A catalog of outer ejecta knots in Cas A

These ejecta fragments are found near or ahead of the remnant's forward shock front and mostly lie from 120" to 300" in radial distance from the remnant's center of expansion. Filter flux ratios when correlated with published spectra show that these knots can be divided into three emission classes: (1) knots dominated by [NII] {lambda}6548,{lambda}6583 emissions, (2) knots dominated by [OII] {lambda}7319, {lambda}7330 emissions, and (3) knots displaying filter flux ratios suggestive of [SII], [OII], and [ArIII] {lambda}7135 emission line strengths similar to the "fast-moving knots" (FMKs) found in the remnant's bright main shell.

Of 1825 knots identified, 444 are strong [NII] emission knots, 192 are strong [OII] emission knots, and 1189 are FMK-like knots. In terms of location around the remnant, 972, 207, and 646 knots are found in the remnant's northeast jet, southwest jet, and non-jet regions, respectively. Assuming a distance of 3.4kpc, derived knot transverse velocities based on proper motion measurements spanning a 9 month interval indicate maximum transverse expansion velocities for these three knot classes of 14500, 13500, and 11500km/s, respectively.