We present ground-based near-infrared imaging and HST optical imaging and spectroscopy of the interaction between the ejecta of SN 1987A and its equatorial circumstellar ring .
This interaction has made a transition , from emission originating in just a few “ hot spots ” at restricted locations in position angle around the ring , to a collision producing optical emission over a nearly continuous distribution , with few breaks larger than 45 degrees .
The centroids of the first three spots are measured to move at 2000 - 3000 km s ^ { -1 } , which we interpret as a lower limit of the velocity of the forward blast front .
Multi-wavelength light curves of the spots show that they do not evolve uniformly , and change significantly on timescales as short as one month ; in particular the first spot shows a significant break in its lightcurve .
Implications of observed delays between spots appearances are discussed , which leads to a generalized model of hot spot evolution , and suggests that the early appearance of the first hot spot is explained by its inward radial position and a fairly uniform forward blast wave , rather than extraordinary physical circumstances .
Data further suggest that the forward blast is reaching the bulk of the inner ring material to the east , the density of which appears higher than elsewhere in the ring .
We study the ring geometry , finding evidence suggestive of an intrinsic ellipticity of 0.95 , and find lower and upper distance limits of 47.9 \pm 0.92 kpc and 54.4 \pm 2.1 kpc , respectively .