Millimetre dust emission from northern Bok globules

We present the results of a 1.3mm continuum study of 59 Bok globules located north of−30◦ declination. The catalogue of Clemens & Barvainis (1988) served as a search list for the target objects investigated here. Based on the analysis of the IRAS point source colour-colour diagram, four distinct groups of globules are distinguished. It is shown that indeed each of these groups has distinctive properties and represents a different stage of star formation. For our observations, we selected a number of candidate pre-protostellar cores, all candidates for globules with protostellar cores, as well as a number of strong 12μm IRAS point sources which are candidates for T Tauri stars associated with globules. Individual distances of the globules are derived with a method which associates the globules with larger molecular cloud complexes. It is shown that most globules are associated with such cloud complexes from which they probably formed. The derived distances range from 140 pc to 2 kpc with the majority of the globules being related to Gould’s Belt at distances of 200 to 300 pc. The average distance of our sample of globules is derived to be 500 pc. Out of the 59 globule cores observed at 1.3mm, 21 objects were detected with average 3σ detection limits of 17mJy/12′′ and 39mJy/23′′. This corresponds to an overall detection rate of 35%. While most of the detected objects are protostellar cores, four pre-protostellar cores and one T Tauri star were detected furthermore. The typical mass of a star formed in a Bok globule is derived to be≈ 0.5M . Using the detection rates and the relative frequencies of the globule groups, lifetimes of the different evolutionary stages are derived.Assuming that all globules form stars at some time of their evolution, the typical lifetime of a Bok globule is derived to be some 106 years. It is speculated that the existence of isolated T Tauri stars can be explained by star formation in Bok globules. In addition, the results of the continuummeasurements are compared with observations of different molecular lines.