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E. S. Howell (NAIC/Arecibo Observatory), A. J. Lovell (Agnes Scott College), B. Butler (NRAO), F. P. Schloerb (U. Mass.), S. A. Torchinsky (NAIC/Arecibo Observatory)
We have monitored the outgassing and OH gas production from Comet 9P/Tempel~1. Pre-impact spectral observations of the 18-cm OH lines have been made with the Arecibo 300m radio telescope, on twelve dates between 8 April and 8 June, 2005, using both ALFA and the single-pixel L-wide receiver. Post-impact observations were made July 4-11 at the 100m Green Bank Telescope (GBT) in WV. These observations provide constraints on the variation in production and velocity of gas in the coma. This in turn places constraints on the sublimation of water, the parent molecule of OH. Spectra are interpreted via best fits of Monte Carlo simulations to the data; thus, the post-impact observations are particularly valuable for estimating the degree to which outgassing asymmetries are detectable with low spatial resolutions (> 4 arcmin). Some pre-impact observations as well as all post-impact observations are mapped over several positions on the sky, enabling some additional constraints on the extent of emission. Preliminary analysis of the pre-impact Arecibo observations suggests that the line strength closely follows the predicted values; however, production rates are low compared to those seen in previous apparitions. We find day-to-day variations of up to 25% in the OH production rate. Initial analysis suggests strong coma asymmetries, which may have an influence on the bulk production rate estimates. The best-fit water outflow velocity increased from 0.4~km/s on 9~April to 0.8~km/s by 16~May.
Post-impact observations of the 18-cm OH lines were carried out daily from the GBT 4-11 July. Line strengths were variable with time, sometimes below the 2 mJy detection threshold. The composite spectrum for the 8 days of observation has a peak of 3.5~mJy, an integrated area of 18~mJy km/s, consistent with an outflow velocity around 0.8~km/s. While variations in the line strengths appear correlated with long-term variations seen at other wavelengths, there are no significant variations related directly to the rotation of the nucleus.
The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.