The Gaia-ESO Survey: membership and initial mass function of the. Velorum cluster

Context. Understanding the properties of young open clusters, such as the initial mass function (IMF), star formation history, and dynamic evolution, is crucial for obtaining reliable theoretical predictions of the mechanisms involved in the star formation process. Aims. We want to obtain a list that is as complete as possible of confirmed members of the young open cluster gamma Velorum, with the aim of deriving general cluster properties such as the IMF. Methods. We used all available spectroscopic membership indicators within the Gaia-ESO public archive, together with literature photometry and X-ray data, and for each method, we derived the most complete list of candidate cluster members. Then, we considered photometry, gravity, and radial velocities as necessary conditions for selecting a subsample of candidates whose membership was confirmed by using the lithium and Ha lines and X-rays as youth indicators. Results. We found 242 confirmed and 4 possible cluster members for which we derived masses using very recent stellar evolutionary models. The cluster IMF in the mass range investigated in this study shows a slope of alpha = 2.6 +/- 0.5 for 0.5 < M/M-circle dot < 1.3 and alpha = 1.1 +/- 0.4 for 0.16 < M/M-circle dot < 0.5, and it is consistent with a standard IMF. Conclusions. The similarity of the IMF of the young population around gamma(2)Vel to that in other star-forming regions and the field suggests it may have formed through very similar processes.