Issue |
A&A
Volume 541, May 2012
|
|
---|---|---|
Article Number | A15 | |
Number of page(s) | 18 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/201118381 | |
Published online | 20 April 2012 |
The double sub-giant branch of NGC 6656 (M 22): a chemical characterization⋆,⋆⋆
1
Max-Planck-Institut für Astrophysik
Karl-Schwarzschild-Str. 1
85741
Garching bei München
Germany
e-mail: amarino@MPA-Garching.MPG.DE;
mbergema@MPA-Garching.MPG.DE; klind@MPA-Garching.MPG.DE
2
Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Canary Islands,
Spain
e-mail: milone@iac.es; aparicio@iac.es
3
Department of Astrophysics, University of La Laguna,
38200 La Laguna, Tenerife,
Canary Islands,
Spain
4
Department of Astronomy and McDonald Observatory, The University
of Texas, Austin,
TX
78712,
USA
e-mail: chris@verdi.as.utexas.edu
5
UCO/Lick Observatory, Department of Astronomy and Astrophysics,
University of California, Santa
Cruz, CA
95064,
USA
e-mail: kraft@ucolick.org
6
Department of Astronomy, University of Washington,
Seattle, WA
98195,
USA
e-mail: wall@astro.washington.edu
7
INAF – Osservatorio Astronomico di Teramo, via M. Maggini,
64100
Teramo,
Italy
e-mail: cassisi@oa-teramo.inaf.it
8
Research School of Astronomy & Astrophysics,
Australian National University, Mt Stromlo Observatory, via Cotter Rd, Weston, ACT
2611,
Australia
e-mail: martin@mso.anu.edu.au
9
INAF – Osservatorio Astronomico di Padova, Vicolo
dell’Osservatorio 5, 35122
Padova,
Italy
e-mail: luigi.bedin@oapd.inaf.it
10
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748
Garching bei München,
Germany
e-mail: mhilker@eso.org
11
European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
e-mail: ymomany@eso.org
12
Dipartimento di Astronomia, Università di Padova,
Vicolo dell’Osservatorio 3,
35122
Padova,
Italy
e-mail: giampaolo.piotto@unipd.it
13
Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA
91101,
USA
e-mail: iur@obs.carnegiescience.edu
14
Herzberg Institute of Astrophysics, National Research Council Canada, 5071 West Saanich Road,
Victoria, BC
V9E 2E7,
Canada
e-mail: Peter.Stetson@nrc-cnrc.gc.ca
15
Pontificia Universidad Católica de Chile, Departmento de
Astronomía y Astrofisíca, Casilla
306, Santiago 22,
Chile
e-mail: mzoccali@astro.puc.cl
Received:
2
November
2011
Accepted:
11
February
2012
We present an abundance analysis of 101 subgiant branch (SGB) stars in the globular cluster M 22. Using low-resolution FLAMES/GIRAFFE spectra we have determined abundances of the neutron-capture strontium and barium and the light element carbon. With these data we explore relationships between the observed SGB photometric split in this cluster and two stellar groups characterized by different contents of iron, slow neutron-capture process (s-process) elements, and the α element calcium, which we previously discovered in M 22’s red-giant stars. We show that the SGB stars correlate in chemical composition and the color–magnitude diagram position. The stars with higher metallicity and relative s-process abundances define a fainter SGB, while stars with lower metallicity and s-process content reside on a relatively brighter SGB. This result has implications for the relative ages of the two stellar groups of M 22. In particular, it is inconsistent with a broad spread in ages of the two SGBs. By accounting for the chemical content of the two stellar groups, isochrone fitting of the double SGB suggests that their agesare not different by more than ~300 Myr.
Key words: techniques: spectroscopic / stars: abundances / stars: Population II / globular clusters: individual: NGC 6656
Based on data collected at the European Southern Observatory with the FLAMES/GIRAFFE spectrograph under the program 085.D-0698A.
Tables 2 and 3 are available in electronic form at http://www.aanda.org
© ESO, 2012
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