Dipartimento di Fisica e Astronomia, Università di
Padova, vicolo Osservatorio
2 INAF−Osservatorio Astronomico di Padova, vicolo Osservatorio 5, 35122 Padova, Italy
3 INAF−Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
4 School of Physics, Astronomy & Maths, University of Hertfordshire, Hatfield, Herts. AL10 9AB, UK
5 Thueringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
6 CASU, Institute of Astronomy, Madingley Road, University of Cambridge, CB3 0HA, UK
7 IGAM, Institute of Physics, University of Graz, Universitätsplatz. 5, 8010 Graz, Austria
8 Departament d’Astronomia i Meteorologia, Universitat de Barcelona, Avda. Diagonal 647, 08028 Barcelona, Spain
9 Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
10 Instituto de Astrofísica de Andalucía, CSIC, Apdo 3004, 18080 Granada, Spain
11 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
12 Department for Astrophysics, Nicolaus Copernicus Astronomical Center, ul. Rabiańska 8, 87-100 Toruń, Poland
13 INAF−Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
14 Dipartimento di Fisica e Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
15 Department of Astronomy, Indiana University, Bloomington, IN 47405, USA
16 Massachusetts Institute of Technology and Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
17 Institute of Theoretical Physics and Astronomy, Vilnius University, Goštauto 12, 01108 Vilnius, Lithuania
18 INAF−Astrophysical Observatory of Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
19 Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Athens, 15784 Athens, Greece
20 INAF−Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
21 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
22 Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00, Sweden
23 INAF−Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
24 Departamento de Astronomía, Universidad de Concepción, Casilla 160- C Concepción, Chile
25 Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
26 Spanish Virtual Observatory, Centro de Astrobiología (INTA-CSIC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
27 Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
28 Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
Accepted: 26 June 2014
Context. Chemically inhomogeneous populations are observed in most globular clusters, but not in open clusters. Cluster mass seems to play a key role in the existence of multiple populations.
Aims. Studying the chemical homogeneity of the most massive open clusters is needed to better understand the mechanism of their formation and determine the mass limit under which clusters cannot host multiple populations. Here we studied NGC 6705, which is a young and massive open cluster located towards the inner region of the Milky Way. This cluster is located inside the solar circle. This makes it an important tracer of the inner disk abundance gradient.
Methods. This study makes use of BVI and ri photometry and comparisons with theoretical isochrones to derive the age of NGC 6705. We study the density profile of the cluster and the mass function to infer the cluster mass. Based on abundances of the chemical elements distributed in the first internal data release of the Gaia-ESO Survey, we study elemental ratios and the chemical homogeneity of the red clump stars. Radial velocities enable us to study the rotation and internal kinematics of the cluster.
Results. The estimated ages range from 250 to 316 Myr, depending on the adopted stellar model. Luminosity profiles and mass functions show strong signs of mass segregation. We derive the mass of the cluster from its luminosity function and from the kinematics, finding values between 3700 M⊙ and 11 000 M⊙. After selecting the cluster members from their radial velocities, we obtain a metallicity of [Fe/H] = 0.10 ± 0.06 based on 21 candidate members. Moreover, NGC 6705 shows no sign of the typical correlations or anti-correlations between Al, Mg, Si, and Na, which are expected in multiple populations. This is consistent with our cluster mass estimate, which is lower than the required mass limit proposed in the literature to develop multiple populations.
Key words: stars: abundances / open clusters and associations: general / open clusters and associations: individual: NGC 6705
Based on the data obtained at ESO telescopes under programme 188.B-3002 (the public Gaia-ESO spectroscopic survey, PIs Gilmore and Randich) and on the archive data of the programme 083.D-0671.
Full Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/569/A17
© ESO, 2014