We discuss high resolution VLT/UVES observations ( FWHM \sim 6 ~ { } km~ { } s ^ { -1 } ) from October 2002 ( day \sim 5700 past explosion ) of the shock interaction of SN 1987A and its circumstellar ring .
A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of ( \sim 1.5 - 5.0 ) \times 10 ^ { 3 } \mbox { cm } ^ { -3 } and temperatures of \sim 6.5 \times 10 ^ { 3 } -2.4 \times 10 ^ { 4 } K. This is consistent with the thermal widths of the lines .
From the shocked component we observe a large range of ionization stages from neutral lines to [ Fe XIV ] .
From a nebular analysis we find that the density in the low ionization region is 4 \times 10 ^ { 6 } -10 ^ { 7 } \mbox { cm } ^ { -3 } .
There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [ Fe X-XIV ] , with the latter extending up to \sim - 390 ~ { } km~ { } s ^ { -1 } in the blue wing for [ Fe XIV ] , while the low ionization lines extend to typically \sim - 260 ~ { } km~ { } s ^ { -1 } .
For H \alpha a faint extension up to \sim - 450 ~ { } km~ { } s ^ { -1 } can be seen probably arising from a small fraction of shocked high density clumps .
We discuss these observations in the context of radiative shock models , which are qualitatively consistent with the observations .
A fraction of the high ionization lines may originate in gas which has yet not had time to cool down , explaining the difference in width between the low and high ionization lines .
The maximum shock velocities seen in the optical lines are \sim 510 ~ { } km~ { } s ^ { -1 } .
We expect the maximum width of especially the low ionization lines to increase with time .