Volume 550, February 2013
|Number of page(s)||15|
|Section||Galactic structure, stellar clusters and populations|
|Published online||22 January 2013|
INAF – Osservatorio Astronomico di Bologna, via Ranzani 1,
2 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
3 Department of Physics and Astronomy, Macquarie University, Balaclava rd, North Ryde, NSW 2109, Australia
4 Monash Centre for Astrophysics, School of Mathematical Sciences, Building 28, Monash University, VIC 3800, Australia
Received: 1 October 2012
Accepted: 2 December 2012
We present aluminium abundances for a sample of about 100 red giant stars in each of the Galactic globular clusters 47 Tuc (NGC 104) and M 4 (NGC 6121). We have derived homogeneous abundances from intermediate-resolution FLAMES/GIRAFFE spectra. Aluminium abundances are from the strong doublet Al i 8772-8773 Å, as in previous works done for giants in NGC 6752 and NGC 1851, and nitrogen abundances are extracted from a large number of features of the CN molecules by assuming a suitable carbon abundance. We added previous homogeneous abundances of O and Na and newly derived abundances of Mg and Si for our samples of 83 stars in M 4 and 116 stars in 47 Tuc to obtain the full set of elements from proton-capture reactions produced by different stellar generations in these clusters. By simultaneously studying the Ne-Na and Mg-Al cycles of H-burning at high temperature, our main aims are to understand the nature of the polluters at work in the first generation and to ascertain whether the second generation of cluster stars was formed in one or, rather, several episodes of star formation. Our data confirm that in M 4 only two stellar populations are visible. On the other hand, for 47 Tuc a cluster analysis performed on our full dataset suggests that at least three distinct groups of stars are present on the giant branch. The abundances of O, Na, Mg, and Al in the intermediate group can be produced within a pollution scenario; results for N are ambiguous, depending on the C abundance we adopt for the three groups.
Key words: stars: abundances / stars: atmospheres / stars: Population II / globular clusters: individual: 47 Tucanae / globular clusters: general / globular clusters: individual: M4
Based on observations collected at ESO telescopes under program 085.D-0205 and on public data from the ESO/ST-ECF Science Archive Facility.
Tables 2 and 3 are available in electronic form at http://www.aanda.org
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.