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Astron. Astrophys. 332, L25-L28 (1998)

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Letter to the Editor

The spectrum of the young star HD 100546 observed with the Infrared Space Observatory *

K. Malfait 1, C. Waelkens 1, L.B.F.M. Waters 2, B. Vandenbussche 1, 3, E. Huygen 1 and M.S. de Graauw 4

1 Instituut voor Sterrenkunde, K.U.Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
2 Astronomical Institute, Universiteit van Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3 ESA Villafranca, P.O. Box 50727, E-28080 Madrid, Spain
4 SRON Laboratory for Space Research Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 7 August 1997 / Accepted 16 December 1997


It is generally assumed that planets form in the dusty disks that surround young stars (Beckwith & Sargent 1996). The Infrared Space Observatory (Kessler et al. 1996) now enables us to determine the characteristics of these disks with unprecedented spectral resolution and signal-to-noise. We present here ISO spectra of the disk that surrounds the young star HD 100546. A remarkable variety of emission features of carbon- and oxygen-rich dust occurs. Most prominent are a series of emission features that can be attributed to silicates in crystalline form, mostly forsterite. In the interstellar medium and HII regions the silicate dust is mostly amorphous, but crystalline silicates are found in comets, meteorites and interplanetary dust particles. The forsterite features of HD 100546 are astonishingly similar to those observed in the ISO spectrum of Comet Hale-Bopp (Crovisier et al. 1997), strengthening the hypothesis that the disk around HD 100546 contains a huge swarm of comets (Grady et al. 1997). We argue that the crystallisation process occurs during the early evolution of the circumstellar disks of young stars and speculate about the formation of an Oort cloud around HD 100546.

Key words: circumstellar matter – stars: individual: HD 100546 – comets: individual: Hale-Bopp – infrared: ISM: lines and bands – solar system: formation

* 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: Koen Malfait, Leuven, (e-mail: koenm@ster.kuleuven.ac.be)

© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998