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19 93Apjs. . .85. .137M the Astrophysical Journal .137M The Astrophysical Journal Supplement Series, 85:137-143, 1993 March © 1993. The American Astronomical Society. All rights reserved. Printed in U.S.A. .85. A NEW SURVEY OF NEBULAE AROUND GALACTIC WOLF-RAYET STARS IN THE NORTHERN SKY 93ApJS. 19 Grant J. Miller Department of Astronomy, San Diego State University, San Diego, CA 92182; and Department of Astronomy, University of Illinois, Urbana, IL 61801 AND You-Hua Chu Department of Astronomy, University of Illinois, Urbana, IL 61801 Received 1992 May 4; accepted 1992 August 6 ABSTRACT Interference filter CCD images have been obtained in Ha and [O m] X5007 for 62 Wolf-Rayet (W-R) stars, representing a complete survey of nebulae around Galactic W-R stars in the northern sky. We find probable new ring nebulae around W-R stars number 113, 116 and 132, and possible new ring nebulae around W-R stars number 133 and 153. All survey images showing nebulosities around W-R stars are presented in this paper. New physical information is derived from the improved images of known ring nebulae. The absence of ring nebulae around most W-R stars is discussed. Subject headings: ISM: general — stars: Wolf-Rayet — surveys 1. INTRODUCTION These different types of nebulae around W-R stars can be used to study a variety of astrophysical problems. The wind- Wolf-Rayet (W-R) stars were first identified spectroscopi- blown bubbles provide a good laboratory to study the dynami- cally by their broad emission fines in a visual survey of the sky cal interaction between stellar winds and the circumstellar or (Wolf & Rayet 1867). Since then it has been understood that interstellar material. The elemental abundances of ejecta-type these broad emission fines are indicative of a thick expanding nebulae can be used to probe the stellar nucleosynthesis yield atmosphere. The expansion velocities implied by the fine (Esteban et al. 1992). The photoionized nebulae can be mod- widths are so high that the outflowing stellar material is gravita- eled to determine the stellar effective temperatures (Rosa & tionally unbound. This mass loss, often called stellar wind, is Mathis 1990). suggested to be driven by radiation pressure (Castor, Abbott, & Klein 1975). W-R stars, typically having mass loss rates of a As studies of W-R ring nebulae grew sophisticated over the -5 -1 last decade, the surveys of ring nebulae in the early 1980s be- few times 10 M0 yr and terminal wind velocities of 1000- 1 came primitive by contrast. All previous surveys used existing 3000 km s" , are the most powerful sources of stellar winds among massive early-type stars (Barlow 1982; Abbott & Conti photographic material taken with broad filters or low spatial resolution. They could have missed many nebulae with low 1987). surface brightness or small angular size. This situation can be Nearly a century after the initial identification of W-R stars, Johnson & Hogg ( 1965) reported the first three ring-shaped greatly improved by a dedicated survey using sensitive modem nebulae around W-R stars, NGC 2359, NGC 6888, and S308, detectors and narrow interference filters. and suggested that the nebulae were shells formed by stellar Therefore, we have started a new CCD survey of nebulae winds sweeping up the ambient interstellar medium. Many around Galactic W-R stars cataloged by van der Hucht et al. more ring nebulae around W-R stars were found in subsequent ( 1981 ). Our objectives are three-fold: to search for new ring systematic searches (e.g., Smith 1967; Chu 1981; Heckathom, nebulae, to obtain high-quality images of known W-R rings, and to examine the interstellar environments of W-R stars. Bruhweiler, & Gull 1982), and a few were individually identi- This paper reports the survey for the northern sky. Section 2 fied (e.g., Johnson 1975; Lortet, Niemela, & Tarsia 1980; describes the observations and presents the results. Section 3 González & Rosado 1984). In Table 1 we compile a fist of reports the probable and possible new W-R rings, and § 4 exam- Galactic W-R stars that have been suggested to be in ring nebulae. ines four known W-R rings. Section 5 discusses the W-R stars that do not have any ring nebula. A summary is given in § 6. Follow-up studies of these nebulae have shown, however, that not all ring nebulae can be described as wind-blown bub- 2. OBSERVATIONS AND RESULTS bles consisting of interstellar material ( see Weaver et al. 1977 ). In some cases, e.g., Ml-67, NGC 6888, and RCW 58, the ring The survey was conducted on the nights of 1991 June 1-7 nebulae contain mostly stellar material, and it is with this cir- and September 28, using the 1 m telescope at Mount Laguna cumstellar material that the stellar winds interact ( Solf & Car- Observatory (MLO). The observations were made with the senty 1982; Smith et al. 1984, 1988; Dufour 1989; Chu 1991 ). f/7.5 secondary and a 3.0X focal reducer, which yielded f/2.5 Still other rings are ionized by the UV flux, but not shaped by for the total system and an image scale of 65'3 mm-1. A winds or ejecta, of the central W-R stars ( Chu & Treffers 1981 ; TI 800 X 800 CCD was used. The total field of view was 13T, Esteban et al. 1990). and the 15 pm pixel size corresponded to 0?98. The full-width 137 © American Astronomical Society • Provided by the NASA Astrophysics Data System .137M 138 MILLER & CHU TABLE 1 .85. Wolf-Rayet Stars and Ring Nebulae WR Name Spec. Nebula WR Catalog HBG CTK Others Type Name 93ApJS. (1) (2) _ÜÜ (5) (6) m (Q) 19 006 HD 50896 WN5 S308 pr 007 HD 56925 WN4 NGC 2359 Pr Oil HD 68273 WC8+09I Gum Nebula 018 HD 89358 WN5 NGC 3199 pr 022 HD 92740 WN7 Carina Nebula po 023 HD 92809 WC6 Anon (MR 26) pr 024 HD 93131 WN7 Carina Nebula 040 HD 96548 WN8 RCW 58 pr 048 HD 113904 WC6+09.5I Anon (0 Mus) pr 052 HD 115473 WC5 Anon (MR 46) pr 055 HD 117688 WN7 RCW 78 pr 075 HD 147419 WN6 RCW 104 pr 085 HD 155603B WN6 RCW 118 po 091 St Sa 1 WN7 RCW 122 093 HD 157504 WC7+07-9 NGC 6357 po 102 LSS 4368 WOl G2.4+1.4 pr 113 HD 168206 WC8+08-9IV S54 116 ST 1 WN8 Anon (ST 1) 124 209 BAG WN8 Ml-67 pr 127 HD 186943 WN4+09.5V S92 128 HD 187282 WN4 Anon (MR 95) pr 130 LS 16 WN8 S98 131 MR 97 WN7 L69.8+1.74 pr 132 HD 190002 WC6 Anon (MR 98) 133 HD 190918 WN4.5+09lb Anon (MR 99) 134 HD 191765 WN6 Anon (MR 100) pr 136 HD 192163 WN6 NGC 6888 pr 139 HD 193576 WN5+06 S109 140 HD 193793 WC7+04-5 S109 152 HD 211564 WN3 S132 153 HD 211853 WN6+0 S132 157 HD 219460 WN4.5 S157-B Col. (1).—van der Hucht et al.’s 1981 catalog number of the W-R star. Col. (2).—Name of the W-R star. Col. (3).—Spectral type of the W-R star, taken from van der Hucht et al. 1988. Col. (4)-—Nebula name. Col. (5).—Ring nebulae tabulated in the Sixth Catalogue of Galactic Wolf-Rayet Stars (van der Hucht et al. 1981). Col. (6).—Ring nebulae identified by Heckathom et al. 1982. “D” for “definite,” and “P” for “probable.” Col. (7).—Ring nebulae recognized by Chu et al. 1983. “pr” for “probable,” and “po” for “possible.” Col. (8).—References for first identification: (a) Johnson & Hogg 1965; (b) Smith 1967; (c) Lortet et al. 1980; (d) Lortet & Testor 1981; (e) Johnson 1975; (f) González & Rosado 1984; (g) this paper; (h) Cohen & Barlow 1975; (i) Crampton 1971. at half maximum (FWHM) of the seeing was typically <2'' take [O m] images for every W-R star. [O m] images were The focal plane was not flat and caused some astigmatism at taken only if nebulosity in Ha+ [N n] had been detected. This the edges of our field of view. Examined closely, the stellar was a safe procedure because no [O m]-bright nebulae were images appear in poor focus. For example, the [O m] image of known to completely lack Ha emission in their vicinity. WR 128 (in Fig. 1 [Plates 5-11]) shows much worse stellar The data reduction used IRAF ( Image Reduction and Analy- images at the NE and SW comers than those near the center. A sis Facility) and followed the standard procedure of bias sub- realistic spatial resolution of these CCD images is ~2", and traction and flat-fielding. Dome flats in each filter were taken can be as bad as 4 "-5" at places. at the end of every night for the flat-fielding calibration. Two filters, centered at the HcxF [N n] and [O m] lines, were Sixty two Galactic W-R stars were observed, representing used in the survey so that we could diagnose the excitation of the complete list down to a declination of -26°. All 62 stars the nebulae if detected. The Ha+[N n] filter had a central were observed at least once in Ha+[N n]; 28 were also ob- wavelength of 6567 Á, a FWHM of 62 Á, and a peak transmis- served in [O in]. The standard exposure time was 600 s, but sion of 60%. This filter was broad enough to include both [N n] ranged from 180 to 1200 s. The observations are summarized XX6548, 6584 lines.
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