Determination of the time of the shell ejection in nova outbursts

THE light curve of novae is characterised by a sharp rise in brightness, followed by a decrease in light intensity at an ever slowing rate (see Fig. 1). The optical spectrum of novae near maximum consists of emission and absorption line systems superimposed on a continuum. One of the main features of the evolution of novae spectra is the fading of the continuum relative to the emission lines. In late stages, all novae develop the 'nebular' spectrum, consisting almost exclusively of emission lines with no continuum or with a very weak one (see ref. 1).The analysis of the light curve of a nova can reveal the time of ejection of its main shell. In four galactic novae this time was found to vary between 19 and 40 d before maximum.