Optical and Radio Emission from the Galactic Supernova Remnant HB 3(G132.6 +1.5)

Wide-field Hα images of the galactic supernova remnant RB 3 are presented and compared to new DRAO radio continuum maps at 408 and 1420 MHz with angular resolutions of 3.5' × 4.O' and 1.0' × 1.13', respectively. RB 3's optical emission appears as a broken shell of filamentary and diffuse emission, most incomplete along the northern rim. New optical filaments are detected along the remnant's southern radio boundary, in an area of suspected greater extinction due to a foreground molecular emission ridge. An optical spectrum of bright, western limb filaments indicates a shock velocity ≤100 km s⁻¹, a [S II] λ6716/λ6731 derived electron density of ≤150 cm⁻³, and an E(B - V) = 0.71±0.04 consistent with x-ray derived column density estimates. The remnant's radio spectral index is - 0.64±0.01, evaluated in regions away from confusing emission from W3. RB 3's scalloped western structure suggests multiple shock fronts, possibly related to the remnant's large size and late evolutionary stage, where the remnant's shock is expanding into density irregularities in the local interstellar medium. Overall, we find a strong correlation between individual radio and optical emission features at both large and small spatial scales. We suggest that a strong radio-optical correlation plus a multishell structure may be better indicators of advanced remnant age than the often mentioned diffuse optical morphology.