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The Viith Catalogue of Galactic Wolf–Rayet Stars

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The Viith Catalogue of Galactic Wolf–Rayet Stars New Astronomy Reviews 45 (2001) 135±232 www.elsevier.nl/locate/newar The VIIth catalogue of galactic Wolf±Rayet stars Karel A. van der Hucht Space Research Organization Netherlands, Sorbonnelaan 2, N3584 CA Utrecht, The Netherlands Received 2 August 2000; accepted 11 August 2000 Abstract The VIIth catalogue of galactic Population I Wolf±Rayet stars provides improved coordinates, spectral types and bv photometry of known WR stars and adds 71 new WR stars to the previous WR catalogue. This census of galactic WR stars reaches 227 stars, comprising 127 WN stars, 87 WC stars, 10 WN/WC stars and 3 WO stars. This includes 15 WNL and 11 WCL stars within 30 pc of the Galactic Center. We compile and discuss WR spectral classi®cation, variability, periodicity, binarity, terminal wind velocities, correlation with open clusters and OB associations, and correlation with H I bubbles, H II regions and ring nebulae. Intrinsic colours and absolute visual magnitudes per subtype are re-assessed for a re-determination of optical photometric distances and galactic distribution of WR stars. In the solar neighbourhood we ®nd projected on the galactic plane a surface density of 3.3 WR stars per kpc2 , with a WC/WN number ratio of 1.5, and a WR binary frequency ] (including probable binaries) of 39%. The galactocentric distance (RWR) distribution per subtype shows R WR increasing with ] → decreasing WR subtype, both for the WN and WC subtypes. This RWR distribution allows for the possibility of WNE WCE and WNL→WCL subtype evolution. 2001 Elsevier Science B.V. All rights reserved. Keywords: Catalogs; Galaxy: center; Galaxy: evolution; Galaxy: open clusters and associations: general; Galaxy: solar neighbourhood; Galaxy: structure; Galaxy: stellar content; ISM: H I bubbles; ISM: H II regions; ISM: ring nebulae; Stars: binaries: spectroscopic; Stars: binaries: visual; Stars: circumstellar matter: dust; Stars: distances; Stars: evolution; Stars: fundamental parameters; Stars: masses; Stars: statistics; Stars: winds; Stars: Wolf±Rayet 1. Introduction raphy on the Hot Star Newsletter website, Eenens, 2000), we present here the VIIth Catalogue, giving The ®rst ®ve catalogues of galactic Population I credit to the discoveries since 1981 of 71 new Wolf±Rayet (WR) stars have been presented by, galactic WR stars, and bringing the number of respectively, Campbell (1884), Fleming (1912), known galactic WR stars to 227. Still, the galactic Payne (1930), Roberts (1962), and Smith (1968a). WR census is very much incomplete due to the Those catalogues were discussed in the VIth ubiquitous interstellar extinction in the Milky Way. Catalogue of Galactic Wolf±Rayet Stars by van der Especially at infrared wavelengths, many more WR Hucht et al. (1981, 159 stars) and are listed in Table stars are likely to be discovered in the near future, in 1. Capitalizing on two decades of WR research, the solar neighbourhood (d,2.5 kpc), and towards resulting in over 2000 papers (see the WR bibliog- the Galactic Center (d.8 kpc, Reid, 1993), embed- ded in dense IS/CS clouds, or simply at large E-mail address: [email protected] (K.A. van der Hucht). distances. 1387-6473/01/$ ± see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S1387-6473(00)00112-3 136 K.A. van der Hucht / New Astronomy Reviews 45 (2001) 135 ±232 Table 1 Galactic Population I Wolf±Rayet catalogues WR Author Reference NWR catalogue I Campbell, 1884 Astronomy and Astrophysics 13, 448 55 (North®eld, Minn: Goodsell Observatory) II Fleming, 1912 Harvard College Obs. Ann. 56, 165 108 III Payne, 1930 The Stars of High Luminosity, 92 Harvard Obs. Monographs No. 3, p. 19 IV Roberts, 1962 AJ 67, 79 123 V Smith, 1968a MNRAS 138, 109 127 VI van der Hucht et al., 1981 SSR 28, 227 157 VII van der Hucht, 2001 this paper 227 WR stars are characterized by strong He, N, C and for already more than a century, it is of obvious O emission lines, originating in their hot stellar relevance to gather detailed knowledge about each of winds with terminal velocities in the range v` .400± its potential progenitors. 5000 km s21 , which drive mass loss rates M~ of the In this paper, Section 2 reviews aspects of WR 25 21 order of 10 M( yr . In these WR winds also their stellar classi®cation. Section 3 contains the VIIth free±free mm-to-cm continuum emission originates, Catalogue. Section 4 summarizes WR stars found in which allows mass loss rate determinations, given Local Group Galaxies. Section 5 discusses galactic estimates of wind ionization, clumping rate, and WR binaries. Section 6 lists galactic WR visual distances of the WR stars (Wright and Barlow, 1975; double and multiple stars. Section 7 reviews the Hillier, 1996; Leitherer et al., 1997; Hamann and correlation between galactic WR stars, H I bubbles, Koesterke, 1998; Crowther, 1999). Comprehensive H II regions and ring nebulae. Section 8 presents reviews on the WR phenomenon have been presented interstellar extinction, intrinsic colours and absolute by, e.g., Abbott and Conti (1987), van der Hucht visual magnitudes of galactic WR stars. Section 9 (1992), Maeder and Conti (1994) and in Proc. IAU presents distances and the ensuing galactic distribu- Symp. No. 143 (van der Hucht and Hidayat, 1991), tion of WR stars. in Proc. IAU Symp. No. 163 (van der Hucht and Williams, 1995), in Proc. 33rd LiegeÁ Intern. Astroph. Coll. (Vreux et al., 1996), and in Proc. IAU Symp. 2. Spectral classi®cation No. 193 (van der Hucht et al., 1999). It is important to discover and monitor WR stars, 2.1. Optical spectral classi®cation while each of them is a unique physics laboratory, a tracer of star formation in spiral arms, and a repre- 2.1.1. WN and WC spectral classi®cation sentative of the one but ®nal phase in the evolution Spectral classi®cation of O-type stars and WR of massive stars, to be followed, probably, by a Type stars was reviewed by van der Hucht (1996). We Ib/Ic supernova explosion (e.g., Langer and El Eid, re-iterate here the essentials of WR classi®cation. 1986; Woosley et al., 1993; Maeder and Conti, 1994; In the case of WR stars, one is dealing primarily Langer and Woosley, 1996; Garcõa-Segura et al., with an emission-line spectrum, formed in an opti- 1996; Chevalier and Li, 2000; Kaper and Chere- cally thick stellar wind. A classi®cation system based pashchuk, 2000; Chu, 2001), either single in origin on such emission lines will therefore not be closely or binary (Langer and Heger, 1999; Wellstein and coupled to the stellar parameters of effective tem- Langer, 1999). We cannot hope to understand the perature and luminosity. However, current WR spec- formation of black holes without understanding the tral classi®cation is still based primarily on the late stages of massive star evolution. And where phenomenology of emission line features (UV, opti- statistically the next galactic supernova is overdue cal, IR), which thus de®nes the WR phenomenon. K.A. van der Hucht / New Astronomy Reviews 45 (2001) 135 ±232 137 The commonly used optical WR classi®cation systems of Hiltner and Schild (1966) and Smith criteria are listed in Table 2, and give only a rough (1968a) provided revisions. The Beals and Smith indication of ionization and temperature in WR systems are one-dimensional, de®ning an ionization stellar winds. The table is based on the scheme of sequence only. The Hiltner±Schild system adds a Smith (1968a), as extended further by van der Hucht second dimension by dividing the WN spectra into et al. (1981, VIth Catalogue), Barlow and Hummer sub-sequences A and B, according to the strength (1982), Torres et al. (1986), Conti (1988), Conti et and width of the emission lines: WN-A stars have al. (1990), Smith et al. (1990), Crowther et al. relatively narrow-weak lines and strong continuum, (1995a), Kingsburgh et al. (1995), Smith et al. while WN-B stars have broad-strong emission lines. (1996), Crowther et al. (1998), and Conti (1999). Smith (1968a) did without the WN-A and -B sub- These studies will be reviewed below. sequences while de®ning her robust classi®cation Since the adoption by the IAU (Beals, 1938) of system for both the WN and WC sequences. Walborn the classi®cation system proposed by Beals and (1974), however, returned to the Hiltner±Schild A± Plaskett (1935), recognizing the WN and WC se- B line-width classi®cation for the WN sequence, and quences, it took 30 years before the classi®cation introduced additional WN-A(B), WN-AB, and WN- Table 2 Smith's (1968a) Wolf±Rayet classi®cation scheme, amended by van der Hucht et al. (1981), Barlow and Hummer (1982), Kingsburgh et al. (1995), Crowther et al. (1995a), and Crowther et al. (1998)a WN types Nitrogen emission lines Other emission criteria WN2 N V weak or absent He II strong WN2.5 N V present, N IV absent WN3 N IV < N V ,NIII weak or absent WN4 N IV. N V ,NIII weak or absent WN4.5 N IV . N V ,NIII weak or absent WN5 N III . N IV. N V WN6 N III . NIV ,NV present but weak WN7 N III . NIV ,NIII , He II 4686 He I weak P-Cyg WN8 N III 4 N IV ,NIII . He II 4686 He I strong P-Cyg WN9 N III . N II ,NIV absent He I P-Cyg WN10 N III . NII Balmer lines, He I P-Cyg WN11 N II . He II ,NIII weak or absent Balmer lines, He I P-Cyg WC types Carbon emission lines Other emission criteria WC4 C IV strong, C II weak or absent O V moderate WC5 C III < C IV C III , O V WC6 C III < C IV C III .
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