The Gaia-ESO survey: Discovery of a spatially extended low-mass population in the Vela OB2 association^⋆,⋆⋆

¹ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
e-mail: gsacco@arcetri.inaf.it
² Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG, UK
³ Institute of Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁴ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
⁶ Dipartimento di Fisica e Chimica, Universitá di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁷ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁸ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁹ Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Universitá di Catania, via S. Sofia 78, 95123 Catania, Italy
¹⁰ Instituto de Física y Astronomía, Universidad de Valparaíso, av. Gran Bretaña 1111, Valparaíso, Chile
¹¹ Depto. de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC campus, 28691 Villanueva de la Cañada, Madrid, Spain
¹² Suffolk University, Madrid Campus, C/ Valle de la Viña 3, 28003 Madrid, Spain
¹³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁴ Instituto de Astrofísica de Canarias, 38205, La Laguna, Tenerife, Spain
¹⁵ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile
¹⁶ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹⁷ Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile

Received: 19 November 2014
Accepted: 23 December 2014

Abstract

The nearby (distance ~ 350–400 pc), rich Vela OB2 association, includes γ² Velorum, one of the most massive binaries in the solar neighbourhood and an excellent laboratory for investigating the formation and early evolution of young clusters. Recent Gaia-ESO survey observations have led to the discovery of two kinematically distinct populations in the young (10–15 Myr) cluster immediately surrounding γ² Velorum. Here we analyse the results of Gaia-ESO survey observations of NGC 2547, a 35 Myr cluster located two degrees south of γ² Velorum. The radial velocity distribution of lithium-rich pre-main sequence stars shows a secondary population that is kinematically distinct from and younger than NGC 2547. The radial velocities, lithium absorption lines, and the positions in a colour-magnitude diagram of this secondary population are consistent with those of one of the components discovered around γ² Velorum. This result shows that there is a young, low-mass stellar population spread over at least several square degrees in the Vela OB2 association. This population could have originally been part of a cluster around γ² Velorum that expanded after gas expulsion or formed in a less dense environment that is spread over the whole Vela OB2 region.