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C. J. Chandler (NRAO), J. S. Richer, A. E. Visser (Cavendish Astrophysics, U. Cambridge)
We have carried out a survey of optically-selected dark clouds using the bolometer array SCUBA at 850~\mum on the JCMT\@. The survey covers a total of 0.5 square degrees and is unbiased with reference to size, star formation activity, or the presence of infrared emission. Several new protostars and starless cores have been discovered; the protostars are confirmed through the detection of their accompanying outflows in CO(2--1) emission. The survey is believed to be complete for Class~0 and Class~I protostars, and yields two important results regarding the lifetimes of these phases. First, the ratio of Class~0 to Class~I protostars in the sample is roughly unity, very different from the 1:10 ratio that has been observed for the \rho Ophiuchi star-forming region. Assuming star formation to be a homogeneous process in the dark clouds this implies that the Class~0 lifetime is similar to the Class~I phase, which from infrared surveys has been established to be ~2 \times 105~yr, and suggests there is no rapid initial accretion phase in these objects. Second, the number of starless cores is approximately twice that of the total number of protostars, indicating a starless core lifetime of ~8 \times 105~yr. A comparison of these statistical lifetimes with those measured for other star-forming regions indicates that the details of the star formation process is highly dependent on the local environment. Furthermore, and most importantly, this survey implies that the starless cores are very short-lived and survive only one or two free-fall times, which in turn implies that their evolution cannot be controlled by magnetic processes.