Establishing [OI] Observations as a Proxy for CO2 Production in Comets

Carbon Dioxide is one of the most abundant volatiles in comets and is an important driver of cometary activity as well as a possible indicator of evolutionary processes. However, severe telluric absorption hinders observations of CO2 in comets from the ground, meaning the only observations of CO2 in comets have come from space-based facilities such as the Spitzer Space Telescope and the (NEO)WISE mission. Therefore, studies of CO2 in comets have been limited. Observations of the [OI] lines in the optical may be able to serve as a ground-based proxy for CO2 in comets. The flux ratio of the [OI]5577 line to the sum of the [OI]6300 and [OI]6364 lines (hereafter referred to as the oxygen line ratio) is sensitive to the abundance of CO2 in the coma, with higher ratios implying higher CO2 abundances. However, the photochemistry responsible for the release of [OI] into the coma is not completely understood, limiting the extent to which observations of the oxygen line ratio can be used as a proxy for CO2 in comets. To address this lack of knowledge, comets themselves can be used as a “laboratory” to better understand [OI] photochemistry in cometary comae. Our group has been coordinating ground-based observations of the oxygen line ratio with space-based observations of CO2 using Spitzer and NEOWISE to build a database of 28 comets with known CO2 abundances and measured oxygen line ratios. We present preliminary analysis of this data set aimed at establishing empirical [OI] release rates that can be used to convert measured oxygen line ratios to CO2 abundances. This will allow for observations of oxygen line ratios to be used as proxies for CO2 in comets, drastically increasing the number of comets with known CO2 abundances. This work is funded by the NASA Solar System Workings Program.