Water in Comet 2/2003 K4 (LINEAR) with Spitzer

TL;DR

This study uses Spitzer spectra to analyze water in comet 2/2003 K4, revealing its water composition, temperature evolution, and production rate, with no evidence of certain other compounds.

Contribution

First infrared spectral detection of water in comet 2/2003 K4 with detailed analysis of water's ortho-to-para ratio and temperature profile.

Findings

Water ortho-to-para ratio of 2.47 +/- 0.27

Water production rate of approximately 2.43 x 10^{29} molecules per second

No detection of PAHs or carbonate minerals in the spectra

Abstract

We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR) obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational band of water is detected with a high signal-to-noise ratio (> 50). Model fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/- 0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra acquired at different offset positions show that the rotational temperature decreases with increasing distance from the nucleus, which is consistent with evolution from thermal to fluorescence equilibrium. The inferred water production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do not show any evidence for emission from PAHs and carbonate minerals, in contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp). However, residual emission is observed near 7.3 micron the origin of which remains unidentified.