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P.D. Feldman, H.A. Weaver (JHU), M.F. A'Hearn (UMd), M.C. Festou (SwRI), J.B. McPhate (UCB), G.-P. Tozzi (Oss. Arcetri)
Comet Lee (C/1999 H1) provided the first opportunity to observe a moderately active comet near 1 AU in the ultraviolet with the Space Telescope Imaging Spectrograph (STIS), installed on the Hubble Space Telescope (HST) in February 1997. Observations were made pre-perihelion on 1999 June 7 at heliocentric and geocentric distances of 0.97 AU and 1.21 AU, respectively, shortly before the comet entered the HST solar avoidance zone. Long-slit spectra were obtained over the range 1150--3200 Å\ with a spatial resolution along the slit of 0.\!''05, which translates to 44 km projected at the comet. The strongest emissions are due to OH, CS and continuum, but the low dust/gas ratio implied by the relative brightness of OH to continuum enables the detection of S2 and C2. This is only the third comet (the other two being IRAS-Araki-Alcock and Hyakutake) in which S2 is positively identified. Atomic oxygen, carbon and sulfur are also detected (in addition to the strong hydrogen Lyman-\alpha) and sensitive upper limits are obtained for CO and CO2. The spatial profiles of CS and the continuum are time-varying and symmetric about the nucleus, while those of the OH bands display significant asymmetry. A lifetime of CS2, the presumed parent of CS, of roughly 1000 seconds is derived from modeling the CS spatial profile away from the nucleus. Production rates of the observed species are derived and will be compared with those obtained from ground-based optical, infrared and radio observations.
The author(s) of this abstract have provided an email address for comments about the abstract: pdf@pha.jhu.edu