Title: Herschel/PACS observations of the 69 mu m band of crystalline olivine around evolved stars
Authors: Blommaert, Joris ×
de Vries, Ben
Waters, L. B. F. M
Waelkens, Christoffel
Min, M
Van Winckel, Hans
Molster, F
Decin, Leen
Groenewegen, M. A. T
Barlow, M
Garcia-Lario, P
Kerschbaum, F
Posch, Th
Royer, Pierre
Ueta, T
Vandenbussche, Bart
Van de Steene, G
van Hoof, P #
Issue Date: May-2014
Series Title: ASTRONOMY & ASTROPHYSICS vol:565 pages:109-125
Abstract: Context. We present 48 Herschel/PACS spectra of evolved stars in the wavelength range of 67-72 mum. This wavelength range covers the 69 mum band of crystalline olivine (Mg2-2xFe(2x)SiO4). The width and wavelength position of this band are sensitive to the temperature and composition of the crystalline olivine. Our sample covers a wide range of objects: from high mass-loss rate AGB stars (OH/IR stars, M >= 10-5 M&sun;/yr), through post-AGB stars with and without circumbinary disks, to planetary nebulae and even a few massive evolved stars.
Aims: The goal of this study is to exploit the spectral properties of the 69 mum band to determine the composition and temperature of the crystalline olivine. Since the objects cover a range of evolutionary phases, we study the physical and chemical properties in this range of physical environments.
Methods: We fit the 69 mum band and use its width and position to probe the composition and temperature of the crystalline olivine.
Results: For 27 sources in the sample, we detected the 69 mum band of crystalline olivine (Mg(2 - 2x)Fe(2x)SiO4). The 69 mum band shows that all the sources produce pure forsterite grains containing no iron in their lattice structure. The temperature of the crystalline olivine as indicated by the 69 mum band, shows that on average the temperature of the crystalline olivine is highest in the group of OH/IR stars and the post-AGB stars with confirmed Keplerian disks. The temperature is lower for the other post-AGB stars and lowest for the planetary nebulae. A couple of the detected 69 mum bands are broader than those of pure magnesium-rich crystalline olivine, which we show can be due to a temperature gradient in the circumstellar environment of these stars. The disk sources in our sample with crystalline olivine are very diverse. They show either no 69 mum band, a moderately strong band, or a very strong band, together with a temperature for the crystalline olivine in their disk that is either very warm (~600 K), moderately warm (~200 K), or cold (~120 K), respectively.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.orgReduced spectra are only available at the CDS via anonymous ftp to ( or via
ISSN: 0004-6361
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Institute of Astronomy
× corresponding author
# (joint) last author

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