Space Telescope Imaging Spectrograph Ultraviolet Spectra of Large Magellanic Cloud Planetary Nebulae: A Study of Carbon Abundances and Stellar Evolution

We acquired spectra of 24 LMC PNe in the 1150--3000 \AA range in order todetermine carbon and other ionic abundances. The sample more than doubles thenumber of LMC PNe with good quality UV spectra in this wavelength range, andwhose optical images are available in the {\it HST} archive. The {\it SpaceTelescope Imaging Spectrograph} was used with a very large aperture to obtainvirtually slit-less spectra, thus the monochromatic images in the major nebulaeemission lines are also available. The analysis of the data shows extremelygood quality spectra. This paper presents the emission lines identified andmeasured, and the calculation of the ionic abundances of the emitting carbonand other ions, and total carbon abundance. P-Cygni profiles have been found ina fraction of the nebulae, and the limiting velocities of the stellar windsestimated. The total carbon abundance can be inferred reliably in most nebulae.We found that the average carbon abundance in round and elliptical PNe is oneorder of magnitude larger than that of the bipolar PNe, while elliptical andround PNe with a bipolar core have a bimodal behavior. This results confirmthat bipolarity in LMC PNe is tightly correlated with high mass progenitors.When compared to predicted yields, we found that the observed abundance ratioshow a shift toward higher carbon abundances, that may be due to initialconditions assumed in the models not appropriate for LMC PNe.Comment: Ap. J., in pres