The Gaia-ESO Survey: properties of newly discovered Li-rich giants^⋆

¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
e-mail: rsmiljanic@camk.edu.pl
² INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
⁴ Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio av. 3, 10257 Vilnius, Lithuania
⁵ Dipartimento di Fisica & Astronomia, Università degli Studi di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
⁶ Space Science Data Center – Agenzia Spaziale Italiana, via del Politecnico, s.n.c., 00133 Roma, Italy
⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁸ Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹⁰ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
¹¹ Université Paris Diderot, AIM, Sorbonne Paris Cité, CEA, CNRS, 91191 Gif-sur-Yvette, France
¹² Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹³ Universidad de La Laguna, Dept. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁴ Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
¹⁵ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, 92195 Meudon, France
¹⁶ Max-Planck-Institut for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹⁷ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
¹⁸ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
²⁰ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Quartier Agora, Allée du 6 Août 19c, Bât. B5C, 4000 Liège, Belgium
²¹ School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
²² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
²³ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
²⁴ INAF – Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁵ Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
²⁶ Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Universitá di Catania, via S. Sofia 78, 95123 Catania, Italy
²⁷ Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, 06304 Nice Cedex 4, 34229 CS, France
²⁸ Instituto de Física y Astronomía, Universidad de Valparaíso, Chile
²⁹ Departamento de Didáctica, Universidad de Cádiz, 11519 Puerto Real, Cádiz, Spain
³⁰ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
³¹ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
³² Laboratoire d’astrophysique, Ecole Polytechnique Fèdèrale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
³³ Departamento de Ciencias Fisicas, Universidad Andres Bello, Fernandez Concha 700, Las Condes, Santiago, Chile
³⁴ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
³⁵ European Southern Observatory, Alonso de Cordova, 3107 Vitacura, Santiago de Chile, Chile
³⁶ Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña, 1111 Valparaíso, Chile

Received: 15 March 2018
Accepted: 17 May 2018

Abstract

Aims. We report 20 new lithium-rich giants discovered within the Gaia-ESO Survey, including the first Li-rich giant with an evolutionary stage confirmed by CoRoT (Convection, Rotation and planetary Transits) data. We present a detailed overview of the properties of these 20 stars.

Methods. Atmospheric parameters and abundances were derived in model atmosphere analyses using medium-resolution GIRAFFE or high-resolution UVES (Ultraviolet and Visual Echelle Spectrograph) spectra. These results are part of the fifth internal data release of the Gaia-ESO Survey. The Li abundances were corrected for non-local thermodynamical equilibrium effects. Other stellar properties were investigated for additional peculiarities (the core of strong lines for signs of magnetic activity, infrared magnitudes, rotational velocities, chemical abundances, and Galactic velocities). We used Gaia DR2 parallaxes to estimate distances and luminosities.

Results. The giants have A(Li) > 2.2 dex. The majority of them (14 of 20 stars) are in the CoRoT fields. Four giants are located in the field of three open clusters, but are not members. Two giants were observed in fields towards the Galactic bulge, but likely lie in the inner disc. One of the bulge field giants is super Li-rich with A(Li) = 4.0 dex.

Conclusions. We identified one giant with infrared excess at 22 μm. Two other giants, with large v sin i, might be Li-rich because of planet engulfment. Another giant is found to be barium enhanced and thus could have accreted material from a former asymptotic giant branch companion. Otherwise, in addition to the Li enrichment, the evolutionary stages are the only other connection between these new Li-rich giants. The CoRoT data confirm that one Li-rich giant is at the core-He burning stage. The other giants are concentrated in close proximity to the red giant branch luminosity bump, the core-He burning stages, or the early-asymptotic giant branch. This is very clear from the Gaia-based luminosities of the Li-rich giants. This is also seen when the CoRoT Li-rich giants are compared to a larger sample of 2252 giants observed in the CoRoT fields by the Gaia-ESO Survey, which are distributed throughout the red giant branch in the T_eff-log g diagram. These observations show that the evolutionary stage is a major factor for the Li enrichment in giants. Other processes, such as planet accretion, contribute at a smaller scale.