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tokens: a systemic velocity for the SNR. The broad range of ejecta space velocities and expansion indices (see Table 1 ) that we measure in our sample may be characteristic for an SNR transitioning from the free-expansion phase to the Sedov–Taylor phase. Measurements of the proper motion at various locations along Kepler’s forward shock by Katsuda et al. ( 2008 ) and Vink ( 2008 ) found expansion indices of 0.47–0.82 and 0.3–0.7, respectively. For remnants nearing the Sedov–Taylor phase, Chevalier ( 1982 ) estimated η = 0.4 for s = 0 and η = 0.67 for s = 2 ambient density power-law solutions. Hence, our ejecta velocity measurements and previous forward shock analyses apparently suggest that the kinematics for some regions in Kepler may be dominated by nearly free expansion, while others are better described by Sedov–Taylor dynamics. New 3D hydrodynamical simulations that focus on Kepler and these high η knots may give some insight into their origin. The knots N2, N5, N1, and N3 have the highest measured space velocities (6100–8700 d 6 km s −1 ), and are all located in the “steep arc” (DeLaney et al. 2002 ) of Kepler’s SNR, a “bar” of bright X-ray emission that runs from east to west, located about halfway between the center of the remnant and the outer edge of the main shell. They are projected close to each other within a small (50′′ × 20′′) area. This proximity, and similarities in their measured Si abundances, space velocity vectors, and expansion indices, suggest that these knots might have originated generally from a “common” layer of the exploding white dwarf. Sato Hughes ( 2017b ) measured properties of another knot (they label “N4”) projected within the steep arc, which exhibited similar properties to N2, N5, N1, and N3. This suggests that ejecta within the steep arc have generally homogeneous kinematic and spectroscopic properties. In the western Ear, we measure high space velocity in region Ear2, v s ∼ 5800 d 6 km s −1 . Such a high velocity may be expected considering the knot’s projected location in the western Ear feature, which protrudes out about 30% beyond the main shell. Interestingly, knot Ear1 has a significantly smaller space velocity, v s ∼ 3300 d 6 km s −1 , even though it is projected very close to the position of Ear2. Knot Ear1 may be interacting with a CSM-dominated feature identified by Burkey et al. ( 2013 ) projected adjacent to it, which could have caused it to significantly decelerate recently. Such an interaction between ejecta and CSM may produce H α emission. We searched for H α emission at the location of Ear1 in the archival Hubble Space Telescope images (with the F656N filter) of Kepler (Sankrit et al. 2016 ). We found a faint wisp centered at Ear1's position, possibly indicating the presence of shocked CSM gas, which would support our conclusion of an ejecta-CSM interaction there. Considering their spatial proximity and similarly high Si abundance, it seems likely that Ear1 and Ear2 were produced very near each