Star formation in 30 Doradus

TL;DR

This study uses Hubble observations to analyze the stellar populations in 30 Doradus, revealing differential extinction, identifying pre-main sequence stars, and indicating prolonged star formation with spatial distribution influenced by massive stars.

Contribution

It provides a detailed characterization of PMS stars and their ages in 30 Doradus, highlighting the extended star formation history and effects of massive stars on circumstellar discs.

Findings

Approximately 1150 PMS stars identified with Halpha excess.

Star formation in 30 Doradus spans up to 30 million years.

Older PMS stars are less common near the cluster center.

Abstract

Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.