HCN IN BOK GLOBULES - A GOOD TRACER OF COLLAPSING CORES

We have conducted an HCN (J = 1-0) survey of dense cores in a sample o f 24 star-forming and quiescent Bok globules. HCN emission was detecte d toward 11 of 13 globules containing embedded point sources, with no HCN detection among 11 starless globules. As in other dark clouds, the J = 1-0 hyperfine line intensity ratios vary from globule to globule and also with position toward the same globule, suggesting the presenc e of either a scattering envelope surrounding the core or a complex de nsity structure. We find that the J = 1-0 transition of the KCN molecu le can be used effectively to search for early stages of star formatio n in small molecular clouds: in the sample of star-forming cores, for three (of five) sources mapped, there is good spatial coincidence (bet ter than 6'') between the position of the peak integrated HCN emission and the location of the associated embedded source. Furthermore, this transition is well correlated with the young stellar object (YSO) cla ss, detecting preferentially class I YSOs. Our results indicate that d etecting strong(>1 K km s(-1)) HCN emission from a molecular cloud cor e seems to imply the presence of an embedded protostar and thus, indir ectly, that of a collapsing core.