Background Method

Specifies the maximum radius, in pixels, for computing the FWHM.

Zero Point

Specifies the photometric zero point magnitude. This is the magnitude corresponding to 1 detected electron per second.

The radius, in pixel units, of the object measuring aperture.

The radius, in pixel units, of the inner background measuring aperture.

The radius, in pixel units, of the outer background measuring aperture.

The ellipticity of the apertures. This is the value of 1 - b/a, where b is the minor axis and a is the major axis. Circular apertures have an ellipticity of 0; a linear aperture has a value of 1. The maximum allowed ellipticity is 0.999.

Angle

The orientation of the major axis of the apertures, in units of degrees. If the Ellipticity is 0, then the apertures are circular and the angle has no significance.

Note: If the ellipticity is 0, the Angle control is disabled.

Note

Aperture Photometry gives the best background estimates when sources are separated by empty background. This is because the local background used by the measurement samples pixels lying inside an annulus surrounding the source. The Modal Brightness Median Brightness background methods do rejection of non-background pixels but still can give a biased result when non background pixels comprise a significant portion (e.g., 10% or more) of the local background sample.