We have completed a survey of the closest giant spiral galaxy beyond our own for Wolf-Rayet stars, using narrow band imaging techniques (cf. Moffat and Shara 1983, Ap. J., 273, 544). About 90% of the main body of M31 has been thoroughly searched to B ≅ 21.5 (MB ≅ −3.5) to a level of emission line equivalent width We(HeII 4686 A) ≳ 60 A. We do not expect interstellar extinction to be a limiting factor in the detection of WR stars, except possibly in the localized neighborhoods of massive HII regions. The mean extinction for stars in the disk is estimated to be AB ≲ 0.9 mag. Although some weak-line WN stars will have escaped detection, the survey should be complete for WC stars.

30 Dor in the LMC and NGC 3603 in the Galaxy are the nearest visible examples of similar giant (or even more massive supergiant) HII regions being studied in other more distant galaxies, where spatial resolution is a much more serious problem. Hence, understanding 30 Dor and NGC 3603 may provide important clues to understanding extragalactic giant HII regions in general.

We present coordinated spectroscopic and photometric observations obtained during the present bright phase of the luminous variable star S Dor in the LMC. High resolution spectrograms in the satellite UV and in the visual range were obtained with IUE and with CASPEC (attached to the ESO 3.6-m telescope), respectively. Moreover, photometric UBVRIJHKL observations were carried out.

Comparing the observed and theoretical HR diagram for massive stars, it is concluded that at least 34 % of the stars within 2.5 kpc from the sun with initial ZAMS mass larger than 35 MO have not yet been detected. It is argued that the number of core helium burning pop I WR stars within 2.5 kpc from the sun may be as low as 26. If the progenitors of WR stars have initial ZAMS masses larger than 35 MO, one then concludes that the observed number ratio (core helium burning pop I WR stars) / (WR progenitors) within 2.5 kpc from the sun ranges between 0.05 and 0.09.

It is well-known that the massive star population exerts a disproportionately great influence on the environment within a galaxy, especially through the ejection of chemically enriched material and the input of energy into the interstellar medium. In order to more fully understand the structure and evolution of galaxies, it is important to determine how the massive star content of a galaxy changes with Hubble type, galaxian luminosity and metallicity. Conversely, if our goal is to understand the evolution of massive stars, it is helpful to observe them in a variety of environments, as stellar wind properties should depend on chemical abundances. We are involved in a long-term project to survey the massive star population in a diverse sample of nearby galaxies. Unfortunately, it is extremely difficult to isolate a sample of relatively unevolved massive stars in an external galaxy, since the colors and absolute visual magnitudes of a 20 MO and 100 MO star are nearly identical, and can be further confused by differential internal extinction. Wolf-Rayet (WR) stars, however, are relatively easy to detect due to their strong emission-line spectra and high luminosities. Since WR stars are known to have evolved from 0 stars and because their space distribution in the solar neighborhood is identical to that of the most massive 0 stars, we have decided to use WR stars as tracers of the massive star population in nearby galaxies.

IRAS PSC. LRS. and CPC observations of Wolf-Rayet stars are used as diagnostics of hot circumstellar dust shells, cool dust in WR ring nebulae, the Ne/He abundance ratio, and the interstellar extinction. In two cases the IR energy distributions are indicative of a WR planetary nucleus status rather than a Population-I WR status.

We present an atlas of high dispersion spectra of 24 of the brightest peculiar emission-line stars of the Magellanic Clouds.

Our spectra cover the wavelength range from 3600 to 4900 Å. They have been obtained from 1970 to 1984 with the coudé spectrograph of the ESO 1.52 m telescope at La Silla, Chile. The spectral resolution is 0.4 Å for most of the spectra and 0.2 Å for the very brightest stars. Up to 11 spectra are available for one star. In addition, we have done UBVRIJHK(LM) photometry at several epochs of all stars of our sample.

We analysed highly resolved CASPEC spectra with a high S/N-ratio of the peculiar emission-line B-star MWC 300, which is surrounded by a circumstellar dust shell. These high quality spectra enabled us to study the photospheric spectrum of MWC 300. By comparing the absorption spectrum of MWC 300 with the ones of early B supergiants we found a close resemblance with the B1 hypergiant HD 169454. We also found luminosity sensitive fluorescence lines of Fe III 115 and 117 both in MWC 300 and in the most luminous stars of our sample, confirming the hypergiant nature of MWC 300. We estimated an absolute visual magnitude Mv = −8 for MWC 300. Assuming a bolometric correction of B.C. = −1.5 mag we derive Mbol = −9.5. This shows that MWC 300 is very similar to the B e supergiants of the Magellanic Clouds. From its absolute magnitude we derive a distance of z = 560 pc from the galactic plane. It is conjectured that MWC 300 is a runaway hypergiant, released via a supernova explosion in a very massive binary star system.

The very peculiar object Eta Car is one of the best laboratory for the study of those physical processes - such as mass loss, superionization, dust condensation, wind interaction with the i.s. medium - that presently are of great astrophysical interest, especially for the study of the most luminous stars. For its light history and high luminosity Eta Car may also be considered as the galactic counterpart of the Hubble-Sandage variables. Eta Car is one of the rare astrophysical objects with evidence of dust condensation from ejected stellar matter (Andriesse et al. 78) On the other side the star is also producing a strong, hard X-ray flux (Chlebowski et al. 1984), and the problem is whether there is any physical reason to have these two quite different processes in the same stellar environment. In any case rather extreme physical conditions are required which cannot be verified in a uniformly, spherically symmetric atmospheric enevelope. Andriesse et al. in fact suggested the presence of strong inhomogeneities, such as filaments, possibly related to the presence of a strong magnetic field. This may also explain the X-ray emission. In the following we shall present new optical and UV observations of Eta Car and its small nebula with the aim of clearfying the physical nature of its wind.

Using stellar evolution models of two different kinds, one with convective cores determined by the Schwarzschild criterion, one with enlarged convective cores, we discuss the masses of the WR stars in a number of double-lined WR binaries. For the main group of systems the mass of the WR-star is between 10 and 20 M.

The upper limt of stellar luminosity in the Hertzsprung-Russell diagram is a line running approximately from (log Teff; log (L/L⊙) = (4.5; 6.3) via (4.0; 5.74) to (3.5; 5.7) (Humphreys and Davidson, 1979; Humpreys, 1983).

Investigations of the 1.0–2.5 μm spectra of high luminosity p Cygni stars reveal the presence of several new emission features. All stars measured show emission in the Brackett and Paschen lines of H I, but the emission strengths of He I 1.083, 1.700, and 2.058 μm relative to the H I lines show large variations. Emission lines of [Fe II] are seen at 1.257 and 1.644 μm in several stars and are particularly strong in HR Car. An interesting subset of these stars show the first-overtone CO bands in emission. The presence of this molecular component associated with hot P Cygni stars has not been inferred from previous optical or UV spectroscopy.

HD 50896 has become one of the most promising candidate WR+collapsar systems (Moffat 1982) exhibiting optical light, RV and polarisation variations with a 3d.763 period (cf Firmani et al. 1980) yet direct evidence for its postulated n.s. component is lacking. UV spectra of analogous OB X-ray binaries show P-Cygni profile changes as a function of binary phase which are well understood in terms of anisotropic wind ionisation caused by X-ray emission from the accreting n.s. - the Hatchett & McCray (1976) effect. Observations of such UV variability in WR+c candidates with a clear phase dependence would thus provide good evidence for any n.s. companion. To this end we have obtained IUE spectra of HD 50896 in sequential NASA/VILSPA shifts over 6 consecutive days in 1983, together with complementary IUE data secured at various epochs during 1978–82, to search for the Hatchett & McCray effect in this star.

Although considerable progress has been made in understanding Wolf-Rayet (WR) stars, the basic mechanisms for producing the nitrogen and carbon emission lines, which characterize a WR's spectrum, are unknown. To determine the mechanisms giving rise to these lines we are currently studying the formation of N and C emission lines in the WN5 star HD 50896.

We carried out a spectroscopic and photometric study of the 8 presently known B[e] -stars of the Magellanic Clouds (MC), i. e. R4 and R50 of the SMC, R66, R82, R126, Hen S12, Hen S22 and Hen S134 of the LMC. These stars are characterized by the following typical properties: a) strong Balmer emission lines, frequently with P Cygni profiles, b) permitted and forbidden emission lines predominantly of Fe II, [Fe II], [O I] etc., c) strong IR excess due to circumstellar dust. Photospheric absorption lines are usually weak or even not detectable.

The star SK 80 in the SMC is classified as 07Iaf by Walborn (1976) who notes that it is the only confirmed Of star in that Galaxy known to date. A knowledge of the mass loss properties of OB stars in the Magellanic Clouds is of interest because of the recent evidence that such stars show reduced mass loss properties than their galactic counterparts (Hutchings 1980) and for Of stars because of the possible link between such stars and Pop I transition WNL stars (Conti 1976).

We have secured HIRES IUE and optical spectra of SK 80 and have attempted to derive the mass loss rate from these data.

Stellar coalescence is suggested as a possible mechanism for doubling the upper stellar mass limit from ∼100M⊙ to ∼200M⊙ in a moderately dense cluster of a few hundred young massive stars (∼105 M⊙ pc−3). The merger will be between the two components of the dominant central tight binary formed in the core of the cluster by the N-body evolution. This process may occur in some giant extragalactic HII regions.

Following the excessive mass loss rates we derived in a previous analysis of the FeII emission and absorption lines of some luminous Magellanic Clouds stars, assuming the two components formed in the same region (Muratorio et al., 1984), we again analysed the FeII data using the same method (Muratorio, 1985), but taking into account the presence of high velocity winds detected in some stars (R66, R126) by the study of the high dispersion IUE spectra (Stahl et al., 1983; Zickgraf et al., 1985).

At first it may be surprising that mass loss, overshooting and mixing, which are indeed very different physical processes, have similar consequences on stellar evolution. These various processes may increase the Main-Sequence (MS) lifetime, extend the width of the MS, bring CNO-processed materials to stellar surfaces and, in extreme cases, lead to quasi-homogeneous evolution. The physical reason of this similarity is that these processes increase the relative mass fraction of the stellar cores. Thus we understand that, on the basis of their evolutionary consequences, it may not be easy to disentangle the contributions of mass loss, overshooting and mixing processes. The present status of our knowledge on these effects, which appear to have major consequences on the evolution of massive stars, is now examined in detail.