The 11 year period in OJ 287 revisited: Is it a true long-enduring period?

The case of the possible 11 yr periodicity in the historical light curve of OJ 287 over a century of observations is examined critically largely indep endently of possible models that may explain it. Although it is evident tha t there is at least a quasiperiodicity in the light curve because of the re gular spacing of the nine observed outbursts, attempts to estimate an exact period have been unconvincing. We show that the principal reason is that t he data sampling is too uneven to permit definitive conclusions to be obtai ned from standard data analysis methods such as Fourier transform analysis. However, it is also shown that this is at least in part because the five m ost recent light-curve events do not refer to the same outburst in the ligh t curve as the previous ones. A simple statistical method is defined to cal culate a best period from both the primary and secondary outbursts. The res ult is a best mean period of 11.844 yr, although there is some evidence tha t the period for the primary maxima may be significantly longer than this v alue. While the periodic model of the light curve has so far demonstrated c onsiderable predictive power, final judgement should be reserved until afte r this predicted maximum in 2006.