Detection and evolution of the CO (v = 2) emission in nova V2615 Ophiuchi (2007)

TL;DR

This study presents near-infrared spectroscopic observations of nova V2615 Ophiuchi, focusing on the evolution of CO emission, and models its properties to understand nova outflow chemistry over 80 days.

Contribution

It provides the first detailed modeling of CO overtone bands in nova V2615 Ophiuchi, tracking their evolution and comparing with chemical models of nova outflows.

Findings

Detection of CO overtone bands over multiple epochs.

Good agreement between observed CO evolution and chemical models.

Identification of FeII line possibly excited by Lyman alpha fluorescence.

Abstract

We present near-infrared (1 - 2.5 micron) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of ~ 80 days starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra are 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 micron and suggest it could be due to FeII 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 micron region. The CO bands are modeled to estimate the temperature and mass of the emitting CO gas and also to place limits on the 12C/13C ratio. The CO bands are recorded over several epochs thereby allowing a rare opportunity to study its evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed timescales 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.