The discovery of the "21" μm and "30" μm emission features in Planetary Nebulae with Wolf-Rayet central stars^*

¹ Astronomical Institute "Anton Pannekoek" , University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
² Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
³ SRON Laboratory for Space Research Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁴ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands

Corresponding author: S. Hony, hony@astro.uva.nl

Received: 25 July 2001
Accepted: 8 September 2001

Abstract

We report the discovery of the "21" μm and "30" μm features in the planetary nebulae around the hydrogen-deficient stars HD 826 and HD 158269. The carriers of these features are known to be produced in outflows around carbon-rich stars. This discovery demonstrates that the bulk of the dust in these nebulae has been produced during a carbon-rich phase before the atmospheres of these stars became hydrogen poor. This is the first time that the "21" μm feature has been detected in any planetary nebula. It shows that once formed its carrier can survive the formation of the nebula and the exposure to the UV radiation of the hot central star. This means that the carrier of "21" μm feature is not transient: the absence of the feature sets limits on the production of its carrier.