Optical properties of silicon carbide for astrophysical applications I. New laboratory infrared reflectance spectra and optical constants

TL;DR

This paper provides new, accurate optical constants for silicon carbide (SiC) that improve modeling of astrophysical dust environments, correcting previous errors and accounting for grain size effects.

Contribution

It introduces revised optical constants for beta- and alpha-SiC derived from single-crystal spectra, addressing inaccuracies in prior data and expanding applicability.

Findings

New optical constants for SiC are more accurate and representative of bulk properties.

Calculated absorption coefficients are significantly higher than previous laboratory measurements.

Differences between alpha- and beta-SiC in infrared spectra are quantitatively assessed.

Abstract

Silicon Carbide (SiC) optical constants are fundamental inputs for radiative transfer models of astrophysical dust environments. However, previously published values contain errors and do not adequately represent the bulk physical properties of the cubic (beta) SiC polytype usually found around carbon stars. We provide new, uncompromised optical constants for beta- and alpha-SiC derived from single-crystal reflectance spectra and investigate quantitatively whether there is any difference between alpha- and beta-SiC that can be seen in infrared spectra and optical functions. Previous optical constants for SiC do not reflect the true bulk properties, and they are only valid for a narrow grain size range. The new optical constants presented here will allow narrow constraints to be placed on the grain size and shape distribution that dominate in astrophysical environments. In addition, our calculated absorption coefficients are much higher than laboratory measurements, which has an impact on the use of previous data to constrain abundances of these dust grains.