X. -W. Liu — Page 5

arXiv1999

Water Ice, Silicate and PAH Emission Features in the ISO Spectrum of the Carbon-rich Planetary Nebula CPD-56 8032

Combined ISO SWS and LWS spectroscopy is presented of the late WC-type planetary nebula nucleus CPD-56 8032 and its carbon-rich nebula. The extremely broad coverage (2.4-197 microns) enables us to recognize the clear and simultaneous presence of emission features from both oxygen- and carbon- rich circumstellar materials. Removing a smooth continuum highlights bright emission bands characteristic of polycyclic aromatic hydrocarbons (hereafter PAHs) in the 3-14 micron region, bands from crystalline silicates longwards of 18 microns, and the 43- and 62-micron bands of crystalline water ice. We discuss the probable evolutionary state and history of this unusual object in terms of (a) a recent transition from an O-rich to a C-rich outflow following a helium shell flash; or (b) a carbon-rich nebular outflow encountering an O-rich comet cloud.

astro-ph↗

arXiv1998

Hubble Space Telescope Images of Magellanic Cloud Planetary Nebulae: Data and Correlations across Morphological Classes

The morphology of planetary nebulae (PNe) provides an essential tool for understanding their origin and evolution, as it reflects both the dynamics of the gas ejected during the TP-AGB phase, and the central star energetics. Here we study the morphology of 27 Magellanic Cloud planetary nebulae (MCPNe) and present an analysis of their physical characteristics across morphological classes. Similar studies have been successfully carried out for galactic PNe, but were compromised by the uncertainty of individual PN distances. We present our own HST/FOC images of 15 Magellanic Cloud PNe (MCPNe) acquired through a narrow-band lambda 5007 [O III] filter. We use the Richardson-Lucy deconvolution technique on these pre-COSTAR images to achieve post-COSTAR quality. Three PNe imaged before and after COSTAR confirm the high reliability of our deconvolution procedure. We derive morphological classes, dimensions, and surface photometry for all these PNe. We have combined this sample with HST/PC1 images of 15 MCPNe, three of which are in common with the FOC set, acquired by Dopita et al. (1996), to obtain the largest MCPN sample ever examined from the morphological viewpoint. By using the whole database, supplemented with published data from the literature, we have analyzed the properties of the MCPNe and compared them to a typical, complete galactic sample. Morphology of the MCPNe is then correlated with PN density, chemistry, and evolution.

astro-ph↗