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Near Infrared (NIR) and optical photometry and spectroscopy are presented forthe nova V1831 Aquilae, covering the early decline and dust forming phasesduring the first $\sim$90 days after its discovery. The nova is highly reddeneddue to interstellar extinction. Based solely on the nature of NIR spectrum weare able to classify the nova to be of the Fe II class. The distance andextinction to the nova are estimated to be 6.1 $\pm$ 0.5 kpc and $A_{\rm v}$$\sim$ 9.02 respectively. Lower limits of the electron density, emissionmeasure and ionized ejecta mass are made from a Case B analysis of the NIRBrackett lines while the neutral gas mass is estimated from the optical [OI]lines. We discuss the cause for a rapid strengthening of the He I 1.0830 $\mu$mline during the early stages. V1831 Aql formed a modest amount of dust fairlyearly ($\sim$ 19.2 days after discovery); the dust shell is not seen to beoptically thick. Estimates are made of the dust temperature, dust mass andgrain size. Dust formation commences around day 19.2 at a condensationtemperature of 1461 $\pm$ 15 K, suggestive of a carbon composition, followingwhich the temperature is seen to gradually decrease to 950K. The dust massshows a rapid initial increase which we interpret as being due to an increasein the number of grains, followed by a period of constancy suggesting theabsence of grain destruction processes during this latter time. A discussion ismade of the evolution of these parameters, including certain peculiarities seenin the grain radius evolution.

Near-infrared and optical studies of the highly obscured nova V1831 Aquilae (Nova Aquilae 2015)