Halpha emission-line stars in molecular clouds. II. The M42 region

TL;DR

This study conducted a comprehensive survey of Halpha emission-line stars in the M42 region, identifying nearly 1700 stars, including over 1000 new discoveries, revealing their distribution and potential association with young stellar populations in Orion.

Contribution

It provides the largest catalog of Halpha emission-line stars in M42, including many newly identified low-mass young stars, independent of infrared or X-ray selection methods.

Findings

Majority of stars follow molecular cloud distribution

Discovery of over 1000 new Halpha emission-line stars

Identification of potential foreground and background stellar populations

Abstract

We present a deep survey of Halpha emission-line stars in the M42 region using wide-field objective prism films. A total of 1699 Halpha emission-line stars were identified, of which 1025 were previously unknown, within an area of 5.5 x 5.5 degrees centred on the Trapezium Cluster. We present Halpha strength estimates, positions, and JHKs photometry extracted from 2MASS, and comparisons to previous surveys. The spatial distribution of the bulk of the stars follows the molecular cloud as seen in CO and these stars are likely to belong to the very young population of stars associated with the Orion Nebula Cluster. Additionally, there is a scattered population of Halpha emission-line stars distributed all over the region surveyed, which may consist partly of foreground stars associated with the young NGC 1980 cluster, as well as some foreground and background dMe or Be stars. The present catalogue adds a large number of candidate low-mass young stars belonging to the Orion population, selected independently of their infrared excess or X-ray emission.