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

摘要

The CO2 production rate has been derived in comets using the Cameron band(a3Pi - X1Sigma) emission of CO molecule assuming that photodissociativeexcitation of CO2 is the main production mechanism of CO in a3Pi metastablestate. We have devoloped a model for the production and loss of CO(a3Pi) whichhas been applied to comet 103P/Hartley 2: the target of EPOXI mission. Ourmodel calculations show that photoelectron impact excitation of CO anddissociative excitation of CO2 can together contribute about 60-90% to theCameron band emission. The modeled brightness of (0-0) Cameron band emission oncomet 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, wherephotoelectron impact contribution is about 50-75%. We suggest that estimationof CO2 abundances on comets using Cameron band emission may be reconsidered. Wepredict the height integrated column brightness of Cameron band of ~1300 Rduring EPOXI mission encounter period.