Water Ice, Silicate, and Polycyclic Aromatic Hydrocarbon Emission Featuresin the [ITAL]Infrared Space Observatory[/ITAL] Spectrum of the Carbon-richPlanetary Nebula CPD −56°8032

Abstract

Combined Infrared Space Observatory Short-Wavelength Spectrometer and Long-Wavelength Spectrometer spectroscopy is presented of the late WC-type planetary nebula nucleus CPD 568032 and its carbon-rich nebula. The extremely broad coverage (2.4-197 mm) 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 in the 3-14 mm region, bands from crystalline silicates longward of 18 mm, and the 43 and 62 mm 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. Subject headings: infrared: ISM: lines and bands-planetary nebulae: individual (CPD 568032)