Disordered Silicates in Space: a Study of Laboratory Spectra of "Amorphous" Silicates

TL;DR

This study provides detailed laboratory infrared spectra of various amorphous silicate glasses relevant to space, highlighting how composition and preparation affect spectral features and aiding in identifying astronomical silicates.

Contribution

It offers comprehensive spectral data and analysis of astrophysically relevant silicate glasses, emphasizing the importance of detailed chemical characterization for accurate dust modeling.

Findings

Spectral features vary with composition and preparation methods.

Synthetic spectra do not perfectly match laboratory or astronomical data.

Comparison helps identify potential astronomical silicate candidates.

Abstract

We present a laboratory study of silicate glasses of astrophysically relevant compositions including olivines, pyroxenes and melilites. With emphasis on the classic Si-O stretching feature near 10 microns, we compare infrared spectra of our new samples with laboratory spectra on ostensibly similar compositions, and also with synthetic silicate spectral data commonly used in dust modeling. Several different factors affect spectral features including sample chemistry (e.g., polymerization, Mg/Fe ratio, oxidation state and Al-content) and different sample preparation techniques lead to variations in porosity, density and water content. The convolution of chemical and physical effects makes it difficult to attribute changes in spectral parameters to any given variable. It is important that detailed chemical and structural characterization be provided along with laboratory spectra. In addition to composition and density, we measured the glass transition temperatures for the samples which place upper limits on the formation/processing temperatures of these solids in space. Popular synthetically-generated optical functions do not have spectral features that match any of our glass samples. However, the ~10 microns feature generated by the synthetic data rarely exactly matches the shape and peak position of astronomically observed silicate features. Our comparison with the synthetic spectra allows astronomers to determine likely candidates amongst our glass samples for matching astronomical observations.