An Etymological Dictionary of Astronomy and Astrophysics

A → photometric system defined by reference to → monochromatic magnitudes in such a way that, when monochromatic → flux f_ν is measured in ergs sec^-1 cm^-2 Hz^-1, the magnitude will be:

AB = -2.5 logf_ν - 48.60.

The constant is set so that AB is equal to the V magnitude for a source with a flat → spectral energy distribution. The → zero point is defined by the flux of the star → Vega at 5546 Å. In this system, an object with constant flux per unit frequency interval has zero color.

See also: → magnitude; → system.