An ATCA radio-continuum study of the Small Magellanic Cloud – V. Long-slit optical spectroscopy of supernova remnants and confirmation of a new candidate supernova remnant

We present optical long-slit spectra and estimated line ratios for 11 of the 16 known radio supernova remnants (SNRs) in the Small Magellanic Cloud (SMC) using observations made with the 2.3-m Advanced Technology Telescope and double-beam spectrograph at Siding Springs Observatory in Australia. We also present spectra and estimated line ratios for a twelfth source, a previously reported candidate radio SNR, J004100−733648. Our new data for this source confirm its classification as a SNR. We find that these shocks show no evolutionary trends, implying that reported relationships between diameter and line ratios may instead be due to selection effects. We have also used the estimated line ratios in the spectra of these SNRs – which we assume to be dominated by the interstellar medium (ISM) at this stage of their evolution – to derive an estimate of 10−4 (based on oxygen to hydrogen ratio) for the abundances of metals in the ISM of the SMC. This value is in general agreement with other values previously published in the literature.