Publikace ÚTF


Daněk, K.; Heyrovský, D.

The interpretation of gravitational microlensing events caused by planetary systems or multiple stars is based on
the n-point-mass lens model. The first planets detected by microlensing were well described by the two-point-mass
model of a star with one planet. By the end of 2014, four events involving three-point-mass lenses had been
announced. Two of the lenses were stars with two planetary companions each; two were binary stars with a planet
orbiting one component. While the two-point-mass model is well understood, the same cannot be said for lenses
with three or more components. Even the range of possible critical-curve topologies and caustic geometries of the
three-point-mass lens remains unknown. In this paper we provide new tools for mapping the critical-curve
topology and caustic cusp number in the parameter space of n-point-mass lenses. We perform our analysis in the
image plane of the lens. We show that all contours of the Jacobian are critical curves of re-scaled versions of the
lens configuration. Utilizing this property further, we introduce the cusp curve to identify cusp-image positions on
all contours simultaneously. In order to track cusp-number changes in caustic metamorphoses, we define the
morph curve, which pinpoints the positions of metamorphosis-point images along the cusp curve. We demonstrate
the usage of both curves on simple two- and three-point-mass lens examples. For the three simplest caustic
metamorphoses we illustrate the local structure of the image and source planes.
journal:The Astrophysical Journal
pages:806:63 (14pp)

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