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We present the analysis of the entire HARPS observations of three stars thathost planetary systems: HD1461, HD40307, and HD204313. The data set spans eightyears and contains more than 200 nightly averaged velocity measurements foreach star. This means that it is sensitive to both long-period and low-massplanets and also to the effects induced by stellar activity cycles. We modelledthe data using Keplerian functions that correspond to planetary candidates andincluded the short- and long-term effects of magnetic activity. A Bayesianapproach was taken both for the data modelling, which allowed us to includeinformation from activity proxies such as $\log{(R'_{\rm HK})}$ in the velocitymodelling, and for the model selection, which permitted determining the numberof significant signals in the system. The Bayesian model comparison overcomesthe limitations inherent to the traditional periodogram analysis. We report anadditional super-Earth planet in the HD1461 system. Four out of the six planetspreviously reported for HD40307 are confirmed and characterised. We discuss theremaining two proposed signals. In particular, we show that when the systematicuncertainty associated with the techniques for estimating model probabilitiesare taken into account, the current data are not conclusive concerning theexistence of the habitable-zone candidate HD40307 g. We also fully characterisethe Neptune-mass planet that orbits HD204313 in 34.9 days.

astronomy and astrophysics

The HARPS search for southern extra-solar planets. XXXVIII. Bayesian  re-analysis of three systems. New super-Earths, unconfirmed signals, and  magnetic cycles