The Gaia-ESO Survey: membership and initial mass function of the γ Velorum cluster^⋆,⋆⋆

¹ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
e-mail: loredana@astropa.inaf.it
² Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK
³ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁴ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁵ Dipartimento di Fisica e Astronomia, Università di Catania, via S. Sofia 78, 95123 Catania, Italy
⁶ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
⁷ Dip. di Fisica e Chimica, Università di Palermo, P.zza del Parlamento 1, 90134 Palermo, Italy
⁸ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna, Italy
⁹ INAF–Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁰ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile
¹¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹² Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹³ Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile
¹⁴ Department of Astronomy, University of Geneva, 51 chemin des Maillettes, 1290 Versoix, Switzerland

Received: 1 December 2015
Accepted: 21 January 2016

Abstract

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 γ 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 Hα 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 α = 2.6 ± 0.5 for 0.5 <M/M_⊙< 1.3 and α = 1.1 ± 0.4 for 0.16 <M/M_⊙< 0.5, and it is consistent with a standard IMF.

Conclusions. The similarity of the IMF of the young population around γ²Vel to that in other star-forming regions and the field suggests it may have formed through very similar processes.