Hubble Space Telescope Observations of Planetary Nebulae in the Magellanic Clouds. II. SMP 85, A Young Planetary

Abstract

We have obtained Hubble Space Telescope Planetary Camera images in the [O III] λ5007 A emission line, and FOS UV spectrophotometry of the low-excitation planetary nebula SMP 85 in the Large Magellanic Cloud. By combining these results with existing optical spectrophotometry, absolute flux measurements, and dynamical and density information, we have been able to construct a fully self-consistent nebular model. This proves that SMP 85 is a dense, young, carbon-rich object which started to be ionized about 500-1000 years ago, and which contains a substantial inner reservoir of atomic or molecular gas, probably in the form of many small cloudlets. These cloudlets have been ejected at a velocity not exceeding 6 km s^-1^, a result which, together with the morphology is an important clue to mass loss during late AGB evolution. We have directly detected the central star through its UV continuum emission, and from both Zanstra techniques and nebular modeling derive a stellar temperature of 46000+/-2000 K, a stellar luminosity of 7300+/-700 L_sun_, and a core mass of 0.63-0.67 M_sun_. The nebular analysis also demonstrates that there is severe depletion of the nebular gases onto dust grains, most likely of the calcium magnesium silicate variety; a surprising result in view of the carbon-rich nature of the ionized nebula.