Spectrophotometry of the supernova remnant IC 443

Spectrophotometry of the line emission at six locations in IC 443 is presented and analyzed. The temperature derived from the [O III] line intensities for two filaments is approximately 24,000 ± 8000 K, while the [N II] and [S II] line intensities indicate lower temperatures in the range 8000-12,000 K. Electron density measurements using the [S II] lines indicate densities ranging from less than 100 up to 500 cm^-3. Comparison of these observations with published shock-wave model calculations shows excellent agreement and indicates shock velocities for the filaments between 65 and 100 km s^-1, with a preshock number density of 10-20 cm^-2 for the denser filaments. The observations suggest that the remnant's shock front is encountering an inhomogeneous interstellar medium whose elemental abundances are depleted with respect to cosmic values. Also observed are relatively strong [Ca II] lines which suggest that the blast wave may partially destroy some interstellar grains. A comparison of X-ray and optical data indicates that the gas in the optical filaments has a lower pressure than the X-ray-emitting gas.