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Issue A&A
Volume 383, Number 2, February IV 2002
Page(s) 502 - 518
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011531



A&A 383, 502-518 (2002)
DOI: 10.1051/0004-6361:20011531

Active star formation in the large Bok globule CB 34

T. Khanzadyan1, M. D. Smith1, R. Gredel2, T. Stanke3 and C. J. Davis4

1  Armagh Observatory, Armagh BT61 9DG, Northern Ireland, UK
    mds@star.arm.ac.uk
2  Centro Astronomico Hispano-Aleman, 04080 Almeria, Spain
    e-mail: gredel@caha.es
3  MPI für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany
    tstanke@mpifr-bonn.mpg.de
4  Joint Astronomy Centre 660 N. A'Ohoku Place, University Park, Hilo, Hawaii 96720, USA
    c.davis@jach.hawaii.edu

(Received 20 June 2001 / Accepted 29 October 2001 )

Abstract
We present near-infrared and millimetre observations of the large Bok globule CB 34. Two long parallel trails of H 2 knots are discovered on wide-field images in the 1-0 S(1) 2.12  $\mu$m emission line. These parsec scale H 2 jets extend to the edge of the dark globule where they disappear without the trace of bow shocks. This suggests that the outflows physically extend into a lower density ambient medium where their terminating bows are beyond present detection limits. The two outflows are extremely well collimated and parallel to within 3°. The outflow mechanical luminosity, derived from CO measurements, and the shocked luminosity, estimated from the H 2 emission, are similar, consistent with jet-driven non-evolving outflow structure. The jets appear to originate from the densest cores, as observed in H 13CO + line emission. A central concentration of reddened stars and a lower density halo of less reddened stars within the globule are revealed by JHK photometry. Disordered motions are observed in the CO J=2-1 line velocity channel maps and can be driven by the power of the outflows emanating from dense cores. We sketch a picture for the star formation history of the globule in which two star phases have been formed. A weak diffuse emission halo is detected in the near infrared with colours consistent with either scattered light or a ro-vibrational H 2 cascade. We propose that the halo is produced by ongoing H 2 formation. Cloud evolution and halo H 2 formation timescales are then both a few $\times$ 10 5 yr. Thus, we may be witnessing the formation of a molecular cloud out of diffuse atomic gas. This supports a scheme in which this Bok globule has formed independently rather than through dislocation from a nearby molecular cloud.


Key words: infrared: ISM -- stars: formation -- ISM: jets and outflows -- ISM: clouds

Offprint request: T. Khanzadyan, tig@star.arm.ac.uk

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© ESO 2002


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