C 18 O Observations of the Dark Molecular Cloud L134 and Gas Depletion onto Dust

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We map the dark molecular cloud core of L134 in the C 18 O ( J = 1−0) emission line using the PMO 13.7 m telescope, and present a contour map of integrated intensity of C 18 O ( J = 1−0) emission. The C 18 O cloud is inside the distribution of extinction A B , the visual extinction of blue light, as well as inside the 13 CO cloud in the L134 region. The depletion factors in this C 18 O cloud are generally greater than unity, which means there is gas depletion onto dust. Since only a minimum A B = 9.7 mag is available, and our observations measure both undepleted and depleted regions along the line of sight, the depletion factors could very likely be larger in the central core than the calculated value. So we conclude that depletion does occur in the bulk of the C 18 O cloud through a comparison between the C 18 O and blue extinction maps in the L134 region. There is no direct evidence as yet for star formation in L134, and so cores on the verge of collapse will not be visible in CO and other gas molecules.