Infrared excess

An infrared excess (also known as an IR excess, or IRX) is a measurement of an astronomical source, typically a star, which has a greater than expected infrared flux in the spectral energy distribution assuming that the source is a blackbody radiator. Infrared excesses in stars are often the result of circumstellar dust grains heated by incident starlight causing re-emission at longer wavelengths, and they are common in young stellar objects, evolved asymptotic branch stars, and white dwarfs. Infrared excesses have also been found during observations of other objects such as active galactic nuclei and black holes.