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Paper: O - C Analysis of FO Aqr, "King of Intermediate Polars"
Volume: 335, The Light-Time Effect in Astrophysics: Causes and Cures of the O - C diagram
Page: 229
Authors: Andronov, I.L.; Ostrova, N.I.; Burwitz, V.
Abstract: V and R CCD observations of FO Aqr have been analysed. The spin period rapidly decreases, being equal to 0.01451718(19) days in 2004. The initial epoch for the seasonal mean maximum is 2453227.20864(9), and a semi-amplitude is 0.092(3) mag. The rate of the spin-up of the white dwarf is variable, with a rapidly increasing value. The historical change in 1987 from spin-down to a spin-up does not reflect the accretion-rate variations, as the mean magnitude remains constant within ~ 0:1 mag, and a fast acceleration of the spin-up may be caused by changes of the magnetosphere e.g. due to the precession of the white dwarf. Our data support the "fit 3" model of Williams (2003) for the cycle counting.
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