Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997arep...41..600e&link_type=abstract
Astronomy Reports, Volume 41, Issue 5, September 1997, pp.600-610
Astronomy and Astrophysics
Astronomy
Scientific paper
The reasons for asynchronous variations in the intensities of forbidden OIII lines in the spectrum of the planetary nebula IC 4997 are considered. It is shown that the strengthening of the 4363 line with a simul- taneous weakening of the N1 and N2 lines can be explained by a severalfold increase of the mass-loss rate from the nucleus, up to 1_2 X 10^-7 M_solar yr^1, in a few years. The ionization model of the nebula under the combined effect of nucleus emission and the emission from a variable hot stellar wind with electron temperature T_e = 500 000 K is used to calculate the theoretical line intensities. The calculations included twelve levels of OIII. In the region of OIII line formation, the electron density n_e 10^6 cm^3 and the electron temperature Te, which changes from 12,000 to 15,000 K, yield theoretical line intensities that are in best agreement with observations. The x-ray luminosity of the stellar wind from the nucleus at energies >= 0.2 keV is of the order of 10^35 erg s^1, but the interstellar extinction rules out the possibility of observing this object.
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