Orbital Motions of Binaries in Orion South

Abstract We present high-angular resolution ( ≃ 0 . ″ 06 ) Very Large Array and Atacama Large Millimeter/submillimeter Array observations of Orion South separated by 15.52 yr. The purpose of this study was to search for orbital motions in three close ( ≃ 0 . ″ 1 ) binary systems in the region. We do not detect changes in the position angle of the binaries, but in two of the cases, we detect significant changes in their separation in the plane of the sky. We use these changes to estimate that the total mass of the binaries is in the ≃1–2 M ⊙ range. We also estimate the disk masses from the millimeter emission. The disk-to-stellar mass ratio is in the range of 0.04–0.18, values consistent with those expected for very early stellar evolution (Class 0) protostars.