1 Introduction

The first systematic search for Wolf-Rayet (${\rm W}-{\rm R}$) stars in the Large Magellanic Cloud (LMC) was carried out by Westerlund & Rodgers (1959). Their observational material consisted of 40 blue-sensitive plates taken with an objective prism attached to the 50 cm Schmidt telescope, at the Uppsala Southern Station of the Mount Stromlo Observatory. The reciprocal dispersion of the spectra was 380 Å mm^-1 at H$\gamma$. This search yielded 50 objects of which 36 were in common with the Harvard spectral surveys (Cannon 1924, 1933; Payne 1930).

Later on, Westerlund & Smith (1964) repeated the survey of the same field of about 100 square degrees and published a list of 58 ${\rm W}-{\rm R}$ stars. These were then considered to represent the quasi totality of the LMC ${\rm W}-{\rm R}$population. In this first catalogue the stars were roughly classified C (carbon-type), N (nitrogen-type) or W+O (binaries); the more accurate spectral types previously assigned to 15 of them by Feast et al. (1960) being however given. The article included a study of the LMC ${\rm W}-{\rm R}$ star surface distribution as well as a discussion of some fundamental physical parameters of the stars, such as luminosity, mass and age. For about 65% of these ${\rm W}-{\rm R}$ stars, spectral types were subsequently presented by Smith (1968b) who also derived mean absolute magnitudes and intrinsic colours for the stars in the various WN and WC sub-classes.

However, further discoveries indicated that the census of the LMC ${\rm W}-{\rm R}$ population was still not complete. In his catalogue of 1272 proven or probable LMC member stars, Sanduleak (1969) denoted for instance as "WR'' 14 objects which were not listed by Westerlund & Smith (1964).

The careful inspection of plates obtained with the ESO 40 cm Objective Prism Astrograph (GPO) - primarily secured for radial velocity measurements - allowed Fehrenbach et al. (1976) to recognize all the stars identified by Westerlund & Smith, to confirm 12 of the 14 Sanduleak ${\rm W}-{\rm R}$ candidates and to discover 6 new ${\rm W}-{\rm R}$ stars. This second catalogue of LMC ${\rm W}-{\rm R}$ stars included 76 classified objects, 29 of which received a spectral type for the first time. A discrimination between the WN3, WN4 and WN5 sub-classes being nevertheless impossible from the objective prism plates, in the nitrogen sequence, most of the stars were only classified WN3-5 by Fehrenbach et al. (1976).

Walborn (1977) added a new member to the LMC ${\rm W}-{\rm R}$ population by finding that the star Sk-67$^\circ$18 - classified Of by Sanduleak (1969) and O9f by Ardeberg et al. (1972) - has a companion of type WN5-6; and Melnick (1978) increased to 83 the number of known ${\rm W}-{\rm R}$ stars in the LMC with the detection of 6 additional ${\rm W}-{\rm R}$ stars near the core of the 30 Doradus nebula.

Finally, Azzopardi & Breysacher (1979, 1980), as a result of a new systematic search for ${\rm W}-{\rm R}$ stars in the LMC with the ESO 40 cm GPO, using an interference filter centered at $\lambda$4650, were able to identify 17 new such objects in this galaxy. The LMC area covered by this survey (23 partially overlapping fields, each 85 arcmin in diameter) is shown in Fig. 1 of the paper by Azzopardi & Breysacher (1980). The third catalogue of LMC ${\rm W}-{\rm R}$stars was published by Breysacher in 1981. It provided accurate spectral types for all the 100 ${\rm W}-{\rm R}$ stars then known in this galaxy. For 92% of the objects the classification was based on slit spectrograms obtained at the 3.6 m and 1.5 m ESO telescopes by the author.

Since the publication of the Breysacher's catalogue, the number of ${\rm W}-{\rm R}$stars identified in the LMC has again increased. Additional ${\rm W}-{\rm R}$ stars have been discovered in the field either as the result of new systematic searches of deep objective-prism plates covering a larger area (Morgan & Good 1985, 1990), or by serendipity (Cowley et al. 1984; Azzopardi & Breysacher 1985; Morgan & Good 1987; Morgan 1999). Others were detected or resolved in compact clusters/HII regions (Weigelt & Baier 1985; Moffat et al. 1987; Heydari-Malayeri et al. 1990; Testor & Schild 1990; Schild & Testor 1992; Heydari-Malayeri et al. 1993; Walborn et al. 1995). The recognition of the genuine or borderline ${\rm W}-{\rm R}$ nature of some already known stars (Conti & Garmany 1983; Bohannan & Walborn 1989; Walborn & Blades 1997) also contributed to the growth of the LMC ${\rm W}-{\rm R}$ population.

The fact that for these objects, neither a complete set of finding charts nor equatorial coordinates with the accuracy required for observations with modern ground-based telescopes or spacecraft exist, has been an incentive for the preparation of this updated fourth catalogue of ${\rm W}-{\rm R}$ stars in the LMC, which now contains 134 objects.

  

Figure 1: a) Spectrograms of ${\rm W}-{\rm R}$ stars in the LMC: the WN4b star BAT99-26 (Brey 20), and the peculiar WN4b/WCE star BAT99-36 (Brey 29) which shows an unusual strong CIV $\lambda 5801$-12 emission line for a WN-type star

 

Figure 1: b) Spectrograms of ${\rm W}-{\rm R}$ stars in the LMC: the WN6(h) star BAT99-32 (Brey 26), and the WN9h star BAT99-76 (Brey 64)

 

Figure 1: c) Spectrograms of ${\rm W}-{\rm R}$ stars in the LMC: the WC4 star BAT99-9 (Brey 7), and the WO3 star BAT99-123 (Brey 93)