Gaia-ESO Survey: Analysis of pre-main sequence stellar spectra

¹ Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, via S. Sofia 78, 95123 Catania, Italy
e-mail: Alessandro.Lanzafame@oact.inaf.it
² INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
³ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁴ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁵ Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁶ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁷ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁸ Universidad Complutense de Madrid, Departamento de Astrofísica, 28040 Madrid, Spain
⁹ Università di Palermo, Dipartimento di Fisica e Chimica, Viale delle Scienze, Ed. 17, 90128 Palermo, Italy
¹⁰ INAF–Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
¹¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹² Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG, UK
¹³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁴ Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia
¹⁵ Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford, OX1 3NP, UK
¹⁶ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
¹⁷ Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane Campus, Hatfield AL10 9AB, UK
¹⁸ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
¹⁹ Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
²⁰ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
²¹ ESA, ESTEC, Keplerlaan 1, Po Box 299 2200 AG Noordwijk, The Netherlands
²² Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²³ INAF–Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁴ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
²⁵ Universidad de La Laguna, Dept. Astrofísica, 38206 La Laguna, Tenerife, Spain
²⁶ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
²⁷ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
²⁸ Moscow MV Lomonosov State University,Sternberg Astronomical Institute, 119992 Moscow, Russia
²⁹ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
³⁰ Laboratoire Lagrange (UMR 7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice Cedex 4, France
³¹ Department for Astrophysics, Nicolaus Copernicus Astronomical Center, ul. Rabiańska 8, 87–100 Toruń, Poland
³² Institut d’Astronomie et d’Astrophysique, Université libre de Brussels, Boulevard du Triomphe, 1050 Brussels, Belgium
³³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³⁴ Instituto de Física y Astronomiía, Universidad de Valparaiíso, 951 Blanco, Chile
³⁵ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile

Received: 5 August 2014
Accepted: 14 January 2015

Abstract

Context. The Gaia-ESO Public Spectroscopic Survey is obtaining high-quality spectroscopy of some 100 000 Milky Way stars using the FLAMES spectrograph at the VLT, down to V = 19 mag, systematically covering all the main components of the Milky Way and providing the first homogeneous overview of the distributions of kinematics and chemical element abundances in the Galaxy. Observations of young open clusters, in particular, are giving new insights into their initial structure, kinematics, and their subsequent evolution.

Aims. This paper describes the analysis of UVES and GIRAFFE spectra acquired in the fields of young clusters whose population includes pre-main sequence (PMS) stars. The analysis is applied to all stars in such fields, regardless of any prior information on membership, and provides fundamental stellar atmospheric parameters, elemental abundances, and PMS-specific parameters such as veiling, accretion, and chromospheric activity.

Methods. When feasible, different methods were used to derive raw parameters (e.g. line equivalent widths) fundamental atmospheric parameters and derived parameters (e.g. abundances). To derive some of these parameters, we used methods that have been extensively used in the past and new ones developed in the context of the Gaia-ESO survey enterprise. The internal precision of these quantities was estimated by inter-comparing the results obtained by these different methods, while the accuracy was estimated by comparison with independent external data, such as effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. A validation procedure based on these comparisons was applied to discard spurious or doubtful results and produce recommended parameters. Specific strategies were implemented to resolve problems of fast rotation, accretion signatures, chromospheric activity, and veiling.

Results. The analysis carried out on spectra acquired in young cluster fields during the first 18 months of observations, up to June 2013, is presented in preparation of the first release of advanced data products. These include targets in the fields of the ρ Oph, Cha I, NGC 2264, γ Vel, and NGC 2547 clusters. Stellar parameters obtained with the higher resolution and larger wavelength coverage from UVES are reproduced with comparable accuracy and precision using the smaller wavelength range and lower resolution of the GIRAFFE setup adopted for young stars, which allows us to provide stellar parameters with confidence for the much larger GIRAFFE sample. Precisions are estimated to be ≈120 K rms in T_eff, ≈0.3 dex rms in log g, and ≈0.15 dex rms in [Fe/H] for the UVES and GIRAFFE setups.