Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....99..218p&link_type=abstract
Astronomy and Astrophysics, vol. 99, no. 2, June 1981, p. 218-220.
Astronomy and Astrophysics
Astrophysics
13
Forbidden Bands, H Gamma Line, Oxygen Spectra, Planetary Nebulae, Stellar Spectra, Variability, Astronomical Spectroscopy, Electron Density (Concentration), Flare Stars, Stellar Oscillations
Scientific paper
More than 250 spectrograms of the planetary nebula IC 4997 were obtained by the L.Figl-Observatory, Austria, between August 1978 and December 1980. It is shown that the line intensity ratios R equals forbidden O III 4363 A/H-gamma 4340 A have again increased, returning to a value exceeding 1. The largest change occurred between May and June 1980, during which time R increased from 0.94 to 1.10. This 17% increase corresponds to a change in the electron temperature of some 200 K and of the incoming ionizing flux by about 6%. The general increasing trend is superimposed by rapid fluctuations with gradients up to Delta R/Delta t equals 0.005/d, suggesting that the star is in a flare-activity stage. It is assumed that R undergoes a long periodic change on a time scale of decades.
Purgathofer A.
Stoll Martin
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