Spectroscopic Study of the Variable Planetary Nebula IC 4997статья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Based on our spectroscopic observations of the variable planetary nebula IC 4997 in 2003-2009, we have obtained the relative fluxes in optical emission lines. The interstellar extinction c = 0.35 has been found from the Balmer decrement by taking into account the effect of self-absorption in hydrogen lines in dense nebular regions. The variations in the Balmer decrement point to variability of the self-absorption and circumstellar extinction. We have investigated the variations in the relative intensities of some spectral lines and their ratios with time. The drop in the ratios F(lambda 4363)/F(H gamma) and F(lambda 4363)/F(lambda 4959) that began back in 1990-1995 has continued, suggesting a decrease in the electron density and temperature in the central nebular region. The ratio F(lambda 6731)/F(lambda 6717) has remained constant. It gives an estimate for the electron density in the outer regions of IC 4997, N-e similar to 10(4) cm(-3).