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A SCUBA survey of compact dark Lynds clouds
We present the first results of a submillimetre continuum survey ofLynds dark clouds. Submillimetre surveys of star-forming regions are animportant tool with which to obtain representative samples of the veryfirst phases of star formation. Maps of 24 small clouds were obtainedwith SCUBA, the bolometer array receiver at the James Clerk MaxwellTelescope, and 19 clouds were detected. The total dark cloud areasurveyed was ~130arcmin2, and a total gas mass of90Msolar was detected. The dust emission is in general ingood agreement with the extinction of optical starlight. The observedclouds contain a newly discovered protostar in L944, and a previouslyknown protostar IRAS 23228+4320 in L1246. Another eight starless cores,either gravitationally unbound or pre-stellar in nature, were alsodetected. All starless cores and protostars were detected in only sevenclouds, and the remaining 17 clouds seem quiescent and do not show anysigns of recent star formation activity. The 850-μm images of alldetected clouds are presented, as well as 450-μm images of L328,L944, L1014 and L1262. The outflows of the protostars in L944 and L1246were also discovered and were mapped in 12CO J=2->1. Thedetection of the young protostar in L944, which is not present in theIRAS Point Source Catalog, shows the capacity of submillimetre surveysto detect unknown protostars.
| Millimetre dust emission from northern BOK globules.
We present the results of a 1.3mm continuum study of 59 Bok globuleslocated north of -30° declination. The catalogue of Clemens &Barvainis (1988ApJS...68..257C) served as a search list for the targetobjects investigated here. Based on the analysis of the IRAS pointsource colour-colour diagram, four distinct groups of globules aredistinguished. It is shown that indeed each of these groups hasdistinctive properties and represents a different stage of starformation. For our observations, we selected a number of candidatepre-protostellar cores, all candidates for globules with protostellarcores, as well as a number of strong 12μm IRAS point sources whichare candidates for T Tauri stars associated with globules. Individualdistances of the globules are derived with a method which associates theglobules with larger molecular cloud complexes. It is shown that mostglobules are associated with such cloud complexes from which theyprobably formed. The derived distances range from 140pc to 2kpc with themajority of the globules being related to Gould's Belt at distances of200 to 300pc. The average distance of our sample of globules is derivedto be 500pc. Out of the 59 globule cores observed at 1.3mm, 21 objectswere detected with average 3σ detection limits of 17mJy/12" and39mJy/23". This corresponds to an overall detection rate of 35%. Whilemost of the detected objects are protostellar cores, fourpre-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=~0.5Msun_. Using the detection rates and the relativefrequencies of the globule groups, lifetimes of the differentevolutionary stages are derived. Assuming that all globules form starsat some time of their evolution, the typical lifetime of a Bok globuleis derived to be some 10^6^years. It is speculated that the existence ofisolated T Tauri stars can be explained by star formation in Bokglobules. In addition, the results of the continuum measurements arecompared with observations of different molecular lines.
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