The infrared companions of T Tauri stars

The infrared companions (IRCs) associated with several normal low-mass pre-main-sequence (T Tauri) stars pose an interesting problem for theories of binary star formation. The IRCs have very low infrared color temperatures and large infrared excesses, which have led observers to suggest that they may be less evolved objects such as protostars. This paper presents an attempt to understand the IRCs as a class by examining a broad range of observations and applying simple arguments and models. We propose that the IRCs may represent relatively normal young low-mass stars experiencing episodes of enhanced circumstellar extinction, possibly due to rapid accretion of disk material perturbed by their gravitational influence at aphelion or perihelion.