Near-infrared studies of V1280 Sco (Nova Scorpii 2007)

We present spectroscopic and photometric results of Nova V1280 Sco which were discovered in outburst in early 2007 February. The large number of spectra obtained of the object leads to one of the most extensive, near-infrared spectral studies of a classical nova. The spectra evolve from a P-Cygni phase to an emission-line phase and at a later stage is dominated by emission from the dust that formed in this nova. A detailed model is computed to identify and study characteristics of the spectral lines. Inferences from the model address the vexing question of which novae have the ability to form dust. It is demonstrated, and strikingly corroborated with observations, that the presence of lines in the early spectra of low-ionization species like Na and Mg-indicative of low-temperature conditions-appears to be reliable indicators that dust will form in the ejecta. It is theoretically expected that mass loss during a nova outburst is a sustained process. Spectroscopic evidence for such a sustained mass loss, obtained by tracing the evolution of a P-Cygni feature in the Brackett gamma line, is presented here allowing a lower limit of 25-27 d to be set for the mass-loss duration. Photometric data recording the novas extended 12 d climb to peak brightness after discovery are used to establish an early fireball expansion and also show that the ejection began well before maximum brightness. The JHK light curves indicate the nova had a fairly strong second outburst similar to 100 d after the first.