A Sérsic profile models projected galactic light, with index controlling curvature and chosen so that encloses half the luminosity. Its logarithmic slope is . The case is exponential; gives the traditional de Vaucouleurs form. Unlike a fixed power law, its slope steepens outward.
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The Sérsic profile is a mathematical function used to describe the brightness distribution of astronomical objects, particularly galaxies and bulges of galaxies. It was introduced by the Argentine astronomer José Sérsic in 1963. This profile is an extension of the simpler exponential (for disk-like structures) and de Vaucouleurs (for elliptical structures) profiles, allowing for a more flexible representation of the surface brightness of an object.