  Stellar activity can induce signals in the radial velocities of stars,
complicating the detection of orbiting low-mass planets. We present a method to
determine the number of planetary signals present in radial-velocity datasets
of active stars, using only radial-velocity observations. Instead of
considering separate fits with different number of planets, we use a
birth-death Markov chain Monte Carlo algorithm to infer the posterior
distribution for the number of planets in a single run. In a natural way, the
marginal distributions for the orbital parameters of all planets are also
inferred. This method is applied to HARPS data of CoRoT-7. We confidently
recover both CoRoT-7b and CoRoT-7c although the data show evidence for
additional signals.
