A New Halpha Emission-Line Survey in the Orion Nebula Cluster

TL;DR

This study conducted a comprehensive Halpha emission-line survey in the Orion Nebula Cluster, identifying new young stars, classifying them, and analyzing their distribution, variability, and properties to better understand star formation and evolution.

Contribution

It presents the first large-scale Halpha emission-line survey in the Orion Nebula Cluster, identifying new emission-line stars and analyzing their properties and distribution.

Findings

Identified 587 Halpha emission stars, including 99 new detections.

Found clustered and dispersed populations with different properties.

Observed variability in Halpha emission with amplitudes up to 2-3 times.

Abstract

We present results from an Halpha emission-line survey in a one square degree area centered on the Orion Nebula Cluster, obtained with the Wide Field Grism Spectrograph-2 on the 2.2-meter telescope of the University of Hawaii. We identified 587 stars with Halpha emission, 99 of which, located mainly in the outer regions of the observed area, have not appeared in previous Halpha surveys. We determined the equivalent width (EW) of the line, and based on it classified 372 stars as classical T Tauri stars (CTTS) and 187 as weak line T Tauri stars (WTTS). Simultaneous r', i' photometry indicates a limiting magnitude of r' ~ 20 mag, but the sample is incomplete at r' > 17 mag. The surface distribution of the Halpha emission stars reveals a clustered and a dispersed population, the former consisting of younger and more massive young stars than the latter. Comparison of the derived EWs with those found in the literature indicates variability of the Halpha line. We found that the typical amplitudes of the variability are not greater than a factor 2-3 in the most cases. We identified a subgroup of low-EW stars with infrared signatures indicative of optically thick accretion disks. We studied the correlations between the equivalent width and other properties of the stars. Based on literature data we examined several properties of our CTTS and WTTS subsamples and found significant differences in mid-infrared color indices, average rotational periods, and spectral energy distribution characteristics of the subsamples.