Publikace ÚTF


Daněk, K.; Heyrovský, D.

Among the 25 planetary systems detected up to now by gravitational microlensing, there are two cases of a star
with two planets, and two cases of a binary star with a planet. Other, yet undetected types of triple lenses include
triple stars or stars with a planet with a moon. The analysis and interpretation of such events is hindered by the lack
of understanding of essential characteristics of triple lenses, such as their critical curves and caustics. We present
here analytical and numerical methods for mapping the critical-curve topology and caustic cusp number in the
parameter space of n-point-mass lenses. We apply the methods to the analysis of four symmetric triple-lens models,
and obtain altogether 9 different critical-curve topologies and 32 caustic structures. While these results include
various generic types, they represent just a subset of all possible triple-lens critical curves and caustics. Using the
analyzed models, we demonstrate interesting features of triple lenses that do not occur in two-point-mass lenses.
We show an example of a lens that cannot be described by the Chang–Refsdal model in the wide limit. In the close
limit we demonstrate unusual structures of primary and secondary caustic loops, and explain the conditions for
their occurrence. In the planetary limit we find that the presence of a planet may lead to a whole sequence of
additional caustic metamorphoses. We show that a pair of planets may change the structure of the primary caustic
even when placed far from their resonant position at the Einstein radius.
journal:The Astrophysical Journal
pages:806:99 (28pp)

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