Morphology and evolution of the Large Magellanic Cloud planetary nebulae

The LMC is ideal for studying the coevolution of planetary nebulae (PNs) an d their central stars in that the debilitating uncertainties of the Galacti c PN distance scale and selection biases from attenuation by interstellar d ust do not apply. We present images and analyze slitless spectra that were obtained in a survey of Large Magellanic Cloud PNs. These data on 29 target s were obtained with the Hubble Space Telescope (HST) using the Space Teles cope Imaging Spectrograph. The data permit us to determine the nebular dime nsions and morphology in the monochromatic light of several emission lines, including those that have traditionally been used for morphological studie s in the Galaxy: H alpha, [N II] lambda 6583, and [O III] lambda 5007, plus others of varying ionization including [O I], He I, and [S II]. Together w ith the 31 resolved LMC PNs for which monochromatic images exist in the HST archive, these data show that the incidence of nonsymmetric nebulae, inclu ding bipolar nebulae (which is an indicator of Population I ancestry in the Galaxy), is significantly higher than that reported for the Galaxy. The on set of asymmetric features appears even in very young nebulae (with dynamic al ages of similar to 1400 yr), suggesting that at least the gross features of the nebular morphology may be more closely tied to PN formation and tha t subsequent shaping of the expanding envelope by the radiation field and w ind from the central star may play the lesser role of amplifying these gros s features. There is some evidence of evolution between two morphological t ypes in the sense that bipolar core nebulae may evolve to pure bipolars lat e in the PN lifetime.