Detection of parent H2O and CO2 molecules in the 2.5--5 micron spectrum of comet C/2007 N3 (Lulin) observed with AKARI

TL;DR

This study used the AKARI satellite to detect and analyze water, carbon dioxide, and carbon monoxide molecules in comet C/2007 N3 (Lulin), revealing its low volatile abundance compared to other comets.

Contribution

First near-infrared detection of CO2 in comet Lulin, providing insights into its molecular composition and abundance ratios.

Findings

Detected H2O and CO2 bands at 2.66 and 4.26 microns.

Found CO abundance less than 2% relative to H2O.

Lulin has relatively low CO and CO2 abundances among observed comets.

Abstract

Comet C/2007 N3 (Lulin) was observed with the Japanese infrared satellite AKARI in the near-infrared at a post-perihelion heliocentric distance of 1.7 AU. Observations were performed with the spectroscopic (2.5--5.0 micron) and imaging (2.4, 3.2, and 4.1 micron) modes on 2009 March 30 and 31 UT, respectively. AKARI images of the comet exhibit a sunward crescent-like shape coma and a dust tail extended toward the anti-solar direction. The 4.1 micron image (CO/CO2 and dust grains) shows a distribution different from the 2.4 and 3.2 micron images (H2O and dust grains). The observed spectrum shows distinct bands at 2.66 and 4.26 micron, attributed to H2O and CO2, respectively. This is the fifth comet in which CO2 has been directly detected in the near-infrared spectrum. In addition, CO at 4.67 micron and a broad 3.2--3.6 micron emission band from C-H bearing molecules were detected in the AKARI spectrum. The relative abundance ratios CO2/H2O and CO/H2O derived from the molecular production rates are \sim 4%--5% and < 2%, respectively. Comet Lulin belongs to the group that has relatively low abundances of CO and CO2 among the comets observed ever.