UV TURN-OFF TIMES OF CLASSICAL NOVAE

We present IUE spectra of classical novae obtained at least one year a fter the outburst. The UV luminosities are compared with the ROSAT obs ervations and significant parameters of the systems. The turn-off time s derived from the IUE data are in agreement with the ROSAT results, s howing that most novae decline in bolometric luminosity 1-5 years afte r 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 cle ar dependence of the turn-off time on the speed class, the chemical co mposition or other parameters of the system. Data indicate that on15 a small fraction of the accreted layer is left on the white dwarf after the outburst.