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Astron. Astrophys. 315, L361-L364 (1996)

Mineralogy of oxygen-rich dust shells*

L.B.F.M. Waters1,2, F.J. Molster1, T. de Jong2,1, D.A. Beintema2, C. Waelkens3, A.C.A. Boogert8, D.R. Boxhoorn2, Th. de Graauw2, S. Drapatz9, H. Feuchtgruber9, R. Genzel9, F.P. Helmich10, A.M. Heras4, R. Huygen3, H. Izumiura7, K. Justtanont2, D.J.M. Kester2, D. Kunze9, F. Lahuis4, H.J.G.L.M. Lamers5, K.J. Leech4, C. Loup6, D. Lutz9, P.W. Morris4, S.D. Price12, P.R. Roelfsema2, A. Salama4, S.G. Schaeidt9, A.G.G.M. Tielens11, N.R. Trams4, E.A. Valentijn2, B. Vandenbussche3,4, M.E. van den Ancker1, E.F. van Dishoeck10, H. van Winckel3, P.R. Wesselius2, and E.T. Young13

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 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200B, B-3001 Heverlee, Belgium
4 ESA Villafranca, P.O. Box 50727, E-28080 Madrid, Spain,
5 SRON Laboratory for Space Research Utrecht, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
6 Institut d'astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris, France
7 Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Konagei, Tokyo 184, Japan
8 Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands
9 Max-Planck-Institut Für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
10 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
11 NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035, USA
12 Geophysics Directorate, Phillips Laboratory, 29 Randolph Rd., Hanscom AFB, MA 01731-3010, USA
13 Steward Observatory, University of Arizona, Tucson, AZ 85721, USA

Received 11 July 1996 / Accepted 21 August 1996

Abstract. Spectra taken with the Short Wavelength Spectrometer on board of the Infrared Space Observatory of dust shells around evolved oxygen-rich stars reveal the presence of several emission features at wavelengths between 20 and 45 img1.gifm. These features have a range of widths and strengths, but are all narrow compared to the well-known amorphous silicate bands at 9.7 and 18 img1.gifm. The emission peaks are tentatively identified with crystalline forms of silicates such as pyroxenes and olivine. The emission features tend to be more prominent for objects with cooler dust shells (T < 300 K). This may be due to an intrinsic change in optical properties of the dust as it cools, or it may be due to an increase in the fraction of crystalline silicates compared to amorphous forms as the mass loss rate increases. The implications for the physics of dust formation in the outflows of cool giants are briefly discussed.

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

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