Powered by the dynamical interaction of the ejecta with the inner circumstellar ring, SN 1987A is
dramatically evolving at all wavelengths on time scales less than a year.
Repeated observations of the ejecta-ring collision have been carried out using the UVES echelle spectrograph
at VLT. My presentation will cover seven epochs of high resolution spectra from October 1999 until November
2007. Three different emission line components are identified from the spectra. A narrow (~10 km/s) velocity
component is coming from the unshocked ring. An intermediate (~250 km/s) component is arising from the
shocked ring and a broad component extending to ~15,000 km/s is coming from the reverse shock. Due to the
high spectral resolution, it has been possible to separate the shocked- from the unshocked ring emission.
For the unshocked gas ion stages from neutral up to Ne V and Fe VII were found. The line fluxes of the
low-ionization lines decline during the period of the observations. However, the fluxes of the [O III] and
[Ne III] lines appear to
increase and this is found to be consistent with the heating of the pre-shock gas by the X-rays from the
shock interactions. The line emission from the shocked ring increases rapidly as more gas is swept up by the
shocks. This emission comes from ions with a range of ionization stages (e.g., Fe II-XIV). The
low-ionization lines show an increase in their line widths and this is consistent with the fact that these
lines originate from radiative shocks. The high-ionization line profiles (Fe X-XIV) show larger extensions,
which indicate that at least a fraction of the emission comes from non-radiative shocks.