Abstrakt
Gravitational microlensing is a useful tool for finding exoplanets orbiting distant stars by detecting their gravitational influence on the passage of light from a more distant star. Knowledge of the lens caustic (formed by positions of point sources with infinite amplification) is necessary for the analysis and interpretation of observed light curves.
It is well known that the binary lens can form caustics of three topologies, which correspond to three topologies of the critical curve (primary image of the caustic). Here we focus on the case of the triple lens.
While the binary lens is characterised by two parameters, three more parameters are needed to describe the triple lens.