Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?^⋆,⋆⋆

¹ Millennium Institute for Astrophysics, Chile
e-mail: lsbordon@astro.puc.cl
² Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago, Chile
³ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
⁴ Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile
⁵ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
⁶ GEPI, Observatoire de Paris, PSL Resarch University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, Place Jules Janssen, 92195 Meudon, France
⁷ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
⁸ INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁹ Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, 11 rue de l’Université, 67000 Strasbourg, France
¹⁰ Astronomical Institute, Tohoku University, Aoba-ku, 980-8578 Sendai, Japan

Received: 12 December 2014
Accepted: 6 May 2015

Abstract

Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated.

Aims. NGC 5053 and NGC 5634 are two of these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634.

Methods. We analyze high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of unassociated MW halo globulars, and of the metal-poor Sgr dSph main body population.

Results. We derive a metallicity of [Fe ii/H] = −2.26 ± 0.10 for NGC 5053, and of [Fe i/H] = −1.99 ± 0.075 and −1.97 ± 0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal-poor globular clusters in the MW. Both clusters display an α enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends.

Conclusions. The chemistry of the Sgr dSph main body populations is similar to that of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system.