Circumstellar materials of SN 1987A

The geometric and physical properties of the circumstellar materials of SN 1987A were studied. The detailed structure of the SN 1987A equatorial inner ring (EIR) was investigated using two dimensional spectral images of the ring obtained on 1997 December 9 (day 3942) with the Space Telescope Imaging Spectrograph (STIS) of the Hubble Space Telescope (HST). The data provided a valuable snapshot of the ring before full fledge interaction with the supernova debris started. Geometric parameters of the EIR were determined for neutral and low-ionization emission line species of H, He, O, N, S, and Ne. We also investigated the electron temperature, density, and elemental abundances around the EIR and we found no azimuthal variation around the ring.