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The Gaia-ESO Survey: Metallicity of the Chamaeleon I Star-Forming Region,

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The Gaia-ESO Survey: Metallicity of the Chamaeleon I Star-Forming Region�, A&A 568, A2 (2014) Astronomy DOI: 10.1051/0004-6361/201424135 & c ESO 2014 Astrophysics The Gaia-ESO Survey: Metallicity of the Chamaeleon I star-forming region, L. Spina1,S.Randich1, F. Palla1, K. Biazzo2, G. G. Sacco1,E.J.Alfaro3,E.Franciosini1,L.Magrini1, L. Morbidelli1, A. Frasca2, V. Adibekyan4, E. Delgado-Mena4,S.G.Sousa4,5, J. I. González Hernández6,7, D. Montes8, H. Tabernero8, G. Tautvaišiene˙9, R. Bonito10, A. C. Lanzafame11,G.Gilmore12,R.D.Jeffries13, A. Vallenari14, T. Bensby15, A. Bragaglia16, E. Flaccomio10,A.J.Korn17,E.Pancino16,18, A. Recio-Blanco19, R. Smiljanic20, M. Bergemann12, M. T. Costado3,F.Damiani10, V. Hill19,A.Hourihane12,P.Jofré12,P.deLaverny19,C.Lardo16, T. Masseron12, L. Prisinzano10, and C. C. Worley12 1 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: [email protected] 2 INAF – Osservatorio Astrofisico di Catania, via S. Sofia, 78, 95123 Catania, Italy 3 Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain 4 Centro de Astrofisica, Universidade do Porto, rua das Estrelas, 4150-762 Porto, Portugal 5 Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, rua do Campo Alegre, 4169-007 Porto, Portugal 6 Instituto de Astrofisica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain 7 Depto. Astrofisica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain 8 Departamento de Astrofisica, Universidad Complutense de Madrid (UCM), Spain 9 Institute of Theoretical Physics and Astronomy, Vilnius University, Gostauto 12, LT-01108 Vilnius, Lithuania 10 INAF − Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy 11 Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Università di Catania, via S. Sofia 78, 95123 Catania, Italy 12 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 13 Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG, UK 14 INAF − Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy 15 Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden 16 INAF − Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy 17 Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden 18 ASI Science Data Center, via del Politecnico SNC, 00133 Roma, Italy 19 Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice Cedex 4, France 20 Department for Astrophysics, Nicolaus Copernicus Astronomical Center, ul. Rabianska´ 8, 87-100 Torun,´ Poland Received 5 May 2014 / Accepted 8 June 2014 ABSTRACT Context. Recent metallicity determinations in young open clusters and star-forming regions suggest that the latter may be character- ized by a slightly lower metallicity than the Sun and older clusters in the solar vicinity. However, these results are based on small statistics and inhomogeneous analyses. The Gaia-ESO Survey is observing and homogeneously analyzing large samples of stars in several young clusters and star-forming regions, hence allowing us to further investigate this issue. Aims. We present a new metallicity determination of the Chamaeleon I star-forming region, based on the products distributed in the first internal release of the Gaia-ESO Survey. Methods. The 48 candidate members of Chamaeleon I have been observed with the high-resolution, spectrograph UVES. We use the surface gravity, lithium line equivalent width, and position in the Hertzsprung-Russell diagram to confirm the cluster members, and we use the iron abundance to derive the mean metallicity of the region. Results. Out of the 48 targets, we confirm 15 high probability members. Considering the metallicity measurements for nine of them, we find that the iron abundance of Chamaeleon I is slightly subsolar with a mean value [Fe/H] = −0.08 ± 0.04 dex. This result agrees with the metallicity determination of other nearby star-forming regions and suggests that the chemical pattern of the youngest stars in the solar neighborhood is indeed more metal-poor than the Sun. We argue that this evidence may be related to the chemical distribution of the Gould Belt that contains most of the nearby star-forming regions and young clusters. Key words. open clusters and associations: individual: Chamaeleon I – stars: pre-main sequence – stars: abundances – techniques: spectroscopic Based on observations collected at the ESO telescopes under programme 188.B3002, the Gaia-ESO large public spectroscopic survey. Tables 1−3 are available in electronic form at http://www.aanda.org Article published by EDP Sciences A2, page 1 of 12 A&A 568, A2 (2014) 1. Introduction substellar masses by Luhman (2007) and, as with other SFRs, it reaches a maximum between 0.1 and 0.2 M. L08, using The metallicity determination in young open clusters (YOCs) Spitzer colors to study the disk population, argued that the life- and star-forming regions (SFRs) has implications for fundamen- times of disks around solar-mass stars are longer in Cha I than in tal topics, such as the origin and early evolution of these en- other young clusters, probably because of the lower stellar den- vironments, the evolution of circumstellar disks, and the abil- sity and resulting reduction in dynamical interactions. On the ity to form planets (see Gilli et al. 2006; Neves et al. 2009; other hand, Cha I is also characterized by a number of subsolar- Ercolano & Clarke 2010; Yasui et al. 2010; Kang et al. 2011; mass stars with unusually short disk lifetimes (Luhman 2007; Spezzi et al. 2012; Adibekyan et al. 2012a,b; Spina et al. 2014, Robberto et al. 2012). The Cha I association can be distinguished and references therein). Furthermore, these young regions are in two sub-clusters, Cha I North (Dec > −77◦) and Cha I South of particular interest, since they are still close to their birth- (Dec < −77◦), with different star formation histories. The dis- place and contain a homogeneous stellar population that had tribution of isochronal ages suggests that star formation began no time to disperse through the Galactic disk. Thus, YOCs and ∼5−6 Myr ago in the northern portion and developed later in the SFRs are key objects to trace the present chemical pattern of the southern extension (Luhman 2007). Galactic thin disk. Indeed, an increasing number of studies has Cha I is relatively isolated from other SFRs and does not focused on the metallicity of YOCs and SFRs in the last few contain numerous massive stars. Two metallicity determinations years (e.g., James et al. 2006; González Hernández et al. 2008; have been already published prior to our study: in the first one, Santos et al. 2008; D’Orazi & Randich 2009; D’Orazi et al. Padgett (1996) derived an average value of [Fe/H] = −0.07 ± 2009, 2011; Viana Almeida et al. 2009; Biazzo et al. 2011a,b, 0.06 dex; a subsequent study by Santos et al. (2008) reports 2012a,b; Spina et al. 2014). These studies suggest that YOCs, [Fe/H] = −0.11 ± 0.14, but this estimate is based on the analy- where star formation has ceased, generally share a metallicity sis of four stars that are located in a wide area of the Chamaeleon close to the solar value; on the other hand, SFRs, in which the complex, which is away from the main SFRs. Furthermore, in a molecular gas is still present and the star formation process is recent work on proper motions, López Martí et al. (2013)have still ongoing, surprisingly seem to be characterized by a some- shown that two of these four stars, namely RX J1158.5−7754a what lower iron content. The question arises whether this result and RX J1159.7−7601, seem to be kinematical members of the / is due to low-number statistics and or to inhomogeneous meth- Cha association; another (RX J1140.3−8321) is of the η Cha ods that derive the metallicity or that the metallicity determina- association, while RX J1233.5−7523 is a field star. Thus, the tion in very young stars in SFRs is more uncertain and generally metallicity of Santos et al. (2008) is not representative of the based on rather cool stars. On the other hand, if confirmed, this SFR, and a new dedicated study is both necessary and timely. result would have important implications for our understanding The paper is organized as follows: in Sect. 2, we describe of the origin of YOCs and SFRs. the target selection and spectral analysis. The identification of The Gaia-ESO Survey (Gilmore et al. 2012; Randich & the cluster members are on the basis of the surface gravity, the Gilmore 2013) is currently observing a significant number of detection of lithium in the stellar atmospheres and their position young environments. While the main goal of the young clus- in the Hertzsprung-Russell diagram is presented in Sect. 3.The ter observations is the study of their kinematics and dynamical results of the elemental abundance determination are discussed evolution through the measurement of accurate radial velocities in Sect. 4. In Sect. 5, we overview and discuss the metal content (e.g., Jeffries et al. 2014), this large amount of data can also be of SFRs in a broader context. Sect. 6 summarizes our findings. used to perform a homogeneous study of the elemental abun- dances of YOCs and SFRs. In this framework, we have deter- mined the metal content of Gamma Velorum in a recent study, 2. Gaia-ESO data which is the first YOC observed by the Gaia-ESO Survey (Spina et al. 2014). The present paper is devoted to the analysis of the The analysis presented in this paper is based on the spectro- metallicity of the first SFR targeted by the Gaia-ESO Survey: scopic data obtained by the Gaia-ESO Survey during the first Chamaeleon I (hereafter, Cha I).
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