Multiwavelength diagnostics for newly discovered PNe in the outer LMC

Abstract

We have extended our PNe survey to the outer ~64deg^2 of the LMC using maps from the Magellanic Cloud Emission Line Survey (MCELS) and the UKST H-alpha and red surveys. Although the MCELS survey has poorer ~5 arcsecond resolution than the UKST survey, it has the advantage of additional narrow-band filters at H-alpha, [OIII] and [SII], providing improved diagnostic capabilities. The UKST survey has a similar angular resolution (~2 arcsec from 0.67 arcsec pixels) to our original median stacked map of the central 25deg^2 of the central LMC, but lacks the depth advantages provided by median stacking. Using these data to uncover new emission line candidates we have so far spectroscopically confirmed an extra 63 LMC PNe which we present here. We have also independently recovered and spectroscopically confirmed 107 of the 109 (98%) PNe that were previously known to exist in the outer LMC. The majority of our newly discovered and previously known PNe were confirmed using the AAOmega, multi-object fibre spectroscopy system on the 3.9-m Anglo-Australian Telescope (AAT) and the 6dF multi-object spectrograph on the UK Schmidt Telescope (UKST). These newly identified PNe were cross-checked using extant multi-wavelength imaging surveys in the near and mid-infrared in particular and against the latest emission-line ratio diagnostic plots for improved confidence in PNe identification. These new identifications raise the number of known PNe in the LMC to 715, approaching the number of 900 predicted by stellar evolutionary theory. We present accurate positions, diagnostic plots based on de-reddened emission lines, multi-wavelength SEDs and mid-infrared plots based on SAGE spitzer data.