The Gaia-ESO Survey: A lithium-rotation connection at 5 Myr? ^⋆

¹ Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France
e-mail: Jerome.Bouvier@obs.ujf-grenoble.fr
² CNRS, IPAG, 38000 Grenoble, France
³ Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, via S. Sofia 78, 95123 Catania, Italy
e-mail: Alessandro.Lanzafame@oact.inaf.it
⁴ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁵ INAF–Osservatorio Astronomico di Palermo G.S. Vaiana, Piazza del Parlamento 1, 90134 Palermo, Italy
⁶ Astrophysics Group, Keele University, Keele, Staffordshire, ST5 5BG, UK
⁷ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁸ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA
⁹ NASA Ames Research Center, Kepler Science Office, Mountain View, CA 94035, USA
¹⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹¹ Instituto de Física y Astronomía, Universidad de Valparaíso, Chile
¹² Lund Observatory, Dept of Astronomy and Theoretical Physics, Box 43, 22100 Lund, Sweden
¹³ INAF–Osservatorio Astronomico si Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁴ European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
¹⁵ Instituto de Astrofisica de Andalucía – CSIC, Apdo. 3004, 18008 Granada, Spain
¹⁶ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁷ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹⁸ Universidad Andres Bello, Departamento de Ciencias Físicas, Facultad de Ciencias Exactas, Fernandez Concha 700, Las Condes, Santiago, Chile
¹⁹ Millennium Institute of Astrophysics, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago, Chile
²⁰ INAF–Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
²¹ University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000 Ljubljana, Slovenia

Received: 18 February 2016
Accepted: 25 April 2016

Abstract

Context. The evolution of lithium abundance in cool dwarfs provides a unique probe of nonstandard processes in stellar evolution.

Aims. We investigate the lithium content of young low-mass stars in the 5 Myr old, star forming region NGC 2264 and its relationship with rotation.

Methods. We combine lithium equivalent width measurements (EW(Li)) from the Gaia-ESO Survey with the determination of rotational periods from the CSI 2264 survey. We only consider bona fide nonaccreting cluster members to minimize the uncertainties on EW(Li).

Results. We report the existence of a relationship between lithium content and rotation in NGC 2264 at an age of 5 Myr. The Li-rotation connection is seen over a restricted temperature range (T_eff = 3800–4400 K), where fast rotators are Li-rich compared to slow rotators. This correlation is similar to, albeit of lower amplitude than, the Li-rotation connection previously reported for K dwarfs in the 125 Myr old Pleiades cluster. We investigate whether the nonstandard pre-main-sequence models developed so far to explain the Pleiades results, which are based on episodic accretion, pre-main-sequence, core-envelope decoupling, and/or radius inflation due to enhanced magnetic activity, can account for early development of the Li-rotation connection. While radius inflation appears to be the most promising possibility, each of these models has issues. We therefore also discuss external causes that might operate during the first few Myr of pre-main-sequence evolution, such as planet engulfment and/or steady disk accretion, as possible candidates for the common origin for Li excess and fast rotation in young low-mass pre-main-sequence stars.

Conclusions. The emergence of a connection between lithium content and rotation rate at such an early age as 5 Myr suggests a complex link between accretion processes, early angular momentum evolution, and possibly planet formation, which likely impacts early stellar evolution and has yet to be fully deciphered.