2014MNRAS.443..559J

Near-infrared spectroscopic and photometric observations are presented for the recent 2011 outburst of recurrent nova T Pyxidis. Spectra, commencing from one day after outburst, are reported for a total of 18 epochs spread over the first 50d of the eruption. A major finding is the transition of the nova from the He/N to the Feii class within a few days after the outburst. The transition is inferred from the appearance of prominent Hei lines soon after the onset of the eruption which then fade rapidly in strength within the next few days. Certain lines of carbon which are near-IR hallmarks of the Feii class of novae are also used to establish and trace the transition. The evolution in the strength and shape of the line profiles is presented and discussed. A Case B recombination analysis is done which shows that the Brackett lines are affected by optical depth effects from the start to the end of the observations. Based on the observation that the Br γ line is clearly optically thick, we are able to place lower limits on the emission measure n_e^2L and show that the electron density of the ejecta ne during the first 50d must be in the range 10⁹-10¹⁰/cm3.