Figure 5. Left: angles relevant to the path of the emitting spot considered here. The observer’s inclination i is measured from the stellar spin axis Ω. The path on the stellar surface along which the emitting spot moves is described in a coordinate system anchored in the star. The center of the circular path considered here is at colatitude θp and azimuth φp ≡ 0 in this coordinate system. The angular radius of the path is ηs . The azimuth ξs of the spot around the center of the path is measured from its lowest latitude. Right: phase and time residuals of the peak, first harmonic (fundamental), and second harmonic (first overtone) of the observed waveform as functions of the azimuth ξs of a circular spot with a radius of 25◦ moving along a circular path like that shown in the left-hand panel. The phase and time residuals are defined in Section 2.3. In this example, the emission from the spot is assumed to be isotropic, θp = 12◦, ηs = 10◦, i = 45◦, the star has a mass of 1.4M and a radius of 5M , and the star’s spin rate is 400 Hz measured at infinity.
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