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[41.19] Spectroscopy of comets Lee and LINEAR S4 in the 3 micron region using NIRSPEC

K. Magee-Sauer (Rowan Univ.), M.J. Mumma (NASA GSFC), M.A. DiSanti, N. Dello Russo (NASA GSFC / CUA), T.W. Rettig (Notre Dame), R. Novak (Iona)

We present results of spectroscopic observations of C/1999 H1 Lee on UT August 21.6, 1999 and C/1999 LINEAR S4 on UT July 13.4, 2000. The data were obtained using the NIRSPEC instrument at the Keck II telescope atop of Mauna Kea, HI. The NIRSPEC instrument is a cross-dispersed cryogenic infrared spectrometer which permits a nearly complete high-dispersion survey of the 2.9 - 3.7 \mum region. The 3 \mum region (3335 cm^-1 - 3285 cm^-1) includes emission from HCN, C₂H₂, OH, NH₂, and strong lines that are preliminarily consistent with the 2\nu₁ - \nu₁ band of H₂O.

Thirteen lines of HCN were detected in comet Lee, permitting an accurate determination of its rotational temperature (72 ± 8 K) and production rate (2.9 ± 0.2) x 10²⁶ molecules/sec. This production rate corresponds to a relative abundance to water of (0.23 ± 0.02)%. Three lines of C₂H₂ were also detected corresponding to a production rate of (3.4 ± 0.3) x 10²⁶ molecules/second and a C₂H₂/H₂O relative abundance of (0.27 ± 0.3)%.

Comet LINEAR S4 was observed under high humidity. Thus, many lines that normally would have been clear of absorption, fell in regions of low atmospheric transmittance. A few relative strong emission lines were detected in the spectrum, but do not correspond with HCN or C₂H₂. A full analysis of this spectrum will be presented.

This research is supported by NSF grant no. 9619461 through the Research at Undergraduate Institutions Program.