Experimental study of amorphous silicate formation

¹ Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofugaoka, Chofu, Tokyo 182-8585, Japan
² Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA

Corresponding author: S. Wada, wada@e-one.uec.ac.jp

Received: 29 January 2003
Accepted: 13 May 2003

Abstract

Broad infrared bands at 10 and 18 μm have often been observed around oxygen-rich evolved stars, and these are thought to arise from amorphous silicate dust grains. In order to study the formation mechanism of silicate dust grains, we have analyzed synthesized silicate dust analogs by reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). The dust analog was produced from SiO and Mg vapors in O₂. The analyses showed that an amorphous silicate is formed at about temperature of 650 K through O-deficient silicate formation. However, when the substrate temperature was below 650 K, the main product is a mixture of SiO_x and MgO, where . Our experimental results indicate that temperature is an important factor for amorphous silicate formation in the circumstellar environment of oxygen-rich evolved stars.