High Velocity Features in the Orion Nebula

TL;DR

This study uses Hubble and ground-based observations to measure velocities of outflows in the Orion Nebula, revealing highly discontinuous stellar outflows with bursts every decade and identifying potential sources for Herbig Haro objects.

Contribution

It provides detailed velocity measurements and new insights into the episodic nature of outflows in the Orion Nebula, including source identification for several Herbig Haro objects.

Findings

Outflows are highly discontinuous with decade-scale bursts.

Most Herbig Haro objects originate from a small region northeast of Orion-S.

Evidence links BN-KL region features to a large-scale outflow 500-1000 years old.

Abstract

We have used widely spaced in time Hubble Space Telescope images to determine tangential velocities of features associated with outflows from young stars. These observations were supplemented by groundbased telescope spectroscopy and from the resultant radial velocities, space velocities were determined for many outflows. Numerous new moving features were found and grouped into known and newly assigned Herbig Haro objects. It was found that stellar outflow is highly discontinuous, as frequently is the case, with long-term gaps of a few hundred years and that these outflow periods are marked by staccato bursts over periods of about ten years. Although this has been observed in other regions, the Orion Nebula Cluster presents the richest display of this property. Most of the large scale Herbig Haro objects in the brightest part of the Orion Nebula appear to originate from a small region northeast of the strong Orion-S radio and infrared sources. With the possible exception of HH 203, we are not able to identify specific stellar sources, but do identify candidate sources for several other bright Herbig Haro objects. We find that there are optical features in the BN-KL region that can be related to the known large scale outflow that originates there. We find additional evidence for this outflow originating 500 to 1000 years ago.