Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code
I. The northern clusters⋆
Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
2 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
3 ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szombathely, Hungary
4 Premium Postdoctoral Fellow of the Hungarian Academy of Sciences, Hungary
5 Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516 751 20 Uppsala, Sweden
6 McDonald Observatory, University of Texas at Austin, Fort Davis, TX 79734, USA
7 Laboratoire Univers et Particules de Montpellier, Université de Montpellier, CNRS, 34095 Montpellier Cedex 05, France
8 Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Copayapu 485 Copiapó, Chile
9 Departamento de Astronomía, Casilla 160-C, Universidad de Concepción, Concepción, Chile
10 Institut Utinam, CNRS UMR 6213, Université Bourgogne-Franche-Comté, OSU THETA Franche-Comté, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France
11 Observatório Nacional/MCTI, Rua Gen. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
12 Steward Observatory, University of Arizona Tucson, 85719, USA
13 Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43 22100 Lund, Sweden
14 Instituto de Investigación Multidisciplinario en Ciencia y Tecnología, Universidad de La Serena, Avenida Raúl Bitrán s/n, La Serena, Chile
15 Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de La Serena, Av. Juan Cisternas, 1200 La Serena, Chile
16 Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556, USA
17 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21210, USA
Accepted: 20 December 2018
Aims. We seek to provide abundances of a large set of light and neutron-capture elements homogeneously analyzed that cover a wide range of metallicity to constrain globular cluster (GC) formation and evolution models.
Methods. We analyzed a large sample of 885 GCs giants from the SDSS IV-Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We used the Cannon results to separate the red giant branch and asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then used the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) to derive metallicity, microturbulence, macroturbulence, many light-element abundances, and the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data.
Results. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for low-metallicity GC stars. Furthermore, while we confirm most of the known correlations and anticorrelation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement. At the same time, these stars show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anticorrelation of the Al spread against clusters metallicity and luminosity, but the data do not allow us to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters.
Conclusions. Large and homogeneously analyzed samples from ongoing spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anticorrelation, thus yielding new constrains for GCs formation/evolution models.
Key words: stars: abundances / globular clusters: general
Full Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A191
© ESO 2019