OPTICAL-IDENTIFICATION OF DUST WITHIN THE CRAB NEBULAS FILAMENTS

We present optical continuum images of the Crab Nebula which reveal numerous, small "dark spots" across the face of the Crab's amorphous synchrotron nebula. These spots range in size from being unresolved at 0″.8 resolution to ≈5″, exhibit Δm4770 = 0.08-0.44, and are most visible in the shorter wavelength continuum images. Comparisons with images taken using interference filters centered on various nebulae emission lines indicate that these dark features are coincident with [O I], [C I], and [S II] bright cores of selected filaments. This positional coincidence plus a wavelength dependence similar to that exhibited by conventional interstellar dust establishes the presence of dust within at least some of the Crab Nebula's filaments. Dust condensation in the Crab's ejecta probably occurred early in the evolution of the remnant when the filament cores were relatively dense and had cooled to below 1000 K.