Variability of Planetary Nebulae: Results of Long-Term Observations

Abstract

The results of spectroscopic and photometric observations of 14 compact planetary nebulae are presented. Observations were conducted at the V.G. Fesenkov Astrophysical Institute (Kazakhstan) since 1973. The aim of this study is to obtain data on the variability of the studied objects over long time spans. The criterion for determining the nebular excitation class was the intensity of the [OIII] lines normalized to the intensity of Hβ. Analysis of the data collected over 40–50 years revealed significant spectral changes in most of the observed objects, likely associated with an increase in the temperature of the central stars and/or changes in the internal structure of the nebular envelopes.