Binary Formation in the Orion Nebula Cluster: Investigating the Low-mass Stellar and Sub-Stellar Population

We present updated results constraining multiplicity demographics for the stellar and substellar population of the Orion Nebula Cluster (ONC), across primary masses 0.012 - 0.6 M . Our study utilizes archival Hubble Space Telescope (HST) data obtained with the Advanced Camera for Surveys(ACS) using multiple filters (PID: 10246, PI M. Robberto). Studying the companion populations of young, star-forming regions provides valuable constraints of how the birth environment affects multiple formation and evolution. Previous multiplicity surveys in low-mass, low-density associations like Taurus identify an excess of companions to low-mass primary stars roughly twice that of the Galactic field, over all mass ratios and for separations of 3-5000 au, and even trends in the companion properties as a function of primary mass (some seemingly consistent with the field population). Our study investigates the companion population of the ONC (a high-mass, high density star-forming region), with a double point-spread function (PSF) fitting algorithm sensitive beyond separations of 10au (0.025”, 0.5λ/D at 555nm) using empirical, position-dependent PSF models. We have identified over 40 companions. We found: 1) the companion frequency (CF) of low-mass stars in the ONC is consistent with the Galactic field over all mass ratios and orbital separations of 10-200 au, in contrast to the higher CF found in low-density regions like Taurus, 2) the power-law fit to the mass ratio distribution of low-mass primaries in the ONC is consistent with that in the field and Taurus, and 3) the CF to brown dwarfs with separations > 20 au in the ONC is in excess of the field, requiring further dynamical evolution destroying binaries with low binding energy to resemble the field.