MEASUREMENTS OF THE DIAMETER OF THE SUPERNOVA SN-1987A

We present speckle interferometric measurements of the angular diameter of SN 1987A in the Large Magellanic Cloud obtained at 664 days after the outburst. Diameters were estimated with milliarcsecond precision at 657 nm and 550 nm by fitting model visibility functions to the data corresponding to different intensity distributions for the supernova disk. Measurements made assuming a uniform intensity distribution were compared to the uniform disk measurements obtained from 30 days after the explosion. Diameter measurements obtained near the center of the H-alpha line are consistent with homologous expansion of the supernova shell with a mean velocity of 2850 kms-1. The linear least-squares fit to the measurements obtained at other wavelengths from 260 days after the explosion yielded a somewhat lower than mean expansion velocity.