Second Epoch Hubble Space Telescope Observations of Kepler's Supernova Remnant: The Proper Motions of Balmer Filaments

TL;DR

This study uses high-resolution Hubble images taken 10 years apart to measure the proper motions of Balmer filaments in Kepler's supernova remnant, revealing shock velocities, distances, and variations in shock properties across the remnant.

Contribution

It provides improved proper motion measurements, revised shock velocities, and insights into the spatial variation of shock properties and circumstellar material in Kepler's supernova remnant.

Findings

Distance to Kepler's remnant is 5.1 kpc.

Main shock speed around northern rim is 1690 km/s.

Shock properties vary over small spatial scales.

Abstract

We report on the proper motions of Balmer-dominated filaments in Kepler's supernova remnant using high resolution images obtained with the Hubble Space Telescope at two epochs separated by about 10 years. We use the improved proper motion measurements and revised values of shock velocities to derive a distance to Kepler of 5.1 [+0.8, -0.7] kpc. The main shock around the northern rim of the remnant has a typical speed of 1690 km/s and is encountering material with densities of about 8 cm^-3. We find evidence for the variation of shock properties over small spatial scales, including differences in the driving pressures as the shock wraps around a curved cloud surface. We find that the Balmer filaments ahead of the ejecta knot on the northwest boundary of the remnant are becoming fainter and more diffuse. We also find that the Balmer filaments associated with circumstellar material in the interior regions of the remnant are due to shocks with significantly lower velocities and that the brightness variations among these filaments trace the density distribution of the material, which may have a disk-like geometry.