Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region

TL;DR

This study measures and analyzes the proper motions of radio sources in the Orion BN/KL region over 15 years, revealing ejection events and morphological changes, and providing insights into the region's dynamical history.

Contribution

It offers the first multi-epoch absolute astrometry of multiple sources in Orion BN/KL, confirming high proper motions and proposing a dynamical ejection scenario.

Findings

BN, I, and n are receding from a common point at 15-26 km/s.

Sources appear to have been ejected about 500 years ago.

GMR A exhibited rapid flux variability during 2006 observations.

Abstract

We present absolute astrometry of four radio sources in the Becklin-Neugebauer/Kleinman-Low (BN/KL) region, derived from archival data (taken in 1991, 1995, and 2000) as well as from new observations (taken in 2006). All data consist of 3.6 cm continuum emission and were taken with the Very Large Array in its highest angular resolution A configuration. We confirm the large proper motions of the BN object, the radio source I (GMR I) and the radio counterpart of the infrared source n (Orion-n), with values from 15 to 26 km/s. The three sources are receding from a point between them from where they seem to have been ejected about 500 years ago, probably via the disintegration of a multiple stellar system. We present simulations of very compact stellar groups that provide a plausible dynamical scenario for the observations. The radio source Orion-n appeared as a double in the first three epochs, but as single in 2006. We discuss this morphological change. The fourth source in the region, GMR D, shows no statistically significant proper motions. We also present new, accurate relative astrometry between BN and radio source I that restrict possible dynamical scenarios for the region. During the 2006 observations, the radio source GMR A, located about 1' to the NW of the BN/KL region, exhibited an increase in its flux density of a factor of ~3.5 over a timescale of one hour. This rapid variability at cm wavelengths is similar to that previously found during a flare at millimeter wavelengths that took place in 2003.