Detection and evolution of the CO (δv=2) emission in Nova V2615 Ophiuchi (2007)

We present near-infrared (1-2.5 mu m) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of similar to 80 d starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra is shown from the initial P Cygni phase to an emission-line phase and finally to a dust formation stage. The characteristics of the JHK spectra are very similar to those observed in a nova outburst occurring on a carbon-oxygen white dwarf. We analyse an observed line at 2.088 mu m and suggest that it could be due to Fe ii excited by Lyman alpha fluorescence. The highlight of the observations is the detection of the first overtone bands of carbon monoxide (CO) in the 2.29-2.40 mu m region. The CO bands are modelled to estimate the temperature and mass of the emitting CO gas and also to place limits on the C-12/C-13 ratio. The CO bands are recorded over several epochs, thereby allowing a rare opportunity to study the evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed time-scales involved in the evolution of the CO emission and find a good agreement with model predictions that investigate the chemistry in a nova outflow during the early stages.