Crystalline silicate dust around evolved stars^*

III. A correlations study of crystalline silicate features

¹ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
² School of Materials Science and Engineering, Georgia Tech, Atlanta, GA 30332-0245, USA
³ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
⁴ SRON, PO Box 800, 9700 AV Groningen, The Netherlands
⁵ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
⁶ Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8412, Japan
⁷ Department of Earth and Space Science, Osaka University, Toyonaka 560-0043, Japan

Corresponding author: F. J. Molster, fmolster@so.estec.esa.nl

Received: 8 June 2001
Accepted: 5 November 2001

Abstract

We have carried out a quantitative trend analysis of the crystalline silicates observed in the ISO spectra of a sample of 14 stars with different evolutionary backgrounds. We have modeled the spectra using a simple dust radiative transfer model and have correlated the results with other known parameters. We confirm the abundance difference of the crystalline silicates in disk and in outflow sources, as found by Molster et al. ([CITE]). We found some evidence that the enstatite over forsterite abundance ratio differs, it is slightly higher in the outflow sources with respect to the disk sources. It is clear that more data is required to fully test this hypothesis. We show that the 69.0 micron feature, attributed to forsterite, may be a very suitable temperature indicator. We found that the enstatite is more abundant than forsterite in almost all sources. The temperature of the enstatite grains is about equal to that of the forsterite grains in the disk sources but slightly lower in the outflow sources. Crystalline silicates are on average colder than amorphous silicates. This may be due to the difference in Fe content of both materials. Finally we find an indication that the ratio of ortho to clino enstatite, which is about 1:1 in disk sources, shifts towards ortho enstatite in the high luminosity (outflow) sources.