The Orion Protostellar Explosion and Runaway Stars Revisited : Stellar Masses, Disk Retention, and an Outflow from the Becklin-Neugebauer Object

Abstract

The proper motions of the three stars ejected from Orion's OMC1 cloud core are combined with the requirement that their center of mass is gravitationally bound to OMC1 to show that radio source I (Src I) is likely to have a mass around 15 M o˙ consistent with recent measurements. Src I, the star with the smallest proper motion, is suspected to be either an astronomical-unit-scale binary or a protostellar merger remnant produced by a dynamic interaction ∼550 yr ago. Near-infrared 2.2 μm images spanning ∼21 yr confirm the ∼55 km s -1 motion of "source x" (Src x) away from the site of stellar ejection and point of origin of the explosive OMC1 protostellar outflow. The radial velocities and masses of the Becklin-Neugebauer (BN) object and Src I constrain the radial velocity of Src x to be. Several high proper-motion radio sources near BN, including Zapata 11 ([ZRK2004] 11) and a diffuse source near IRc 23, may trace a slow bipolar outflow from BN. The massive disk around Src I is likely the surviving portion of a disk that existed prior to the stellar ejection. Though highly perturbed, shocked, and reoriented by the N-body interaction, enough time has elapsed to allow the disk to relax with its spin axis roughly orthogonal to the proper motion.