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Fig. 1.


Geometry of the problem. The Cartesian (x, y, z) and spherical (with θ and ϕ) coordinate systems are shown. The star has an oblate shape, because it is rotating rapidly around the z-axis. Therefore, the radial vector and the surface normal differ from each other. The photon from the hot spot is initially emitted towards but due to the light bending it reaches the observer in direction of .

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