2012MNRAS.425.2576R

We present near-infrared (near-IR) and optical observations of the nova Scuti 2009 (V496 Sct) covering various phases – pre-maximum, early decline and nebular – during the first 10 months of its discovery followed by limited observations in the early part of 2011 April. The spectra follow the evolution of the nova when the lines had strong P Cygni profiles to a phase dominated by prominent emission lines. The notable feature of the near-IR spectra in the early decline phase is the rare presence of first overtone bands of carbon monoxide in emission. Later about 150 days after the peak brightness, the IR spectra show clear dust formation in the expanding ejecta. Dust formation in V496 Sct is consistent with the presence of lines of elements with low ionization potentials like Na and Mg in the early spectra and the detection of CO bands in emission. The light curve shows a slow rise to the maximum and a slow decline indicating a prolonged mass loss. This is corroborated by the strengthening of P Cygni profiles during the first 30 days. In the spectra taken close to the optical maximum brightness, the broad and single absorption components seen at the time of discovery are replaced by two sharper components. During the early decline phase, two sharp dips that show increasing outflow velocities are seen in the P Cygni absorption components of FeII and HI lines. The spectra in 2010 March showed the onset of the nebular phase. Several emission lines display saddle-like profiles during the nebular phase. In the nebular stage, the observed fluxes of [OIII] and Hβ lines are used to estimate the electron number densities and the mass of the ejecta. The optical spectra show that the nova is evolved in the P_feA_o spectral sequence. The physical conditions in the ejecta are estimated. The absolute magnitude and the distance to the nova are estimated to be M_V= -7.0±0.2 and d=2.9±0.3kpc, respectively.