(a) The ring diameter versus spin for inclinations for a Kerr black hole (solid lines) and for a quasi-Kerr black hole with a value of the deviation parameter (dashed lines). The diameter is practically independent of the spin, inclination, and deviation parameter with a constant value of M for a Kerr black hole. (b) The displacement of the ring of light as a function of for various values of the parameter . The displacement depends only weakly on the parameter . (c) The ring asymmetry versus for various inclinations and . The asymmetry is nearly independent of the spin and hence provides a direct measure of a violation of the no-hair theorem .
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