http://arxiv.org/abs/1901.08610
Since the first observation of triple-lens gravitational microlensing in 2006, analyses of six more events have been published by the end of 2018. In three events the lens was a star with two planets; four involved a binary star with a planet. Other possible triple lenses such as triple stars or stars with a planet with a moon are yet to be detected. The analysis of triple-lens events is hindered by the lack of understanding of the diversity of their caustics and critical curves. We present a method for identifying all critical-curve topologies for a triple lens with a given combination of masses in an arbitrary spatial configuration. We compute their boundaries in parameter space, identify the topologies in the partitioned regions, and evaluate their probabilities of occurrence. We illustrate the analysis on three triple-lens models. For three equal masses the computed boundary surfaces divide the parameter space into 39 regions yielding nine critical-curve topologies. The other models include a binary star with a planet, and a hierarchical star–planet–moon combination of masses. For both we find the same set of eleven topologies, including new topologies with doubly-nested loops of the critical curve. The number of lensing regimes thus depends on the combination of masses — unlike in the double lens which has the same three regimes for any mass ratio. The presented approach is suitable for further investigations, such as studies of the changes occurring in non-static lens configurations due to orbital motion of the components or other parallax-type effects.
K. Danek and D. Heyrovsky
Mon, 28 Jan 19
15/55
Comments: 41 pages, 16 figures, 3 animations attached as ancillary files, submitted to ApJ
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