Figure 2. Contour plots of the total fractional rms amplitude produced by isotropic emission from a single stable spot (left-hand panel) and from two stable antipodal spots (right-hand panel), as a function of the spot radius and the inclination of the primary spot relative to the spin axis, for a 1.4M star with a radius of 5M spinning at 400 Hz observed at an inclination of 45◦. The heavier lines highlight the contours where the total flux modulation is 2%. This figure demonstrates that even very large spots must be centered close to the stellar spin axis in order to explain the low oscillation amplitudes observed in the AMXPs, unless almost the entire stellar surface is uniformly emitting.
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