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A. L. Cochran, W. D. Cochran (University of Texas)
We obtained observations of comet C/1999\,S4 (LINEAR) using the 2DCoudé spectrograph on the 2.7-m Harlan J. Smith telescope of McDonald Observatory. The spectrograph was used at a resolving power of R=\lambda/\Delta \lambda=60,000. In this mode, complete wavelength coverage is achieved from 3700Å\ to 5800Å\ with continued coverage to 1\,\mum with increasing interorder gaps. Observations were obtained on 25 and 26 June 2000 UT, 6 through 9 July 2000 UT and 14 through 17 July 2000 UT. Comet LINEAR appears to be depleted in C2 and C3 relative to other comets which we have observed with the same instrument. This depletion, coupled with significant radial velocity shifts of the cometary lines with respect to the telluric spectral lines, leads to a detection of the O~(1S) line in the comet with no contamination from either the telluric O~(1S) nor with the cometary C2. In addition, we obtained observations of the cometary O~(1D) 6300 and 6363Å\ lines simultaneously with the O~(1S) line. The red lines were similarly uncontaminated. We report on the ratio of the green to red oxygen lines in the comet as a function of date and position within the coma. While the Earth's atmospheric lines were wildly varying, the cometary ratio was more constant. The implications of the green to red line ratio and its variations with time and position will be discussed.
This work was performed under NASA grant NAG5-9003.