Near-Infrared Spectroscopy of V1493 Aquilae and V4642 Sagittarii: Two Novae with Unusual Spectral Features

Abstract

We present 0.8–2.5 μm spectroscopy of two novae with uncommon spectral features at different stages in their decline after outburst. Nova Aql 1999 No. 1 (V1493 Aql) was a very fast nova that initially exhibited a rapid decline in brightness that flattened by day 20 and actually reversed to show an unusual secondary peak. The near-infrared spectrum was observed during this secondary peak at 46 days after initial peak brightness. Blended low-excitation lines such as H I Brackett and Paschen and O I largely populated the spectrum, which also showed a strong continuum declining monotonically toward the red (1.4–2.5 μm). He II lines were just beginning to emerge. The overall spectral appearance was much more representative of the period a few days after outburst. A possible explanation for this, and the secondary peak in the visible light curve, is that the nova experienced a second period of mass loss, but of a more continuous rather than explosive nature. Nova Sgr 2000 (V4642 Sgr) was a moderately fast nova, observed 160 days after peak brightness. High-excitation lines, including coronal lines, were present in the spectrum. However, their profiles were distinctly different from those of the lower excitation lines. Also present were four emission lines that have only recently been detected in the spectra of novae and which remain unidentified.