Context : In a previous paper we reported a planetary companion to the young and very active K5Ve star BD+20 1790 .
We found that this star has a high level of stellar activity ( logR ^ { \prime } _ { HK } =-3.7 ) that manifests in a plethora of phenomena ( starspots , prominences , plages , large flares ) .
Based on a careful study of these activity features and a deep discussion and analysis of the effects of the stellar activity on the radial velocity measurements , we demonstrated that the presence of a planet provided the best explanation for the radial velocity variations and all the peculiarities of this star .
The orbital solution resulted in a close-in massive planet with a period of 7.78 days .
However , a paper by Figueira et al .
( 2010 ) questioned the evidence for the planetary companion .

Aims : This paper aims to more rigorously assess the nature of the radial velocity measurements with an expanded dataset and new methods of analysis .

Methods : We have employed Bayesian methods to simultaneously analyse the radial velocity and activity measurements based on a combined dataset that includes new and previously published observations .

Results : We conclude that the Bayesian analysis and the new activity study support the presence of a planetary companion to BD+20 1790 .
A new orbital solution is presented , after removing the two main contributions of stellar jitter , one that varies with the photometric period ( 2.8 days ) and another that varies with the synodic period of the star-planet system ( 4.36 days ) .
We present a new method to determine these jitter components , considering them as second and third signals in the system .
A discussion on possible star-planet-interaction is included , based on the Bayesian analysis of the activity indices , which indicates that they modulate with the synodic period .
We propose two different sources for flare events in this system : one related to the geometry of the system and the relative movement of the star and planet , and a second one purely stochastic source that is related to the evolution of stellar surface active regions .
Also , we observe for the first time the magnetic field of the star , from spectropolarimetric data .

Conclusions :