CHANGES IN THE OPTICAL REMNANT OF KEPLER SUPERNOVA DURING THE PERIOD 1942-1989

Images of the optical nebulosity associated with Kepler's supernova = 3C 358 = G4.5 + 6.8 have been obtained at the Mount Wilson Observatory in 1941-1943, at the Palomar Observatory in 1950-1983, and on La Silla in 1989. These data have been used to study the luminosity evolution of individual knots and the expansion and translation of the optical remnant of Kepler's supernova of 1604. From a study of the motions of 50 long-lived knots we find <mu-x> = -0".623 +/- 0".045 century-1, <mu-y> = 0".484 +/- 0".049 century-1 and an expansion time scale of 32,000 +/- 12,000 yr. For an assumed distance of 4.5 kpc the centroid of the nebulosity has a tangential velocity of 117 +/- 10 km s-1 to the W and 105 +/- 11 km s-1 to the N. By combining astrometric and spectroscopic information, a space velocity of 278 +/- 12 km s-1 is estimated. This indicates that the progenitor of SN 1604 was a high-velocity object. It could have been either a Population II star or a massive high-velocity runaway star. Comparison of old and new images indicates that most new knots occur along the outer part of the northern rim of the supernova remnant (SNR). Recently some knots have also appeared near the center of the remnant, to the south of those already existing. The evolutionary time scales of knots in Kepler's SNR are similar to those of quasi-stationary flocculi in Cassiopeia A, but considerably longer than those of fast-moving knots in Cas A.