The accurate automated classification of variable stars into their respective sub-types is difficult. Machine learning based solutions often fall foul of the imbalanced learning problem, which causes poor generalisation performance in practice, especially on rare variable star sub-types. In previous work, we attempted to overcome such deficiencies via the development of a hierarchical machine learning classifier. This algorithm-level approach to tackling imbalance, yielded promising results on Catalina Real-Time Survey (CRTS) data, outperforming the binary and multi-class classification schemes previously applied in this area. In this work, we attempt to further improve hierarchical classification performance by applying data-level approaches to directly augment the training data so that they better describe under-represented classes. We apply and report results for three data augmentation methods in particular: $textit{R}$andomly $textit{A}$ugmented $textit{S}$ampled $textit{L}$ight curves from magnitude $textit{E}$rror ($texttt{RASLE}$), augmenting light curves with Gaussian Process modelling ($texttt{GpFit}$) and the Synthetic Minority Over-sampling Technique ($texttt{SMOTE}$). When combining the algorithm-level (i.e. the hierarchical scheme) together with the data-level approach, we further improve variable star classification accuracy by 1-4$%$. We found that a higher classification rate is obtained when using $texttt{GpFit}$ in the hierarchical model. Further improvement of the metric scores requires a better standard set of correctly identified variable stars and, perhaps enhanced features are needed.
Download