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We analyze and model the infrared spectrum of the Cassiopeia A supernovaremnant, with the aim of determining the masses of various elements in theunshocked ejecta. In this way we complement the survey of the X-ray emittingejecta of Hwang & Laming (2012) to provide a complete census of the elementalcomposition of the Cas A ejecta. We calculate photoionization-recombinationequilibria to determine the ionization balance of various elements in theejecta as a function of density, using the X-ray and UV emission from theforward and reverse shocks as the ionizing radiation. With the assumption thatall emission lines are principally excited at the ejecta density that maximizestheir emission, we can convert observed line intensities into element masses.We find that the majority of the $\sim 3 $M_sun ejecta have already beenthrough the reverse shock and are seen today in X-rays. A minority, $\sim0.47\pm 0.05$ M_sun, with uncertainties quoted here coming from the datafitting procedure only, are still expanding inside the reverse shock andemitting in the infrared. This component is comprised mainly of O, Si, and S,with no Fe readily detectable. Incorporating uncertainties estimated to comefrom our modeling, we quote $0.47 \pm {0.47\atop 0.24}$ M_sun. We speculatethat up to a further 0.07 M_sun of Fe may be present in diffuse gas in theinner ejecta, depending on the Fe charge state.

Element Abundances in the Unshocked Ejecta of Cassiopeia A