Coronal emission from the shocked circumstellar ring of SN 1987A

High resolution spectra with UVES/VLT of SN 1987A from December 2000 until November 2005 show a number of high ionization lines from gas with velocities of roughly 350 km/s, emerging from the shocked gas formed by the ejecta-ring collision. These include coronal lines from [Fe X], [Fe XI] and [Fe XIV] which have increased by a factor of about 20 during the observed period. The evolution of the lines is similar to that of the soft X-rays, indicating that they arise in the same component. The line ratios are consistent with those expected from radiative shocks with velocity 310-390 km/s, corresponding to a shock temperature of (1.6-2.5) x 10^6 K. A fraction of the coronal emission may, however, originate in higher velocity adiabatic shocks.