Hubble Tarantula Treasury Project – VI. Identification of Pre–Main-Sequence Stars using Machine Learning techniques

The Hubble Tarantula Treasury Project (HTTP) has provided an unprecedented photometric coverage of the entire starburst region of 30 Doradus down to the half Solar mass limit. We use the deep stellar catalogue of HTTP to identify all the pre-main-sequence (PMS) stars of the region, i.e. stars that have not started their lives on the main-sequence yet. The photometric distinction of these stars from the more evolved populations is not a trivial task due to several factors that alter their colour-magnitude diagram positions. The identification of PMS stars requires, thus, sophisticated statistical methods. We employ machine-learning classification techniques on the HTTP survey of more than 800 000 sources to identify the PMS stellar content of the observed field. Our methodology consists of (1) carefully selecting the most probable low-mass PMS stellar population of the star-forming cluster NGC 2070, (2) using this sample to train classification algorithms to build a predictive model for PMS stars, and (3) applying this model in order to identify the most probable PMS content across the entire Tarantula Nebula. We employ decision tree, random forest (RF), and support vector machine (SVM) classifiers to categorize the stars as PMS and non-PMS. The RF and SVM provided the most accurate models, predicting about 20 000 sources with a candidateship probability higher than 50 per cent, and almost 10 000 PMS candidates with a probability higher than 95 per cent. This is the richest and most accurate photometric catalogue of extragalactic PMS candidates across the extent of a whole star-forming complex.