HCN in Bok globules: a good tracer of collapsing cores.
AFONSO J.M., YUN J.L. and CLEMENS D.P.
Abstract (from CDS):
We have conducted an HCN (J = 1-0) survey of dense cores in a sample of 24 star-forming and quiescent Bok globules. HCN emission was detected 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 presence of either a scattering envelope surrounding the core or a complex density structure. We find that the J = 1-0 transition of the HCN molecule can be used effectively to search for early stages of star formation in small molecular clouds: in the sample of star-forming cores, for three (of five) sources mapped, there is good spatial coincidence (better 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) class, detecting preferentially class I YSOs. Our results indicate that detecting strong (>1 K.km.s–1) HCN emission from a molecular cloud core seems to imply the presence of an embedded protostar and thus, indirectly, that of a collapsing core.