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Nova V5579 Sgr 2008: near-infrared studies during maximum and the early decline phase

We present near-infrared spectroscopic and photometric observations of the nova V5579 Sgr during the maximum and early decline phase. The spectra follow the evolution of the nova from peak brightness when the lines had strong P Cygni profiles to a phase dominated by prominent emission lines. The spectra during the emission phase are dominated by strong H I lines from the Brackett and Paschen series, O I and C I lines. The spectra in the final stages of our observations show a rising continuum towards longer wavelengths, indicating dust formation. Dust formation in V5579 Sgr is consistent with the presence of lines of elements with low-ionization potentials like Na and Mg in the early spectra. The early presence of such lines had been earlier suggested by us to be potential indicators of dust formation later in the nova's development. We also discuss the possibility of using P Cygni profiles to probe the properties of the erupting white dwarf during the early outburst.