Timing of the Shell Ejection in Nova Outbursts

Abstract

Some time after the outburst of a nova in the visible light its light intensity is dominated by the flux in the emission lines. The rate of fading of the nova in such times is the rate of weakening of the emission lines. The intensity of a recombination or a forbidden line emitted by a given mass of ionized gas is proportional to the density. Thus the light curve gives the expansion rate of the nova shell. For a shell with a constant expansion velocity the light curve therefore enables the determination of the beginning of the expansion process, namely the timing of the ejection of the shell. In four classical Galactic novae the ejection of the main shell is found to occur between 19 and 40 days before the outburst in the visible light.