# Hierarchical Classification of Variable Stars Using Deep Convolutional Neural Networks

**Authors:** Mahdi Abdollahi, Nooshin Torabi, Sadegh Raeisi, Sohrab Rahvar  
**arXiv:** [2301.08497](https://arxiv.org/abs/2301.08497)  
**Date:** 2023-01-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2301.08497v1/

## Key points

- Fast and automatic methods are increasingly important for classifying variable stars in large datasets
- Traditional algorithms like Random Forest have been used, but neural networks have gained attention due to lower computational cost
- Mahdi Abdollahi et al. present a hierarchical model for classification of variable stars using deep convolutional neural networks
- The Hierarchical Classification technique contains two main steps: predicting class and then subclass of stars
- Both Convolutional Neural Networks (CNN) and Recurrent Neural Networks (RNN) are tested in the study
- Pre-processing method uses light curves and period of stars as input data
- Authors consider most classes and subclasses of variable stars in OGLE-IV database and show that using Hierarchical Classification technique with appropriate preprocessing can increase accuracy of predicting smaller classes such as ACep and T2Cep
- Accuracy rate obtained is 98% for class classification and 93% for subclasses classification
- Using folded light curves has the disadvantage of losing period information which is a critical feature for classification, so the value of the period is provided as a separate feature to the model
- Authors compare accuracy and runtime of each type of neural network used to classify variable stars, and use several classifiers to achieve better accuracy through hierarchical classification.
- Future work could include including other datasets like WISE and Gaia.
- Pre-processing method is challenging due to its high cost because of processing needed for calculating the period, but it has a significant advantage over other methods based on features extracted from light curves.

## Summary

In recent years, the use of fast and automatic methods to classify variable stars for large amounts of data has become increasingly important. Traditional algorithms like Random Forest have been used in the past to classify variable stars, but neural networks as classifiers have gained attention due to their lower computational cost. In a recent study published in the Iranian Journal of Astronomy and Astrophysics, Mahdi Abdollahi et al. present a hierarchical model for classification of variable stars using deep convolutional neural networks. The Hierarchical Classification technique used in this study contains two main steps: predicting class and then subclass of stars. All models in both steps have the same network structure, and both Convolutional Neural Networks (CNN) and Recurrent Neural Networks (RNN) are tested. The pre-processing method uses light curves and period of stars as input data. The authors consider most classes and subclasses of variable stars in OGLE-IV database and show that using Hierarchical Classification technique with appropriate preprocessing can increase accuracy of predicting smaller classes such as ACep and T2Cep. The authors obtain an accuracy rate of 98% for class classification and 93% for subclasses classification. They also note that using folded light curves has the disadvantage of losing period information which is a critical feature for classification of variable stars. To solve this problem, the value of the period is provided as a separate feature to the model. In addition to discussing their methodology, Abdollahi et al. compare the accuracy and runtime of each type of neural network used to classify variable stars. They also explain how they use several classifiers to achieve better accuracy through hierarchical classification. While this study was done using OGLE-IV dataset, future work could include including other datasets like WISE and Gaia. The authors note that although their pre-processing method is challenging due to its high cost because of processing needed for calculating the period, it has a significant advantage over other methods based on features extracted from light curves. Overall, this study highlights the importance of using efficient and accurate methods for classifying variable stars in large datasets which can help improve astronomical research efforts worldwide by providing more reliable results faster than traditional methods can offer.