Search for X-ray line emission from Cassiopeia A

The large area graphite crystal spectrometer aboard OSO 8 has been used to search for X-ray line emission from Cas A from ions of Si, S, and Fe over the energy band 1.865 to 8 keV. No evidence was obtained for line emission. The upper limits for the Si and S line fluxes are used to establish upper limits on the abundances of these elements. The limit on the Fe line flux is consistent with the strength of the emission feature reported in proportional counter experiments. Questions of nonequilibrium in ionization in Cas A and the effects on X-ray line emission are considered.