Wolf-Rayet star to OB star number ratios in some selected regions in the Galaxy are presented. The variations of the number ratio as a function of location is found to be marginal.

Surveys of the Galaxy for Wolf-Rayet (WR) stars are mostly based on objective prism searches, and are generally complete to only about 13th visual magnitude. We are using direct narrowband and broadband Schmidt plates to survey large areas of the southern Milky Way for WR stars to 17-18th magnitude. We expect to find more than 50 new WR stars. The newly detected stars should be among the most distant and/or reddened known in the Galaxy. The survey is also designed to test the completeness of previous bright WR star surveys, and thus to help settle debates over the Initial Mass Function of the most massive stars. We have now located 13 new WR stars in a 40 square degree region in Carina where 24 WR stars were already known. A 25% incompleteness in detection of WR stars as close as 2-3 kpc is suggested.

We present the results of our search for WR stars in three of M33's most massive giant HII regions, namely NGC 604, NGC 595 and NGC 592. A few of the putative “superluminous” WR stars are shown to be crowded multiple systems. We also compare the WR populations of the most massive GHRs in the Local Group. WN stars are 5 times more numerous on the average than WC stars in these large complexes. The variations among GHR WR populations are discussed in the context of metallicity and age differences.

The Wolf-Rayet (WR) feature at 4650 A is observed in about 10% of the dwarf galaxies with high surface brightness knots. The intensity of the feature implies the presence of tens to thousands of WR stars. Hbeta fluxes imply correspondingly large numbers of O stars. The easily observed intensity ratio WRbump/Hbeta is a measure of the WR/O star numbers.

The metallicity of dwarf galaxies ranges from Z = Zo/30 to Zo/2, or O/H” = log(O/H)+12 = 7.4 to 8.6. WRbump/Hbeta correlates with O/H′ and O/H″ > 7.9 appears to be a necessary condition for the presence of the WR feature. Giant HII regions in ordinary galaxies extend to higher than solar metallicities and, in extreme cases, WR/O ≈ 1 are implied.

The subtypes present in giant HII regions in nearby galaxies appear to be exclusively late type WN and, occasionally, early type WC. Spectra of most BCD galaxies are compatible with a similar population. However, some high metallicity giant HII regions in large galaxies appear to have stronger NIII4640 relative to HeII4686 than occurs in WN subtypes in the Galaxy and the Magellanic Clouds.

The data needed for more detailed analysis of dwarf galaxy observations is collected.

We present synthetic populations of massive stars that constrain the properties of the star formation episodes, predict the occurence, subtype distribution and evolution of WR star populations at solar and SMC metallicities. Instantaneous burst and continuous star formation rates have been considered. Our predictions have been tested on a sample of 17 galaxies. The evolution of the WR stars is qualitatively well reproduced. The IMF slope is flatter on average than in the solar vicinity and is not correlated with the metallicity. The extinction law is in general similar to that of the SMC, independently of metallicity.

The different methods for detecting WR stars in nearby galaxies are reviewed and compared. Each one has its own advantages and drawbacks, and they are complementary rather than competing. Both monochromatic filter imaging and field- or single-object spectroscopy are required for an absolutely safe detection of objects near the limit. The results obtained to-date are shortly reviewed and perspectives are discussed.

The evolution and nucleosynthesis in massive stars are briefly reviewed, and compared with the information derived from SN1987A in LMC. Most of the theoretical models agree with the measured abundances and they can be used in models of galactic evolution.

Models of chemical evolution of galaxies are presented and the role of massive stars in their evolution is discussed.

Finally, the role of Wolf-Rayet stars in galactic evolution is studied, particularly from the point of view of their final fate. It is shown that, if Wolf-Rayet were the progenitors of type Ib supernovae, the Galactic chemical evolution would not change substantially with respect to the case of white dwarfs being the progenitors of type Ib supernovae. However, the predicted frequency of type Ib supernovae in the Wolf- Rayet case would be far too low in comparison with observational estimates.

The WN5 star HD 50896 lies in the same sightline as the open cluster Cr 121. In order to investigate the possibility of cluster membership, we observed the interstellar Na D lines in the spectra of HD 50896 (=EZ CMa, =WR6) and stars in its neighbourhood (on the plane of the sky) at high spectral resolution (R=80,000 and 105,000). The observations were obtained with the 1.4-m coudé auxiliary telescope and the coudé echelle spectrograph of the European Southern Observatory.

From the strengths and velocity structure of the interstellar features it is immediately clear that HD 50896 is not a member of Cr 121; rather, it is a background object. A comparison with spectra of other background stars shows that the line of sight towards HD 50896 is very similar to those of HD 51854 (B1 V) and HD 50562 (B3 III). From intermediate-band and Hβ photometry the distances to these two B stars are 1.75 kpc and 1.95 kpc, respectively. The most red-shifted absorption component in the spectrum of HD 50896 is displaced only slightly more than that of HD 51854, and a little less than that of HD 50562. We conclude that the the most probable distance to HD 50896 is 1.8 kpc.

Recent observations of Wolf-Rayet stars by Massey (1984) and Torres-Dodgen and Massey (1988) have yielded high quality, absolutely calibrated spectra of nearly all known Wolf- Rayet objects. These observations also indicate that discontinuities, or “jumps”, are present in the continuum spectra of some Wolf-Rayet stars. Such continuum jumps are predicted by the current theoretical models of Wolf-Rayet atmospheres. In general, these models provide good fits to the observed spectra of Wolf-Rayet stars. The models also indicate that, between jumps, the intrinsic continuum can be closely approximated by a power law in wavelength. In this case, we have the following relation between the intrinsic colors: where and Z3645 is the strength of the He II (η = 4) jump at 3645 Å in mags. This relation holds because the central wavelength of the u filter (λu = 3650 Å) is nearly coincident with that of the He II jump. In addition, models of WN stars with helium-dominated atmospheres predict a correlation between D3645 and (6 - v)o:

From the m12 – m25vs. spectral type diagram (see for example: Habing, 1987, Figure 5), it can be seen that there are no early M giant stars with m12 – m25 > 0.7. On the other hand all early M stars with m12 – m25 > 0.7 are M supergiants. These early type M supergiants have typically infrared excesses at 12 μm in the range of 20 to 170 times higher than their photosperic fluxes.

It is generally accepted that mass loss and overshooting are the two main processes that play important roles in the formation of Wolf-Rayet stars (Chiosi & Maeder, 1986). Such mechanisms modify the interior of a star. We cannot, however, disregard the possibility that there are external factors, which can influence the formation and evolution of Wolf-Rayet stars.

The stellar content of this stellar association, related to the supernova remnant N 157B = SNR 0538-691, was up to now unknown, except for three Wolf-Rayet stars and a few red supergiant candidates. A thorough study based on UBV photometry, spectra of 95 stars and nebular spectra will be described elsewhere (see also Schild et al. in these Proceedings).The outstanding properties of this region are :

A. the presence of a shell-shaped supernova, which dominates the thermal radio continuum. It is relatively faint in [OUI], strong in [Sil], [Fe 4658] and He II 4686. The expansion velocity reported by Chu and Kennicutt (1988) is 180 km/s. In addition, many extensions and filaments are found all over a wide area, and possibly there has been more than one supernova responsible.

Are there very massive stars (VMSs) of mass greater than 100 M⊙? This question constitutes one of the fundamental problems of astrophysics. We present observational evidence against the existence of such stars in the Magellanic Clouds. The multiplicity of VMSs has several important consequences for astrophysics. If VMSs do not exist we need to revise our ideas about the formation and evolution of stars.

We have discovered the only WC9 star in the Large Magellanic Cloud on the basis of observations made at several ESO telescopes, especially NTT. The latest Wolf-Rayet stars of the carbon sequence so far observed in the LMC are WC5-6. The lack of late type WC stars is understood in terms of an abundance effect, according to the models of Maeder. Our observations therefore pose a new observational challenge to the theory of the evolution of massive stars.

We observed several OB associations of M31 (OB 33, 42, 59 and 69) and of M33 (OB 4 and 137) in UBVI and through interference filters centered on lines of HeII and CIII, as well as a narrow continuum comparison filter at 4749 å (Armandroff & Massey, 1985). The observations were made at the CFH 3.6m telescope with a RCA-CCD. The stellar photometry was obtained using DAOPHOT.

We present new optical spectroscopy obtained with the Faint Object Spectrograph on the William Herschel Telescope of 6 WR stars in the local group galaxy M33 and 6 WR stars in M31. These spectra cover the wavelength range λλ3500-9750 å. We confirm the previous WR classifications of the M31 stars. In the M33 sample, 4 stars are classified as WC4-5, one is confirmed as WN-WCE and a further WN-WCE star has been identified. The widths of the CIV λ5800 emission differ by a factor of three amongst the M33 WC4-5 sample, spanning values exhibited by galactic WC8-WC4 stars and confirming the existence of narrow-lined WC4-5 stars in M33. We find that the M33 WCE line widths appear to be correlated with galactocentric distance and loosely connected to ambient metallicity. The narrowest lined WCE star MC 53 is in an unusually high (above solar) metallicity region. Further observations of a larger sample of M33 stars are required to confirm these preliminary results.

An imaging and spectroscopic survey for WR stars in IC 4662 revealed the presence of a cluster consisting of a mix of about 10 WN 7-8 and WC 5 stars plus the equivalent of some 5 OV stars at a projected distance of about 100 pc from the cluster core of the bright central H ii complex.