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

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 0.7 0.8 -+ kpc. The main shock around the northern rim of the remnant has a typical speed of 1690 km s −1 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.

Freely Expanding Knots of X-Ray-emitting Ejecta in Kepler’s Supernova Remnant

“…The distance to Kepler's SNR is not well known with estimates ranging from ∼4.0 kpc to > 7 kpc; here we use a value of 5 kpc which is consistent with H I absorption measurements (Reynoso & Goss 1999) and recent optical proper motion measurements of Balmer shocks (Sankrit et al 2016). Figure 7 presents the scatter plot of 3D space velocity versus expansion index.…”

“…3). We also identified three CSM knots and the northwest ejecta knots (Ej1, 2, 3, and 4, which we combined into two separate knots Ej1-2, Ej3-4) whose proper motions were recently measured with the Hubble Space Telescope (HST; Sankrit et al 2016). None of the N, NE, and SW knots showed any evidence for optical emission in the HST images, while the CSM and Ej knots all did.…”

“…The N and SW knots have high radial speeds (5,590 km s −1 < v < 10,020 km s −1 ) that are ∼2-3 times higher than the ejecta knot speeds quoted by Sankrit et al (2016) from HST proper motions: ∼ 1,600-3,000 km s −1 . On the other hand, the CSM and Ej knots show relatively low speeds (< 2,300 km s −1 ).…”

“…We report on three knots with near-solar abundances that show little proper motion or radial velocity. The Ej knots were selected because their associated Hα shocks had measured proper motions from HST data (Sankrit et al 2016). In the X-ray band these knots have metal-enhanced abundances but with a larger abundance of low-Z species (O, Ne, Mg) compared to Si, S, and Fe than the other X-ray ejecta knots studied here.…”

An Ejecta Kinematics Study of Kepler’s Supernova Remnant with High-resolution Chandra HETG Spectroscopy

“…Such an interaction between ejecta and CSM may produce Hα emission. We searched for Hα emission at the location of R8 in the archival Hubble Space Telescope images (with the F656N filter) of Kepler (Sankrit et al 2016). We found a faint wisp centered at R8's position, possibly indicating the presence of shocked CSM gas, which would support our conclusion of an ejecta-CSM interaction there.…”