D. P. K. Banerjee and N. M. Ashok
Abstract.We review the near-infrared properties of classical novae in the J, H and K bands
at wavelengths between 1.08 to 2.4 μm. A classification system exists for the early
post-outburst optical spectra of novae on the basis of the strength of group of non-hydrogen emission lines.
A similar scheme for the near-infrared regime, which is not available at present, is presented here. In the optical system
there are two principal classes, namely, "Fe II" and "He/N" for novae with either prominent Fe II lines or
prominent "He/N" lines. There is also a small subset of the hybrid Fe IIb type. From spectroscopic observations we show the
differences and similarities between
these classes of novae in the near-infrared. The spectral lines common to the two principal classes arise from H, He, N and O. However, the near-IR features that separate these two classes are the numerous, and often strong, carbon lines which are seen only in the spectra of the Fe II class of novae. The dust formation process in novae is discussed based on broad-band observations. The first-overtone carbon monoxide (CO) detections in novae are analyzed to understand the formation and evolution of this molecule in the nova ejecta and to discuss the observed 12C/13C ratio.
Keywords:techniques: spectroscopic -- (stars:) novae, cataclysmic variables -- infrared: general -- stars: circumstellar matter
Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat 380009, India