NGC 2264 - Christmas Tree Cluster
NGC 2264 is a young galactic cluster of stars in the Monoceros OB 1 association which resides in the Orion arm of the galaxy. The cluster has a total of over 600 stars ranging in age from from 1 to 4 million years old. The diverse population of the cluster includes several dozen OB stars and over 400 lower mass stars. The brightest members of the cluster resemble a "Christmas Tree" with S Monocerotis at its base and the Cone Nebula at its apex. The juxtaposition of dark dust clouds and glowing gas has carved out the landscape we see in the cone nebula region. The conical shaped pillar of gas and dust is called the Cone Nebula. It spans about 7 light years in length. A protruding portion of the cloud near S Monocerotis has been compared to the shape of a fox and was nicknamed the "Foxfur" nebula by the astrophotographer David Malin.
The most massive stellar member of NGC 2264 is the O-type supergiant, S Monocerotis which dominates the northern half of the cluster and is probably the ionizing source of the Cone Nebula. It is about 8000 times more luminous than our sun. NGC 2264 is associated with an extensive molecular cloud spanning several degrees of sky. Ongoing star formation within the cloud is suspected by the presence of numerous T Tauri stars, Herbig-Haro objects and molecular outflows within the cloud. Young protostars often show violent ejections of mass as they evolve towards maturity. These gaseous outflows can be detected by interferometry and are indicators of active star formation in a molecular cloud. Several hundred T Tauri stars have been found among the clusters members. T Tauri stars are very young stellar objects (less than 10 million years old) and are thought to represent the precursors of low mass stars like our sun. They are found in nebulae and young clusters and are an intermediate stage between protostars and main sequence stars. T Tauri stars are characterized by their variability. They have large circumstellar disks known as accretion disks which may become unstable leading to variation in light output. The presence of lithium in their spectra also indicates their young age as lithium is destroyed early in the star forming process.
© Robert Gendler