We have developed a new model for analysing light curves of planetary transits when there are starspots on the stellar disc .
Because the parameter space contains a profusion of local minima we developed a new optimisation algorithm which combines the global minimisation power of a genetic algorithm and the Bayesian statistical analysis of the Markov chain .
With these tools we modelled three transit light curves of WASP-19 .
Two light curves were obtained on consecutive nights and contain anomalies which we confirm as being due to the same spot .
Using these data we measure the star ’ s rotation period and velocity to be 11.76 \pm 0.09 d and 3.88 \pm 0.15 km s ^ { -1 } , respectively , at a latitude of 65 ^ { \circ } .
We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is \lambda = 1.0 ^ { \circ } \pm 1.2 ^ { \circ } , indicating axial alignment .
Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter-McLaughlin effect .