Detection of GRBs and OTs by All-Sky Optical and SID Monitors
Figure 9
The ellipticity of star profiles (simulation). Profiles of stars also are not circular but rather elliptical, especially for worse objectives and greater distance from the middle of the image. The ellipticity is qualified by sigma and sigma (while considering the Gaussian function), where sigma and sigma are the distance from the centre of the Gaussian in which the Gaussian is equal to exp(0,5) of its central value. Sigma and sigma are the major and minor half-axis of the ellipse, perpendicular to each other. The ellipticity in radial direction can significantly grow with the angle distance from the middle of the image, especially for wide-angle images.
