Adaptive optics imaging of the Orion Trapezium cluster

We have imaged an area ∼5 arcmin² at the center of the Trapezium cluster in Orion in the K band using the University of Hawaii (UH) adaptive optics system at the UH 2.2 m telescope. Our survey detects 292 stars brighter than K = 18.2 mag and resolves pairs to the 0″.23 diffraction limit of the telescope. The binary fraction in the angular separation range 0″.3-0″.6, corresponding to 132-264 AU at 440 pc, is indistinguishable from that of the solar-like stars in the solar neighborhood. Proplyds are associated with both single stars and visual binaries. About half the stars in our sample have also been measured at V and I by Prosser et al.; most of these seem to be about 10⁶ yr old, observed through moderate extinction, and having some excess emission at K. The luminosity function turns over before the stellar limit of ∼13.5 mag, indicating that the cluster does not contain a large population of massive brown dwarfs.