Effects of a deformation of a star on the gravitational lensing |
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Authors: | H Asada |
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Institution: | GReCO, Institute for Astrophysics at Paris, 98bis boulevard Arago, 75014 Paris, France;Faculty of Science and Technology, Hirosaki University, Hirosaki 036-8561, Japan |
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Abstract: | We study analytically a gravitational lens due to a deformed star, which is modelled by using a monopole and a quadrupole moment. Positions of the images are discussed for a source on the principal axis. We present explicit expressions for the lens equation for this gravitational lens as a single real 10th-order algebraic equation. Furthermore, we compute an expression for the caustics as a discriminant for the polynomial. Another simple parametric representation of the caustics is also presented in a more tractable form. A simple expression for the critical curves is obtained to clarify a topological feature of the critical curves; the curves are simply connected if and only if the distortion is sufficiently large. |
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Keywords: | gravitational lensing stars: general |
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