A spectroscopic study of moderately bright planetary nebulae

Spectroscopic results are presented for most of the nebulae observed in a programme involving some forty planetaries measured with an image tube scanner at Lick Observatory and with a photo-electric spectrum scanner at Mt. Wilson Observatory. The spectroscopic range normally covered, λ 3700 to λ 8700 is supplemented for a few objects with appropriate photographic data calibrated photoelectrically for the region λ 3120-λ 3800. Available published photoelectric data are also employed to improve the calibration of the finally adopted system of intensities.The main thrust of the programme is to investigate weaker lines, arising from less abundant ions, or due to less favorable excitation conditions. Information pertaining to additional ions gives further diagnostic data on the nebular plasma.For a given nebula, different diagnostics suggest different values of the electron temperature and density. These are believed to represent actual variations in physical conditions from point to point within the nebula, although in some instances, they may reflect inadequacies in atomic parameters, particularly collisional cross-sections. The spectroscopically most interesting nebulae show a wide variation in physical conditions, indicated by lines ranging in excitation from those of Mgi to [Fevii]. Relatively cool clouds of denser material appear to be immersed in a high excitation plasma excited by a hot central star.

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