ON THE VARIATIONS OF [OIII] LINE-INTENSITIES IN THE SPECTRUM OF THE PLANETARY-NEBULA IC-4997

The reasons for asynchronous variations in the intensities of forbidde n OIII lines in the spectrum of the planetary nebula IC 4997 are consi dered. It is shown that the strengthening of the lambda 4363 line with a simultaneous weakening of the N-1 and N-2 lines can be explained by a severalfold increase of the mass-loss rate from the nucleus, up to 1-2 x 10(-7) M. yr(-1), in a few years. The ionization model of the ne bula under the combined effect of nucleus emission and the emission fr om a variable hut stellar wind with electron temperature T-c= 500000 K is used to calculate the theoretical line intensities. The calculatio ns included twelve levels of OIII. In the region of OIII line formatio n, the electron density n(e) similar or equal to 10(6) cm(-3) and the election temperature T-e, which changes from 12000 to 15000 K, yield t heoretical line intensities that are in best agreement with observatio ns. The x-ray luminosity of the stellar wind from the nucleus at energ ies greater than or equal to 0.2 keV is of the order of 10(35) erg s(- 1),but the interstellar extinction rules out the possibility of observ ing this object.