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.
NGC 362 : Carretta et al. 2013b
NGC6219 (M12) : Carretta et al. 2007a
NGC6388 : Carretta et al. 2007c
Terzan8 : Carretta et al. 2014a
NGC4833 : Carretta et al. 2014b
NGC6093 : Carretta et al. 2015
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