Near-Infrared Variability in the Orion Nebula Cluster

TL;DR

This study presents a comprehensive near-infrared variability survey of the Orion Nebula Cluster, revealing diverse variability mechanisms, timescales, and new variable star phenomena in young stellar objects over nearly three years.

Contribution

It provides the first extensive near-infrared variability dataset for the Orion Nebula Cluster, identifying key variability mechanisms and long-term behaviors in young stars.

Findings

1203 variable stars identified out of 15,000 monitored.

Longer timescale variability is associated with disk/accretion processes.

Discovery of new eclipsing binaries and long-period variables.

Abstract

Using the United Kingdom Infrared Telescope on Mauna Kea, we have carried out a new near-infrared J, H, K monitoring survey of almost a square degree of the star-forming Orion Nebula Cluster with observations on 120 nights over three observing seasons, spanning a total of 894 days. We monitored ~15,000 stars down to J=20 using the WFCAM instrument, and have extracted 1203 significantly variable stars from our data. By studying variability in young stellar objects (YSOs) in the H-K, K color-magnitude diagram, we are able to distinguish between physical mechanisms of variability. Many variables show color behavior indicating either dust-extinction or disk/accretion activity, but we find that when monitored for longer periods of time, a number of stars shift between these two variability mechanisms. Further, we show that the intrinsic timescale of disk/accretion variability in young stars is longer than that of dust-extinction variability. We confirm that variability amplitude is statistically correlated with evolutionary class in all bands and colors. Our investigations of these 1203 variables have revealed 73 periodic AA Tau type variables, many large-amplitude and long-period (P > 15 day) YSOs, including three stars showing widely-spaced periodic brightening events consistent with circumbinary disk activity, and four new eclipsing binaries. These phenomena and others indicate the activity of long-term disk/accretion variability processes taking place in young stars. We have made the light curves and associated data for these 1203 variables available online.