Nova Sco

Abstract. Observations of CO emission in Nova Sco 1992 are discussed. Observations of CO in this and other novae, notably NQ Vul (Nova Vul 1976) suggest that CO formation is a necessary precursor to the formation of an optically thidc dust shell. 

Three near-infrared spectra of Nova Sco are shown in Figure 1. The first spectrum (3 June 1992 UT) shows no evidence for dust emission. Instead, the CO Av = 2 bands are seen prominently in emission longward of 2.29 foa. Examination of the spectrum around 1 /mi shows the 1.0695 /mi line of C I to be quite strong, while He 1 1.0830 /im, though present, is relatively weak. Strong CO emission was also inferred on 19 June by Harrison (1992) from broadband photometry. 

Fig. 1. hifraied qiectia of Nova Sco 1992. The left-hand panel shows the ectrmn ftom... 

In summary, those novae which show large metal overabundances are decreasing in mass while those that show an overabundance of He can be either increasing or decreasing. Obviously, only the latter that are increasing in mass can eventually produce a SNI. U Sco seems to be the best prospect (Starrfield, Sparks, and Truran 1985). 

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