The remnant of Kepler's supernova

Abstract

Proper-motion observations covering the period 1942-1976 show that the expansion time scale for the optical remnant of SN 1604 is greater than the order of 10,000 years. This indicates that the remnant consists of circumstellar material that was excited by the supernova shell. The optical remnant is found to have a tangential velocity of 525 + or - 117 km/s. This suggests that Kepler's supernova (which was of Type I) was produced by a star with a Population II-type orbit. A few emission flocculi have brightened significantly during the last 35 years. No flocculi have faded, however, during this same period of time. Both seventeenth-century color observations and photometry of field stars give a foreground reddening of 0.7 + or - 0.2. This reddening value and the assumption that SN 1604 occurred in the nuclear bulge of the Galaxy yield an absolute visual magnitude at maximum light of -19.3 + or - 0.7.