Companions usually have no infrared excess, nor do primaries with massive companions.
Furthermore, X-ray emission in some HAeBe stars may well be explained by the presence of a T Tauri companion. First, any stellar formation theory must explain the large abundance of multiple systems among Main Sequence and young low-mass T Tauri stars. Second, binary studies allow the direct determination of physical parameters. HAeBe binaries observed with PUEO at 2.2 and view in 3D projection. Smallest peak is the infrared companion.