Volume 532, August 2011
|Number of page(s)||24|
|Section||Galactic structure, stellar clusters and populations|
|Published online||12 July 2011|
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei München, Germany
2 Dipartimento di Astronomia, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
e-mail: firstname.lastname@example.org; email@example.com
3 Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712, USA
4 UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
5 Department of Astronomy, University of Washington, Seattle, WA 98195, USA
6 Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611, Australia
e-mail: firstname.lastname@example.org; email@example.com
7 Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
8 Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
9 Department of Physics and Astronomy, The University of Utah, Salt Lake City, UT 84112, USA
10 Physics Department, Grove City College, 100 Campus Drive, Grove City, 16127 Pennsylvania, USA
11 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
12 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
13 Pontificia Universidad Católica de Chile, Departmento de Astronomía y Astrofisíca, Casilla 306, Santiago 22, Chile
14 Herzberg Institute of Astrophysics, National Research Council Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
Received: 19 January 2011
Accepted: 26 April 2011
We present a detailed chemical composition analysis of 35 red giant stars in the globular cluster M 22. High resolution spectra for this study were obtained at five observatories, and analyzed in a uniform manner. We have determined abundances of representative light proton-capture, α, Fe-peak and neutron-capture element groups. Our aim is to better understand the peculiar chemical enrichment history of this cluster, in which two stellar groups are characterized by a different content in iron, neutron capture elements Y, Zr and Ba, and α element Ca. The principal results of this study are: (i) substantial star-to-star metallicity scatter (− 2.0 ≲ [Fe/H] ≲ −1.6); (ii) enhancement of s-process/r-process neutron-capture abundance ratios in a fraction of giants, positively correlated with metallicity; (iii) sharp separation between the s-process-rich and s-process-poor groups by [La/Eu] ratio; (iv) possible increase of [Cu/Fe] ratios with increasing [Fe/H], suggesting that this element also has a significant s-process component; and (v)presence of Na-O and C-N anticorrelations in both the stellar groups.
Key words: techniques: spectroscopic / stars: abundances / stars: Population II / globular clusters: individual: M 22 (NGC 6656)
Based on data collected at: Anglo-Australian Telescope with the University College London Echelle Spectrograph, Apache Point Observatory with the ARC Echelle Spectrograph, Lick Shane 3.0 m Telescope with the Hamilton Echelle Spectrograph, McDonald Smith 2.7 m Telescope with the Robert G. Tull Coudé Spectrograph, and European Southern Observatory with the FLAMES/UVES spectrograph.
Tables 3–6 are available in electronic form at http://www.aanda.org
© ESO, 2011
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