Observations of Binaries in the Orion Nebula Cluster

The binary frequency of low-mass stars in the Orion Nebula Cluster (ONC) is about the same or even lower than for main-sequence field stars.  In contrast to this, almost all stars in the Taurus-Auriga association have a companion.  On the other hand, almost all the high-mass stars in the Trapezium have companions, often more than one.

Resolving binaries in the ONC is challenging because of the necessary high angular resolution.  This is even more true for other, more distant clusters.  Currently the only way to achieve a resolution better than 20 mas (~10 AU in the ONC) is optical long-baseline interferometry with arrays like CHARA or the VLTI.  New and improved beam combiners have the sensitivity to conduct surveys with enough stars to yield statistically significant results.