars (Minit > 40 M⊙). Their low numbers and extreme peculiarity make each of these objects worth of continuous monitoring. HD 15570 dominates the very young open cluster IC 1805 and is thought to have had an initial mass ≥ 100 M⊙. Low-, intermediate- and high-resolution spectra were collected at the Loiano and San Pedro Mártir telescopes since 1992. The comparison of our high- and low-resolution spectra shows clear variability of a number of spectral features. It is worth noticing, that the variation of Hα seems to follow a repeated secular trend, increasing its equivalent width from ~ 3Å to more than 8 Å in a few years. At the same time, its profile is varying, from a shape quite similar to the theoretical one corresponding to the Klein & Castor (1978) model C, to a much more developed P-Cygni profile, with a deep blue absorption wing. The possibility of instrumental effects is ruled out by the remarkable constancy of the nearby diffuse interstellar band at 6613 Å and of the He ii 6683 Å absorption. The Hβ profile variability is evident from the comparison of the 1996 and 1998 high-resolution spectra. The emission component, which is clearly visible at all epochs, is absent in the 1996 spectrum when the line appears in pure absorption. No relevant line-profile variation seems to be present in the He ii and N iii lines contributing to the ‘feature f’, that looks remarkably constant, as well as Hγ, while their equivalent widths seem to show a modest amount of random variability.

We present a moving periodic box technique to study the outer-wind evolution of instability-generated structure in hot-star winds. This has considerable computational and conceptual advantages

High resolution imaging with HST-wfpc2 of seven of the most luminous evolved cool stars shows that the three OH/IR stars NML Cyg, VX Sgr and S Per have circumstellar nebulae while no ejecta was detected for the M-type supergiant μ Cep and the yellow hypergiants ρ Cas, HR 8752 and HR 5171a.

We present results of the Australia Telescope Compact Array (ATCA) radio continuum observations of massive stars in the Sco OB1 association. Most stars detected in the program show spectral indices lower than value expected from thermal free-free emission.

We present results of a search for the most massive LBV-like stars in M 33 and discuss the list of OB+Hα stars. Spectral studies of the 70 brightest stars (V < 17.7) from the list have isolated 14 new LBV candidates. They are evolved the most massive stars, some of them are variable stars.

The fast, dense winds which characterize Wolf-Rayet stars obscure their underlying cores, and complicate the verification of evolving core and nucleosynthesis models. A powerful technique for probing WR core evolution involves measuring abundances of wind-borne nuclear processed elements. Neon, in particular, undergoes a remarkable change in abundance during the later stages of a WR star's lifetime. By the end of the WC phase, it becomes the fourth most abundant element, after He, C and O (Maeder 1983).

HST-stis spectroscopy of the Homunculus reflection nebula around η Carinae provides a rare opportunity to observe a star from more than one direction, and reveals that η Car has an aspherical stellar wind. Relatively high velocities and strong absorption are seen near the polar axis, suggesting higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. The bipolar wind geometry may imply that intrinsically asymmetric ejection helped form the Homunculus. It is also critical for understanding this star's variability and evolution.

We present FUSE observations of the SMC WO4+O4V binary Sand 1. Our spectra show variations in S iv, C iii, C iv and O vi lines, which we attribute mainly to emission from the shock cone, resulting from the collision between the two winds, and to atmospheric eclipses of the O-star continuum light by the WR wind. From this variability, we deduce a cone opening angle of 120°.

Luminous Blue Variables (LBVs or S Dor Variables) are showing characteristic variability of very long timescales of a decade and more. During their expansion and contraction phases, they move across a wide part of the H-R diagram with dramatic changes of their stellar wind characteristics, radius and temperature. We present results of our long-term spectroscopic monitoring campaigns for the galactic star HR Car with optical spectra taken over 13 years and two minimum and maximum phases observed during this time.

We present the spatial distribution of chemical species in M 31, as derived from intermediate resolution spectra of seven B-type supergiants, lying within four OB associations, covering a galactocentric distance of 5 – 12 kpc. We do not detect any systematic oxygen gradient across this galactocentric range. We find that the inner regions of M 31 are not, as previously thought, very ‘metal-rich’. Our abundances of C, N, O, Mg, Si, Al, S and Fe in the M 31 supergiants are very similar to those of massive stars in the solar neighbourhood.

We present numerical magnetohydrodynamic simulations of the effect of stellar dipole magnetic fields on line-driven wind outflows from hot, luminous stars. Unlike previous fixed-field analyses, the simulations here take full account of the dynamical competition between field and flow, and thus apply to a full range of magnetic field strength, and within both closed and open magnetic topologies. A key result is that the overall degree to which the wind is influenced by the field depends largely on a single, dimensionless, ‘wind magnetic confinement parameter’, η* = B2eqR2*/Mv∞, which characterizes the ratio between magnetic field energy density and kinetic energy density of the wind. For weak confinement η* ≤ 1, the field is fully opened by the wind outflow, but nonetheless for confinements as small as η* = 1/10 can have a significant back-influence in enhancing the density and reducing the flow speed near the magnetic equator. For stronger confinement η* > 1, the magnetic field remains closed over a limited range of latitude and height about the equatorial surface, but eventually is opened into a nearly radial configuration at large radii. Within closed loops, the flow is channeled toward loop tops into shock collisions that are strong enough to produce hard X-rays, with the stagnated material then pulled by gravity back onto the star in quite complex and variable inflow patterns. Within open field flow, the equatorial channeling leads to oblique shocks that are again strong enough to produce X-rays, and also lead to a thin, dense, slowly outflowing ‘disk’ at the magnetic equator. The polar flow is characterized by a faster-than-radial expansion that is more gradual than anticipated in previous 1d flow-tube analyses, and leads to a much more modest increase in terminal speed (< 30%), consistent with observational constraints. Overall, the results here provide a dynamical groundwork for interpreting many types of observations, e.g., UV line-profile variability; red-shifted absorption or emission features; enhanced density-squared emission; and X-ray emission, that might be associated with perturbation of hot-star winds by surface magnetic fields.

We present the analysis of UV and optical spectra of M 33 early B-type supergiants. Stellar parameters, metal abundances (Si, Mg, O and N) and mass loss rates are derived from anlyses of optical spectra by means of non-LTE unblanketed unified model atmospheres (fastwind code, Santolaya-Rey, Puls & Herrero 1997). These analyses use wind terminal velocities previously derived from the analysis of UV P-Cygni profiles. Stellar radial gradients of Si, O and Mg are derived for the M 33 disk. Differential abundances of those elements with respect to Galactic counterparts are also presented, along with nitrogen. Finally, the wind momenta of M 33 stars is derived and compared with the one found for Galactic B-type supergiants.

Many late WC type Wolf-Rayet (WR) stars are known to form dust in their winds. While, in the case of episodic dust makers, it is now clear that dust formation takes place due to a colliding wind phenomenon, we still do not know for sure if binarity is the main reason for dust formation in persistent dust makers. This work is to understand, if persistent dust formation is also due to colliding winds in close binary systems. A systematic search for colliding winds is taken up via high resolution spectroscopy of the He i λ1.083μm emission line. Preliminary indications of binarity in many persistent dust makers are seen.

The near-IR spectrum of the periodic dust making WCpd+O4-5 binary WR 140 was monitored to cover the 2001 periastron passage and maximum colliding-wind activity. The He i λ1.083μm emission-line profile showed the appearence of a subpeak on epochs close to periastron passage. The evolution of the subpeak was consistent with the motion of the stars and the colliding wind region. The appearance and evolution of the emission subpeak suggests that the theoretical 1/r dependence of X-ray flux does not hold, so that there is no need to change the values of eccentricity and epoch of periastron passage derived from the RV orbit. JHK spectra show variations of the continuum and and dilution of the emission lines, in agreement with the production and cooling of dust.

We have searched for magnetic signatures in A-type supergiants. The obtained magnetic values for seven of these stars are presented here.

In 2001, we carried out a series of polarimetric observations of the SMC Wolf-Rayet binary HD 5980 near secondary eclipse, in order to study the mass-outflow of the system. Our observations revealed the presence of intense density enhancements along the poles and equatorial plane, that fluctuate on a very short timescale.

We present radiation-driven wind models for Luminous Blue Variables and predictions of their mass-loss rates. A comparison between our theoretical results and observations of AG Car shows that the variable mass loss behaviour of LBVs is due the recombination/ionisation of Fe iv/iii and Fe iii/ii. A present-day mass of 35 M⊙ for AG Car is derived.

Infrared photometry of the WC9vd+B0I spectroscopic binary WR 70 over two decades shows variable dust emission. The variations are relatively slow and show evidence for an underlying process with a period P = 1045 ± 60 d, together with modulation on shorter and longer time-scales.

An overview of a new far-ultraviolet spectral atlas of Wolf-Rayet stars in the Galaxy and the Large and Small Magellanic Clouds is presented.