Issue |
A&A
Volume 508, Number 2, December III 2009
|
|
---|---|---|
Page(s) | 759 - 771 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/200911769 | |
Published online | 27 October 2009 |
Unveiling the molecular environment of the ring nebula RCW 78*
1
Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina e-mail: ccappa@fcaglp.fcaglp.unlp.edu.ar
2
Instituto Argentino de Radioastronomía, C.C. 5, 1894 Villa Elisa, Argentina
3
Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
4
Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Chile
Received:
2
February
2009
Accepted:
28
September
2009
Aims. We present a study of the ionized, neutral atomic, and molecular gas associated with the ring nebula RCW 78 around the WR star HD 117688 (=WR 55) with the aim of analyzing the distribution of the associated gas and investigating its energetics.
Methods. We base our study on 12CO(1–0) and 12CO(2–1) observations of
the brightest section of the nebula carried out with the SEST telescope with
angular resolutions of 45´´ and 22´´, respectively; and on
complementary 12CO(1–0) data of a larger area obtained with the
NANTEN telescope with an angular resolution of 2 7, Hi 21-cm
line data taken from the ATCA
survey, IRAS HIRES data, and radio continuum data at 4.85 GHz
from the Parkes survey.
Results. We report the detection of molecular gas having velocities in the range
–56 to –33 km s-1 associated with the western region of RCW 78. A few
patches of molecular gas possibly linked to the eastern faint section are
detected. The CO emission appears concentrated in a region of
23′18′ in size, with a total molecular mass of
(1.3±0.5)
105
, mainly connected to the western section.
The analysis of the neutral atomic gas distribution reveals the H i envelope
of the molecular cloud, while the radio continuum emission shows a ring-like
structure, which is the radio counterpart of the
optical nebula.
The gas distribution is compatible with the western section of RCW 78 having
originated in the photodissociation and ionization of the molecular gas by
the UV photons of the WN7 star HD 117688, and with the action of the stellar
winds of the WR star on the surrounding gas. In this scenario, the
interstellar
bubble expanded more easily towards the east than towards the west due to
the lack of dense molecular gas in the eastern section. The proposed
scenario also explains the off center location of WR 55. A number
of infrared point sources classified as YSO candidates showed that
star formation activity is present in the molecular gas linked to the
nebula. The possibility that the expansion of the bubble triggered
star formation in this region cannot be discarded.
Key words: ISM: bubbles / ISM: individual objects: RCW 78 / stars: Wolf-Rayet / stars: individual: WR 55
© ESO, 2009
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