  We discuss the findings of a comprehensive imaging and spectroscopic survey
of the optical emission associated with the supernova remnant 3C 58 (Fesen et
al. 2007) as they relate to the topic of pre-SN mass loss. Spectroscopically
measured radial velocities of ~450 emission knots within the remnant show two
distinct kinematic populations of optical knots: a high-velocity group with
radial velocities in the range of 700 - 1100 km/s and a lower velocity group
exhibiting radial expansion velocities below ~250 km/s. We interpret the
high-velocity knots as ejecta from the SN explosion and the low-velocity knots
as shocked circumstellar material likely resulting from pre-SN mass loss. The
chemical signatures of the two populations also show marked differences. The
high velocity group includes a substantial number of knots with notably higher
[N II]/H-alpha ratios not seen in the lower velocity population, suggesting
greater nitrogen enrichment in the SN ejecta than in the CSM. These results are
compared with evidence for pre-SN mass loss in the Crab Nebula, perhaps the SNR
most similar to 3C 58. These SNRs may comprise two case studies of pre-SN mass
loss in relatively low mass (~8 - 10 solar masses) core-collapse SN
progenitors.
