# New Evidence for the Dynamical Decay of a Multiple System in the Orion Kleinmann-Low Nebula

## TL;DR

This study provides new astrometric evidence supporting the dynamical decay of a multiple star system in the Orion Kleinmann-Low Nebula, revealing the ejection of a runaway star and clarifying the origins of several high-velocity stars.

## Contribution

It offers the first direct astrometric measurement confirming the dynamical decay event in the Orion Kleinmann-Low Nebula and identifies the source of a runaway star.

## Key findings

- Star source x has high proper motion consistent with ejection 540 years ago.
- The proper motion of source x supports its origin from the same decay event as BN, I, and n.
- Source n's motion suggests it was not part of the decay event.

## Abstract

We have measured astrometry for members of the Orion Nebula Cluster with images obtained in 2015 with the Wide Field Camera 3 on board the Hubble Space Telescope. By comparing those data to previous measurements with NICMOS on Hubble in 1998, we have discovered that a star in the Kleinmann-Low Nebula, source x from Lonsdale et al. (1982), is moving with an unusually high proper motion of 29 mas/yr, which corresponds to 55 km/s at the distance of Orion. Previous radio observations have found that three other stars in the Kleinmann-Low Nebula (BN and sources I and n) have high proper motions (5-14 mas/yr) and were near a single location ~540 years ago, and thus may have been members of a multiple system that dynamically decayed. The proper motion of source x is consistent with ejection from that same location 540 years ago, which provides strong evidence that the dynamical decay did occur and that the runaway star BN originated in the Kleinmann-Low Nebula rather than the nearby Trapezium cluster. However, our constraint on the motion of source n is significantly smaller than the most recent radio measurement, which indicates that it did not participate in the event that ejected the other three stars.