A Refined Orbital Ephemeris for the Intermediate Polar FO Aquarii and Evidence for a Period Derivative

We combine more than 40 years of eclipse timings of the intermediate polar FO Aqr and derive new orbital ephemerides. The eclipse times are best fit with a second order polynomial, implying an $8\sigma$ detection of a period derivative. The results show that the orbital period of FO Aqr is currently increasing, with a derivative of $\dot{P}=6.65\pm 0.81\times {10}^{-11}$.