Active star formation in the large Bok globule CB 34^*

¹ Armagh Observatory, Armagh BT61 9DG, Northern Ireland, UK e-mail: 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 e-mail: tstanke@mpifr-bonn.mpg.de
⁴ Joint Astronomy Centre 660 N. A'Ohoku Place, University Park, Hilo, Hawaii 96720, USA e-mail: c.davis@jach.hawaii.edu

Corresponding author: T. Khanzadyan, tig@star.arm.ac.uk

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 H₂ knots are discovered on wide-field images in the 1–0 S(1) 2.12 μm emission line. These parsec scale H₂ 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 H₂ emission, are similar, consistent with jet-driven non-evolving outflow structure. The jets appear to originate from the densest cores, as observed in H¹³CO⁺ 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 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 H₂ cascade. We propose that the halo is produced by ongoing H₂ formation. Cloud evolution and halo H₂ formation timescales are then both a few 10⁵ 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.