A Wide-Field Survey of the Orion Nebula Cluster in the Near-Infrared

Abstract

We present J, H, and K _S photometry of the Orion Nebula Cluster (ONC) obtained at the CTIO/Blanco 4 m telescope at Cerro Tololo with the Infrared Side Port Imager camera. From the observations we have assembled a catalog of about ~7800 sources distributed over an area of approximately 30' × 40', the largest of any survey deeper than the Two Micron All Sky Survey (2MASS) in this region. The catalog provides absolute coordinates accurate to about 0.15 arcsec and 3σ photometry in the 2MASS system down to J≃ 19.5 mag, H≃ 18.0 mag, K{_S} ≃ 18.5 mag, enough to detect planetary size objects 1 Myr old under A_V ~= 10 mag of extinction at the distance of the Orion Nebula. We present a preliminary analysis of the catalog, done by comparing the (J-H, H-K _S ) color-color diagram, the (H, J-H) and (K _S , H-K _S ) color-magnitude diagrams, and the J H K _S luminosity functions (LFs) of three regions at an increasing projected distance from the Trapezium. Sources in the inner region typically show IR colors compatible with reddened T Tauri stars, whereas the outer fields are dominated by field stars seen through an amount of extinction which decreases with the distance from the center. The color-magnitude diagrams make it possible to clearly distinguish between the main ONC population, spread across the full field, and background sources. The LFs of the inner region, corrected for completeness, remain relatively flat in the substellar regime regardless of the strategy adopted to remove background contamination.