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[68.16] Detection of Methanol in a Class 0 Protostellar Disk

P.F. Goldsmith (NAIC, Cornell University), W.D. Langer, T. Velusamy (JPL, Calif. Inst. Technology)

We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, Class 0 protostellar object. In addition, we identify a spectral feature in the outflow corresponding to an ethanol transition. Using the Caltech Owens Valley Millimeter Array with a synthesized beam size of 2\arcsec, we detect spatially unresolved methanol in the 2_k -- 1_k transitions at 3mm, which is coincident in position with the peak of the continuum emission. The gas phase methanol could be located in the central region (< 100 AU radius) of a flat disk, or in an extended heated surface layer (~ 200 AU radius) of a flared disk. The fractional abundance of methanol X(CH₃OH) is ~ 2\times 10^-8 in the flat disk model, and ~ 3\times 10^-7 for the flared di sk. The fractional abundance is small in the disk as a whole, but considerably larger in the warm portions. This difference indicates that substantial chemical processing probably takes place in the disk via depletion and desorption.

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