  This paper presents the simultaneous Bayesian analysis of the radial velocity
and activity indices for the K5Ve active star BD+20 1790, that was proposed to
host a close-in massive planet by Hern\'an-Obispo et al. (2010). The Bayesian
analysis supports the hypothesis of a planetary companion. We present a new
orbital solution after removing the two main contributions to the stellar
jitter, one that varies with the photometric period and another that varies
with the synodic period of the star+planet system. We use a new method to
determine these jitter components, considering them as a second and third
signals in the system. A discussion on possible magnetic
star-planet-interaction is included, based on the Bayesian analysis of the
activity indices. We propose two possible sources for flare events of this
star: one related to the geometry of the system and the relative movement of
the star+planet, and a second one purely stochastic source that is related to
the evolution of stellar active regions. Also, we observe for the first time
the magnetic field of the star, from spectropolarimetric data.
