SIMBAD references

We present a detailed multi-epoch analysis of 31 potential Southern hemisphere radio calibrators that were originally observed as part of a programme to maintain the International Celestial Reference Frame. At radio wavelengths, the primary calibrators are active galactic nuclei (AGNs), powerful radio emitters which exist at the centre of most galaxies. These are known to vary at all wavelengths at which they have been observed. By determining the amount of radio source structure and variability of these AGNs, we determine their suitability as phase calibrators for long baseline radio interferometry at 2.3 GHz. For this purpose, we have used a set of complementary metrics to classify these 31 southern sources into five categories pertaining to their suitability as very long baseline interferometry calibrators. We find that all of the sources in our sample would be good interferometric calibrators, and almost ninety per cent of them would be very good calibrators.