THE SPECTRUM OF THE PLANETARY-NEBULA NGC-6572

A detailed, high-spectral-resolution study of the spectrum of the planetary nebula NGC 6572 is made for the optical region 365 to 1005 nm, using the Hamilton echelle spectrograph of Lick Observatory, and for the ultraviolet (UV) spectral region 125 to 3 20 nm with the high-dispersion mode of the International Ultraviolet Explorer (IUE) satellite. NGC 6572 is a rather young planetary nebula, with a high surface brightness and a seemingly relatively regular spatial structure. This nebula and especially its central star are also variable. The rich spectrum in both the optical and UV regions offers outstanding opportunities for diagnostic studies, abundance determinations, and even checking atomic processes. The prominent line spectrum of permitted lines of C II, N II, 0 II etc. may arise primarily from recombination. A density-contrast model is constructed to obtain chemical abundances by two methods and to predict isophotal contours. The metal/hydrogen ratio appears to be smaller than in the Sun. We suggest that NGC 6572 originated from a star of about one solar mass, and that the core may have a mass of about 0.57 M.. The expansion age of the nebula appears to be about 2600 yr.