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Astron. Astrophys. 331, L61-L64 (1998)

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Letter to the Editor

Crystalline silicates in planetary nebulae with [WC] central stars *

L.B.F.M. Waters 1, 2, D.A. Beintema 2, A.A. Zijlstra 3, A. de Koter 1, F.J. Molster 1, J. Bouwman 1, T. de Jong 2, 1, S.R. Pottasch 4 and Th. de Graauw 2

1 Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 SRON Laboratory for Space Research Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
3 Department of Physics, UMIST, P.O. Box 88, Manchester M60 1QD, UK
4 Kapteyn Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 23 October 1997 / Accepted 13 November 1997


We present ISO-SWS spectroscopy of the cool dusty envelopes surrounding two Planetary Nebulae with [WC] central stars, BD+30 3639 and He 2-113. The [FORMULA]   [FORMULA]  15 µm region is dominated by a rising continuum with prominent emission from C-rich dust (PAHs), while the long wavelength part shows narrow solid state features from crystalline silicates. This demonstrates that the chemical composition of both stars changed very recently (less than 1000 years ago). The most likely explanation is a thermal pulse at the very end of the AGB or shortly after the AGB. The H-rich nature of the C-rich dust suggests that the change to C-rich chemistry did not remove all H. The present-day H-poor [WC] nature of the central star may be due to extensive mass loss and mixing following the late thermal pulse.

Key words: Infrared: stars – stars: AGB and post-AGB; mass loss – planetary nebulae - dust

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

Send offprint requests to: L.B.F.M. Waters (Amsterdam address)

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998