Infrared excess

The term infrared excess in astrophysics describes an unexpected excess of infrared radiation.

Introduction

In a first approximation, the radiation of stars or other astronomical objects than that of a black body can be described. By specifying a temperature of the star's surface, the distribution of electromagnetic radiation in the optical and infrared spectral range by means of Planck's radiation law can be calculated. An infrared excess reveals a clear excess of measured radiation in the infrared compared to the expected value according to Planck's radiation law.

An infrared excess of a system created by

• A circumstellar shell of dust, which absorbs radiation in the optical range, thereby heated to a few hundred Kelvin, and the radiation in the infrared radiating again, eg in dust, transition, Protoplanetary or debris discs
• In a circumstellar shell of ionized gas by thermal bremsstrahlung
• An unresolved red or brown dwarf in a binary star system

In addition, an infrared excess due to external influences come into being:

• A background galaxy
• A foreground object
• Interstellar matter in the direction of the star

Example

An example of an observed infrared excess is Beta Pictoris