The Gaia-ESO survey: the inner disk intermediate-age open cluster NGC 6802^⋆

¹ Departamento de Astronomía, Casilla 160-CUniversidad de Concepción, Concepción, Chile
² Department of Astronomy, Indiana University, Bloomington, IN, USA
³ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Florence, Italy
⁶ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan 1, 44001 Teruel, Spain
⁷ European Southern Observatory, Casilla 19001, Santiago, Chile
⁸ INAF–Osservatorio Astronomico di Bologna, via Ranzani, 1, 40127 Bologna, Italy
⁹ Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio Av. 3, 10222 Vilnius, Lithuania
¹⁰ School of Physics, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, 02455 Seoul, Republic of Korea
¹¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹² Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
¹³ Observatoire de Genève, Université de Genève, 1290 Versoix, Switzerland
¹⁴ Centro de Astrobiología (INTA-CSIC), Dpto. de Astrofísica, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁵ Suffolk University, Madrid Campus, C/ Valle de la Viña 3, 28003 Madrid, Spain
¹⁶ Department of Physics and Astronomy, University of Padova, via Marzolo, 8, 35131 Padova, Italy
¹⁷ University of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia
¹⁸ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹⁹ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
²⁰ INAF–Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²¹ INAF–Oss. Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
²² Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
²³ Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, via S. Sofia 78, 95123 Catania, Italy
²⁴ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
²⁵ ASI Science Data Center, via del Politecnico SNC, 00133 Roma, Italy
²⁶ Instituto de Física y Astronomía, Universidad de Valparaíso, Chile
²⁷ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
²⁸ Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile

^⋆⋆ Corresponding author: B. Tang, e-mail: btang@astro-udec.cl

Received: 11 October 2016
Accepted: 20 January 2017

Abstract

Milky Way open clusters are very diverse in terms of age, chemical composition, and kinematic properties. Intermediate-age and old open clusters are less common, and it is even harder to find them inside the solar Galactocentric radius, due to the high mortality rate and strong extinction inside this region. NGC 6802 is one of the inner disk open clusters (IOCs) observed by the Gaia-ESO survey (GES). This cluster is an important target for calibrating the abundances derived in the survey due to the kinematic and chemical homogeneity of the members in open clusters. Using the measurements from Gaia-ESO internal data release 4 (iDR4), we identify 95 main-sequence dwarfs as cluster members from the GIRAFFE target list, and eight giants as cluster members from the UVES target list. The dwarf cluster members have a median radial velocity of 13.6 ± 1.9 km s^-1, while the giant cluster members have a median radial velocity of 12.0 ± 0.9 km s^-1 and a median [Fe/H] of 0.10 ± 0.02 dex. The color–magnitude diagram of these cluster members suggests an age of 0.9 ± 0.1 Gyr, with (m−M)₀ = 11.4 and E(B−V) = 0.86. We perform the first detailed chemical abundance analysis of NGC 6802, including 27 elemental species. To gain a more general picture about IOCs, the measurements of NGC 6802 are compared with those of other IOCs previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs. These elements are compared with nucleosynthetic models as a function of cluster turn-off mass. The α, iron-peak, and neutron-capture elements are also explored in a self-consistent way.