Physical variations in the planetary nebula IC 4997

Details Physical variations in the planetary nebula IC 4997 Physical variations in the planetary nebula IC 4997

Feb 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...253..679k&link_type=abstract

Astrophysical Journal, Part 1, vol. 253, Feb. 15, 1982, p. 679-681.

Astronomy and Astrophysics

Astrophysics

7

Astrophysics, Planetary Nebulae, Stellar Spectra, Electron Density (Concentration), Electron Energy, Forbidden Bands, H Gamma Line, Oxygen Spectra, Stellar Mass Ejection, Stellar Structure, Stellar Temperature, Thermodynamic Equilibrium, White Dwarf Stars

Scientific paper

The planetary nebula IC 4997 has a spectrum which shows a variation in the forbidden O III 4363 A/H-gamma line intensity ratio that ranges from 1.6 in 1938 to 0.68 in 1962. Approximate values for the electron temperature and electron density of IC 4997 in 1962 are calculated from line intensity ratios of O III and N II ions. The equation of thermal equilibrium is used to calculate the electron temperature and electron density of the nebula in 1938. The changes in electron temperature and electron density in IC 4997 between 1938 and 1962 are then shown to be possible consequences of the physical expansion of the nebula and not necessarily due, as has previously been suggested, to a change in the temperature of the central star. If the explanation offered here for the 1938 to 1962 variation of forbidden O III 4363 A/H-gamma line intensity ratio is valid, the recent behavior of this line ratio suggests that the central star may have undergone an additional episode of mass loss.

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