1997A&A...318..571P

Long slit blue and red spectra of the planetary nebula NGC 5189 (PK 307 -3°1) with its O VI sequence central object were obtained with the ESO 1.52m telescope, in order to establish criteria that allow the discrimination between the high mass WO stars and lower mass objects having similar spectral features. The NGC 5189 stellar nucleus shows a very high ionization spectrum with emission features of He II, C IV, and O V. N V should also be weakly present. The line width suggests a maximum wind velocity of 2800km/s. Long slit spectra on various positions across the nebula were used to study the physical structure of NGC 5189. From the [S II] 671.7/673.2nm line ratio we find that the electron density varies from 200 to 900cm^–3. The ionization, as described by the He⁺⁺/He⁺ ratio, largely changes from one region to another, reaching a maximum of 2.5 in a low density region 20"E of the central star, and a minimum in the regions more distant from the star. NGC 5189 appears nitrogen enriched by about a factor 5 with respect to the cosmic value, while the helium abundance is normal. The chemical composition appears homogeneous throughout the nebula. We thus conclude that, in addition to the wind velocity, the chemical composition and homogeneity of the nebulae can be used to discriminate between high mass WO stars and "O VI sequence" PNN's.