The numbers, space distribution and energy distributions of Wolf-Rayet stars are reviewed. The numbers of known WR stars in the Galaxy, the LMC and the SMC are 189, 114, and 10, respectively. Distances and galactic distributions determined by various authors are compared and consequences for with evolutionary studies are discussed. Finally energy distributions from the optical to the radio regime are reviewed.

Differences in the evolution of massive single stars and components of massive close binary systems are investigated. While for stars above the red supergiant luminosity limit, single star and case B primary evolution merge into a single scenario, large differences for less massive stars are demonstrated to occur at the example of MZAMS = 40M⊙, concerning the various WR subtypes, the nucleosynthesis yields, and the supernova stage.

Wolf-Rayet (WR) stars and their possible precursors, the Luminous Blue Variables (LBVs), are often surrounded by ring nebulae. It is believed that these nebulae are formed by the action of the stellar wind, matter being ejected from the star in the past, or a combination of these two processes. The various research applications of LBV and WR nebulae are reviewed with regard to the information they provide on the properties of the central stars. They are very useful probes of stellar evolution since the details of the previous evolutionary phases of the central stars are contained in the nebulae. In particular, abundance studies can provide insights into the chemical processes operating during the precursor phases. The nebulae can also be used as probes of the far-UV ionizing flux distribution of the central WR stars by comparing the observed levels of nebular ionization with those produced with non-LTE WR model flux distributions. Comparisons of stellar effective temperatures and luminosities derived using this technique with those determined by modelling stellar emission lines can identify deficiencies such as the lack of line-blanketing in WR model atmospheres. Very hot WR stars can also be identified by searching for nebular HeII emission. Studies of bipolar structures in LBV and WR nebulae provide valuable clues on wind asymmetries in the central stars.

Multi-wavelength investigations of the interstellar environment around WR stars using IUE, IRAS, and optical data have led to the discovery of extended shells of gas and dust 50-100 pc in diameter in the lines of sight to the WR stars HD 50896, HD 96548, and HD 192163. These three stars share several common characteristics: (1) associated N- and He-enriched ring nebula, (2) spectral class WN5-8, and (3) spectral and photometric variability. Surveys of IUE spectra and IRAS images reveal a few additional candidates for such extended shells. Although positional coincidences cannot be excluded, possible origins of these extended shells include interstellar bubbles formed by stellar winds, non-conservative mass loss from binary systems, and supernova remnants. Current data suggest these three stars may be in a post X-ray binary stage, representing the second WR phase of massive binary star evolution. The discovery of extended shells of gas and dust possibly related to WR stars is important because the search for stars in the second WR phase, after the supernova of the primary, has been quite elusive. However, the observational evidence and available theoretical models for post-supernova massive binary star evolution and subsequent non-conservative mass transfer are not yet sufficient to firmly identify the origins of these extended shells.

We present diffraction-limited speckle-masking observations of the central object HD 97950 in the giant HII region and star cluster NGC 3603. Twenty-eight stellar components have been detected in the 6.″3 x 6.″3 field from our reconstructed images. Four different filter combinations were used for the selection of distinct spectral regions comprising Hα emission, the main Wolf-Rayet and Of-type emission lines, and two continuum bands. Stellar components having WN-type characteristics have been found. A color-magnitude diagram has been constructed. Isochrone fits yield a cluster age of about 3.2 Myr, which is in accordance with the time-scale of Wolf-Rayet star evolution.

The unsatisfactory present state of the classification system for WN stars is summarised and the three dimensions of a new system are presented and justified.

The ultraviolet spectra of 94 WR stars obtained from Vilspa IUE archive are used here to look for classification criteria in the UV region alone. We have tried to select as many single and SB1 type stars as possible in the Galaxy and the LMC to get the complete, flux-calibrated spectra between 1150 and 3250 Å. Altogether 56 (34 of WN and 22 of WC type) stars in the Galaxy and 38 (31 of WN and 7 of WC type) in the LMC were found, for which at least single SWP and LWR (or LWP) low resolution images are accessible – note that this is about one third of the number of known galactic and LMC WR stars. The set of stars we study is representative according to spectral subtype and brightness (it is almost complete to 12 magnitude for galactic stars). See Niedzielski & Rochowicz (1994) for the list of program stars and associated IUE images as well as for the details of reduction.

To look for classification criteria of WR stars in the ultraviolet region we will use the equivalent width (EW) and line width (FWHM) data.

Preliminary results of spectroscopic monitoring of the WN5-B star WR1 (HD 4004) are presented, showing evidence for a 0d.775 period.

CCD spectra for the unusual Wolf-Rayet star EZ CMa (WR6) are presented. The analysis of the profile changes of HeII lines shows a correlation between the gravity center of the line and the skewness (Robert et al. 1992). The fourth moment (kurtosis) changes with phase and looks epoch independent. These observable effects could be treated as manifestations of wind variability rather than consequence of orbital motion.

Several suggestion have been put forward to explain the 3.d766 periodicity of EZ CMa (WR6): (i) WR+c system; (ii) rotating single WR star; (iii) pulsations (non—radial (NRP) or radial) with frequency reduced by some kind of filtering in the wind. In this paper, we report on a photometric investigation based on a long continuous observing run, in an attempt to verify whether EZ CMa does in fact show a unique periodicity. In particular, this work was motivated by the claim by Gosset & Vreux (1987), based on the data from Lamontagne et al. (1986, hereafter LML), that EZ CMa may have a shorter period besides the one at 3.d766, a frequency close to but not equal to the third harmonic of the 3.d766 period.

A periodogram analysis of the radial velocities and absorption line strengths from IUE spectra of HD 50896 show evidence of the 3.766 day period usually associated with this star. The dominant line variations occur on time scales of ∼ 1 day but may be interpreted as higher order harmonics of the 3.766 day period.

A new powerful mathematical tool for the analysis of structures on spectral lines is presented: wavelet analysis. Applied to variable Wolf-Rayet emission lines, it allows one to extract efficiently and in an objective way, individual sub-structures and compare some of their physical properties: integrated flux f, velocity dispersion σv, projected velocity v and acceleration a.

We report a first result from an extensive observing campaign for the WN8 star WR66 (HD 134877). We obtained 219 photometric observations of WR66 in a standard broadband V-filter during 61 nights, distributed in a T = 83d interval. Details of observations and data reduction can be found in Antokhin et al. (1994). The power spectra of WR66-C1, WR66-C2 and C2-C1 are shown in Fig.1. Both the WR66-C1 and WR66-C2 spectra clearly show high frequency components. The overall structure of the peaks is evidently determined by 1-day aliasing. The highest peak in both spectra has frequency v1 = 6.828 d−1 (period P = 3h.51). Inspection of the power spectra shows that C1 is a low-amplitude variable, but luckily at low frequencies only. We conclude that WR66 is significantly variable with a period of 3h.5. A phase plot of the data (WR-C2 and C2-C1) with this frequency is shown in Fig.2. Plausible scenarios which could potentially account for the observed variability are: (i) non-radial pulsations (NRP); (ii) rotational light-modulation by spots or (magnetic) loops at the stellar surface; (iii) spiral-in system (WR+c), like the massive X-ray binary Cyg X-3 (van Kerkwijk 1993).