Near-infrared studies of V2944 Ophiuchi (Nova Ophiuchi 2015)

We present multi-epoch near-infrared observations of Nova Ophiuchi 2015 which was discovered during outburst in March 2015. This nova showed a few special properties viz. (i) it displayed an unusual prolonged flat-top light curve which does not easily fit into known classes of nova light curves, (ii) it showed evidence for possessing an evolved secondary in the outbursting binary system, and (iii) it made a rare reverse hybrid transition from the He/N class to Fe II class early during its outburst. The present studies focus on the spectroscopic evolution of the object around maximum light and early decline. We show that there was a unique, rapid strengthening and decline in the He 1.0831, 2.0581 mu m line strengths during this stage, wherein the nova combined the traits of both the He/N and Fe II classes. Possible causes for this behaviour are discussed. The relative strengths of the Ly beta fluoresced OI 0.8446, 1.1287 mu m lines are used to estimate the reddening to the nova. A recombination Case B analysis of the early spectra is used to set constraints on the electron density and emission measure, and a later time spectrum when the ejecta were optically thin is used to estimate the ejecta mass to be (0.95-1.9) x 10(-4) M-circle dot. Power-law fits made to study the evolution of the continuum, show a fairly constant slope which differs from the trend generally expected during a nova's evolution viz. beginning with a blackbody and evolving to a free-free distribution at later stages.