Deep imaging at J, H, and K is required to identify all stellar objects, brown dwarfs, and planetary mass objects in the central region of the Orion Nebula Cluster down to masses comparable to that of Jupiter. This is required to establish the initial mass function, i.e., the number of stars of each mass that have formed, in this region of intense massive star formation. A detailed knowledge of the stellar and substellar initial mass function is fundamental to understanding fragmentation processes in the molecular clouds from which stars form, determining the nature of starburst galaxies that are rapidly converting their gas into stars, and describing the chemical evolution of the Universe since stars of different mass have produced the chemical elements in different ways and at different rates.
The potential for high quality astrometry with MCAO provides a new means of identifying contaminating foreground stars. The Orion Nebula Cluster motion is predominantly along the line of sight, so large transverse motions indicate contaminating sources. The correct interpretation of stars seen towards Orion will critically depend on assigning accurate membership probabilities. This will permit a robust determination of the Orion Nebula Cluster mass function down to below the 10 Jupiter mass deuterium-burning limit. This mass range overlaps with mass function measurements for extra-solar planets already being obtained from radial velocity work.
Images of the center of the Orion Nebula Cluster in the visible (left panels) and near-infrared (right panels) take from the ground (top panels) and with the Hubble Space Telescope (bottom panels). The fields of the GSAOI detectors are shown as four green squares in each frame.