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. 2010, Carretta 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. 2009b, Gratton et al. 2013
- NGC6121 (M4) : Carretta et al. 2009a, Carretta et al. 2009b, Carretta 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