1995A&A...300..493L

We have mapped the ρ Oph main cloud in the J=2-1 transition of CS with the Nagoya 4m millimetre-wave telescope. The overall morphology of the cloud is similar to that mapped in C¹⁸O, but the high density regions ρ Oph A and B are more evident in CS. Depending on the adopted model for the CS excitation, these observations lead to estimated cloud masses 540M_☉ (LTE) or 2500M_☉ (NLTE) for a value of the CS abundance equal to 10^–9. We find, in particular, that the assumption of LTE is inadequate and that the mass of the ρ Oph main cloud may previously have been underestimated by at least a factor of three. This does also imply that the formerly determined high star formation efficiency of the cloud would have to be revised downwards accordingly. From IRAS observations we determine the mass of the dust emitting at 60µm to be at least 5.5M_☉. Average mass ratios of the gas-to-dust are thus found to be 100 or 450. Detailed comparison of the CS and IRAS images reveals, however, that average values are rarely, if ever, found on local scales on the order of 0.15pc.