AD warmly acknowledges the award of an international Macquarie University Research Excellence Scholarship (iMQRES). BE is supported by the German Research Foundation (DFG) Cluster of Excellence “Origin and Structure of the Universe”. AYK acknowledges the support from the National Research Foundation (NRF) of South Africa. We would like to thank Prof. Wolf-Rainer Hamann, Prof. Simon Jeffery and Dr. Amanda Karakas for illuminating discussions and helpful comments. We would also like to thank Dr. Kyle DePew for carrying out the 2010 ANU 2.3 m observing run. AD thanks Dr. Milorad Stupar for assisting with the 2012 ANU 2.3 m observing run and his guidance on the IRAF pipeline WIFES, Prof. Quentin A. Parker and Dr. David J. Frew for helping in the observing proposal writing stage, and the staff at the ANU Siding Spring Observatory for their support. We would also like to thank the anonymous referee for helpful suggestions.