Model for Cameron band emission in comets: A case for EPOXI mission target comet 103P/Hartley 2

TL;DR

This paper presents a model for Cameron band emission in comet 103P/Hartley 2, highlighting the significant roles of photoelectron impact and CO2 dissociation, and suggests reevaluating CO2 abundance estimates from Cameron band observations.

Contribution

Developed a comprehensive model for CO Cameron band emission in comets, incorporating photoelectron impact and CO2 dissociation, applied to Hartley 2, and provided insights for interpreting observational data.

Findings

Photoelectron impact contributes 50-75% to Cameron band emission.

Model brightness aligns with Hubble observations at 3-5% CO2.

Predicted Cameron band brightness during EPOXI encounter is ~1300 R.

Abstract

The CO2 production rate has been derived in comets using the Cameron band (a3Pi - X1Sigma) emission of CO molecule assuming that photodissociative excitation of CO2 is the main production mechanism of CO in a3Pi metastable state. We have devoloped a model for the production and loss of CO(a3Pi) which has been applied to comet 103P/Hartley 2: the target of EPOXI mission. Our model calculations show that photoelectron impact excitation of CO and dissociative excitation of CO2 can together contribute about 60-90% to the Cameron band emission. The modeled brightness of (0-0) Cameron band emission on comet Hartley 2 is consistent with Hubble Space Telescope observations for 3-5% CO2 (depending on model input solar flux) and 0.5% CO relative to water, where photoelectron impact contribution is about 50-75%. We suggest that estimation of CO2 abundances on comets using Cameron band emission may be reconsidered. We predict the height integrated column brightness of Cameron band of ~1300 R during EPOXI mission encounter period.