Lambda Orionis Cluster

The Lambda Orionis Cluster (also known as the Collinder 69) is an open star cluster located north-west of the star Betelgeuse in the constellation of Orion. It is about five million years old and roughly 400 pc away from the Sun. Included within the cluster is a double star named Meissa. With the rest of Orion, it is visible from the middle of August in the morning sky, to late April before Orion becomes too close to the Sun to be seen well. It can be seen from both the northern hemisphere and the southern hemisphere.

Description
The cluster is following an orbit through the Milky Way that has a period of 227.4 million years with an ellipticity of 0.06, carrying it as far as 8.6 kpc from the Galactic Center, and as close as 7.7 kpc. The inclination of the orbit carries it up to 80 pc away from the galactic plane. On average it crosses the plane every 33.3 million years.

The star cluster is young and contains a large number of low-mass stars, some T Tauri stars and brown dwarfs. One notable member is LOri167, which is a wide binary consisting of a potential planetary-mass object and a brown dwarf. Observations of the star cluster with the Spitzer Space Telescope have shown that 25% of the low-mass stars and 40% of the substellar objects are surrounded by a circumstellar disk. Two of these being actively photoevaporated by Meissa.

Molecular ring and cluster evolution
The cluster might have formed in the central region of an elongated cloud, which is supported by the distribution of pre-main-sequence star candidates, which are concentrated in the cluster and nearby regions in an elongated shape. Massive OB stars and low-mass stars formed in the central regions of these clouds. The low-mass stars closest to the massive stars likely lost their circumstellar disks due to photoevaporation. Many low-mass stars parsecs away were unaffected by this and represent the current population of low-mass stars with a circumstellar disk. The cluster is surrounded by a large molecular ring, called the Lambda Orionis ring. This was interpreted as a remnant of a supernova that exploded one million years ago. The supernova blast encountered the clouds and gas in the region and the blast dispersed the parent core, creating the molecular ring.