Compositional dependence of infrared absorption spectra of crystalline silicates

III. Melilite solid solution

¹ Department of Earth and Space Science, Graduate school of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka 560-0043, Japan e-mail: chi@ess.sci.osaka-u.ac.jp
² Laboratory of Physics, Kyoto Pharmaceutical University, Misasagi, Yamashina, Kyoto 607-8414, Japan

Received: 11 July 2006
Accepted: 13 October 2006

Abstract

The infrared optical properties and absorption spectra of the melilite solid solution series are reported. Melilite is a high-temperature condensate, and is expected to condense during the early phase of the condensation sequence. In this study, samples of the melilite solid solution series were newly synthesized between the aluminium end member (gehlenite) and the magnesium end member (åkermanite) at ~10% intervals in chemical composition, and the infrared absorption spectra of their samples were measured. Variation in the absorption features were detected: such variations include changes in numbers of absorption peaks, peak intensity, peak position, and peak width. The prominent absorption peaks appeared at 10–13 micron, 14, 15, 17, 19, 21, 24, 30, 37 and in the 60 micron region. In particular, the 10 micron feature complex and the 60 micron broad features are very sensitive to chemical composition. For application to and implications for astronomical data, we focused on the 60 micron feature, and carried out a comparison with ISO data of NGC 6302. Our data set will supply the spectroscopic basis for the interpretation of astronomical data accumulated by space and ground based observatories such as ISO, the Spitzer Space Telescope, the AKARI (ASTRO-F) and the Subaru telescope.