High resolution spectroscopy of the inner ring of SN 1987A ***

We discuss high resolution VLT/UVES observations (FWHM~ 6 km s-1) from October 2002 (day ~5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A large number of narrow emission lines from the unshocked ring, with ion stages from neutral up to Ne V and Fe VII, have been identified. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (~1.5-5.0)$\times$103cm-3and temperatures of ~6.5$\times$103-2.4$\times$104K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4$\times$106-107cm-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 ~-390 km s-1in the blue wing for [Fe XIV], while the low ionization lines extend to typically ~-260 km s-1. For Hαa faint extension up to ~-450 km s-1can 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, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ~510 km s-1. We expect the maximum width of especially the low ionization lines to increase with time.