Talk abstract details

We acquired IRS/Spitzer 5-38 um spectra of ~150 compact Galactic planetary nebulae (PN) in Cycle 5 to study the early dust properties. Misclassified PNe are about 5% of the sample. The PN spectra typically present a dust continuum, dust emission features, and nebular emission lines. The sample is complete, flux-limited for those PNe with optical diameters smaller than about 4 arcsec. We found that PNe characterized by carbon-rich dust have progenitors within a narrow mass range, as opposed to the oxygen-rich and the mixed-chemistry dust PNe. We also found differences in the Galactic distribution of the different dust types. Dust temperature and infrared luminosity has been derived for all PNe, and trends among these quantities, compared to those of Magellanic Cloud PNe, disclose the early dust evolution in relation to the metallicity of the progenitors. Within the studied sample we found four PNe presenting the characteristic fullerene emission features.