5 Summary

We have obtained and analysed wide-field near-infrared images of the Bok Globule CB34 in the JHK continua and the H₂ 2.12 $\mu$m, which reveal some of the properties of the cloud mass, distribution of young stars and their jets and shocked outflows. We have also obtained velocity channel maps in molecular lines, CO maps revealing the cool outflows and turbulent motions, and H¹³CO⁺ maps displaying the dense cores.

Two new long extended infrared jets were discovered. These jets are detected over 1.2pc and 1.6pc to the outskirts of the globule. Since no terminating bow shock is found and the tracing H₂ knots are confined to the dark cloud, it is proposed that the jets extend much further into a lower density halo. The two jets are extremely well collimated and are parallel to within 3$^\circ$.

We estimate that the total shocked luminosity is comparable to the mechanical luminosity, derived from CO measurement, consistent with jet-driven non-evolving outflow structure. With an estimated dynamical age of 7.6$\times$10⁵ years, the mechanical luminosity and shocked luminosities are both $L_{\rm mech}$ = 0.02 $L_\odot$. These outflows may be driven by low-mass very young stars. We note, however, that a more viable explanation is that the CO outflows are dominated by the accumulated outflowing mass from older outflows whereas the H₂ is from shocks generated by the latest generation of outflows.

JHK photometry yields the presence of a central concentration of reddened stars, and a surrounding lower density region of less reddened stars within the globule. The spatial spread suggests that the stars have been generated for $\sim$10⁶yr within the cores. The presence of a pre-main-sequence star, CB34FU (see Fig. 1), with an age of $\sim$10⁶yr supports this as a minimum age (Alves et al. 1997).

The two outflows appear to be driven from the two densest submillimetre cores which we detect here in the H¹³CO⁺molecule, a tracer of dense gas. The axis separating these cores is roughly transverse to the outflow direction.

A diffuse halo is detected in J, H and K-band images, at a level consistent with that associated with the rapid formation of molecular hydrogen at a density of 10⁴ cm^-3in a time of order 10⁶yr. This suggests that the globule has formed directly out of an atomic cloud associated with a dust ridge, from which it continues to accrete mass. The alternative remains that the diffuse halo is purely scattered light from infrared-excess protostars. There is, however, a clear observed deficit in the number of protostars as well as the dust bolometric luminosity, which makes this interpretation problematic.

Two phases of star formation are suggested. The first phase generated the wide distribution of young stars. This activity triggered further core formation in the north of the globule, leading to the present generation of dense cores, outflows and protostars.

Acknowledgements

We would like to thank Tracy Huard for supplying the far infrared images. We are extremely grateful to Martin Murphy for his support in establishing the data reduction software.