On the Propinquity of Shock-Excited and Photoionized Plasma:The Supernova Remnant and the H II Region of N63A

Abstract

We present spectra covering the range {λ}3400-{λ}10100 ofnebula N63A in the Large Magellanic Cloud. This object contains asupernova remnant adjacent to an H II region and thus illustratesvividly the optical and near-infrared differences between shock-ionizedand photoionized emission nebulae. Species of low ionization potential,such as [S II] and [C I], predominate and emit strongly in theshock-heated region, while these elements are more highly ionized in theH II region. The gas-phase abundance of elements also affects theiremission line strengths, and this depends on the particular excitationmechanism. A supernova shock can liberate calcium that is bound tointerstellar grains, while photoionization does not reduce gas-phasedepletion. In addition to providing a laboratory for comparison of theeffects of shocks and photons on the interstellar medium, N63A is abright object, which enables the measurement of lines that are typicallytoo weak to observe elsewhere. In the shocked region we identify fivelines of the 1F multiplet of Cr II and measure lines of [Cl II] and [CI].