  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.
