Detection limits for α   Cen   B   (K1V) for different activity levels and strategies. The thick line at the top corresponds to the present HARPS observational strategy (one measurement per night of 15 min, 10 consecutive days each month) for an activity level . The second thick line at the very bottom corresponds to the detection limit, using ESPRESSO, for the 3N3 strategy and an activity level . Besides these two thick lines, from top to bottom, the dashed thin lines correspond to the 3N1 strategy using HARPS, for an activity level ,  − 4.9 and  − 5, respectively. The 3N3 strategy using HARPS corresponds to the continuous thin lines on the same order of activity level. Finally, the small dots represent the planets expected from Bern’s model with a random sini for each body. We see that the cut-off in period around 12 days of the model introduces an anomaly in the planet distribution. The habitable zone is derived using the model of Selsis et al. (2007) applied to the temperature and the luminosity of a K1V dwarf, calculated using the results of de Jager & Nieuwenhuijzen (1987).