The ultraviolet properties of cool material ejected by hydrogen-deficient stars.

Abstract

Carbon-rich H-deficient stars which shed dusty material in the line-of-sight exhibit RCrB-like optical variations. The UV extinction toward several such objects differs significantly from the average interstellar extinction law; these data have been re-examined. The observed peak in extinction at 4.1μm^-1^(=240nm) has previously been explained in terms of anhydrous carbon grains but difficulties remain, particularly regarding the low observed extinction at shorter wavelengths. Laboratory absorption measurements of C_60_ and related molecules are found to be consistent with the UV 4.1μm^-1^ extinction peak, but do not provide sufficient extinction at 1/λ<3.5μm^-1^ and have insufficient wavelength coverage to compare with the crucial short wavelength observations.