EDP Sciences
Free access
Volume 412, Number 2, December III 2003
Page(s) 431 - 445
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20031455

A&A 412, 431-445 (2003)
DOI: 10.1051/0004-6361:20031455

A $\mathsf{^{12}}$CO (J = 1 $\rightarrow$ 0) study towards the Ara OB1 region

E. M. Arnal1, 2, J. May3 and G. A. Romero1

1  Instituto Argentino de Radioastronomía (IAR), C.C. No. 5, 1894 Villa Elisa, Argentina
2  Facultad de Ciencias Astronómicas y Geofísica Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina
3  Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

(Received 19 May 2003 / Accepted 8 September 2003 )

Intermediate angular resolution ( $HPBW=8\farcm7$) carbon monoxide ( 12CO  J=1 $\rightarrow$0) line observations towards the OB association Ara OB1 are reported. The molecular line observations cover an area of  $2\fdg75 \times 3\fdg00$, and disclose a rich and complex distribution of the molecular line emission. The molecular features likely to be associated with the OB-association Ara OB1 span the velocity range from  -28 to  -20 km s -1. The most negative radial velocities are observed along NGC 6188 ( $\equiv$Rim nebula). This nebula marks the interface between the HII region RCW 108 and the highly absorbing molecular material located westwards of the ionised region. The dominant CO structures, labeled E and F, have a radial velocity of about  -23.5 and  -21.8 km s -1, respectively. The former harbours a bright optical knot, the infrared cluster RCW-108 and the strong IRAS source 16362 -4845. IRAS point sources are also seen in projection onto 12CO concentrations F and H. This may indicate that the star forming process is a widespread phenomenon in this molecular complex. Extended continuum emission, having a high degree of spatial correlation with both the infrared and molecular emission, is observed in the region. We believe that this emission, thermal in nature, arises from the ionised surface layers of the molecular complex. The ionising agents are the high mass stars of NGC 6193, the nucleus of Ara OB1. The total amount of molecular gas related to Ara OB1 is about ~ $1.4\times 10^4$  $M_\odot$.

Key words: HII regions: individual: RCW 108 -- ISM: molecules -- open clusters and associations: individual: NGC 6193 -- open clusters and associations: individual: Ara OB1 -- radio continuum: ISM -- radio lines: ISM

Offprint request: E. M. Arnal, arnal@iar.unlp.edu.ar

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