astro (version 1.2)

petro: Petrosian Function

Description

Calculates Petrosian parameters based on input Sersic parameters.

Usage

petro(mag, n, e = 0, rp = 3, i = 0.5)

Arguments

mag

total magnitude

n

Sersic index

e

ellipticity (1 - b/a)

rp

integrate out to this many multiples of the Petrosian radius

i

use this value of 1/petrosian index

Value

mag

magnitude within r

magdiff

difference between total magnitude and magnitude within r

mu

surface brightness at r

muavg

average surface brightness within r

inten

intensity at r

lum

luminosity within r

lumtot

total luminosity

lumfrac

fraction of total luminosity contained within r

Details

The Petrosian function describes the ratio between the average intensity within some projected radius and the intensity at that radius. The value of this ratio is known as the Petrosian index. Typically, a fixed value of 1/Petrosian index, i (usually i = 0.2 or i = 0.5) is chosen in order to define the Petrosian radius. The Petrosian magnitude is then defined as the magnitude lying within a given multiple of the Petrosian radius, Rp (typically, Rp = 2 or Rp = 3 for i = 0.2 and i = 0.5, respectively).

References

Graham A. W., Driver S. P., 2005, PASA, 22, 118

See Also

The astronomy package: astro.