1 Instituto Argentino de Radioastronomía, Argentina2 Facultad de Ciencias Astronómicas y Geofísicas, UNLP, La Plata, Argentina3 Departamento de Astronomía, Universidad de Chile, Chile4 Australia Telescope Compact Array, Australia

Atomic and molecular gas in the Atomic and molecular gas in the environs of the ring nebula RCW 78environs of the ring nebula RCW 78

C. Cappa1,2, M. Rubio3,

M.C. Martin1 and N. McClure-Griffiths4

Valparaiso, Chile, October 2004

IntroductionIntroductionWolf-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)

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

RCW58 (E)

NGC6888 (W+E)

IntroductionIntroduction

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(WR101), VLA, 1465 MHz, 38 arcsec

Anon(WR23), HI emission, 2.5 arcmin

Molecular observations towards ring Molecular observations towards ring nebulaenebulae

CO observations (black contours): SEST, 22 arcsec)

Velocity: 54 km/sHI data (white contours):

VLA, 45 arcsec

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)

Studies of molecular material associated with ring nebulae are needed to investigate the physical state of the gas, their kinematics and energetics.

The ring nebula RCW 78 around WR 55The 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

H image (Treffers et al. 1983)

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 H 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)

H image (Treffers et al. 1983)

HD92206WR 55

-44 km/s

-53 km/s

DatabaseDatabase 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

RCW 78 in CO RCW 78 in CO emissionemission

13h33m15.0s, -62o17’30”

Molecular components with velocities in the range –65 to -8 km/s are detected. Sample of CO profiles:

13h33m36.0s, -62o16’01”

13h33m21.0s, -62o22’01”

CO(1-0)

CO(2-1)

RCW 78 in CO RCW 78 in CO emissionemission

CO contour lines: 1 to 7 K in steps of 1 K

Mean Tmb [-54.4,-53.1] km/s

Mean Tmb [-53.1,-49.1] km/s

Mean Tmb [-48.7,-44.7] km/s

Mean Tmb [-42.5,-39.4] km/s

RCW 78 in CO RCW 78 in CO emissionemission

Some results

CO emission within the range –54 to –33 km/s is associated with the ring nebula.

CO velocities agree with H 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

Mean Tmb [-38.5,-36.7] km/s

CO contour lines: 1 to 7 K in steps of 1 K

RCW 78 in the HI RCW 78 in the HI line emission line emission distributiondistribution

Colour scale: 82 to 110 K

Some results:

HI cavity and shell detected within the velocity range -54 to –36 km/sHI emission borders the NE, E and SE sections of RCW 78, the agreement is not so clear to the WHI velocties agrees with CO and H 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

HI emission [-49,-40] km/s

WR 55

RCW 78 in the radio RCW 78 in the radio continuumcontinuum

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

Valparaiso, Chile, 2004 October

RCW 78: energeticsRCW 78: energetics

Kinetic energy Ek (10 48 erg) 3-10

Stellar wind luminosity (1036 erg/s) 4

Mechanical energy of the wind Ew (1050 erg) 1.7

Energy conversion eficiency = Ek / Ew <0.04

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

ConclusionsConclusions

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 H 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

Future prospectsFuture 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.