The Structure and Evolution of the Circumstellar Ring Around SN1987A
Session 31 -- Supernovae
Oral presentation, Wednesday, January 12, 2:15-3:45, Salon V Room (Crystal Gateway)

## [31.01] The Structure and Evolution of the Circumstellar Ring Around SN1987A

P.Plait (U.Virginia), P.Lundqvist (Stockholm Observatory), R.Chevalier (U.Virginia), R.P.Kirshner (Center for Astrophysics)

Continuing Hubble Space Telescope observations through May 1993 show that the narrow line emission of the circumstellar ring around SN1987A has faded substantially since the first images were made in 1990 August, but has not changed substantially in structure. Images in [OIII], H$\beta$, and [NII] give an opportunity to determine some of the physical parameters of the ring. Assuming the gas was initially excited by the UV burst from the supernova and has been undergoing recombination, we model the spatially resolved electron density of the ring. We find the maximum electron density from the [OIII] $\lambda 5007$ emission line to be 1.2 x $10^4 \quad \!\!{\rm cm^{-3}}$ on average. The physical morphology of the ring is significantly different when imaged in different lines, providing a method of mapping different density regions. Knowledge of the velocity field of the ring allows the structure to be remapped into a velocity profile, and we predict the appearance of high resolution line profiles. By assuming the currently observered structure in optical lines applies to the early structure in ultraviolet lines, we construct UV line light curve models to be compared to the early IUE observations. We find that the clumpy structure of the ring has relatively little effect on the shape of the light curve. We report of the existence of a star superposed on the ring which is consistent with a main sequence A type dwarf ($\rm V_{\rm mag} = 20.2$) at the approximate distance of the supernova. The [OIII] images also show extensive nebulosity associated with the bipolar nebula around SN1987A, which may affect the observations of the ring. Finally, we speculate on the evidence for expansion versus contraction of the circumstellar ring.