Context :

Aims : In this study , we aim at investigating the properties of the active longitude system of the young solar analogue HD 116956 in detail , especially concentrating on determining the rotation period of the spot-generating mechanism with respect to the photometric rotation period of the star itself .
Because the nonparametric approach , like the Kuiper method , can only give the period of active longitudes , we formulate a new method that can determine the parameters the active longitude distribution uniquely .

Methods : For this purpose , we have developed an analysis method , based on Bayesian statistics using Markov chain Monte Carlo , presented in this manuscript .
One of the advantages of this method is that an estimate of the active longitude system rotation period , as well as the parameters of the shape and location of the active longitudes together with their respective error estimates .
This allows us to compare the active longitude and mean photospheric rotation periods of the star .

Results : Our analysis confirms previous results of the object having two stable active longitudes with a phase difference of \Delta \phi \approx 0.5 , the other longitude having dominated over the other one during almost the entire span of the time series .
Our method gives the rotation period of the active longitude system P _ { al } = 7.8412 \pm 0.00002 d , which is significantly different from the mean photospheric rotation period of the star P _ { rot } = 7.817 \pm 0.003 d .

Conclusions : Our analysis indicates that the spot-generating mechanism , manifesting itself as a system of two active longitudes , is lagging behind the overall rotation of the star .
This behaviour may be interpreted as a nonaxisymmetric dynamo wave propagating in the rotational reference frame of the stellar surface .