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

摘要

Combined ISO SWS and LWS spectroscopy is presented of the late WC-typeplanetary nebula nucleus CPD-56 8032 and its carbon-rich nebula. The extremelybroad coverage (2.4-197 microns) enables us to recognize the clear andsimultaneous presence of emission features from both oxygen- and carbon- richcircumstellar materials. Removing a smooth continuum highlights bright emissionbands characteristic of polycyclic aromatic hydrocarbons (hereafter PAHs) inthe 3-14 micron region, bands from crystalline silicates longwards of 18microns, and the 43- and 62-micron bands of crystalline water ice. We discussthe 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 heliumshell flash; or (b) a carbon-rich nebular outflow encountering an O-rich cometcloud.