We present high resolution interferometric and single dish observations of molecular gas in the Serpens cluster-forming core. Star formation does not appear to be homogeneous throughout the core, but is localised in spatiallyand kinematically-separated sub-clusters. The stellar (or proto-stellar) density in each of the sub-clusters is much higher than the mean for the entire Serpens cluster. This is the first observational evidence for the hierarchical fragmentation of proto-cluster cores suggested by cluster formation models.

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The conversion factor, between the velocity-integrated CO(1È0) antenna temperature, W (CO), X CO , and the column density, is determined for 32 positions in two translucent high-latitude molec-H 2 N(H 2 ), ular clouds, MBM 40 and MBM 16.is calculated using CH observations of theThe latter quantity, divided by W (CO) yields for various posi-N(H 2 ). X CO tions across the clouds. We observed 24 positions in MBM 16, and values were derived in the range X CO (1.6È17.3) ] 1020 cm~2 (K km s~1)~1, with a mean value of 7.6 ] 1020. Eleven lines of sight were sampled in MBM 40 yielding values of in the range (0.7È9.7) ] 1020, with a mean value of X CO 2.6 ] 1020. An inverse relationship between and W (CO) may exist, suggesting that the variation in X CO for these two translucent clouds arises from varying CO abundances. This paper also reports the X CO existence of a broad component in the CH spectra observed throughout much of MBM 16. This component possibly originates in the disturbed outer regions of the cloud where the gas is not gravitationally bound to the core of the cloud. It is unclear how sensitive the CO rotational transitions are to this component, but it is likely that the ratio in this broad-line gas is less than 10~5. However, if the CO/H 2 ratio is the same for the gas in the extended wings as it is for the typical cloud gas, then up to CH/H 2 40% of the cloud mass could be contained in this difficult to trace molecular component.

We observed 51 positions in the OH 1667 MHz main line transitions in the translucent high latitude cloud MBM40. We detected OH emission in 8 out of 8 positions in the molecular core of the cloud and 24 out of 43 in the surrounding, lower extinction envelope and periphery of the cloud. Using a linear relationship between the integrated OH line intensity and E(B-V), we estimate the mass in the core, the envelope, and the periphery of the cloud to be 4, 8, and 5 M ⊙ . As much as a third of the total cloud mass may be found in the periphery (E(B-V) < 0.12 mag) and about a half in the envelope (0.12 ≤ E(B-V) ≤ 0.17 mag). If these results are applicable to other translucent clouds, then the OH 1667 MHz line is an excellent tracer of gas in very low extinction regions and high-sensitivity mapping of the envelopes of translucent molecular clouds may reveal the presence of significant quantities of molecular mass.

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