1 Instituto Argentino de Radioastronomía, Argentina

1. Atomic and molecular gas in the environs of the ring nebula RCW 78C. Cappa1,2, M. Rubio3, M.C. Martin1 and N. McClure-Griffiths4 1 Instituto Argentino de Radioastronomía, Argentina 2 Facultad de Ciencias Astronómicas y Geofísicas, UNLP, La Plata, Argentina 3 Departamento de Astronomía, Universidad de Chile, Chile 4 Australia Telescope Compact Array, Australia Valparaiso, Chile, October 2004

2. Introduction Wolf-Rayet stars: Mdot~ 10-5 Mo/yr (van der Hucht 2001) Terminal velocities: Vw = 1000-3000 km/s (Prinja et al. 1997)  contribute to the shaping and the chemical enrichment of the ISM  create interstellar bubbles (IB) RCW58 (E) • Interstellar bubbles are detected as: • Optical ring nebulae(e.g. Chu et al. 1982, Lozinskaya 1982; Heckathorn et al. 1982; Marston et al. 1994a,b) • Different formation mechanisms (Chu 1991): mass lost by the star (E type) or swept-up material (UV radiation [Rstype], Stellar winds [W type]) • 25-30 % of the 227 Galactic WR stars are surrounded by ring nebulae NGC6888 (W+E)

3. Introduction Anon(WR101), VLA, 1465 MHz, 38 arcsec • Interstellar bubbles are detected as: • Thermal radio continuum shells (e.g. Goss & Lozinskaya 1995, Cappa et al. 2002) • Cavities and expanding shells in the HI 21 cm line emission distribution (Cappa et al. 2003 and references therein) • Infrared shells (Marston 1991; Mathis et al. 1992) • X-rays sources(Bochkarev et al. 1987; Chu et al. 2004) • Molecular lines Anon(WR23), HI emission, 2.5 arcmin

4. Molecular observations towards ring nebulae • Molecular material was found to be related to some WR ring nebulae: - Anon (WR16) (Marston et al. 1999) - NGC3199 (Marston 2001) - NGC2359 (Rizzo et al 2001, Cappa, Rubio and Goss 2001) - Anon (WR134) and NGC 6888 (Rizzo et al. 2001) - Anon(WR16), nebula around WR 103 (Duronea and Arnal 2004) • Origin of the molecular gas: - NGC 3199: stellar wind material (Marston 2001) - All the other nebulae: interstellar matter - NGC2359: interstellar matter, PDR (Cappa et al. 2001), shock fronts are also present (Rizzo et al. 2001) NGC2359 • Other molecules detected in NGC2359: - H2 lines (St-Louis et al. 1999) - CS, HCO+, CN, HCN (Rizzo et al. 2001b) CO observations(black contours): SEST, 22 arcsec) Velocity: 54 km/s HI data (white contours): VLA, 45 arcsec Studies of molecular material associated with ring nebulae are needed to investigate the physical state of the gas, their kinematics and energetics.

5. The ring nebula RCW 78 around WR 55  Here, we present CO and HI observations in the environs of the ring nebula RCW 78 associated with the WR star HD 117688. WR 55 = HD 117688 = MR 49 • (l,b) = (307.8°,+0.16°), (a,d)2000 = (13h 33m 30.1S, -62° 19’ 1.2’’) • Spectral type: WN7 (van der Hucht 2001) • Distance: 5.5 kpc (Conti & Vacca 1990) 6.0 kpc (van der Hucht 2001) • Terminal wind velocity: 1100 km/s (Hamann et al. 1995) WR 55 Ha image (Treffers et al. 1983)

6. The ring nebula RCW 78 around WR 55 RCW 78 • Optical appearance: Brightest region to the W and fainter regions to the E • RS-type ring nebula, no shell structure (Chu & Treffers 1981). • Size: 35 arcmin in diameter • Brightest region to the west: 10 arcmin in size • Kinematics from Ha line: from –44 km/s near the star to –53 km/s 7 arcmin north of the star. • Kinematical distance: 5 kpc (Brand & Blitz 1993) -53 km/s -44 km/s HD92206 WR 55 Ha image (Treffers et al. 1983)

7. Database • CO data: SEST telescope at La Silla, January 2002, March 2003 • 12CO(1-0) at 115 GHz: - HPBW = 44 arcsec - velocity resolution = 0.43 km/s after smoothing - rms noise = 0.20 K (Tmb) • 12CO(2-1) at 230 GHz: - HPBW = 22 arcsec - velocity resolution = 0.32 km/s after smoothing - rms noise = 0.15 K (Tmb) • Both lines acquired simultaneously in the position-switching mode on a grid spacing 45 arcsec • HI data: Southern Galactic Plane Survey (SGPS) (McClure-Griffiths et al. 2000), obtained with the ATCA and Parkes radiotelescopes • Synthesized beam = 2.4 x 2.1 arc min, Velocity resolution = 1.6 km/s, RMS noise: 1.5 K_Tb • Radio continuum at 4.9 GHz from the Parkes-MIT-NRAO Survey (PMN) (Griffith et al. 1993) • Angular resolution: 5 arcmin, rms noise: 8 mJy/b

8. RCW 78 in CO emission • Molecular components with velocities in the range –65 to -8 km/s are detected. • Sample of CO profiles: 13h33m15.0s, -62o17’30” 13h33m36.0s, -62o16’01” 13h33m21.0s, -62o22’01” CO(1-0) CO(2-1)

9. RCW 78 in CO emission  Mean Tmb [-48.7,-44.7] km/s  Mean Tmb [-54.4,-53.1] km/s  Mean Tmb [-42.5,-39.4] km/s  Mean Tmb [-53.1,-49.1] km/s CO contour lines: 1 to 7 K in steps of 1 K

10. RCW 78 in CO emission  Mean Tmb [-38.5,-36.7] km/s Some results • CO emission within the range –54 to –33 km/s is associated with the ring nebula. • CO velocities agree with Ha velocities. • The slight velocity gradient within the range –54 to –40 km/s is similar to the one observed for the ionized gas. • Molecular mass = about 3 x 104 Mo  Mean Tmb [-35.8,-32.7] km/s CO contour lines: 1 to 7 K in steps of 1 K

11. RCW 78 in the HI line emission distribution Some results: • HI cavity and shell detected within the velocity range -54 to –36 km/s • HI emission borders the NE, E and SE sections of RCW 78, the agreement is not so clear to the W • HI velocties agrees with CO and Ha velocities • Systemic velocity: -47 km/s • Expansion velocity: about 10 km/s • HI shell: neutral atomic counterpart of the optical nebula • Radius of the HI bubble: 15.5 arcmin or 26 pc (at d = 6 kpc) • Dynamical age: 1.4 x 106 yr • Neutral swept-up mass: 1800 Mo Colour scale: 82 to 110 K HI emission [-49,-40] km/s WR 55

12. RCW 78 in the radio continuum • The image at 4.9 GHz shows a radio source coincident in position with the brightest part of RCW 78 • Flux density: S 4.9 = 0.5 Jy • Physical parameters of the ionized gas in the brightest part of the nebula : • EM = (1.0  0.1)x103 pc cm-6 • Angular diameter = 8 arcmin • Adopted distance = 6.0 kpc • Mion = 900 Mo • rms Ne = 7 cm-3 RCW 78 at 4.9 GHz

13. RCW 78: energetics • Some results: • The value of  indicates that the stellar wind of WR 55 is strong enough to blow the interstellar bubble • RCW 78 is in the momentum conserving phase or in an intermediate stage between energy and momentum conserving stages. • This value is typical for interstellar bubbles around Wolf-Rayet stars. Valparaiso, Chile, 2004 October

14. Conclusions • WR 55 is the only massive star related to RCW 78 and the main responsible for the ionization of the gas. • The HI gas emission distribution reveals an HI shell associated with RCW 78, which can be interpreted as an HI bubble linked to the ionized ring nebula. • CO observations show the presence of molecular gas related to the nebula with velocities similar to those of the HI and HII material. The same velocity gradient is observed in CO and Ha lines. The surface of the molecular cloud has probably been photodisociated and ionized by the stellar UV photons. • The stellar winds from the WR star are strong enough to create the interstellar bubble. Since the dynamical age is larger than the duration of the WR phase of the star, the progenitor of the current WR star has also contributed in shaping the nebula. • The nebula is in the momentum conserving stage or in an intermediate stage between energy and momentum conservation. Valparaiso, Chile, 2004 October

15. Future prospects • To perform molecular observations towards other ring nebulae to investigate the presence of PDRs and shock fronts. • To investigate if star formation occurs in the surrounding shells. • To investigate the energetics of these nebulae taking into account all the gas components linked to the nebulae. Valparaiso, Chile, 2004 October