Ultra-hot stars and their surrounding nebulae

Properties of the hottest stars and their surrounding nebulae have been derived. Mean electron densities, distances and filling factors were derived for over 100 galactic planetary nebulae (PN). Reddenings, nebidar electron temperatures and densities, and elemental abundances were derived for a sample of 70 southern hemisphere PN. Reddenings, terminal velocities, and relative abundances of carbon, oxygen and helium were derived in the winds of population I WO Wolf-Rayet stars. Distances to PN which are optically thin in the Lyman continuum were derived via a variation on the Shklovsky constant ionized mass method, which uses mean [O II] 3726,29 A doublet ratio electron densites, and requires no assumption about angidar radius or nebular filling factor. Distances to PN which are optically thick in the Lyman continuum were derived by assuming a constant Hβ flux. The validity of the constant mass and constant Hβ flux assumptions, and calibration for each quantity were based on recent extensive observations of Magellanic Cloud PN by Barlow (1987) and Barlow et al. (1992). The derived distances to galactic PN were found to have consistency with independent distance estimates. For PN in the southern hemisphere, simultaneous integrated observations of the [S II] 6717,31 Å and [O II] 3726,29 Å doublets were made. The electron densities derived by the [O II] and [S II] doublet ratios were found to agree within observational error, hence essentially the same volume is traced by the O⁺ and S⁺ emission. Filling factors were derived for 97 PN. The derived filling factors were found to decrease with increasing absolute angular radii, however it is argued that such a trend can result from errors in adopted angular diameters. Reddenings, electron temperatures and densities, and elemental abundances were derived for 70 southern hemisphere PN, where both optical and UV spectra were analyzed. The derived abundances were extensively compared with predictions made by evolutionary theory (Becker & Iben 1980, Renzini & Voli 1981). Finally, the properties of the population I WO stars were derived, using ultraviolet, optical and infrared spectra. The analysis included a derivation of the terminal velocities, the reddenings and the relative oxygen, carbon and helium abundances via recombination theory for four WO stars. The derived abundances show promising agreement with the recent evolutionary models of Schaller et al. (1992)