Near-infrared studies of the carbon monoxide and dust-forming Nova V5668 Sgr

We present near-infrared (NIR) observations of Nova V5668 Sgr, discovered in outburst on 2015 March 15.634 ut, between 2 and 107 d after outburst. NIR spectral features are used to classify it as a Fe ii class of nova. The spectra follow the evolution of the spectral lines from a P Cygni stage to a pure emission phase where the shape of the profiles suggests the presence of a bipolar flow. A notable feature is the presence of carbon monoxide first overtone bands which are seen in emission. The CO emission is modelled to make estimates of the mass, temperature and column density to be (0.5–2.0) × 10−8 M⊙, 4000 ± 300 K and (0.36–1.94) × 1019 cm−2, respectively. The 12C/13C ratio is estimated to be ∼1.5. V5668 Sgr was a strong dust producer exhibiting the classical deep dip in its optical light curve during dust formation. Analysis of the dust SED yields a dust mass of 2.7 × 10-7 M⊙, a blackbody angular diameter of the dust shell of 42 mas and a distance estimate to the nova of 1.54 kpc which agrees with estimates made from MMRD relations.