[ITAL]Hubble Space Telescope[/ITAL] Spectroscopy of Spot 1 on the Circumstellar Ring of SN 1987A

Abstract

We present ultraviolet and optical spectra of the first bright spot (P.A. = 29°) on SN 1987A's equatorial circumstellar ring taken with the Space Telescope Imaging Spectrograph. We interpret this spot as the emission produced by radiative shocks that occur where the supernova blast wave strikes an inward protrusion of the ring. The observed line widths and intensity ratios indicate the presence of radiative shocks with velocities ranging from 100 to 250 km s-1 entering dense (≳104 cm-3) gas. These observations, and future observations of the development of the spectra and line profiles, provide a unique opportunity to study the hydrodynamics of radiative shocks.