Volume 632, December 2019
|Number of page(s)||12|
|Section||Galactic structure, stellar clusters and populations|
|Published online||10 December 2019|
A MUSE study of the inner bulge globular cluster Terzan 9: a fossil record in the Galaxy⋆
Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
2 UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
3 IfA, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
4 ESO, Alonso de Córdova 3107, Vitacura, Santiago, Chile
5 Departamento de Física, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. Fernandez Concha 700, Las Condes, Santiago, Chile
6 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
7 Universitá di Padova, Dipartimento di Fisica e Astronomia, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
8 INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
9 Universidade Federal do Rio Grande so Sul, Departamento de Astronomia, Av. Bento Gonçalves 9500, Rio Grande do Sul, Brazil
10 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
Accepted: 14 October 2019
Context. Moderately metal-poor inner bulge globular clusters are relics of a generation of long-lived stars that formed in the early Galaxy. Terzan 9, projected at 4°.12 from the Galactic center, is among the most central globular clusters in the Milky Way, showing an orbit which remains confined to the inner 1 kpc.
Aims. Our aim is the derivation of the cluster’s metallicity, together with an accurate measurement of the mean radial velocity. In the literature, metallicities in the range between −2.0 < [Fe/H] < −1.0 have been estimated for Terzan 9 based on color-magnitude diagrams and CaII triplet (CaT) lines.
Methods. Given its compactness, Terzan 9 was observed using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope. The extraction of spectra from several hundreds of individual stars allowed us to derive their radial velocities, metallicities, and [Mg/Fe]. The spectra obtained with MUSE were analysed through full spectrum fitting using the ETOILE code.
Results. We obtained a mean metallicity of [Fe/H] ≈ −1.10 ±0.15, a heliocentric radial velocity of vhr = 58.1 ± 1.1 km s−1, and a magnesium-to-iron [Mg/Fe] = 0.27 ± 0.03. The metallicity-derived character of Terzan 9 sets it among the family of the moderately metal-poor Blue Horizontal Branch clusters HP 1, NGC 6558, and NGC 6522.
Key words: stars: abundances / Galaxy: bulge / globular clusters: individual: Terzan 9
© ESO 2019
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