  We present analysis of observations of CO2 and OI emission in three comets to
measure the CO2 abundance and evaluate the possibility of employing
observations of OI emission in comets as a proxy for CO2. We obtained NIR
imaging sensitive to CO2 of comets C/2012 K1 (PanSTARRS), C/2012 K5 (LINEAR),
and 290P/Jager with the IRAC instrument on Spitzer. We acquired observations of
OI emission in these comets with the ARCES echelle spectrometer mounted on the
3.5-meter telescope at Apache Point Observatory and observations of OH with the
Swift observatory (PanSTARRS) and with Keck HIRES (Jager). The CO2/H2O ratios
derived from the Spitzer images are 12.6 +/- 1.3% (PanSTARRS), 28.9 +/- 3.6%
(LINEAR), and 31.3 +/- 4.2% (Jager). These abundances are derived under the
assumption that contamination from CO emission is negligible. The CO2 abundance
for PanSTARRS is close to the average abundance measured in comets at similar
heliocentric distance to date, while the abundances measured for LINEAR and
Jager are significantly larger than the average abundance. From the coma
morphology observed in PanSTARRS and the assumed gas expansion velocity, we
derive a rotation period for the nucleus of about 9.2 hours. Comparison of H2O
production rates derived from ARCES and Swift data, as well as other
observations, suggest the possibility of sublimation from icy grains in the
inner coma. We evaluate the possibility that the OI emission can be employed as
a proxy for CO2 by comparing CO2/H2O ratios inferred from the OI lines to those
measured directly by Spitzer. We find that for PanSTARRS we can reproduce the
observed CO2 abundance to an accuracy of ~20%. For LINEAR and Jager, we were
only able to obtain upper limits on the CO2 abundance inferred from the OI
lines. These upper limits are consistent with the CO2 abundances measured by
Spitzer.
