Morphological effects on IR band profiles

Experimental spectroscopic analysis with application to observed spectra of oxygen-rich AGB stars

¹ Astrophysical Institute and University Observatory, Friedrich-Schiller-University Jena, Schillergäßchen 3, 07745 Jena, Germany e-mail: akemi@astro.uni-jena.de
² Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
³ Institut für Astronomie, Türkenschanzstrasse 17, 1180 Wien, Austria
⁴ Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
⁵ Department of Physics, Wichita State University, Wichita KS67260-0032, USA

Received: 2 January 2009
Accepted: 24 March 2009

Abstract

Aims. To trace the source of the unique 13, 19.5, and 28 μm emission features in the spectra of oxygen-rich circumstellar shells around AGB stars, we have compared dust extinction spectra obtained by aerosol measurements.

Methods. We have measured the extinction spectra for 19 oxide powder samples of eight different types, such as Ti-compounds (TiO, TiO₂, Ti₂O₃, Ti₃O₅, Al₂TiO₅, CaTiO₃), α-, γ-, χ-δ-κ-Al₂O₃, and MgAl₂O₄ in the infrared region (10–50 μm) paying special attention to the morphological (size, shape, and agglomeration) effects and the differences in crystal structure.

Results. Anatase (TiO₂) particles with rounded edges are the possible 13, 19.5 and 28 μm band carriers as the main contributor in the spectra of AGB stars, and spherically shaped nano-sized spinel and Al₂TiO₅ dust grains are possibly associated with the anatase, enhancing the prominence of the 13 μm feature and providing additional features at 28 μm. The extinction data sets obtained by the aerosol and CsI pellet measurements have been made available for public use at http://elbe.astro.uni-jena.de.