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

Accepted version
Repository DOI

Type
Article
Change log
Authors
Bouvier, J 
Lanzafame, AC 
Venuti, L 
Klutsch, A 
Jeffries, R 
Abstract

© 2016 ESO. 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.

Description
Keywords
stars: abundances, stars: pre-main sequence, stars: rotation, open clusters and associations: individual: NGC 2264
Journal Title
Astronomy and Astrophysics
Conference Name
Journal ISSN
0004-6361
1432-0746
Volume Title
590
Publisher
EDP Sciences
Sponsorship
European Research Council (320360)
Leverhulme Trust (RPG-2012-541)
J. Bouvier and E. Moraux thank the staff of the Osservatorio Astrofisico di Catania for their kind hospitality in automn of 2015. They acknowledge the Agence Nationale pour la Recherche program ANR 2010 JCJC 0501 1 “DESC (Dynamical Evolution of Stellar Clusters)” for the funding of their stay at OACT during which this study was performed. This study was also supported by the Agence Nationale pour la Recherche program ANR 2011 Blanc SIMI 5-6 020 01 “Toupies (Towards understanding the spin evolution of stars)”. A. Bayo acknowledges financial support from the Proyecto Fondecyt Iniciación 11140572. S.G. Sousa acknowledges the support from FCT through Investigador FCT contract of reference IF/00028/2014. E. Delgado Mena acknowledges the support from FCT in the form of the grant SFRH/BPD/76606/2011. S.G.S. and E.D.M. also acknowledge the support from FCT through the project PTDC/FIS-AST/7073/2014 Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’ Istruzione, dell’ Uni- versità’ e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012” and “The Chemical and Dynamical Evolution of the Milky Way and the Local Group Galaxies" (prot. 2010LY5N2T). The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme.