UV turn–off times of classical novae

Abstract

We present IUE spectra of classical novae obtained at least one year after the outburst. The UV luminosities are compared with the ROSAT observations and significant parameters of the systems. The turn–off times derived from the IUE data are in agreement with the ROSAT results, showing that most novae decline in bolometric luminosity $1{-}5$ years after the outburst. This is a signal of the exhaustion of the fuel in the hydrogen–burning layer on top of the white dwarf. There is not any clear dependence of the turn–off time on the speed class, the chemical composition or other parameters of the system. Data indicate that only a small fraction of the accreted layer is left on the white dwarf after the outburst.