Periodic Variable Star Classification with Deep Learning: Handling Data Imbalance in an Ensemble Augmentation Way

TL;DR

This paper introduces a novel ensemble deep learning approach combining RNN and CNN architectures, augmented with Gaussian Process-generated synthetic light curves, to improve classification of imbalanced periodic variable stars in large sky surveys.

Contribution

It proposes a new ensemble augmentation method using Gaussian Process-generated data and combines RNN and CNN models for better classification of imbalanced periodic variable stars.

Findings

Compound RNN-CNN network achieves 86.2% balanced accuracy.

Ensemble augmentation effectively addresses class imbalance.

Method improves classification for future large-scale sky surveys.

Abstract

Time-domain astronomy is progressing rapidly with the ongoing and upcoming large-scale photometric sky surveys led by the Vera C. Rubin Observatory project (LSST). Billions of variable sources call for better automatic classification algorithms for light curves. Among them, periodic variable stars are frequently studied. Different categories of periodic variable stars have a high degree of class imbalance and pose a challenge to algorithms including deep learning methods. We design two kinds of architectures of neural networks for the classification of periodic variable stars in the Catalina Survey's Data Release 2: a multi-input recurrent neural network (RNN) and a compound network combing the RNN and the convolutional neural network (CNN). To deal with class imbalance, we apply Gaussian Process to generate synthetic light curves with artificial uncertainties for data augmentation. For better performance, we organize the augmentation and training process in a "bagging-like" ensemble learning scheme. The experimental results show that the better approach is the compound network combing RNN and CNN, which reaches the best result of 86.2% on the overall balanced accuracy and 0.75 on the macro F1 score. We develop the ensemble augmentation method to solve the data imbalance when classifying variable stars and prove the effectiveness of combining different representations of light curves in a single model. The proposed methods would help build better classification algorithms of periodic time series data for future sky surveys (e.g., LSST).