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Although there is no obvious reason to include a quadratic term I will nevertheless consider a quadratic model. I will do this by again using IDL's CURVEFIT procedure and the MPFIT package (also IDL) which is a more sophisticated fitting tool utilizing the Levenberg-Marquardt least-squares minimisation algorithm developed by Marwardt.  \subsection{Quadratic ephemeris using CURVEFIT}  The results from CURVEFIT are surprising. The best-fit $\chi^2$ value was 3718.89 yielding a reduced $\chi^2$ of 95.36 with (42-3 DoF). The RMS scatter of the residuals around the quadratic model fit was 31 seconds. This means that the fit became worse compared to a linear ephemeris model. The resulting residual plot is shown in Fig.~\ref{quadfit_res}. The corresponding best-fit parameters along with formal uncertainties  for a quadratic ephemeris is are  \begin{eqnarray}  T(E) &=& T + P \times E + A \times E^2 \\  &=& 24550021.778895(6) + 0.0878654269(3) \times E + 4.3(5)\times 10^{-14} \times E^2  
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