The spectrum of the planetary nebula IC 351

Abstract

International Ultraviolet Explorer (WE) and optical region spectroscopic observations are presented for the moderately high-excitation planetary nebula IC 351. Most of the atoms are distributed over a narrow range of ionization. Thus [N ii] and [S ii] are weak; [Ne iv] is prominent, but [Ne v] is missing. It appears that the metal/hydrogen ratio is smaller than in the Sun. No Si lines are seen either in optical or UV regions. It is suggested that virtually all Si atoms are locked in grains. The ionization correction factor method fails utterly for N, for example. Hence IUE data are essential for chemical composition estimates. Until high spatial resolution images are available, construction of a new theoretical model does not seem warranted.