Institute for Advanced Study Astrophysics Seminar

ABSTRACT: Astronomers have given two independent sets of names to a single set of phenomena -- the aberrations of images by telescopes and by non-uniform mass distributions. One such phenomenon is called astigmatism when it arises in telescopes and shear when it is caused by a galaxy or a cluster of galaxies. Likewise coma is the same phenomenon as gravitational 1-flexion. Not surprisingly, measurements of different gravitational lensing phenomena are vulnerable to different telescope aberrations. The origin of telescope aberrations and the patterns that they exhibit across a wide field will be briefly described. A case will be made for the use of 1-flexion and 3-flexion in studying the shapes of dark matter halos.