The Volatile Composition of Comet C/2003 K4 (LINEAR) at Near-IR Wavelengths—Comparisons with Results from the NanÇay Radio Telescope and from the Odin, Spitzer, and SOHO Space Observatories

Abstract

We observed comet C/2003 K4 (LINEAR) using NIRSPEC at the Keck Observatory on UT 2004 November 28, when the comet was at 1.28 AU from the Sun (post-perihelion) and 1.38 AU from Earth. We detected six gaseous species (H₂O, OH*, C₂H₆, CH₃OH, CH₄, and HCN) and obtained upper limits for three others (H₂CO, C₂H₂, and NH₃). Our results indicate a water production rate of (1.72 ± 0.18) × 10²⁹ molecules s^-1, in reasonable agreement with production rates from SOHO (on the same day), Odin (one day earlier), and Nançay (about two weeks earlier). We also report abundances (relative to water) for seven trace species: CH₃OH (∼1.8%), CH₄ (∼0.9%), and C₂H₆ (∼0.4%) that were consistent with mean values among Oort cloud (OC) comets, while NH₃ (<0.55%), HCN (∼0.07%), H₂CO (<0.07%), and C₂H₂ (<0.04%) were “lower” than the mean values in other OC comets. We extracted inner-coma rotational temperatures for four species (H₂O, C₂H₆, CH₃OH, and CH₄), all of which are consistent with 70 K (within 1σ). The extracted ortho-para ratio for water was 3.0 ± 0.15, corresponding to spin temperatures larger than 39 K (at the 1σ level) and agreeing with those obtained with the Spitzer Space Telescope at the 2σ level.