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Multiple populations in Globular Clusters: the Na-O FLAMES survey

The main contributors to this project are Eugenio Carretta and Angela Bragaglia (at OA BO), Raffaele Gratton and Sara Lucatello (at OA Padova), Valentina D’Orazi (Macquarie Univ., AU), but many more researchers both in Bologna, in Italy and worldwide are collaborating (among them Antonio Sollima as post-doc at OA BO).

The Galactic globular clusters are now widely recognized as complex stellar systems, where different  populations (generations) of stars (with small age difference but even hugely different chemical composition) coexist. This is demonstrated by evidence both spectroscopic (peculiar chemistry patterns) and photometric (spread or split evolutionary sequences in the colour-magnitude diagrams).

Among the chemical signatures, the Na-O anticorrelations in GC stars (see figure below) is the most evident and widespread manifestation of the action of proton-burning reactions at high temperature in stars of the first generation, more massive than the ones alive today. The ejecta from these first-generation stars polluted the intracluster gas from which the currently observed second-generation stars formed. Both first and second-generations stars are seen in the GCs.

We are studying the chemical composition of 25 MW GCs using the multi-object, high-resolution spectrograph FLAMES@VLT. We obtain mainly Fe, Na, and O abundances (but also of alpha-elements, Fe-group and neutron-capture elements) from spectra of nearly 3000 stars. This is the largest homogeneous analysis of GCs abundances. It permitted to quantitatively study the Na-O anticorrelation and its relations with clusters’ properties (mass, metallicity, age, location in the Galaxy, horizontal branch morphology, etc). A by-product of  our survey is a new, homogeneous scale of metallicity for GCs, based on high-resolution spectra. Results have been published in a long series of papers starting from 2001 and still on-going.

The Na-O anticorrelation in 20 MW GCs (Gratton, Carretta & Bragaglia 2012, A&ARv, 20, 50)

Analysis of individual clusters

NGC 104 (47 Tuc)  : Carretta et al. 2009a,  Carretta et al. 2009b, D’Orazi et al. 2010Carretta et al. 2013a, Gratton et al. 2013

NGC 288  : Carretta et al. 2009a,  Carretta et al. 2009b

NGC 362 : Carretta et al. 2013b

NGC1851 : Carretta et al. 2010a, Carretta et al. 2011, Carretta et al. 2012b, Gratton et al. 2012a

NGC1904 (M79) :  Carretta et al. 2009a,  Carretta et al. 2009b

NGC2808  : Carretta et al. 2006, Bragaglia et al. 2010, Gratton et al. 2012a

NGC3201  :   Carretta et al. 2009a,  Carretta et al. 2009b, Carretta et al. 2010b

NGC4590 (M68)  : Carretta et al. 2009a,  Carretta et al. 2009b

NGC5904 (M5)  : Carretta et al. 2009a,  Carretta et al. 2009bGratton et al. 2013

NGC6121 (M4)  : Carretta et al. 2009a,  Carretta et al. 2009bCarretta et al. 2013a

NGC6171 (M107) : Carretta et al. 2009a,  Carretta et al. 2009b

NGC6219 (M12) : Carretta et al. 2007a

NGC6254 (M10) : Carretta et al. 2009a,  Carretta et al. 2009b

NGC6388 : Carretta et al. 2007c

NGC 6397 : Carretta et al. 2009a,  Carretta et al. 2009b

NGC6441 : Gratton et al. 2006, Gratton et al. 2007

NGC6715 (M54): Carretta et al. 2010c, Carretta et al. 2010d

NGC6752 : Carretta et al. 2007b, Carretta et al. 2012c

NGC6809 (M55) : Carretta et al. 2009a,  Carretta et al. 2009b

NGC6838 (M71) : Carretta et al. 2009a,  Carretta et al. 2009b

NGC7078 (M15) : Carretta et al. 2009a,  Carretta et al. 2009b

NGC7099 (M30) : Carretta et al. 2009a,  Carretta et al. 2009b

Terzan8 : Carretta et al. 2014a

NGC4833 : Carretta et al. 2014b

NGC6093 : Carretta et al. 2015

NGC6139 : Bragaglia et al. (2015 (to appear on A&A 583)

Selected publications

Carretta, E.; Bragaglia, A.; Gratton, R. G., et al. 2009, A&A, 505, 117: Na-O anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra

Carretta, E.; Bragaglia, A.; Gratton, R.; Lucatello, S. 2009, A&A, 505, 139: Na-O anticorrelation and HB. VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra

Carretta, E.; Bragaglia, A.; Gratton, R.; D’Orazi, V.; Lucatello, S. 2009, A&A, 508, 595: Intrinsic iron spread and a new metallicity scale for globular clusters

Carretta, E.; Bragaglia, A.; Gratton, R. G.; et al. 2010, A&A, 516, A55: Properties of stellar generations in globular clusters and relations with global parameters

Carretta, E.; Bragaglia, A.; Gratton, R. G.; et al. 2010, ApJ,  714, L7: M54 + Sagittarius = ω Centauri

Bragaglia, A.; Carretta, E.; Gratton, R. G.; et al. 2010, ApJ,  720, L41: X-shooter Observations of Main-sequence Stars in the Globular Cluster NGC 2808: First Chemical Tagging of a He-normal and a He-rich Dwarf 

Carretta, E.; Bragaglia, A.; Gratton, R.; D’Orazi, V.; Lucatello, S. 2011, A&A,  535, A121: A Strömgren view of the multiple populations in globular clusters

Bellazzini, M.; Bragaglia, A.; Carretta, E.; et al. 2012, A&A, 538, A18: Na-O anticorrelation and HB. IX. Kinematics of the program clusters A link between systemic rotation and HB morphology?

Carretta, E.; Bragaglia, A.; Gratton, R. G.; Lucatello, S.; D’Orazi, V. 2012, ApJ, 750, L14: Chemical Tagging of Three Distinct Populations of Red Giants in the Globular Cluster NGC 6752

Bragaglia, A.; Gratton, R. G.; Carretta, E.; D’Orazi, V.; Sneden, C.; Lucatello, S. 2012, A&A, 548, A122: Searching for multiple stellar populations in the massive, old open cluster Berkeley 39

Gratton, R. G.; Lucatello, S.; Sollima, A.; et al, 2013, A&A, 549, A41: The Na-O anticorrelation in horizontal branch stars. III. 47 Tucanae and M 5

Carretta, E.; Bragaglia, A.; Gratton, R. G.;  et al, 2013, A&A, 557, A138:  NGC 362: another globular cluster with a split red giant branch