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F.P. Schloerb (FCRAO/UMass), A. Lovell (Agnes Scott College), E. Howell (NAIC/Arecibo Obs.)
We present observations of the 18-cm OH lines in comet C/1999 LINEAR S4 obtained at Arecibo Observatory. The 305m radio telescope provides the world's largest collecting area for radio OH observations. Thus, it allows sensitive maps of the radial brightness distribution of the OH emission to be obtained. Such maps are very useful to studies of the collisional quenching of the OH molecule in the coma, and the goal of this project is to estimate the size of the quenched region by fitting models to the maps. The comet was observed in the 1667, 1665, and 1612 MHz lines simultaneously at a spectral resolution of 380 Hz, corresponding to 70 m/s. A first set of observations was made during June 1, 3, 4, 5, and 7, 2000. The OH lines were detected at this time and then mapped in order to provide constraints on the radial brightness profile for subsequent model fitting. A second set of observations, obtained on July 27, 30, and August 4, 2000, did not yield a detection, presumably due to the breakup of the nucleus that was observed at this time. This observing campaign represents the first effort to observe the radio OH lines in a comet since the completion of the Arecibo upgrade project, and detailed calibration of the data is in progress. The results of the analysis of the June maps of the coma will be presented.